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Sample records for accreting x-ray pulsars

  1. Accretion onto Fast X-Ray Pulsars

    NASA Technical Reports Server (NTRS)

    Rappaport, S. A.; Fregeau, J. M.; Spruit, H.

    2004-01-01

    The recent emergence of a new class of accretion-powered, transient, millisecond X-ray pulsars presents some difficulties for the conventional picture of accretion onto rapidly rotating magnetized neutron stars and their spin behavior during outbursts. In particular, it is not clear that the standard paradigm can accommodate the wide range in M(i.e., approx. greater than a factor of 50) over which these systems manage to accrete and the high rate of spindown that the neutron stars exhibit in at least a number of cases. When the accretion rate drops sufficiently, the X-ray pulsar is said to become a "fast rotator," and in the conventional view, this is accompanied by a transition from accretion to "propellering," in which accretion ceases and the matter is ejected from the system. On the theoretical side, we note that this scenario for the onset of propellering cannot be entirely correct because it is not energetically self-consistent. We show that, instead, the transition is likely to take place through disks that combine accretion with spindown and terminate at the corotation radius. We demonstrate the existence of such disk solutions by modifying the Shakura-Sunyaev equations with a simple magnetic torque prescription. The solutions are completely analytic and have the same dependence on M and a (the viscosity parameter) as the original Shakura-Sunyaev solutions, but the radial profiles can be considerably modified, depending on the degree of fastness. We apply these results to compute the torques expected during the outbursts of the transient millisecond pulsars and find that we can explain the large spin-down rates that are observed for quite plausible surface magnetic fields of approx. 10(exp 90 G.

  2. Accretion powered X-ray pulsars

    NASA Technical Reports Server (NTRS)

    White, N. E.; Swank, J. H.; Holt, S. S.

    1982-01-01

    A unified description of the properties of 14 X-ray pulsars is presented and compared with the current theoretical understanding of these systems. The sample extends over six orders of magnitude in luminosity, with the only trend in the phase averaged spectra being that the lower luminosity systems appear to have less abrupt high energy cutoffs. There is no correlation of luminosity with power law index, high energy cutoff energy or iron line EW. Detailed pulse phase spectroscopy is given for five systems.

  3. Quasispherical subsonic accretion in X-ray pulsars

    NASA Astrophysics Data System (ADS)

    Shakura, Nikolai I.; Postnov, Konstantin A.; Kochetkova, A. Yu; Hjalmarsdotter, L.

    2013-04-01

    A theoretical model is considered for quasispherical subsonic accretion onto slowly rotating magnetized neutron stars. In this regime, the accreting matter settles down subsonically onto the rotating magnetosphere, forming an extended quasistatic shell. Angular momentum transfer in the shell occurs via large-scale convective motions resulting, for observed pulsars, in an almost iso-angular-momentum \\omega \\sim 1/R^2 rotation law inside the shell. The accretion rate through the shell is determined by the ability of the plasma to enter the magnetosphere due to Rayleigh-Taylor instabilities, with allowance for cooling. A settling accretion regime is possible for moderate accretion rates \\dot M \\lesssim \\dot M_* \\simeq 4\\times 10^{16} g s ^{-1}. At higher accretion rates, a free-fall gap above the neutron star magnetosphere appears due to rapid Compton cooling, and the accretion becomes highly nonstationary. Observations of spin-up/spin-down rates of quasispherically wind accreting equilibrium X-ray pulsars with known orbital periods (e.g., GX 301-2 and Vela X-1) enable us to determine the main dimensionless parameters of the model, as well as to estimate surface magnetic field of the neutron star. For equilibrium pulsars, the independent measurements of the neutron star magnetic field allow for an estimate of the stellar wind velocity of the optical companion without using complicated spectroscopic measurements. For nonequilibrium pulsars, a maximum value is shown to exist for the spin-down rate of the accreting neutron star. From observations of the spin-down rate and the X-ray luminosity in such pulsars (e.g., GX 1+4, SXP 1062, and 4U 2206+54), a lower limit can be put on the neutron star magnetic field, which in all cases turns out to be close to the standard value and which agrees with cyclotron line measurements. Furthermore, both explains the spin-up/spin-down of the pulsar frequency on large time-scales and also accounts for the irregular short

  4. Partial accretion in the propeller stage of accreting millisecond X-ray pulsars

    NASA Astrophysics Data System (ADS)

    Gungor, Can; Gogus, Ersin; Eksi, Kazim Yavuz; Guver, Tolga

    2016-07-01

    Accreting millisecond X-ray pulsars (AMXPs) are very important objects for studying the stages of disk - magnetosphere interaction as these objects may show different stages in an observable duration. A typical X-ray light curve of an outburst of AMXP has a fast rise and an exponential decay phases. Most of the outbursts have a knee where the flux goes from the slow decay stage to the rapid decay stage. This knee may be linked to the transition from accretion to propeller stage. Since, after the knee, the X-ray luminosity of the source is still higher than its quiescent level, the accretion from inner disc must be continuing in the propeller stage with a lower fraction than in the accretion stage. The X-ray does not only come from accretion onto the poles but the inner parts of the disk may also contribute to the total X-ray luminosity. To infer what fraction (f) of the inflowing matter accretes onto the star the light curve in the propeller stage, one should first separate the emission originating from the disk and obtain a light curve of X-ray emission only from the magnetic poles. We provide a new method to infer from the observational data the fraction of accreting matter onto the neutron star pole to the mass transferring from outer layers of the disc to the inner disc (f), as a function of the fastness parameter (ω_{*}), assuming the knee is due to the transition from accretion to the propeller stage. We transform X-ray luminosities to the mass fraction, f, and the time scale of outburst to fastness parameter, ω_*. It allows us to compare different types of outbursts of an AMXP in f - ω_* space which is universal for a unique system. We analysed the Rossi X-ray Timing Explorer/Proportional Counter Array (RXTE/PCA) observations of the 2000 and the 2011 outbursts and the Swift Gamma-Ray Burst Mission/X-ray Telescope (SWIFT/XRT) data of the 2013 outburst of the most known AMXP, Aql X-1 using a combination of blackbody representing hot spot, disk blackbody

  5. Dips in the pulse profiles of accretion powered X-ray pulsars

    NASA Astrophysics Data System (ADS)

    Devasia, Jincy; Paul, Biswajit; James, Marykutty; Indulekha, Kavila

    We will report detection of sharp dips in the pulse profiles of several persistent and transient accretion powered X-ray pulsars using RXTE observations.The pulse profiles of accretion pow-ered pulsars carry a lot of information regarding the radiative processes near the surface of the star, magnetic fields that channel the accretion flow etc. The dips in pulse profiles can be due to the interaction of accretion column with the emitting radiation as it passes through the line of sight. We have also investigated the energy dependence and phase width of these dips to get a better understanding of the nature of this feature.

  6. Theory of quasi-spherical accretion in X-ray pulsars

    NASA Astrophysics Data System (ADS)

    Shakura, N.; Postnov, K.; Kochetkova, A.; Hjalmarsdotter, L.

    2012-02-01

    A theoretical model for quasi-spherical subsonic accretion on to slowly rotating magnetized neutron stars is constructed. In this model, the accreting matter subsonically settles down on to the rotating magnetosphere forming an extended quasi-static shell. This shell mediates the angular momentum removal from the rotating neutron star magnetosphere during spin-down episodes by large-scale convective motions. The accretion rate through the shell is determined by the ability of the plasma to enter the magnetosphere. The settling regime of accretion can be realized for moderate accretion rates ? g s-1. At higher accretion rates, a free-fall gap above the neutron star magnetosphere appears due to rapid Compton cooling, and accretion becomes highly non-stationary. From observations of the spin-up/spin-down rates (the angular rotation frequency derivative ?, and ? near the torque reversal) of X-ray pulsars with known orbital periods, it is possible to determine the main dimensionless parameters of the model, as well as to estimate the magnetic field of the neutron star. We illustrate the model by determining these parameters for three wind-fed X-ray pulsars GX 301-2, Vela X-1 and GX 1+4. The model explains both the spin-up/spin-down of the pulsar frequency on large time-scales and the irregular short-term frequency fluctuations, which can correlate or anticorrelate with the X-ray flux fluctuations in different systems. It is shown that in real pulsars an almost iso-angular-momentum rotation law with ω˜ 1/R2, due to strongly anisotropic radial turbulent motions sustained by large-scale convection, is preferred.

  7. Radio upper limits for the accreting millisecond X-ray pulsar IGR J17511-3057

    NASA Astrophysics Data System (ADS)

    Miller-Jones, J. C. A.; Russell, D. M.; Migliari, S.

    2009-10-01

    We report on recent radio observations of the newly-detected accreting millisecond X-ray pulsar, IGR J17511-3057 (ATels #2196, #2197, #2198, #2199, #2215, #2216, #2220, #2221). We used the Very Large Array (VLA) to observe the source under observing program AM971. The array was in its relatively compact 'C' and 'DNC' configurations, and the observations were made at 8.46 GHz. In no case was the source significantly detected.

  8. Accretion X-ray ms pulsar as a probe of NS EOS

    NASA Astrophysics Data System (ADS)

    Zhang, Shu; Ji, Long

    2016-07-01

    Equation state of NS is one of the core sciences for future mission. Regarding to the possible probes, apart from the bursting ms pulsars for which the relation between the spinning light curve and the mass/radius of NS is well established theoretically, the accretion X-ray ms pulsars are the potential alternatives. However, the emission mechanism of the latter is more complicated since one has to account for the corona on top of the NS surface which provides Comptonizations that mix/distort the black body underneath. Thus disentangling the model components between the black body and the Comptonization becomes a big challenge in case of relating the spinning light curve to the mass/radius of NS. This problem is hard to be handled even with a powerful telescope owning a very large detection area. X-ray polarimetry shows us a new insight on model discrimination, and we take the accretion X-ray ms pulsar XTEJ1751-305 as an example to show how this issue could be addressed with a polarization telescope.

  9. Signs of magnetic accretion in the young Be/X-ray pulsar SXP 1062

    NASA Astrophysics Data System (ADS)

    Ikhsanov, N. R.

    2012-07-01

    The spin behaviour of the neutron star in the newly discovered young Be/X-ray long-period pulsar SXP 1062 is discussed. The star is observed to rotate with the period of 1062 s, and spin down at the rate ˜-2.6 × 10-12 Hz s-1. I show that all of the conventional accretion scenarios encounter major difficulties in explaining the rapid spin-down of the pulsar. These difficulties can be, however, avoided within the magnetic accretion scenario in which the neutron star is assumed to accrete from a magnetized wind. The spin-down rate of the pulsar can be explained within this scenario provided the surface magnetic field of the neutron star is B*˜ 4 × 1013 G. I show that the age of the pulsar in this case lies in the range (2-4) × 104 yr, which is consistent with observations. The spin evolution of the pulsar is briefly discussed.

  10. Pulse-to-pulse variations in accreting X-ray pulsars

    NASA Astrophysics Data System (ADS)

    Kretschmar, Peter; Marcu, Diana; Kühnel, Matthias; Klochkov, Dmitry; Pottschmidt, Katja; Staubert, Rüdiger; Wilson-Hodge, Colleen A.; Jenke, Peter A.; Caballero, Isabel; Fürst, Felix

    2014-01-01

    In most accreting X-ray pulsars, the periodic signal is very clear and easily shows up as soon as data covering sufficient pulse periods (a few ten) are available. The mean pulse profile is often quite typical for a given source and with minor variations repeated and recognisable across observations done years or even decades apart. At the time scale of individual pulses, significant pulse-to-pulse variations are commonly observed. While at low energies some of these variations might be explained by absorption, in the hard X-rays they will reflect changes in the accretion and subsequent emission. The amount of these variations appears to be quite different between sources and contains information about the surrounding material as well ass possibly interactions at the magnetosphere. We investigate such variations for a sample of well-known sources.

  11. X-ray observations of the accreting Be/X-ray binary pulsar A 0535+26 in outburst

    NASA Astrophysics Data System (ADS)

    Caballero, I.

    2009-04-01

    the cyclotron line energy with the X-ray luminosity are thought to be related to a change in the height of the accretion column as the mass accretion rate varies. A detailed timing analysis has been performed, and we find for the first time the onset of a spin-up, at a phase close to the periastron passage, during a normal outburst, providing evidence for an accretion disk around the neutron star. Energy-dependent pulse profiles of the source have been studied and compared to historical observations. During the rising part of the outburst a series of flares were observed. RXTE observed one of these flares, and we found during the flare the energy of the fundamental cyclotron line shifted to a significantly higher position compared to the rest of the outburst. Also, the energy-dependent pulse profiles during the flare were found to vary significantly from the rest of the outburst. These differences have been interpreted in terms of a theoretical model, based on the presence of magnetospheric instabilities at the onset of the accretion. We applied a decomposition method to A 0535+26 energy-dependent pulse profiles. Basic assumptions of the method are that the asymmetry observed in the pulse profiles is caused by non-antipodal magnetic poles, and that the emission regions have axisymmetric beam patterns. Using pulse profiles obtained from RXTE observations, the contribution of the two emission regions has been disentangled. Constraints on the geometry of the pulsar and a possible solution of the beam pattern are given. The reconstructed beam pattern is interpreted in terms of a geometrical model that includes relativistic light deflection.

  12. A New Two-fluid Radiation-hydrodynamical Model for X-Ray Pulsar Accretion Columns

    NASA Astrophysics Data System (ADS)

    West, Brent F.; Wolfram, Kenneth D.; Becker, Peter A.

    2017-02-01

    Previous research centered on the hydrodynamics in X-ray pulsar accretion columns has largely focused on the single-fluid model, in which the super-Eddington luminosity inside the column decelerates the flow to rest at the stellar surface. This type of model has been relatively successful in describing the overall properties of the accretion flows, but it does not account for the possible dynamical effect of the gas pressure. On the other hand, the most successful radiative transport models for pulsars generally do not include a rigorous treatment of the dynamical structure of the column, instead assuming an ad hoc velocity profile. In this paper, we explore the structure of X-ray pulsar accretion columns using a new, self-consistent, “two-fluid” model, which incorporates the dynamical effect of the gas and radiation pressures, the dipole variation of the magnetic field, the thermodynamic effect of all of the relevant coupling and cooling processes, and a rigorous set of physical boundary conditions. The model has six free parameters, which we vary in order to approximately fit the phase-averaged spectra in Her X-1, Cen X-3, and LMC X-4. In this paper, we focus on the dynamical results, which shed new light on the surface magnetic field strength, the inclination of the magnetic field axis relative to the rotation axis, the relative importance of gas and radiation pressures, and the radial variation of the ion, electron, and inverse-Compton temperatures. The results obtained for the X-ray spectra are presented in a separate paper.

  13. Dynamical and Radiative Properties of X-Ray Pulsar Accretion Columns: Phase-averaged Spectra

    NASA Astrophysics Data System (ADS)

    West, Brent F.; Wolfram, Kenneth D.; Becker, Peter A.

    2017-02-01

    The availability of the unprecedented spectral resolution provided by modern X-ray observatories is opening up new areas for study involving the coupled formation of the continuum emission and the cyclotron absorption features in accretion-powered X-ray pulsar spectra. Previous research focusing on the dynamics and the associated formation of the observed spectra has largely been confined to the single-fluid model, in which the super-Eddington luminosity inside the column decelerates the flow to rest at the stellar surface, while the dynamical effect of gas pressure is ignored. In a companion paper, we have presented a detailed analysis of the hydrodynamic and thermodynamic structure of the accretion column obtained using a new self-consistent model that includes the effects of both gas and radiation pressures. In this paper, we explore the formation of the associated X-ray spectra using a rigorous photon transport equation that is consistent with the hydrodynamic and thermodynamic structure of the column. We use the new model to obtain phase-averaged spectra and partially occulted spectra for Her X-1, Cen X-3, and LMC X-4. We also use the new model to constrain the emission geometry, and compare the resulting parameters with those obtained using previously published models. Our model sheds new light on the structure of the column, the relationship between the ionized gas and the photons, the competition between diffusive and advective transport, and the magnitude of the energy-averaged cyclotron scattering cross-section.

  14. Discovery of a new accreting millisecond X-ray pulsar in the globular cluster NGC 2808

    NASA Astrophysics Data System (ADS)

    Sanna, A.; Papitto, A.; Burderi, L.; Bozzo, E.; Riggio, A.; Di Salvo, T.; Ferrigno, C.; Rea, N.; Iaria, R.

    2017-01-01

    We report on the discovery of coherent pulsations at a period of 2.9 ms from the X-ray transient MAXI J0911-655 in the globular cluster NGC 2808. We observed X-ray pulsations at a frequency of 339.97 Hz in three different observations of the source performed with XMM-Newton and NuSTAR during the source outburst. This newly discovered accreting millisecond pulsar is part of an ultra-compact binary system characterised by an orbital period of 44.3 min and a projected semi-major axis of 17.6 lt-ms. Based on the mass function, we estimate a minimum companion mass of 0.024 M⊙, which assumes a neutron star mass of 1.4 M⊙ and a maximum inclination angle of 75° (derived from the lack of eclipses and dips in the light-curve of the source). We find that the Roche-lobe of the companion star could either be filled by a hot (5 × 106 K) pure helium white dwarf with a 0.028 M⊙ mass (implying i ≃ 58°) or an old (>5 Gyr) brown dwarf with metallicity abundances between solar/sub-solar and mass ranging in the interval 0.065 to 0.085 (16 < i < 21). During the outburst, the broad-band energy spectra are well described by a superposition of a weak black-body component (kT 0.5 keV) and a hard cut-off power-law with photon index Γ 1.7 and cut-off at a temperature kTe 130 keV. Up until the latest Swift-XRT observation performed on 19th July, 2016, the source had been observed in outburst for almost 150 days, which makes MAXI J0911-655 the second accreting millisecond X-ray pulsar with outburst duration longer than 100 days.

  15. IGR J17062–6143 Is an Accreting Millisecond X-Ray Pulsar

    NASA Astrophysics Data System (ADS)

    Strohmayer, Tod; Keek, Laurens

    2017-02-01

    We present the discovery of 163.65 Hz X-ray pulsations from IGR J17062‑6143 in the only observation obtained from the source with the Rossi X-ray Timing Explorer. This detection makes IGR J17062‑6143 the lowest-frequency accreting millisecond X-ray pulsar presently known. The pulsations are detected in the 2–12 keV band with an overall significance of 4.3σ and an observed pulsed amplitude of 5.54% ± 0.67% (in this band). Both dynamic power spectral and coherent phase timing analysis indicate that the pulsation frequency is decreasing during the ≈1.2 ks observation in a manner consistent with orbital motion of the neutron star. Because the observation interval is short, we cannot precisely measure the orbital period; however, periods shorter than 17 minutes are excluded at 90% confidence. For the range of acceptable circular orbits the inferred binary mass function substantially overlaps the observed range for the AMXP population as a whole.

  16. IGR J170626143 is an Accreting Millisecond X-Ray Pulsar

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod E.; Keek, Laurens

    2017-01-01

    We present the discovery of 163.65 Hz X-ray pulsations from IGR J17062-6143 in the only observation obtained from the source with the Rossi X-ray Timing Explorer. This detection makes IGR J17062-6143 the lowest frequency accreting millisecond X-ray pulsar presently known. The pulsations are detected in the 2-12 keV band with an overall significance of 4.3sigma and an observed pulsed amplitude of 5.54% +/-0.67% (in this band). Both dynamic power spectral and coherent phase timing analysis indicate that the pulsation frequency is decreasing during the approx. =1.2 ks observation in a manner consistent with orbital motion of the neutron star. Because the observation interval is short, we cannot precisely measure the orbital period; however, periods shorter than 17 minutes are excluded at 90% confidence. For the range of acceptable circular orbits the inferred binary mass function substantially overlaps the observed range for the AMXP population as a whole.

  17. Contrasting Behaviour from Two Be/X-ray Binary Pulsars: Insights into Differing Neutron Star Accretion Modes

    NASA Technical Reports Server (NTRS)

    Townsend, L. J.; Drave, S. P.; Hill, A. B.; Coe, M. J.; Corbet, R. H. D.; Bird, A. J.

    2013-01-01

    In this paper we present the identification of two periodic X-ray signals coming from the direction of the Small Magellanic Cloud (SMC). On detection with the Rossi X-ray Timing Explorer (RXTE), the 175.4 s and 85.4 s pulsations were considered to originate from new Be/X-ray binary (BeXRB) pulsars with unknown locations. Using rapid follow-up INTEGRAL and XMM-Newton observations, we show the first pulsar (designated SXP175) to be coincident with a candidate high-mass X-ray binary (HMXB) in the northern bar region of the SMC undergoing a small Type II outburst. The orbital period (87d) and spectral class (B0-B0.5IIIe) of this system are determined and presented here for the first time. The second pulsar is shown not to be new at all, but is consistent with being SXP91.1 - a pulsar discovered at the very beginning of the 13 year long RXTE key monitoring programme of the SMC. Whilst it is theoretically possible for accreting neutron stars to change spin period so dramatically over such a short time, the X-ray and optical data available for this source suggest this spin-up is continuous during long phases of X-ray quiescence, where accretion driven spin-up of the neutron star should be minimal.

  18. A radiation-hydrodynamics model of accretion columns for ultra-luminous X-ray pulsars

    NASA Astrophysics Data System (ADS)

    Kawashima, Tomohisa; Mineshige, Shin; Ohsuga, Ken; Ogawa, Takumi

    2016-10-01

    Prompted by the recent discovery of pulsed emission from an ultra-luminous X-ray source, M 82 X-2 ("ULX-pulsar"), we perform a two-dimensional radiation-hydrodynamics simulation of a supercritical accretion flow onto a neutron star through a narrow accretion column. We set an accretion column with a cone shape filled with tenuous gas with the density of 10-4 g cm-3 above a neutron star and solve the two-dimensional gas motion and radiative transfer within the column. The side boundaries are set such that radiation can freely escape, but gas cannot. Since the initial gas layer is not in a hydrostatic balance, the column gas falls onto the neutron-star surface, and thereby a shock is generated. As a result, the accretion column is composed of two regions: an upper, nearly free-fall region and a lower settling region, as noted by Basko and Sunyaev (1976, MNRAS, 175, 395). The average accretion rate is very high; dot{M}˜ 10^{2{-}3} L_E/c2 (with LE being the Eddington luminosity), and so radiation energy dominates over gas internal energy entirely within the column. Despite the high accretion rate, the radiation flux in the laboratory frame is kept barely below LE/(4πr2) at a distance r in the settling region so that matter can slowly accrete. This adjustment is made possible, since a large amount of photons produced via dissipation of kinetic energy of matter can escape through the side boundaries. The total luminosity can greatly exceed LE by several orders of magnitude, whereas the apparent luminosity observed from the top of the column is much less. Due to such highly anisotropic radiation fields, the observed flux should exhibit periodic variations with the rotation period, provided that the rotation and magnetic axes are misaligned.

  19. A Suzaku View of Accretion-powered X-Ray Pulsar GX 1+4

    NASA Astrophysics Data System (ADS)

    Yoshida, Yuki; Kitamoto, Shunji; Suzuki, Hiroo; Hoshino, Akio; Naik, Sachindra; Jaisawal, Gaurava K.

    2017-03-01

    We present results obtained from a Suzaku observation of the accretion-powered X-ray pulsar GX 1+4. A broadband continuum spectrum of the pulsar was found to be better described by a simple model consisting of a blackbody component and an exponential cutoff power law than the previously used compTT continuum model. Though the pulse profile had a sharp dip in soft X-rays (<10 keV), phase-resolved spectroscopy confirmed that the dimming was not due to an increase in photoelectric absorption. Phase-sliced spectral analysis showed the presence of a significant spectral modulation beyond 10 keV except for the dip phase. A search for the presence of a cyclotron resonance scattering feature in the Suzaku spectra yielded a negative result. Iron K-shell (K{}α and {{{K}}}β ) emission lines from nearly neutral iron ions (

  20. The Stochastic X-Ray Variability of the Accreting Millisecond Pulsar MAXI J0911-655

    NASA Technical Reports Server (NTRS)

    Bult, Peter

    2017-01-01

    In this work, I report on the stochastic X-ray variability of the 340 hertz accreting millisecond pulsar MAXI J0911-655. Analyzing pointed observations of the XMM-Newton and NuSTAR observatories, I find that the source shows broad band-limited stochastic variability in the 0.01-10 hertz range with a total fractional variability of approximately 24 percent root mean square timing residuals in the 0.4 to 3 kiloelectronvolt energy band that increases to approximately 40 percent root mean square timing residuals in the 3 to 10 kiloelectronvolt band. Additionally, a pair of harmonically related quasi-periodic oscillations (QPOs) are discovered. The fundamental frequency of this harmonic pair is observed between frequencies of 62 and 146 megahertz. Like the band-limited noise, the amplitudes of the QPOs show a steep increase as a function of energy; this suggests that they share a similar origin, likely the inner accretion flow. Based on their energy dependence and frequency relation with respect to the noise terms, the QPOs are identified as low-frequency oscillations and discussed in terms of the Lense-Thirring precession model.

  1. The Stochastic X-Ray Variability of the Accreting Millisecond Pulsar MAXI J0911–655

    NASA Astrophysics Data System (ADS)

    Bult, Peter

    2017-03-01

    In this work, I report on the stochastic X-ray variability of the 340 Hz accreting millisecond pulsar MAXI J0911–655. Analyzing pointed observations of the XMM-Newton and NuSTAR observatories, I find that the source shows broad band-limited stochastic variability in the 0.01{--}10 {Hz} range with a total fractional variability of ∼ 24 % rms in the 0.4{--}3 {keV} energy band that increases to ∼ 40 % rms in the 3–10 keV band. Additionally, a pair of harmonically related quasi-periodic oscillations (QPOs) are discovered. The fundamental frequency of this harmonic pair is observed between frequencies of 62 and 146 mHz. Like the band-limited noise, the amplitudes of the QPOs show a steep increase as a function of energy; this suggests that they share a similar origin, likely the inner accretion flow. Based on their energy dependence and frequency relation with respect to the noise terms, the QPOs are identified as low-frequency oscillations and discussed in terms of the Lense–Thirring precession model.

  2. The optical counterparts of accreting millisecond X-ray pulsars during quiescence

    NASA Astrophysics Data System (ADS)

    D'Avanzo, P.; Campana, S.; Casares, J.; Covino, S.; Israel, G. L.; Stella, L.

    2009-12-01

    Context: Eight accreting millisecond X-ray pulsars (AMXPs) are known to date. Although these systems are well studied at high energies, very little information is available for their optical/NIR counterparts. Up to now, only two of them, SAX J1808.4-3658 and IGR J00291+5934, have a secure multi-band detection of their optical counterparts in quiescence. Aims: All these systems are transient low-mass X-ray binaries. Optical and NIR observations carried out during quiescence give a unique opportunity to constrain the nature of the donor star and to investigate the origin of the observed quiescent luminosity at long wavelengths. In addition, optical observations can be fundamental as they ultimately allow us to estimate the compact object mass through mass function measurements. Methods: Using data obtained with the ESO-Very Large Telescope, we performed a deep optical and NIR photometric study of the fields of XTE J1814-338 and of the ultracompact systems XTE J0929-314 and XTE J1807-294 during quiescence in order to look for the presence of a variable counterpart. If suitable candidates were found, we also carried out optical spectroscopy. Results: We present here the first multi-band (VR) detection of the optical counterpart of XTE J1814-338 in quiescence together with its optical spectrum. The optical light curve shows variability in both bands consistent with a sinusoidal modulation at the known 4.3 h orbital period and presents a puzzling decrease of the V-band flux around superior conjunction that may be interpreted as a partial eclipse. The marginal detection of the very faint counterpart of XTE J0929-314 and deep upper limits for the optical/NIR counterpart of XTE J1807-294 are also reported. We also briefly discuss the results reported in the literature for the optical/NIR counterpart of XTE J1751-305. Conclusions: Our findings are consistent with AMXPs being systems containing an old, weakly magnetized neutron star, reactivated as a millisecond radio pulsar

  3. Monitoring Accreting X-ray Pulsars with the GLAST Burst Monitor

    NASA Technical Reports Server (NTRS)

    Wilson, Colleen A.; Finger, Mark H.; Patel, Sandeep K.; Bhat, P. Narayana; Preece, Robert D.; Meegan, Charles A.

    2007-01-01

    Accreting pulsars are exceptionally good laboratories for probing the detailed physics of accretion onto magnetic stars. While similar accretion flows also occur in other types of astrophysical systems, e.g. magnetic CVs, only neutron stars have a small enough moment of inertia for the accretion of angular momentum to result in measurable changes in spin-frequency in a timescale of days. Long-term monitoring of accreting pulsar spin-frequencies and fluxes was demonstrated with the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory. Here we present sample results from BATSE, discuss measurement techniques appropriate for GBM, and estimate the expected GBM sensitivity.

  4. An accreting pulsar with extreme properties drives an ultraluminous x-ray source in NGC 5907

    NASA Astrophysics Data System (ADS)

    Israel, Gian Luca; Belfiore, Andrea; Stella, Luigi; Esposito, Paolo; Casella, Piergiorgio; De Luca, Andrea; Marelli, Martino; Papitto, Alessandro; Perri, Matteo; Puccetti, Simonetta; Castillo, Guillermo A. Rodríguez; Salvetti, David; Tiengo, Andrea; Zampieri, Luca; D’Agostino, Daniele; Greiner, Jochen; Haberl, Frank; Novara, Giovanni; Salvaterra, Ruben; Turolla, Roberto; Watson, Mike; Wilms, Joern; Wolter, Anna

    2017-02-01

    Ultraluminous x-ray sources (ULXs) in nearby galaxies shine brighter than any x-ray source in our Galaxy. ULXs are usually modeled as stellar-mass black holes (BHs) accreting at very high rates or intermediate-mass BHs. We present observations showing that NGC 5907 ULX is instead an x-ray accreting neutron star (NS) with a spin period evolving from 1.43 seconds in 2003 to 1.13 seconds in 2014. It has an isotropic peak luminosity of ~1000 times the Eddington limit for a NS at 17.1 megaparsec. Standard accretion models fail to explain its luminosity, even assuming beamed emission, but a strong multipolar magnetic field can describe its properties. These findings suggest that other extreme ULXs (x-ray luminosity ≥ 1041 erg second‑1) might harbor NSs.

  5. An accreting pulsar with extreme properties drives an ultraluminous x-ray source in NGC 5907.

    PubMed

    Israel, Gian Luca; Belfiore, Andrea; Stella, Luigi; Esposito, Paolo; Casella, Piergiorgio; De Luca, Andrea; Marelli, Martino; Papitto, Alessandro; Perri, Matteo; Puccetti, Simonetta; Castillo, Guillermo A Rodríguez; Salvetti, David; Tiengo, Andrea; Zampieri, Luca; D'Agostino, Daniele; Greiner, Jochen; Haberl, Frank; Novara, Giovanni; Salvaterra, Ruben; Turolla, Roberto; Watson, Mike; Wilms, Joern; Wolter, Anna

    2017-02-24

    Ultraluminous x-ray sources (ULXs) in nearby galaxies shine brighter than any x-ray source in our Galaxy. ULXs are usually modeled as stellar-mass black holes (BHs) accreting at very high rates or intermediate-mass BHs. We present observations showing that NGC 5907 ULX is instead an x-ray accreting neutron star (NS) with a spin period evolving from 1.43 seconds in 2003 to 1.13 seconds in 2014. It has an isotropic peak luminosity of [Formula: see text]1000 times the Eddington limit for a NS at 17.1 megaparsec. Standard accretion models fail to explain its luminosity, even assuming beamed emission, but a strong multipolar magnetic field can describe its properties. These findings suggest that other extreme ULXs (x-ray luminosity [Formula: see text] 10(41) erg second[Formula: see text]) might harbor NSs.

  6. The anomalous X-ray pulsars

    NASA Astrophysics Data System (ADS)

    Chen, Rui; Li, Xiangdong

    2002-03-01

    In the last few years it has been recognized that a group of X-ray pulsars have peculiar properties which set them apart from the majority of accreting pulars in X-ray binaries. They are called the Anomalous X-ray Pulsars (AXP). These objects are characterized by very soft X-ray spectra with low and steady X-ray fluxes, narrow-distributed spin periods, steady spin-down, no optical/infrared counterparts. Some of them may associate with supernova remnants. The nature of AXP remains mysterious. It has been suggested that AXP are accreting neutron stars, or solitary "magnetars", neutron stars with super strong magnetic fields (≍1010-1011T). In this paper we review the recent progress in the studies of AXP, and discuss the possible implications from comparison of AXP with other neutron stars, such as radio pulsars, radio quiet X-ray pulsar candidates and soft γ-ray repeaters.

  7. The End of Accretion: The X-Ray Binary/Millisecond Pulsar Transition Object PSR J1023+0038

    NASA Astrophysics Data System (ADS)

    Archibald, Anne

    2015-04-01

    Millisecond radio pulsars (MSRPs), those spinning hundreds of times per second, have long been understood to be old pulsars that have been spun up by the accretion of matter from a companion in a low-mass X-ray binary (LMXB) phase. Yet the details of this transformation, particularly the end of the accretion process and the birth of a radio pulsar, remain mysterious. I will describe the discovery and detailed study of the first object known to transition between MSRP and LMXB states, PSR J1023+0038. By dint of a multiwavelength campaign of observations in the RMSP state, we are able to measure all the key system parameters and show the existence of an X-ray shock close to the pulsar-facing side of the companion. Since the discovery of PSR J1023+0038, two more objects (XSS J12270-4859 and M28I) have been found to make the same transition, and the study of these transitioning objects has become an active field of research. Most interestingly, PSR J1023+0038 has transitioned back into an LMXB state, with an active accretion disk and a puzzling increase in gamma-ray flux. Our detailed picture of the system allows us to test models of accretion against the phenomena we observe in PSR J1023+0038, and in fact these observations challenge current models: in spite of the low luminosity of the system (and low inferred accretion rate) some material is penetrating the centrifugal barrier and falling on the neutron-star surface. Key evidence for explaining this puzzling behaviour will come when PSR J1023+0038 returns to an MSRP state and we are able to compare pulsar timing models from after the LMXB state with those we obtained in this work.

  8. NuSTAR DETECTION OF HARD X-RAY PHASE LAGS FROM THE ACCRETING PULSAR GS 0834–430

    SciTech Connect

    Miyasaka, Hiromasa; Harrison, Fiona A.; Fürst, Felix; Bellm, Eric C.; Grefenstette, Brian W.; Madsen, Kristin K.; Walton, Dominic J.; Bachetti, Matteo; Barret, Didier; Boggs, Steven E.; Craig, William W.; Tomsick, John A.; Chakrabarty, Deepto; Chenevez, Jerome; Christensen, Finn E.; Hailey, Charles J.; Natalucci, Lorenzo; Pottschmidt, Katja; Stern, Daniel; Wilms, Jörn; and others

    2013-09-20

    The Nuclear Spectroscopic Telescope Array hard X-ray telescope observed the transient Be/X-ray binary GS 0834–430 during its 2012 outburst—the first active state of this system observed in the past 19 yr. We performed timing and spectral analysis and measured the X-ray spectrum between 3-79 keV with high statistical significance. We find the phase-averaged spectrum to be consistent with that observed in many other magnetized, accreting pulsars. We fail to detect cyclotron resonance scattering features that would allow us to constrain the pulsar's magnetic field in either phase-averaged or phase-resolved spectra. Timing analysis shows a clearly detected pulse period of ∼12.29 s in all energy bands. The pulse profiles show a strong, energy-dependent hard phase lag of up to 0.3 cycles in phase, or about 4 s. Such dramatic energy-dependent lags in the pulse profile have never before been reported in high-mass X-ray binary pulsars. Previously reported lags have been significantly smaller in phase and restricted to low energies (E < 10 keV). We investigate the possible mechanisms that might produce this energy-dependent pulse phase shift. We find the most likely explanation for this effect is a complex beam geometry.

  9. THE QUIESCENT X-RAY PROPERTIES OF THE ACCRETING MILLISECOND X-RAY PULSAR AND ECLIPSING BINARY SWIFT J1749.4-2807

    SciTech Connect

    Degenaar, N.; Patruno, A.; Wijnands, R.

    2012-09-10

    Swift J1749.4-2807 is a transient neutron star low-mass X-ray binary that contains an accreting millisecond X-ray pulsar spinning at 518 Hz. It is the first of its kind that displays X-ray eclipses, which holds significant promise to precisely constrain the mass of the neutron star. We report on a {approx_equal} 105 ks long XMM-Newton observation performed when Swift J1749.4-2807 was in quiescence. We detect the source at a 0.5-10 keV luminosity of {approx_equal}1 Multiplication-Sign 10{sup 33}(D/6.7 kpc){sup 2} erg s{sup -1}. The X-ray light curve displays three eclipses that are consistent in orbital phase and duration with the ephemeris derived during outburst. Unlike most quiescent neutron stars, the X-ray spectrum can be adequately described with a simple power law, while a pure-hydrogen atmosphere model does not fit the data. We place an upper limit on the 0.01-100 keV thermal luminosity of the cooling neutron star of {approx}< 2 Multiplication-Sign 10{sup 33} erg s{sup -1} and constrain its temperature to be {approx}< 0.1 keV (for an observer at infinity). Timing analysis does not reveal evidence for X-ray pulsations near the known spin frequency of the neutron star or its first overtone with a fractional rms of {approx}< 34% and {approx}< 28%, respectively. We discuss the implications of our findings for dynamical mass measurements, the thermal state of the neutron star, and the origin of the quiescent X-ray emission.

  10. DISCOVERY OF A 205.89 Hz ACCRETING MILLISECOND X-RAY PULSAR IN THE GLOBULAR CLUSTER NGC 6440

    SciTech Connect

    Altamirano, D.; Patruno, A.; Linares, M.; Wijnands, R.; Van der Klis, M.; Heinke, C. O.; Markwardt, C.; Strohmayer, T. E.; Swank, J. H.

    2010-03-20

    We report on the discovery of the second accreting millisecond X-ray pulsar (AMXP) in the globular cluster NGC 6440. Pulsations with a frequency of 205.89 Hz were detected with RXTE on 2009 August 30, October 1 and October 28, during the decays of {approx}<4 day outbursts of a newly X-ray transient source in NGC 6440. By studying the Doppler shift of the pulsation frequency, we find that the system is an ultra-compact binary with an orbital period of 57.3 minutes and a projected semimajor axis of 6.22 lt-ms. Based on the mass function, we estimate a lower limit to the mass of the companion to be 0.0067 M {sub sun} (assuming a 1.4 M {sub sun} neutron star). This new pulsar shows the shortest outburst recurrence time among AMXPs ({approx}1 month). If this behavior does not cease, this AMXP has the potential to be one of the best sources in which to study how the binary system and the neutron star spin evolve. Furthermore, the characteristics of this new source indicate that there might exist a population of AMXPs undergoing weak outbursts which are undetected by current all-sky X-ray monitors. NGC 6440 is the only globular cluster to host two known AMXPs, while no AMXPs have been detected in any other globular cluster.

  11. Broad-band spectral analysis of the accreting millisecond X-ray pulsar SAX J1748.9-2021

    NASA Astrophysics Data System (ADS)

    Pintore, F.; Sanna, A.; Di Salvo, T.; Del Santo, M.; Riggio, A.; D'Aì, A.; Burderi, L.; Scarano, F.; Iaria, R.

    2016-04-01

    We analysed a 115-ks XMM-Newton observation and the stacking of 8 d of INTEGRAL observations, taken during the raise of the 2015 outburst of the accreting millisecond X-ray pulsar SAX J1748.9-2021. The source showed numerous type-I burst episodes during the XMM-Newton observation, and for this reason we studied separately the persistent and burst epochs. We described the persistent emission with a combination of two soft thermal components, a cold thermal Comptonization component (˜2 keV) and an additional hard X-ray emission described by a power law (Γ ˜ 2.3). The continuum components can be associated with an accretion disc, the neutron star (NS) surface and a thermal Comptonization emission coming out of an optically thick plasma region, while the origin of the high-energy tail is still under debate. In addition, a number of broad (σ = 0.1-0.4 keV) emission features likely associated with reflection processes have been observed in the XMM-Newton data. The estimated 1.0-50 keV unabsorbed luminosity of the source is ˜5 × 1037 erg s-1, about 25 per cent of the Eddington limit assuming a 1.4 M⊙ NS. We suggest that the spectral properties of SAX J1748.9-2021 are consistent with a soft state, differently from many other accreting X-ray millisecond pulsars which are usually found in the hard state. Moreover, none of the observed type-I burst reached the Eddington luminosity. Assuming that the burst ignition and emission are produced above the whole NS surface, we estimate an NS radius of ˜7-8 km, consistent with previous results.

  12. A MODEL FOR THE WAVEFORM BEHAVIOR OF ACCRETING MILLISECOND X-RAY PULSARS: NEARLY ALIGNED MAGNETIC FIELDS AND MOVING EMISSION REGIONS

    SciTech Connect

    Lamb, Frederick K.; Boutloukos, Stratos; Van Wassenhove, Sandor; Chamberlain, Robert T.; Lo, Ka Ho; Clare, Alexander; Yu Wenfei; Miller, M. Coleman

    2009-11-20

    We investigate further a model of the accreting millisecond X-ray pulsars we proposed earlier. In this model, the X-ray-emitting regions of these pulsars are near their spin axes but move. This is to be expected if the magnetic poles of these stars are close to their spin axes, so that accreting gas is channeled there. As the accretion rate and the structure of the inner disk vary, gas is channeled along different field lines to different locations on the stellar surface, causing the X-ray-emitting areas to move. We show that this 'nearly aligned moving spot model' can explain many properties of the accreting millisecond X-ray pulsars, including their generally low oscillation amplitudes and nearly sinusoidal waveforms; the variability of their pulse amplitudes, shapes, and phases; the correlations in this variability; and the similarity of the accretion- and nuclear-powered pulse shapes and phases in some. It may also explain why accretion-powered millisecond pulsars are difficult to detect, why some are intermittent, and why all detected so far are transients. This model can be tested by comparing with observations the waveform changes it predicts, including the changes with accretion rate.

  13. NuSTAR Discovery of a Cyclotron Line in the Accreting X-Ray Pulsar IGR J16393-4643

    NASA Astrophysics Data System (ADS)

    Bodaghee, Arash; Tomsick, John A.; Fornasini, Francesca M.; Krivonos, Roman; Stern, Daniel; Mori, Kaya; Rahoui, Farid; Boggs, Steven E.; Christensen, Finn E.; Craig, William W.; Hailey, Charles J.; Harrison, Fiona A.; Zhang, William W.

    2016-06-01

    The high-mass X-ray binary and accreting X-ray pulsar IGR J16393-4643 was observed by the Nuclear Spectroscope Telescope Array in the 3-79 keV energy band for a net exposure time of 50 ks. We present the results of this observation which enabled the discovery of a cyclotron resonant scattering feature with a centroid energy of {29.3}-1.3+1.1 keV. This allowed us to measure the magnetic field strength of the neutron star for the first time: B = (2.5 ± 0.1) × 1012 G. The known pulsation period is now observed at 904.0 ± 0.1 s. Since 2006, the neutron star has undergone a long-term spin-up trend at a rate of \\dot{P}=-2× {10}-8 s s-1 (-0.6 s per year, or a frequency derivative of \\dot{ν }=3× {10}-14 Hz s-1). In the power density spectrum, a break appears at the pulse frequency which separates the zero slope at low frequency from the steeper slope at high frequency. This addition of angular momentum to the neutron star could be due to the accretion of a quasi-spherical wind, or it could be caused by the transient appearance of a prograde accretion disk that is nearly in corotation with the neutron star whose magnetospheric radius is around 2 × 108 cm.

  14. A possible 55-d X-ray period of the ultraluminous accreting pulsar M82 X-2

    NASA Astrophysics Data System (ADS)

    Kong, Albert K. H.; Hu, Chin-Ping; Lin, Lupin Chun-Che; Li, K. L.; Jin, Ruolan; Liu, C. Y.; Yen, David Chien-Chang

    2016-10-01

    We report on the possible detection of a 55-d X-ray modulation for the ultraluminous accreting pulsar M82 X-2 from archival Chandra observations. Because M82 X-2 is known to have a 2.5-d orbital period, if the 55-d period is real, then it will be the superorbital period of the system. We also investigated variabilities of three other nearby ultraluminous X-ray sources in the central region of M82 with the Chandra data, and we did not find any evidence of periodicities. Furthermore, we re-examined the previously reported 62-d periodicity near the central region of M82 by performing a systematic timing study with all the archival Rossi X-Ray Timing Explorer and Swift data. Using various dynamic timing analysis methods, we have confirmed that the 62-d period is not stable, suggesting that it is not the orbital period of M82 X-1; this is in agreement with previous work.

  15. DISCOVERY OF ECLIPSES FROM THE ACCRETING MILLISECOND X-RAY PULSAR SWIFT J1749.4-2807

    SciTech Connect

    Markwardt, C. B.; Strohmayer, T. E.

    2010-07-10

    We report the discovery of X-ray eclipses in the recently discovered accreting millisecond X-ray pulsar SWIFT J1749.4-2807. This is the first detection of X-ray eclipses in a system of this type and should enable a precise neutron star mass measurement once the companion star is identified and studied. We present a combined pulse and eclipse timing solution that enables tight constraints on the orbital parameters and inclination and shows that the companion mass is in the range 0.6-0.8 M{sub sun} for a likely range of neutron star masses, and that it is larger than a main-sequence star of the same mass. We observed two individual eclipse egresses and a single ingress. Our timing model shows that the eclipse features are symmetric about the time of 90{sup 0} longitude from the ascending node, as expected. Our eclipse timing solution gives an eclipse duration (from the mid-points of ingress to egress) of 2172 {+-} 13 s. This represents 6.85% of the 8.82 hr orbital period. This system also presents a potential measurement of 'Shapiro' delay due to general relativity; through this technique alone, we set an upper limit to the companion mass of 2.2 M{sub sun}.

  16. Discovery of Eclipses from the Accreting Millisecond X-Ray Pulsar Swift J1749.4-2807

    NASA Technical Reports Server (NTRS)

    Markwardt, C. B.; Stromhmayer, T. E.

    2010-01-01

    We report the discovery of X-ray eclipses in the recently discovered accreting millisecond X-ray pulsar SWIFT J1749.4-2807. This is the first detection of X-ray eclipses in a system of this type and should enable a precise neutron star mass measurement once the companion star is identified and studied. We present a combined pulse and eclipse timing solution that enables tight constraints on the orbital parameters and inclination and shows that the companion mass is in the range 0.6-0.8 solar mass for a likely range of neutron star masses, and that it is larger than a main-sequence star of the same mass. We observed two individual eclipse egresses and a single ingress. Our timing model shows that the eclipse features are symmetric about the time of 90 longitude from the ascending node, as expected. Our eclipse timing solution gives an eclipse duration (from the mid-points of ingress to egress) of 2172+/-13 s. This represents 6.85% of the 8.82 hr orbital period. This system also presents a potential measurement of "Shapiro" delay due to general relativity; through this technique alone, we set an upper limit to the companion mass of 2.2 Solar mass .

  17. X-Ray and Near-infrared Observations of the Obscured Accreting Pulsar IGR J18179-1621

    NASA Astrophysics Data System (ADS)

    Nowak, M. A.; Paizis, A.; Rodriguez, J.; Chaty, S.; Del Santo, M.; Grinberg, V.; Wilms, J.; Ubertini, P.; Chini, R.

    2012-10-01

    IGR J18179-1621 is an obscured accreting X-ray pulsar discovered by INTEGRAL on 2012 February 29. We report on our 20 ks Chandra-High Energy Transmission Gratings Spectrometer observation of the source performed on 2012 March 17, on two short contemporaneous Swift observations, and on our two near-infrared (Ks , Hn , and Jn ) observations performed on 2012 March 13 and 26. We determine the most accurate X-ray position of IGR J18179-1621, αJ2000 = 18h17m52.s18, δJ2000 = -16°21'31farcs68 (90% uncertainty of 0farcs6). A strong periodic variability at 11.82 s is clearly detected in the Chandra data, confirming the pulsating nature of the source, with the light-curve softening at the pulse peak. The quasi-simultaneous Chandra-Swift spectra of IGR J18179-1621 can be well fit by a heavily absorbed hard power law (N H = 2.2 ± 0.3 × 1023 cm-2 and photon index Γ = 0.4 ± 0.1) with an average absorbed 2-8 keV flux of 1.4 × 10-11 erg cm-2 s-1. At the Chandra-based position, a source is detected in our near-infrared (NIR) maps with Ks = 13.14 ± 0.04 mag, Hn = 16 ± 0.1 mag, and no Jn -band counterpart down to ~18 mag. The NIR source, compatible with 2MASS J18175218-1621316, shows no variability between 2012 March 13 and 26. Searches of the UKIDSS database show similar NIR flux levels at epochs six months prior to and after a 2007 February 11 archival Chandra observation where the source's X-ray flux was at least 87 times fainter. In many ways IGR J18179-1621 is unusual: its combination of a several week long outburst (without evidence of repeated outbursts in the historical record), high absorption column (a large fraction of which is likely local to the system), and 11.82 s period does not fit neatly into existing X-ray binary categories.

  18. X-RAY AND NEAR-INFRARED OBSERVATIONS OF THE OBSCURED ACCRETING PULSAR IGR J18179-1621

    SciTech Connect

    Nowak, M. A.; Paizis, A.; Rodriguez, J.; Chaty, S.; Grinberg, V.; Wilms, J.; Chini, R. E-mail: ada@iasf-milano.inaf.it

    2012-10-01

    IGR J18179-1621 is an obscured accreting X-ray pulsar discovered by INTEGRAL on 2012 February 29. We report on our 20 ks Chandra-High Energy Transmission Gratings Spectrometer observation of the source performed on 2012 March 17, on two short contemporaneous Swift observations, and on our two near-infrared (K{sub s} , H{sub n} , and J{sub n} ) observations performed on 2012 March 13 and 26. We determine the most accurate X-ray position of IGR J18179-1621, {alpha}{sub J2000} = 18{sup h}17{sup m}52.{sup s}18, {delta}{sub J2000} = -16 Degree-Sign 21'31.''68 (90% uncertainty of 0.''6). A strong periodic variability at 11.82 s is clearly detected in the Chandra data, confirming the pulsating nature of the source, with the light-curve softening at the pulse peak. The quasi-simultaneous Chandra-Swift spectra of IGR J18179-1621 can be well fit by a heavily absorbed hard power law (N{sub H} = 2.2 {+-} 0.3 Multiplication-Sign 10{sup 23} cm{sup -2} and photon index {Gamma} = 0.4 {+-} 0.1) with an average absorbed 2-8 keV flux of 1.4 Multiplication-Sign 10{sup -11} erg cm{sup -2} s{sup -1}. At the Chandra-based position, a source is detected in our near-infrared (NIR) maps with K{sub s} 13.14 {+-} 0.04 mag, H{sub n} = 16 {+-} 0.1 mag, and no J{sub n} -band counterpart down to {approx}18 mag. The NIR source, compatible with 2MASS J18175218-1621316, shows no variability between 2012 March 13 and 26. Searches of the UKIDSS database show similar NIR flux levels at epochs six months prior to and after a 2007 February 11 archival Chandra observation where the source's X-ray flux was at least 87 times fainter. In many ways IGR J18179-1621 is unusual: its combination of a several week long outburst (without evidence of repeated outbursts in the historical record), high absorption column (a large fraction of which is likely local to the system), and 11.82 s period does not fit neatly into existing X-ray binary categories.

  19. THE TRANSIENT ACCRETING X-RAY PULSAR XTE J1946+274: STABILITY OF X-RAY PROPERTIES AT LOW FLUX AND UPDATED ORBITAL SOLUTION

    SciTech Connect

    Marcu-Cheatham, Diana M.; Pottschmidt, Katja; Kühnel, Matthias; Müller, Sebastian; Falkner, Sebastian; Kreykenbohm, Ingo; Caballero, Isabel; Jenke, Peter J.; Wilson-Hodge, Colleen A.; Fürst, Felix; Grinberg, Victoria; Hemphill, Paul B.; Rothschild, Richard E.; Klochkov, Dmitry; Terada, Yukikatsu; and others

    2015-12-10

    We present a timing and spectral analysis of the X-ray pulsar XTE J1946+274 observed with Suzaku during an outburst decline in 2010 October and compare with previous results. XTE J1946+274 is a transient X-ray binary consisting of a Be-type star and a neutron star with a 15.75 s pulse period in a 172 days orbit with 2–3 outbursts per orbit during phases of activity. We improve the orbital solution using data from multiple instruments. The X-ray spectrum can be described by an absorbed Fermi–Dirac cut-off power-law model along with a narrow Fe Kα line at 6.4 keV and a weak Cyclotron Resonance Scattering Feature (CRSF) at ∼35 keV. The Suzaku data are consistent with the previously observed continuum flux versus iron line flux correlation expected from fluorescence emission along the line of sight. However, the observed iron line flux is slightly higher, indicating the possibility of a higher iron abundance or the presence of non-uniform material. We argue that the source most likely has only been observed in the subcritical (non-radiation dominated) state since its pulse profile is stable over all observed luminosities and the energy of the CRSF is approximately the same at the highest (∼5 × 10{sup 37} erg s{sup −1}) and lowest (∼5 × 10{sup 36} erg s{sup −1}) observed 3–60 keV luminosities.

  20. X-Ray States of Redback Millisecond Pulsars

    NASA Astrophysics Data System (ADS)

    Linares, M.

    2014-11-01

    Compact binary millisecond pulsars with main-sequence donors, often referred to as "redbacks," constitute the long-sought link between low-mass X-ray binaries and millisecond radio pulsars and offer a unique probe of the interaction between pulsar winds and accretion flows. We present a systematic study of eight nearby redbacks, using more than 100 observations obtained with Swift's X-ray Telescope. We distinguish between three main states: pulsar, disk, and outburst states. We find X-ray mode switching in the disk state of PSR J1023+0038 and XSS J12270-4859, similar to what was found in the other redback that showed evidence for accretion: rapid, recurrent changes in X-ray luminosity (0.5-10 keV, L X), between (6-9) × 1032 erg s-1 (disk-passive state) and (3-5) × 1033 erg s-1 (disk-active state). This strongly suggests that mode switching—which has not been observed in quiescent low-mass X-ray binaries—is universal among redback millisecond pulsars in the disk state. We briefly explore the implications for accretion disk truncation and find that the inferred magnetospheric radius in the disk state of PSR J1023+0038 and XSS J12270-4859 lies outside the light cylinder. Finally, we note that all three redbacks that have developed accretion disks have relatively high L X in the pulsar state (>1032 erg s-1).

  1. NuSTAR observations of the supergiant X-ray pulsar IGR J18027-2016: accretion from the stellar wind and possible cyclotron absorption line

    NASA Astrophysics Data System (ADS)

    Lutovinov, Alexander A.; Tsygankov, Sergey S.; Postnov, Konstantin A.; Krivonos, Roman A.; Molkov, Sergey V.; Tomsick, John A.

    2017-04-01

    We report on the first focused hard X-ray view of the absorbed supergiant system IGR J18027-2016 performed with the Nuclear Spectroscopic Telescope Array observatory. The pulsations are clearly detected with a period of Pspin = 139.866(1) s and a pulse fraction of about 50-60 per cent at energies from 3 to 80 keV. The source demonstrates an approximately constant X-ray luminosity on a time-scale of more than dozen years with an average spin-down rate of dot{P}≃ 6× 10^{-10} s s-1. This behaviour of the pulsar can be explained in terms of the wind accretion model in the settling regime. The detailed spectral analysis at energies above 10 keV was performed for the first time and revealed a possible cyclotron absorption feature at energy ∼23 keV. This energy corresponds to the magnetic field B ≃ 3 × 1012 G at the surface of the neutron star, which is typical for X-ray pulsars.

  2. Discovery of a soft X-ray 8 mHz QPO from the accreting millisecond pulsar IGR J00291+5934

    NASA Astrophysics Data System (ADS)

    Ferrigno, C.; Bozzo, E.; Sanna, A.; Pintore, F.; Papitto, A.; Riggio, A.; Burderi, L.; Di Salvo, T.; Iaria, R.; D'Aì, A.

    2017-04-01

    We report on the analysis of the peculiar X-ray variability displayed by the accreting millisecond X-ray pulsar IGR J00291+5934 in a 80 ks-long joint NuSTAR and XMM-Newton observation performed during the source outburst in 2015. The light curve of the source is characterized by a flaring-like behaviour, with typical rise and decay time-scales of ∼120 s. The flares are accompanied by a remarkable spectral variability, with the X-ray emission being generally softer at the peak of the flares. A strong quasi-periodic oscillation (QPO) is detected at ∼8 mHz in the power spectrum of the source and clearly associated with the flaring-like behaviour. This feature has the strongest power at soft X-rays ( ≲ 3 keV). We carried out a dedicated hardness-ratio-resolved spectral analysis and a QPO phase-resolved spectral analysis, together with an in-depth study of the source-timing properties, to investigate the origin of this behaviour. We suggest that the unusual variability of IGR J00291+5934 observed by XMM-Newton and NuSTAR could be produced by a heartbeat-like mechanism, similar to that observed in black hole X-ray binaries. The possibility that this variability, and the associated QPO, are triggered by phases of quasi-stable nuclear burning, as sustained in the literature for a number of other neutron star binaries displaying a similar behaviour, cannot be solidly tested in the case of IGR J00291+5934 due to the paucity of type I X-ray bursts detected from this source.

  3. Spacecraft Navigation Using X-ray Pulsars

    DTIC Science & Technology

    2006-01-01

    make them attractive as potential natural naviga- tion beacons and why a practical implementation looks most feasible in the X-ray band. We then...describe the history of the X-ray navigation program at NRL up through our current Defense Advanced Research Proj- ects Agency (DARPA) program. Finally, we...that produce the powerful radiation beams. These pulsars then turn off and inhabit the “pulsar graveyard.” During their lives, these pulsars make very

  4. The superslow pulsation X-ray pulsars in high mass X-ray binaries

    NASA Astrophysics Data System (ADS)

    Wang, Wei

    2013-03-01

    There exists a special class of X-ray pulsars that exhibit very slow pulsation of P spin > 1000 s in the high mass X-ray binaries (HMXBs). We have studied the temporal and spectral properties of these superslow pulsation neutron star binaries in hard X-ray bands with INTEGRAL observations. Long-term monitoring observations find spin period evolution of two sources: spin-down trend for 4U 2206+54 (P spin ~ 5560 s with Ṗ spin ~ 4.9 × 10-7 s s-1) and long-term spin-up trend for 2S 0114+65 (P spin ~ 9600 s with Ṗ spin ~ -1 × 10-6 s s-1) in the last 20 years. A Be X-ray transient, SXP 1062 (P spin ~ 1062 s), also showed a fast spin-down rate of Ṗ spin ~ 3 × 10-6 s s-1 during an outburst. These superslow pulsation neutron stars cannot be produced in the standard X-ray binary evolution model unless the neutron star has a much stronger surface magnetic field (B > 1014 G). The physical origin of the superslow spin period is still unclear. The possible origin and evolution channels of the superslow pulsation X-ray pulsars are discussed. Superslow pulsation X-ray pulsars could be younger X-ray binary systems, still in the fast evolution phase preceding the final equilibrium state. Alternatively, they could be a new class of neutron star system - accreting magnetars.

  5. X-ray states of redback millisecond pulsars

    SciTech Connect

    Linares, M.

    2014-11-01

    Compact binary millisecond pulsars with main-sequence donors, often referred to as 'redbacks', constitute the long-sought link between low-mass X-ray binaries and millisecond radio pulsars and offer a unique probe of the interaction between pulsar winds and accretion flows. We present a systematic study of eight nearby redbacks, using more than 100 observations obtained with Swift's X-ray Telescope. We distinguish between three main states: pulsar, disk, and outburst states. We find X-ray mode switching in the disk state of PSR J1023+0038 and XSS J12270-4859, similar to what was found in the other redback that showed evidence for accretion: rapid, recurrent changes in X-ray luminosity (0.5-10 keV, L {sub X}), between (6-9) × 10{sup 32} erg s{sup –1} (disk-passive state) and (3-5) × 10{sup 33} erg s{sup –1} (disk-active state). This strongly suggests that mode switching—which has not been observed in quiescent low-mass X-ray binaries—is universal among redback millisecond pulsars in the disk state. We briefly explore the implications for accretion disk truncation and find that the inferred magnetospheric radius in the disk state of PSR J1023+0038 and XSS J12270-4859 lies outside the light cylinder. Finally, we note that all three redbacks that have developed accretion disks have relatively high L {sub X} in the pulsar state (>10{sup 32} erg s{sup –1}).

  6. Be/X-Ray Pulsar Binary Science with LOFT

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, Colleen A.

    2011-01-01

    Accretion disks are ubiquitous in astronomical sources. Accretion powered pulsars are a good test bed for accretion disk physics, because unlike for other objects, the spin of the neutron star is directly observable allowing us to see the effects of angular momentum transfer onto the pulsar. The combination of a sensitive wide-field monitor and the large area detector on LOFT will enable new detailed studies of accretion powered pulsars which I will review. RXTE observations have shown an unusually high number of Be/X-ray pulsar binaries in the SMC. Unlike binaries in the Milky Way, these systems are all at the same distance, allowing detailed population studies using the sensitive LOFT WFM, potentially providing connections to star formation episodes. For Galactic accreting pulsar systems, LOFT will allow measurement of spectral variations within individual pulses, mapping the accretion column in detail for the first time. LOFT will also provide better constraints on magnetic fields in accreting pulsars, allowing measurements of cyclotron features, observations of transitions into the centrifugal inhibition regime, and monitoring of spin-up rate vs flux correlations. Coordinated multi-wavelength observations are crucial to extracting the best science from LOFT from these and numerous other objects.

  7. Partial accretion regime of accreting millisecond pulsars

    NASA Astrophysics Data System (ADS)

    Eksi, Kazim

    2016-07-01

    The inner parts of the disks around neutron stars in low mass X-ray binaries may become geometrically thick due to inhibition of accretion at the disk mid-plane when the central object is rotating rapidly. In such a case matter inflowing through the disk may keep accreting onto the poles of the neutron star from the parts of the disk away from the disk mid-plane while the matter is propelled at the disk mid-plane. An important ingredient of the evolution of millisecond pulsars is then the fraction of the inflowing matter that can accrete onto the poles in the fast rotation regime depending on the fastness parameter. This ``soft'' propeller regime may be associated with the rapid decay stage observed in the light curves of several accreting millisecond pulsars. To date only a few studies considered the partial accretion regime. By using geometrical arguments we improve the existing studies and test the model by reproducing the lightcurves of millisecond X-ray pulsars via time dependent simulations of disk evolution. We also present analytical solutions that represent disks with partial accretion.

  8. Classical Accreting Pulsars with NICER

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, Colleen A.

    2014-01-01

    Soft excesses are very common center dot Lx > 1038 erg/s - reprocessing by optically thick material at the inner edge of the accretion disk center dot Lx < 1036 erg/s - photoionized or collisionally heated diffuse gas or thermal emission from the NS surface center dot Lx 1037 erg/s - either or both types of emission center dot NICER observations of soft excesses in bright X-ray pulsars combined with reflection modeling will constrain the ionization state, metalicity and dynamics of the inner edge of the magnetically truncated accretion disk Reflection models of an accretion disk for a hard power law - Strong soft excess below 3 keV from hot X-ray heated disk - For weakly ionized case: strong recombination lines - Are we seeing changes in the disk ionization in 4U1626-26? 13 years of weekly monitoring with RXTE PCA center dot Revealed an unexpectedly large population of Be/X-ray binaries compared to the Milky Way center dot Plotted luminosities are typical of "normal" outbursts (once per orbit) center dot The SMC provides an excellent opportunity to study a homogenous population of HMXBs with low interstellar absorption for accretion disk studies. Monitoring with NICER will enable studies of accretion disk physics in X-ray pulsars center dot The SMC provides a potential homogeneous low-absorption population for this study center dot NICER monitoring and TOO observations will also provide measurements of spinfrequencies, QPOs, pulsed fluxes, and energy spectra.

  9. A radio pulsar/x-ray binary link.

    PubMed

    Archibald, Anne M; Stairs, Ingrid H; Ransom, Scott M; Kaspi, Victoria M; Kondratiev, Vladislav I; Lorimer, Duncan R; McLaughlin, Maura A; Boyles, Jason; Hessels, Jason W T; Lynch, Ryan; van Leeuwen, Joeri; Roberts, Mallory S E; Jenet, Frederick; Champion, David J; Rosen, Rachel; Barlow, Brad N; Dunlap, Bart H; Remillard, Ronald A

    2009-06-12

    Radio pulsars with millisecond spin periods are thought to have been spun up by the transfer of matter and angular momentum from a low-mass companion star during an x-ray-emitting phase. The spin periods of the neutron stars in several such low-mass x-ray binary (LMXB) systems have been shown to be in the millisecond regime, but no radio pulsations have been detected. Here we report on detection and follow-up observations of a nearby radio millisecond pulsar (MSP) in a circular binary orbit with an optically identified companion star. Optical observations indicate that an accretion disk was present in this system within the past decade. Our optical data show no evidence that one exists today, suggesting that the radio MSP has turned on after a recent LMXB phase.

  10. Modelling X-ray Pulse Profiles of Millisecond Pulsars

    NASA Astrophysics Data System (ADS)

    Leahy, D. A.; Morsink, S.; Tian, W.

    2013-03-01

    The modelling of X-ray pulse profiles from accreting millisecond pulsars is a way to infer masses and radii of neutron stars. We briefly describe how a pulse shape encodes information on the mass and radius, but also depends on other parameters such as hot spot location and observer viewing angle. A numerical model that we have developed is then described. The model includes light bending, time-delay effects, and Doppler effects for photons. The model accounts for oblateness of the neutron star, caused by the rapid rotation, and for scattered light from the surface of the accretion disk. The millisecond pulsar SAX J1808-3658 has multiple observations taken during different outbursts. The observed pulse shapes vary greatly, and it is a challenging test to fit the different observations. Some of the latest results are given.

  11. Precision Timing of Two Anomalous X-Ray Pulsars.

    PubMed

    Kaspi; Chakrabarty; Steinberger

    1999-11-01

    We report on long-term X-ray timing of two anomalous X-ray pulsars, 1RXS J170849.0-400910 and 1E 2259+586, using the Rossi X-Ray Timing Explorer. In monthly observations made over 1.4 and 2.6 yr for the two pulsars, respectively, we have obtained phase-coherent timing solutions which imply that these objects have been rotating with great stability throughout the course of our observations. For 1RXS J170849.0-400910, we find a rotation frequency of 0.0909169331(5) Hz and frequency derivative -15.687&parl0;4&parr0;x10-14 Hz s-1 for epoch MJD 51215.931. For 1E 2259+586, we find a rotation frequency of 0.1432880613(2) Hz and frequency derivative -1.0026&parl0;7&parr0;x10-14 Hz s-1 for epoch MJD 51195.583. The rms phase residuals from these simple models are only approximately 0.01 cycles for both sources. We show that the frequency derivative for 1E 2259+586 is inconsistent with that inferred from incoherent frequency observations made over the last 20 yr. Our observations are consistent with the magnetar hypothesis and make binary accretion scenarios appear unlikely.

  12. Toward an understanding of thermal X-ray emission of pulsars

    NASA Astrophysics Data System (ADS)

    Yu, M.; Xu, R. X.

    2011-01-01

    We present a theoretical model for the thermal X-ray emission properties and cooling behaviors of isolated pulsars, assuming that pulsars are solid quark stars. We calculate the heat capacity for such a quark star, including the component of the crystalline lattice and that of the extremely relativistic electron gas. The results show that the residual thermal energy cannot sustain the observed thermal X-ray luminosities seen in typical isolated X-ray pulsars. We conclude that other heating mechanisms must be in operation if the pulsars are in fact solid quark stars. Two possible heating mechanisms are explored. Firstly, for pulsars with little magnetospheric activities, accretion from the interstellar medium or from the material in the associated supernova remnants may power the observed thermal emission. In the propeller regime, a disk-accretion rate M˙˜1% of the Eddington rate with an accretion onto the stellar surface at a rate of ˜0.1%M˙ could explain the observed emission luminosities of the dim isolated neutron stars and the central compact objects. Secondly, for pulsars with significant magnetospheric activities, the pulsar spindown luminosities may have been as the sources of the thermal energy via reversing plasma current flows. A phenomenological study between pulsar bolometric X-ray luminosities and the spin energy loss rates presents the probable existence of a 1/2-law or a linear law, i.e. Lbol∞∝E˙ or Lbol∞∝E˙. This result together with the thermal properties of solid quark stars allow us to calculate the thermal evolution of such stars. Thermal evolution curves, or cooling curves, are calculated and compared with the 'temperature-age' data obtained from 17 active X-ray pulsars. It is shown that the bolometric X-ray observations of these sources are consistent with the solid quark star pulsar model.

  13. The unique opportunity to determine the mass of an accreting neutron star: the eclipsing accretion powered X-ray pulsar SWIFTJ1749.4-2807

    NASA Astrophysics Data System (ADS)

    Jonker, Peter; Eikenberry, Steve; Torres, Manuel; Steeghs, Daniel; Chakrabarty, Deepto

    2014-02-01

    In 2010 it was discovered that the peculiar transient SWIFT J1749.4-2807 exhibits pulsations at 518 Hz. Furthermore, it turned out that the source was eclipsing in a 8.8 hr orbit thereby holding the promise of a model independent neutron star mass determination. Optical or near-infrared dynamical studies offer the best prospects for constraining the neutron star equation of state, as they do not rely on any specific models concerning the neutron star itself. Using Gemini NIRI observations we identified the NIR counterpart to the pulsar. Here, we propose for Gemini near-infrared spectroscopy with FLAMINGOS-2 to obtain spectra over the orbit to measure the radial velocity semi-amplitude of the mass donor star, which will lead to a model independent mass measurement of the neutron star.

  14. X-ray studies of three binary millisecond pulsars

    NASA Astrophysics Data System (ADS)

    Webb, N. A.; Olive, J.-F.; Barret, D.

    2005-10-01

    It is thought that millisecond pulsars with white dwarf companions are born from X-ray binaries. The majority of known systems have been studied uniquely in the radio domain, which limits our understanding of such systems. We present here the X-ray observations of the millisecond pulsar PSR J0218+4232 and the two faint millisecond pulsars PSR J0751+1807 and PSR J1012+5307, which we discuss in conjunction with radio observations. We confirm the previously detected X-ray pulsations of PSR J0218+4232 and we show that its folded lightcurve is strongly dependent on energy. We present evidence to suggest that the broad band X-ray spectrum for this pulsar may not be a simple power law, but that there is some evidence for an excess of soft thermal emission over the power law spectrum, in particular from the strongest pulse, in support of a heated polar cap model for this pulsar. We also present the X-ray spectra of the two faint millisecond pulsars as well as some evidence to suggest that both of these millisecond pulsars show pulsations in the X-ray band. We then discuss the implied nature of the magnetic field configuration as a means of discriminating between competing magnetic field evolution theories in millisecond pulsars.

  15. X-Ray Pulsar Studies With RXTE

    NASA Technical Reports Server (NTRS)

    Rappaport, Saul

    2004-01-01

    Our activities here at MIT have largely concentrated on four different binary X-ray pulsars: LMC X-4; 4UO352+3O/XPer; 4U0115+63; and X1908+075. We have also recently initiated a search for millisecond X-ray pulsations in RXTE archival data for several bright LMXBs using a new technique. Since this study is just getting under way, we will not report any results here. Using RXTE timing observations of LMC X-4 we have definitively measured, for the first time, the orbital decay of this high-mass X-ray binary. The e-folding decay time scale is very close to lo6 years, comparable to, but somewhat longer than, the corresponding orbital decay times for SMC X-1 and Cen X-3. We find that the orbital decay in LMC X-4 is likely driven by tidal interactions, where the asynchronism between the orbital motion and the rotation of the companion star is maintained by the evolutionary expansion of the companion. Under NASA grant NAGS7479 we carried out RXTE observations of X Per/4U0352+30 in order to track the pulse phase over a one year interval. This effort was successful in tentatively identifying a N 250-day orbital period. However, due to the fact that the observing interval was only somewhat longer than the orbital period, we asked for the observations of X Per to continue as public, or non-proprietary observations. Dr. Jean Swank kindly agreed to the continuation of the observations and they were carried out on a less frequent basis over the next year and a half. After 72 separate observations of X Per, we have the orbital period and semimajor axis firmly determined. In addition, we were able to measure the orbital eccentricity-which turns out to be remarkably small (e = 0.10) for such a wide binary orbit. This has led us establish the birth of a neutron star with a very small (or zero) natal kick.

  16. Pulsed X-rays from the Vela pulsar

    NASA Technical Reports Server (NTRS)

    Oegelman, H.; Finley, J. P.; Zimmerman, H. U.

    1993-01-01

    An unambiguous detection by the Rosat satellite of pulsed X-ray emission from the Vela pulsar is reported. The pulse signal is soft, appearing mainly at energies less than 1 keV. The Rosat observations resolve the two sources of emission and show that the pointlike emission centered on the pulsars is soft, whereas the emission from the compact nebula is hard. The observations show that Vela more closely resembles older pulsars that the archetypal young pulsar embedded in an SNR.

  17. The energy spectrum of anomalous X-ray pulsars and soft gamma-ray repeaters

    NASA Astrophysics Data System (ADS)

    Trümper, J. E.; Zezas, A.; Ertan, Ü.; Kylafis, N. D.

    2010-07-01

    Context. Anomalous X-ray pulsars (AXPs) and soft gamma-ray repeaters (SGRs) exhibit characteristic X-ray luminosities (both soft and hard) of around 1035 erg s-1 and characteristic power-law, hard X-ray spectra extending to about 200 keV. Two AXPs also exhibit pulsed radio emission. Aims: Assuming that AXPs and SGRs accrete matter from a fallback disk, we attempt to explain both the soft and the hard X-ray emission as the result of the accretion process. We also attempt to explain their radio emission or the lack of it. Methods: We test the hypothesis that the power-law, hard X-ray spectra are produced in the accretion flow mainly by bulk-motion Comptonization of soft photons emitted at the neutron star surface. Fallback disk models invoke surface dipole magnetic fields of 1012 - 1013 G, which is what we assume here. Results: Unlike normal X-ray pulsars, for which the accretion rate is highly super-Eddington, the accretion rate is approximately Eddington in AXPs and SGRs and thus the bulk-motion Comptonization operates efficiently. As an illustrative example we reproduce both the hard and the soft X-ray spectra of AXP 4U 0142+61 well using the XSPEC package compTB. Conclusions: Our model seems to explain both the hard and the soft X-ray spectra of AXPs and SGRs, as well as their radio emission or the lack of it, in a natural way. It might also explain the short bursts observed in these sources. On the other hand, it cannot explain the giant X-ray outbursts observed in SGRs, which may result from the conversion of magnetic energy in local multipole fields.

  18. THERMAL X-RAY EMISSION FROM THE SHOCKED STELLAR WIND OF PULSAR GAMMA-RAY BINARIES

    SciTech Connect

    Zabalza, V.; Paredes, J. M.; Bosch-Ramon, V.

    2011-12-10

    Gamma-ray-loud X-ray binaries are binary systems that show non-thermal broadband emission from radio to gamma rays. If the system comprises a massive star and a young non-accreting pulsar, their winds will collide producing broadband non-thermal emission, most likely originated in the shocked pulsar wind. Thermal X-ray emission is expected from the shocked stellar wind, but until now it has neither been detected nor studied in the context of gamma-ray binaries. We present a semi-analytic model of the thermal X-ray emission from the shocked stellar wind in pulsar gamma-ray binaries, and find that the thermal X-ray emission increases monotonically with the pulsar spin-down luminosity, reaching luminosities of the order of 10{sup 33} erg s{sup -1}. The lack of thermal features in the X-ray spectrum of gamma-ray binaries can then be used to constrain the properties of the pulsar and stellar winds. By fitting the observed X-ray spectra of gamma-ray binaries with a source model composed of an absorbed non-thermal power law and the computed thermal X-ray emission, we are able to derive upper limits on the spin-down luminosity of the putative pulsar. We applied this method to LS 5039, the only gamma-ray binary with a radial, powerful wind, and obtain an upper limit on the pulsar spin-down luminosity of {approx}6 Multiplication-Sign 10{sup 36} erg s{sup -1}. Given the energetic constraints from its high-energy gamma-ray emission, a non-thermal to spin-down luminosity ratio very close to unity may be required.

  19. Galactic X-ray emission from pulsars

    NASA Technical Reports Server (NTRS)

    Harding, A. K.

    1981-01-01

    The contribution of pulsars to the gamma-ray flux from the galactic plane is examined using data from the most recent pulsar surveys. It is assumed that pulsar gamma-rays are produced by curvature radiation from relativistic particles above the polar cap and attenuated by pair production in the strong magnetic and electric fields. Assuming that all pulsars produce gamma-rays in this way, their luminosities can be predicted as a function of period and magnetic field strength. Using the distribution of pulsars in the galaxy as determined from data on 328 pulsars detected in three surveys, the local gamma-ray production spectrum, the longitude profile, and the latitude profile of pulsar gamma-ray flux are calculated. The largest sources of uncertainty in the size of the pulsar contribution are the value of the mean interstellar electron density, the turnover in the pulsar radio luminosity function, and the average pulsar magnetic field strength. A present estimate is that pulsars contribute from 15 to 20 % of the total flux of gamma-rays from the galactic plane.

  20. FORMATION OF MILLISECOND PULSARS FROM INTERMEDIATE- AND LOW-MASS X-RAY BINARIES

    SciTech Connect

    Shao Yong; Li Xiangdong

    2012-09-01

    We present a systematic study of the evolution of intermediate- and low-mass X-ray binaries consisting of an accreting neutron star of mass 1.0-1.8 M{sub Sun} and a donor star of mass 1.0-6.0 M{sub Sun }. In our calculations we take into account physical processes such as unstable disk accretion, radio ejection, bump-induced detachment, and outflow from the L{sub 2} point. Comparing the calculated results with the observations of binary radio pulsars, we report the following results. (1) The allowed parameter space for forming binary pulsars in the initial orbital period-donor mass plane increases with increasing neutron star mass. This may help explain why some millisecond pulsars with orbital periods longer than {approx}60 days seem to have less massive white dwarfs than expected. Alternatively, some of these wide binary pulsars may be formed through mass transfer driven by planet/brown-dwarf-involved common envelope evolution. (2) Some of the pulsars in compact binaries might have evolved from intermediate-mass X-ray binaries with anomalous magnetic braking. (3) The equilibrium spin periods of neutron stars in low-mass X-ray binaries are in general shorter than the observed spin periods of binary pulsars by more than one order of magnitude, suggesting that either the simple equilibrium spin model does not apply or there are other mechanisms/processes spinning down the neutron stars.

  1. Pulsars, X-ray synchrotron nebulae, and guest stars

    NASA Technical Reports Server (NTRS)

    Seward, Frederick D.; Wang, Zhen-Ru

    1988-01-01

    X-ray observations of supernova remnants and radio pulsars are used to derive luminosities of neutron stars and synchrotron nebulae. Observations of known isolated pulsars are used to develop an empirical relationship between the X-ray luminosity and the rate of loss of rotational energy. This is used to derive the characteristics of pulsars hidden in remnants which show evidence for a central compact object or associated nebular emission, but no clear pulsed signal from the neutron star itself. Possible periods and period derivatives for the hidden pulsars are discussed. Some might have periods as long as 0.5 s, and period derivatives considerably higher than that of PSR 1509 - 58, currently the pulsar with the highest known period derivative.

  2. X-ray Pulsar Navigation Algorithms and Testbed for SEXTANT

    NASA Technical Reports Server (NTRS)

    Winternitz, Luke M. B.; Hasouneh, Monther A.; Mitchell, Jason W.; Valdez, Jennifer E.; Price, Samuel R.; Semper, Sean R.; Yu, Wayne H.; Ray, Paul S.; Wood, Kent S.; Arzoumanian, Zaven; Grendreau, Keith C.

    2015-01-01

    The Station Explorer for X-ray Timing and Navigation Technology (SEXTANT) is a NASA funded technologydemonstration. SEXTANT will, for the first time, demonstrate real-time, on-board X-ray Pulsar-based Navigation (XNAV), a significant milestone in the quest to establish a GPS-like navigation capability available throughout our Solar System and beyond. This paper describes the basic design of the SEXTANT system with a focus on core models and algorithms, and the design and continued development of the GSFC X-ray Navigation Laboratory Testbed (GXLT) with its dynamic pulsar emulation capability. We also present early results from GXLT modeling of the combined NICER X-ray timing instrument hardware and SEXTANT flight software algorithms.

  3. X-ray observations of black widow pulsars

    SciTech Connect

    Gentile, P. A.; McLaughlin, M. A.; Roberts, M. S. E.; Camilo, F.; Hessels, J. W. T.; Kerr, M.; Ransom, S. M.; Ray, P. S.; Stairs, I. H.

    2014-03-10

    We describe the first X-ray observations of five short orbital period (P{sub B} < 1 day), γ-ray emitting, binary millisecond pulsars (MSPs). Four of these—PSRs J0023+0923, J1124–3653, J1810+1744, and J2256–1024—are 'black-widow' pulsars, with degenerate companions of mass <<0.1 M {sub ☉}, three of which exhibit radio eclipses. The fifth source, PSR J2215+5135, is an eclipsing 'redback' with a near Roche-lobe filling ∼0.2 solar mass non-degenerate companion. Data were taken using the Chandra X-Ray Observatory and covered a full binary orbit for each pulsar. Two pulsars, PSRs J2215+5135 and J2256–1024, show significant orbital variability while PSR J1124–3653 shows marginal orbital variability. The lightcurves for these three pulsars have X-ray flux minima coinciding with the phases of the radio eclipses. This phenomenon is consistent with an intrabinary shock emission interpretation for the X-rays. The other two pulsars, PSRs J0023+0923 and J1810+1744, are fainter and do not demonstrate variability at a level we can detect in these data. All five spectra are fit with three separate models: a power-law model, a blackbody model, and a combined model with both power-law and blackbody components. The preferred spectral fits yield power-law indices that range from 1.3 to 3.2 and blackbody temperatures in the hundreds of eV. The spectrum for PSR J2215+5135 shows a significant hard X-ray component, with a large number of counts above 2 keV, which is additional evidence for the presence of intrabinary shock emission. This is similar to what has been detected in the low-mass X-ray binary to MSP transition object PSR J1023+0038.

  4. Polarized X-rays from accreting neutron stars

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Dipankar

    2016-07-01

    Accreting neutron stars span a wide range in X-ray luminosity and magnetic field strength. Accretion may be wind-fed or disk-fed, and the dominant X-ray flux may originate in the disk or a magnetically confined accretion column. In all such systems X-ray polarization may arise due to Compton or Magneto-Compton scattering, and on some occasions polarization of non-thermal emission from jet-like ejection may also be detectable. Spectral and temporal behaviour of the polarized X-rays would carry information regarding the radiation process, as well as of the matter dynamics - and can assist the detection of effects such as the Lense-Thirring precession. This talk will review our current knowledge of the expected X-ray polarization from accreting neutron stars and explore the prospects of detection with upcoming polarimetry missions.

  5. Patterns of variability in Be/X-ray pulsars during giant outbursts

    NASA Astrophysics Data System (ADS)

    Reig, P.; Nespoli, E.

    2013-03-01

    Context. The discovery of source states in the X-ray emission of black-hole binaries and neutron-star low-mass X-ray binaries constituted a major step forward in the understanding of the physics of accretion onto compact objects. While there are numerous studies on the correlated timing and spectral variability of these systems, very little work has been done on high-mass X-ray binaries, the third major type of X-ray binaries. Accretion-powered pulsars with Be companions represent the most numerous group of high-mass X-ray binaries. When active, they are amongst the brightest extra-solar objects in the X-ray sky and are characterised by dramatic variability in brightness on timescales of days. Aims: The main goal of this work is to investigate whether Be accreting X-ray pulsars display source states and characterise those states through their spectral and timing properties. Methods: We have made a systematic study of the power spectra, energy spectra and X-ray hardness-intensity diagrams of nine Be/X-ray pulsars. Energy spectra were fitted with an absorbed power-law modified by an exponential cutoff. Discrete components such as iron emission lines and cyclotron lines were represented by Gaussian and pseudo-Lorentzian profiles, respectively. Power spectra were fitted by a combination of Lorentzian functions. The evolution of the timing and spectral parameters were monitored through changes over two orders of magnitude in luminosity. Results: We find that Be/X-ray pulsars trace two different branches in the hardness-intensity diagram: the horizontal branch corresponds to a low-intensity state of the source and it is characterised by fast colour and spectral changes and high X-ray variability. The diagonal branch is a high-intensity state that emerges when the X-ray luminosity exceeds a critical limit. The photon index anticorrelates with X-ray flux in the horizontal branch but correlates with it in the diagonal branch. The correlation between quasi

  6. On the magnetic fields of Be/X-ray pulsars in the Small Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Ikhsanov, N. R.; Mereghetti, S.

    2015-12-01

    We explore the possibility of explaining the properties of the Be/X-ray pulsars observed in the Small Magellanic Cloud (SMC) within the magnetic levitation accretion scenario. This implies that their X-ray emission is powered by a wind-fed accretion on to a neutron star (NS) which captures matter from a magnetized stellar wind. The NS in this case is accreting matter from a non-Keplerian magnetically levitating disc which is surrounding its magnetosphere. This allows us to explain the observed periods of the pulsars in terms of spin equilibrium without the need of invoking dipole magnetic fields outside the usual range ˜1011-1013 G inferred from cyclotron features of Galactic high-mass X-ray binaries. We find that the equilibrium period of a NS, under certain conditions, depends strongly on the magnetization of the stellar wind of its massive companion and, correspondingly, on the magnetic field of the massive companion itself. This may help to explain why similar NSs in binaries with similar properties rotate with different periods yielding a large scatter of periods of the accretion-powered pulsar observed in SMC and our galaxy.

  7. Discovery of the Orbit of the X-ray pulsar OAO 1657-415

    NASA Technical Reports Server (NTRS)

    Chakrabarty, Deepto; Grunsfeld, John M.; Prince, Thomas A.; Bildsten, Lars; Finger, Mark H.; Wilson, Robert B.; Fishman, Gerald J.; Meegan, Charles A.; Paciesas, William S.

    1993-01-01

    Timing observations of the 38 s accreting X-ray pulsar OAO 1657-415 made with the BATSE large-area detectors on the Compton Gamma Ray Observatory have revealed a binary orbit with an X-ray eclipse by the stellar companion. From the pulsar mass function fx(M) = 11.7 +/- 0.2 solar masses and the measured eclipse half-angle theta(e) = 29.7 +/- 1.3 deg, we infer that the stellar companion is a supergiant of spectral class B0-B6. If the companion can be identified and its orbital velocity measured, the neutron star mass can be constrained. Both intrinsic spin-up and spin-down of the pulsar were measured during our observation.

  8. On the Magnetic Field of the Ultraluminous X-Ray Pulsar M82 X-2

    NASA Astrophysics Data System (ADS)

    Xu, Kun; Li, Xiang-Dong

    2017-04-01

    The discovery of the ultraluminous X-ray pulsar M82 X-2 has stimulated lively discussion on the nature of the accreting neutron star. In most of the previous studies the magnetic field of the neutron star was derived from the observed spin-up/down rates based on the standard thin, magnetized accretion disk model. However, under super-Eddington accretion the inner part of the accretion disk becomes geometrically thick. In this work we consider both radiation feedback from the neutron star and the sub-Keplerian rotation in a thick disk and calculate the magnetic moment–mass accretion rate relations for the measured rates of spin change. We find that the derived neutron star's dipole magnetic field depends on the maximum accretion rate adopted, but is likely ≲1013 G. The predicted accretion rate change can be used to test the proposed models by comparison with observations.

  9. Accreting Millisecond Pulsars: Neutron Star Masses and Radii

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod

    2004-01-01

    High amplitude X-ray brightness oscillations during thermonuclear X-ray bursts were discovered with the Rossi X-ray Timing Explorer (RXTE) in early 1996. Spectral and timing evidence strongly supports the conclusion that these oscillations are caused by rotational modulation of the burst emission and that they reveal the spin frequency of neutron stars in low mass X-ray binaries. The recent discovery of X-ray burst oscillations from two accreting millisecond pulsars has confirmed this basic picture and provided a new route to measuring neutron star properties and constraining the dense matter equation of state. I will briefly summarize the current observational understanding of accreting millisecond pulsars, and describe recent attempts to determine the mass and radius of the neutron star in XTE J1814-338.

  10. X-ray bounds on the r-mode amplitude in millisecond pulsars

    NASA Astrophysics Data System (ADS)

    Schwenzer, Kai; Boztepe, Tuğba; Güver, Tolga; Vurgun, Eda

    2017-04-01

    r-mode asteroseismology provides a unique way to study the internal composition of compact stars. Due to their precise timing, recycled millisecond radio pulsars present a particularly promising class of sources. Although their thermal properties are still poorly constrained, X-ray data is very useful for asteroseismology since r-modes could strongly heat a star. Using known and new upper bounds on the temperatures and luminosities of several non-accreting millisecond radio pulsars, we derive bounds on the r-mode amplitude as low as α ≲ 10-8 and discuss the impact on scenarios for their internal composition.

  11. X-Ray Observations of High-B Radio Pulsars

    NASA Astrophysics Data System (ADS)

    Olausen, S. A.; Zhu, W. W.; Vogel, J. K.; Kaspi, V. M.; Lyne, A. G.; Espinoza, C. M.; Stappers, B. W.; Manchester, R. N.; McLaughlin, M. A.

    2013-02-01

    The study of high-magnetic-field pulsars is important for examining the relationships between radio pulsars, magnetars, and X-ray-isolated neutron stars (XINSs). Here, we report on X-ray observations of three such high-magnetic-field radio pulsars. We first present the results of a deep XMM-Newton observation of PSR J1734-3333, taken to follow up on its initial detection in 2009. The pulsar's spectrum is well fit by a blackbody with a temperature of 300 ± 60 eV, with bolometric luminosity L_{{bb}}=2.0_{-0.7}^{+2.2}× 10^{32} {erg s^{-1}}≈ 0.0036 \\dot{E} for a distance of 6.1 kpc. We detect no X-ray pulsations from the source, setting a 1σ upper limit on the pulsed fraction of 60% in the 0.5-3 keV band. We compare PSR J1734-3333 to other rotation-powered pulsars of similar age and find that it is significantly hotter, supporting the hypothesis that the magnetic field affects the observed thermal properties of pulsars. We also report on XMM-Newton and Chandra observations of PSRs B1845-19 and J1001-5939. We do not detect either pulsar, setting 3σ upper limits on their blackbody temperatures of 48 and 56 eV, respectively. Despite the similarities in rotational properties, these sources are significantly cooler than all but one of the XINSs, which we attribute to the two groups having been born with different magnetic fields and hence evolving differently.

  12. X-RAY OBSERVATIONS OF HIGH-B RADIO PULSARS

    SciTech Connect

    Olausen, S. A.; Kaspi, V. M.; Zhu, W. W.; Vogel, J. K.; Lyne, A. G.; Espinoza, C. M.; Stappers, B. W.; Manchester, R. N.; McLaughlin, M. A.

    2013-02-10

    The study of high-magnetic-field pulsars is important for examining the relationships between radio pulsars, magnetars, and X-ray-isolated neutron stars (XINSs). Here, we report on X-ray observations of three such high-magnetic-field radio pulsars. We first present the results of a deep XMM-Newton observation of PSR J1734-3333, taken to follow up on its initial detection in 2009. The pulsar's spectrum is well fit by a blackbody with a temperature of 300 {+-} 60 eV, with bolometric luminosity L{sub bb}=2.0{sub -0.7}{sup +2.2} Multiplication-Sign 10{sup 32} erg s{sup -1}{approx}0.0036 E-dot for a distance of 6.1 kpc. We detect no X-ray pulsations from the source, setting a 1{sigma} upper limit on the pulsed fraction of 60% in the 0.5-3 keV band. We compare PSR J1734-3333 to other rotation-powered pulsars of similar age and find that it is significantly hotter, supporting the hypothesis that the magnetic field affects the observed thermal properties of pulsars. We also report on XMM-Newton and Chandra observations of PSRs B1845-19 and J1001-5939. We do not detect either pulsar, setting 3{sigma} upper limits on their blackbody temperatures of 48 and 56 eV, respectively. Despite the similarities in rotational properties, these sources are significantly cooler than all but one of the XINSs, which we attribute to the two groups having been born with different magnetic fields and hence evolving differently.

  13. New micro pore optics for x-ray pulsar navigation

    NASA Astrophysics Data System (ADS)

    Jin, Ge; Zhang, Qindong; Xu, Zhao; Zhang, Zhengjun; Zhang, Zhiyong; Xu, Wei; Li, Jingwen; Wang, Jian

    2016-01-01

    Solutions of focusing pulsars X-ray is a key factor in improving the accuracy of pulsar navigation. Based on the focusing principle of lobster eye grazing incidence, new micro pore optics (MPO) for pulsar navigation which is glass-substrated X-ray MPO is researched and developed. The effective areas on MPO when single grazing incidence or double grazing incidence happens are analyzed in detail and the first generation of MPO is produced. By illumination of parallel X-ray beam with 1.49keV and 8.05keV on the MPO, it is found that the crossing focusing image can be clearly visible, and the arm of cross image of 1.49keV and 8.05keV are is respectively 30mm and 17mm in length. Moreover, the center intensity was significantly higher than the cross arm which is consistent with theoretical calculation. Besides, the angular resolution of first generation of MPO with 8.05keV parallel X-ray beam illuminated is 4.19'.

  14. Synchrotron X-ray emission from old pulsars

    NASA Astrophysics Data System (ADS)

    Kisaka, Shota; Tanaka, Shuta J.

    2014-09-01

    We study the synchrotron radiation as the observed non-thermal emission by the X-ray satellites from old pulsars (≳1-10 Myr) to investigate the particle acceleration in their magnetospheres. We assume that the power-law component of the observed X-ray spectra is caused by the synchrotron radiation from electrons and positrons in the magnetosphere. We consider two pair-production mechanisms of X-ray emitting particles, the magnetic and the photon-photon pair productions. High-energy photons, which ignite the pair production, are emitted via the curvature radiation of the accelerated particles. We use the analytical description for the radiative transfer and estimate the luminosity of the synchrotron radiation. We find that for pulsars with the spin-down luminosity Lsd ≲ 1033 erg s-1, the locations of the particle acceleration and the non-thermal X-ray emission are within ≲107 cm from the centre of the neutron star, where the magnetic pair production occurs. For pulsars with the spin-down luminosity Lsd ≲ 1031 erg s-1 such as J0108-1431, the synchrotron radiation is difficult to explain the observed non-thermal component even if we consider the existence of the strong and small-scale surface magnetic field structures.

  15. X-ray spectra of the Crab pulsar and nebula

    NASA Technical Reports Server (NTRS)

    Pravdo, S. H.; Serlemitsos, P. J.

    1981-01-01

    The spectrum of the Crab pulsar was measued from 2 to 50 keV as a function of pulse phase and a progressive hardening and subsequent softening of the spectrum across the pulse was found. The fraction of the pulsed flux which exhibits spectral variability is 0.14 and is concentrated solely in the region between the two peaks. A model is suggested in which the pulsed X-ray emission from the Crab pulsar consists of two components: one which has no spectral dependence with pulse phase and which is physically related to the double peaked gama ray pulse and, perhaps, the radio and optical pulses; and another component which exhibits spectral variability with pulse phase is confined to and comprises the interpeak emission, and which is only seen at X-ray energies. These results and studies of the binary X-ray pulsar Hercules X-1 suggest a phenomonological similarity. If the spectrally varying component in the Crab pulsar arises from a hot, magnetized plasma near the neutron star surface then higher energy spectral observations of this phase region might reveal spectral features which can be used to determine the surface field strength.

  16. Models for X-Ray Emission from Isolated Pulsars

    NASA Technical Reports Server (NTRS)

    Wang, F. Y.-H.; Ruderman, M.; Halpern, Jules P.; Zhu, T.; Oliversen, Ronald (Technical Monitor)

    2001-01-01

    A model is proposed for the observed combination of power-law and thermal X-rays from rotationally powered pulsars. For gamma-ray pulsars with accelerators very many stellar radii above the neutron star surface, 100 MeV curvature gamma-rays from e(-) or e(+) flowing starward out of such accelerators are converted to e1 pairs on closed field lines all around the star. These pairs strongly affect X-ray emission from near the star in two ways. (1) The pairs are a source of synchrotron emission immediately following their creation in regions where B approx. 10(exp 10) G. This emission, in the photon energy range 0.1 keV less than E(sub X) less than 5 MeV, has a power-law spectrum with energy index 0.5 and X-ray luminosity that depends on the back-flow current, and is typically approx. 10(exp 33) ergs/ s. (2) The pairs ultimately a cyclotron resonance "blanket" surrounding the star except for two holes along the open field line bundles which pass through it. In such a blanket the gravitational pull on e(+,-) pairs toward the star is balanced by the hugely amplified push of outflowing surface emitted X-rays wherever cyclotron resonance occurs. Because of it the neutron star is surrounded by a leaky "hohlraum" of hot blackbody radiation with two small holes, which prevents direct X-ray observation of a heated polar cap of a gamma-ray pulsar. Weakly spin modulated radiation from the blanket together with more strongly spin-modulated radiation from the holes through it would then dominate observed low energy (0.1-10 keV) emission. For non-y-ray pulsars, in which no such accelerators with their accompanying extreme relativistic back-flow toward the star are expected, optically thick e1 resonance blankets should not form (except in special cases very close to the open field line bundle). From such pulsars blackbody radiation from both the warm stellar surface and the heated polar caps should be directly observable. In these pulsars, details of the surface magnetic field

  17. Clump Accretion in Supergiant Fast X-Ray Transients

    NASA Astrophysics Data System (ADS)

    Chase, Eve; Raymer, E.; Blondin, J. M.

    2014-01-01

    Supergiant Fast X-Ray Transients (SFXTs) are a subclass of High-Mass X-Ray Binaries that consist of a neutron star and OB supergiant donor star. These systems display short, bright x-ray flares lasting a few minutes to a few hours with luminosities reaching 1036 erg/s, several orders of magnitude larger than the quiescent luminosities of 1032 erg/s. The clumpy wind hypothesis has been proposed as a possible mechanism for these transient flares; in this model, a portion of the stellar wind from the donor star forms into clumps and is accreted onto the neutron star, inducing flares. We use high-resolution 3D hydrodynamic simulations to test the clumpy wind hypothesis, tracking the mass and angular momentum accretion rates to infer properties of the resulting x-ray flare and secular evolution of the neutron star rotation. Our results are significantly different from the predictions of Hoyle-Lyttleton Accretion (HLA) theory, which assume steady, laminar, axisymmetric flow. For example, an off-axis clump initiated with an impact parameter greater than the clump radius (for which HLA predicts no effect) produces a small spike in mass accretion and induces a long period of disk-like flow that dramatically reduces the accretion rate below the steady HLA value. The result is a brief, weak flare with a net decrease in total accreted mass compared with steady wind accretion accompanied by a substantial accretion of angular momentum.

  18. Soft X ray properties of the Geminga pulsar

    NASA Astrophysics Data System (ADS)

    Halpern, J. P.; Ruderman, M.

    1993-01-01

    The ROSAT soft x ray spectrum and pulse profile of the Geminga pulsar are analyzed and interpreted in terms of thermal emission from the surface of the neutron star. The x ray spectrum appears to consist of two blackbody components with T1 = (5.2 +/- 1.0) x 10 5 K and T2 approximately 3 x 106 K, respectively. The inferred ratio of surface areas, A2/A1, is approximately 3 x 10-5. Both components are highly modulated at the pulsar rotation period, but the harder x ray pulse is narrower, and leads the main (soft) x ray pulse by about 105 deg of phase. The soft x ray component is interpreted as photospheric cooling of much of the neutron star's surface area, while the small, hot region could be part of the much smaller polar cap heated by energetic particles flowing inward from the magnetospheric accelerator which is responsible for the production of Geminga's gamma rays. Geminga's gamma ray emission is consistent with outer-magnetosphere accelerator models for highly inclined dipoles. These predict the beaming of energetic gamma rays close enough to the star to give copious e(+/-) production in the stellar magnetic field and a large circumstellar pair density from pair inflow toward the surface. These pairs may quench radio emission, and also reflect most of the hard polar cap x rays back to the stellar surface by cyclotron resonance scattering. They are then reemitted from that much larger area at the lower temperature T1. The single-peaked nature of the x ray pulse and its energy-dependent phase suggest an off-center dipole geometry for the surface magnetic field. Under the assumption that the soft x ray emission comes from the full surface of a neutron star of radius R = 10 km, a distance estimate of (150-400) pc is derived. This range is consistent with the fit interstellar column density of (1.5 +/- 0.5) x 1020 cm-2. Distances less than 150 pc are probably ruled out both by the lower limit on the column density, and also by the requirement that the Rayleigh

  19. Heating Before Eating: X-Ray Observations of Redback Millisecond Pulsar Systems in the Ablation State

    NASA Astrophysics Data System (ADS)

    Roberts, Mallory; McLaughlin, Maura; Ray, Paul S.; Ransom, Scott M.; Hessels, Jason

    2015-01-01

    Redbacks are eclipsing millisecond radio pulsars in close orbits around companions which are non-degenerate and nearly Roche-lobe filling. Several have been observed to transition between a state where the radio pulsar is visible and there is X-ray emission from a shock between the pulsar wind and the ablated material off of the companion, and a state where there appears to be an accretion disk and the radio pulsations are not visible. Here we present X-Ray studies of two recently discovered systems. A Chandra observation of PSR J1628-3205 over its entire 5 hour orbit with Chandra shows little evidence for X-Ray variability. An XMM-Newton observation of PSR J2129-0429 over its 15.2 hour orbit shows strong orbital variability with an intriguing two peaked light curve. We compare these systems' X-Ray properties to other redbacks and comment on the differences between their properities and those of black widows.

  20. EXTINCTION AND DISTANCE TO ANOMALOUS X-RAY PULSARS FROM X-RAY SCATTERING HALOS

    SciTech Connect

    Rivera-Ingraham, A.; Van Kerkwijk, M. H. E-mail: mhvk@astro.utoronto.c

    2010-02-10

    We analyze the X-ray scattering halos around three Galactic Anomalous X-ray Pulsars in order to constrain the distance and the optical extinction of each source. We obtain surface brightness distributions from EPIC-pn data obtained with XMM-Newton, compare the profiles of different sources, and fit them with a model based on the standard theory of X-ray scattering by dust grains, both for a uniform distribution of dust along the line of sight, and for dust distributions constrained by previous measurements. Somewhat surprisingly, we find that for all three sources, the uniform distribution reproduces the observed surface brightness as well as or better than the distributions that are informed by previous constraints. Nevertheless, the inferred total dust columns are robust, and serve to confirm that previous measurements based on interstellar edges in high-resolution X-ray spectra and on modeling of broadband X-ray spectra were reliable. Specifically, we find A{sub V} {approx_equal} 4, 6, and 8 mag for 4U 0142+61, 1E 1048.1 - 5937, and 1RXS J170849.0 - 400910, respectively. For 1E 1048.1 - 5937, this is well in excess of the extinction expected toward an H I bubble along the line of sight, thus casting further doubt on the suggested association with the source.

  1. Observations of x ray pulsars from the Kvant module

    NASA Technical Reports Server (NTRS)

    Gilfanov, M.; Sunyaev, Rashid A.; Churazov, E.; Loznikov, V.; Efremov, V. V.; Kaniovskiy, A.; Kuznetsov, A. V.; Yamburenko, N.; Melioranskiy, A.; Skinner, G. K.

    1991-01-01

    The Roentgen international x ray observatory on the Kvant module of the Mir space station has been successfully operating since the beginning of June 1987. Many x ray sources were observed and among them were several x ray pulsars. Four telescopes mounted on board the Kvant module cover a wide energy range with good timing resolution. Timing analysis of the Kvant module data suffers from the presence of only short continuous intervals of source observations, separated by 90 min gaps (90 min is the orbital period of the Mir space station around the Earth). The presence of 90 min gaps leads to the appearance of beat frequencies v=v sub 0 + or - n/90 min (n = 1, 2, 3). Special analysis was applied to avoid this difficulty. Results are presented of the pulsation period measurements of the x ray pulsars Her X-1, Cen X-3, SMC X-1, Vela X-1, A0535 + 26 by the instruments on board the Kvant module in 1987 to 1989. The values of the periods are reduced to the solar system barycenter and to the binary system barycenter (excluding A0535 + 26).

  2. The soft X-ray spectrum of transient pulsars in the Small Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    La Palombara, N.; Sidoli, L.; Esposito, P.; Pintore, F.; Tiengo, A.; Mereghetti, S.

    2016-06-01

    The Small Magellanic Cloud is characterized by a high number of transient accreting pulsars, which can reach luminosities up to 10^{38} erg s^{-1} during their outbursts. Due to the low Galactic interstellar absorption in the SMC direction, these sources offer a unique opportunity to investigate the soft end of the X-ray spectrum in accreting pulsars. In the last two years we observed with XMM-Newton the large outburst of two of these transient pulsars (RX J0059.2-7138 and SMC X-2). Thanks to the high throughput and spectral resolution of XMM, these observations allowed us to investigate at an unprecedented level of detail their spectral and timing properties at soft X-ray energies. We found that both sources show a pulsed emission also at low energies, and that they are characterized by a thermal component which dominates the source spectrum below 0.5 keV; moreover, we discovered several emission and absorption features, which are very likely produced by photoionization of plasma located above the inner regions of the accretion disc.

  3. BOOK REVIEW: Rotation and Accretion Powered Pulsars

    NASA Astrophysics Data System (ADS)

    Kaspi, V. M.

    2008-03-01

    Pulsar astrophysics has come a long way in the 40 years since the discovery of the first pulsar by Bell and Hewish. From humble beginnings as bits of 'scruff' on the Cambridge University group's chart recorder paper, the field of pulsars has blossomed into a major area of mainstream astrophysics, with an unparalleled diversity of astrophysical applications. These range from Nobel-celebrated testing of general relativity in the strong-field regime to constraining the equation-of-state of ultradense matter; from probing the winds of massive stars to globular cluster evolution. Previous notable books on the subject of pulsars have tended to focus on some particular topic in the field. The classic text Pulsars by Manchester and Taylor (1977 San Francisco, CA: Freeman) targeted almost exclusively rotation-powered radio pulsars, while the Mészáros book High-Energy Radiation from Magnetized Neutron Stars (1992 Chicago, IL: University of Chicago Press) considered both rotation- and accretion-powered neutron stars, but focused on their radiation at x-ray energies and above. The recent book Neutron Stars 1 by Haensel et al (2007 Berlin: Springer) considers only the equation of state and neutron-star structure. Into this context appears Rotation and Accretion Powered Pulsars, by Pranab Ghosh. In contrast to other books, here the author takes an encyclopedic approach and attempts to synthesize practically all of the major aspects of the two main types of neutron star. This is ambitious. The only comparable undertaking is the useful but more elementary Lyne and Graham-Smith text Pulsar Astronomy (1998 Cambridge: Cambridge University Press), or Compact Stellar X-ray Sources (eds Lewin and van der Klis, 2006 Cambridge: Cambridge University Press), an anthology of technical review articles that also includes black hole topics. Rotation and Accretion Powered Pulsars thus fills a clear void in the field, providing a readable, graduate-level book that covers nearly everything you

  4. Optical pulsations from the anomalous X-ray pulsar 4U0142+61.

    PubMed

    Kern, B; Martin, C

    2002-05-30

    Anomalous X-ray pulsars (AXPs) differ from ordinary radio pulsars in that their X-ray luminosity is orders of magnitude greater than their rate of rotational energy loss, and so they require an additional energy source. One possibility is that AXPs are highly magnetized neuron stars or 'magnetars' having surface magnetic fields greater than 10(14) G. This would make them similar to the soft gamma-ray repeaters (SGRs), but alternative models that do not require extreme magnetic fields also exist. An optical counterpart to the AXP 4U0142+61 was recently discovered, consistent with emission from a magnetar, but also from a magnetized hot white dwarf, or an accreting isolated neutron star. Here we report the detection of optical pulsations from 4U0142+61. The pulsed fraction of optical light (27 per cent) is five to ten times greater than that of soft X-rays, from which we conclude that 4U0142+61 is a magnetar. Although this establishes a direct relationship between AXPs and the soft gamma-ray repeaters, the evolutionary connection between AXPs, SGRs and radio pulsars remains controversial.

  5. Probing AGN Accretion History Through X-Ray Variability

    NASA Astrophysics Data System (ADS)

    Paolillo, Maurizio; Papadakis, I.; Brandt, W. N.; Xue, Y. Q.; Luo, B.; Tozzi, P.; Shemmer, O.; Allevato, V.; Bauer, F.; Koekemoer, A.; Vignali, C.; Vito, F.; Yang, G.; Wang, J. X.; Zheng, X.

    2016-10-01

    I will present recent results on AGN variability in the CDFS survey. Using over 10 years of X-ray monitoring and comparison with local AGNs we are able to constrain the variability dependence on BH mass and accreton rate, and use it to trace the accretion hisory of the AGN population up to z=3.

  6. X-ray flares from postmerger millisecond pulsars.

    PubMed

    Dai, Z G; Wang, X Y; Wu, X F; Zhang, B

    2006-02-24

    Recent observations support the suggestion that short-duration gamma-ray bursts are produced by compact star mergers. The x-ray flares discovered in two short gamma-ray bursts last much longer than the previously proposed postmerger energy-release time scales. Here, we show that they can be produced by differentially rotating, millisecond pulsars after the mergers of binary neutron stars. The differential rotation leads to windup of interior poloidal magnetic fields and the resulting toroidal fields are strong enough to float up and break through the stellar surface. Magnetic reconnection-driven explosive events then occur, leading to multiple x-ray flares minutes after the original gamma-ray burst.

  7. Soft x ray properties of the Geminga pulsar

    NASA Technical Reports Server (NTRS)

    Halpern, J. P.; Ruderman, M.

    1993-01-01

    The ROSAT soft x ray spectrum and pulse profile of the Geminga pulsar are analyzed and interpreted in terms of thermal emission from the surface of the neutron star. The x ray spectrum appears to consist of two blackbody components with T(sub 1) = (5.2 +/- 1.0) x 10 (exp 5) K and T(sub 2) approximately 3 x 10(exp 6) K, respectively. The inferred ratio of surface areas, A(sub 2)/A(sub 1), is approximately 3 x 10(exp -5). Both components are highly modulated at the pulsar rotation period, but the harder x ray pulse is narrower, and leads the main (soft) x ray pulse by about 105 deg of phase. The soft x ray component is interpreted as photospheric cooling of much of the neutron star's surface area, while the small, hot region could be part of the much smaller polar cap heated by energetic particles flowing inward from the magnetospheric accelerator which is responsible for the production of Geminga's gamma rays. Geminga's gamma ray emission is consistent with outer-magnetosphere accelerator models for highly inclined dipoles. These predict the beaming of energetic gamma rays close enough to the star to give copious e(+/-) production in the stellar magnetic field and a large circumstellar pair density from pair inflow toward the surface. These pairs may quench radio emission, and also reflect most of the hard polar cap x rays back to the stellar surface by cyclotron resonance scattering. They are then reemitted from that much larger area at the lower temperature T(sub 1). The single-peaked nature of the x ray pulse and its energy-dependent phase suggest an off-center dipole geometry for the surface magnetic field. Under the assumption that the soft x ray emission comes from the full surface of a neutron star of radius R = 10 km, a distance estimate of (150-400) pc is derived. This range is consistent with the fit interstellar column density of (1.5 +/- 0.5) x 10(exp 20) cm(exp -2). Distances less than 150 pc are probably ruled out both by the lower limit on the column

  8. Hard X-ray Characteristics of Anomalous X-ray Pulsars: Results from RXTE and INTEGRAL

    NASA Astrophysics Data System (ADS)

    den Hartog, Peter R.

    Until recently anomalous X-ray pulsars (AXPs) were known as soft X-ray emitters. This has changed drastically since the discovery of hard X-ray emission (>10 keV) from several AXPs by INTEGRAL (Molkov et al. 2004, Revnivtsev et al. 2004 and den Hartog et al. 2004). Kuiper et al. (2004) discovered pulsed emission in the same energy range using RXTE (PCA and HEXTE) data. Currently four AXPs (1RXS J170849.0-400910, 1E 1841-045, 4U 0142+614 and 1E 2259+586) have been detected, some of them showing emission up to 200 keV. The spectra exhibit extremely hard power laws with photon indices < 1.0 and with apparent luminosities 2-3 orders of magnitude above the rotational energy loss. The origin of this behaviour is not yet understood. An overview containing the current observational status in the temporal and the spectral domains as well as future prospects of AXPs at high energies is presented.

  9. X-ray reverberation of the inner accretion disc in X-ray binaries

    NASA Astrophysics Data System (ADS)

    Uttley, Phil; Cassatella, Pablo; Wilkinson, Tony; Wilms, Joern; Pottschmidt, Katja; Hanke, Manfred; Boeck, Moritz

    Rapid fluctuations in the Comptonised emission close to accreting compact objects should lead to reverberation of the accretion disc, both through X-ray heating of the disc (to produce a variable blackbody component) and also correlated changes in the disc reflection component, including the iron K line. If they can be detected, these reverberation signatures can provide powerful constraints on the geometry of the disc and Comptonising regions. The measure-ment of the reverberation delays will provide a natural 'yardstick' to measure the inner disc radius (in km, not R/M!) and so constrain the black hole spin or the neutron star equation of state. I will present new results from XMM-Newton and RXTE observations, which confirm the presence of X-ray reverberation in X-ray binary systems and allow the first measurement of reverberation delays. These results are a pathfinder which highlights the enormous po-tential of high-throughput spectral-timing with the proposed HTRS instrument on board the International X-ray Observatory.

  10. Unusual Braking Indices in Young X-ray Pulsars

    NASA Astrophysics Data System (ADS)

    Frederic Archibald, Robert; Kaspi, Victoria M.; Beardmore, Andrew P.; Gehrels, Neil; Kennea, Jamie; Gotthelf, Eric V.; Ferdman, Robert; Guillot, Sebastien; Harrison, Fiona; Keane, Evan; Pivovaroff, Michael; Stern, Daniel; Tendulkar, Shriharsh P.; Tomsick, John

    2016-04-01

    Pulsars spin down over time. By measuring braking indices of pulsars, effectively the change in the spin-down rate over time, we can probe the underlying driving engine of the spin-down. For a magnetic dipole in a vacuum, n is predicted to be 3. To date, all measured braking indices are less than 3, which can be explained, e.g. by particle winds, changes in the magnetic field. In all models of braking indices, n should be nearly constant on year time-scales. Here, I will discuss two recent observation results that challenge this model, interestingly both coming from young X-ray pulsars with no detected radio emission. The first, a long-lived decrease in the braking index of PSR J1846-0258 following a burst of magnetar-like activity, and secondly, the first stationary braking index greater than three. Understanding neutron-star spin evolution is key to constraining these objects' long-term energy output and has relevance to topics ranging from pulsar wind nebulae and supernova remnants to core-collapse supernova rates, physics, and expected outcomes.

  11. TW Hya: SPECTRAL VARIABILITY, X-RAYS, AND ACCRETION DIAGNOSTICS

    SciTech Connect

    Dupree, A. K.; Brickhouse, N. S.; Cranmer, S. R.; Luna, G. J. M.; Schneider, E. E.; Bessell, M. S.; Bonanos, A.; Crause, L. A.; Lawson, W. A.; Mallik, S. V.; Schuler, S. C.

    2012-05-01

    The nearest accreting T Tauri star, TW Hya was intensively and continuously observed over {approx}17 days with spectroscopic and photometric measurements from four continents simultaneous with a long segmented exposure using the Chandra satellite. Contemporaneous optical photometry from WASP-S indicates a 4.74 day period was present during this time. The absence of a similar periodicity in the H{alpha} flux and the total X-ray flux which are dominated by accretion processes and the stellar corona, respectively, points to a different source of photometric variations. The H{alpha} emission line appears intrinsically broad and symmetric, and both the profile and its variability suggest an origin in the post-shock cooling region. An accretion event, signaled by soft X-rays, is traced spectroscopically for the first time through the optical emission line profiles. After the accretion event, downflowing turbulent material observed in the H{alpha} and H{beta} lines is followed by He I ({lambda}5876) broadening near the photosphere. Optical veiling resulting from the heated photosphere increases with a delay of {approx}2 hr after the X-ray accretion event. The response of the stellar coronal emission to an increase in the veiling follows {approx}2.4 hr later, giving direct evidence that the stellar corona is heated in part by accretion. Subsequently, the stellar wind becomes re-established. We suggest a model that incorporates the dynamics of this sequential series of events: an accretion shock, a cooling downflow in a supersonically turbulent region, followed by photospheric and later, coronal heating. This model naturally explains the presence of broad optical and ultraviolet lines, and affects the mass accretion rates determined from emission line profiles.

  12. Tugboat model for OB binaries, X-ray stars and pulsars.

    PubMed

    Helfand, D J; Tademaru, E

    1977-05-12

    An examination of the kinematical properties of binary OB stars, binary X-ray sources and pulsars suggests an evolutionary sequence linking an apparent low-velocity class of pulsars to the binary nature of their extreme Population I progenitors.

  13. On the power spectra of the wind-fed X-ray binary pulsar GX 301 - 2

    NASA Technical Reports Server (NTRS)

    Orlandini, Mauro; Morfill, G. E.

    1992-01-01

    A phenomenological model of accretion which is applied to the wind-fed X-ray binary pulsar GX 301 - 2 is developed, assuming that the accretion onto the neutron star does not occur from a continuous flux of plasma, but from blobs of matter which are threaded by the magnetic field lines onto the magnetic polar caps of the neutron star. These 'lumps' are produced at the magnetospheric limit by magnetohydrodynamical instability, introducing a 'noise' in the accretion process, due to the discontinuity in the flux of matter onto the neutron star. This model is able to describe the change of slope observed in the continuum component of the power spectra of the X-ray binary pulsar GX 301 - 2, in the frequency range 0.01 - 0.1 Hz. The physical properties of the infalling blobs derived in the model are in agreement with the constraints imposed by observations.

  14. HIGH-RESOLUTION X-RAY SPECTROSCOPY OF THE BURSTING PULSAR GRO J1744-28

    SciTech Connect

    Degenaar, N.; Miller, J. M.; Harrison, F. A.; Kennea, J. A.; Kouveliotou, C.; Younes, G.

    2014-11-20

    The bursting pulsar GRO J1744-28 is a Galactic low-mass X-ray binary that distinguishes itself by displaying type-II X-ray bursts: brief, bright flashes of X-ray emission that likely arise from spasmodic accretion. Combined with its coherent 2.1 Hz X-ray pulsations and relatively high estimated magnetic field, it is a particularly interesting source to study the physics of accretion flows around neutron stars. Here we report on Chandra/High Energy Transmission Grating observations obtained near the peak of its bright 2014 accretion outburst. Spectral analysis suggests the presence of a broad iron emission line centered at E {sub l} ≅ 6.7 keV. Fits with a disk reflection model yield an inclination angle of i ≅ 52° and an inner disk radius of R {sub in} ≅ 85 GM/c {sup 2}, which is much further out than typically found for neutron star low-mass X-ray binaries. Assuming that the disk is truncated at the magnetospheric radius of the neutron star, we estimate a magnetic field strength of B ≅ (2-6) × 10{sup 10} G. Furthermore, we identify an absorption feature near ≅ 6.85 keV that could correspond to blue-shifted Fe XXV and point to a fast disk wind with an outflow velocity of v {sub out} ≅ (7.5-8.2) × 10{sup 3} km s{sup –1} (≅ 0.025c-0.027c). If the covering fraction and filling factor are large, this wind could be energetically important and perhaps account for the fact that the companion star lost significant mass while the magnetic field of the neutron star remained strong.

  15. High-resolution X-Ray Spectroscopy of the Bursting Pulsar GRO J1744-28

    NASA Astrophysics Data System (ADS)

    Degenaar, N.; Miller, J. M.; Harrison, F. A.; Kennea, J. A.; Kouveliotou, C.; Younes, G.

    2014-11-01

    The bursting pulsar GRO J1744-28 is a Galactic low-mass X-ray binary that distinguishes itself by displaying type-II X-ray bursts: brief, bright flashes of X-ray emission that likely arise from spasmodic accretion. Combined with its coherent 2.1 Hz X-ray pulsations and relatively high estimated magnetic field, it is a particularly interesting source to study the physics of accretion flows around neutron stars. Here we report on Chandra/High Energy Transmission Grating observations obtained near the peak of its bright 2014 accretion outburst. Spectral analysis suggests the presence of a broad iron emission line centered at E l ~= 6.7 keV. Fits with a disk reflection model yield an inclination angle of i ~= 52° and an inner disk radius of R in ~= 85 GM/c 2, which is much further out than typically found for neutron star low-mass X-ray binaries. Assuming that the disk is truncated at the magnetospheric radius of the neutron star, we estimate a magnetic field strength of B ~= (2-6) × 1010 G. Furthermore, we identify an absorption feature near ~= 6.85 keV that could correspond to blue-shifted Fe XXV and point to a fast disk wind with an outflow velocity of v out ~= (7.5-8.2) × 103 km s-1 (sime 0.025c-0.027c). If the covering fraction and filling factor are large, this wind could be energetically important and perhaps account for the fact that the companion star lost significant mass while the magnetic field of the neutron star remained strong.

  16. The Use of X-Ray Pulsars for Aiding GPS Satellite Orbit Determination

    DTIC Science & Technology

    2005-03-01

    pulsar used was PSR B0531+21 (Crab Pulsar) which is a very well known bright pulsar in the Crab Nebula [28]. Feasibly, if GPS x-ray detectors were 4...Variations Within the Pulse Profile Peaks of the Crab Nebula Pulsar,” The Astrophysical Journal , 467 (1996). 18. Halsell, Charles A. Orbit

  17. EVOLUTION OF TRANSIENT LOW-MASS X-RAY BINARIES TO REDBACK MILLISECOND PULSARS

    SciTech Connect

    Jia, Kun; Li, Xiang-Dong

    2015-11-20

    Redback millisecond pulsars (MSPs; hereafter redbacks) are a subpopulation of eclipsing MSPs in close binaries. The formation processes of these systems are not clear. The three pulsars showing transitions between rotation- and accretion-powered states belong to both redbacks and transient low-mass X-ray binaries (LMXBs), suggesting a possible evolutionary link between them. Through binary evolution calculations, we show that the accretion disks in almost all LMXBs are subject to the thermal-viscous instability during certain evolutionary stages, and the parameter space for the disk instability covers the distribution of known redbacks in the orbital period—companion mass plane. We accordingly suggest that the abrupt reduction of the mass accretion rate during quiescence of transient LMXBs provides a plausible way to switch on the pulsar activity, leading to the formation of redbacks, if the neutron star has been spun up to be an energetic MSP. We investigate the evolution of redbacks, taking into account the evaporation feedback, and discuss its possible influence on the formation of black widow MSPs.

  18. Radio and X-Ray Observations of the Intermittent Pulsar J1832+0029

    NASA Astrophysics Data System (ADS)

    Lorimer, D. R.; Lyne, A. G.; McLaughlin, M. A.; Kramer, M.; Pavlov, G. G.; Chang, C.

    2012-10-01

    We report on radio and X-ray observations of PSR J1832+0029, a 533 ms radio pulsar discovered in the Parkes Multibeam Pulsar Survey. From radio observations taken with the Parkes, Lovell, and Arecibo telescopes, we show that this pulsar exhibits two spin-down states akin to PSRs B1931+24 reported by Kramer et al. and J1841-0500 reported by Camilo et al. Unlike PSR B1931+24, which switches between "on" and "off" states on a 30-40 day timescale, PSR J1832+0029 is similar to PSR J1841-0500 in that it spends a much longer period of time in the off-state. So far, we have fully sampled two off-states. The first one lasted between 560 and 640 days and the second one lasted between 810 and 835 days. From our radio timing observations, the ratio of on/off spin-down rates is 1.77 ± 0.03. Chandra observations carried out during both the on- and off-states of this pulsar failed to detect any emission. Our results challenge but do not rule out models involving accretion onto the neutron star from a low-mass stellar companion. In spite of the small number of intermittent pulsars currently known, difficulties in discovering them and in quantifying their behavior imply that their total population could be substantial.

  19. An x-ray nebula associated with the millisecond pulsar B1957+20.

    PubMed

    Stappers, B W; Gaensler, B M; Kaspi, V M; van der Klis, M; Lewin, W H G

    2003-02-28

    We have detected an x-ray nebula around the binary millisecond pulsar B1957+20. A narrow tail, corresponding to the shocked pulsar wind, is seen interior to the known Halpha bow shock and proves the long-held assumption that the rotational energy of millisecond pulsars is dissipated through relativistic winds. Unresolved x-ray emission likely represents the shock where the winds of the pulsar and its companion collide. This emission indicates that the efficiency with which relativistic particles are accelerated in the postshock flow is similar to that for young pulsars, despite the shock proximity and much weaker surface magnetic field of this millisecond pulsar.

  20. Radiative efficiency of hot accretion flow and the radio/X-ray correlation in X-ray binaries

    NASA Astrophysics Data System (ADS)

    Xie, Fu-Guo

    2016-02-01

    Significant progresses have been made since the discovery of hot accretion flow, a theory successfully applied to the low-luminosity active galactic nuclei (LLAGNs) and black hole (BH) X-ray binaries (BHBs) in their hard states. Motivated by these updates, we re-investigate the radiative efficiency of hot accretion flow. We find that, the brightest regime of hot accretion flow shows a distinctive property, i.e. it has a constant efficiency independent of accretion rates, similar to the standard thin disk. For less bright regime, the efficiency has a steep positive correlation with the accretion rate, while for faint regime typical of advection-dominated accretion flow, the correlation is shadower. This result can naturally explain the observed two distinctive correlations between radio and X-ray luminosities in black hole X-ray binaries. The key difference in systems with distinctive correlations could be the viscous parameter, which determines the critical luminosity of different accretion modes.

  1. The Emerging Population of Pulsar Wind Nebulae in Hard X-rays

    NASA Astrophysics Data System (ADS)

    Mattana, F.; Götz, D.; Terrier, R.; Renaud, M.; Falanga, M.

    2009-05-01

    The hard X-ray synchrotron emission from Pulsar Wind Nebulae probes energetic particles, closely related to the pulsar injection power at the present time. INTEGRAL has disclosed the yet poorly known population of hard X-ray pulsar/PWN systems. We summarize the properties of the class, with emphasys on the first hard X-ray bow-shock (CTB 80 powered by PSR B1951+32), and highlight some prospects for the study of Pulsar Wind Nebulae with the Simbol-X mission.

  2. CHANDRA PHASE-RESOLVED X-RAY SPECTROSCOPY OF THE CRAB PULSAR

    SciTech Connect

    Weisskopf, Martin C.; Tennant, Allyn F.; O'Dell, Stephen L.; Elsner, Ronald F.; Yakovlev, Dmitry G.; Harding, Alice; Zavlin, Vyacheslav E.; Becker, Werner

    2011-12-20

    We present a new study of the X-ray spectral properties of the Crab Pulsar. The superb angular resolution of the Chandra X-Ray Observatory enables distinguishing the pulsar from the surrounding nebulosity. Analysis of the spectrum as a function of pulse phase allows the least-biased measure of interstellar X-ray extinction due primarily to photoelectric absorption and secondarily to scattering by dust grains in the direction of the Crab Nebula. We modify previous findings that the line of sight to the Crab is underabundant in oxygen and provide measurements with improved accuracy and less bias. Using the abundances and cross sections from Wilms et al. we find [O/H] = (5.28 {+-} 0.28) Multiplication-Sign 10{sup -4} (4.9 Multiplication-Sign 10{sup -4} is solar abundance). We also measure for the first time the impact of scattering of flux out of the image by interstellar grains. We find {tau}{sub scat} = 0.147 {+-} 0.043. Analysis of the spectrum as a function of pulse phase also measures the X-ray spectral index even at pulse minimum-albeit with increasing statistical uncertainty. The spectral variations are, by and large, consistent with a sinusoidal variation. The only significant variation from the sinusoid occurs over the same phase range as some rather abrupt behavior in the optical polarization magnitude and position angle. We also compare these spectral variations to those observed in gamma-rays and conclude that our measurements are both a challenge and a guide to future modeling and will thus eventually help us understand pair cascade processes in pulsar magnetospheres. The data are also used to set new, and less biased, upper limits to the surface temperature of the neutron star for different models of the neutron star atmosphere. We discuss how such data are best connected to theoretical models of neutron star cooling and neutron star interiors. The data restrict the neutrino emission rate in the pulsar core and the amount of light elements in the heat

  3. 10 micron detection of the hard X-ray transient GRO J0422+32: Free-free emission from an X-ray-driven accretion disk wind?

    NASA Technical Reports Server (NTRS)

    Paradijs, Van J.; Telesco, C. M.; Kouveliotou, C.; Fishman, G. J.

    1994-01-01

    We report the detection of 10 micrometer emission from the transient low-mass X-ray binary (LMXB) and optical nova GRO J0422+32 near the maximum of its outburst. We discuss this result in terms of (1) a 'standard' model according to which low-energy radiation of LMXB is caused by reprocessing of X-rays in an accretion disk; (2) emission from a cool secondary star; (3) emission from dust grains heated by the transient X-rays, and (4) free-free emission from an X-ray-driven wind from the accretion disk. Only the fourth alternative provides a viable explanation for the observed 10 micrometer emission, with a mass-loss rate in the disk wind that may be substantially higher than the rate of accretion onto the compact star. The presence of such a wind may have a profound effect on the evolution of the binary, and contribute to the solution of the 'birthrate problem' of millisecond ratio pulsars.

  4. An ultraluminous X-ray source powered by an accreting neutron star.

    PubMed

    Bachetti, M; Harrison, F A; Walton, D J; Grefenstette, B W; Chakrabarty, D; Fürst, F; Barret, D; Beloborodov, A; Boggs, S E; Christensen, F E; Craig, W W; Fabian, A C; Hailey, C J; Hornschemeier, A; Kaspi, V; Kulkarni, S R; Maccarone, T; Miller, J M; Rana, V; Stern, D; Tendulkar, S P; Tomsick, J; Webb, N A; Zhang, W W

    2014-10-09

    The majority of ultraluminous X-ray sources are point sources that are spatially offset from the nuclei of nearby galaxies and whose X-ray luminosities exceed the theoretical maximum for spherical infall (the Eddington limit) onto stellar-mass black holes. Their X-ray luminosities in the 0.5-10 kiloelectronvolt energy band range from 10(39) to 10(41) ergs per second. Because higher masses imply less extreme ratios of the luminosity to the isotropic Eddington limit, theoretical models have focused on black hole rather than neutron star systems. The most challenging sources to explain are those at the luminous end of the range (more than 10(40) ergs per second), which require black hole masses of 50-100 times the solar value or significant departures from the standard thin disk accretion that powers bright Galactic X-ray binaries, or both. Here we report broadband X-ray observations of the nuclear region of the galaxy M82 that reveal pulsations with an average period of 1.37 seconds and a 2.5-day sinusoidal modulation. The pulsations result from the rotation of a magnetized neutron star, and the modulation arises from its binary orbit. The pulsed flux alone corresponds to an X-ray luminosity in the 3-30 kiloelectronvolt range of 4.9 × 10(39) ergs per second. The pulsating source is spatially coincident with a variable source that can reach an X-ray luminosity in the 0.3-10 kiloelectronvolt range of 1.8 × 10(40) ergs per second. This association implies a luminosity of about 100 times the Eddington limit for a 1.4-solar-mass object, or more than ten times brighter than any known accreting pulsar. This implies that neutron stars may not be rare in the ultraluminous X-ray population, and it challenges physical models for the accretion of matter onto magnetized compact objects.

  5. Accreting Millisecond Pulsars and Fundamental Physics

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod

    2005-01-01

    X-ray emission from the surfaces of rapidly rotating neutron stars encodes information about their global properties as well as physical conditions locally. Detailed modelling of, for example, the energy dependent pulse profiles observed from accreting millisecond pulsars and thermonuclear burst oscillations can be used to derive constraints on the masses and radii of neutron stars. These measurements provide direct information on the properties of the dense matter equation of state of the supranuclear density matter in their interiors. Study of absorption lines created in the surface layers can also provide measurements of masses and radii, and may be able to probe aspects of relativistic gravity, such as frame dragging. I will discuss the results of recent efforts to carry out such measurements and their implications for the properties of dense matter.

  6. Observations of the γ-ray pulsar J1932+1916 in X-rays

    NASA Astrophysics Data System (ADS)

    Karpova, A.; Shternin, P.; Zyuzin, D.; Danilenko, A.; Shibanov, Yu.

    2017-04-01

    We present the analysis of the archival Suzaku and Swift X-ray observations of the young γ-ray pulsar J1932+1916 field. The data revealed a point-like object at the γ-ray position of the pulsar and diffuse X-ray emission around it. Spectra of the point-like source and diffuse emission are well-described by absorbed power-law models with spectral parameters typical for pulsar plus pulsar wind nebula systems. Therefore, we suggest that Suzaku and Swift detected the X-ray counterpart of PSR J1932+1916. Assuming this interpretation, we constrain the distance to the pulsar in the range of 2-6 kpc. We also suggest possible association of the pulsar with the nearby supernova remnant G54.4-0.3 and discuss its implications for the pulsar proper motion, age and distance.

  7. Swings between rotation and accretion power in a binary millisecond pulsar.

    PubMed

    Papitto, A; Ferrigno, C; Bozzo, E; Rea, N; Pavan, L; Burderi, L; Burgay, M; Campana, S; Di Salvo, T; Falanga, M; Filipović, M D; Freire, P C C; Hessels, J W T; Possenti, A; Ransom, S M; Riggio, A; Romano, P; Sarkissian, J M; Stairs, I H; Stella, L; Torres, D F; Wieringa, M H; Wong, G F

    2013-09-26

    It is thought that neutron stars in low-mass binary systems can accrete matter and angular momentum from the companion star and be spun-up to millisecond rotational periods. During the accretion stage, the system is called a low-mass X-ray binary, and bright X-ray emission is observed. When the rate of mass transfer decreases in the later evolutionary stages, these binaries host a radio millisecond pulsar whose emission is powered by the neutron star's rotating magnetic field. This evolutionary model is supported by the detection of millisecond X-ray pulsations from several accreting neutron stars and also by the evidence for a past accretion disc in a rotation-powered millisecond pulsar. It has been proposed that a rotation-powered pulsar may temporarily switch on during periods of low mass inflow in some such systems. Only indirect evidence for this transition has hitherto been observed. Here we report observations of accretion-powered, millisecond X-ray pulsations from a neutron star previously seen as a rotation-powered radio pulsar. Within a few days after a month-long X-ray outburst, radio pulses were again detected. This not only shows the evolutionary link between accretion and rotation-powered millisecond pulsars, but also that some systems can swing between the two states on very short timescales.

  8. X-RAY POLARIZATION FROM ACCRETING BLACK HOLES: CORONAL EMISSION

    SciTech Connect

    Schnittman, Jeremy D.; Krolik, Julian H. E-mail: jhk@pha.jhu.ed

    2010-04-01

    We present new calculations of X-ray polarization from accreting black holes (BHs), using a Monte Carlo ray-tracing code in full general relativity. In our model, an optically thick disk in the BH equatorial plane produces thermal seed photons with polarization oriented parallel to the disk surface. These seed photons are then inverse-Compton scattered through a hot (but thermal) corona, producing a hard X-ray power-law spectrum. We consider three different models for the corona geometry: a wedge 'sandwich' with aspect ratio H/R and vertically integrated optical depth tau{sub 0} constant throughout the disk; an inhomogeneous 'clumpy' corona with a finite number of hot clouds distributed randomly above the disk within a wedge geometry; and a spherical corona of uniform density, centered on the BH and surrounded by a truncated thermal disk with inner radius R{sub edge}. In all cases, we find a characteristic transition from horizontal polarization at low energies to vertical polarization above the thermal peak; the vertical direction is defined as the projection of the BH spin axis on the plane of the sky. We show how the details of the spectropolarization signal can be used to distinguish between these models and infer various properties of the corona and BH. Although the bulk of this paper focuses on stellar-mass BHs, we also consider the effects of coronal scattering on the X-ray polarization signal from supermassive BHs in active galactic nuclei.

  9. THE RADIATIVE X-RAY AND GAMMA-RAY EFFICIENCIES OF ROTATION-POWERED PULSARS

    SciTech Connect

    Vink, Jacco; Bamba, Aya; Yamazaki, Ryo

    2011-02-01

    We present a statistical analysis of the X-ray luminosity of rotation-powered pulsars and their surrounding nebulae using the sample of Kargaltsev and Pavlov, and we complement this with an analysis of the {gamma}-ray emission of Fermi-detected pulsars. We report a strong trend in the efficiency with which spin-down power is converted to X-ray and {gamma}-ray emission with characteristic age: young pulsars and their surrounding nebulae are efficient X-ray emitters, whereas in contrast old pulsars are efficient {gamma}-ray emitters. We divided the X-ray sample in a young ({tau}{sub c} < 1.7 x 10{sup 4} yr) and old sample and used linear regression to search for correlations between the logarithm of the X-ray and {gamma}-ray luminosities and the logarithms of the periods and period derivatives. The X-ray emission from young pulsars and their nebulae are both consistent with L{sub X}{proportional_to} P-dot{sup 3}/P{sup 6}. For old pulsars and their nebulae the X-ray luminosity is consistent with a more or less constant efficiency {eta}{identical_to}L{sub X}/ E-dot{sub rot}{approx}8x10{sup -5}. For the {gamma}-ray luminosity we confirm that L{sub {gamma}} {proportional_to} {radical}E-dot{sub rot}. We discuss these findings in the context of pair production inside pulsar magnetospheres and the striped wind model. We suggest that the striped wind model may explain the similarity between the X-ray properties of the pulsar wind nebulae and the pulsars themselves, which according to the striped wind model may both find their origin outside the light cylinder, in the pulsar wind zone.

  10. Revisiting the Magnetic and Spin Evolution of Two Young X-ray Pulsars

    NASA Astrophysics Data System (ADS)

    Ferdman, Robert; Kaspi, Victoria M.; Archibald, Robert Frederic

    2014-08-01

    We present results from timing analysis of two young X-ray pulsars found in the large Magellanic Cloud: the Crab-like energetic pulsar PSR B0540-69 and the so-called "big glitcher", PSR J0537-6910. In both cases, we analyze data taken with the Rossi X-ray Timing Explorer. This work extends the published data sets for these pulsars by approximately doubling their respective data spans. We revisit the glitching activity of these neutron stars, particularly that of PSR J0537-6910, determine more precise glitch and spin parameters, and discuss the implications for the spin and magnetospheric evolution of these interesting pulsars.

  11. Accretion and Outflows in X-ray Binaries: What's Really Going on During X-ray Quiescence

    NASA Astrophysics Data System (ADS)

    MacDonald, Rachel K. D.; Bailyn, Charles D.; Buxton, Michelle

    2015-01-01

    X-ray binaries, consisting of a star and a stellar-mass black hole, are wonderful laboratories for studying accretion and outflows. They evolve on timescales quite accessible to us, unlike their supermassive cousins, and allow the possibility of gaining a deeper understanding of these two common astrophysical processes. Different wavelength regimes reveal different aspects of the systems: radio emission is largely generated by outflows and jets, X-ray emission by inner accretion flows, and optical/infrared (OIR) emission by the outer disk and companion star. The search for relationships between these different wavelengths is thus an area of active research, aiming to reveal deeper connections between accretion and outflows.Initial evidence for a strong, tight correlation between radio and X-ray emission has weakened as further observations and newly-discovered sources have been obtained. This has led to discussions of multiple tracks or clusters, or the possibility that no overall relation exists for the currently-known population of X-ray binaries. Our ability to distinguish among these options is hampered by a relative lack of observations at lower luminosities, and especially of truly X-ray quiescent (non-outbursting) systems. Although X-ray binaries spend the bulk of their existence in quiescence, few quiescent sources have been observed and multiple observations of individual sources are largely nonexistent. Here we discuss new observations of the lowest-luminosity quiescent X-ray binary, A0620-00, and the place this object occupies in investigations of the radio/X-ray plane. For the first time, we also incorporate simultaneous OIR data with the radio and X-ray data.In December 2013 we took simultaneous observations of A0620-00 in the X-ray (Chandra), the radio (EVLA), and the OIR (SMARTS 1.3m). These X-ray and radio data allowed us to investigate similarities among quiescent X-ray binaries, and changes over time for this individual object, in the radio/X-ray

  12. X-Ray Binary Phenomenology and Their Accretion Disk Structure

    NASA Astrophysics Data System (ADS)

    Kazanas, Demosthenes

    We propose a scheme that accounts for the broader spectral and temporal properties of galactic black hole X-ray transients. The fundamental notion behind this proposal is that the mass accretion rate, dot{M}, of the disks of these systems depends on the radius, as it has been proposed for ADIOS. We propose that, because of this dependence of dot{M} on radius, an accretion disk which is geometrically thin and cool at large radii converts into a geometrically thick, advection dominated, hot disk interior to a transition radius at which the local accretion rate drops below the square of the viscosity parameter, a condition for the existence of advection dominated flows. We argue also that such a transition requires in addition that the vertical disk support be provided by magnetic fields. As discussed in other chapters of this book, the origin of these fields is local to the disk by the Poynting Robertson battery, thereby providing a complete self-contained picture for the spectra and evolution of these systems.

  13. X-ray Pulsar in the Crab Nebula.

    PubMed

    Fritz, G; Henry, R C; Meekins, J F; Chubb, T A; Friedman, H

    1969-05-09

    X-ray pulsations have been observed in the Crab Nebula at a frequency closely matching the radio and optical pulsations. About 5 percent of the total x-ray power of the nebula appears in the pulsed component. The x-ray pulsations have the form of a main pulse and an interpulse separated by about 12 milliseconds.

  14. Chandra X-ray Observations of 12 Millisecond Pulsars in the Globular Cluster M28

    NASA Astrophysics Data System (ADS)

    Bogdanov, Slavko; van den Berg, Maureen; Servillat, Mathieu; Heinke, Craig O.; Grindlay, Jonathan E.; Stairs, Ingrid H.; Ransom, Scott M.; Freire, Paulo C. C.; Bégin, Steve; Becker, Werner

    2011-04-01

    We present a Chandra X-ray Observatory investigation of the millisecond pulsars in the globular cluster M28 (NGC 6626). In what is one of the deepest X-ray observations of a globular cluster, we firmly detect seven and possibly detect two of the 12 known M28 pulsars. With the exception of PSRs B1821-24 and J1824-2452H, the detected pulsars have relatively soft spectra, with X-ray luminosities 1030-1031 erg s-1 (0.3-8 keV), similar to most "recycled" pulsars in 47 Tucanae and the field of the Galaxy, implying thermal emission from the pulsar magnetic polar caps. We present the most detailed X-ray spectrum to date of the energetic PSR B1821-24. It is well described by a purely non-thermal spectrum with spectral photon index Γ = 1.23 and luminosity 1.4 × 1033Θ(D/5.5 kpc)2 erg s-1 (0.3-8 keV), where Θ is the fraction of the sky covered by the X-ray emission beam(s). We find no evidence for the previously reported line emission feature around 3.3 keV, most likely as a consequence of improvements in instrument calibration. The X-ray spectrum and pulse profile of PSR B1821-24 suggest that the bulk of unpulsed emission from this pulsar is not of thermal origin, and is likely due to low-level non-thermal magnetospheric radiation, an unresolved pulsar wind nebula, and/or small-angle scattering of the pulsed X-rays by interstellar dust grains. The peculiar binary PSR J1824-2452H shows a relatively hard X-ray spectrum and possible variability at the binary period, indicative of an intrabinary shock formed by interaction between the relativistic pulsar wind and matter from its non-degenerate companion star.

  15. Young rotation-powered pulsars as ultraluminous X-ray sources

    NASA Astrophysics Data System (ADS)

    Medvedev, Aleksei S.; Poutanen, Juri

    2013-05-01

    The aim of this paper is to investigate a possible contribution of the rotation-powered pulsars and pulsar wind nebulae to the population of ultraluminous X-ray sources (ULXs). We first develop an analytical model for the evolution of the distribution function of pulsars over the spin period and find both the steady-state and the time-dependent solutions. Using the recent results on the X-ray efficiency dependence on pulsar characteristic age, we then compute the X-ray luminosity function (XLF) of rotation-powered pulsars. In a general case, it has a broken power-law shape with a high-luminosity cutoff, which depends on the distributions of the birth spin period and the magnetic field. Using the observed XLF of sources in the nearby galaxies and the condition that the pulsar XLF does not exceed that, we find the allowed region for the parameters describing the birth period distribution. We find that the mean pulsar period should be greater than 10-40 ms. These results are consistent with the constraints obtained from the X-ray luminosity of core-collapse supernovae. We estimate that the contribution of the rotation-powered pulsars to the ULX population is at a level exceeding 3 per cent. For a wide birth period distribution, this fraction grows with luminosity and above 1040 erg s-1 pulsars can dominate the ULX population.

  16. Swift Detection of a 65 Day X-Ray Period from the Ultraluminous Pulsar NGC 7793 P13

    NASA Astrophysics Data System (ADS)

    Hu, Chin-Ping; Li, K. L.; Kong, Albert K. H.; Ng, C.-Y.; Chun-Che Lin, Lupin

    2017-01-01

    NGC 7793 P13 is an ultraluminous X-ray source harboring an accreting pulsar. We report on the detection of a ∼65 day period X-ray modulation with Swift observations in this system. The modulation period found in the X-ray band is P = 65.05 ± 0.10 days and the profile is asymmetric with a fast rise and a slower decay. On the other hand, the u-band light curve collected by Swift UVOT confirmed an optical modulation with a period of P = 64.24 ± 0.13 days. We explored the phase evolution of the X-ray and optical periodicities and propose two solutions. A superorbital modulation with a period of ∼2700–4700 days probably caused by the precession of a warped accretion disk is necessary to interpret the phase drift of the optical data. We further discuss the implication if this ∼65 day periodicity is caused by the superorbital modulation. Estimated from the relationship between the spin-orbital and orbital-superorbital periods of known disk-fed high-mass X-ray binaries, the orbital period of P13 is roughly estimated as 3–7 days. In this case, an unknown mechanism with a much longer timescale is needed to interpret the phase drift. Further studies on the stability of these two periodicities with a long-term monitoring could help us to probe their physical origins.

  17. Analysis and design of grazing incidence x-ray optics for pulsar navigation

    NASA Astrophysics Data System (ADS)

    Zuo, Fuchang; Chen, Jianwu; Li, Liansheng; Mei, Zhiwu

    2013-10-01

    As a promising new technology for deep space exploration due to autonomous capability, pulsar navigation has attracted extensive attentions from academy and engineering domains. The pulsar navigation accuracy is determined by the measurement accuracy of Time of Arrival (TOA) of X-ray photon, which can be enhanced through design of appropriate optics. The energy band of X-ray suitable for pulsar navigation is 0.1-10keV, the effective focusing of which can be primely and effectively realized by the grazing incidence reflective optics. The Wolter-I optics, originally proposed based on a paraboloid mirror and a hyperboloid mirror for X-ray imaging, has long been widely developed and employed in X-ray observatory. Some differences, however, remain in the requirements on optics between astronomical X-ray observation and pulsar navigation. X-ray concentrator, the simplified Wolter-I optics, providing single reflection by a paraboloid mirror, is more suitable for pulsar navigation. In this paper, therefore, the requirements on aperture, effective area and focal length of the grazing incidence reflective optics were firstly analyzed based on the characteristics, such as high time resolution, large effective area and low angular resolution, of the pulsar navigation. Furthermore, the preliminary design of optical system and overall structure, as well as the diaphragm, was implemented for the X-ray concentrator. Through optical and FEA simulation, system engineering analysis on the X-ray concentrator was finally performed to analyze the effects of environmental factors on the performance, providing basis and guidance for fabrication of the X-ray concentrator grazing incidence optics.

  18. X-ray emission from cataclysmic variables with accretion disks. I - Hard X-rays. II - EUV/soft X-ray radiation

    NASA Technical Reports Server (NTRS)

    Patterson, J.; Raymond, J. C.

    1985-01-01

    Theoretical models explaining the hard-X-ray, soft-X-ray, and EUV emission of accretion-disk cataclysmic variables in terms of the disk boundary layer (DBL) are developed on the basis of a survey of the published observational data. The data are compared with model predictions in graphs for systems with high or low (greater than or less than 10-Pg/s) accretion rates. Good agreement is obtained both at low accretion rates, where an optically thin rarefied hot (Te = 10 to the 8th K) DBL radiates most of its energy as hard X-rays, and at high accretion rates, where an optically thick 100,000-K DBL radiates most of its energy in the EUV and as soft X-rays. Detailed analysis of the old nova V603 Aql suggests that previous models predicting more detections of soft-X-ray/EUV emissions from thick-DBL objects (Ferland et al., 1982) used inappropriate dwarf masses, interstellar column densities, or classical-nova space densities.

  19. Detection of X-Ray Emission from the Very Old Pulsar J0108-1431

    NASA Astrophysics Data System (ADS)

    Pavlov, G. G.; Kargaltsev, O.; Wong, J. A.; Garmire, G. P.

    2009-01-01

    PSR J0108-1431 is a nearby, 170 Myr old, very faint radio pulsar near the "pulsar death line" in the P-\\dot{P} diagram. We observed the pulsar field with the Chandra X-ray Observatory and detected a point source (53 counts in a 30 ks exposure; energy flux (9 ± 2) × 10-15 erg cm-2 s-1 in the 0.3-8 keV band) close to the radio pulsar position. Based on the large X-ray/optical flux ratio at the X-ray source position, we conclude that the source is the X-ray counterpart of PSR J0108-1431. The pulsar spectrum can be described by a power-law model with photon index Γ ≈ 2.2 and luminosity L 0.3-8 keV ≈ 2 × 1028 d 2 130 erg s-1, or by a blackbody model with temperature kT ≈ 0.28 keV and bolometric luminosity L bol ≈ 1.3 × 1028 d 2 130 erg s-1, for a plausible hydrogen column density N H = 7.3 × 1019 cm-2 (d 130 = d/130 pc). The pulsar converts ~0.4% of its spin-down power into X-ray luminosity, i.e., its X-ray efficiency is higher than for most younger pulsars. From the comparison of the X-ray position with the previously measured radio positions, we estimated the pulsar proper motion of 0.2 arcsec yr-1 (V bottom ≈ 130d 130 km s-1), in the south-southeast direction.

  20. X-ray and γ-ray studies of the millisecond pulsar and possible X-ray binary/radio pulsar transition object PSR J1723-2837

    SciTech Connect

    Bogdanov, Slavko; Esposito, Paolo; Crawford III, Fronefield; Possenti, Andrea; McLaughlin, Maura A.; Freire, Paulo

    2014-01-20

    We present X-ray observations of the 'redback' eclipsing radio millisecond pulsar (MSP) and candidate radio pulsar/X-ray binary transition object PSR J1723-2837. The X-ray emission from the system is predominantly non-thermal and exhibits pronounced variability as a function of orbital phase, with a factor of ∼2 reduction in brightness around superior conjunction. Such temporal behavior appears to be a defining characteristic of this variety of peculiar MSP binaries and is likely caused by a partial geometric occultation by the main-sequence-like companion of a shock within the binary. There is no indication of diffuse X-ray emission from a bow shock or pulsar wind nebula associated with the pulsar. We also report on a search for point source emission and γ-ray pulsations in Fermi Large Area Telescope data using a likelihood analysis and photon probability weighting. Although PSR J1723-2837 is consistent with being a γ-ray point source, due to the strong Galactic diffuse emission at its position a definitive association cannot be established. No statistically significant pulsations or modulation at the orbital period are detected. For a presumed detection, the implied γ-ray luminosity is ≲5% of its spin-down power. This indicates that PSR J1723-2837 is either one of the least efficient γ-ray producing MSPs or, if the detection is spurious, the γ-ray emission pattern is not directed toward us.

  1. A CHANDRA OBSERVATION OF THE BURSTING MILLISECOND X-RAY PULSAR IGR J17511-3057

    SciTech Connect

    Paizis, A.; Nowak, M. A.; Rodriguez, J.; Chaty, S.; Del Santo, M.; Ubertini, P. E-mail: mnowak@space.mit.edu

    2012-08-10

    IGR J17511-3057 is a low-mass X-ray binary hosting a neutron star and is one of the few accreting millisecond X-ray pulsars with X-ray bursts. We report on a 20 ks Chandra grating observation of IGR J17511-3057, performed on 2009 September 22. We determine the most accurate X-ray position of IGR J17511-3057, {alpha}{sub J2000} = 17{sup h}51{sup m}08.{sup s}66, {delta}{sub J2000} = -30 Degree-Sign 57'41.''0 (90% uncertainty of 0.''6). During the observation, a {approx}54 s long type-I X-ray burst is detected. The persistent (non-burst) emission has an absorbed 0.5-8 keV luminosity of 1.7 Multiplication-Sign 10{sup 36} erg s{sup -1} (at 6.9 kpc) and can be well described by a thermal Comptonization model of soft, {approx}0.6 keV, seed photons upscattered by a hot corona. The type-I X-ray burst spectrum, with average luminosity over the 54 s duration L{sub 0.5-8{sub keV}} = 1.6 Multiplication-Sign 10{sup 37} erg s{sup -1}, can be well described by a blackbody with kT{sub bb} {approx} 1.6 keV and R{sub bb} {approx} 5 km. While an evolution in temperature of the blackbody can be appreciated throughout the burst (average peak kT{sub bb} = 2.5{sup +0.8}{sub -0.4} keV to tail kT{sub bb} = 1.3{sup +0.2}{sub -0.1} keV), the relative emitting surface shows no evolution. The overall persistent and type-I burst properties observed during the Chandra observation are consistent with what was previously reported during the 2009 outburst of IGR J17511-3057.

  2. SXP 214: An X-Ray Pulsar in the Small Magellanic Cloud, Crossing the Circumstellar Disk of the Companion

    NASA Astrophysics Data System (ADS)

    Hong, JaeSub; Antoniou, Vallia; Zezas, Andreas; Haberl, Frank; Drake, Jeremy J.; Plucinsky, Paul P.; Gaetz, Terrance; Sasaki, Manami; Williams, Benjamin; Long, Knox S.; Blair, William P.; Winkler, P. Frank; Wright, Nicholas J.; Laycock, Silas; Udalski, Andrzej

    2016-07-01

    Located in the Small Magellanic Cloud (SMC), SXP 214 is an X-ray pulsar in a high mass X-ray binary system with a Be-star companion. A recent survey of the SMC under a Chandra X-ray Visionary program found that the source was in a transition when the X-ray flux was on a steady rise. The Lomb-Scargle periodogram revealed a pulse period of 211.49 ± 0.42 s, which is significantly (>5σ) shorter than the previous measurements made with XMM-Newton and RXTE. This implies that the system has gone through sudden spin-up episodes recently. The pulse profile shows a sharp eclipse-like feature with a modulation amplitude of >95%. The linear rise of the observed X-ray luminosity from ≲2× to 7× {10}35 erg s-1 is correlated with a steady softening of the X-ray spectrum, which can be described by the changes in the local absorption from N H ˜ 1024 to ≲1020 cm-2 for an absorbed power-law model. The soft X-ray emission below 2 keV was absent in the early part of the observation when only the pulsating hard X-ray component was observed, whereas at later times, both soft and hard X-ray components were observed to be pulsating. A likely explanation is that the neutron star was initially hidden in the circumstellar disk of the companion, and later came out of the disk with the accreted material that continued fueling the observed pulsation.

  3. X-ray and UV radiation from accreting nonmagnetic degenerate dwarfs. II

    NASA Technical Reports Server (NTRS)

    Kylafis, N. D.; Lamb, D. Q.

    1982-01-01

    Numerical calculations of X-ray and UV emission from accreting nonmagnetic degenerate dwarfs are reported, which span the entire range of accretion rates and stellar masses. Calculations include the effects of bremsstrahlung, Compton cooling, radiation pressure, albedo of the stellar surface, Compton degradation and free-free abscription of the X-ray spectrum by the accreting matter. Maximum X-ray luminosity for degenerate dwarfs undergoing spherical accretion is found to be 2.2 x 10 to the 36th ergs/s, which is little changed if accretion occurs radially over only a fraction of the stellar surface, so that the emitted radiation escapes without significant scattering. The temperature characterizing the X-ray spectra produced by degenerate dwarfs strongly depends on the stellar mass and the accretion rate, and it is suggested that the correlation between spectral temperature and luminosity is an important signature of degenerate X-ray sources.

  4. Numerical Solution of the Radiative Transfer Equation: X-Ray Spectral Formation from Cylindrical Accretion onto a Magnetized Neutron Star

    NASA Technical Reports Server (NTRS)

    Fairnelli, R.; Ceccobello, C.; Romano, P.; Titarchuk, L.

    2011-01-01

    Predicting the emerging X-ray spectra in several astrophysical objects is of great importance, in particular when the observational data are compared with theoretical models. This requires developing numerical routines for the solution of the radiative transfer equation according to the expected physical conditions of the systems under study. Aims. We have developed an algorithm solving the radiative transfer equation in the Fokker-Planck approximation when both thermal and bulk Comptonization take place. The algorithm is essentially a relaxation method, where stable solutions are obtained when the system has reached its steady-state equilibrium. Methods. We obtained the solution of the radiative transfer equation in the two-dimensional domain defined by the photon energy E and optical depth of the system pi using finite-differences for the partial derivatives, and imposing specific boundary conditions for the solutions. We treated the case of cylindrical accretion onto a magnetized neutron star. Results. We considered a blackbody seed spectrum of photons with exponential distribution across the accretion column and for an accretion where the velocity reaches its maximum at the stellar surface and at the top of the accretion column, respectively. In both cases higher values of the electron temperature and of the optical depth pi produce flatter and harder spectra. Other parameters contributing to the spectral formation are the steepness of the vertical velocity profile, the albedo at the star surface, and the radius of the accretion column. The latter parameter modifies the emerging spectra in a specular way for the two assumed accretion profiles. Conclusions. The algorithm has been implemented in the XPEC package for X-ray fitting and is specifically dedicated to the physical framework of accretion at the polar cap of a neutron star with a high magnetic field (approx > 10(exp 12) G). This latter case is expected to be of typical accreting systems such as X-ray

  5. New, fast X-ray pulsar in the supernova remnant MSH 15--52

    SciTech Connect

    Seward, F.D.; Harnden, F.R. Jr.

    1982-05-15

    A pulsing X-ray source has been discovered within the shell of the supernova remnant MSH 15--52. The period is 0.150 s, and the rate of increase of period with time is the highest measured for any pulsar. These characteristics and the fact that the pulsar is surrounded by a small, bright nebula indicate that this object is very similar to the Crab pulsar.

  6. A new, fast X-ray pulsar in the supernova remnant MSH 15-52

    NASA Technical Reports Server (NTRS)

    Seward, F. D.; Harnden, F. R., Jr.

    1982-01-01

    A pulsing X-ray source has been discovered within the shell of the supernova remnant MSH 15-52. The period is 0.150 s, and the rate of increase of period with time is the highest measured for any pulsar. These characteristics and the fact that the pulsar is surrounded by a small, bright nebula indicate that this object is very similar to the Crab pulsar.

  7. A Study of the X-Ray Emission from Three Radio Pulsars

    NASA Technical Reports Server (NTRS)

    Slane, Patrick O. (Principal Investigator)

    1996-01-01

    The subject grant is for work on a study of x-ray emission from isolated pulsars. The purpose of the study was to: determine whether the pulsars were x-ray sources; and, if so, search for evidence of pulsations at the known radio period; and study the nature of the x-ray emission. Observation of the pulsar PSR 0355+54 were obtained, and the analysis of these data is complete. These results were reported at the 183rd AAS Meeting, and in a paper entitled 'X-Ray Emission from PSR 0355+54' which as published in the The Astrophysical Journal. Also obtained an approx. 3 ks PSPC observations of PSR 1642-03. A summary of the results from these data were reported in a Conference Proceedings for the 'New Horizon of X-ray Astronomy' symposium. In addition, as part of a study with a student from the SAO Summer Intern Program, I incorporated ROSAT archival data in an extended study of pulsar emission. These results were reported at the 185th AAS Meeting, and in a paper entitled 'Soft X-ray Emission from Selected Isolated Pulsars' which was published in The Astrophysical Journal (Letters).

  8. High energy X-ray observations of the 38-second pulsar

    NASA Technical Reports Server (NTRS)

    Byrne, P. F.; Levine, A. M.; Bautz, M.; Howe, S. K.; Lang, F. L.; Primini, F. A.; Lewin, W. H. G.; Gruber, D. E.; Knight, F. K.; Nolan, P. L.

    1981-01-01

    The results of observations of the 38-second pulsar obtained at high X-ray energies (13-180 keV) with the UCSD/MIT instrument aboard HEAO 1 are reported. The results include a measurement of the source location, measurement of the pulse profile, and determination of the average intensity and spectrum during each of three time intervals spanning a baseline of 1 year. The total intensity of the pulsar is seen to vary on a 6-month time scale. The spectrum is hard but, like other X-ray pulsars, steepens at energies above 20 keV.

  9. X-ray studies of the black widow pulsar PSR B1957+20

    NASA Astrophysics Data System (ADS)

    Huang, R. H. H.; Kong, A. K. H.; Takata, J.; Hui, C. Y.; Lin, L. C. C.; Cheng, K. S.

    2013-03-01

    We report on Chandra observations of the black widow pulsar, PSR B1957+20. Evidence for a binary-phase dependence of the X-ray emission from the pulsar is found with a deep observation. The binary-phase resolved spectral analysis reveals non-thermal X-ray emission of PSR B1957+20, confirming the results of previous studies. This suggests that the X-rays are mostly due to intra-binary shock emission which is strongest when the pulsar wind interacts with the ablated material from the companion star. The geometry of the peak emission is determined in our study. The marginal softening of the spectrum of the non-thermal X-ray tail may indicate that particles injected at the termination shock is dominated by synchrotron cooling.

  10. X-Ray Studies of the Black Widow Pulsar PSR B1957+20

    NASA Astrophysics Data System (ADS)

    Huang, R. H. H.; Kong, A. K. H.; Takata, J.; Hui, C. Y.; Lin, L. C. C.; Cheng, K. S.

    2012-11-01

    We report on Chandra observations of the black widow pulsar, PSR B1957+20. Evidence for a binary-phase dependence of the X-ray emission from the pulsar is found with a deep observation. The binary-phase-resolved spectral analysis reveals non-thermal X-ray emission of PSR B1957+20, confirming the results of previous studies. This suggests that the X-rays are mostly due to intra-binary shock emission, which is strongest when the pulsar wind interacts with the ablated material from the companion star. The geometry of the peak emission is determined in our study. The marginal softening of the spectrum of the non-thermal X-ray tail may indicate that particles injected at the termination shock are dominated by synchrotron cooling.

  11. X-RAY STUDIES OF THE BLACK WIDOW PULSAR PSR B1957+20

    SciTech Connect

    Huang, R. H. H.; Kong, A. K. H.; Takata, J.; Cheng, K. S.; Hui, C. Y.; Lin, L. C. C.

    2012-11-20

    We report on Chandra observations of the black widow pulsar, PSR B1957+20. Evidence for a binary-phase dependence of the X-ray emission from the pulsar is found with a deep observation. The binary-phase-resolved spectral analysis reveals non-thermal X-ray emission of PSR B1957+20, confirming the results of previous studies. This suggests that the X-rays are mostly due to intra-binary shock emission, which is strongest when the pulsar wind interacts with the ablated material from the companion star. The geometry of the peak emission is determined in our study. The marginal softening of the spectrum of the non-thermal X-ray tail may indicate that particles injected at the termination shock are dominated by synchrotron cooling.

  12. Two populations of X-ray pulsars produced by two types of supernova.

    PubMed

    Knigge, Christian; Coe, Malcolm J; Podsiadlowski, Philipp

    2011-11-09

    Two types of supernova are thought to produce the overwhelming majority of neutron stars in the Universe. The first type, iron-core-collapse supernovae, occurs when a high-mass star develops a degenerate iron core that exceeds the Chandrasekhar limit. The second type, electron-capture supernovae, is associated with the collapse of a lower-mass oxygen-neon-magnesium core as it loses pressure support owing to the sudden capture of electrons by neon and/or magnesium nuclei. It has hitherto been impossible to identify the two distinct families of neutron stars produced in these formation channels. Here we report that a large, well-known class of neutron-star-hosting X-ray pulsars is actually composed of two distinct subpopulations with different characteristic spin periods, orbital periods and orbital eccentricities. This class, the Be/X-ray binaries, contains neutron stars that accrete material from a more massive companion star. The two subpopulations are most probably associated with the two distinct types of neutron-star-forming supernova, with electron-capture supernovae preferentially producing systems with short spin periods, short orbital periods and low eccentricities. Intriguingly, the split between the two subpopulations is clearest in the distribution of the logarithm of spin period, a result that had not been predicted and which still remains to be explained.

  13. Synchronous x-ray and radio mode switches: a rapid global transformation of the pulsar magnetosphere.

    PubMed

    Hermsen, W; Hessels, J W T; Kuiper, L; van Leeuwen, J; Mitra, D; de Plaa, J; Rankin, J M; Stappers, B W; Wright, G A E; Basu, R; Alexov, A; Coenen, T; Grießmeier, J-M; Hassall, T E; Karastergiou, A; Keane, E; Kondratiev, V I; Kramer, M; Kuniyoshi, M; Noutsos, A; Serylak, M; Pilia, M; Sobey, C; Weltevrede, P; Zagkouris, K; Asgekar, A; Avruch, I M; Batejat, F; Bell, M E; Bell, M R; Bentum, M J; Bernardi, G; Best, P; Bîrzan, L; Bonafede, A; Breitling, F; Broderick, J; Brüggen, M; Butcher, H R; Ciardi, B; Duscha, S; Eislöffel, J; Falcke, H; Fender, R; Ferrari, C; Frieswijk, W; Garrett, M A; de Gasperin, F; de Geus, E; Gunst, A W; Heald, G; Hoeft, M; Horneffer, A; Iacobelli, M; Kuper, G; Maat, P; Macario, G; Markoff, S; McKean, J P; Mevius, M; Miller-Jones, J C A; Morganti, R; Munk, H; Orrú, E; Paas, H; Pandey-Pommier, M; Pandey, V N; Pizzo, R; Polatidis, A G; Rawlings, S; Reich, W; Röttgering, H; Scaife, A M M; Schoenmakers, A; Shulevski, A; Sluman, J; Steinmetz, M; Tagger, M; Tang, Y; Tasse, C; ter Veen, S; Vermeulen, R; van de Brink, R H; van Weeren, R J; Wijers, R A M J; Wise, M W; Wucknitz, O; Yatawatta, S; Zarka, P

    2013-01-25

    Pulsars emit from low-frequency radio waves up to high-energy gamma-rays, generated anywhere from the stellar surface out to the edge of the magnetosphere. Detecting correlated mode changes across the electromagnetic spectrum is therefore key to understanding the physical relationship among the emission sites. Through simultaneous observations, we detected synchronous switching in the radio and x-ray emission properties of PSR B0943+10. When the pulsar is in a sustained radio-"bright" mode, the x-rays show only an unpulsed, nonthermal component. Conversely, when the pulsar is in a radio-"quiet" mode, the x-ray luminosity more than doubles and a 100% pulsed thermal component is observed along with the nonthermal component. This indicates rapid, global changes to the conditions in the magnetosphere, which challenge all proposed pulsar emission theories.

  14. Spectral variability in the X-ray pulsar GX 1+4

    NASA Technical Reports Server (NTRS)

    Becker, R. H.; Boldt, E. A.; Holt, S. S.; Pravdo, S. H.; Rothschild, R. E.; Serlemitsos, P. J.; Swank, J. H.

    1976-01-01

    Observations of the galactic center region, hard X-ray source GX 1+4 by the GSFC X-ray spectroscopy experiment on OSO-8 confirm that GX 1+4 is a slow X-ray pulsar. The amount of absorption by cold matter in the spectrum of GX 1+4 varies significantly within a 24 hour period, behavior typical of many X-ray binary systems. The light curve for the pulsations from GX 1+4 appears to be energy dependent.

  15. The effect of vacuum birefringence on the polarization of X-ray binaries and pulsars

    NASA Technical Reports Server (NTRS)

    Novick, R.; Weisskopf, M. C.; Angel, J. R. P.; Sutherland, P. G.

    1977-01-01

    In a strong magnetic field the vacuum becomes birefringent. This effect is especially important for pulsars at X-ray wavelengths. Any polarized X-ray emission from the surface of a magnetic neutron star becomes depolarized as it propagates through the magnetic field. The soft X-ray emission from AM Her, believed to be a magnetic white dwarf, may show about one radian of phase retardation. In this case, circular polarization of the X-ray flux would be a characteristic signature of vacuum birefringence.

  16. Neutron Star Seismology with Accreting Millisecond Pulsars

    NASA Astrophysics Data System (ADS)

    Strohmayer, Tod

    Neutron stars provide natural laboratories for the study of a number of important topics in fundamental physics, including the composition and equation of state (EOS) of cold matter at the highest densities achievable in nature. The physical conditions in their deep interiors cannot be replicated in terrestrial laboratories, and the nature of matter under such extreme conditions remains one of the major unsolved problems in physics. Direct measurement of the mass - radius relationship for neutron stars is very important for constraining the EOS of dense matter, however, since different phases of dense matter can have similar equations of state, mass and radius measurements alone are not very efficient in determining their interior composition. Additional, complementary observables are needed to more definitively probe the composition of neutron star cores. Asteroseismology, the measurement of the characteristic frequencies of the normal modes of oscillation of stars, can provide a powerful probe of their interiors. For example, helioseismology has provided unprecedented insights about the deep interior of the Sun. Comparable capabilities for neutron star seismology have not yet been achieved, but our recent work indicates that sensitive searches for the signatures of neutron star oscillations can be carried out using the high time resolution, pulse timing data obtained by the Rossi X-ray Timing Explorer (RXTE)-and in the case of a single source the XMM-Newton pn camera-from the population of accreting millisecond X-ray pulsars (AMXPs, Strohmayer & Mahmoodifar 2014a), and in some thermonuclear burst sources (Strohmayer & Mahmoodifar 2014b). It is the primary aim of this proposal to carry out the first such comprehensive search for global oscillation modes across this entire source class of neutron stars using approximately 6 M-sec of RXTE and 100 k-sec of XMMNewton archival data, and thereby significantly advance the nascent field of neutron star seismology. We will

  17. Disentangling X-Ray Emission Processes in Vela-Like Pulsars

    NASA Technical Reports Server (NTRS)

    Gaensler, Bryan; Mushotzky, Richard (Technical Monitor)

    2003-01-01

    We present a deep observation with the X-Ray Multimirror Mission of PSR B1823-13, a young pulsar with similar properties to the Vela pulsar. We detect two components to the X-ray emission associated with PSR B1823-13: an elongated core of extent 30 min immediately surrounding the pulsar embedded in a fainter, diffuse component of emission 5 sec in extent, seen only on the southern side of the pulsar. The pulsar itself is not detected, either as a point source or through its pulsations. Both components of the X-ray emission are well fitted by a power-law spectrum, with photon index Gamma approx. 1.6 and X-ray luminosity (0.5-10 keV) L(sub X) approx. 9 x 10(exp 32) ergs/s for the core and Gamma approx. 2.3 and L(sub X) approx. 3 x 10(exp 33) ergs/s for the diffuse emission, for a distance of 4 kpc. We interpret both components of emission as corresponding to a pulsar wind nebula, which we designate G18.0-0.7. We argue that the core region represents the wind termination shock of this nebula, while the diffuse component indicates the shocked downstream wind. We propose that the asymmetric morphology of the diffuse emission with respect to the pulsar is the result of a reverse shock from an associated supernova remnant, which has compressed and distorted the pulsar-powered nebula. Such an interaction might be typical for pulsars at this stage in their evolution. The associated supernova remnant is not detected directly, most likely being too faint to be seen in existing X-ray and radio observations.

  18. X-ray observations of XSS J12270-4859 in a new low state: A transformation to a disk-free rotation-powered pulsar binary

    SciTech Connect

    Bogdanov, Slavko; Patruno, Alessandro; Archibald, Anne M.; Bassa, Cees; Hessels, Jason W. T.; Janssen, Gemma H.; Stappers, Ben W.

    2014-07-01

    We present XMM-Newton and Chandra observations of the low-mass X-ray binary XSS J12270-4859, which experienced a dramatic decline in optical/X-ray brightness at the end of 2012, indicative of the disappearance of its accretion disk. In this new state, the system exhibits previously absent orbital-phase-dependent, large-amplitude X-ray modulations with a decline in flux at superior conjunction. The X-ray emission remains predominantly non-thermal but with an order of magnitude lower mean luminosity and significantly harder spectrum relative to the previous high flux state. This phenomenology is identical to the behavior of the radio millisecond pulsar (MSP) binary PSR J1023+0038 in the absence of an accretion disk, where the X-ray emission is produced in an intra-binary shock driven by the pulsar wind. This further demonstrates that XSS J12270-4859 no longer has an accretion disk and has transformed to a full-fledged eclipsing 'redback' system that hosts an active rotation-powered MSP. There is no evidence for diffuse X-ray emission associated with the binary that may arise due to outflows or a wind nebula. An extended source situated 1.'5 from XSS J12270-4859 is unlikely to be associated, and is probably a previously uncataloged galaxy cluster.

  19. A Comprehensive Spectral Analysis of the X-Ray Pulsar 4U 1907+09 from Two Observations with the Suzaku X-Ray Observatory

    NASA Technical Reports Server (NTRS)

    Rivers, Elizabeth; Markowitz, Alex; Pottschmidt, Katja; Roth, Stefanie; Barragan, Laura; Furst, Felix; Suchy, Slawomir; Kreykenbohm, Ingo; Wilms, Jorn; Rothschild, Richard

    2009-01-01

    We present results from two observations of the wind-accreting X-ray pulsar 4U 1907+09 using the Suzaku observatory, The broadband time-averaged spectrum allows us to examine the continuum emission of the source and the cyclotron resonance scattering feature at approx. 19 keV. Additionally, using the narrow CCD response of Suzaku near 6 ke V allows us to study in detail the Fe K bandpass and to quantify the Fe Kp line for this source for the first time. The source is absorbed by fully-covering material along the line of sight with a column density of N(sub H) approx. 2 x 10(exp 22)/sq cm, consistent with a wind accreting geometry, and a high Fe abundance (approx. 3 - 4 x solar). Time and phase-resolved analyses allow us to study variations in the source spectrum. In particular, dips found in the 2006 observation which are consistent with earlier observations occur in the hard X-ray bandpass, implying a variation of the whole continuum rather than occultation by intervening material, while a dip near the end of the 2007 observation occurs mainly in the lower energies implying an increase in NH along the line of sight, perhaps indicating clumpiness in the stellar wind

  20. X-ray jets from B2224+65: A Middle-aged Pulsar's New Trick

    NASA Astrophysics Data System (ADS)

    Wang, Q. Daniel; Johnson, Seth

    2015-01-01

    Pulsars, though typically not aged ones, are believed to be an important source of energetic cosmic rays. Therefore, it may not be too surprising to detect an X-ray jet associated with the middle-aged radio/X-ray pulsar B2224+65, which is well known for its very high proper motion and its trailing ``Guitar Nebula''. Most unexpected, however, is that this jet is offset from its proper motion direction by 118 degree. Furthermore, an X-ray counter jet and a faint X-ray trail associated with the ``Guitar Nebula'' are now identified in the combined data set of three epoch Chandra observations with a total exposure of 200 ks. We are carrying out a detailed measurements of the X-ray spectral variation with time and across the jets and are critically testing scenarios proposed to explain this enigmatic phenomenon. The study should have strong implications for understanding the origin of cosmic rays, as well as similar linear nonthermal X-ray-emitting features that are associated with more distant pulsars, especially pulsar wind nebula candidates in the central 100 pc region of the Galaxy.

  1. X-rays from radio pulsars - The detection of PSR 1055-52

    NASA Technical Reports Server (NTRS)

    Cheng, A. F.; Helfand, D. J.

    1983-01-01

    The short-period pulsar PSR 1055-52 has been detected as a soft X-ray source in the course of an Einstein Observatory survey of radio pulsars. Its X-ray to radio luminosity ratio is about 10,000, although the X-rays are not modulated at the neutron star's rotation frequency. High spatial resolution observations suggest that a significant fraction of the emission comes from an extended region surrounding the pulsar. Several possible scenarios for the origin of both point and extended X-ray emission from isolated neutron stars are investigated: radiation from the hot stellar surface, from hot polar caps, and from an optically thick atmosphere, as well as from a circumstellar nebula emitting thermal bremsstrahlung or synchrotron radiation. It is concluded that the spatial, spectral, and temporal characteristics of this source are most consistent with a model in which relativistic particles generated by the pulsar are radiating synchrotron X-rays in the surrounding magnetic field; i.e., that PSR 1055 is embedded in a mini-Crab nebula. Observational tests of this hypothesis are suggested, and the implications of this result for pulsar evolution are briefly discussed.

  2. Discovery of a 0.42-s pulsar in the ultraluminous X-ray source NGC 7793 P13

    NASA Astrophysics Data System (ADS)

    Israel, G. L.; Papitto, A.; Esposito, P.; Stella, L.; Zampieri, L.; Belfiore, A.; Rodríguez Castillo, G. A.; De Luca, A.; Tiengo, A.; Haberl, F.; Greiner, J.; Salvaterra, R.; Sandrelli, S.; Lisini, G.

    2017-03-01

    NGC 7793 P13 is a variable (luminosity range ∼100) ultraluminous X-ray source proposed to host a stellar-mass black hole of less than 15 M⊙ in a binary system with orbital period of 64 d and a 18-23 M⊙ B9Ia companion. Within the EXTraS (Exploring the X-ray Transient and variable Sky) project, we discovered pulsations at a period of ∼0.42 s in two XMM-Newton observations of NGC 7793 P13, during which the source was detected at LX ∼ 2.1 × 1039 and 5 × 1039 erg s-1 (0.3-10 keV band). These findings unambiguously demonstrate that the compact object in NGC 7793 P13 is a neutron star accreting at super-Eddington rates. While standard accretion models face difficulties accounting for the pulsar X-ray luminosity, the presence of a multipolar magnetic field with B ∼ few × 1013 G close to the base of the accretion column appears to be in agreement with the properties of the system.

  3. A FAST X-RAY DISK WIND IN THE TRANSIENT PULSAR IGR J17480-2446 IN TERZAN 5

    SciTech Connect

    Miller, Jon M.; Maitra, Dipankar; Cackett, Edward M.; Bhattacharyya, Sudip; Strohmayer, Tod E.

    2011-04-10

    Accretion disk winds are revealed in Chandra gratings spectra of black holes. The winds are hot and highly ionized (typically composed of He-like and H-like charge states) and show modest blueshifts. Similar line spectra are sometimes seen in 'dipping' low-mass X-ray binaries (LMXBs), which are likely viewed edge-on; however, that absorption is tied to structures in the outer disk, and blueshifts are not typically observed. Here, we report the detection of blueshifted He-like Fe XXV (3100 {+-} 400 km s{sup -1}) and H-like Fe XXVI (1000 {+-} 200 km s{sup -1}) absorption lines in a Chandra/HETG spectrum of the transient pulsar and LMXB IGR J17480-2446 in Terzan 5. These features indicate a disk wind with at least superficial similarities to those observed in stellar-mass black holes. The wind does not vary strongly with numerous weak X-ray bursts or flares. A broad Fe K emission line is detected in the spectrum, and fits with different line models suggest that the inner accretion disk in this system may be truncated. If the stellar magnetic field truncates the disk, a field strength of B= (0.7-4.0)x10{sup 9} G is implied, which is in line with estimates based on X-ray timing techniques. We discuss our findings in the context of accretion flows onto neutron stars and stellar-mass black holes.

  4. ORIGIN OF INTERMITTENT ACCRETION-POWERED X-RAY OSCILLATIONS IN NEUTRON STARS WITH MILLISECOND SPIN PERIODS

    SciTech Connect

    Lamb, Frederick K.; Boutloukos, Stratos; Van Wassenhove, Sandor; Chamberlain, Robert T.; Lo, Ka Ho; Coleman Miller, M.

    2009-11-01

    We have shown previously that many of the properties of persistent accretion-powered millisecond pulsars can be understood if their X-ray emitting areas are near their spin axes and move as the accretion rate and structure of the inner disk vary. Here, we show that this 'nearly aligned moving spot model' may also explain the intermittent accretion-powered pulsations that have been detected in three weakly magnetic accreting neutron stars. We show that movement of the emitting area from very close to the spin axis to approx10 deg. away can increase the fractional rms amplitude from approx<0.5%, which is usually undetectable with current instruments, to a few percent, which is easily detectable. The second harmonic of the spin frequency usually would not be detected, in agreement with observations. The model produces intermittently detectable oscillations for a range of emitting area sizes and beaming patterns, stellar masses and radii, and viewing directions. Intermittent oscillations are more likely in stars that are more compact. In addition to explaining the sudden appearance of accretion-powered millisecond oscillations in some neutron stars with millisecond spin periods, the model explains why accretion-powered millisecond oscillations are relatively rare and predicts that the persistent accretion-powered millisecond oscillations of other stars may become undetectable for brief intervals. It suggests why millisecond oscillations are frequently detected during the X-ray bursts of some neutron stars but not others and suggests mechanisms that could explain the occasional temporal association of intermittent accretion-powered oscillations with thermonuclear X-ray bursts.

  5. LONG-TERM X-RAY MONITORING OF THE YOUNG PULSAR PSR B1509-58

    SciTech Connect

    Livingstone, Margaret A.; Kaspi, Victoria M.

    2011-11-20

    It has long been thought that the pulsed X-ray properties of rotation-powered pulsars are stable on long timescales. However, long-term, systematic studies of individual sources have been lacking. Furthermore, dramatic X-ray variability has now been observed from two pulsars having inferred sub-critical dipole magnetic fields. Here we present an analysis of the long-term pulsed X-ray properties of the young, energetic pulsar PSR B1509-58 using data from the Rossi X-ray Timing Explorer. We measured the 2-50 keV pulsed flux for 14.7 yr of X-ray observations and found that it is consistent with being constant on all relevant timescales, and place a 3{sigma} upper limit on day-to-week variability of <28%. In addition, we searched for magnetar-like X-ray bursts in all observations and found none, which we use to constrain the measurable burst rate to less than one per 750 ks of observations. We also searched for variability in the pulse profile and found that it is consistent with being stable on timescales of days to decades. This supports the hypothesis that X-ray properties of rotation-powered X-ray pulsars can be stable on decade-long timescales. In addition, we extend the existing timing solution by 7.1 yr to a total of 28.4 yr and report updated values of the braking index, n = 2.832 {+-} 0.003, and the second braking index, m = 17.6 {+-} 1.9.

  6. Towards Practical Deep-Space Navigation using X-ray Pulsar Timing

    NASA Astrophysics Data System (ADS)

    Shemar, Setnam; Fraser, George; Heil, Lucy; Hindley, David; Martindale, Adrian; Molyneux, Philippa; Pye, John P.; Warwick, Robert; Lamb, Andrew

    2015-08-01

    We describe a recent study, conducted by the National Physical Laboratory and the University of Leicester for the European Space Agency, on the feasibility of using X-ray timing observations of pulsars for deep space navigation, a technique commonly referred to as ‘XNAV’. We have considered all primary aspects of the ‘system’, i.e. suitable pulsars and their sky distribution, available and future instrumentation, navigation methods and algorithms, and overall performance (e.g. position accuracy). We have used simulations to identify the best combinations of navigation method and X-ray pulsars with respect to predicted performance, taking account of current and future X-ray instrumentation. The XNAV technique would allow increased spacecraft autonomy, improved position accuracies and lower mission operating costs compared to the NASA and ESA Deep Space Networks (DSN). We have also used a high-level navigation algorithm together with real data (from the RXTE mission archive) for the Crab pulsar to demonstrate key elements of XNAV. X-ray instrumentation suitable for use as a spacecraft operational subsystem must be designed to use only modest spacecraft resources. We show that instrumentation designed for the Mercury Imaging X-ray Spectrometer, in production for the ESA/JAXA BepiColombo mission to Mercury, offers a roadmap for a practical XNAV system. We identify key areas for future study.

  7. CHANDRA X-RAY OBSERVATIONS OF 12 MILLISECOND PULSARS IN THE GLOBULAR CLUSTER M28

    SciTech Connect

    Bogdanov, Slavko; Van den Berg, Maureen; Servillat, Mathieu; Grindlay, Jonathan E.; Heinke, Craig O.; Stairs, Ingrid H.; Begin, Steve; Ransom, Scott M.; Freire, Paulo C. C.; Becker, Werner

    2011-04-01

    We present a Chandra X-ray Observatory investigation of the millisecond pulsars in the globular cluster M28 (NGC 6626). In what is one of the deepest X-ray observations of a globular cluster, we firmly detect seven and possibly detect two of the 12 known M28 pulsars. With the exception of PSRs B1821-24 and J1824-2452H, the detected pulsars have relatively soft spectra, with X-ray luminosities 10{sup 30}-10{sup 31} erg s{sup -1} (0.3-8 keV), similar to most 'recycled' pulsars in 47 Tucanae and the field of the Galaxy, implying thermal emission from the pulsar magnetic polar caps. We present the most detailed X-ray spectrum to date of the energetic PSR B1821-24. It is well described by a purely non-thermal spectrum with spectral photon index {Gamma} = 1.23 and luminosity 1.4 x 10{sup 33}{Theta}(D/5.5 kpc){sup 2} erg s{sup -1} (0.3-8 keV), where {Theta} is the fraction of the sky covered by the X-ray emission beam(s). We find no evidence for the previously reported line emission feature around 3.3 keV, most likely as a consequence of improvements in instrument calibration. The X-ray spectrum and pulse profile of PSR B1821-24 suggest that the bulk of unpulsed emission from this pulsar is not of thermal origin, and is likely due to low-level non-thermal magnetospheric radiation, an unresolved pulsar wind nebula, and/or small-angle scattering of the pulsed X-rays by interstellar dust grains. The peculiar binary PSR J1824-2452H shows a relatively hard X-ray spectrum and possible variability at the binary period, indicative of an intrabinary shock formed by interaction between the relativistic pulsar wind and matter from its non-degenerate companion star.

  8. Discovery of X-Ray Emission from the Crab Pulsar at Pulse Minimum

    NASA Technical Reports Server (NTRS)

    Tennant, Allyn F.; Becker, Werner; Juda, Michael X.; Elsner, Ronald F.; Kolodziejczak, Jeffery J.; Murray, Stephen S.; ODell, Stephen L.; Paerels, Frits; Swartz, Douglas A.; Shibazaki, Noriaki; Weisskopf, Martin C.; Rose, M. Franklin (Technical Monitor)

    1999-01-01

    The Chandra X-ray Observatory observed the Crab Nebula and Pulsar using the Low-Energy Transmission Grating (LETG) with the High-Resolution Camera (HRC). Time-resolved zeroth-order images reveal that the pulsar emits x rays at all pulse phases. Analysis of the flux at minimum -- most likely nonthermal in origin -- places an upper limit (T(sub infinity) < 2.1 MK) on the surface temperature of the underlying neutron star. In addition, analysis of the pulse profile appears to confirm the absolute timing of the Observatory to within about 0.2 ms.

  9. Discovery of X-Ray Emission from the Crab Pulsar at Pulse Minimum

    NASA Technical Reports Server (NTRS)

    Tennant, Allyn F.; Becker, Werner; Juda, Michael; Elsner, Ronald F.; Kolodziejczak, Jeffery J.; Murray, Stephen S.; ODell, Stephen L.; Paerels, Frits; Swartz, Douglas A.

    2001-01-01

    The Chandra X-Ray Observatory observed the Crab pulsar using the Low-Energy Transmission Grating with the High-Resolution Camera. Time-resolved zeroth-order images reveal that the pulsar emits X-rays at all pulse phases. Analysis of the flux at minimum - most likely non-thermal in origin - places an upper limit (T(sub infinity) < 2.1 MK) on the surface temperature of the underlying neutron star. In addition, analysis of the pulse profile establishes that the error in the Chandra-determined absolute time is quite small, -0.2 +/- 0.1 ms.

  10. X-ray Measurements of Variable Accretion onto the Young Star TW Hydrae

    NASA Astrophysics Data System (ADS)

    Brickhouse, Nancy S.; Cranmer, S. R.; Dupree, A. K.; Wolk, S. J.; Guenther, H. M.

    2013-06-01

    We report X-ray line ratio diagnostics of the electron temperature, electron density and hydrogen column density observed from the classical T Tauri star (CTTS) TW Hydrae using the High Energy Transmission Grating (HETG) spectrometer onboard Chandra. Applying a classical model of magnetically channeled flow from an accretion disk onto the stellar surface, and making the assumption that the absorber of the X-ray shock is the accreting stream itself, we are able to determine all the properties of the accretion, namely the mass accretion rate, stellar magnetic field strength, disk truncation radius, and surface filling factor. We find that the diagnostic ratios, and thus the accretion parameters, are variable, lending support to the absorption assumption. We also report X-ray and optical signatures that respond to the variable accretion, with timescales suggesting the response of the stellar atmosphere to the impact of accretion.

  11. X-RAY PULSATIONS FROM THE RADIO-QUIET GAMMA-RAY PULSAR IN CTA 1

    SciTech Connect

    Caraveo, P. A.; De Luca, A.; Marelli, M.; Bignami, G. F.; Ray, P. S.; Saz Parkinson, P. M.; Kanbach, G.

    2010-12-10

    Prompted by the Fermi-LAT discovery of a radio-quiet gamma-ray pulsar inside the CTA 1 supernova remnant, we obtained a 130 ks XMM-Newton observation to assess the timing behavior of this pulsar. Exploiting both the unprecedented photon harvest and the contemporary Fermi-LAT timing measurements, a 4.7{sigma} single-peak pulsation is detected, making PSR J0007+7303 the second example, after Geminga, of a radio-quiet gamma-ray pulsar also seen to pulsate in X-rays. Phase-resolved spectroscopy shows that the off-pulse portion of the light curve is dominated by a power-law, non-thermal spectrum, while the X-ray peak emission appears to be mainly of thermal origin, probably from a polar cap heated by magnetospheric return currents, pointing to a hot spot varying throughout the pulsar rotation.

  12. Spectral and temporal properties of the X-ray pulsar SMC X-1 at hard X-rays

    NASA Technical Reports Server (NTRS)

    Kunz, M.; Gruber, D. E.; Kendziorra, E .; Kretschmar, P.; Maisack, M.; Mony, B.; Staubert, R.; Doebereiner, S.; Englhauser, J.; Pietsch, W.

    1993-01-01

    The binary X-ray pulsar SMC X- 1 has been observed at hard X-rays with the High Energy X-Ray Experiment (HEXE) on nine occasions between Nov. 1987 and March 1989. A thin thermal bremsstrahlung fit to the phase averaged spectrum yields a plasma temperature (14.4 +/- 1.3) keV and a luminosity above (1.1 +/- 0.1) x 10 exp 38 erg/s in the 20-80 keV band. Pulse period values have been established for three observations, confirming the remarkably stable spin-up trend of SMC X-1. In one of the three observations the pulse profile was seen to deviate from a dominant double pulsation, while at the same time the pulsed fraction was unusually large. For one observation we determined for the first time the pulsed fraction in narrow energy bands. It increases with photon energy from about 20 percent up to over 60 percent in the energy range from 20 to 80 keV.

  13. A Library of known X-ray Pulsars in the Small Magellanic Cloud: Time Evolution of their Luminosities and Spin Periods

    NASA Astrophysics Data System (ADS)

    Yang, Jun; Laycock, Silas; Christodoulou, Dimitris; Drake, Jeremy J.; Hong, Jaesub; Antoniou, Vallia; Zezas, Andreas; Coe, Malcolm; Ho, Wynn

    2017-01-01

    We have collected and analyzed 116 {\\itshape XMM-Newton\\/}, 151 {\\itshape Chandra\\/}, and 952 {\\itshape RXTE\\/} observations of the Small Magellanic Cloud (SMC), spanning 1997-2014. The resulting observational library provides a comprehensive view of the physical, temporal and statistical properties of the SMC pulsar population across the luminosity range of $L_X= 10^{31.5}-10^{38}$~erg~s$^{-1}$. We report $\\sim$1600 individual pulsar detections, yielding $\\sim$1300 pulse period measurements. Our pipeline generates a suite of products for each pulsar detection: period, flux, event list, high time-resolution light-curve, pulse-profile, periodogram and X-ray spectrum. Upper-limits are estimated for all non-detections bringing the combined database to $\\sim$37,000 observations of 67 pulsars. Combining all three satellites, we generated complete histories of the spin periods, pulse amplitudes, pulse fractions and X-ray luminosities. Many of the pulsars show variations in pulse period due to the combination of orbital motion and accretion torques. Long-term spin-up/down trends are seen in 27/25 pulsars respectively, pointing to sustained transfer of mass and angular momentum to the neutron star on decadal timescales. The distributions of pulse-detection and flux as functions of spin-period provide interesting findings: mapping boundaries of accretion-driven X-ray luminosity, and showing that fast pulsars ($P<$10 s) are rarely detected, yet are more prone to giant outburst. Accompanying this paper is an initial public release of the library so that it can be used by other researchers. We intend the database and pulse profile library to be useful in driving improved models of neutron star magnetospheres and accretion physics.

  14. Distance Estimation for Eclipsing X-ray Pulsars

    NASA Astrophysics Data System (ADS)

    Wilson, R. E.; Raichur, H.; Paul, B.

    Distance of an X-ray binary can be computed from a rigorous flux scaling law that connects model stellar atmosphere output with observed standard magnitudes of the optical star via either of two standard magnitude calibrations that agree within 4 percent. Accordingly the corresponding distance disagreement (due to the calibrations only) is only 2 percent, which is negligible compared to several other error sources. The flux-distance scaling is not the usual one for spherical stars but preserves directional (i.e. aspect) information, and therefore is not limited to well detached binaries. Bolometric corrections are not needed, so errors in their estimation are avoided. The procedure also models dependence of system brightness and spectroscopically observable temperature on orbital phase and inclination due to tides, irradiance, and eccentric orbits, although those effects cause only minor distance uncertainties for most X-ray binaries. Not taken into account, due to their largely stochastic nature, are radial velocity variations caused by dynamical tides. Expressions are given for derivatives ∂d/∂p, of distance with respect to various parameters. Some of the derivatives are entirely analytic while others are partly numerical. Upper and lower limits to the relative radius, r= R/a, of an X-ray binary's optical star can be measured, although actual rand inclination are otherwise uncertain. An application to the High Mass X-ray Binary Vela X-1/GP Vel, based on archival pulse arrival times and radial velocities, finds a distance of about 2.2 kiloparsecs and also finds distance uncertainties due to estimated magnitude, interstellar extinction, metallicity, orbit size, optical star size, surface temperature, and surface gravity.

  15. X-ray deficiency on strongly accreting T Tauri stars. Comparing Orion with Taurus

    NASA Astrophysics Data System (ADS)

    Bustamante, I.; Merín, B.; Bouy, H.; Manara, C. F.; Ribas, Á.; Riviere-Marichalar, P.

    2016-03-01

    Context. Depending on whether a T Tauri star accretes material from its circumstellar disk or not, different X-ray emission properties can be found. The accretion shocks produce cool heating of the plasma, contributing to the soft X-ray emission from the star. Aims: Using X-ray data from the Chandra Orion Ultra-deep Project and accretion rates that were obtained with the Hubble Space Telescope/WFPC2 photometric measurements in the Orion Nebula Cluster (ONC), we studied the relation between the accretion processes and the X-ray emissions of a coherent sample of T Tauri sources in the region. Methods: We performed regression and correlation analyses of our sample of T Tauri stars between the X-ray parameters, stellar properties, and the accretion measurements. Results: We find that a clear anti-correlation is present between the residual X-ray luminosity and the accretion rates in our samples in Orion that is consistent with that found on the XMM-Newton Extended Survey of the Taurus molecular cloud (XEST) study. A considerable number of classified non-accreting sources show accretion rates comparable to those of classical T Tauri Stars (CTTS). Our data do not allow us to confirm the classification between classical and weak-line T Tauri stars (WTTS), and the number of WTTS in this work is small compared to the complete samples. Thus, we have used the entire samples as accretors in our analysis. We provide a catalog with X-ray luminosities (corrected from distance) and accretion measurements of an ONC T Tauri stars sample. Conclusions: Although Orion and Taurus display strong differences in their properties (total gas and dust mass, star density, strong irradiation from massive stars), we find that a similar relation between the residual X-ray emission and accretion rate is present in the Taurus molecular cloud and in the accreting samples from the ONC. The spread in the data suggests dependencies of the accretion rates and the X-ray luminosities other than the

  16. A Sequence of Outbursts from the Transient X-Ray Pulsar GS 0834-430

    NASA Technical Reports Server (NTRS)

    Wilson, Colleen A.; Finger, Mark H.; Harmon, B.Alan; Scott, D. Matthew; Wilson, Robert B.; Bildsten, Lars; Chakrabarty, Deepto; Prince, Thomas A.

    1997-01-01

    GS 0834-430, a 12.3 s accretion-powered pulsar, has been observed in seven outbursts with the BATSE large-area detectors on the Compton Gamma Ray Observatory. The first five outbursts observed by BATSE occurred at intervals of about 107 days, while the final two outbursts were separated by about 140 days. The photon energy spectrum, measured by Earth occultation in the 20 100 keV band, can be fitted by a power law with photon index alpha approximately equals -3.7 or by an exponential spectrum with temperature kT approximately equals 15 keV, with some variations within outbursts. The source has a low pulse fraction, less than or equal to 0.15 in the 20-50 keV band. We have observed significant temporal and energy-dependent variations in epoch folded pulse profiles. Because the intrinsic torque effects for this system are at least comparable to orbital effects, pulse timing analysis did not produce a unique orbital solution. However, confidence regions for the orbital elements yielded the following 1 sigma limits: orbital period P(sub orb) = 105.8 +/- 0.4 days and eccentricity 0.10 less than or approximately equals epsilon less than or approximately equals 0.17. GS 0834-430 is most likely a Be/X-ray binary.

  17. X-RAY OBSERVATIONS OF DISRUPTED RECYCLED PULSARS: NO REFUGE FOR ORPHANED CENTRAL COMPACT OBJECTS

    SciTech Connect

    Gotthelf, E. V.; Halpern, J. P.; Allen, B.; Knispel, B.

    2013-08-20

    We present a Chandra X-ray survey of the disrupted recycled pulsars (DRPs), isolated radio pulsars with P > 20 ms and B{sub s} < 3 Multiplication-Sign 10{sup 10} G. These observations were motivated as a search for the immediate descendants of the Almost-Equal-To 10 central compact objects (CCOs) in supernova remnants (SNRs), 3 of which have similar timing and magnetic properties as the DRPs, but are bright, thermal X-ray sources consistent with minimal neutron star (NS) cooling curves. Since none of the DPRs were detected in this survey, there is no evidence that they are ''orphaned'' CCOs, NSs whose SNRs has dissipated. Upper limits on their thermal X-ray luminosities are in the range of log L{sub x} [erg s{sup -1}] = 31.8-32.8, which implies cooling ages >10{sup 4}-10{sup 5} yr, roughly 10 times the ages of the Almost-Equal-To 10 known CCOs in a similar volume of the Galaxy. The order of a hundred CCO descendants that could be detected by this method are thus either intrinsically radio quiet or occupy a different region of (P, B{sub s} ) parameter space from the DRPs. This motivates a new X-ray search for orphaned CCOs among radio pulsars with larger B-fields, which could verify the theory that their fields are buried by the fall-back of supernova ejecta, but quickly regrow to join the normal pulsar population.

  18. Denoising of X-ray pulsar observed profile in the undecimated wavelet domain

    NASA Astrophysics Data System (ADS)

    Xue, Meng-fan; Li, Xiao-ping; Fu, Ling-zhong; Liu, Xiu-ping; Sun, Hai-feng; Shen, Li-rong

    2016-01-01

    The low intensity of the X-ray pulsar signal and the strong X-ray background radiation lead to low signal-to-noise ratio (SNR) of the X-ray pulsar observed profile obtained through epoch folding, especially when the observation time is not long enough. This signifies the necessity of denoising of the observed profile. In this paper, the statistical characteristics of the X-ray pulsar signal are studied, and a signal-dependent noise model is established for the observed profile. Based on this, a profile noise reduction method by performing a local linear minimum mean square error filtering in the un-decimated wavelet domain is developed. The detail wavelet coefficients are rescaled by multiplying their amplitudes by a locally adaptive factor, which is the local variance ratio of the noiseless coefficients to the noisy ones. All the nonstationary statistics needed in the algorithm are calculated from the observed profile, without a priori information. The results of experim! ents, carried out on simulated data obtained by the ground-based simulation system and real data obtained by Rossi X-Ray Timing Explorer satellite, indicate that the proposed method is excellent in both noise suppression and preservation of peak sharpness, and it also clearly outperforms four widely accepted and used wavelet denoising methods, in terms of SNR, Pearson correlation coefficient and root mean square error.

  19. SEXTANT X-Ray Pulsar Navigation Demonstration: Flight System and Test Results

    NASA Technical Reports Server (NTRS)

    Winternitz, Luke M. B.; Mitchell, Jason W.; Hassouneh, Munther A.; Valdez, Jennifer E.; Price, Samuel R.; Semper, Sean R.; Yu, Wayne H.; Ray, Paul S.; Wood, Kent S.; Arzoumanian, Zaven; Gendreau, Keith C.

    2016-01-01

    The Station Explorer for X-ray Timing and Navigation Technology (SEXTANT) is a technology demonstration enhancement to the Neutron-star Interior Composition Explorer (NICER) mission. NICER is a NASA Explorer Mission of Opportunity that will be hosted on the International Space Station (ISS). SEXTANT will, for the first time, demonstrate real-time, on-board X-ray Pulsar Navigation (XNAV), a significant milestone in the quest to establish a GPS-like navigation capability available throughout our Solar System and beyond. This paper gives an overview of the SEXTANT system architecture and describes progress prior to environmental testing of the NICER flight instrument. It provides descriptions and development status of the SEXTANT flight software and ground system, as well as detailed description and results from the flight software functional and performance testing within the highfidelity Goddard Space Flight Center (GSFC) X-ray Navigation Laboratory Testbed (GXLT) software and hardware simulation environment. Hardware-in-the-loop simulation results are presented, using the engineering model of the NICER timing electronics and the GXLT pulsar simulator-the GXLT precisely controls NASA GSFC's unique Modulated X-ray Source to produce X-rays that make the NICER detector electronics appear as if they were aboard the ISS viewing a sequence of millisecond pulsars.

  20. SEXTANT X-Ray Pulsar Navigation Demonstration: Flight System and Test Results

    NASA Technical Reports Server (NTRS)

    Winternitz, Luke; Mitchell, Jason W.; Hassouneh, Munther A.; Valdez, Jennifer E.; Price, Samuel R.; Semper, Sean R.; Yu, Wayne H.; Ray, Paul S.; Wood, Kent S.; Arzoumanian, Zaven; Gendreau, Keith C.

    2016-01-01

    The Station Explorer for X-ray Timing and Navigation Technology (SEXTANT) is a technology demonstration enhancement to the Neutron-star Interior Composition Explorer (NICER) mission. NICER is a NASA Explorer Mission of Opportunity that will be hosted on the International Space Station (ISS). SEXTANT will, for the first time, demonstrate real-time, on-board X-ray Pulsar Navigation (XNAV), a significant milestone in the quest to establish a GPS-like navigation capability available throughout our Solar System and beyond. This paper gives an overview of the SEXTANT system architecture and describes progress prior to environmental testing of the NICER flight instrument. It provides descriptions and development status of the SEXTANT flight software and ground system, as well as detailed description and results from the flight software functional and performance testing within the high-fidelity Goddard Space Flight Center (GSFC) X-ray Navigation Laboratory Testbed (GXLT) software and hardware simulation environment. Hardware-in-the-loop simulation results are presented, using the engineering model of the NICER timing electronics and the GXLT pulsar simulator-the GXLT precisely controls NASA GSFC's unique Modulated X-ray Source to produce X-rays that make the NICER detector electronics appear as if they were aboard the ISS viewing a sequence of millisecond pulsars

  1. The pulsar B2224+65 and its jets: a two epoch X-ray analysis

    NASA Astrophysics Data System (ADS)

    Johnson, S. P.; Wang, Q. D.

    2010-10-01

    We present an X-ray morphological and spectroscopic study of the pulsar B2224+65 and its apparent jet-like X-ray features based on two epoch Chandra observations. The main X-ray feature, which shows a large directional offset from the ram-pressure confined pulsar wind nebula (Guitar nebula), is broader in apparent width and shows evidence for spectral hardening (at 95 per cent confidence) in the second epoch compared to the first. Furthermore, the sharp leading edge of the feature is found to have a proper motion consistent with that of the pulsar (~180 mas yr-1). The combined data set also provides evidence for the presence of a counter feature, albeit substantially fainter and shorter than the main one. Additional spectral trends along the major and minor axes of the feature are only marginally detected in the two epoch data, including softening counter to the direction of proper motion. Possible explanations for the X-ray features include diffuse energetic particles being confined by an organized ambient magnetic field as well as a simple ballistic jet interpretation; however, the former may have difficulty in explaining observed spectral trends between epochs and along the feature's major axis, whereas the latter may struggle to elucidate its linearity. Given the low counting statistics available in the two epoch observations, it remains difficult to determine a physical production scenario for these enigmatic X-ray emitting features with any certainty.

  2. Broad-band spectroscopy of the transient X-ray binary pulsar KS 1947+300 during 2013 giant outburst: Detection of pulsating soft X-ray excess component

    NASA Astrophysics Data System (ADS)

    Epili, Prahlad; Naik, Sachindra; Jaisawal, Gaurava K.

    2016-05-01

    We present the results obtained from detailed timing and spectral studies of the Be/X-ray binary pulsar KS 1947+300 during its 2013 giant outburst. We used data from Suzaku observations of the pulsar at two epochs, i.e. on 2013 October 22 (close to the peak of the outburst) and 2013 November 22. X-ray pulsations at ˜18.81 s were clearly detected in the light curves obtained from both observations. Pulse periods estimated during the outburst showed that the pulsar was spinning up. The pulse profile was found to be single-peaked up to ˜10 keV beyond which a sharp peak followed by a dip-like feature appeared at hard X-rays. The dip-like feature has been observed up to ˜70 keV. The 1-110 keV broad-band spectroscopy of both observations revealed that the best-fit model was comprised of a partially absorbed Negative and Positive power law with EXponential cutoff (NPEX) continuum model along with a blackbody component for the soft X-ray excess and two Gaussian functions at 6.4 and 6.7 keV for emission lines. Both the lines were identified as emission from neutral and He-like iron atoms. To fit the spectra, we included the previously reported cyclotron absorption line at 12.2 keV. From the spin-up rate, the magnetic field of the pulsar was estimated to be ˜1.2×1012 G and found to be comparable to that obtained from the detection of the cyclotron absorption feature. Pulse-phase resolved spectroscopy revealed the pulsating nature of the soft X-ray excess component in phase with the continuum flux. This confirms that the accretion column and/or accretion stream are the most probable regions of the soft X-ray excess emission in KS1947+300. The presence of the pulsating soft X-ray excess in phase with continuum emission may be the possible reason for not observing the dip at soft X-rays.

  3. Chandra Phase-Resolved X-Ray Spectroscopy of the Crab Pulsar

    NASA Technical Reports Server (NTRS)

    Weisskopf, Martin C.; ODell, Stephen L.; Paerels, Frits; Elsner, Ronald F.; Becker, Werner E.; Tennant, Allyn F.; Swartz, Douglas A.

    2003-01-01

    We present here the first phase-resolved study of the X-ray spectral properties of the Crab Pulsar that covers all pulse phases. The superb angular resolution of the Chandra X-ray Observatory enables distinguishing the pulsar from the surrounding nebulosity, even at pulse minimum. Analysis of the pulse-averaged spectrum measures interstellar photoelectric absorption and scattering by dust grains in the direction of the Crab Nebula. Analysis of the spectrum as a function of pulse phase measures the low-energy X-ray spectral index even at pulse minimum - albeit with large statistical uncertainty. The data are used to set a new upper limit to any thermal component.

  4. Application of X-Ray Pulsar Navigation: A Characterization of the Earth Orbit Trade Space

    NASA Technical Reports Server (NTRS)

    Yu, Wayne

    2016-01-01

    The potential for pulsars as a navigation source has been studied since their discovery in 1967. X-ray pulsar navigation (XNAV) is a celestial navigation system that uses the consistent timing nature of x-ray photons from milli-second pulsars (MSP) to perform space navigation. By comparing the detected arrival of x-ray photons to a reference database of expected pulsar lightcurve timing models, one can infer a range and range rate measurement based on light time delay. Much of the challenge of XNAV comes from the faint signal, availability, and distant nature of pulsars. This is a study of potential pulsar XNAV measurements to measure extended Kalman filter (EKF) tracking performance with a wide trade space of bounded Earth orbits, using a simulation of existing x-ray detector space hardware. An example of an x-ray detector for XNAV is the NASA Station Explorer for X-ray Timing and Navigation (SEXTANT) mission, a technology demonstration of XNAV set to perform on the International Space Station (ISS) in late 2016early 2017. XNAV hardware implementation is driven by trajectory and environmental influences which add noise to the x-ray pulse signal. In a closed Earth orbit, the radiation environment can exponentially increase the signal noise from x-ray pulsar sources, decreasing the quality and frequency of measurements. The SEXTANT mission in particular improves on the signal to noise ratio by focusing an array of 56 x-ray silicon drift detectors at one pulsar target at a time. This reduces timing glitches and other timing noise contributions from ambient x-ray sources to within a 100 nanosecond resolution. This study also considers the SEXTANT scheduling challenges inherent in a single target observation. Finally, as the navigation sources are now relatively inertial targets, XNAV measurements are also subject to periods of occultation from various celestial bodies. This study focuses on the characterization of these drivers in closed Earth orbits and is not a

  5. Application of X-Ray Pulsar Navigation: A Characterization of the Earth Orbit Trade Space

    NASA Technical Reports Server (NTRS)

    Yu, Wayne Hong

    2016-01-01

    The potential for pulsars as a navigation source has been studied since their discovery in 1967. X-ray pulsar navigation (XNAV) is a celestial navigation system that uses the consistent timing nature of x-ray photons from millisecond pulsars (MSP) to perform space navigation. By comparing the detected arrival of x-ray photons to a reference database of expected pulsar light-curve timing models, one can infer a range and range rate measurement based on light time delay. Much of the challenge of XNAV comes from the faint signal, availability, and distant nature of pulsars. This is a study of potential pulsar XNAV measurements to measure extended Kalman filter (EKF) tracking performance with a wide trade space of bounded Earth orbits, using a simulation of existing x-ray detector space hardware. An example of an x-ray detector for XNAV is the NASA Station Explorer for X-ray Timing and Navigation (SEXTANT) mission, a technology demonstration of XNAV set to perform on the International Space Station (ISS) in late 2016early 2017. XNAV hardware implementation is driven by trajectory and environmental influences which add noise to the x-ray pulse signal. In a closed Earth orbit, the radiation environment can exponentially increase the signal noise from x-ray pulsar sources, decreasing the quality and frequency of measurements. The SEXTANT mission in particular improves on the signal to noise ratio by focusing an array of 56 x-ray silicon drift detectors at one pulsar target at a time. This reduces timing glitches and other timing noise contributions from ambient x-ray sources to within a 100 nanosecond resolution. This study also considers the SEXTANT scheduling challenges inherent in a single target observation. Finally, as the navigation sources are now relatively inertial targets, XNAV measurements are also subject to periods of occultation from various celestial bodies. This study focuses on the characterization of these drivers in closed Earth orbits and is not a

  6. Modeling the optical-X-ray accretion lag in LMC X-3: Insights into black-hole accretion physics

    SciTech Connect

    Steiner, James F.; McClintock, Jeffrey E.; Orosz, Jerome A.; Buxton, Michelle M.; Bailyn, Charles D.; Remillard, Ronald A.; Kara, Erin

    2014-03-10

    The X-ray persistence and characteristically soft spectrum of the black hole X-ray binary LMC X-3 make this source a touchstone for penetrating studies of accretion physics. We analyze a rich, ten-year collection of optical/infrared (OIR) time-series data in conjunction with all available contemporaneous X-ray data collected by the All-Sky Monitor and Proportional Counter Array detectors aboard the Rossi X-ray Timing Explorer. A cross-correlation analysis reveals an X-ray lag of ≈2 weeks. Motivated by this result, we develop a model that reproduces the complex OIR light curves of LMC X-3. The model is comprised of three components of emission: stellar light, accretion luminosity from the outer disk inferred from the time-lagged X-ray emission, and light from the X-ray-heated star and outer disk. Using the model, we filter a strong noise component out of the ellipsoidal light curves and derive an improved orbital period for the system. Concerning accretion physics, we find that the local viscous timescale in the disk increases with the local mass accretion rate; this in turn implies that the viscosity parameter α decreases with increasing luminosity. Finally, we find that X-ray heating is a strong function of X-ray luminosity below ≈50% of the Eddington limit, while above this limit X-ray heating is heavily suppressed. We ascribe this behavior to the strong dependence of the flaring in the disk upon X-ray luminosity, concluding that for luminosities above ≈50% of Eddington, the star lies fully in the shadow of the disk.

  7. The dynamic X-ray nebula powered by the pulsar B1259-63

    SciTech Connect

    Kargaltsev, Oleg; Volkov, Igor; Hare, Jeremy; Pavlov, George G.; Durant, Martin

    2014-04-01

    We present observations of the eccentric γ-ray binary B1259-63/LS 2883 with the Chandra X-ray Observatory. The images reveal a variable, extended (about 4'', or ∼1000 times the binary orbit size) structure, which appears to be moving away from the binary with the velocity of 0.05 of the speed of light. The observed emission is interpreted as synchrotron radiation from relativistic particles supplied by the pulsar. However, the fast motion through the circumbinary medium would require the emitting cloud to be loaded with a large amount of baryonic matter. Alternatively, the extended emission can be interpreted as a variable extrabinary shock in the pulsar wind outflow launched near binary apastron. The resolved variable X-ray nebula provides an opportunity to probe pulsar winds and their interaction with stellar winds in a previously inaccessible way.

  8. The Effect of Transient Accretion on the Spin-up of Millisecond Pulsars

    NASA Astrophysics Data System (ADS)

    Bhattacharyya, Sudip; Chakrabarty, Deepto

    2017-01-01

    A millisecond pulsar is a neutron star that has been substantially spun up by accretion from a binary companion. A previously unrecognized factor governing the spin evolution of such pulsars is the crucial effect of nonsteady or transient accretion. We numerically compute the evolution of accreting neutron stars through a series of outburst and quiescent phases, considering the drastic variation of the accretion rate and the standard disk–magnetosphere interaction. We find that, for the same long-term average accretion rate, X-ray transients can spin up pulsars to rates several times higher than can persistent accretors, even when the spin-down due to electromagnetic radiation during quiescence is included. We also compute an analytical expression for the equilibrium spin frequency in transients, by taking spin equilibrium to mean that no net angular momentum is transferred to the neutron star in each outburst cycle. We find that the equilibrium spin rate for transients, which depends on the peak accretion rate during outbursts, can be much higher than that for persistent sources. This explains our numerical finding. This finding implies that any meaningful study of neutron star spin and magnetic field distributions requires the inclusion of the transient accretion effect, since most accreting neutron star sources are transients. Our finding also implies the existence of a submillisecond pulsar population, which is not observed. This may point to the need for a competing spin-down mechanism for the fastest-rotating accreting pulsars, such as gravitational radiation.

  9. A Chandra X-Ray Observation of the Binary Millisecond Pulsar PSR J1023+0038

    NASA Astrophysics Data System (ADS)

    Bogdanov, Slavko; Archibald, Anne M.; Hessels, Jason W. T.; Kaspi, Victoria M.; Lorimer, Duncan; McLaughlin, Maura A.; Ransom, Scott M.; Stairs, Ingrid H.

    2011-12-01

    We present a Chandra X-Ray Observatory ACIS-S variability, spectroscopy, and imaging study of the peculiar binary containing the millisecond pulsar J1023+0038. The X-ray emission from the system exhibits highly significant (12.5σ) large-amplitude (factor of two to three) orbital variability over the five consecutive orbits covered by the observation, with a pronounced decline in the flux at all energies at superior conjunction. This can be naturally explained by a partial geometric occultation by the secondary star of an X-ray-emitting intrabinary shock, produced by the interaction of outflows from the two stars. The depth and duration of the eclipse imply that the intrabinary shock is localized near or at the surface of the companion star and close to the inner Lagrangian point. The energetics of the shock favor a magnetically dominated pulsar wind that is focused into the orbital plane, requiring close alignment of the pulsar spin and orbital angular momentum axes. The X-ray spectrum consists of a dominant non-thermal component and at least one thermal component, likely originating from the heated pulsar polar caps, although a portion of this emission may be from an optically thin "corona." We find no evidence for extended emission due to a pulsar wind nebula or bow shock down to a limiting luminosity of L X <~ 3.6 × 1029 erg s-1 (0.3-8 keV), <~ 7 × 10-6 of the pulsar spin-down luminosity, for a distance of 1.3 kpc and an assumed power-law spectrum with photon index Γ = 1.5.

  10. The 1997 event in the Crab Pulsar in X-rays

    NASA Astrophysics Data System (ADS)

    Vivekanand, M.

    2016-02-01

    Context. In October 1997, radio pulses from the Crab Pulsar underwent abnormal delay. This was reported by two radio observatories, both of which explained this frequency dependent and time varying delay as being due to refractive effects of ionized shells in the Crab Nebula. Both groups also noted that, curiously and confusingly coincident with the frequency dependent delay, the Crab Pulsar also underwent an unusual slowing down, which they believed to be unrelated to the Crab Nebula and instead intrinsic to the Crab Pulsar, resulting in an additional delay that was frequency independent. However, it now appears that one of the groups attributes the frequency independent delay also to refractive effects. Aims: This work aims to verify whether at least a part of the frequency independent delay is indeed due to intrinsic slowing down of the Crab Pulsar. Methods: Timing analysis of the Crab Pulsar's October 1997 event has been done in X-rays, which are not delayed by the refractive and diffractive effects that affect radio waves; at X-rays only the intrinsic slowing down should contribute to any observed delay. Data mainly from the PCA instrument aboard the RXTE satellite have been used, along with a small amount of data from the PDS instrument aboard the BeppoSAX satellite. Results: Analysis of the X-ray data, using the very accurate reference timing model derived at radio frequencies, strongly supports the intrinsic slowing down hypothesis. Analysis using the reference timing model derived self-consistently from the limited X-ray data, which is less accurate, is not completely unambiguous regarding the above two hypotheses, but provides reasonable support for the intrinsic slowing down hypothesis. Conclusions: A significant fraction of the frequency independent delay during the October 1997 event is indeed due to intrinsic slowing down of the Crab Pulsar.

  11. LMXB X-ray Transients: Revealing Basic Accretion Parameters in Non-stationary Regimes

    NASA Astrophysics Data System (ADS)

    Yu, Wenfei; Yan, Zhen; Zhang, Hui; Zhang, Wenda

    2014-08-01

    X-ray observations of low mass X-ray binaries(LMXBs), especially those black hole transient systems, have been very important in shaping up our understanding of black hole accretion and testing accretion theory in a broad range of accretion regimes. We show strong evidence for non-stationary accretion regimes in the X-ray observations of spectral states and multi-wavelength observations of disk-jet coupling in more than 100 outbursts of 36 black hole and neutron star transients in the past decade or so. The occurrence of spectral state transitions and the peak episodic jet power during the rising phase of transient outbursts are found correlated with rate-of-increase of the X-ray luminosity, indicating the rate-of-change of the mass accretion rate, in addition to the mass accretion rate, must be considered when interpreting observations of spectral state transitions and disk-jet coupling in these X-ray transients. This is supported by observations since the increase of the mass accretion rate due to its rate-of-change on the observational time scale of interest is significant during outbursts.

  12. Discovery of radio pulsations from the X-ray pulsar in the supernova remnant G32. 4-1. 2

    SciTech Connect

    Manchester, R.N.; Tuohy, I.R.; D'Amico, N.

    1982-11-15

    A radio counterpart to the X-ray pulsar discovered by Seward and Harnden in the supernova remnant G320.4-1.2 (MSH 15--52) has been detected. The radio observations confirm the very large period derivative indicated by the X-ray data. This implies that the object is not a member of a binary system and hence is an isolated pulsar similar in some ways to the Crab pulsar. Association of the pulsar and the supernova remnant is supported by the observed pulsar dispersion measure.

  13. Short-term Variability of X-Rays from Accreting Neutron Star Vela X-1. I. Suzaku Observations

    NASA Astrophysics Data System (ADS)

    Odaka, Hirokazu; Khangulyan, Dmitry; Tanaka, Yasuyuki T.; Watanabe, Shin; Takahashi, Tadayuki; Makishima, Kazuo

    2013-04-01

    We have analyzed the time variability of the wide-band X-ray spectrum of Vela X-1, the brightest wind-fed accreting neutron star, on a short timescale of 2 ks by using Suzaku observations with an exposure of 100 ks. During the observation, the object showed strong variability, including several flares and so-called "low states," in which the X-ray luminosity decreases by an order of magnitude. Although the spectral hardness increases with the X-ray luminosity, the majority of the recorded flares do not show any significant changes in circumstellar absorption. However, a sign of heavy absorption was registered immediately before one short flare that showed a significant spectral hardening. In the low states, the flux level is modulated with the pulsar spin period, indicating that even at this state the accretion flow reaches the close proximity of the neutron star. Phenomenologically, the broadband X-ray spectra, which are integrated over the entire spin phase, are well represented by the "NPEX" function (a combination of negative and positive power laws with an exponential cutoff by a common folding energy) with a cyclotron resonance scattering feature at 50 keV. Fitting of the data allowed us to infer a correlation between the photon index and X-ray luminosity. Finally, the circumstellar absorption shows a gradual increase in the orbital phase interval 0.25-0.3, which can be interpreted as an impact of a bow shock imposed by the motion of the compact object in the supersonic stellar wind.

  14. SHORT-TERM VARIABILITY OF X-RAYS FROM ACCRETING NEUTRON STAR VELA X-1. I. SUZAKU OBSERVATIONS

    SciTech Connect

    Odaka, Hirokazu; Khangulyan, Dmitry; Watanabe, Shin; Takahashi, Tadayuki; Tanaka, Yasuyuki T.; Makishima, Kazuo

    2013-04-10

    We have analyzed the time variability of the wide-band X-ray spectrum of Vela X-1, the brightest wind-fed accreting neutron star, on a short timescale of 2 ks by using Suzaku observations with an exposure of 100 ks. During the observation, the object showed strong variability, including several flares and so-called 'low states', in which the X-ray luminosity decreases by an order of magnitude. Although the spectral hardness increases with the X-ray luminosity, the majority of the recorded flares do not show any significant changes in circumstellar absorption. However, a sign of heavy absorption was registered immediately before one short flare that showed a significant spectral hardening. In the low states, the flux level is modulated with the pulsar spin period, indicating that even at this state the accretion flow reaches the close proximity of the neutron star. Phenomenologically, the broadband X-ray spectra, which are integrated over the entire spin phase, are well represented by the 'NPEX' function (a combination of negative and positive power laws with an exponential cutoff by a common folding energy) with a cyclotron resonance scattering feature at 50 keV. Fitting of the data allowed us to infer a correlation between the photon index and X-ray luminosity. Finally, the circumstellar absorption shows a gradual increase in the orbital phase interval 0.25-0.3, which can be interpreted as an impact of a bow shock imposed by the motion of the compact object in the supersonic stellar wind.

  15. Probing X-ray burst - accretion disk interaction in low mass X-ray binaries through kilohertz quasiperiodic oscillations

    NASA Astrophysics Data System (ADS)

    Peille, P.; Olive, J.-F.; Barret, D.

    2014-07-01

    The intense radiation flux of Type I X-ray bursts is expected to interact with the accretion flow around neutron stars. High frequency quasiperiodic oscillations (kHz QPOs), observed at frequencies matching orbital frequencies at tens of gravitational radii, offer a unique probe of the innermost disk regions. In this paper, we follow the lower kHz QPOs, in response to Type I X-ray bursts, in two prototypical QPO sources, namely 4U 1636-536 and 4U 1608-522, as observed by the Proportional Counter Array of the Rossi X-ray Timing Explorer. We have selected a sample of 15 bursts for which the kHz QPO frequency can be tracked on timescales commensurable with the burst durations (tens of seconds). We find evidence that the QPOs are affected for over ~200 s during one exceptionally long burst and ~100 s during two others (although at a less significant level), while the burst emission has already decayed to a level that would enable the pre-burst QPO to be detected. On the other hand, for most of our burst-kHz QPO sample, we show that the QPO is detected as soon as the statistics allow and in the best cases, we are able to set an upper limit of ~20 s on the recovery time of the QPO. This diversity of behavior cannot be related to differences in burst peak luminosity. We discuss these results in the framework of recent findings that accretion onto the neutron star may be enhanced during Type I X-ray bursts. The subsequent disk depletion could explain the disappearance of the QPO for ~100 s, as possibly observed in two events. However, alternative scenarios would have to be invoked for explaining the short recovery timescales inferred from most bursts. Heating of the innermost disk regions would be a possibility, although we cannot exclude that the burst does not affect the QPO emission at all. Clearly the combination of fast timing and spectral information of Type I X-ray bursts holds great potential in the study of the dynamics of the inner accretion flow around neutron

  16. Some observational tests of X-ray pulsar emission models

    NASA Technical Reports Server (NTRS)

    Meszaros, P.

    1981-01-01

    The understanding of neutron star physics which relies heavily on knowing values of their mass, radius and magnetic field strength was studied. The only information about these till now comes from the surface radiation. Major uncertainties concerning the nature of the mass exchange and the accretion flow, the magnetopause structure, the infall deceleration, the actual pulsation mechanism and the atmosphere geometry are examined. The alternatives and several possible observational tests are discussed.

  17. X-RAY OUTFLOWS AND SUPER-EDDINGTON ACCRETION IN THE ULTRALUMINOUS X-RAY SOURCE HOLMBERG IX X-1

    SciTech Connect

    Walton, D. J.; Harrison, F. A.; Miller, J. M.; Reis, R. C.; Fabian, A. C.; Roberts, T. P.; Middleton, M. J.

    2013-08-10

    Studies of X-ray continuum emission and flux variability have not conclusively revealed the nature of ultraluminous X-ray sources (ULXs) at the high-luminosity end of the distribution (those with L{sub X} {>=} 10{sup 40} erg s{sup -1}). These are of particular interest because the luminosity requires either super-Eddington accretion onto a black hole of mass {approx}10 M{sub Sun} or more standard accretion onto an intermediate-mass black hole. Super-Eddington accretion models predict strong outflowing winds, making atomic absorption lines a key diagnostic of the nature of extreme ULXs. To search for such features, we have undertaken a long, 500 ks observing campaign on Holmberg IX X-1 with Suzaku. This is the most sensitive data set in the iron K bandpass for a bright, isolated ULX to date, yet we find no statistically significant atomic features in either emission or absorption; any undetected narrow features must have equivalent widths less than 15-20 eV at 99% confidence. These limits are far below the {approx}>150 eV lines expected if observed trends between mass inflow and outflow rates extend into the super-Eddington regime and in fact rule out the line strengths observed from disk winds in a variety of sub-Eddington black holes. We therefore cannot be viewing the central regions of Holmberg IX X-1 through any substantial column of material, ruling out models of spherical super-Eddington accretion. If Holmberg IX X-1 is a super-Eddington source, any associated outflow must have an anisotropic geometry. Finally, the lack of iron emission suggests that the stellar companion cannot be launching a strong wind and that Holmberg IX X-1 must primarily accrete via Roche-lobe overflow.

  18. Time-dependent spherically symmetric accretion onto compact X-ray sources

    NASA Technical Reports Server (NTRS)

    Cowie, L. L.; Ostriker, J. P.; Stark, A. A.

    1978-01-01

    Analytical arguments and a numerical hydrodynamic code are used to investigate spherically symmetric accretion onto a compact object, in an attempt to provide some insight into gas flows heated by an outgoing X-ray flux. It is shown that preheating of spherically symmetric accretion flows by energetic radiation from an X-ray source results in time-dependent behavior for a much wider range of source parameters than was determined previously and that there are two distinct types of instability. The results are compared with observations of X-ray bursters and transients as well as with theories on quasars and active galactic nuclei that involve quasi-spherically symmetric accretion onto massive black holes. Models based on spherically symmetric accretion are found to be inconsistent with observations of bursters and transients.

  19. Short-term variability of X-rays from accreting neutron star Vela X-1. II. Monte Carlo modeling

    SciTech Connect

    Odaka, Hirokazu; Khangulyan, Dmitry; Watanabe, Shin; Takahashi, Tadayuki; Tanaka, Yasuyuki T.; Makishima, Kazuo

    2014-01-01

    We develop a Monte Carlo Comptonization model for the X-ray spectrum of accretion-powered pulsars. Simple, spherical, thermal Comptonization models give harder spectra for higher optical depth, while the observational data from Vela X-1 show that the spectra are harder at higher luminosity. This suggests a physical interpretation where the optical depth of the accreting plasma increases with the mass accretion rate. We develop a detailed Monte Carlo model of the accretion flow, including the effects of the strong magnetic field (∼10{sup 12} G), both in geometrically constraining the flow into an accretion column and in reducing the cross section. We treat bulk-motion Comptonization of the infalling material as well as thermal Comptonization. These model spectra can match the observed broadband Suzaku data from Vela X-1 over a wide range of mass accretion rates. The model can also explain the so-called 'low state' in which the luminosity decreases by an order of magnitude. Here, thermal Comptonization should be negligible, so the spectrum is instead dominated by bulk-motion Comptonization.

  20. Period Clustering of the Anomalous X-Ray Pulsars and Magnetic Field Decay in Magnetars.

    PubMed

    Colpi; Geppert; Page

    2000-01-20

    We confront theoretical models for the rotational, magnetic, and thermal evolution of an ultramagnetized neutron star, or magnetar, with available data on the anomalous X-ray pulsars (AXPs). We argue that, if the AXPs are interpreted as magnetars, their clustering of spin periods between 6 and 12 s (observed at present in this class of objects), their period derivatives, their thermal X-ray luminosities, and the association of two of them with young supernova remnants can only be understood globally if the magnetic field in magnetars decays significantly on a timescale of the order of 104 yr.

  1. A model of an X-ray-illuminated accretion disk and corona

    NASA Technical Reports Server (NTRS)

    Raymond, John C.

    1993-01-01

    The X-ray-illuminated surface of the accretion disk in a low-mass X-ray Binary (LMXRB) and the X-ray-heated corona above the disk produce optical, UV, and soft X-ray emission lines. This paper presents 1D models of the emission line spectra and the vertical temperature and density structures at different radii. The models include a detailed treatment of the important atomic processes and an escape probability treatment of radiative transfer. Soker and Raymond (1993) use the density structure predicted by these models for a 2D Monte Carlo simulation of the photon scattering in the accretion disk corona (ADC) to examine the effects of the ADC on the angular distribution of X-rays and the flux of X-rays incident on the outer disk. This paper concentrates on the emission line fluxes for various elemental abundances and disk parameters. The UV lines of the classic LMXRBs are consistent with the model predictions. Some CNO processing is necessary to account for the nitrogen and helium abundances in Sco X-1 and other LMXRBs. Comparison of the models with observed spectra also points to a soft X-ray component with luminosity comparable to the hard X-rays. The models predict a substantial luminosity in the group of highly ionized iron lines near 100 A.

  2. INTEGRAL and XMM-Newton Observations of the X-Ray Pulsar IGR J16320-4751/AX J1691.9-4752

    NASA Technical Reports Server (NTRS)

    Rodriquez, J.; Bodaghee, A.; Kaaret, P.; Tomsick, J. A.; Kuulkers, E.; Malaguti, G.; Petrucci, P.-O.; Cabanac, C.; Chernyakova, M.; Corbel, S.; Deluit, S.; DiCocco, G.; Ebisawa, K.; Goldwurm, A.; Henri, G.; Lebrun, F.; Paizis, A.; Walter, R.; Foschini, L.

    2006-01-01

    We report on observations of the X-ray pulsar IGR J16320-4751 (also known as AX J1631.9-4752) performed simultaneously with International Gamma-Ray Astrophysics Laboratory (INTEGRAL) and XMM-Newton. We refine the source position and identify the most likely infrared counterpart. Our simultaneous coverage allows us to confirm the presence of X-ray pulsations at approximately 1300 s, that we detect above 20 keV with INTEGRAL for the first time. The pulse fraction is consistent with being constant with energy, which is compatible with a model of polar accretion by a pulsar. We study the spectral properties of IGR J16320-4751 during two major periods occurring during the simultaneous coverage with both satellites, namely a flare and a non-flare period. We detect the presence of a narrow 6.4 keV iron line in both periods. The presence of such a feature is typical of supergiant wind accretors such as Vela X-1 or GX 301-2. We inspect the spectral variations with respect to the pulse phase during the non-flare period, and show that the pulse is solely due to variations of the X-ray flux emitted by the source and not due to variations of the spectral parameters. Our results are therefore compatible with the source being a pulsar in a High Mass X-ray Binary. We detect a soft excess appearing in the spectra as a blackbody with a temperature of approximately 0.07 keV. We discuss the origin of the X-ray emission in IGR J16320-4751: while the hard X-rays are likely the result of Compton emission produced in the close vicinity of the pulsar, based on energy argument we suggest that the soft excess is likely the emission by a collisionally energized cloud in which the compact object is embedded.

  3. First X-ray Observations of the Young Pulsar J1357-6429

    NASA Technical Reports Server (NTRS)

    Zavlin, Vyacheslav E.

    2007-01-01

    The first short Chandra and XMM-Newton observations of the young and energetic pulsar J1357-6429 provided strong indications of a tail-like pulsar-wind nebula associated with this object, as well as strong pulsations of its X-ray flux with a pulsed fraction above 40% and a thermal component dominating at lower photon energies (below 2 keV). The elongated nebular is very compact in size. about 1" x 1.5" and might be interpreted as a pulsar jet. The thermal radiation is most plausibly emitted from the entire neutron star surface of an effective temperature about 1 MK covered with a magnetized hydrogen atmosphere At higher energies the pulsar's emission is of a nonthermal (magnetospheric) origin, with a power-law spectrum of a photon index Gamma approx. equals 1.1. This makes the X-ray properties of PSR J1357-6429 very similar to those of the youngest pulsars J1119-6127 and Vela with a detected thermal radiation.

  4. X-ray observations of the Vela pulsar: Statistics and spectrum

    NASA Technical Reports Server (NTRS)

    Pravdo, S. H.; Becker, R. H.; Boldt, E. A.; Holt, S. S.; Rothschild, R. E.; Serlemitsos, P. J.; Swank, J. H.

    1976-01-01

    The Vela pulsar was observed in the range 2-60 keV by the GSFC proportional counter experiment onboard OSO-8 with temporal resolution sufficient to make possible a sensitive search for pulsed X-rays at the radio pulsar period. A statistical analysis yielded 8 per cent as the 3 sigma upper limit on the pulsed fraction. The energy spectrum is fit well by a structureless power law with number index 2.21 + or - 0.2 and absorption by a hydrogen column density of N sub H equals 2.9 + or - 2.0 times ten to the twenty-second power per sq.cm.

  5. TINY HICCUPS TO TITANIC EXPLOSIONS: Tackling Transients in Anomalous X-ray Pulsars

    NASA Astrophysics Data System (ADS)

    Kaspi, Victoria

    2008-09-01

    The past decade has seen major progress in neutron star astrophysics, with the discovery of magnetars in general, and the recognition that the Anomalous X-ray Pulsars (AXPs) fall in this class. AXPs have recently revealed surprising and dramatic variability behavior, which theorists have begun to show are highly constraining of physical models of magnetars, including their crusts, atmospheres, coronae and magnetospheres. In this proposal, we request Chandra/ACIS-S Target-of-Opportunity observations of one major Anomalous X-ray Pulsar (AXP) outburst in A10, in order to study in detail the evolution of the spectrum, pulsed fraction and pulse profile, for quantitative confrontation with recently developed models for the structure and electrodynamics of magnetars.

  6. TINY HICCUPS TO TITANIC EXPLOSIONS: Tackling Transients in Anomalous X-ray Pulsars

    NASA Astrophysics Data System (ADS)

    Kaspi, Victoria

    2009-09-01

    The past decade has seen major progress in neutron star astrophysics, with the discovery of magnetars in general, and the recognition that the Anomalous X-ray Pulsars (AXPs) fall in this class. AXPs have recently revealed surprising and dramatic variability behavior, which theorists have begun to show are highly constraining of physical models of magnetars, including their crusts, atmospheres, coronae and magnetospheres. In this proposal, we request Chandra/ACIS-S Target-of-Opportunity observations of one major Anomalous X-ray Pulsar (AXP) outburst in A11, in order to study in detail the evolution of the spectrum, pulsed fraction and pulse profile, for quantitative confrontation with recently developed models for the structure and electrodynamics of magnetars.

  7. TINY HICCUPS TO TITANIC EXPLOSIONS: Tackling Transients in Anomalous X-ray Pulsars

    NASA Astrophysics Data System (ADS)

    Kaspi, Victoria

    2011-09-01

    The past decade has seen major progress in neutron star astrophysics, with the discovery of magnetars in general, and the recognition that the Anomalous X-ray Pulsars (AXPs) fall in this class. AXPs have recently revealed surprising and dramatic variability behavior, which theorists have begun to show are highly constraining of physical models of magnetars, including their crusts, atmospheres, coronae and magnetospheres. In this proposal, we request Chandra/ACIS-S Target-of-Opportunity observations of one major Anomalous X-ray Pulsar (AXP) outburst in AO13, in order to study in detail the evolution of the spectrum, pulsed fraction and pulse profile, for quantitative confrontation with recently developed models for the structure and electrodynamics of magnetars.

  8. TINY HICCUPS TO TITANIC EXPLOSIONS: Tackling Transients in Anomalous X-ray Pulsars

    NASA Astrophysics Data System (ADS)

    Kaspi, Victoria

    2010-09-01

    The past decade has seen major progress in neutron star astrophysics, with the discovery of magnetars in general, and the recognition that the Anomalous X-ray Pulsars (AXPs) fall in this class. AXPs have recently revealed surprising and dramatic variability behavior, which theorists have begun to show are highly constraining of physical models of magnetars, including their crusts, atmospheres, coronae and magnetospheres. In this proposal, we request Chandra/ACIS-S Target-of-Opportunity observations of one major Anomalous X-ray Pulsar (AXP) outburst in AO12, in order to study in detail the evolution of the spectrum, pulsed fraction and pulse profile, for quantitative confrontation with recently developed models for the structure and electrodynamics of magnetars.

  9. The nature of the X-ray pulsar in M 31: An intermediate-mass X-ray binary?

    NASA Astrophysics Data System (ADS)

    Karino, Shigeyuki

    2016-12-01

    The first finding of the spin period of an accreting neutron star in M 31 was recently reported. The observed spin period is 1.2 s, and it shows 1.27 d modulations due to orbital motion. From the orbital information, the mass donor could not be a giant massive star. On the other hand, its observed properties are very odd as those of typical low-mass X-ray binaries. In this study, we compare the observed binary parameters with theoretical models given by a stellar evolution track, and give a restriction on the possible mass range of the donor. According to the standard stellar evolution model, the donor star should be larger than 1.5 M⊙, which suggests that this system is a new member of a rare category, an intermediate-mass X-ray binary. The magnetic field strength of the neutron star suggested by the spin-up/down tendency in this system supports the possibility of an intermediate-mass donor.

  10. X-Ray and Rotational Luminosity Correlation and Magnetic Heating of Radio Pulsars

    NASA Astrophysics Data System (ADS)

    Shibata, S.; Watanabe, E.; Yatsu, Y.; Enoto, T.; Bamba, A.

    2016-12-01

    Previous works have suggested a correlation between the X-ray luminosity {L}{{x}} and the rotational luminosity {L}{rot} of radio pulsars. However, none of the obtained regression lines is statistically acceptable due to large scatter. We construct a statistical model that has an intrinsic {L}{{x}}-{L}{rot} relation and reproduces the observed {L}{{x}} distribution about it by using a Monte Carlo simulator, which takes into account the effects obscuring the intrinsic relation, i.e., the anisotropy of radiation, additional heating, uncertainty in distance, and the detection limit of the instruments. From the ATNF pulsar catalog we collect 57 “ordinary radio pulsars” with significant detection and 42 with upper limits. The sample does not include high-magnetic-field pulsars (>1013 G), which are analyzed separately. We obtain a statistically acceptable relation {L}{{x}}{(0.5{--}10{keV})={10}31.69({L}{rot}/{L}0)}{c1} with c 1 = 1.03 ± 0.27 and L 0 = 1035.38. The distribution about the obtained {L}{{x}}-{L}{rot} relation is reproduced well by the simulator. Pulsars with abnormally high {L}{{x}} fall into two types: one is the soft gamma-ray pulsars, and the other is pulsars that are thermally bright in comparison with the standard cooling curve. On the other hand, pulsars showing low {L}{{x}} are found to have dim pulsar wind nebulae (PWNs). We argue that there is an unknown mechanism that governs both the magnetospheric emission and the PWNs, and it might involve the production rate of electron-positron pairs. High-field pulsars form a population that is distinct from ordinary pulsars due to their excess luminosities.

  11. Optical and X-ray radiation from fast pulsars - Effects of duty cycle and spectral shape

    NASA Technical Reports Server (NTRS)

    Pacini, F.; Salvati, M.

    1987-01-01

    The optical luminosity of PSR 0540 is considerably stronger than what one would have predicted in a simple model developed earlier where the pulses are synchrotron radiation by secondary electrons near the light cylinder. This discrepancy can be eliminated if one incorporates into the model the effects of the large duty cycle and the spectral properties of PSR 0540. It is also shown that the same model can provide a reasonable fit to the observed X-ray fluxes from fast pulsars.

  12. The Fading of Transient Anomalous X-Ray Pulsar XTE J1810-197

    NASA Astrophysics Data System (ADS)

    Halpern, J. P.; Gotthelf, E. V.

    2005-01-01

    Three observations of the 5.54 s transient anomalous X-ray pulsar XTE J1810-197 obtained over 6 months with the Newton X-ray Multi-Mirror (XMM-Newton) mission are used to study its spectrum and pulsed light curve as the source fades from outburst. The decay is consistent with an exponential of time constant ~300 days but not a power law as predicted in some models of sudden deep crustal heating events. All spectra are well fitted by a blackbody plus a steep power law, a problematic model that is commonly fitted to anomalous X-ray pulsars (AXPs). A two-temperature blackbody fit is also acceptable and better motivated physically in view of the faint optical/IR fluxes, the X-ray pulse shapes that weakly depend on energy in XTE J1810-197, and the inferred emitting areas that are less than or equal to the surface area of a neutron star. The fitted temperatures remained the same while the flux declined by 46%, which can be interpreted as a decrease in area of the emitting regions. The pulsar continues to spin down, albeit at a reduced rate of (5.1+/-1.6)×10-12 s s-1. The inferred characteristic age τc≡P/2P~17,000 yr, magnetic field strength Bs~1.7×1014 G, and outburst properties are consistent with both the outburst and quiescent X-ray luminosities being powered by magnetic field decay, i.e., XTE J1810-197 is a magnetar.

  13. Optical orbit of the X-ray pulsar binary 0535 - 668 (= A0538 - 66)

    SciTech Connect

    Hutchings, J.B.; Crampton, D.; Cowley, A.P.; Olszewski, E.; Thompson, I.B.; Suntzeff, N.

    1985-05-01

    Spectroscopic data are presented from the optical primary of the LMC X-ray source 0535 - 668 during its optical low state. From these data the star appears as a normal B1 star, slightly evolved off the main sequence. Adopting the X-ray outburst period of 16.65 days, radial velocities indicate an orbit with a high eccentricity, and periastron passage very close to the X-ray flux peak. Probable masses are normal for the primary and the pulsar. At periastron, the center of mass separation is less than the primary-star diameter, and during optical outburst the photosphere is larger than the minimum separation. Orbital parameters and implied quantities are discussed. 18 references.

  14. The period history of the X-ray pulsar in MSH 15-52

    NASA Technical Reports Server (NTRS)

    Weisskopf, M. C.; Elsner, R. F.; Darbo, W.; Leahy, D.; Naranan, S.; Harnden, F. R.; Seward, F. D.; Sutherland, P. G.; Grindlay, J. E.

    1983-01-01

    New and refined mesurements of the pulse period of the X-ray pulsar in the supernova remnant MSH 15-52 are presented. The data were obtained with the Monitor proportional Counter on board the HEAO 2 observatory. The period measurements were obtained by analyzing pulse arrival times determined by cross-correlating sample pulse profiles with a master template. The period history for the source and a representative 0.15 s X-ray light curve are shown. The X-ray measurements alone lead to a refined value of the period derivative of (1.5382 + or -0.0024) x 10 to the -12th s/s, while including the results of more recent radio observations leads to a value of (1.54029 + or -0.00095) x 10 to the -12th s/s. These results indicate a hard-point source surrounded by diffuse nebular emission.

  15. The hard X-ray emission spectra from accretion columns in intermediate polars

    NASA Technical Reports Server (NTRS)

    Yi, Insu; Vishniac, Ethan T.

    1994-01-01

    We consider the hard (greater than 2 keV) X-ray emission from accretion columns in an intermediate polar system, GK Per, using a simple settling solution. The rate of photon emission per logarithmic energy interval can be fitted with a power law, E(exp -gamma), with gamma approximately 2.0, in agreement with observations. This index is only weakly dependent on the mass accretion rate, dot-M, for dot-M in the range of a few times 10(exp 16-18) g/s. The peak energy of the photon spectra (after photoelectric absorption) is expected to be E(sub p) approximately (5 keV) gamma(exp -1/3) (N(sub H)/10(exp 23)/sq cm)(exp 1/3) where N(sub H) is the hydrogen column density along the line of sight. The observed spectra of GK Per and possibly of V1223 Sgr suggest N(sub H) approximately 10(exp 23)/sq cm. This large N(sub H) may be due to partially ionized preshock column material. Alternatively, we also consider absorption by the cool outer parts of an accretion disk. In this case the photoelectric absorption depth in the disk is a sensitive function of inclination. For GK Per the required inclination is approximately 83 deg. For mass accretion rates larger than a critical rate of approximately 10(exp 18) g/s, X-ray emission from the column accretion is significantly affected by radiation drag. Although the mass accretion rate increases dramatically during outbursts, the observed hard (greater than 2 keV) X-ray luminosity will not rise proportionately. The slope and peak energy of the outburst spectra are only weakly affected. We conclude that the observed X-ray spectra can be explained by this simple analytic solution and that the production of hard X-rays from the accretion shock at the magnetic poles in the intermediate polars is in general agreement with the observations. However, since the X-ray emission and absorption depend on the mass accretion rate in a complicated manner, observed hard X-ray luminosities (greater than 2 keV) are not a good indicator of the mass

  16. X-ray pulsars/Doppler integrated navigation for Mars final approach

    NASA Astrophysics Data System (ADS)

    Cui, Pingyuan; Wang, Shuo; Gao, Ai; Yu, Zhengshi

    2016-05-01

    The performance of the navigation system during the Mars final approach phase determines the initial accuracy of Mars entry phase, which is critical for a pin-point landing. An X-ray pulsars/Doppler integrated navigation strategy is proposed to improve the estimation accuracy of the spacecraft's entry state, as well as to enhance the autonomy, real-time and reliability. The navigation system uses the X-ray pulsar measurements and Doppler velocity measurements which are complementary to each other. The performance degradation in velocity estimation at the end of the final approach phase for X-ray pulsar based navigation can thus be eliminated. The nonlinearity of the system and the performance of Extended Kalman Filter are analyzed in this paper. Furthermore, in order to optimize the navigation scheme, a principle for navigation beacons selection based on the Fisher information matrix is used. Finally, a navigation scenario based on the 2012 encounter at Mars of Mars Science Laboratory spacecraft is considered to demonstrate the feasibility and accuracy of the proposed scheme. Simulation results also indicate that the proposed navigation scheme has reference value for the design of the future Mars explorations.

  17. SEXTANT: A Demonstration of X-ray Pulsar-Based Navigation Using NICER

    NASA Astrophysics Data System (ADS)

    Ray, Paul S.; Mitchell, Jason W; Winternitz, Luke M; Hasouneh, Monther A; Price, Samuel R; Valdez, Jennifer; Yu, Wayne H; Semper, Sean R; Wood, Kent S.; Wolff, Michael Thomas; Arzoumanian, Zaven; Litchford, Ronald J; Gendreau, Keith

    2014-08-01

    The Station Explorer for X-ray Timing and Navigation Technology (SEXTANT) is a technology-demonstration enhancement to the Neutron-star Interior Composition Explorer (NICER) mission. NICER is a NASA Explorer Mission of Opportunity that will be hosted on the International Space Station (ISS). SEXTANT will, for the first time, demonstrate real-time, on-board X-ray pulsar-based navigation (XNAV), a significant milestone in the quest to establish a GPS-like navigation capability available throughout our Solar System and beyond. The SEXTANT XNAV demonstration will exploit the large collecting area (>1800 cm^2), low background (<0.2 counts/s), and precise timing (<300 ns) of the NICER X-ray Timing Instrument (XTE). Taking advantage of NICER’s science observations of X-ray emitting millisecond pulsars, which are nature’s most stable clocks, the SEXTANT flight software will demonstrate real-time orbit determination with error less than 10 km in any direction, through measurements made over 2 weeks or less in the highly dynamic low-Earth ISS orbit. The completed technology demonstration will bring the XNAV concept and algorithms to a Technology Readiness Level of 8 and will inform the design and configuration of future practical XNAV implementations.

  18. THE CORRELATION BETWEEN DISPERSION MEASURE AND X-RAY COLUMN DENSITY FROM RADIO PULSARS

    SciTech Connect

    He, C.; Ng, C.-Y.; Kaspi, V. M.

    2013-05-01

    Pulsars are remarkable objects that emit across the entire electromagnetic spectrum, providing a powerful probe of the interstellar medium. In this study, we investigate the relation between dispersion measure (DM) and X-ray absorption column density N{sub H} using 68 radio pulsars detected at X-ray energies with the Chandra X-Ray Observatory or XMM-Newton. We find a best-fit empirical linear relation of N{sub H} (10{sup 20} cm{sup -2})= 0.30{sup +0.13}{sub -0.09} DM (pc cm{sup -3}), which corresponds to an average ionization of 10{sup +4}{sub -3}%, confirming the ratio of one free electron per 10 neutral hydrogen atoms commonly assumed in the literature. We also compare different N{sub H} estimates and note that some N{sub H} values obtained from X-ray observations are higher than the total Galactic H I column density along the same line of sight, while the optical extinction generally gives the best N{sub H} predictions.

  19. Performance enhancement of X-ray pulsar navigation using autonomous optical sensor

    NASA Astrophysics Data System (ADS)

    Kai, Xiong; Chunling, Wei; Liangdong, Liu

    2016-11-01

    This paper develops an integrated navigation method based on the X-ray pulsar navigation (XNAV) system and an autonomous optical navigation system for spacecrafts. The X-ray pulsar navigation is implemented by using the difference between the measured and predicated pulse arrival time, which is calculated by comparing an observed pulse profile with a standard pulse profile. A problem arises from the X-ray signal processing in that the spacecraft's orbit information, which may be unknown, is required to construct the observed pulse profile. The effect of the spacecraft orbit error on the accuracy of the pulse TOA (time of arrival) difference determination is analyzed. It is specified that the performance of the XNAV system may be degraded in the presence of large orbit error. In order to improve the navigation accuracy, an integrated navigation scheme is presented by fusing the measurement information of a X-ray detector and an ultraviolet optical sensor. The XNAV/optical integrated navigation system is effective to mitigate the effect of the spacecraft orbit error. The superiority of the presented scheme is illustrated through numerical simulations.

  20. Accretion Disks in Supersoft X-ray Sources

    NASA Technical Reports Server (NTRS)

    Popham, Robert; DiStefano, Rosanne

    1996-01-01

    We examine the role of the accretion disk in the steady-burning white dwarf model for supersoft sources. The accretion luminosity of the disk is quite small compared to the nuclear burning luminosity of the central source. Thus, in contrast to standard accretion disks, the main role of the disk is to reprocess the radiation from the white dwarf. We calculate models of accretion disks around luminous white dwarfs and compare the resulting disk fluxes to optical and UV observations of the LMC supersoft sources CAL 83, CAL 87, and RX J0513.9-6951. We find that if the white dwarf luminosity is near the upper end of the steady-burning region, and the flaring of the disk is included, then reprocessing by the disk can account for the UV fluxes and a substantial fraction of the optical fluxes of these systems. Reprocessing by the companion star can provide additional optical flux, and here too the disk plays an important role: since the disk is fairly thick, it shadows a significant fraction of the companion's surface.

  1. Interstellar X-Ray Absorption Spectroscopy of the Crab Pulsar with the LETGS

    NASA Technical Reports Server (NTRS)

    Paerels, Frits; Weisskopf, Martin C.; Tennant, Allyn F.; ODell, Stephen L.; Swartz, Douglas A.; Kahn, Steven M.; Behar, Ehud; Becker, Werner; Whitaker, Ann F. (Technical Monitor)

    2001-01-01

    We study the interstellar X-ray absorption along the line of sight to the Crab Pulsar. The Crab was observed with the Low Energy Transmission Grating Spectrometer on the Chandra X-ray Observatory, and the pulsar, a point source, produces a full resolution spectrum. The continuum spectrum appears smooth, and we compare its parameters with other measurements of the pulsar spectrum. The spectrum clearly shows absorption edges due to interstellar Ne, Fe, and O. The O edge shows spectral structure that is probably due to O bound in molecules or dust. We search for near-edge structure (EXAFS) in the O absorption spectrum. The Fe L absorption spectrum is largely due to a set of unresolved discrete n=2-3 transitions in neutral or near-neutral Fe, and we analyze it using a new set of dedicated atomic structure calculations, which provide absolute cross sections. In addition to being interesting in its own right, the ISM absorption needs to be understood in quantitative detail in order to derive spectroscopic constraints on possible soft thermal radiation from the pulsar.

  2. Binarity and Accretion: X-Ray Emission from AGB stars with FUV Excesses

    NASA Astrophysics Data System (ADS)

    Sahai, Raghvendra

    2012-10-01

    We propose a pilot survey for X-ray emission from AGB stars that are candidates for having binary companions with active accretion. These objects were identified via our innovative technique to search for FUV/NUV excesses in AGB stars using GALEX. The detection (or non-detection) of X-rays from this sample will enable us to begin testing models for the origin of the UV-excesses, leading to vital breakthroughs in our understanding of accretion-related phenomena and binarity in AGB stars. A larger survey, optimised using results fron this study, will be proposed in future cycles.

  3. Absorption Features in the X-ray Spectrum of an Ordinary Radio Pulsar

    NASA Astrophysics Data System (ADS)

    Kargaltsev, Oleg; Durant, Martin; Misanovic, Zdenka; Pavlov, George G.

    2012-08-01

    The vast majority of known nonaccreting neutron stars (NSs) are rotation-powered radio and/or γ-ray pulsars. So far, their multiwavelength spectra have all been described satisfactorily by thermal and nonthermal continuum models, with no spectral lines. Spectral features have, however, been found in a handful of exotic NSs and were thought to be a manifestation of their unique traits. Here, we report the detection of absorption features in the x-ray spectrum of an ordinary rotation-powered radio pulsar, J1740+1000. Our findings bridge the gap between the spectra of pulsars and other, more exotic, NSs, suggesting that the features are more common in the NS spectra than they have been thought so far.

  4. Absorption features in the x-ray spectrum of an ordinary radio pulsar.

    PubMed

    Kargaltsev, Oleg; Durant, Martin; Misanovic, Zdenka; Pavlov, George G

    2012-08-24

    The vast majority of known nonaccreting neutron stars (NSs) are rotation-powered radio and/or γ-ray pulsars. So far, their multiwavelength spectra have all been described satisfactorily by thermal and nonthermal continuum models, with no spectral lines. Spectral features have, however, been found in a handful of exotic NSs and were thought to be a manifestation of their unique traits. Here, we report the detection of absorption features in the x-ray spectrum of an ordinary rotation-powered radio pulsar, J1740+1000. Our findings bridge the gap between the spectra of pulsars and other, more exotic, NSs, suggesting that the features are more common in the NS spectra than they have been thought so far.

  5. Chandra X-Ray Observatory Observations of the Globular Cluster M28 and its Millisecond Pulsar PSR B1821-24

    NASA Technical Reports Server (NTRS)

    Becker, Werner; Swartz, Douglas A.; Pavlov, George G.; Elsner, Ronald F.; Grindlay, Jonathan; Mignani, Roberto; Tennant, Allyn F.; Backer, Don; Weisskopf, Martin C.

    2003-01-01

    We report here the results of the first Chandra X-Ray Observatory observations of the globular cluster M28 (NGC 6626). We detect 46 X-ray sources of which 12 lie within one core radius of the center. We show that the apparently extended X-ray core emission seen with the ROSAT HRI is due to the superposition of multiple discrete sources for which we determine the X-ray luminosity function down to a limit of about 6 x 10(exp 30) erg/s. We measure the radial distribution of the X-ray sources and fit it to a King profile finding a core radius of r(sub c,x) approx. 11 sec. We obtain the best-fit mass of the X-ray sources to be M(sub x) approx. 1.9 solar masses. We measure for the first time the unconfused phase-averaged X-ray spectrum of the 3.05-ms pulsar B1821-24 and find it best described by a power law with photon-index Gamma approx. equal to 1.2. We find marginal evidence of an emission line centered at 3.3 kev in the pulsar spectrum, which could be interpreted as cyclotron emission from a corona above the pulsar's polar cap if the the magnetic field is strongly different from a centered dipole. The unabsorbed pulsar flux in the 0.5-8.0 keV band is approx. 3.5 x 10(exp -13) ergs/s/sq cm. We present spectral analyses of the 5 brightest unidentified sources. Based on the spectral parameters of the brightest of these sources, we suggest that it is a transiently accreting neutron star in a low-mass X-ray binary, in quiescence. Fitting its spectrum with a hydrogen neutron star atmosphere model yields the effective temperature T(sup infinity)(sub eff) = 90(sup +30)(sub -10) eV and the radius R(sup infinity)(sub NS) = 14.5(sup +6.9)(sub -3.8) km. In addition to the resolved sources, we detect fainter, unresolved X-ray emission from the central core. Using the Chandra-derived positions, we also present a preliminary report on the result of searching archival Hubble Space Telescope data for possible optical counterparts.

  6. Constraining black hole masses in low-accreting active galactic nuclei using X-ray spectra

    NASA Astrophysics Data System (ADS)

    Jang, I.; Gliozzi, M.; Hughes, C.; Titarchuk, L.

    2014-09-01

    In a recent work we demonstrated that a novel X-ray scaling method, originally introduced for Galactic black holes (BHs), can be reliably extended to estimate the mass of supermassive BHs accreting at a moderate to high level. Here we investigate the limits of applicability of this method to low-accreting active galactic nuclei (AGN), using a control sample with good-quality X-ray data and dynamically measured mass. For low-accreting AGN (LX/LEdd ≤ 10-4), because the basic assumption that the photon index positively correlates with the accretion rate no longer holds the X-ray scaling method cannot be used. Nevertheless, the inverse correlation in the Γ-LX/LEdd diagram, found in several low-accreting BHs and confirmed by this sample, can be used to constrain MBH within a factor of ˜10 from the dynamically determined values. We provide a simple recipe to determine MBH using solely X-ray spectral data, which can be used as a sanity check for MBH determination based on indirect optical methods.

  7. Accretion states in X-ray binaries and their connection to GeV emission

    NASA Astrophysics Data System (ADS)

    Koerding, Elmar

    Accretion onto compact objects is intrinsically a multi-wavelength phenomenon: it shows emis-sion components visible from the radio to GeV bands. In X-ray binaries one can well observe the evolution of a single source under changes of the accretion rate and thus study the interplay between the different emission components.I will introduce the phenomenology of X-ray bina-ries and their accretion states and present our current understanding of the interplay between the optically thin and optically thick part of the accretion flow and the jet.The recent detection of the Fermi Large Area Telescope of a variable high-energy source coinciding with the position of the x-ray binary Cygnus X-3 will be presented. Its identification with Cygnus X-3 has been secured by the detection of its orbital period in gamma rays, as well as the correlation of the LAT flux with radio emission from the relativistic jets of Cygnus X-3. This will be interpreted in the context of the accretion states of the X-ray binary.

  8. The binary millisecond pulsar PSR J1023+0038 during its accretion state - I. Optical variability

    NASA Astrophysics Data System (ADS)

    Shahbaz, T.; Linares, M.; Nevado, S. P.; Rodríguez-Gil, P.; Casares, J.; Dhillon, V. S.; Marsh, T. R.; Littlefair, S.; Leckngam, A.; Poshyachinda, S.

    2015-11-01

    We present time-resolved optical photometry of the binary millisecond `redback' pulsar PSR J1023+0038 (=AY Sex) during its low-mass X-ray binary phase. The light curves taken between 2014 January and April show an underlying sinusoidal modulation due to the irradiated secondary star and accretion disc. We also observe superimposed rapid flaring on time-scales as short as ˜20 s with amplitudes of ˜0.1-0.5 mag and additional large flare events on time-scales of ˜5-60 min with amplitudes of ˜0.5-1.0 mag. The power density spectrum of the optical flare light curves is dominated by a red-noise component, typical of aperiodic activity in X-ray binaries. Simultaneous X-ray and UV observations by the Swift satellite reveal strong correlations that are consistent with X-ray reprocessing of the UV light, most likely in the outer regions of the accretion disc. On some nights we also observe sharp-edged, rectangular, flat-bottomed dips randomly distributed in orbital phase, with a median duration of ˜250 s and a median ingress/egress time of ˜20 s. These rectangular dips are similar to the mode-switching behaviour between disc `active' and `passive' luminosity states, observed in the X-ray light curves of other redback millisecond pulsars. This is the first time that the optical analogue of the X-ray mode-switching has been observed. The properties of the passive- and active-state light curves can be explained in terms of clumpy accretion from a trapped inner accretion disc near the corotation radius, resulting in rectangular, flat-bottomed optical and X-ray light curves.

  9. Experimental Validation of Pulse Phase Tracking for X-Ray Pulsar Based

    NASA Technical Reports Server (NTRS)

    Anderson, Kevin

    2012-01-01

    Pulsars are a form of variable celestial source that have shown to be usable as aids for autonomous, deep space navigation. Particularly those sources emitting in the X-ray band are ideal for navigation due to smaller detector sizes. In this paper X-ray photons arriving from a pulsar are modeled as a non-homogeneous Poisson process. The method of pulse phase tracking is then investigated as a technique to measure the radial distance traveled by a spacecraft over an observation interval. A maximum-likelihood phase estimator (MLE) is used for the case where the observed frequency signal is constant. For the varying signal frequency case, an algorithm is used in which the observation window is broken up into smaller blocks over which an MLE is used. The outputs of this phase estimation process were then looped through a digital phase-locked loop (DPLL) in order to reduce the errors and produce estimates of the doppler frequency. These phase tracking algorithms were tested both in a computer simulation environment and using the NASA Goddard Space flight Center X-ray Navigation Laboratory Testbed (GXLT). This provided an experimental validation with photons being emitted by a modulated X-ray source and detected by a silicon-drift detector. Models of the Crab pulsar and the pulsar B1821-24 were used in order to generate test scenarios. Three different simulated detector trajectories were used to be tracked by the phase tracking algorithm: a stationary case, one with constant velocity, and one with constant acceleration. All three were performed in one-dimension along the line of sight to the pulsar. The first two had a constant signal frequency and the third had a time varying frequency. All of the constant frequency cases were processed using the MLE, and it was shown that they tracked the initial phase within 0.15% for the simulations and 2.5% in the experiments, based on an average of ten runs. The MLE-DPLL cascade version of the phase tracking algorithm was used in

  10. Chandra Phase-Resolved X-ray Spectroscopy of the Crab Pulsar II

    NASA Technical Reports Server (NTRS)

    Weisskopf, Martin C.; Tennant, Allyn F.; Yakovlev, Dimitry G.; Harding, Alice; Zavlin, Vyacheslav E.; Elsner, Ronald F.; Becker, Werner

    2012-01-01

    We present a new study of the X-ray spectral properties of the Crab Pulsar. The superb angular resolution of the Chandra X-ray Observatory enables distinguishing the pulsar from the surrounding nebulosity. Analysis of the spectrum as a function of pulse phase allows the least-biased measure of interstellar X-ray extinction due primarily to photoelectric absorption and secondarily to scattering by dust grains in the direction of the Crab Nebula. We modify previous findings that the line-of-sight to the Crab is under-abundant in oxygen and provide measurements with improved accuracy and less bias. Using the abundances and cross sections from Wilms, Allen & McCray (2000) we find [O/H] = (5.28+\\-0.28) x 10(exp -4) (4.9 x 10(exp -4) is solar abundance). \\rVe also measure for the first time the impact of scattering of flux out of the image by interstellar grains. \\rYe find T(sub scat) = 0.147+/-0.043. Analysis of the spectrum as a function of pulse phase also measures the X-ray spectral index even at pulse minimum - albeit with increasing statistical uncertainty. The spectral variations are, by and large, consistent with a sinusoidal variation. The only significant variation from the sinusoid occurs over the same phase range as some rather abrupt behavior in the optical polarization magnitude and position angle. We compare these spectral variations to those observed in Gamma-rays and conclude that our measurements are both a challenge and a guide to future modeling and will thus eventually help us understand pair cascade processes in pulsar magnetospheres. The data were also used to set new. and less biased, upper limits to the surface temperature of the neutron star for different models of the neutron star atmosphere.

  11. Outburst of the 2 s Anomalous X-ray Pulsar 1E 1547.0-5408

    NASA Technical Reports Server (NTRS)

    Halpern, J. P.; Gotthelf, E. V.; Camilo, F.; Reynolds, J.; Ransom, S. M.

    2008-01-01

    Following our discovery of radio pulsations from the newly recognized anomalous X-ray pulsar (AXP) 1E 1547.0-5408, we initiated X-ray monitoring with the Swift X-ray telescope and obtained a single target-of-opportunity observation with the Newton X-ray Multi-Mirror Mission (XMM-Newton). In comparison with its historic minimum flux of 3 x 10(exp -l3)ergs/sq cm/s, the source was found to be in a record high state, f(sub x)(1-8 keV) = 5 x 10(exp -12)ergs/sq cm/s, or L(sub x) = 1.7 x 10(exp 35)(d/9 kpc )(sup 2)ergs/s, and declining by 25% in 1 month. Extrapolating the decay, we bound the total energy in this outburst to 1042 ergs < E < ergs. The spectra (fitted with a Comptonized blackbody) show that an increase in the temperature and area of a hot region, to 0.5 keV and -16% of the surface area of the neutron star, respectively, are primarily responsible for its increase in luminosity. The energy, spectrum, and timescale of decay are consistent with a deep crustal heating event, similar to an interpretation of the X-ray turn-on of the transient AXP XTE J18 10- 197. Simultaneous with the 4.6 hr ATdA4-Newton observation, we observed at 6.4 GHz with the Parkes telescope, measuring the phase relationship of the radio and X-ray pulse. The X-ray pulsed fraction of 1E 1547.0-5408 is only approx. 7 %, while its radio pulse is relatively broad for such a slow pulsar, which may indicate a nearly aligned rotator. As also inferred from the transient behavior of XTE J18 10-197, the only other AXP known to emit in the radio, the magnetic field rearrangement responsible for this X-ray outburst of 1E 1547.0-5408 is probably the cause of its radio turn-on.

  12. Time-dependent X-ray emission from unstable accretion disks around black holes

    NASA Technical Reports Server (NTRS)

    Mineshige, Shin; Kim, Soon-Wook; Wheeler, J. Craig

    1990-01-01

    The spectral evolution of accretion disks in X-ray binaries containing black holes is studied, based on the disk instability model. The thermal transition of the outer portions of the disk controls the mass flow rate into the inner portions of the disk, thus modulating the soft X-ray flux which is thought to arise from the inner disk. Calculated soft X-ray spectra are consistent with the observations of the X-ray transient A0620 - 00 and especially ASM 2000 + 25, the soft X-ray spectra of which are well fitted by blackbody radiation with a fixed inner edge of the disk, Rin, and with monotonically decreasing temperature at Rin with time. Since the gas pressure is always dominant over the radiation pressure during the decay in these models, a two-temperature region is difficult to create. Instead, it is suggested that hard X-rays are generated in a hot (kT greater than 10 keV) accretion disk corona above the cool (kT less than 1 keV) disk.

  13. X-Ray/GeV Emissions from Crab-like Pulsars in the LMC

    NASA Astrophysics Data System (ADS)

    Takata, J.; Cheng, K. S.

    2017-01-01

    We discuss X-ray and gamma-ray emissions from Crab-like pulsars, PSRs J0537-6910 and J0540-6919, in the Large Magellanic Cloud. Fermi-LAT observations have resolved the gamma-ray emissions from these two pulsars and found pulsed emissions from PSR J0540-6919. The total pulsed radiation in the X-ray/gamma-ray energy bands of PSR J0540-6919 is observed with efficiency {η }J0540∼ 0.06 (in 4π sr), which is about a factor of ten larger than {η }{Crab}∼ 0.006 of the Crab pulsar. Although PSR J0537-6910 has the highest spin-down power among currently known pulsars, the efficiency of the observed X-ray emissions is about two orders of magnitude smaller than that of PSR J0540-6919. This paper mainly discusses what causes the difference in the radiation efficiencies of these three energetic Crab-like pulsars. We discuss electron/positron acceleration and high-energy emission processes within the outer gap model. By solving the outer gap structure with the dipole magnetic field, we show that the radiation efficiency decreases as the inclination angle between the magnetic axis and the rotation axis increases. To explain the difference in the pulse profile and in the radiation efficiency, our model suggests that PSR J0540-6919 has an inclination angle much smaller than that of the Crab pulsar (here we assume the inclination angles of both pulsars are α < 90^\\circ ). On the other hand, we speculate that the difference in the radiation efficiencies between PSRs J0537-6910 and J0549-6919 is mainly caused by the difference in the Earth viewing angle, and that we see PSR J0537-6910 with an Earth viewing angle \\zeta \\gg 90^\\circ (or \\ll 90^\\circ ) measured from the spin axis, while we see PSR J0540-6919 with \\zeta ∼ 90^\\circ .

  14. X-Ray Spectra from MHD Simulations of Accreting Black Holes

    NASA Technical Reports Server (NTRS)

    Schnittman, Jeremy D.; Noble, Scott C.; Krolik, Julian H.

    2011-01-01

    We present new global calculations of X-ray spectra from fully relativistic magneto-hydrodynamic (MHO) simulations of black hole (BH) accretion disks. With a self consistent radiative transfer code including Compton scattering and returning radiation, we can reproduce the predominant spectral features seen in decades of X-ray observations of stellar-mass BHs: a broad thermal peak around 1 keV, power-law continuum up to >100 keV, and a relativistically broadened iron fluorescent line. By varying the mass accretion rate, different spectral states naturally emerge: thermal-dominant, steep power-law, and low/hard. In addition to the spectral features, we briefly discuss applications to X-ray timing and polarization.

  15. Probing the Accretion Geometry of Black Holes with X-Ray Polarization

    NASA Technical Reports Server (NTRS)

    Schnitman, Jeremy D.

    2011-01-01

    In the coming years, new space missions will be able to measure X-ray polarization at levels of 1% or better in the approx.1-10 keV energy band. In particular, X-ray polarization is an ideal tool for determining the nature of black hole (BH) accretion disks surrounded by hot coronae. Using a Monte Carlo radiation transport code in full general relativity, we calculate the spectra and polarization features of these BH systems. At low energies, the signal is dominated by the thermal flux coming directly from the optically thick disk. At higher energies, the thermal seed photons have been inverse-Compton scattered by the corona, often reflecting back off the disk before reaching the observer, giving a distinctive polarization signature. By measuring the degree and angle of this X-ray polarization, we can infer the BH inclination, the emission geometry of the accretion flow, and also determine the spin of the black hole.

  16. Spectroscopy of Low Mass X-Ray Binaries: New Insights into Accretion. Revised

    NASA Technical Reports Server (NTRS)

    DilVrtilek, Saeqa; Mushotzky, Richard (Technical Monitor)

    2001-01-01

    This project is to observe two low mass X-ray binaries, chosen for their X-ray brightness, low column density, and diversity of accretion behavior. The high spectral resolution of the RGS, the broad energy range and tremendous collecting power of EPIC, and simultaneous optical monitoring with the OM are particularly well-suited to these studies. observation of one of the two objects has taken place and the data were received in late November. The second object is yet to be observed. Over the next year we will: investigate the physical conditions of the emitting gas using emission and recombination line diagnostics to determine temperatures, densities, elemental abundances, and ionization structure; study the behavior of emission features as a function of binary orbit; and test and improve models of X-ray line emission developed by us over the past decade. We will gain insight on both the geometry of the accretion flow and on the evolutionary history of LMXBs.

  17. Spectroscopy of Low Mass X-Ray Binaries: New Insights into Accretion

    NASA Technical Reports Server (NTRS)

    Vrtilek, Saeqa Dil; Mushotzky, Richard F. (Technical Monitor)

    2002-01-01

    This project is to observe two low mass X-ray binaries, chosen for their X-ray brightness, low column density, and diversity of accretion behavior. The high spectral resolution of the RGS, the broad energy range and tremendous collecting power of EPIC, and simultaneous optical monitoring with the OM are particularly well-suited to these studies. The second of two objects was not observed until September of 2002. Data analysis for the new observation is underway. over the next year we will: investigate the physical conditions of the emitting gas using emission and recombination line diagnostics to determine temperatures, densities, elemental abundances, and ionization structure; study the behavior of emission features as a function of binary orbit; and test and improve models of X-ray line emission developed by us over the past decade. We will gain insight on both the geometry of the accretion flow and on the evolutionary history of LMXBs.

  18. MN Lup: X-RAYS FROM A WEAKLY ACCRETING T TAURI STAR

    SciTech Connect

    Guenther, H. M.; Wolk, S. J.; Wolter, U.; Robrade, J.

    2013-07-01

    Young T Tauri stars (TTS) are surrounded by an accretion disk, which over time disperses due to photoevaporation, accretion, and possibly planet formation. The accretion shock on the central star produces an UV/optical veiling continuum, line emission, and X-ray signatures. As the accretion rate decreases, the impact on the central star must change. In this article we study MN Lup, a young star where no indications of a disk are seen in IR observations. We present XMM-Newton and VLT/UVES observations, some of them taken simultaneously. The X-ray data show that MN Lup is an active star with L{sub X} /L{sub bol} close to the saturation limit. However, we find high densities (n{sub e} > 3 Multiplication-Sign 10{sup 10} cm{sup -3}) in the X-ray grating spectrum. This can be well fitted using an accretion shock model with an accretion rate of 2 Multiplication-Sign 10{sup -11} M{sub Sun} yr{sup -1}. Despite the simple H{alpha} line profile which has a broad component, but no absorption signatures as typically seen on accreting TTS, we find rotational modulation in Ca II K and in photospheric absorption lines. These line profile modulations do not clearly indicate the presence of a localized hot accretion spot on the star. In the H{alpha} line we see a prominence in absorption about 2R{sub *} above the stellar surface-the first of its kind on a TTS. MN Lup is also the only TTS where accretion is seen, but no dust disk is detected that could fuel it. We suggest that MN Lup presents a unique and short-lived state in the disk evolution. It may have lost its dust disk only recently and is now accreting the remaining gas at a very low rate.

  19. Interference as an Origin of the Peaked Noise in Accreting X-Ray Binaries

    NASA Astrophysics Data System (ADS)

    Veledina, Alexandra

    2016-12-01

    We propose a physical model for the peaked noise in the X-ray power density spectra of accreting X-ray binaries. We interpret its appearance as an interference of two Comptonization continua: one coming from the upscattering of seed photons from the cold thin disk and the other fed by the synchrotron emission of the hot flow. Variations of both X-ray components are caused by fluctuations in mass accretion rate, but there is a delay between them corresponding to the propagation timescale from the disk Comptonization radius to the region of synchrotron Comptonization. If the disk and synchrotron Comptonization are correlated, the humps in the power spectra are harmonically related and the dips between them appear at frequencies related as odd numbers 1:3:5. If they are anti-correlated, the humps are related as 1:3:5, but the dips are harmonically related. Similar structures are expected to be observed in accreting neutron star binaries and supermassive black holes. The delay can be easily recovered from the frequency of peaked noise and further used to constrain the combination of the viscosity parameter and disk height-to-radius ratio α(H/R)2 of the accretion flow. We model multi-peak power spectra of black hole X-ray binaries GX 339-4 and XTE J1748-288 to constrain these parameters.

  20. Free-fall accretion and emitting caustics in wind-fed X-ray sources

    NASA Astrophysics Data System (ADS)

    Illarionov, Andrei F.; Beloborodov, Andrei M.

    2001-05-01

    In wind-fed X-ray binaries the accreting matter is Compton-cooled and falls freely on to the compact object. The matter has a modest angular momentum l and accretion is quasi-spherical at large distances from the compact object. Initially small non-radial velocities grow in the converging supersonic flow and become substantial in the vicinity of the accretor. The streamlines with l>(GMR*)1/2 (where M and R* are the mass and radius of the compact object) intersect outside R* and form a two-dimensional caustic which emits X-rays. The streamlines with low angular momentum, l<(GMR*)1/2, run into the accretor. If the accretor is a neutron star, a large X-ray luminosity results. We show that the distribution of accretion rate/luminosity over the star surface is sensitive to the angular momentum distribution of the accreting matter. The apparent luminosity depends on the side from which the star is observed and can change periodically with the orbital phase of the binary. The accretor then appears as a `Moon-like' X-ray source.

  1. Towards practical autonomous deep-space navigation using X-Ray pulsar timing

    NASA Astrophysics Data System (ADS)

    Shemar, Setnam; Fraser, George; Heil, Lucy; Hindley, David; Martindale, Adrian; Molyneux, Philippa; Pye, John; Warwick, Robert; Lamb, Andrew

    2016-10-01

    We investigate the feasibility of deep-space navigation using the highly stable periodic signals from X-ray pulsars in combination with dedicated instrumentation on the spacecraft: a technique often referred to as `XNAV'. The results presented are based on the outputs from a study undertaken for the European Space Agency. The potential advantages of this technique include increased spacecraft autonomy and lower mission operating costs. Estimations of navigation uncertainties have been obtained using simulations of different pulsar combinations and navigation strategies. We find that the pulsar PSR B1937 + 21 has potential to allow spacecraft positioning uncertainties of 2 and 5 km in the direction of the pulsar after observation times of 10 and 1 h respectively, for ranges up to 30 AU. This could be achieved autonomously on the spacecraft using a focussing X-ray instrument of effective area 50 cm2 together with a high performance atomic clock. The Mercury Imaging X-ray Spectrometer (MIXS) instrument, due to be launched on the ESA/JAXA BepiColombo mission to Mercury in 2018, is an example of an instrument that may be further developed as a practical telescope for XNAV. For a manned mission to Mars, where an XNAV system could provide valuable redundancy, observations of the three pulsars PSR B1937 + 21, B1821-24 and J0437-4715 would enable a three-dimensional positioning uncertainty of 30 km for up to 3 months without the need to contact Earth-based systems. A lower uncertainty may be achieved, for example, by use of extended observations or, if feasible, by use of a larger instrument. X-ray instrumentation suitable for use in an operational XNAV subsystem must be designed to require only modest resources, especially in terms of size, mass and power. A system with a focussing optic is required in order to reduce the sky and particle background against which the source must be measured. We examine possible options for future developments in terms of simpler, lower

  2. Quiescent accretion disks in black hole X-ray novae

    NASA Technical Reports Server (NTRS)

    Orosz, Jerome A.; Bailyn, Charles D.; Remillard, Ronald A.; Mcclintock, Jeffrey E.; Foltz, Craig B.

    1994-01-01

    We present detailed time-resolved spectroscopy of the Balmer emission lines from two black hole binary systems in quiescence, A0620-00 and Nova Muscae 1991. We find extraordinary similarities between the two systems. There are 30-40 km/s velocity variations of the emission lines over the orbital period, the phases of which are not aligned with the expected phase of the motion of the compact primary. Detailed modeling of both systems is complicated by variable hot spot components, regions of optical thickness, and intermittent excess emission in the blue line wings of the H-alpha lines. Both sources also display low velocities at the outer edge of the accretion disk, implying a large primary Roche lobe and extreme mass ratios. These complications suggest that although simple optically thin, Keplerian alpha-disk models provide a useful parameterization of emission lines from these systems, the straightforward physical models they imply should be treated with great caution.

  3. Chandra X-Ray Observatory Observations of the Globular Cluster M28 and its Milisecond Pulsar PSR B1821-24

    NASA Technical Reports Server (NTRS)

    Becker, Werner; Swartz, Douglas A.; Pavlov, George G.; Elsner, Ronald F.; Grindlay, Jonathan; Mignani, Roberto; Tennant, Allyn F.; Backer, Don; Pulone, Luigi; Testa, Vincenzo

    2003-01-01

    We report here the results of the first Chandra X-Ray Observatory observations of the globular cluster M28 (NGC 6626). We detect 46 X-ray sources, of which 12 lie within 1 core radius of the center. We show that the apparently extended X-ray core emission seen with the ROSAT HRI is due to the superposition of multiple discrete sources, for which we determine the X-ray luminosity function down to a limit of about 6 x 10(exp 30) ergs/s. We measure the radial distribution of the X-ray sources and fit it to a King profile finding a core radius of r(sub c,X) approx. = 5 11". We measure for the first time the unconfused phase-averaged X-ray spectrum of the 3.05 ms pulsar B1821-24 and find that it is best described by a power law with photon index Gamma approx. = 1.2. We find marginal evidence of an emission line centered at 3.3 keV in the pulsar spectrum, which could be interpreted as cyclotron emission from a corona above the pulsar s polar cap if the magnetic field is strongly different from a centered dipole. The unabsorbed pulsar flux in the 0.1 - 8.0 keV band is approx. = 3.5 x 10(exp -13) ergs/s sq cm. We present spectral analyses of the five brightest unidentified sources. Based on the spectral parameters of the brightest of these sources, we suggest that it is a transiently accreting neutron star in a low-mass X-ray binary, in quiescence. Fitting its spectrum with a hydrogen neutron star atmosphere model yields the effective temperature T(sub eff, sup infinity) = 90(sup +30, sub -10) eV and the radius R(sub NS, sup infinity) = 14.5(sup +6.9, sub -3.8) km. In addition to the resolved sources, we detect fainter, unresolved X-ray emission from the central core. Using the Chandra-derived positions, we also report on the result of searching archival Hubble Space Telescope data for possible optical counterparts.

  4. RXTE and BeppoSAX Observations of the Transient X-ray Pulsar XTE J 18591+083

    NASA Technical Reports Server (NTRS)

    Corbet, R. H. D.; intZand, J. J. M.; Levine, A. M.; Marshall, F. E.

    2008-01-01

    We present observations of the 9.8 s X-ray pulsar XTE J159+083 made with the All-Sky Monitor (ASM) and Proportional Counter Array (PCA) on board the Rossi X-ray Timing Explorer (RXTE), and the Wide Field Cameras (WFC) on board BeppoSAX. The ASM data cover a 12 year time interval and show that an extended outburst occurred between approximately MJD50, 250, and 50, 460 (1996 June 16 to 1997 January 12). The ASM data excluding this outburst interval suggest a possible 61 day modulation. Eighteen sets of PCA observations were obtained over an approx. one month interval in 1999. The flux variability measured with the PCA appears consistent with the possible period found with the ASM. The PCA measurements of the pulse period showed it to decrease non-monotonically and then to increase significantly. Doppler shifts due to orbital motion rather than accretion torques appear to be better able to explain the pulse period changes. Observations with the WFC during the extended outburst give an error box which is consistent with a previously determined PCA error box but is significantly smaller. The transient nature of XTE J1859+083 and the length of its pulse period are consistent with it being a Be/neutral star binary. The possible 61 day orbital period would be of the expected length for a Be star system with a 9.8 s pulse period.

  5. Accretion-driven star formation in central dominant galaxies in X-ray clusters

    NASA Astrophysics Data System (ADS)

    Sarazin, C. L.; Oconnell, R. W.

    1983-05-01

    Analytical and observational evidence for the formation of low-mass stars in the gas accreting in the central dominant galaxies in clusters is presented. Observations of the (U-V) and (K-V) color gradients in accreting galaxies are suggested to reveal colors altered by the appearance of young stars, e.g., the excess blue and the A star spectrum detected in NGC 1275. Low-temperature X ray line emissions from accreting galaxies have been partially surveyed with the result that 10 pct of the brightest cluster galaxies in a magnitude-limited sample show evidence of significant accretion. Photometric data from the quasar 3C 48, located in a galaxy with a very blue population, also suggests low-mass star formation, especially when compared to measurements of NGC 1275, which has the highest accretion rate among observed central dominant cluster galaxies. The quasar, however, would not be accreting interstellar gas.

  6. Propeller Effect in the Transient X-Ray Pulsar SMC X-2

    NASA Astrophysics Data System (ADS)

    Lutovinov, Alexander A.; Tsygankov, Sergey S.; Krivonos, Roman A.; Molkov, Sergey V.; Poutanen, Juri

    2017-01-01

    We report the results of the monitoring campaign of the transient X-ray pulsar SMC X-2 performed with the Swift/XRT telescope over the period of 2015 September–2016 January during the Type II outburst. During this event, the bolometric luminosity of the source ranged from ≃1039 down to several ×1034 erg s‑1. Moreover, we discovered its dramatic drop by a factor of more than 100 below the limiting value of {L}{lim}≃ 4× {10}36 erg s‑1, which can be interpreted as a transition to the propeller regime. These measurements make SMC X-2 the sixth pulsating X-ray source where such a transition is observed and allow us to estimate the magnetic field of the neutron star in the system B ≃ 3 × 1012 G, which is in agreement with independent results of the spectral analysis.

  7. Tiny Tremors to Titanic Explosions: Tackling Transients in Anomalous X-Ray Pulsars

    NASA Astrophysics Data System (ADS)

    Kaspi, Victoria

    We are requesting the target-of-oppurtunity (ToO) component of an ongoing, successful, long-term RXTE monitoring campaign of anomalous X- ray pulsars (AXPs). Their nature had been a mystery, but with our discoveries of X-ray bursts from AXPs, there is compelling evidence that they are young, isolated, ultra-magnetized neutron stars or "magnetars." We request ToO observations of any of the known and candidate AXPs as well as of any newly discovered AXPs should they exhibit anomalous behavior of one or more of the following types: bursts, significant sudden pulse profile changes, glitches or other rotational anomalies, or pulse fractions changes. These observations will allow us to answer basic physical questions about neutron star structure.

  8. Tiny Hiccups to Titanic Explosions: Tackling Transients in Anomalous X-Ray Pulsars

    NASA Astrophysics Data System (ADS)

    Kaspi, Victoria

    We request the Target-of-Opportunity (TOO) component of an ongoing, successful, long-term RXTE monitoring campaign of anomalous X-ray pulsars (AXPs). Their nature had been a long-standing mystery, but with our discoveries of soft gamma-ray repeater-like X-ray bursts from two AXPs, there is compelling evidence that they are magnetars. We request TOO observations of any of five AXPs (and one candidate) should they exhibit anomalous behavior of one or more of the following types: bursts, significant pulse profile changes, glitches or other rotational anomalies, or pulse fractions changes. These observations will allow us to answer basic physical questions about neutron star structure and constrain the physics of magnetars.

  9. Tiny Tremors to Titanic Explosions: Tackling Transients in Anomalous X-Ray Pulsars (core Program)

    NASA Astrophysics Data System (ADS)

    We are requesting the target-of-oppurtunity (ToO) component of an ongoing, successful, long-term RXTE monitoring campaign of anomalous X- ray pulsars (AXPs). Their nature had been a mystery, but with our discoveries of X-ray bursts from AXPs, there is compelling evidence that they are young, isolated, ultra-magnetized neutron stars or "magnetars." We request ToO observations of any of the known and candidate AXPs as well as of any newly discovered AXPs should they exhibit anomalous behavior of one or more of the following types: bursts, significant sudden pulse profile changes, glitches or other rotational anomalies, or pulse fractions changes. These observations will allow us to answer basic physical questions about neutron star structure.

  10. Tiny Hiccups to Titanic Explosions: Tackling Transients in Anomalous X-Ray Pulsars

    NASA Astrophysics Data System (ADS)

    Kaspi, Victoria

    We are requesting the target-of-oppurtunity (ToO) component of an ongoing, successful, long-term RXTE monitoring campaign of anomalous X- ray pulsars (AXPs). Their nature had been a mystery, but with our discoveries of X-ray bursts from AXPs, there is compelling evidence that they are young, isolated, ultra-magnetized neutron stars or "magnetars." We request ToO observations of any of the known and candidate AXPs should they exhibit anomalous behavior of one or more of the following types: bursts, significant sudden pulse profile changes, glitches or other rotational anomalies, or pulse fractions changes. These observations will allow us to answer basic physical questions about neutron star structure.

  11. RADIO-QUIET AND RADIO-LOUD PULSARS: SIMILAR IN GAMMA-RAYS BUT DIFFERENT IN X-RAYS

    SciTech Connect

    Marelli, M.; Mignani, R. P.; Luca, A. De; Salvetti, D.; Parkinson, P. M. Saz; Hartog, P. R. Den

    2015-04-01

    We present new Chandra and XMM-Newton observations of a sample of eight radio-quiet (RQ) γ-ray pulsars detected by the Fermi Large Area Telescope. For all eight pulsars we identify the X-ray counterpart, based on the X-ray source localization and the best position obtained from γ-ray pulsar timing. For PSR J2030+4415 we found evidence for a ∼10″-long pulsar wind nebula. Our new results consolidate the work from Marelli et al. and confirm that, on average, the γ-ray-to-X-ray flux ratios (F{sub γ}/F{sub X}) of RQ pulsars are higher than for the radio-loud (RL) ones. Furthermore, while the F{sub γ}/F{sub X} distribution features a single peak for the RQ pulsars, the distribution is more dispersed for the RL ones, possibly showing two peaks. We discuss possible implications of these different distributions based on current models for pulsar X-ray emission.

  12. Super-Eddington accretion disks in Ultraluminous X-ray sources

    NASA Astrophysics Data System (ADS)

    Fabrika, S.; Vinokurov, A.; Atapin, K.; Sholukhova, O.

    2016-06-01

    The origin of Ultraluminous X-ray sources (ULXs) in external galaxies whose X-ray luminosities exceed those of the brightest black holes in our Galaxy hundreds and thousands times is mysterious. The most popular models for the ULXs involve either intermediate mass black holes (IMBHs) or stellar-mass black holes accreting at super-Eddington rates. Here we review the ULX properties, their X-ray spectra indicate the presence of hot winds in their accretion disks supposing the supercritical accretion. However, the strongest evidences come from optical spectroscopy. The spectra of the ULX counterparts are very similar to that of SS433, the only known supercritical accretor in our Galaxy. The spectra are apparently of WNL type (late nitrogen Wolf-Rayet stars) or LBV (luminous blue variables) in their hot state, which are very scarce stellar objects. We find that the spectra do not originate from WNL/LBV type donors but from very hot winds from the accretion disks, whose physical conditions are similar to those in stellar winds from these stars. The results suggest that bona-fide ULXs must constitute a homogeneous class of objects, which most likely have supercritical accretion disks.

  13. SXP 1062, a young Be X-ray binary pulsar with long spin period. Implications for the neutron star birth spin

    NASA Astrophysics Data System (ADS)

    Haberl, F.; Sturm, R.; Filipović, M. D.; Pietsch, W.; Crawford, E. J.

    2012-01-01

    Context. The Small Magellanic Cloud (SMC) is ideally suited to investigating the recent star formation history from X-ray source population studies. It harbours a large number of Be/X-ray binaries (Be stars with an accreting neutron star as companion), and the supernova remnants can be easily resolved with imaging X-ray instruments. Aims: We search for new supernova remnants in the SMC and in particular for composite remnants with a central X-ray source. Methods: We study the morphology of newly found candidate supernova remnants using radio, optical and X-ray images and investigate their X-ray spectra. Results: Here we report on the discovery of the new supernova remnant around the recently discovered Be/X-ray binary pulsar CXO J012745.97-733256.5 = SXP 1062 in radio and X-ray images. The Be/X-ray binary system is found near the centre of the supernova remnant, which is located at the outer edge of the eastern wing of the SMC. The remnant is oxygen-rich, indicating that it developed from a type Ib event. From XMM-Newton observations we find that the neutron star with a spin period of 1062 s (the second longest known in the SMC) shows a very high average spin-down rate of 0.26 s per day over the observing period of 18 days. Conclusions: From the currently accepted models, our estimated age of around 10 000-25 000 years for the supernova remnant is not long enough to spin down the neutron star from a few 10 ms to its current value. Assuming an upper limit of 25 000 years for the age of the neutron star and the extreme case that the neutron star was spun down by the accretion torque that we have measured during the XMM-Newton observations since its birth, a lower limit of 0.5 s for the birth spin period is inferred. For more realistic, smaller long-term average accretion torques our results suggest that the neutron star was born with a correspondingly longer spin period. This implies that neutron stars in Be/X-ray binaries with long spin periods can be much younger

  14. Thermal cycles from a two-zone accreting model - X-ray bursts and shell flashes

    NASA Astrophysics Data System (ADS)

    Regev, O.; Livio, M.

    1984-05-01

    The mechanisms of red-giant shell-flash emission and neutron-star X-ray bursts are investigated theoretically, extending the two-zone model of Barranco et al. (1980) by means of a third time-dependent nonlinear equation to account for the accretion process. The physical assumptions are explained, the equations are derived, and the results of numerical integration are presented graphically for a set of standard input parameters and several variants. Two types of limit-cycle oscillations are identified: thermal oscillations arising from nuclear burning in a thin shell of red giants (leading to shell flashes) and oscillations driven by both nuclear burning and mass accretion in the high-density thermonuclear-ignition region at the surface of neutron stars (leading to X-ray bursts). The two-zone model is shown to account for such burster properties as high-accretion rate stabilization, core heat-exchange effects, and double-peaked bursts.

  15. X-rays and Doppler imaging: Do soft emission and accretion coincide?

    NASA Astrophysics Data System (ADS)

    Wolter, Uwe

    2010-10-01

    Classical T Tauri stars (CTTS) are young, accreting systems. The accretion causes a variable soft X-ray excess and unusual line ratios in the He-like triplets. Accretion signatures can also be seen in optical Doppler images. However, the true correlation of these different signatures only accessible by simultaneous X-ray and ground-based observations has not been studied to date. We propose an 80 ksec XMM-Newton observation covering two full rotations of the CTTS MN Lup; furthermore, we propose simultaneous VLT/UVES spectral observations to obtain a Doppler image of its surface. With its short rotation period and fast rotation, MN Lup is a truly unique target for these observations.

  16. Modeling High-resolution Spectra from X-ray Illuminated Accretion Disks

    NASA Astrophysics Data System (ADS)

    Garcia, Javier; Kallman, T.

    2010-01-01

    This work is focused on the study of X-ray illuminated accretion disks around compact objects by modeling their structure and reprocessed spectra. Use of low-accuracy and incomplete atomic data is a key limitation in models which have been calculated so far. We remedy this situation by incorporating data for line energies, transition probabilities and photoionization cross sections taken from various sources, most notably calculations using the R-matrix suite of codes. We also implement a self-consistent approach for the radiative transfer of X-rays and the heating and ionization of the gas. These promise to lead to significant improvements in the understanding of the X-ray observations of active galactic nuclei (AGN), X-ray binaries and galactic black holes. By performing detailed radiative transfer calculations we have computed the reflected spectra from constant density slabs for different input parameters (e.g., density, strength of incident X-rays, iron abundance), including the redistribution of photons due to Compton scattering. Although broad and skewed iron emission lines observed in many accreting systems are often attributed to the Doppler effect and gravitational redshift, our results show that Comptonization can be responsible for a significant fraction of the line broadening. By analyzing simulated Suzaku observations from our models, we provide equivalent and physical widths and line centroid energies for atomic lines, absorption edges and recombination continua (among other features). These are provided in tabular and graphical form that can be used directly in the interpretation of observational data.

  17. Implications of rapid rotation for pulse profile models of millisecond-period x-ray pulsars

    NASA Astrophysics Data System (ADS)

    Cadeau, Coire

    2007-08-01

    The rapid rotation of recycled neutron stars in accretion-powered millisecond- period X-ray pulsars has important consequences for models of their pulsed emission, and by extension, the analysis of observations of these objects. We begin by considering the problem of calculating the time-varying bolometric flux arising due to emission from a bright spot on the surface of a rapidly rotating neutron star, with rotational period on the order of a millisecond. We restrict to the case of isotropic emission from an infinitesimal emission zone, but carry out the calculations with sufficient generality to incorporate a precisely solved spacetime metric and stellar structure. The geodesic equation is integrated numerically. Using the computer code developed for this work, we investigate the effect that commonly-used simplifying approximations have on the shape of the pulse profile compared to the full calculation. In particular, we consider the effect of neglecting the phase-dependent travel time of photons, approximating the exterior metric as either Schwarzschild or Kerr, and neglecting the rotation- induced oblateness of the neutron star. We also consider the consequences that result when approximate pulse profiles are used to obtain neutron star parameters such as mass, radius, emission inclination, and observer inclination via least squares fitting. Specifically, we look at fitting light curves calculated using the Schwarzschild metric and a spherical star to a light curve calculated using a precisely-solved metric and stellar structure. We are able to conclude that, in an idealised case where there is no random noise component and all light curves are for bolometric fluxes from isotropic emission, neglecting photon times-of-flight or stellar oblateness in model light curves used for fitting can introduce errors at the level of several tens of percent on the determination of mass and radius individually. However, these errors will often offset each other such that the

  18. TINY HICCUPS TO TITANIC EXPLOSIONS: Tackling Transients in Anomalous X-ray Pulsars

    NASA Astrophysics Data System (ADS)

    Kaspi, Victoria

    2005-09-01

    Recently discovered transient events in Anomalous X-ray Pulsars (AXPs) may be a Rosetta Stone for understanding the persistent emission from magnetars. They also may hold the key to quantifying the number of magnetars in the Galaxy. Here we request Chandra TOO time to observe any AXP following a rare transient event, including a major outburst or a long-duration flare. Specifically, the requested observations will determine the pulsed fraction and spectral evolution of a transient AXP event as the source relaxes back to quiescence, in order to quantitatively test the "twisted magnetosphere" model for magnetars, and establish the basic phenomenology of transient AXP events.

  19. Tiny Hiccups To Titanic Explosions: Tackling Transients in Anomalous X-ray Pulsars

    NASA Astrophysics Data System (ADS)

    Kaspi, Victoria

    2006-09-01

    Recently discovered transient events in Anomalous X-ray Pulsars (AXPs) may be a Rosetta Stone for understanding the persistent emission from magnetars. They also may hold the key to quantifying the number of magnetars in the Galaxy. Here we request Chandra TOO time to observe any AXP following a rare transient event, including a major outburst or a long-duration flare. Specifically, the requested observations will determine the pulsed fraction and spectral evolution of a transient AXP event as the source relaxes back to quiescence, in order to quantitatively test the "twisted magnetosphere" model for magnetars, and establish the basic phenomenology of transient AXP events.

  20. TINY HICCUPS TO TITANIC EXPLOSIONS: Tackling Transients in Anomalous X-ray Pulsars

    NASA Astrophysics Data System (ADS)

    Kaspi, Victoria

    2007-09-01

    Recently discovered transient events in Anomalous X-ray Pulsars (AXPs) may be a Rosetta Stone for understanding the persistent emission from magnetars. They also may hold the key to quantifying the number of magnetars in the Galaxy. Here we request Chandra TOO time to observe any AXP following a rare transient event, including a major outburst or a long-duration flare. Specifically, the requested observations will determine the pulsed fraction and spectral evolution of a transient AXP event as the source relaxes back to quiescence, in order to quantitatively test the "twisted magnetosphere" model for magnetars, and establish the basic phenomenology of transient AXP events.

  1. A Optical Synchrotron Nebula around the X-Ray Pulsar 0540-693

    NASA Astrophysics Data System (ADS)

    Chanan, G.; Helfand, D.; Reynolds, S.

    The authors report the discovery of extended optical continuum emission around the recently discovered 50 ms X-ray pulsar in the supernova remnant 0540-693. Exposures in blue and red broadband filters made with the CTIO 4 m telescope and prime focus CCD show a center-brightened but clearly extended nebula about 4arcsec in diameter (FWHM), while an image in an [O III] filter shows an 8arcsec diameter shell (as reported earlier) which encloses the continuum source. 0540-693 is a system very similar to the Crab nebula and represents the second detection of optical synchrotron radiation in a supernova remnant.

  2. On the Extended Emission of the Anomalous X-ray Pulsar IE 1547.0-5408

    NASA Technical Reports Server (NTRS)

    Olausen, S. A.; Kaspi, V. M.; Ng, C. -Y.; Zhu, W. W.; Gavriil, F. P.; Woods, P. M.

    2012-01-01

    We present an analysis of the extended emission around the anomalous X-ray pulsar IE 1547.0-5408 using four XMM-Newton observations taken with the source in varying states of outburst as well as in quiescence. We find that the extended emission flux is highly variable and strongly correlated with the flux of the magnetar. Based on this result, as well as on spectral and energetic considerations, we conclude that the extended emission is dominated by a dust-scattering halo and not a pulsar wind nebula (P-VVN), as has been previously argued. We obtain an upper limit on the 2-10 keV flux of a possible PWN of 4.7 x 10(exp -14) erg/s/sq cm, three times less than the previously claimed value, implying an efficiency for conversion of spin-down energy into nebular luminosity of <9 x 10(exp -4) .

  3. EXTraS discovery of an 1.2-s X-ray pulsar in M 31

    NASA Astrophysics Data System (ADS)

    Esposito, P.; Israel, G. L.; Belfiore, A.; Novara, G.; Sidoli, L.; Rodríguez Castillo, G. A.; De Luca, A.; Tiengo, A.; Haberl, F.; Salvaterra, R.; Read, A. M.; Salvetti, D.; Sandrelli, S.; Marelli, M.; Wilms, J.; D'Agostino, D.

    2016-03-01

    During a search for coherent signals in the X-ray archival data of XMM-Newton, we discovered a modulation at 1.2 s in 3XMM J004301.4+413017 (3X J0043), a source lying in the direction of an external arm of M 31. This short period indicates a neutron star (NS). Between 2000 and 2013, the position of 3X J0043 was imaged by public XMM-Newton observations 35 times. The analysis of these data allowed us to detect an orbital modulation at 1.27 d and study the long-term properties of the source. The emission of the pulsar was rather hard (most spectra are described by a power law with Γ < 1) and, assuming the distance to M 31, the 0.3-10 keV luminosity was variable, from ˜3 × 1037 to 2 × 1038 erg s-1. The analysis of optical data shows that, while 3X J0043 is likely associated to a globular cluster in M 31, a counterpart with V ≳ 22 outside the cluster cannot be excluded. Considering our findings, there are two main viable scenarios for 3X J0043: a peculiar low-mass X-ray binary, similar to 4U 1822-37 or 4U 1626-67, or an intermediate-mass X-ray binary resembling Her X-1. Regardless of the exact nature of the system, 3X J0043 is the first accreting NS in M 31 in which the spin period has been detected.

  4. DETECTION OF ACCRETION X-RAYS FROM QS Vir: CATACLYSMIC OR A LOT OF HOT AIR?

    SciTech Connect

    Matranga, Marco; Drake, Jeremy J.; Kashyap, Vinay; Steeghs, Danny

    2012-03-10

    An XMM-Newton observation of the nearby 'pre-cataclysmic' short-period (P{sub orb} = 3.62 hr) binary QS Vir (EC 13471-1258) revealed regular narrow X-ray eclipses when the white dwarf passed behind its M2-4 dwarf companion. The X-ray emission provides a clear signature of mass transfer and accretion onto the white dwarf. The low-resolution XMM-Newton EPIC spectra are consistent with a cooling flow model and indicate an accretion rate of M-dot = 1.7 Multiplication-Sign 10{sup -13} M{sub sun} yr{sup -1}. At 48 pc distant, QS Vir is then the second nearest accreting cataclysmic variable known, with one of the lowest accretion rates found to date for a non-magnetic system. To feed this accretion through a wind would require a wind mass-loss rate of M-dot {approx}2 Multiplication-Sign 10{sup -12} M{sub sun} yr{sup -1} if the accretion efficiency is of the order of 10%. Consideration of likely mass-loss rates for M dwarfs suggests this is improbably high and pure wind accretion unlikely. A lack of accretion disk signatures also presents some difficulties for direct Roche lobe overflow. We speculate that QS Vir is on the verge of Roche lobe overflow, and that the observed mass transfer could be supplemented by upward chromospheric flows on the M dwarf, analogous to spicules and mottles on the Sun, that escape the Roche surface to be subsequently swept up into the white dwarf Roche lobe. If so, QS Vir would be in a rare evolutionary phase lasting only a million years. The X-ray luminosity of the M dwarf estimated during primary eclipse is L{sub X} = 3 Multiplication-Sign 10{sup 28} erg s{sup -1}, which is consistent with that of rapidly rotating 'saturated' K and M dwarfs.

  5. Probing the Evolving X-ray Sources of Accreting Black Holes

    NASA Astrophysics Data System (ADS)

    Wilkins, Dan

    2013-04-01

    Material spiralling into black holes powers some of the most luminous objects we see in the Unviverse; AGN and galactic black hole binaries. X-rays are emitted from a corona of energetic particles around the black hole and are seen to reflect off of the accretion disc. As well as being impressive objects in their own right, the black holes in AGN can emit such large amounts of energy that they are important in governing the growth of galaxies and clusters. Through detailed analysis of the observed reflection features in the X-ray spectrum and the variability of the detected emission showing reverberation time lags between the directly observed continuum and the reflection, it is possible to detect the emission from material right down to the innermost stable orbit around the black hole. Comparing these observations to the results of general relativistic ray tracing simulations allows them to be analysed in the context of the geometry of the X-ray emitting region and it has been possible to constrain the locations of the X-ray sources in a number of AGN including 1H 0707-495, IRAS 13224-3809 and MCG-6-30-15. With high quality data from long X-ray observations of these sources, it has, for the first time, been possible to follow the evolution of the coronal X-ray source as the luminosity of the source goes up and down. We are able to find evidence that the size and other properties of the X-ray source changes on the timescale of a few hours, giving rise to the extreme variability seen in these sources with the source increasing in size as the luminosity increases. Such detailed analysis of observations (both of spectra and variability) and studies of how the X-ray source is changing is paving the way to the science that will be possible with the next generation of X-ray instruments (NuStar and Astro-H) and will allow us to understand the processes at work in the innermost regions of accretion black holes, releasing energy from the accretion flow to power some of the

  6. X-ray emission properties of the old pulsar PSR B2224+65

    NASA Astrophysics Data System (ADS)

    Hui, C. Y.; Becker, W.

    2007-06-01

    Using archival Chandra data we studied the X-ray emission properties of PSR B2224+65 and its environment. Albeit limited by photon statistics the spectral analysis suggests that the bulk of the emission from PSR B2224+65 is non-thermal. Fitting a power-law model to the observed energy spectrum yields a photon index of Γ=1.58+0.43-0.33. The possible origin of the non-thermal pulsar emission is discussed in the context of the outer-gap model. We did not find any evidence for a compact nebula around PSR B2224+65 though the Chandra data reveal the existence of an extended feature which appears to be associated with PSR B2224+65. It extends from the pulsar position about 2 arcmin to the north-west. Its orientation deviates by ˜118° from the pulsar's proper motion direction. Investigating its energy spectrum shows that the emission of this extended feature is much harder than that of the pulsar itself and is non-thermal in nature.

  7. Flares from Galactic Centre pulsars: a new class of X-ray transients?

    NASA Astrophysics Data System (ADS)

    Giannios, Dimitrios; Lorimer, Duncan R.

    2016-06-01

    Despite intensive searches, the only pulsar within 0.1 pc of the central black hole in our Galaxy, Sgr A*, is a radio-loud magnetar. Since magnetars are rare among the Galactic neutron star population, and a large number of massive stars are already known in this region, the Galactic Centre (GC) should harbour a large number of neutron stars. Population syntheses suggest several thousand neutron stars may be present in the GC. Many of these could be highly energetic millisecond pulsars which are also proposed to be responsible for the GC gamma-ray excess. We propose that the presence of a neutron star within 0.03 pc from Sgr A* can be revealed by the shock interactions with the disc around the central black hole. As we demonstrate, these interactions result in observable transient non-thermal X-ray and gamma-ray emission over time-scales of months, provided that the spin-down luminosity of the neutron star is Lsd ˜ 1035 erg s-1. Current limits on the population of normal and millisecond pulsars in the GC region suggest that a number of such pulsars are present with such luminosities.

  8. X-Ray Spectra of Young Pulsars and Their Wind Nebulae: Dependence on Spin-Down Energy Loss Rate

    NASA Technical Reports Server (NTRS)

    Gotthelf, E. V.

    2003-01-01

    An observational model is presented for the spectra of young rotation-powered pulsars and their nebulae based on a study of nine bright Crab-like pulsar systems observed with the Chandra X-ray observatory. A significant correlation is discovered between the X-ray spectra of these pulsars and that of their associated pulsar wind nebulae, both of which are observed to be a function of the spin-down energy loss rate, E. The 2-10 keV spectra of these objects are well characterized by an absorbed power-law model with photon indices, Gamma, in the range of 0.6 < Gamma (sub PSR) < 2.1 and 1.3 < Gamma(sub PWN) < 2.3, for the pulsars and their nebulae, respectively. A linear regression fit relating these two sets of indexes yields Gamma(sub PWN) = 0.91 +/- 0.18 + (0.66 +/- 0.11) Gamma (sub PSR), with a correlation coefficient of r = 0.97. The spectra of these pulsars are found to steepen as Gamma = Gamma(sub max) + alpha E (exp -1/2), with Gamma(sub max) providing an observational limit on the spectral slopes of young rotation-powered pulsars. These results reveal basic properties of young pulsar systems, allow new observational constraints on models of pulsar wind emission, and provide a means of predicting the energetics of pulsars lacking detected pulsations.

  9. Pulsed Thermal Emission from the Accreting Pulsar XMMU J054134.7-682550

    NASA Astrophysics Data System (ADS)

    Manousakis, Antonis; Walter, Roland; Audard, Marc; Lanz, Thierry

    2009-05-01

    XMMU J054134.7-682550, located in the LMC, featured a type II outburst in August 2007. We analyzed XMM-Newton (EPIC-MOS) and RXTE (PCA) data in order to derive the spectral and temporal characteristics of the system throughout the outburst. Spectral variability, spin period evolution, energy dependent pulse shape are discussed. The outburst (LX~3×1038 erg/s~LEDD) spectrum can be modeled using, cutoff power law, soft X-ray blackbody, disk emission, and cyclotron absorption line. The blackbody component shows a sinusoidal behavior, expected from hard X-ray reprocessing on the inner edge of the accretion disk. The thickness of the inner accretion disk (width of ~75 km) can be constrained. The spin-up of the pulsar during the outburst is the signature of a (huge) accretion rate. Simbol-X will provide similar capabilities as XMM-Newton and RXTE together, for such bright events.

  10. Unveiling slim accretion disc in AGN through X-ray and Infrared observations

    NASA Astrophysics Data System (ADS)

    Castelló-Mor, Núria; Kaspi, Shai; Netzer, Hagai; Du, Pu; Hu, Chen; Ho, Luis C.; Bai, Jin-Ming; Bian, Wei-Hao; Yuan, Ye-Fei; Wang, Jian-Min

    2017-01-01

    In this work, which is a continuation of Castello-Mor et al. (2016), we present new X-ray and infrared (IR) data for a sample of active galactic nuclei (AGN) covering a wide range in Eddington ratio over a small luminosity range. In particular, we rigorously explore the dependence of the optical-to-X-ray spectral index αOX and the IR-to-optical spectral index on the dimensionless accretion rate, dot{M}=dot{m}/η where dot{m}=LAGN/LEdd and η is the mass-to-radiation conversion efficiency, in low and high accretion rate sources. We find that the SED of the faster accreting sources are surprisingly similar to those from the comparison sample of sources with lower accretion rate. In particular: I) the optical-to-UV AGN SED of slow and fast accreting AGN can be fitted with thin AD models. II) The value of αOX is very similar in slow and fast accreting systems up to a dimensionless accretion rate dot{M}c ˜10. We only find a correlation between αOX and dot{M} for sources with dot{M}>dot{M}c. In such cases, the faster accreting sources appear to have systematically larger αOX values. III) We also find that the torus in the faster accreting systems seems to be less efficient in reprocessing the primary AGN radiation having lower IR-to-optical spectral slopes. These findings, failing to recover the predicted differences between the SEDs of slim and thin ADs within the observed spectral window, suggest that additional physical processes or very special geometry act to reduce the extreme UV radiation in fast accreting AGN. This may be related to photon trapping, strong winds, and perhaps other yet unknown physical processes.

  11. Black holes in short period X-ray binaries and the transition to radiatively inefficient accretion

    NASA Astrophysics Data System (ADS)

    Knevitt, G.; Wynn, G. A.; Vaughan, S.; Watson, M. G.

    2014-02-01

    By comparing the orbital period distributions of black hole and neutron star low-mass X-ray binaries (LMXBs) in the Ritter-Kolb catalogue we show that there is statistical evidence for a dearth of black hole systems at short orbital periods (Porb < 4 h). This could either be due to a true divergence in orbital period distributions of these two types of system, or to black hole LMXBs being preferentially hidden from view at short orbital periods. We explore the latter possibility, by investigating whether black hole LMXBs could be concealed by a switch to radiatively inefficient accretion at low luminosities. The peak luminosity and the duration of X-ray binary outbursts are related to the disc radius and, hence, the orbital period. At short periods, where the peak outburst luminosity drops close to the threshold for radiatively inefficient accretion, black hole LMXBs have lower outburst luminosities, shorter outburst durations and lower X-ray duty cycles than comparable neutron star systems. These factors can combine to severely reduce the detection probability of short period black hole LMXBs relative to those containing neutron stars. We estimate the outburst properties and orbital period distribution of black hole LMXBs using two models of the transition to radiatively inefficient accretion: an instantaneous drop in accretion efficiency (η) to zero, at a fraction (f) of the Eddington luminosity (LEdd) and a power-law efficiency decrease, η ∝ dot{M}^n, for L < f LEdd. We show that a population of black hole LMXBs at short orbital periods can only be hidden by a sharp drop in efficiency, either instantaneous or for n ≳ 3. This could be achieved by a genuine drop in luminosity or through abrupt spectral changes that shift the accretion power out of a given X-ray band.

  12. EXPLAINING THE EARLY EXIT OF ETA CARINAE FROM ITS 2009 X-RAY MINIMUM WITH THE ACCRETION MODEL

    SciTech Connect

    Kashi, Amit; Soker, Noam E-mail: soker@physics.technion.ac.il

    2009-08-10

    We use the accretion model to explain the early exit of {eta} Car from its 2009 X-ray minimum. In the accretion model, the secondary star accretes mass from the primary wind near periastron passage, a process that suppresses the secondary wind. As the shocked secondary wind is responsible for most of the X-ray emission, the accretion process accounts for the X-ray minimum. The early exit from the 2009 X-ray minimum after four weeks, instead of 10 weeks as in the two previous minima, is attributed to the primary wind that during the last minimum was somewhat faster and of lower mass-loss rate than during the two previous X-ray minima. This results in a much lower mass accretion rate during the X-ray minimum. We show that using fluctuations in these quantities that are within the range deduced from fluctuations in the X-ray flux outside the minimum, can account for the short duration of the last X-ray minimum. The shorter X-ray minimum may have further implications on the recovery of the system from the spectroscopic event.

  13. X-ray Reflected Spectra from Accretion Disk Models. II. Diagnostic Tools for X-ray Observations

    NASA Astrophysics Data System (ADS)

    García, J.; Kallman, T. R.; Mushotzky, R. F.

    2011-04-01

    We present a comprehensive study of the emission spectra from accreting sources. We use our new reflection code to compute the reflected spectra from an accretion disk illuminated by X-rays. This set of models covers different values of ionization parameter, solar iron abundance, and photon index for the illuminating spectrum. These models also include the most complete and recent atomic data for the inner shell of the iron and oxygen isonuclear sequences. We concentrate our analysis on the 2-10 keV energy region and in particular on the iron K-shell emission lines. We show the dependency of the equivalent width (EW) of the Fe Kα on the ionization parameter. The maximum value of the EW is ~800 eV for models with log ξ ~ 1.5 and decreases monotonically as ξ increases. For lower values of ξ, the Fe Kα EW decreases to a minimum near log ξ ~ 0.8. We produce simulated CCD observations based on our reflection models. For low-ionized, reflection-dominated cases, the 2-10 keV energy region shows a very broad, curving continuum that cannot be represented by a simple power law. We show that in addition to the Fe K-shell emission, there are other prominent features such as the Si and S Lα lines, a blend of Ar VIII-XI lines, and the Ca X Kα line. In some cases, the S XV blends with the He-like Si radiative recombination continua producing a broad feature that cannot be reproduced by a simple Gaussian profile. This could be used as a signature of reflection.

  14. X-RAY REFLECTED SPECTRA FROM ACCRETION DISK MODELS. II. DIAGNOSTIC TOOLS FOR X-RAY OBSERVATIONS

    SciTech Connect

    GarcIa, J.; Kallman, T. R.; Mushotzky, R. F. E-mail: timothy.r.kallman@nasa.gov

    2011-04-20

    We present a comprehensive study of the emission spectra from accreting sources. We use our new reflection code to compute the reflected spectra from an accretion disk illuminated by X-rays. This set of models covers different values of ionization parameter, solar iron abundance, and photon index for the illuminating spectrum. These models also include the most complete and recent atomic data for the inner shell of the iron and oxygen isonuclear sequences. We concentrate our analysis on the 2-10 keV energy region and in particular on the iron K-shell emission lines. We show the dependency of the equivalent width (EW) of the Fe K{alpha} on the ionization parameter. The maximum value of the EW is {approx}800 eV for models with log {xi} {approx} 1.5 and decreases monotonically as {xi} increases. For lower values of {xi}, the Fe K{alpha} EW decreases to a minimum near log {xi} {approx} 0.8. We produce simulated CCD observations based on our reflection models. For low-ionized, reflection-dominated cases, the 2-10 keV energy region shows a very broad, curving continuum that cannot be represented by a simple power law. We show that in addition to the Fe K-shell emission, there are other prominent features such as the Si and S L{alpha} lines, a blend of Ar VIII-XI lines, and the Ca X K{alpha} line. In some cases, the S XV blends with the He-like Si radiative recombination continua producing a broad feature that cannot be reproduced by a simple Gaussian profile. This could be used as a signature of reflection.

  15. X-Ray Reflected Spectra from Accretion Disk Models. II. Diagnostic Tools for X-Ray Observations

    NASA Technical Reports Server (NTRS)

    Garcia, J.; Kallman, T. R.; Mushotzky, R. F.

    2011-01-01

    We present a comprehensive study of the emission spectra from accreting sources. We use our new reflection code to compute the reflected spectra from an accretion disk illuminated by X-rays. This set of models covers different values of ionization parameter, solar iron abundance and photon index for the illuminating spectrum. These models also include the most complete and recent atomic data for the inner-shell of the iron and oxygen isonuclear sequences. We concentrate our analysis to the 2 - 10 keV energy region, and in particular to the iron K-shell emission lines. We show the dependency of the equivalent width (EW) of the Fe Ka with the ionization parameter. The maximum value of the EW is approx. 800 eV for models with log Epsilon approx. 1.5, and decreases monotonically as Epsilon increases. For lower values of Epsilon the Fe K(alpha) EW decreases to a minimum near log Epsilon approx. 0.8. We produce simulated CCD observations based on our reflection models. For low ionized, reflection dominated cases, the 2 -10 keV energy region shows a very broad, curving continuum that cannot be represented by a simple power-law. We show that in addition to the Fe K-shell emission, there are other prominent features such as the Si and S L(alpha) lines, a blend of Ar VIII-XI lines, and the Ca x K(alpha) line. In some cases the S xv blends with the He-like Si RRC producing a broad feature that cannot be reproduced by a simple Gaussian profile. This could be used as a signature of reflection.

  16. Luminosity-dependent change of the emission diagram in the X-ray pulsar 4U 1626-67

    NASA Astrophysics Data System (ADS)

    Koliopanos, Filippos; Gilfanov, Marat

    2016-03-01

    We detect variability of the Fe K α emission line in the spectrum of X-ray pulsar 4U 1626-67, correlated with changes in its luminosity and in the shape of its pulse profile. Analysis of archival Chandra and RXTE observations revealed the presence of an intrinsically narrow Fe K α emission line in the spectrum obtained during the source's current high-luminosity period. However, the line was not present during an XMM-Newton observation seven years earlier, when the source was ˜three times fainter. The line is resolved by the high-energy grating of Chandra at the 98 per cent confidence level, and its small intrinsic width, σ =36.4_{-11.3}^{+15.3} eV, suggests reflection off an accretion disc at the radius R≈ (7.5_{-3.8}^{+8.2})× 10^8 cm assuming a Keplerian disk, viewed at an inclination angle of 20°. This value is consistent with the radius of the magnetosphere of the pulsar, suggesting that the line originates near the inner edge of a disc that is truncated by the magnetic field of the neutron star. Timing analysis of the XMM-Newton and RXTE data revealed a major change in the pulse profile of the source from a distinct double-peaked shape during the high-luminosity state when the line was present, to a much more complex multipeak structure during the low-luminosity state. We argue that the appearance of the line and the change in the shape of the pulse profile are correlated and are the result of a major change in the emission diagram of the accretion column, from a pencil-beam pattern at low luminosity, to a fan-beam pattern at high luminosity.

  17. Spectroscopy of Low Mass X-Ray Binaries: New Insights into Accretion

    NASA Technical Reports Server (NTRS)

    DilVrtilek, Saeqa; Mushotsky, Richard (Technical Monitor)

    2004-01-01

    This project is to observe two low mass X-ray binaries, chosen for their X-ray brightness, low column density, and diversity of accretion behavior. The high spectral resolution of the RGS, the broad energy range and tremendous collecting power of EPIC, and simultaneous optical monitoring with the OM are particularly well-suited to these studies. The second of two objects was observed on September of 2002. Data analysis for both observation has been completed: an investigation of the physical conditions of the emitting gas using emission and recombination line diagnostics to determine temperatures, densities, elemental abundances, and ionization structure. A study of behavior of the emission features as a function of binary orbit shows modulated behavior in one of the systems. A paper on "High-resolution observations of low-mass X-ray binaries" is near completion. The paper includes observations with the Chandra HETG that are not yet completed.

  18. X-ray reflection from black-hole accretion discs with a radially stratified ionisation

    NASA Astrophysics Data System (ADS)

    Svoboda, J.; Domcek, V.; Dovčiak, M.; Guainazzi, M.; Marinucci, A.

    2015-07-01

    Recent X-ray observations have suggested a very high compactness of coronae in Active Galactic Nuclei as well as in X-ray Binaries. The compactness of the source implies that the black-hole accretion disc irradiation is a strong function of radius. We will show how the X-ray spectra are modified assuming the radially stratified ionisation according to the illumination by a point-like source on the black-hole rotational axis. We will discuss how this affects the measurements of the other model parameters, such as spin and radial emissivity. We will show the application of this model to the recent XMM-Newton/NUSTAR data of an active galaxy MCG-6-30-15.

  19. Interpreting the radio/X-ray correlation of black hole X-ray binaries based on the accretion-jet model

    NASA Astrophysics Data System (ADS)

    Xie, Fu-Guo; Yuan, Feng

    2016-03-01

    Two types of correlations between the radio and X-ray luminosities (LR and LX) have been found in black hole X-ray binaries. For some sources, they follow the `original' type of correlation which is described by a single power law. Later it was found that some other sources follow a different correlation consisting of three power-law branches, with each branch having different power-law indexes. In this work, we explain these two types of correlation under the coupled accretion-jet model. We attribute the difference between these two types of sources to the different value of viscosity parameter α. One possible reason for different α is the different configuration of magnetic field in the accretion material coming from the companion stars. For the `single power-law' sources, their α is high; so their accretion is always in the mode of advection-dominated accretion flow (ADAF) for the whole range of X-ray luminosity. For those `hybrid power-law' sources, the value of α is small so their accretion mode changes from an ADAF to a luminous hot accretion flow, and eventually to two-phase accretion as the accretion rate increases. Because the dependence of radiative efficiency on the mass accretion rate is different for these three accretion modes, different power-law indexes in the LR-LX correlation are expected. Constraints on the ratio of the mass-loss rate into the jet and the mass accretion rate in the accretion flow are obtained, which can be tested in future by radiative magnetohydrodynamic numerical simulations of jet formation.

  20. ANISOTROPY OF X-RAY BURSTS FROM NEUTRON STARS WITH CONCAVE ACCRETION DISKS

    SciTech Connect

    He, C.-C.; Keek, L.

    2016-03-01

    Emission from neutron stars and accretion disks in low-mass X-ray binaries is anisotropic. The non-spherical shape of the disk as well as blocking of the neutron star by the disk make the observed flux dependent on the inclination angle of the disk with respect to the line of sight. This is of importance for the interpretation of thermonuclear X-ray bursts from neutron stars. Because part of the X-ray burst is reflected off the disk, the observed burst flux depends on the anisotropies for both direct emission from the neutron star and reflection off the disk. This influences measurements of source distance, mass accretion rate, and constraints on the neutron star’s equation of state. Previous predictions of the anisotropy factors assumed a geometrically flat disk. Detailed observations of two so-called superbursts allowed for the direct and the reflected burst fluxes to each be measured separately. The reflection fraction was much higher than what the anisotropies of a flat disk can account for. We create numerical models to calculate the anisotropy factors for different disk shapes, including concave disks. We present the anisotropy factors of the direct and reflected burst fluxes separately, as well as the anisotropy of the persistent flux. Reflection fractions substantially larger than unity are produced in the case where the inner accretion disk increases steeply in height, such that part of the star is blocked from view. Such a geometry could possibly be induced by the X-ray burst if X-ray heating causes the inner disk to puff up.

  1. Population synthesis of accreting white dwarfs - II. X-ray and UV emission

    NASA Astrophysics Data System (ADS)

    Chen, Hai-Liang; Woods, T. E.; Yungelson, L. R.; Gilfanov, M.; Han, Zhanwen

    2015-11-01

    Accreting white dwarfs (WDs) with non-degenerate companions are expected to emit in soft X-rays and the UV, if accreted H-rich material burns stably. They are an important component of the unresolved emission of elliptical galaxies, and their combined ionizing luminosity may significantly influence the optical line emission from warm interstellar medium (ISM). In an earlier paper, we modelled populations of accreting WDs, first generating WD with main-sequence, Hertzsprung gap and red giant companions with the population synthesis code BSE, and then following their evolution with a grid of evolutionary tracks computed with MESA. Now we use these results to estimate the soft X-ray (0.3-0.7 keV), H- and He II-ionizing luminosities of nuclear burning WDs and the number of supersoft X-ray sources for galaxies with different star formation histories. For the starburst case, these quantities peak at ˜1 Gyr and decline by ˜1-3 orders of magnitude by the age of 10 Gyr. For stellar ages of ˜10 Gyr, predictions of our model are consistent with soft X-ray luminosities observed by Chandra in nearby elliptical galaxies and He II 4686 Å/H β line ratio measured in stacked Sloan Digital Sky Survey spectra of retired galaxies, the latter characterizing the strength and hardness of the UV radiation field. However, the soft X-ray luminosity and He II 4686 Å/H β ratio are significantly overpredicted for stellar ages of ≲4-8 Gyr. We discuss various possibilities to resolve this discrepancy and tentatively conclude that it may be resolved by a modification of the typically used criteria of dynamically unstable mass-loss for giant stars.

  2. Chandra X-Ray Observations of 19 Millisecond Pulsars in the Globular Cluster 47 Tucanae

    NASA Astrophysics Data System (ADS)

    Bogdanov, Slavko; Grindlay, Jonathan E.; Heinke, Craig O.; Camilo, Fernando; Freire, Paulo C. C.; Becker, Werner

    2006-08-01

    We present spectral and long-timescale variability analyses of Chandra X-Ray Observatory ACIS-S observations of the 19 millisecond pulsars (MSPs) with precisely known positions in the globular cluster 47 Tucanae. The X-ray emission of the majority of these MSPs is well described by a thermal (blackbody or neutron star hydrogen atmosphere) spectrum with a temperature Teff~(1-3)×106 K, emission radius Reff~0.1-3 km, and luminosity LX~1030-1031 ergs s-1. For several MSPs, there are indications that a second thermal component is required, similar to what is seen in some nearby field MSPs. The observed radiation most likely originates from the heated magnetic polar caps of the MSPs. The small apparent scatter in LX is consistent with thermal emission from the polar caps of a global dipole field, although the small emission areas may imply either a more complex small-scale magnetic field configuration near the neutron star surface or nonuniform polar cap heating. The radio eclipsing binary MSPs 47 Tuc J, O, and W show a significant nonthermal (power-law) component, with spectral photon index Γ~1-1.5, which most likely originates in an intrabinary shock formed due to interaction between the relativistic pulsar wind and matter from the stellar companion. We reexamine the X-ray-spin-down luminosity relation (LX-E˙ relation) and find that for the MSPs with thermal spectra LX~E˙β, where β~0.2+/-1.1. Due to the large uncertainties in both parameters, the result is consistent with both the linear LX-E˙ relation and the flatter LX~E˙0.5 predicted by polar cap heating models. In terms of X-ray properties, we find no clear systematic differences between MSPs in globular clusters and in the field of the Galaxy. We discuss the implications of these results on the present understanding of the X-ray emission properties of MSPs.

  3. X-ray accretion signatures in the close CTTS binary V4046 Sagittarii

    NASA Astrophysics Data System (ADS)

    Günther, H. M.; Liefke, C.; Schmitt, J. H. M. M.; Robrade, J.; Ness, J.-U.

    2006-11-01

    We present Chandra HETGS observations of the classical T Tauri star (CTTS) V4046 Sgr. The He-like triplets of O VII, Ni IX, and Si XIII are clearly detected. Similar to the CTTS TW Hya and BP Tau, the forbidden lines of O VII and Ne IX are weak compared to the intercombination line, indicating high plasma densities in the X-ray emitting regions. The Si XIII triplet, however, is within the low-density limit, in agreement with the predictions of the accretion funnel infall model with an additional stellar corona. V4046 Sgr is the first close binary exhibiting these features. Together with previous high-resolution X-ray data on TW Hya and BP Tau, and in contrast to T Tau, now three out of four CTTS show evidence of accretion funnels.

  4. Restablished Accretion in Post-outburst Classical Novae Revealed by X-rays

    NASA Astrophysics Data System (ADS)

    Hernanz, Margarita; Ferri, Carlo; Sala, Glòria

    2009-05-01

    Classical novae are explosions on accreting white dwarfs (hereinafter WDs) in cataclysmic variables (hereinafter CVs) a hydrogen thermonuclear runaway on top of the WD is responsible for the outburst. X-rays provide a unique way to study the turn-off of H-burning, because super soft X-rays reveal the hot WD photosphere, but also to understand how accretion is established again in the binary system. Observations with XMM-Newton of some post-outburst novae have revealed such a process, but a coverage up to larger energies -as Simbol-X will provide- is fundamental to well understand the characteristics of the binary system and of the nova ejecta. We present a brief summary of our results up to now and prospects for the Simbol-X mission.

  5. Information about accretion flows from X-ray timing of pulsating sources

    NASA Technical Reports Server (NTRS)

    Lamb, F. K.; Pines, D.; Shaham, J.

    1976-01-01

    The response was studied of a rotating neutron star to fluctuating torques and it was found that the observed variations in the pulsation periods of the compact X-ray sources Cen X-3 and Her X-1 could be caused by short time scale fluctuations in the accretion torques acting on the neutron stars. The sizes and rates of the required fluctuations are consistent with current accretion models. Such fluctuations can cause period variations either (a) directly, by causing a random walk of the star's angular velocity or (b) indirectly, by exciting a long-period mode of the neutron star, such as the Tkachenko mode of the rotating neutron superfluid. Phenomena in compact X-ray sources and cataclysmic variables which may be caused by fluctuating mass flow rates are also discussed.

  6. X-ray Reflected Spectra from Accretion Disk Models. I. Constant Density Atmospheres

    NASA Technical Reports Server (NTRS)

    Garcia, Javier; Kallman, Timothy R.

    2009-01-01

    We present new models for illuminated accretion disks, their structure and reprocessed emission. We consider the effects of incident X-rays on the surface of an accretion disk by solving simultaneously the equations of radiative transfer, energy balance and ionization equilibrium over a large range of column densities. We assume plane-parallel geometry and azimuthal symmetry, such that each calculation corresponds to a ring at a given distance from the central object. Our models include recent and complete atomic data for K-shell of the iron and oxygen isonuclear sequences. We examine the effect on the spectrum of fluorescent Ka line emission and absorption in the emitted spectrum. We also explore the dependence of the spectrum on the strength of the incident X-rays and other input parameters, and discuss the importance of Comptonization on the emitted spectrum.

  7. DISCOVERY OF X-RAY PULSATION FROM THE GEMINGA-LIKE PULSAR PSR J2021+4026

    SciTech Connect

    Lin, L. C. C.; Hui, C. Y.; Seo, K. A.; Hu, C. P.; Chou, Y.; Wu, J. H. K.; Huang, R. H. H.; Trepl, L.; Takata, J.; Wang, Y.; Cheng, K. S.

    2013-06-10

    We report the discovery of an X-ray periodicity of {approx}265.3 ms from a deep XMM-Newton observation of the radio-quiet {gamma}-ray pulsar, PSR J2021+4026, located at the edge of the supernova remnant G78.2+2.1 ({gamma}-Cygni). The detected frequency is consistent with the {gamma}-ray pulsation determined by the observation of the Fermi Gamma-ray Space Telescope at the same epoch. The X-ray pulse profile resembles the modulation of a hot spot on the surface of the neutron star. The phase-averaged spectral analysis also suggests that the majority of the observed X-rays have thermal origins. This is the third member in the class of radio-quiet pulsars with significant pulsations detected from both X-ray and {gamma}-ray regimes.

  8. HST UV observations of the accretion disk corona X-ray binary X1822-371

    NASA Technical Reports Server (NTRS)

    Puchnarewicz, E. M.; Mason, K. O.; Cordova, F. A.

    1995-01-01

    The Faint Object Spectrograph (FOS) on the Hubble Space Telescope (HST) has provided the first ultraviolet orbital light curve of the low-mass X-ray binary X1822-371. The shape of the UV light curve changes with wavelength providing the first direct clues to the temperature of the various system components. The data support the idea that the system contains a thick, structured accretion disk.

  9. Black hole accretion rings revealed by future X-ray spectroscopy

    NASA Astrophysics Data System (ADS)

    Sochora, V.; Karas, V.; Svoboda, J.; Dovčiak, M.

    2011-11-01

    Spectral features can arise by reflection of coronal X-rays on a black hole accretion disc. The resulting profile bears various imprints of a strong gravitational field acting on the light-emitting gas. The observed shape of the reflection line is formed by integrating contributions over a range of radii across the accretion disc plane, where the individual photons experience a different level of energy shifts, boosting and amplification by relativistic effects. These have to be convolved with the intrinsic emissivity of the line, which is a function of radius and the emission angle in the local frame. We study if the currently discussed instruments on-board X-ray satellites will be able to reveal the departure of the line radial emissivity from a simple smooth power-law function, which is often assumed in data fitting and its interpretation. Such a departure can be a result of excess emission occurring at a certain distance. This could be used to study variations with a radius of the line production or to constrain the position of the inner edge of the accretion disc. By simulating artificial data from a bright active galactic nucleus of a type 1 Seyfert galaxy (inclination ≃30°, X-ray flux ≃1-2 mCrab in a keV energy band) we show that the required sensitivity and energy resolution could be reached with a large area detector of the proposed Large Observatory for X-ray Timing mission. Galactic black holes will provide another category of potentially suitable targets if the relativistic spectral features are indeed produced by reflection from their accretion discs.

  10. EVIDENCE OF FAST MAGNETIC FIELD EVOLUTION IN AN ACCRETING MILLISECOND PULSAR

    SciTech Connect

    Patruno, A.

    2012-07-01

    The large majority of neutron stars (NSs) in low-mass X-ray binaries (LMXBs) have never shown detectable pulsations despite several decades of intense monitoring. The reason for this remains an unsolved problem that hampers our ability to measure the spin frequency of most accreting NSs. The accreting millisecond X-ray pulsar (AMXP) HETE J1900.1-2455 is an intermittent pulsar that exhibited pulsations at about 377 Hz for the first two months and then turned into a nonpulsating source. Understanding why this happened might help us to understand why most LMXBs do not pulsate. We present a seven-year coherent timing analysis of data taken with the Rossi X-ray Timing Explorer. We discover new sporadic pulsations that are detected on a baseline of about 2.5 years. We find that the pulse phases anti-correlate with the X-ray flux as previously discovered in other AMXPs. We place stringent upper limits of 0.05% rms on the pulsed fraction when pulsations are not detected and identify an enigmatic pulse phase drift of {approx}180 Degree-Sign in coincidence with the first disappearance of pulsations. Thanks to the new pulsations we measure a long term spin frequency derivative whose strength decays exponentially with time. We interpret this phenomenon as evidence of magnetic field burial.

  11. The Orbital Period of the Accreting Pulsar GX 1+4.

    PubMed

    Pereira; Braga; Jablonski

    1999-12-01

    We report strong evidence for a approximately 304 day periodicity in the spin history of the accretion-powered pulsar GX 1+4 that is most probably associated with the orbital period of the system. We have used data from the Burst and Transient Source Experiment on the Compton Gamma-Ray Observatory to show a clear periodic modulation of the pulsar frequency from 1991 to date, in excellent agreement with the ephemeris proposed by Cutler, Dennis, & Dolan in 1986. Our results indicate that the orbital period of GX 1+4 is 303.8+/-1.1 days, making it the widest known low-mass X-ray binary system by more than 1 order of magnitude and putting this long-standing question to rest. A likely scenario for this system is an elliptical orbit in which the neutron star decreases its spin-down rate (or even exhibits a momentary spin-up behavior) at periastron passages due to the higher torque exerted by the accretion disk onto the magnetosphere of the neutron star. These results are not inconsistent with either the X-ray pulsed flux light curve measured by BATSE during the same epoch or the X-ray flux history from the All-Sky Monitor on board the Rossi X-Ray Timing Explorer.

  12. An X-ray outburst from the rapidly accreting young star that illuminates McNeil's nebula.

    PubMed

    Kastner, J H; Richmond, M; Grosso, N; Weintraub, D A; Simon, T; Frank, A; Hamaguchi, K; Ozawa, H; Henden, A

    2004-07-22

    Young, low-mass stars are luminous X-ray sources whose powerful X-ray flares may exert a profound influence over the process of planet formation. The origin of the X-ray emission is uncertain. Although many (or perhaps most) recently formed, low-mass stars emit X-rays as a consequence of solar-like coronal activity, it has also been suggested that X-ray emission may be a direct result of mass accretion onto the forming star. Here we report X-ray imaging spectroscopy observations which reveal a factor approximately 50 increase in the X-ray flux from a young star that is at present undergoing a spectacular optical/infrared outburst (this star illuminates McNeil's nebula). The outburst seems to be due to the sudden onset of a phase of rapid accretion. The coincidence of a surge in X-ray brightness with the optical/infrared eruption demonstrates that strongly enhanced high-energy emission from young stars can occur as a consequence of high accretion rates. We suggest that such accretion-enhanced X-ray emission from erupting young stars may be short-lived, because intense star-disk magnetospheric interactions are quenched rapidly by the subsequent flood of new material onto the star.

  13. Time dependent spectrum of an X-ray irradiated accretion disc with stochastic perturbations

    NASA Astrophysics Data System (ADS)

    Maqbool, Bari; Wani, Naveel; Iqbal, Naseer; Misra, Ranjeev

    2016-07-01

    The X-rays emitted by the inner regions of the accretion disk induce structural changes in the outer regions of the disk. We study here how the effective temperature and hence the corresponding spectrum of the disk is altered by stochastic perturbations in the outer regions and thereby try to study the long term variability which has been observed in some X-ray binaries. We use a time dependent global hydrodynamic code to study the variations in the effective temperature of the disk in response to sinusoidal accretion rate perturbations introduced at different radii and with different time periods. To quantify the results, we calculate the root mean square effective temperature at different radii and the root mean square flux at different frequencies. From our calculations of the time-lags in accretion rate, effective temperature and the different frequencies, we find that the time-lags in presence of X-ray irradiation is significantly smaller than the expected viscous time-scale.

  14. Discovery of a Second Millisecond Accreting Pulsar: XTE J1751-305

    NASA Astrophysics Data System (ADS)

    Markwardt, C. B.; Swank, J. H.; Strohmayer, T. E.; in 't Zand, J. J. M.; Marshall, F. E.

    2002-08-01

    We report the discovery by the Rossi X-Ray Timing Explorer Proportional Counter Array of a second transient accreting millisecond pulsar, XTE J1751-305, during regular monitoring observations of the Galactic bulge region. The pulsar has a spin frequency of 435 Hz, making it one of the fastest pulsars. The pulsations contain the signature of orbital Doppler modulation, which implies an orbital period of 42 minutes, the shortest orbital period of any known radio or X-ray millisecond pulsar. The mass function, fX=(1.278+/-0.003)×10-6 Msolar, yields a minimum mass for the companion of between 0.013 and 0.017 Msolar, depending on the mass of the neutron star. No eclipses were detected. A previous X-ray outburst in 1998 June was discovered in archival All-Sky Monitor data. Assuming mass transfer in this binary system is driven by gravitational radiation, we constrain the orbital inclination to be in the range 30°-85° and the companion mass to be 0.013-0.035 Msolar. The companion is most likely a heated helium dwarf. We also present results from the Chandra High Resolution Camera-S observations, which provide the best-known position of XTE J1751-305.

  15. EXTENDED HARD X-RAY EMISSION FROM THE VELA PULSAR WIND NEBULA

    SciTech Connect

    Mattana, F.; Terrier, R.; Zurita Heras, J. A.; Goetz, D.; Caballero, I.; Soldi, S.; Schanne, S.; Ponti, G.; Falanga, M.; Renaud, M.

    2011-12-10

    The nebula powered by the Vela pulsar is one of the best examples of an evolved pulsar wind nebula, allowing access to the particle injection history and the interaction with the supernova ejecta. We report on the INTEGRAL discovery of extended emission above 18 keV from the Vela nebula. The northern side has no known counterparts and it appears larger and more significant than the southern one, which is in turn partially coincident with the cocoon, the soft X-ray, and TeV filament toward the center of the remnant. We also present the spectrum of the Vela nebula in the 18-400 keV energy range as measured by IBIS/ISGRI and SPI on board the INTEGRAL satellite. The apparent discrepancy between IBIS/ISGRI, SPI, and previous measurements is understood in terms of the point-spread function, supporting the hypothesis of a nebula more diffuse than previously thought. A break at {approx}25 keV is found in the spectrum within 6' from the pulsar after including the Suzaku XIS data. Interpreted as a cooling break, this points out that the inner nebula is composed of electrons injected in the last {approx}2000 years. Broadband modeling also implies a magnetic field higher than 10 {mu}G in this region. Finally, we discuss the nature of the northern emission, which might be due to fresh particles injected after the passage of the reverse shock.

  16. Discovery of a cyclotron absorption line in the spectrum of the binary X-ray pulsar 4U 1538 - 52 observed by Ginga

    NASA Technical Reports Server (NTRS)

    Clark, George W.; Woo, Jonathan W.; Nagase, Fumiaki; Makishima, Kazuo; Sakao, Taro

    1990-01-01

    A cyclotron absorption line near 20 keV has been found in the spectrum of the massive eclipsing binary X-ray pulsar 4U 1538 - 52 in observations with the Ginga observatory. The line is detected throughout the 529 s pulse cycle with a variable equivalent width that has its maximum value during the smaller peak of the two-peak pulse profile. It is found that the profile of the pulse and the phase-dependence of the cyclotron line can be explained qualitatively by a pulsar model based on recent theoretical results on the properties of pencil beams emitted by accretion-heated slabs of magnetized plasma at the magnetic poles of a neutron star. The indicated field at the surface of the neutron star is 1.7 (1 + z) x 10 to the 12th G, where z is the gravitational redshift.

  17. Soft X-Ray Excess from Shocked Accreting Plasma in Active Galactic Nuclei

    NASA Astrophysics Data System (ADS)

    Fukumura, Keigo; Hendry, Douglas; Clark, Peter; Tombesi, Francesco; Takahashi, Masaaki

    2016-08-01

    We propose a novel theoretical model to describe the physical identity of the soft X-ray excess that is ubiquitously detected in many Seyfert galaxies, by considering a steady-state, axisymmetric plasma accretion within the innermost stable circular orbit around a black hole (BH) accretion disk. We extend our earlier theoretical investigations on general relativistic magnetohydrodynamic accretion, which implied that the accreting plasma can develop into a standing shock under suitable physical conditions, causing the downstream flow to be sufficiently hot due to shock compression. We perform numerical calculations to examine, for sets of fiducial plasma parameters, the physical nature of fast magnetohydrodynamic shocks under strong gravity for different BH spins. We show that thermal seed photons from the standard accretion disk can be effectively Compton up-scattered by the energized sub-relativistic electrons in the hot downstream plasma to produce the soft excess feature in X-rays. As a case study, we construct a three-parameter Comptonization model of inclination angle θ obs, disk photon temperature kT in, and downstream electron energy kT e to calculate the predicted spectra in comparison with a 60 ks XMM-Newton/EPIC-pn spectrum of a typical radio-quiet Seyfert 1 active galactic nucleus, Ark 120. Our χ 2-analyses demonstrate that the model is plausible for successfully describing data for both non-spinning and spinning BHs with derived ranges of 61.3 keV ≲ kT e ≲ 144.3 keV, 21.6 eV ≲ kT in ≲ 34.0 eV, and 17.°5 ≲ θ obs ≲ 42.°6, indicating a compact Comptonizing region of three to four gravitational radii that resembles the putative X-ray coronae.

  18. PSR J0357+3205: A FAST-MOVING PULSAR WITH A VERY UNUSUAL X-RAY TRAIL

    SciTech Connect

    De Luca, A.; Mignani, R. P.; Marelli, M.; Salvetti, D.; Sartore, N.; Caraveo, P. A.; Bignami, G. F.; Belfiore, A.; Saz Parkinson, P.

    2013-03-01

    The middle-aged PSR J0357+3205 is a nearby, radio-quiet, bright {gamma}-ray pulsar discovered by the Fermi mission. Our previous Chandra observation revealed a huge, very peculiar structure of diffuse X-ray emission originating at the pulsar position and extending for >9' on the plane of the sky. To better understand the nature of such a nebula, we have studied the proper motion of the parent pulsar. We performed relative astrometry on Chandra images of the field spanning a time baseline of 2.2 yr, unveiling a significant angular displacement of the pulsar counterpart, corresponding to a proper motion of 0.''165 {+-} 0.''030 yr{sup -1} at a position angle (P.A.) of 314 Degree-Sign {+-} 8 Degree-Sign . At a distance of {approx}500 pc, the space velocity of the pulsar would be of {approx}390 km s{sup -1} assuming no inclination with respect to the plane of the sky. The direction of the pulsar proper motion is aligned very well with the main axis of the X-ray nebula (P.A. = 315. Degree-Sign 5 {+-} 1. Degree-Sign 5), pointing to a physical, yet elusive, link between the nebula and the pulsar space velocity. No optical emission in the H{alpha} line is seen in a deep image collected at the Gemini telescope, which implies that the interstellar medium into which the pulsar is moving is fully ionized.

  19. An unexpected drop in the magnetic field of the X-ray pulsar V0332+53 after the bright outburst occurred in 2015

    NASA Astrophysics Data System (ADS)

    Cusumano, G.; La Parola, V.; D'Aì, A.; Segreto, A.; Tagliaferri, G.; Barthelmy, S. D.; Gehrels, N.

    2016-07-01

    How the accreted mass settling on the surface of a neutron star affects the topology of the magnetic field and how the secular evolution of the binary system depends on the magnetic field change is still an open issue. We report evidence for a clear drop in the observed magnetic field in the accreting pulsar V0332+53 after undergoing a bright 3-month long X-ray outburst. We determine the field from the position of the fundamental cyclotron line in its X-ray spectrum and relate it to the luminosity. For equal levels of luminosity, in the declining phase we measure a systematically lower value of the cyclotron line energy with respect to the rising phase. This results in a drop of ˜1.7 × 1011 G of the observed field between the onset and the end of the outburst. The settling of the accreted plasma on to the polar cap seems to induce a distortion of the magnetic field lines weakening their intensity along the accretion columns. Therefore, the dissipation rate of the magnetic field could be much faster than previously estimated, unless the field is able to restore its original configuration on a time-scale comparable with the outbursts recurrence time.

  20. On the X-ray spectra of luminous, inhomogeneous accretion flows

    NASA Astrophysics Data System (ADS)

    Merloni, A.; Malzac, J.; Fabian, A. C.; Ross, R. R.

    2006-08-01

    We discuss the expected X-ray spectral and variability properties of black hole accretion discs at high luminosity, under the hypothesis that radiation-pressure-dominated discs are subject to violent clumping instabilities and, as a result, have a highly inhomogeneous two-phase structure. After deriving the full accretion disc solutions explicitly in terms of the parameters of the model, we study their radiative properties both with a simple two-zone model, treatable analytically, and with radiative transfer simulations which account simultaneously for energy balance and Comptonization in the hot phase, together with reflection, reprocessing, ionization and thermal balance in the cold phase. We show that, if not only the density, but also the heating rate within these flows is inhomogeneous, then complex reflection-dominated spectra can be obtained for a high enough covering fraction of the cold phase. In general, large reflection components in the observed X-ray spectra should be associated with strong soft excesses, resulting from the combined emission of ionized atomic emission lines. The variability properties of such systems are such that, even when contributing to a large fraction of the hard X-ray spectrum, the reflection component is less variable than the power-law-like emission originating from the hot Comptonizing phase, in agreement with what is observed in many Narrow Line Seyfert 1 galaxies and bright Seyfert 1. Our model falls within the family of those trying to explain the complex X-ray spectra of bright AGN with ionized reflection, but presents an alternative, specific, physically motivated, geometrical set-up for the complex multiphase structure of the inner regions of near-Eddington accretion flows.

  1. X-RAY SPECTRA FROM MAGNETOHYDRODYNAMIC SIMULATIONS OF ACCRETING BLACK HOLES

    SciTech Connect

    Schnittman, Jeremy D.; Krolik, Julian H.; Noble, Scott C. E-mail: jhk@pha.jhu.edu

    2013-06-01

    We present the results of a new global radiation transport code coupled to a general relativistic magnetohydrodynamic simulation of an accreting, non-rotating black hole. For the first time, we are able to explain from first principles in a self-consistent way all the components seen in the X-ray spectra of stellar-mass black holes, including a thermal peak and all the features associated with strong hard X-ray emission: a power law extending to high energies, a Compton reflection hump, and a broad iron line. Varying only the mass accretion rate, we are able to reproduce a wide range of X-ray states seen in most galactic black hole sources. The temperature in the corona is T{sub e} {approx} 10 keV in a boundary layer near the disk and rises smoothly to T{sub e} {approx}> 100 keV in low-density regions far above the disk. Even as the disk's reflection edge varies from the horizon out to Almost-Equal-To 6M as the accretion rate decreases, we find that the shape of the Fe K{alpha} line is remarkably constant. This is because photons emitted from the plunging region are strongly beamed into the horizon and never reach the observer. We have also carried out a basic timing analysis of the spectra and find that the fractional variability increases with photon energy and viewer inclination angle, consistent with the coronal hot spot model for X-ray fluctuations.

  2. Soft x-ray properties of the binary millisecond pulsar J0437-4715

    NASA Technical Reports Server (NTRS)

    Halpern, Jules P.; Martin, Christopher; Marshall, Herman L.

    1995-01-01

    We obtained a light curve for the 5.75 ms pulsar J0437-4715 in the 65-120 A range with 0.5 ms time resolution using the Deep Survey instrument on the EUVE satellite. The single-peaked profile has a pulsed fraction of 0. 27 +/- 0.05, similar to the ROSAT data in the overlapping energy band. A combined analysis of the EUVE and ROSAT data is consistent with a power-law spectrum of energy index alpha = 1.2-1.5, intervening column density NH = (5-8) x 10(exp 19)/sq cm, and luminosity 5.0 x 10(exp 30) ergs/s in the 0.1-2. 4 keV band. We also use a bright EUVE/ROSAT source only 4.3 deg from the pulsar, the Seyfert galaxy RX J0437.4-4711 (= EUVE J0437-471 = lES 0435-472), to obtain an independent upper limit on the intervening absorption to the pulsar, NH less than 1.2 x 10(exp 20)/sq cm. Although a blackbody spectrum fails to fit the ROSAT data, two-component spectral fits to the combined EUVE/ROSAT data are used to limit the temperatures and surface areas of thermal emission that might make partial contributions to the flux. A hot polar cap of radius 50-600 m and temperature (1.0-3.3) x 10(exp 6) K could be present. Alternatively, a larger region with T = (4-12) x 10(exp 5) K and area less than 200 sq km, might contribute most of the EUVE and soft X-ray flux, but only if a hotter component were present as well. Any of these temperatures would require some mechanism(s) of surface reheating to be operating in this old pulsar, the most plausible being the impact of accelerated electrons and positrons onto the polar caps. The kinematically corrected spin-down power of PSR J0437-4715 is only 4 x 10(exp 33) ergs/s, which is an order of magnitude less than that of the lowest-luminosity gamma-ray pulsars Geminga and PSR B1055-52. The absence of high-energy gamma-rays from PSR J0437-4715 might signify an inefficient or dead outer gap accelerator, which in turn accounts for the lack of a more luminous reheated surface such as those intermediate-age gamma-ray pulsars may have.

  3. Soft X-Ray Properties of the Binary Millisecond Pulsar J0437-4715

    NASA Technical Reports Server (NTRS)

    Halpern, Jules P.; Martin, Christopher; Marshall, Herman, L.; Oliversen, Ronald (Technical Monitor)

    2001-01-01

    We obtained a light curve for the 5.75 ms pulsar J0437-4715 in the 65-120 A range with 0.5 ms time resolution using the Deep Survey instrument on the EUVE satellite. The single-peaked profile has a pulsed fraction of 0.27 +/- 0.05, similar to the ROSAT data in the overlapping energy band. A combined analysis of the EUVE and ROSAT data is consistent with a power-law spectrum of energy index alpha = 1.2 - 1.5, intervening column density N(sub H) = (5 - 8) x 10(exp 19)/sq cm, and luminosity 5.0 x 10(exp 30) ergs/s in the 0.1 - 2.4 keV band. We also use a bright EUVE/ROSAT source only 4.2 min. from the pulsar, the Seyfert galaxy RX J0437.4-4711 (= EUVE J0437-471 = IES 0435-472), to obtain an independent upper limit on the intervening absorption to the pulsar, N(sub H) less than 1.2 x 10(exp 20)/sq cm. Although a blackbody spectrum fails to fit the ROSAT data, two-component spectral fits to the combined EUVE/ROSAT data are used to limit the temperatures and surface areas of thermal emission that might make partial contributions to the flux. A hot polar cap of radius 50 - 600 m and temperature (1.0 - 3.3) x 10(exp 6) K could be present. Alternatively, a larger region with T = (4 - 12) x 10(exp 5) K and area less than 200 sq km, might contribute most of the EUVE and soft X-ray flux, but only if a hotter component were present as well. Any of these temperatures would require some mechanism(s) of surface reheating to be operating in this old pulsar, the most plausible being the impact of accelerated electrons and positrons onto the polar caps. The kinematically corrected spin-down power of PSR J0437-4715 is only 4 x 10(exp 33) ergs/s, which is an order of magnitude less than that of the lowest-luminosity gamma-ray pulsars Geminga and PSR B1055-52. The absence of high-energy gamma-rays from PSR J0437-4715 might signify an inefficient or dead outer gap accelerator, which in turn accounts for the lack of a more luminous reheated surface such as those intermediate-age gamma

  4. X-ray Fe-lines from Relativistic Accretion Disks Around Neutron Stars and Black Holes

    NASA Astrophysics Data System (ADS)

    Stella, Luigi

    2013-01-01

    The Gas Scintillation Proportional Counter (GSPC) on board the European X-ray Satellite EXOSAT (1983-1986) provided detections of Fe K-alpha emission features around 6-7 keV in the X-ray spectra of accreting neutron star and black hole candidates in X-ray binaries. Surprisingly the width of these lines was found to be broader than the GSPC resolution 10% at 6 keV): it could not be explained by thermal broadening, nor blending of (unresolved) lines from different ionization stages of Fe; very large Doppler shifts and, perhaps, thermal Comptonisation provided more promising interpretations. In 1989 Nick White and I developed the first general relativistic model for the Fe-line profile that is produced by matter orbiting in an accretion disk. By fitting the GSPC Fe-line of the black hole candidate Cyg X-1 with our model we inferred an emitting line region extending to a few tens Schwarzschild radii from the black hole, where matter orbits at ~0.1-0.2 the speed of light and effects such as relativistic Doppler shifts and boosting, as well as gravitational and transverse redshifts are conspicuous. We joined forces with Andy Fabian and Martin Rees, who were working on the same interpretation, and published the results in a MNRAS paper. The relativistic disk interpretation of the broad Fe-lines gave rise to much interest on the possibility of measuring black hole mass and spin and probing the innermost regions of accretion flows and the very strong gravitational fields close to compact objects. Very broad and sometimes highly redshifted Fe-lines have been studied by now in tens of X-ray binaries and bright Active Galactic Nuclei with the CCD detectors of the Chandra and XMM/Newton X-ray telescopes; in some cases the line profile implies the presence of a fast spinning black hole. The potential of the Fe-line diagnostics remains to be largely exploited. Moreover some alternative interpretations are not yet ruled out. An X-ray instrument with a broad energy response

  5. X-Ray Constraints on Accretion and Starburst Processes in Galactic Nuclei

    NASA Astrophysics Data System (ADS)

    Ptak, Andrew Francis

    The results of X-ray observations of a sample of nearby low-luminosity active galactic nuclei (LLAGN), low-ionization nuclear emission line regions (LINERs), and starburst galaxies are presented. In general the 0.4-10.0 keV spectra of this heterogenous sample are fit well by a two-component model consisting of an optically-thin plasma with a temperature of ~0.7 keV and a power-law model with a photon index of ~1.7. Both the hot gas component and the hard, possibly nonthermal, X-ray emission appear to be common features of galaxies showing signs of nuclear activity. The spectrum of the hard component (roughly in the 2-10 keV bandpass) is most consistent with AGN, which are postulated to be accreting supermassive blackholes. X-ray binaries that are probably accreting blackhole candidates also appear to contribute significantly to the hard, and possibly to a lesser extent, the soft X-ray emission. Very hot (T~108 K) gas in a 'superwind' may also be contributing to the hard flux in some cases, probably concentrated in the nuclear regions of the galaxies. Another possible contributor to the featureless X-ray continuum may be inverse-Compton scattering of infrared photons, but the contribution of this component is sensitive to model assumptions. The soft emission appears to be supernovae-heated interstellar medium (ISM). In some cases, the SN-heating is actually in the form of a superwind, in which case ~90% of the X-ray emitting gas is 'swept-up' ISM and the remainder is (cooling) superwind emission out in the disks of the galaxies. Very low absolutes abundances are observed, but the uncertainties are large. Relative abundances are more secure and suggest that Fe is underabundant relative to α-process elements. The low relative Fe abundance may be due to enrichment by Type-II supernovae and∨ dust depletion, but non-equilibrium ionization may also be playing a part. Future observations by X-ray telescopes with high spatial and spectral resolution and improved

  6. The Relation Between Accretion Rate And Jet Power in X-Ray Luminous Elliptical Galaxies

    SciTech Connect

    Allen, Steven W.; Dunn, R.J.H.; Fabian, A.C.; Taylor, G.B.; Reynolds, C.S.; /Maryland U.

    2006-03-10

    Using Chandra X-ray observations of nine nearby, X-ray luminous elliptical galaxies with good optical velocity dispersion measurements, we show that a tight correlation exists between the Bondi accretion rates calculated from the observed gas temperature and density profiles and estimated black hole masses, and the power emerging from these systems in relativistic jets. The jet powers, which are inferred from the energies and timescales required to inflate cavities observed in the surrounding X-ray emitting gas, can be related to the accretion rates using a power law model of the form log (P{sub Bondi}/10{sup 43} erg s{sup -1}) = A + B log (P{sub jet}/10{sup 43} erg s{sup -1}), with A = 0.62 {+-} 0.15 and B = 0.77 {+-} 0.18. Our results show that a significant fraction of the energy associated with the rest mass of material entering the Bondi accretion radius (2.4{sub -0.7}{sup +1.0} per cent, for P{sub jet} = 10{sup 43} erg s{sup -1}) eventually emerges in the relativistic jets. Our results have significant implications for studies of accretion, jet formation and galaxy formation. The observed tight correlation suggests that the Bondi formulae provide a reasonable description of the accretion process in these systems, despite the likely presence of magnetic pressure and angular momentum in the accreting gas. The similarity of the P{sub Bondi} and P{sub jet} values argues that a significant fraction of the matter entering the accretion radius flows down to regions close to the black holes, where the jets are presumably formed. The tight correlation between P{sub Bondi} and P{sub jet} also suggests that the accretion flows are approximately stable over timescales of a few million years. Our results show that the black hole ''engines'' at the hearts of large elliptical galaxies and groups feed back sufficient energy to stem cooling and star formation, leading naturally to the observed exponential cut off at the bright end of the galaxy luminosity function.

  7. Magnetic fields in Supernova Remnants and Pulsar-Wind Nebulae: Deductions from X-ray Observations

    NASA Astrophysics Data System (ADS)

    Reynolds, S. P.

    2016-06-01

    Magnetic field strengths B in synchrotron sources are notoriously difficult to measure. Simple arguments such as equipartition of energy can give values for which the total energy is a minimum, but there is no guarantee that Nature obeys it, or even if so, what particle population (just electrons? electrons plus ions?) should have an energy density comparable to that in magnetic field. However, the operation of synchrotron losses can provide additional information, if those losses are manifested in the synchrotron spectra as steepenings of the spectral-energy distribution above some characteristic frequency often called a "break" (though it is more typically a gradual curvature). A source of known age, if it has been accelerating particles continuously, will have such a break above the energy at which particle radiative lifetimes equal the source age, and this can give B. However, in spatially resolved sources such as supernova remnants (SNRs) and pulsar-wind nebulae (PWNe), systematic advection of particles, if at a known rate, gives a second measure of particle age to compare with radiative lifetimes. In most young SNRs, synchrotron X-rays make a contribution to the X-ray spectrum, and are usually found in thin rims at the remnant edges. If the rims are thin in the radial direction due to electron energy losses, a magnetic-field strength can be estimated. I present recent modeling of this process, along with models in which rims are thin due to decay of magnetic turbulence, and apply them to the remnants of SN 1006 and Tycho. In PWNe, outflows of relativistic plasma behind the pulsar wind termination shock are likely quite inhomogeneous, so magnetic-field estimates based on source lifetimes and assuming spatial uniformity can give misleading values for B. I shall discuss inhomogeneous PWN models and the effects they can have on B estimates.

  8. The Geminga Pulsar: Soft X-Ray Variability and an EUVE Observation

    NASA Technical Reports Server (NTRS)

    Halpern, Jules P.; Martin, Christopher; Marshall, Herman L.; Oliversen, Ronald (Technical Monitor)

    2001-01-01

    We observed the Geminga pulsar with the EUVE satellite, detecting pulsed emission in the Deep Survey imager. Joint spectral fits of the EUVE flux with ROSAT PSPC data are consistent with thermal plus power-law models in which the thermal component makes the dominant contribution to the soft X-ray flux seen by EUVE and ROSAT. The data are consistent with blackbody emission of T = (4 - 6) x 10(exp 5) K over most of the surface of the star at the measured parallax distance of 160 pc. Although model atmospheres are more realistic, and can fit the data with effective temperatures a factor of 2 lower, current data would not discriminate between these and blackbody models. We also find evidence for variability of Geminga's soft X-ray pulse shape. Narrow dips in the light curve that were present in 1991 had largely disappeared in 1993/1994, causing the pulsed fraction to decline from 32% to 18%. If the dips are attributed to cyclotron resonance scattering by an e1 plasma on closed magnetic field lines, then the process that resupplies that plasma must be variable.

  9. The Geminga Pulsar: Soft X-Ray Variability and an EUVE Observation

    NASA Technical Reports Server (NTRS)

    Halpern, Jules P.; Martin, Christopher; Marshall, Herman L.

    1996-01-01

    We observed the Geminga pulsar with the EUVE satellite, detecting pulsed emission in the Deep Survey imager. Joint spectral fits of the EUVE flux with ROSAT PSPC data are consistent with thermal plus power-law models in which the thermal component makes the dominant contribution to the soft X-ray flux seen by EUVE and ROSAT. The data are consistent with blackbody emission of T = (4-6) x 10(exp 5) K over most of the surface of the star at the measured parallax distance of 160 pc. Although model atmospheres are more realistic, and can fit the data with effective temperatures a factor of 2 lower, current data would not discriminate between these and blackbody models. We also find evidence for variability of Geminga's soft X-ray pulse shape. Narrow dips in the light curve that were present in 1991 had largely disappeared in 1993/1994, causing the pulsed fraction to decline from 32% to 18%. If the dips are attributed to cyclotron resonance scattering by an e(+/-) plasma on closed magnetic field lines, then the process that resupplies that plasma must be variable.

  10. Disentangling X-Ray Emission Processes In Vela-Like Pulsars

    NASA Technical Reports Server (NTRS)

    Gaensler, Bryan; Mushotzky, Richard (Technical Monitor)

    2002-01-01

    This grant is to support analysis of data from the X-ray Multi-mirror Mission (XMM). Specifically, we have been awarded time to observe two young neutron stars, B1823-13 and B1046-58, whose X-ray emission is expected to be a complicated combination of emission from an associated supernova remnant, from a wind-powered synchrotron nebula, from magnetospheric pulsations, and from the surface of the neutron star itself. It is only with XMM's unique combination of spectral, temporal and angular resolution that all these different processes can be separated and studied. Observations of B1823-13 have been conducted and analyzed. We interpret the data as follows: The unpulsed extended non-thermal nature of the central core argues that the extended source of emission corresponds to synchrotron emission from a nebula powered by the pulsar. The temperature of the diffuse component is too high to be interpreted as thermal emission; we rather argue that this extended component is non-thermal emission from a surrounding supernova remnant shell.

  11. On the Dramatic Spin-up/Spin-Down Torque Reversals in Accreting Pulsars

    NASA Technical Reports Server (NTRS)

    Nelson, Robert W.; Bildsten, Lars; Chakrabarty, Deepto; Finger, Mark H.; Koh, Danny T.; Prince, Thomas A.; Rubin, Bradley C.; Scott, D. Mathew; Vaughan, Brian A.; Wilson, Robert B.

    1997-01-01

    Dramatic torque reversals between spin-up and spin-down have been observed in half of the persistent X-ray pulsars monitored by the Burst and Transient Space Experiment (BATSE) all-sky monitor on the Compton Gamma Ray Observatory. Theoretical models developed to explain early pulsar timing data can explain spin-down torques via a disk-magnetosphere interaction if the star nearly corotates with the inner accretion disk. To produce the observed BATSE torque reversals, however, these equilibrium models require the disk to alternate between two mass accretion rates, with M+/- producing accretion torques of similar magnitude but always of opposite sign. Moreover, in at least one pulsar (GX 1+4) undergoing secular spin-down, the neutron star spins down faster during brief (approximately 20 day) hard X-ray flares-this is opposite the correlation expected from standard theory, assuming that BATSE pulsed flux increases with mass accretion rate. The 10 day to 10 yr intervals between torque reversals in these systems are much longer than any characteristic magnetic or viscous timescale near the inner disk boundary and are more suggestive of a global disk phenomenon. We discuss possible explanations of the observed torque behavior. Despite the preferred sense of rotation defined by the binary orbit, the BATSE observations are surprisingly consistent with an earlier suggestion for GX 1+4: the disks in these systems somehow alternate between episodes of prograde and retrograde rotation. We are unaware of any mechanism that could produce a stable retrograde disk in a binary undergoing Roche lobe overflow, but such flip-flop behavior does occur in numerical simulations of wind-fed systems. One possibility is that the disks in some of these binaries are fed by an X-ray-excited wind.

  12. Measuring X-ray Binary Accretion State Distributions in Extragalactic Environments using XMM-Newton

    NASA Astrophysics Data System (ADS)

    West, Lacey; Lehmer, Bret; Yukita, Mihoko; Hornschemeier, Ann E.; Ptak, Andrew; Wik, Daniel R.; Zezas, Andreas

    2017-01-01

    X-ray binary systems (XRBs) in the MW can exist in several different accretion states, and many have been found to vary along specific tracks on intensity-color diagrams. Observationally measuring the distributions of these accretion states in a variety of environments can aid in population synthesis modeling and ultimately help us understand the formation and evolution of XRBs and their compact object components (i.e., black holes and neutron stars). Recent innovative studies with NuSTAR have demonstrated the utility of color-color and intensity-color diagrams in differentiating between XRB accretion states in extragalactic environments (NGC 253, M83, and M31). The key to NuSTAR’s success is its sensitivity above »10keV, where spectral differences between accretion states are most pronounced. However, due to the relatively low spatial resolution and large background of NuSTAR, the constraints from these diagrams is limited to only bright sources in nearby galaxies. In this poster, we present evidence that XMM-Newton observations of M83 in the 4.0-12.0 keV range can be used to create similar color-intensity and color-color diagrams and therefore differentiate between these accretion states. We will further discuss plans to leverage XMM-Newton’s vast archive and 17-year baseline to dramatically expand studies of accretion state distributions and state transitions for XRB populations in extragalactic environments.

  13. Probing the effects of a thermonuclear X-ray burst on the neutron star accretion flow with NuSTAR

    NASA Astrophysics Data System (ADS)

    Degenaar, N.; Koljonen, K. I. I.; Chakrabarty, D.; Kara, E.; Altamirano, D.; Miller, J. M.; Fabian, A. C.

    2016-03-01

    Observational evidence has been accumulating that thermonuclear X-ray bursts ignited on the surface of neutron stars influence the surrounding accretion flow. Here, we exploit the excellent sensitivity of NuSTAR up to 79 keV to analyse the impact of an X-ray burst on the accretion emission of the neutron star LMXB 4U 1608-52. The ≃200 s long X-ray burst occurred during a hard X-ray spectral state, and had a peak intensity of ≃30-50 per cent of the Eddington limit with no signs of photospheric radius expansion. Spectral analysis suggests that the accretion emission was enhanced up to a factor of ≃5 during the X-ray burst. We also applied a linear unsupervised decomposition method, namely non-negative matrix factorization (NMF), to study this X-ray burst. We find that the NMF performs well in characterizing the evolution of the burst emission and is a promising technique to study changes in the underlying accretion emission in more detail than is possible through conventional spectral fitting. For the burst of 4U 1608-52, the NMF suggests a possible softening of the accretion spectrum during the X-ray burst, which could potentially be ascribed to cooling of a corona. Finally, we report a small (≃3 per cent) but significant rise in the accretion emission ≃0.5 h before the X-ray burst, although it is unclear whether this was related to the X-ray burst ignition.

  14. X-Ray Spectra from MHD Simulations of Accreting Black Holes

    NASA Technical Reports Server (NTRS)

    Schnittman, Jeremy D.; Krolik, Julian H.; Noble, Scott C.

    2012-01-01

    We present the results of a new global radiation transport code coupled to a general relativistic magneto-hydrodynamic simulation of an accreting, nonrotating black hole. For the first time, we are able to explain from first principles in a self-consistent way the X-ray spectra observed from stellar-mass black holes, including a thermal peak, Compton reflection hump, power-law tail, and broad iron line. Varying only the mass accretion rate, we are able to reproduce the low/hard, steep power-law, and thermal-dominant states seen in most galactic black hole sources. The temperature in the corona is T(sub e) 10 keV in a boundary layer near the disk and rises smoothly to T(sub e) greater than or approximately 100 keV in low-density regions far above the disk. Even as the disk's reflection edge varies from the horizon out to approximately equal to 6M as the accretion rate decreases, we find that the shape of the Fe Ka line is remarkably constant. This is because photons emitted from the plunging region are strongly beamed into the horizon and never reach the observer. We have also carried out a basic timing analysis of the spectra and find that the fractional variability increases with photon energy and viewer inclination angle, consistent with the coronal hot spot model for X-ray fluctuations.

  15. REVISITING PUTATIVE COOL ACCRETION DISKS IN ULTRALUMINOUS X-RAY SOURCES

    SciTech Connect

    Miller, J. M.; King, A. L.; Reynolds, M. T.; Reis, R. C.; Walton, D. J.; Fabian, A. C.; Miller, M. C.

    2013-10-20

    Soft, potentially thermal spectral components observed in some ultra-luminous X-ray sources (ULXs) can be fit with models for emission from cool, optically thick accretion disks. If that description is correct, the low temperatures that are observed imply accretion onto 'intermediate-mass' black holes. Subsequent work has found that these components may follow an inverse relationship between luminosity and temperature, implying a non-blackbody origin for this emission. We have re-analyzed numerous XMM-Newton spectra of extreme ULXs. Crucially, observations wherein the source fell on a chip gap were excluded owing to their uncertain flux calibration, and the neutral column density along the line of sight to a given source was jointly determined by multiple spectra. The luminosity of the soft component is found to be positively correlated with temperature, and to be broadly consistent with L∝T {sup 4} in the measured band pass, as per blackbody emission from a standard thin disk. These results are nominally consistent with accretion onto black holes with masses above the range currently known in Galactic X-ray binaries, though there are important caveats. Emission from inhomogeneous or super-Eddington disks may also be consistent with the data.

  16. X-RAY EMISSION FROM J1446–4701, J1311–3430, AND OTHER BLACK WIDOW PULSARS

    SciTech Connect

    Arumugasamy, Prakash; Pavlov, George G.; Garmire, Gordon P.

    2015-12-01

    We present the results of detailed X-ray analysis of two black-widow pulsars (BWPs), J1446–4701 and J1311–3430. PSR J1446–4701 is a BWP with orbital parameters near the median values of the sample of known BWPs. Its X-ray emission that was detected by XMM-Newton is well characterized by a soft power-law (PL) spectrum (photon index Γ ≈ 3), and it shows no significant orbital modulations. In view of a lack of radio eclipses and an optical non-detection, the system most likely has a low orbital inclination. PSR J1311–3430 is an extreme BWP with a very compact orbit and the lowest minimum mass companion. Our Chandra data confirm the hard Γ ≈ 1.3 emission seen in previous observations. Through phase-restricted spectral analysis, we found a hint (∼2.6σ) of spectral hardening around pulsar inferior conjunction. We also provide a uniform analysis of the 12 BWPs observed with Chandra and compare their X-ray properties. Pulsars with soft, Γ > 2.5 emission seem to have lower than average X-ray and γ-ray luminosities. We do not, however, see any other prominent correlation between the pulsar’s X-ray emission characteristics and any of its other properties. The contribution of the intra-binary shock to the total X-ray emission, if any, is not discernible in this sample of pulsars with shallow observations.

  17. X-Ray Emission from J1446--4701, J1311--3430, and Other Black Widow Pulsars

    NASA Astrophysics Data System (ADS)

    Arumugasamy, Prakash; Pavlov, George G.; Garmire, Gordon P.

    2015-12-01

    We present the results of detailed X-ray analysis of two black-widow pulsars (BWPs), J1446-4701 and J1311-3430. PSR J1446-4701 is a BWP with orbital parameters near the median values of the sample of known BWPs. Its X-ray emission that was detected by XMM-Newton is well characterized by a soft power-law (PL) spectrum (photon index Γ ≈ 3), and it shows no significant orbital modulations. In view of a lack of radio eclipses and an optical non-detection, the system most likely has a low orbital inclination. PSR J1311-3430 is an extreme BWP with a very compact orbit and the lowest minimum mass companion. Our Chandra data confirm the hard Γ ≈ 1.3 emission seen in previous observations. Through phase-restricted spectral analysis, we found a hint (˜2.6σ) of spectral hardening around pulsar inferior conjunction. We also provide a uniform analysis of the 12 BWPs observed with Chandra and compare their X-ray properties. Pulsars with soft, Γ > 2.5 emission seem to have lower than average X-ray and γ-ray luminosities. We do not, however, see any other prominent correlation between the pulsar’s X-ray emission characteristics and any of its other properties. The contribution of the intra-binary shock to the total X-ray emission, if any, is not discernible in this sample of pulsars with shallow observations.

  18. Guitar with a bow: a jet-like X-ray-emitting feature associated a fast-moving pulsar

    NASA Astrophysics Data System (ADS)

    Wang, Q. Daniel

    2011-09-01

    The Guitar Nebula is known to be a ram-pressure confined pulsar wind nebula associated with the very fast-moving pulsar B2224+65. Existing observations at two epochs have shown an unexpected 2 arcmin long X-ray-emitting jet-like feature emanating from the pulsar and offset from its proper motion direction by 118 degree. We propose a deep third epoch observation of this system in order to measure the X-ray spectral gradient across the feature as well as to confirm its proper motion, its morphological variation with time, and the presence of a counter jet. We will then critically test scenarios proposed to explain this system, which represents a class of similarly enigmatic objects recently discovered locally and in the central region of our Galaxy.

  19. The rotation-powered nature of some soft gamma-ray repeaters and anomalous X-ray pulsars

    NASA Astrophysics Data System (ADS)

    Coelho, Jaziel G.; Cáceres, D. L.; de Lima, R. C. R.; Malheiro, M.; Rueda, J. A.; Ruffini, R.

    2017-03-01

    Context. Soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs) are slow rotating isolated pulsars whose energy reservoir is still matter of debate. Adopting neutron star (NS) fiducial parameters; mass M = 1.4 M⊙, radius R = 10 km, and moment of inertia, I = 1045 g cm2, the rotational energy loss, Ėrot, is lower than the observed luminosity (dominated by the X-rays) LX for many of the sources. Aims: We investigate the possibility that some members of this family could be canonical rotation-powered pulsars using realistic NS structure parameters instead of fiducial values. Methods: We compute the NS mass, radius, moment of inertia and angular momentum from numerical integration of the axisymmetric general relativistic equations of equilibrium. We then compute the entire range of allowed values of the rotational energy loss, Ėrot, for the observed values of rotation period P and spin-down rate Ṗ. We also estimate the surface magnetic field using a general relativistic model of a rotating magnetic dipole. Results: We show that realistic NS parameters lowers the estimated value of the magnetic field and radiation efficiency, LX/Ėrot, with respect to estimates based on fiducial NS parameters. We show that nine SGRs/AXPs can be described as canonical pulsars driven by the NS rotational energy, for LX computed in the soft (2-10 keV) X-ray band. We compute the range of NS masses for which LX/Ėrot< 1. We discuss the observed hard X-ray emission in three sources of the group of nine potentially rotation-powered NSs. This additional hard X-ray component dominates over the soft one leading to LX/Ėrot > 1 in two of them. Conclusions: We show that 9 SGRs/AXPs can be rotation-powered NSs if we analyze their X-ray luminosity in the soft 2-10 keV band. Interestingly, four of them show radio emission and six have been associated with supernova remnants (including Swift J1834.9-0846 the first SGR observed with a surrounding wind nebula). These observations give

  20. THE PROPER MOTION AND X-RAY ANALYSIS OF THE PULSAR WIND NEBULA, PSR J1741-2054 USING CHANDRA.

    NASA Astrophysics Data System (ADS)

    Auchettl, Katie; Slane, Patrick O.; Romani, Roger W.; Kargaltsev, Oleg; Pavlov, George G.

    2014-08-01

    A pulsar dissipates its rotational energy by generating relativistic winds, which in turn produces a population of high energy electrons and positions that we observe as a synchrotron emitting nebula. If the pulsar has a high space velocity, the corresponding nebula will have a bow-shock morphology due to the pulsar wind being confined by ram pressure. Pulsar wind nebulae (PWNe) provide a good test bed to study the dynamics and interaction of relativistic outflows with their environment and the corresponding shocks that result from these interactions. They can also aid in understanding the evolution of the neutron star and the properties of the local medium with which they are interacting. Here we report on the X-ray analysis of PSR J1741-2054 carried out as a part of the Chandra XVP program (6 ACIS-S observations, totalling ~300 ks over 5 months). By registering this new epoch of observations using X-ray point sources in the field of view to an archival observation taken 3.2 years earlier, we are able to measure the proper motion of the pulsar with >3σ significance. We also investigate the spatial and spectral properties of the pulsar, its compact nebula and extended tail. We find that the compact nebula can be well described with an absorbed power-law with photon index of Γ=1.6+/-0.2, while the tail shows no evidence of variation in the spectral index with the distance from the pulsar. We have also investigated the X-ray spectrum of the neutron star. We find nonthermal emission accompanied by a significant thermal component and will provide constraints on the overall nature of the emission.

  1. Modeling X-ray Absorbers in AGNs with MHD-Driven Accretion-Disk Winds

    NASA Astrophysics Data System (ADS)

    Fukumura, Keigo; Kazanas, D.; Shrader, C. R.; Tombesi, F.; Contopoulos, J.; Behar, E.

    2013-04-01

    We have proposed a systematic view of the observed X-ray absorbers, namely warm absorbers (WAs) in soft X-ray and highly-ionized ultra-fast outflows (UFOs), in the context of magnetically-driven accretion-disk wind models. While potentially complicated by variability and thermal instability in these energetic outflows, in this simplistic model we have calculated 2D kinematic field as well as density and ionization structure of the wind with density profile of 1/r corresponding to a constant column distribution per decade of ionization parameter. In particular we show semi-analytically that the inner layer of the disk-wind manifests itself as the strongly-ionized fast outflows while the outer layer is identified as the moderately-ionized absorbers. The computed characteristics of these two apparently distinct absorbers are consistent with X-ray data (i.e. a factor of ~100 difference in column and ionization parameters as well as low wind velocity vs. near-relativistic flow). With the predicted contour curves for these wind parameters one can constrain allowed regions for the presence of WAs and UFOs.The model further implies that the UFO's gas pressure is comparable to that of the observed radio jet in 3C111 suggesting that the magnetized disk-wind with density profile of 1/r is a viable agent to help sustain such a self-collimated jet at small radii.

  2. Discovery of a Second Millesecond Accreting Pulsar: XTE J1751-305

    NASA Technical Reports Server (NTRS)

    Markwardt, C. B.; Swank, J. H.; Strohmayer, T. E.; intZand, J. J. M.; Marshall, F. E.; White, Nicholas E. (Technical Monitor)

    2002-01-01

    We report the discovery by the RXTE PCA of a second transient accreting millisecond pulsar, XTE J1751-305, during regular monitoring observations of the galactic bulge region. The pulsar has a spin frequency of 435 Hz, making it one of the fastest pulsars. The pulsations contain the signature of orbital Doppler modulation, which implies an orbital period of 42 minutes, the shortest orbital period of any known radio or X-ray millisecond pulsar. The mass function, f(sub x) = (1.278 +/- 0.003) x 10 (exp -6) solar mass, yields a minimum mass for the companion of between 0.013 and 0.0017 solar mass depending on the mass of the neutron star. No eclipses were detected. A previous X-ray outburst in June, 1998, was discovered in archival All-Sky Monitor data. Assuming mass transfer in this binary system is driven by gravitational radiation, we constrain the orbital inclination to be in the range 30 deg-85 deg and the companion mass to be 0.013-0.035 solar mass. The companion is most likely a heated helium dwarf. We also present results from the Chandra HRC-S observations which provide the best known position of XTE J1751-305.

  3. Accretion and ejection in black-hole X-ray transients

    NASA Astrophysics Data System (ADS)

    Kylafis, N. D.; Belloni, T. M.

    2015-02-01

    Context. A rich phenomenology has been accumulated over the years regarding accretion and ejection in black-hole X-ray transients (BHTs) and it needs an interpretation. Aims: Here we summarize the current observational picture of the outbursts of BHTs, based on the evolution traced in a hardness-luminosity diagram (HLD), and we offer a physical interpretation. Methods: The basic ingredient in our interpretation is the Poynting-Robertson cosmic battery (PRCB), which provides locally the poloidal magnetic field needed for the ejection of the jet. In addition, we make two assumptions, easily justifiable. The first is that the mass-accretion rate to the black hole in a BHT outburst has a generic bell-shaped form, whose characteristic time scale is much longer than the dynamical or the cooling ones. This is guaranteed by the observational fact that all BHTs start their outburst and end it at the quiescent state, i.e., at very low accretion rate, and that state transitions take place over long time scales (hours to days). The second assumption is that at low accretion rates the accretion flow is geometrically thick, ADAF-like, while at high accretion rates it is geometrically thin. Last, but not least, we demonstrate that the previous history of the system is absolutely necessary for the interpretation of the HLD. Results: Both, at the beginning and the end of an outburst, the PRCB establishes a strong poloidal magnetic field in the ADAF-like part of the accretion flow, and this explains naturally why a jet is always present in the right part of the HLD. In the left part of the HLD, the accretion flow is in the form of a thin disk, and such a disk cannot sustain a strong poloidal magnetic filed. Thus, no jet is expected in this part of the HLD. Finally, the counterclockwise traversal of the HLD is explained as follows: all outbursts start from the quiescent state, in which the inner part of the accretion flow is ADAF-like, threaded by a poloidal magnetic field. As the

  4. Measuring the stellar wind parameters in IGR J17544-2619 and Vela X-1 constrains the accretion physics in supergiant fast X-ray transient and classical supergiant X-ray binaries

    NASA Astrophysics Data System (ADS)

    Giménez-García, A.; Shenar, T.; Torrejón, J. M.; Oskinova, L.; Martínez-Núñez, S.; Hamann, W.-R.; Rodes-Roca, J. J.; González-Galán, A.; Alonso-Santiago, J.; González-Fernández, C.; Bernabeu, G.; Sander, A.

    2016-06-01

    two stars is their terminal velocities (ν∞ = 1500 km s-1 in IGR J17544-2619 and ν∞ = 700 km s-1 in Vela X-1), which have important consequences on the X-ray luminosity of these sources. Conclusions: The donors of IGR J17544-2619 and Vela X-1 have similar spectral types as well as similar parameters that physically characterize them and their spectra. In addition, the orbital parameters of the systems are similar too, with a nearly circular orbit and short orbital period. However, they show moderate differences in their stellar wind velocity and the spin period of their neutron star which has a strong impact on the X-ray luminosity of the sources. This specific combination of wind speed and pulsar spin favors an accretion regime with a persistently high luminosity in Vela X-1, while it favors an inhibiting accretion mechanism in IGR J17544-2619. Our study demonstrates that the relative wind velocity is critical in class determination for the HMXBs hosting a supergiant donor, given that it may shift the accretion mechanism from direct accretion to propeller regimes when combined with other parameters.

  5. Ionization break-out from millisecond pulsar wind nebulae: an X-ray probe of the origin of superluminous supernovae

    NASA Astrophysics Data System (ADS)

    Metzger, Brian D.; Vurm, Indrek; Hascoët, Romain; Beloborodov, Andrei M.

    2014-01-01

    Magnetic spin-down of a rapidly rotating (millisecond) neutron star has been proposed as the power source of hydrogen-poor `superluminous' supernovae (SLSNe-I). However, producing an unambiguous test that can distinguish this model from alternatives, such as circumstellar interaction, has proven challenging. After the supernova explosion, the pulsar wind inflates a hot cavity behind the expanding stellar ejecta: the nascent millisecond pulsar wind nebula. Electron/positron pairs injected by the wind cool through inverse Compton scattering and synchrotron emission, producing a pair cascade and hard X-ray spectrum inside the nebula. These X-rays ionize the inner exposed side of the ejecta, driving an ionization front that propagates outwards with time. Under some conditions this front can breach the ejecta surface within months after the optical supernova peak, allowing ˜0.1-1 keV photons to escape the nebula unattenuated with a characteristic luminosity LX ˜ 1043-1045 erg s-1. This `ionization break-out' may explain the luminous X-ray emission observed from the transient SCP 06F, providing direct evidence that this SLSN was indeed engine powered. Luminous break-out requires a low ejecta mass and that the spin-down time of the pulsar be comparable to the photon diffusion time-scale at optical maximum, the latter condition being similar to that required for a supernova with a high optical fluence. These relatively special requirements may explain why most SLSNe-I are not accompanied by detectable X-ray emission. Global asymmetry of the supernova ejecta increases the likelihood of an early break-out along the direction of lowest density. Atomic states with lower threshold energies are more readily ionized at earlier times near optical maximum, allowing `UV break-out' across a wider range of pulsar and ejecta properties than X-ray break-out, possibly contributing to the blue/UV colours of SLSNe-I.

  6. X-RAY INVESTIGATION OF THE DIFFUSE EMISSION AROUND PLAUSIBLE {gamma}-RAY EMITTING PULSAR WIND NEBULAE IN KOOKABURRA REGION

    SciTech Connect

    Kishishita, Tetsuichi; Bamba, Aya; Uchiyama, Yasunobu

    2012-05-10

    We report on the results from Suzaku X-ray observations of the radio complex region called Kookaburra, which includes two adjacent TeV {gamma}-ray sources HESS J1418-609 and HESS J1420-607. The Suzaku observation revealed X-ray diffuse emission around a middle-aged pulsar PSR J1420-6048 and a plausible pulsar wind nebula (PWN) Rabbit with elongated sizes of {sigma}{sub X} = 1.'66 and {sigma}{sub X} = 1.'49, respectively. The peaks of the diffuse X-ray emission are located within the {gamma}-ray excess maps obtained by H.E.S.S. and the offsets from the {gamma}-ray peaks are 2.'8 for PSR J1420-6048 and 4.'5 for Rabbit. The X-ray spectra of the two sources were well reproduced by absorbed power-law models with {Gamma} = 1.7-2.3. The spectral shapes tend to become softer according to the distance from the X-ray peaks. Assuming the one-zone electron emission model as the first-order approximation, the ambient magnetic field strengths of HESS J1420-607 and HESS J1418-609 can be estimated as 3 {mu}G and 2.5 {mu}G, respectively. The X-ray spectral and spatial properties strongly support that both TeV sources are PWNe, in which electrons and positrons accelerated at termination shocks of the pulsar winds are losing their energies via the synchrotron radiation and inverse Compton scattering as they are transported outward.

  7. Hercules X-1: Spectral Variability of an X-Ray Pulsar in a Stellar Binary System. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Pravdo, S. H.

    1976-01-01

    A cosmic X-ray spectroscopy experiment onboard the Orbiting Solar Observatory 8 (OSO-8), observed Her x-1 continuously for approximately 8 days. Spectral-temporal correlations of the X-ray emission were obtained. The major results concern observations of: (1) iron band emission, (2) spectral hardening (increase in effective x-ray temperature) within the X-ray pulse, and (3) a transition from an X-ray low state to a high state. The spectrum obtained prior to the high state can be interpreted as reflected emission from a hot coronal gas surrounding an accretion disk, which itself shields the primary X-ray source from the line of sight during the low state. The spectral hardening within the X-ray pulse was indicative of the beaming mechanism at the neutron star surface. The hardest spectrum by pulse phase was identified with the line of sight close to the Her x-1 magnetic dipole axis, and the X-ray pencil beam become harder with decreasing angle between the line of sight and the dipole axis.

  8. 16 yr of RXTE monitoring of five anomalous X-ray pulsars

    SciTech Connect

    Dib, Rim; Kaspi, Victoria M. E-mail: vkaspi@physics.mcgill.ca

    2014-03-20

    We present a summary of the long-term evolution of various properties of the five non-transient anomalous X-ray pulsars (AXPs) 1E 1841–045, RXS J170849.0–400910, 1E 2259+586, 4U 0142+61, and 1E 1048.1–5937, regularly monitored with RXTE from 1996 to 2012. We focus on three properties of these sources: the evolution of the timing, pulsed flux, and pulse profile. We report several new timing anomalies and radiative events, including a putative anti-glitch seen in 1E 2259+586 in 2009, and a second epoch of very large spin-down rate fluctuations in 1E 1048.1–5937 following a large flux outburst. We compile the properties of the 11 glitches and 4 glitch candidates observed from these 5 AXPs between 1996 and 2012. Overall, these monitoring observations reveal several apparent patterns in the behavior of this sample of AXPs: large radiative changes in AXPs (including long-lived flux enhancements, short bursts, and pulse profile changes) are rare, occurring typically only every few years per source; large radiative changes are almost always accompanied by some form of timing anomaly, usually a spin-up glitch; only 20%-30% of timing anomalies are accompanied by any form of radiative change. We find that AXP radiative behavior at the times of radiatively loud glitches is sufficiently similar to suggest common physical origins. The similarity in glitch properties when comparing radiatively loud and radiatively silent glitches in AXPs suggests a common physical origin in the stellar interior. Finally, the overall similarity of AXP and radio pulsar glitches suggests a common physical origin for both phenomena.

  9. Accretion in young stars: measure of the stream velocity of TW Hya from the X-ray Doppler shift

    NASA Astrophysics Data System (ADS)

    Argiroffi, Costanza; Bonito, Rosaria; Orlando, Salvatore; Miceli, Marco; Peres, Giovanni

    2015-09-01

    High-resolution X-ray spectra are a unique tool to investigate the accretion process in young stars. In fact X-rays allow to investigate the accretion-shock region, where the infalling material is heated by strong shocks due to the impact with the denser stellar atmosphere. Here we show for the first time that it is possible to constrain the velocity of the accretion stream by measuring the Doppler shift of the emitted X-rays. To this aim we analyzed the deep Chandra/HETGS observation of the accreting young star TW Hya. We selected a sample of emission lines free from significant blends, fitted them with gaussian profiles, computed the radial velocity corresponding to each line, and averaged these velocities to obtain an accurate estimate of the global velocity of the X-ray emitting plasma. After correcting for Earth's motion, we compared this observed velocity with the photospheric radial velocity. In order to check this procedure we applied the same technique to other Chandra/HETGS spectra of single stars, whose X-rays are due only to coronal plasma. While spectra of pure coronal sources provide Doppler shifts in agreement with the known stellar radial velocity, we found that the X-ray spectrum of TW Hya is red-shifted by ~30-40 km/s with respect to the stellar photosphere. This proves that the X-ray emitting plasma on TW Hya is moving with respect to the stellar surface, definitively confirming that it originates in the accretion-shock region. The observed velocity suggests that the base of the accretion region is located at low latitudes of the stellar surface.

  10. Multi-wavelength emissions from the millisecond pulsar binary PSR J1023+0038 during an accretion active state

    SciTech Connect

    Takata, J.; Leung, Gene C. K.; Wu, E. M. H.; Cheng, K. S.; Li, K. L.; Kong, A. K. H.; Tam, P. H. T.; Hui, C. Y.; Xing, Yi; Wang, Zhongxiang; Cao, Yi; Tang, Sumin E-mail: akong@phys.nthu.edu.tw

    2014-04-20

    Recent observations strongly suggest that the millisecond pulsar binary PSR J1023+0038 has developed an accretion disk since 2013 June. We present a multi-wavelength analysis of PSR J1023+0038, which reveals that (1) its gamma-rays suddenly brightened within a few days in 2013 June/July and has remained at a high gamma-ray state for several months; (2) both UV and X-ray fluxes have increased by roughly an order of magnitude; and (3) the spectral energy distribution has changed significantly after the gamma-ray sudden flux change. Time variabilities associated with UV and X-rays are on the order of 100-500 s and 50-100 s, respectively. Our model suggests that a newly formed accretion disk, due to the sudden increase of the stellar wind, could explain the changes of all these observed features. The increase of UV is emitted from the disk, and a new component in gamma-rays is produced by inverse Compton scattering between the new UV component and pulsar wind. The increase of X-rays results from the enhancement of injection pulsar wind energy into the intra-binary shock due to the increase of the stellar wind. We also predict that the radio pulses may be blocked by the evaporated winds from the disk, and the pulsar is still powered by rotation.

  11. The Magnetar Nature and the Outburst Mechanism of a Transient Anomalous X-ray Pulsar

    NASA Technical Reports Server (NTRS)

    Guver, Tolga; Ozel, Feryal; Gogus, Ersin; Kouveliotou, Chryssa

    2007-01-01

    Anomalous X-ray Pulsars (AXPs) belong to a class of neutron stars believed to harbor the strongest magnetic fields in the universe, as indicated by their energetic bursts and their rapid spindowns. However, a direct measurement of their surface field strengths has not been made to date. It is also not known whether AXP outbursts result from changes in the neutron star magnetic field or crust properties. Here we report the first, spectroscopic measurement of the surface magnetic field strength of an AXP, XTE J1810-197, and solidify its magnetar nature. The field strength obtained from detailed spectral analysis and modeling is remarkably close to the value inferred from the rate of spindown of this source and remains nearly constant during numerous observations spanning over two orders of magnitude in source flux. The surface temperature, on the other hand, declines steadily and dramatically following the 2003 outburst of this source. Our findings demonstrate that heating occurs in the upper neutron star crust during an outburst and sheds light on the transient behaviour of AXPs.

  12. Detailed Physical Modeling Reveals the Magnetar Nature of a Transient Anomalous X-ray Pulsar

    NASA Technical Reports Server (NTRS)

    Guever, T.; Oezel, F.; Goegues, E.; Kouveliotou, C.

    2007-01-01

    Anomalous X-ray Pulsars (AXPs) belong to a class of neutron stars believed to harbor the strongest magnetic fields in the universe, as indicated by their energetic bursts and their rapid spindowns. However, a direct measurement of their surface field strengths has not been made to date. It is also not known whether AXP outbursts result from changes in the neutron star magnetic field or crust properties. Here we report the first, spectroscopic measurement of the surface magnetic field strength of an AXP, XTE J1810-197, and solidify its magnetar nature. The field strength obtained from detailed spectral analysis and modeling is remarkably close to the value inferred from the rate of spindown of this source and remains nearly constant during numerous observations spanning over two orders of magnitude in source flux. The surface temperature, on the other hand, declines steadily and dramatically following the 2003 outburst of this source. Our findings demonstrate that heating occurs in the upper neutron star crust during an outburst and sheds light on the transient behaviour of AXPs.

  13. The Multi-Component Nature of the Vela Pulsar Nonthermal X-ray Spectrum

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.; Strickman, Mark S.; Gwinn, Carl; McCulloch, P.; Moffet, D.; White, Nicholas E. (Technical Monitor)

    2002-01-01

    We report on our analysis of a 274 ks observation of the Vela pulsar with the Rossi X-Ray Timing Explorer (RXTE). The double-peaked, pulsed emission at 2 - 30 keV, which we had previously detected during a 93 ks observation, is confirmed with much improved statistics. There is now clear evidence, both in the spectrum and the light curve, that the emission in the RXTE band is a blend of two separate non-thermal components. The spectrum of the harder component connects smoothly with the OSSE, COMPTEL and EGRET spectrum and the peaks in the light curve are in phase coincidence with those of the high-energy light curve. The spectrum of the softer component is consistent with an extrapolation to the pulsed optical flux, and the second RXTE pulse is in phase coincidence with the second optical peak. In addition, we see a peak in the 2-8 keV RXTE pulse profile at the radio phase.

  14. X-rays and gamma-rays from accretion flows onto black holes in Seyferts and X-ray binaries

    NASA Technical Reports Server (NTRS)

    Zdziarski, Andrzej A.; Johnson, W. Neil; Poutanen, Juri; Magdziarz, Pawel; Gierlinski, Marek

    1997-01-01

    Observations and theoretical models of X-ray/gamma ray spectra of radio quiet Seyfert galaxies and Galactic black hole candidates are reviewed. The spectra from these objects share the following characteristics: an underlying power law with a high energy cutoff above 200 keV; a Compton reflection component with a Fe K alpha line, and a low energy absorption by intervening cold matter. The X-ray energy spectral index, alpha, is typically in the range between 0.8 and 1 in Seyfert spectra, and that of the hard state spectra of the black hole candidates Cygnus X-1 and GX 339-4 is typically between 0.6 and 0.8. The Compton reflection component corresponds with cold matter covering a solid angle of between 0.8pi and 2pi as seen from the X-ray source. The broadband spectra of both classes of sources are well fitted by Compton upscattering of soft photons in thermal plasma. The fits yield a thermal plasma temperature of 100 keV and the Thomson optical depth of 1. All the spectra presented are cut off before the electron rest energy 511 keV, indicating that electron/positron pair production is an important process.

  15. Detection of cyclotron resonance scattering feature in high-mass X-ray binary pulsar SMC X-2

    NASA Astrophysics Data System (ADS)

    Jaisawal, Gaurava K.; Naik, Sachindra

    2016-09-01

    We report broad-band spectral properties of the high-mass X-ray binary pulsar SMC X-2 by using three simultaneous Nuclear Spectroscopy Telescope Array and Swift/XRT observations during its 2015 outburst. The pulsar was significantly bright, reaching a luminosity up to as high as ˜5.5 × 1038 erg s-1 in 1-70 keV range. Spin period of the pulsar was estimated to be 2.37 s. Pulse profiles were found to be strongly luminosity dependent. The 1-70 keV energy spectrum of the pulsar was well described with three different continuum models such as (i) negative and positive power law with exponential cutoff, (ii) Fermi-Dirac cutoff power law and (iii) cutoff power-law models. Apart from the presence of an iron line at ˜6.4 keV, a model independent absorption like feature at ˜27 keV was detected in the pulsar spectrum. This feature was identified as a cyclotron absorption line and detected for the first time in this pulsar. Corresponding magnetic field of the neutron star was estimated to be ˜2.3 × 1012 G. The cyclotron line energy showed a marginal negative dependence on the luminosity. The cyclotron line parameters were found to be variable with pulse phase and interpreted as due to the effect of emission geometry or complicated structure of the pulsar magnetic field.

  16. 2S 1553-542: a Be/X-ray binary pulsar on the far side of the Galaxy

    NASA Astrophysics Data System (ADS)

    Lutovinov, Alexander A.; Buckley, David A. H.; Townsend, Lee J.; Tsygankov, Sergey S.; Kennea, Jamie

    2016-11-01

    We report the results of a comprehensive analysis of X-ray (Chandra and Swift observatories), optical (Southern African Large Telescope, SALT) and near-infrared (the VVV survey) observations of the Be/X-ray binary pulsar 2S 1553-542. Accurate coordinates for the X-ray source are determined and are used to identify the faint optical/infrared counterpart for the first time. Using VVV and SALTICAM photometry, we have constructed the spectral energy distribution (SED) for this star and found a moderate NIR excess that is typical for Be stars and arises due to the presence of circumstellar material (disc). A comparison of the SED with those of known Be/X-ray binaries has allowed us to estimate the spectral type of the companion star as B1-2V and the distance to the system as >15 kpc. This distance estimation is supported by the X-ray data and makes 2S 1553-542 one of the most distant X-ray binaries within the Milky Way, residing on the far side in the Scutum-Centaurus arm or even further.

  17. A New Supernova Remnant Coincident with the Slow X-Ray Pulsar AX J1845-0258.

    PubMed

    Gaensler; Gotthelf; Vasisht

    1999-11-20

    We report on Very Large Array observations in the direction of the recently discovered slow X-ray pulsar AX J1845-0258. In the resulting images, we find a 5&arcmin; shell of radio emission; the shell is linearly polarized with a nonthermal spectral index. We classify this source as a previously unidentified, young (<8000 yr) supernova remnant (SNR), G29.6+0.1, which we propose is physically associated with AX J1845-0258. The young age of G29.6+0.1 is then consistent with the interpretation that anomalous X-ray pulsars (AXPs) are isolated, highly magnetized neutron stars ("magnetars"). Three of the six known AXPs can now be associated with SNRs; we conclude that AXPs are young ( less, similar10,000 yr) objects and that they are produced in at least 5% of core-collapse supernovae.

  18. X-ray selected Type-2 QSOs: ongoing star formation and obscured accretion.

    NASA Astrophysics Data System (ADS)

    Mainieri, Vincenzo; Cosmos Collaboration

    2009-09-01

    Although the fraction of obscured AGN is found to decrease with luminosity from several studies, a non-negligible population of obscured QSOs is still required by the X-ray background synthesis models. We present a large sample (121 objects) of X-ray selected Type-2 QSOs from the XMM-COSMOS survey: sources with high X-ray luminosity (LX>10^{44} erg s^{-1}) and heavy obscuration (NH>10^{22} cm^{-2}), as derived from a detailed X-ray spectral analysis (see Mainieri et al.,2007, ApJS, 172, 368) of the 1800 X-ray point-like sources in this survey. Few (˜5%) of the Type-2 QSOs are best fitted with a pure reflection model. We have performed optical spectroscopy for ˜ 30% of the sample and for the remaining sources we have derived accurate photometric redshifts. The redshift range covered is wide, 0.30.8).We compare the general properties of the host galaxies with the ongoing accretion in their nuclei. Morphology: using five non-parametric diagnostics (asymmetry, concentration, Gini coefficient, M20, ellipticity) we found that ˜10% of the Type-2 QSOs are in elliptical galaxies, ˜55% in disk galaxies and ˜35% in irregular galaxies. The majority of the irregular hosts can be described as undergoing merger activity or show tidal debris. Stellar masses have been derived from SED fitting to the observed photometry(from 0.3 to 4.5 micron) and star formation rates from the [OII] or Hα line fluxes. The majority (˜75%) of QSO-2 host galaxies have stellar masses above log(Mstar)˜10.5 MSun and have ongoing star formation (˜100 MSun/yr). The value of 10.5 MSun is similar to the characteristic mass for obscured AGN (Kauffmann et al. 2003) and radio-loud AGN (Best et al. 2005) in the SDSS. It is also consistent with the more general result that the fraction of galaxies hosting AGN increases with the stellar mass.

  19. A Brown Dwarf Companion for the Accreting Millisecond Pulsar SAX J1808.4-3658

    NASA Astrophysics Data System (ADS)

    Bildsten, Lars; Chakrabarty, Deepto

    2001-08-01

    The BeppoSAX Wide Field Cameras have revealed a population of faint neutron star X-ray transients in the Galactic bulge. King conjectured that these neutron stars are accreting from brown dwarfs with a time-averaged mass transfer rate ~10-11 Msolar yr-1 that is low enough for accretion disk instabilities. We show that the measured orbital parameters of the 401 Hz accreting millisecond pulsar SAX J1808.4-3658 support this hypothesis. A main-sequence mass donor requires a nearly face-on inclination and a higher than observed, and can thus be excluded. However, the range of allowed inclinations is substantially relaxed, and the predicted is consistent with that observed if a hot 0.05 Msolar dwarf is the donor. The remaining puzzle is explaining the brown dwarf radius required (0.13 Rsolar) to fill the Roche lobe. Recent observational and theoretical work has shown that all transiently accreting neutron stars have a minimum luminosity in quiescence set by the time-averaged mass transfer rate onto the neutron star. We show here that the constant heating of the brown dwarf by this quiescent neutron star emission appears adequate to maintain the higher entropy implied by a 0.13 Rsolar radius. All of our considerations very strongly bolster the case that SAX J1808.4-3658 is a progenitor to compact millisecond radio pulsar binaries (e.g., like those found by Camilo and collaborators in 47 Tuc). The very low of SAX J1808.4-3658 implies that the progenitors to these radio pulsars are long-lived (~Gyr) transient systems, rather than short-lived (~Myr) Eddington-limited accretors. Hence, the accreting progenitor population to millisecond radio pulsars in 47 Tuc could still be present and found in quiescence with Chandra.

  20. Detection of a Cool, Accretion-Shock-Generated X-Ray Plasma in EX Lupi During the 2008 Optical Eruption

    NASA Technical Reports Server (NTRS)

    Teets, William K.; Weintraub, David A.; Kastner, Joel H.; Grosso, Nicholas; Hamaguchi, Kenji; Richmond, Michael

    2012-01-01

    EX Lupi is the prototype for a class of young, pre-main-sequence stars which are observed to undergo irregular, presumably accretion-generated, optical outbursts that result in a several magnitude rise of the optical flux. EX Lupi was observed to optically erupt in 2008 January, triggering Chandra ACIS Target of Opportunity observations shortly thereafter. We find very strong evidence that most of the X-ray emission in the first few months after the optical outburst is generated by accretion of circumstellar material onto the stellar photosphere. Specifically, we find a strong correlation between the decreasing optical and X-ray fluxes following the peak of the outburst in the optical, which suggests that these observed declines in both the optical and X-ray fluxes are the result of declining accretion rate. In addition, in our models of the X-ray spectrum, we find strong evidence for an approx 0.4 keV plasma component, as expected for accretion shocks on low-mass, pre-main-sequence stars. From 2008 March through October, this cool plasma component appeared to fade as EX Lupi returned to its quiescent level in the optical, consistent with a decrease in the overall emission measure of accretion-shock-generated plasma. The overall small increase of the X-ray flux during the optical outburst of EX Lupi is similar to what was observed in previous X-ray observations of the 2005 optical outburst of the EX Lupi-type star V1118 Ori but contrasts with the large increase of the X-ray flux from the erupting young star V1647 Ori during its 2003 and 2008 optical outbursts.

  1. Revealing the accretion disc corona in Mrk 335 with multi-epoch X-ray spectroscopy

    NASA Astrophysics Data System (ADS)

    Keek, L.; Ballantyne, D. R.

    2016-03-01

    Active galactic nuclei host an accretion disc with an X-ray producing corona around a supermassive black hole. In bright sources, such as the Seyfert 1 galaxy Mrk 335, reflection of the coronal emission off the accretion disc has been observed. Reflection produces spectral features such as an Fe Kα emission line, which allow for properties of the inner accretion disc and the corona to be constrained. We perform a multi-epoch spectral analysis of all XMM-Newton, Suzaku, and NuSTAR observations of Mrk 335, and we optimize our fitting procedure to unveil correlations between the Eddington ratio and the spectral parameters. We find that the disc's ionization parameter correlates strongly with the Eddington ratio: the inner disc is more strongly ionized at higher flux. The slope of the correlation is less steep than previously predicted. Furthermore, the cut-off of the power-law spectrum increases in energy with the Eddington ratio, whereas the reflection fraction exhibits a decrease. We interpret this behaviour as geometrical changes of the corona as a function of the accretion rate. Below ˜10 per cent of the Eddington limit, the compact and optically thick corona is located close to the inner disc, whereas at higher accretion rates the corona is likely optically thin and extends vertically further away from the disc surface. Furthermore, we find a soft excess that consists of two components. In addition to a contribution from reflection in low ionization states, a second component is present that traces the overall flux.

  2. Simultaneous X-ray and radio observations of the radio-mode-switching pulsar PSR B1822-09

    NASA Astrophysics Data System (ADS)

    Hermsen, W.; Kuiper, L.; Hessels, J. W. T.; Mitra, D.; Rankin, J. M.; Stappers, B. W.; Wright, G. A. E.; Basu, R.; Szary, A.; van Leeuwen, J.

    2017-04-01

    We report on simultaneous X-ray and radio observations of the radio-mode-switching pulsar PSR B1822-09 with ESA's XMM-Newton and the Westerbork Synthesis Radio Telescope, Giant Metrewave Radio Telescope and Lovell radio telescopes. PSR B1822-09 switches between a radio-bright and radio-quiet mode, and we discovered a relationship between the durations of its modes and a known underlying radio-modulation time-scale within the modes. We discovered X-ray (energies 0.2-1.4 keV) pulsations with a broad sinusoidal pulse, slightly lagging the radio main pulse in phase by 0.094 ± 0.017, with an energy-dependent pulsed fraction varying from ∼0.15 at 0.3 keV to ∼0.6 at 1 keV. No evidence is found for simultaneous X-ray and radio mode switching. The total X-ray spectrum consists of a cool component (T ∼0.96 × 106 K, hotspot radius R ∼2.0 km) and a hot component (T ∼2.2 × 106 K, R ∼100 m). The hot component can be ascribed to the pulsed emission and the cool component to the unpulsed emission. The high-energy characteristics of PSR B1822-09 resemble those of middle-aged pulsars such as PSR B0656+14, PSR B1055-52 and Geminga, including an indication for pulsed high-energy gamma-ray emission in Fermi Large Area Telescope data. Explanations for the high pulsed fraction seem to require different temperatures at the two poles of this orthogonal rotator, or magnetic anisotropic beaming effects in its strong magnetic field. In our X-ray skymap, we found a harder source at only 5.1 ± 0.5 arcsec from PSR B1822-09, which might be a pulsar wind nebula.

  3. Discovery of a Be/X-ray pulsar binary and associated supernova remnant in the Wing of the Small Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Hénault-Brunet, V.; Oskinova, L. M.; Guerrero, M. A.; Sun, W.; Chu, Y.-H.; Evans, C. J.; Gallagher, J. S., III; Gruendl, R. A.; Reyes-Iturbide, J.

    2012-02-01

    We report on a new Be/X-ray pulsar binary located in the Wing of the Small Magellanic Cloud (SMC). The strong pulsed X-ray source was discovered with the Chandra and XMM-Newton X-ray observatories. The X-ray pulse period of 1062 s is consistently determined from both Chandra and XMM-Newton observations, revealing one of the slowest rotating X-ray pulsars known in the SMC. The optical counterpart of the X-ray source is the emission-line star 2dFS 3831. Its B0-0.5(III)e+ spectral type is determined from VLT-FLAMES and 2dF optical spectroscopy, establishing the system as a Be/X-ray binary (Be-XRB). The hard X-ray spectrum is well fitted by a power law with additional thermal and blackbody components, the latter reminiscent of persistent Be-XRBs. This system is the first evidence of a recent supernova in the low-density surroundings of NGC 602. We detect a shell nebula around 2dFS 3831 in Hα and [O III] images and conclude that it is most likely a supernova remnant. If it is linked to the supernova explosion that created this new X-ray pulsar, its kinematic age of (2-4) × 104 yr provides a constraint on the age of the pulsar.

  4. DISCOVERY OF PSR J1227−4853: A TRANSITION FROM A LOW-MASS X-RAY BINARY TO A REDBACK MILLISECOND PULSAR

    SciTech Connect

    Roy, Jayanta; Bhattacharyya, Bhaswati; Stappers, Ben; Ray, Paul S.; Wolff, Michael; Wood, Kent S.; Chengalur, Jayaram N.; Deneva, Julia; Camilo, Fernando; Johnson, Tyrel J.; Hessels, Jason W. T.; Bassa, Cees G.; Keane, Evan F.; Ferrara, Elizabeth C.; Harding, Alice K.

    2015-02-10

    XSS J12270−4859 is an X-ray binary associated with the Fermi Large Area Telescope gamma-ray source 1FGL J1227.9−4852. In 2012 December, this source underwent a transition where the X-ray and optical luminosity dropped and the spectral signatures of an accretion disk disappeared. We report the discovery of a 1.69 millisecond pulsar (MSP), PSR J1227−4853, at a dispersion measure of 43.4 pc cm{sup −3} associated with this source, using the Giant Metrewave Radio Telescope (GMRT) at 607 MHz. This demonstrates that, post-transition, the system hosts an active radio MSP. This is the third system after PSR J1023+0038 and PSR J1824−2452I showing evidence of state switching between radio MSP and low-mass X-ray binary states. We report timing observations of PSR J1227−4853 with the GMRT and Parkes, which give a precise determination of the rotational and orbital parameters of the system. The companion mass measurement of 0.17–0.46 M{sub ⊙} suggests that this is a redback system. PSR J1227−4853 is eclipsed for about 40% of its orbit at 607 MHz with additional short-duration eclipses at all orbital phases. We also find that the pulsar is very energetic, with a spin-down luminosity of ∼10{sup 35} erg s{sup −1}. We report simultaneous imaging and timing observations with the GMRT, which suggests that eclipses are caused by absorption rather than dispersion smearing or scattering.

  5. Accretion Column Structure of Magnetic Cataclysmic Variables from X-ray Spectroscopy

    SciTech Connect

    Hoogerwerf, R; Brickhouse, N S; Mauche, C W

    2006-02-27

    Using Chandra HETG data we present light curves for individual spectral lines of Mg XI and Mg XII for EX Hydrae, an intermediate-polar type cataclysmic variable. The Mg XI light curve, folded on the white dwarf spin period, shows two spikes that are not seen in the Mg XII or broad-band light curves. Occultation of the accretion column by the body of the white dwarf would produce such spikes for an angle between the rotation axis and the accretion columns of {alpha} = 18{sup o} and a height of the Mg XI emission above the white dwarf surface of {approx}< 0.0004 white dwarf radii or {approx}< 4 km. The absence of spikes in the Mg XII and broad-band light curves could then be explained if the bulk of its emission forms at much larger height, > 0.004 white dwarf radii or > 40 km, above the white dwarf surface. The technique described in this letter demonstrates that high signal-to-noise ratio and high spectral resolution X-ray spectra can be used to map the temperature and density structure of accretion flows in magnetic cataclysmic variables. The Mg XI and Mg XII light curves are not consistent with the temperature and density structure predicted by the standard Aizu model.

  6. A test of truncation in the accretion discs of X-ray Binaries.

    NASA Astrophysics Data System (ADS)

    Eckersall, A.

    2016-06-01

    The truncated-disc model is generally used to help explain the change between the soft and hard states in X-ray Binaries, where the standard accretion disc is truncated in the inner regions and replaced by a radiatively inefficient accretion flow. There is still disagreement though in the extent of this truncation, particularly in at what point truncation begins. Here we analyze XMM EPIC-pn spectra in both the soft and hard states for a number of galactic XRBs, along with RGS data and the latest absorption and emission models to get an independent fit for the ISM column densities for each source. Specifically, we assume the 'canonical' model where the luminous accretion disc extends down to the innermost stable orbit at 6r_g, and construct a spectral model accounting for thermal, reflection and Compton processes ensuring consistent geometrical properties of the models. Rather than attempting to infer the inner disc location from spectral fitting and/or reflection models, we instead attempt a direct test of whether a consistent model will fit assuming no truncation. We discuss the implications for emission models of XRBs.

  7. Rapid oscillations in cataclysmic variables. V - H2252-035, a single-sideband X-ray and optical pulsar

    NASA Technical Reports Server (NTRS)

    Patterson, J.; Price, C. M.

    1981-01-01

    Photometric and spectroscopic observations of the optical counterpart of the X-ray source H2252-035 reveal the existence of stable periodicities of 3.59 hr and 14.31 min. Both radial velocity and photometric variations occur at the longer period, suggesting that it is the true orbital period of the underlying cataclysmic binary. The shorter period appears as a 10% modulation in the light curve, superposed on the 3.59 hr variation. The frequency is the lower orbital sideband of the X-ray pulsation frequency, suggesting that the optical pulses arise from reprocessing in the atmosphere of the secondary. Unlike the majority of X-ray pulsars, H2252-035 appears to contain a white dwarf rather than a neutron star.

  8. Long-Term Time Variability in the X-Ray Pulse Shape of the Crab Nebula Pulsar

    NASA Technical Reports Server (NTRS)

    Fazio, Giovanni G.

    2000-01-01

    This is the final performance report for our grant 'Long-Term Time Variability in the X-Ray Pulse Shape of the Crab Nebula Pulsar.' In the first year of this grant, we received the 50,000-second ROSAT (German acronym for X-ray satellite) High Resolution Images (HRI) observation of the Crab Nebula pulsar. We used the data to create a 65-ms-resolution pulse profile and compared it to a similar pulse profile obtained in 1991. No statistically significant differences were found. These results were presented at the January 1998 meeting of the American Astronomical Society. Since then, we have performed more sensitive analyses to search for potential changes in the pulse profile shape between the two data sets. Again, no significant variability was found. In order to augment this long (six-year) baseline data set, we have analyzed archival observations of the Crab Nebula pulsar with the Rossi X-Ray Timing Explorer (RXTE). While these observations have shorter time baselines than the ROSAT data set, their higher signal-to-noise offers similar sensitivity to long-term variability. Again, no significant variations have been found, confirming our ROSAT results. This work was done in collaboration with Prof. Stephen Eikenberry, Cornell University. These analyses will be included in Cornell University graduate student Dae-Sik Moon's doctoral thesis.

  9. Application of the Ghosh & Lamb relation to the spin-up/down behavior in the X-ray binary pulsar 4U 1626-67

    NASA Astrophysics Data System (ADS)

    Takagi, Toshihiro; Mihara, Tatehiro; Sugizaki, Mutsumi; Makishima, Kazuo; Morii, Mikio

    2016-06-01

    We analyzed continuous Monitor of All-sky X-ray Image/Gas Slit Camera (MAXI/GSC) data of the X-ray binary pulsar 4U 1626-67 from 2009 October to 2013 September, and determined the pulse period and the pulse-period derivative for every 60-d interval by the epoch folding method. The obtained periods are consistent with those provided by the Fermi/Gamma-ray Burst Monitor pulsar project. In all the 60-d intervals, the pulsar was observed to spin up, with the spin-up rate positively correlated with the 2-20 keV flux. We applied the accretion torque model proposed by Ghosh and Lamb (1979, ApJ, 234, 296) to the MAXI/GSC data, as well as the past data including both spin-up and spin-down phases. The "Ghosh & Lamb" relation was confirmed to successfully explain the observed relation between the spin-up/down rate and the flux. By comparing the model-predicted luminosity with the observed flux, the source distance was constrained as 5-13 kpc, which is consistent with that found by Chakrabarty (1998, ApJ, 492, 342). Conversely, if the source distance is assumed, the data can constrain the mass and radius of the neutron star, because the Ghosh & Lamb model depends on these parameters. We attempted this idea, and found that an assumed distance of, e.g., 10 kpc gives a mass in the range of 1.81-1.90 solar mass, and a radius of 11.4-11.5 km, although these results are still subject to considerable systematic uncertainties, other than distance.

  10. System mass constraints for the accreting millisecond pulsar XTE J1814-338 using Bowen fluorescence

    NASA Astrophysics Data System (ADS)

    Wang, L.; Steeghs, D.; Casares, J.; Charles, P. A.; Muñoz-Darias, T.; Marsh, T. R.; Hynes, R. I.; O'Brien, K.

    2017-04-01

    We present phase-resolved spectroscopy of the millisecond X-ray pulsar XTE J1814-338 obtained during its 2003 outburst. The spectra are dominated by high-excitation emission lines of He II λ4686, Hβ, and the Bowen blend C III/N III 4630-50 Å. We exploit the proven Bowen fluorescence technique to establish a complete set of dynamical system parameter constraints using bootstrap Doppler tomography, a first for an accreting millisecond X-ray pulsar binary. The reconstructed Doppler map of the N III λ4640 Bowen transition exhibits a statistically significant (>4σ) spot feature at the expected position of the companion star. If this feature is driven by irradiation of the surface of the Roche lobe filling companion, we derive a strict lower limit to the true radial velocity semi-amplitude K2. Combining our donor constraint with the well-constrained orbit of the neutron star leads to a determination of the binary mass ratio: q = 0.123^{+0.012}_{-0.010}. The component masses are not tightly constrained given our lack of knowledge of the binary inclination. We cannot rule out a canonical neutron star mass of 1.4 M⊙ (1.1 M⊙ < M1 < 3.1 M⊙; 95 per cent). The 68/95 per cent confidence limits of M2 are consistent with the companion being a significantly bloated, M-type main-sequence star. Our findings, combined with results from studies of the quiescent optical counterpart of XTE J1814-338, suggest the presence of a rotation-powered millisecond pulsar in XTE J1814-338 during an X-ray quiescent state. The companion mass is typical of the so-called redback pulsar binary systems (M2 ∼ 0.2 M⊙).

  11. X-ray Binaries

    NASA Astrophysics Data System (ADS)

    Lewin, Walter H. G.; van Paradijs, Jan; van den Heuvel, Edward Peter Jacobus

    1997-01-01

    Preface; 1. The properties of X-ray binaries, N. E. White, F. Nagase and A. N. Parmar; 2. Optical and ultraviolet observations of X-ray binaries J. van Paradijs and J. E. McClintock; 3. Black-hole binaries Y. Tanaka and W. H. G. Lewin; 4. X-ray bursts Walter H. G. Lewin, Jan Van Paradijs and Ronald E. Taam; 5. Millisecond pulsars D. Bhattacharya; 6. Rapid aperiodic variability in binaries M. van der Klis; 7. Radio properties of X-ray binaries R. M. Hjellming and X. Han; 8. Cataclysmic variable stars France Anne-Dominic Córdova; 9. Normal galaxies and their X-ray binary populations G. Fabbiano; 10. Accretion in close binaries Andrew King; 11. Formation and evolution of neutron stars and black holes in binaries F. Verbunt and E. P. J. van den Heuvel; 12. The magnetic fields of neutron stars and their evolution D. Bhattacharya and G. Srinivasan; 13. Cosmic gamma-ray bursts K. Hurley; 14. A catalogue of X-ray binaries Jan van Paradijs; 15. A compilation of cataclysmic binaries with known or suspected orbital periods Hans Ritter and Ulrich Kolb; References; Index.

  12. Hard X-ray emission from accretion shocks around galaxy clusters

    NASA Astrophysics Data System (ADS)

    Kushnir, Doron; Waxman, Eli

    2010-02-01

    We show that the hard X-ray (HXR) emission observed from several galaxy clusters is consistent with a simple model, in which the nonthermal emission is produced by inverse Compton scattering of cosmic microwave background photons by electrons accelerated in cluster accretion shocks: The dependence of HXR surface brightness on cluster temperature is consistent with that predicted by the model, and the observed HXR luminosity is consistent with the fraction of shock thermal energy deposited in relativistic electrons being lesssim0.1. Alternative models, where the HXR emission is predicted to be correlated with the cluster thermal emission, are disfavored by the data. The implications of our predictions to future HXR observations (e.g. by NuStar, Simbol-X) and to (space/ground based) γ-ray observations (e.g. by Fermi, HESS, MAGIC, VERITAS) are discussed.

  13. Hard X-ray emission from accretion shocks around galaxy clusters

    SciTech Connect

    Kushnir, Doron; Waxman, Eli E-mail: eli.waxman@weizmann.ac.il

    2010-02-01

    We show that the hard X-ray (HXR) emission observed from several galaxy clusters is consistent with a simple model, in which the nonthermal emission is produced by inverse Compton scattering of cosmic microwave background photons by electrons accelerated in cluster accretion shocks: The dependence of HXR surface brightness on cluster temperature is consistent with that predicted by the model, and the observed HXR luminosity is consistent with the fraction of shock thermal energy deposited in relativistic electrons being ∼<0.1. Alternative models, where the HXR emission is predicted to be correlated with the cluster thermal emission, are disfavored by the data. The implications of our predictions to future HXR observations (e.g. by NuStar, Simbol-X) and to (space/ground based) γ-ray observations (e.g. by Fermi, HESS, MAGIC, VERITAS) are discussed.

  14. The Origin of Warped, Precessing Accretion Disks in X-ray Binaries

    NASA Technical Reports Server (NTRS)

    Maloney, Philip R.; Begelman, Mitchell C.

    1997-01-01

    The radiation-driven warping instability discovered by Pringle holds considerable promise as the mechanism responsible for producing warped, precessing accretion disks in X-ray binaries. This instability is an inherently global mode of the disk, thereby avoiding the difficulties with earlier models for the precession. Here we follow up on earlier work to study the linear behavior of the instability in the specific context of a binary system. We treat the influence of the companion as an orbit-averaged quadrupole torque on the disk. The presence of this external torque allows the existence of solutions in which the direction of precession of the warp is retrograde with respect to disk rotation, in addition to the prograde solutions that exist in the absence of external torques.

  15. Determination of Local Densities in Accreted Ice Samples Using X-Rays and Digital Imaging

    NASA Technical Reports Server (NTRS)

    Broughton, Howard; Sims, James; Vargas, Mario

    1996-01-01

    At the NASA Lewis Research Center's Icing Research Tunnel ice shapes, similar to those which develop in-flight icing conditions, were formed on an airfoil. Under cold room conditions these experimental samples were carefully removed from the airfoil, sliced into thin sections, and x-rayed. The resulting microradiographs were developed and the film digitized using a high resolution scanner to extract fine detail in the radiographs. A procedure was devised to calibrate the scanner and to maintain repeatability during the experiment. The techniques of image acquisition and analysis provide accurate local density measurements and reveal the internal characteristics of the accreted ice with greater detail. This paper will discuss the methodology by which these samples were prepared with emphasis on the digital imaging techniques.

  16. ON THE TRANSITION FROM ACCRETION-POWERED TO ROTATION-POWERED MILLISECOND PULSARS

    SciTech Connect

    Takata, J.; Cheng, K. S.; Taam, Ronald E. E-mail: hrspksc@hkucc.hku.h

    2010-11-01

    The heating associated with the deposition of {gamma}-rays in an accretion disk is proposed as a mechanism to facilitate the transformation of a low-mass X-ray binary to the radio millisecond pulsar (MSP) phase. The {gamma}-ray emission produced in the outer gap accelerator in the pulsar magnetosphere likely irradiates the surrounding disk, resulting in its heating and the possible escape of matter from the system. We apply the model to PSR J1023+0038, which has recently been discovered as a newly born rotation-powered MSP. The predicted {gamma}-ray luminosity {approx}6 x 10{sup 34} erg s{sup -1} can be sufficient to explain the disappearance of the truncated disk existing during the 8 month-2 yr period prior to the 2002 observations of J1023+0038 and the energy input required for the anomalously bright optical emission of its companion star.

  17. A cold neutron star in the transient low-mass X-ray binary HETE J1900.1-2455 after 10 yr of active accretion

    NASA Astrophysics Data System (ADS)

    Degenaar, N.; Ootes, L. S.; Reynolds, M. T.; Wijnands, R.; Page, D.

    2017-02-01

    The neutron star low-mass X-ray binary and intermittent millisecond X-ray pulsar HETE J1900.1-2455 returned to quiescence in late 2015, after a prolonged accretion outburst of ≃10 yr. Using a Chandra observation taken ≃180 d into quiescence, we detect the source at a luminosity of ≃4.5 × 1031 (D/4.7 kpc)2 erg s-1 (0.5-10 keV). The X-ray spectrum can be described by a neutron star atmosphere model with a temperature of ≃54 eV for an observer at infinity. We perform thermal evolution calculations based on the 2016 quiescent data and a ≲98 eV temperature upper limit inferred from a Swift observation taken during an unusually brief (≲2 weeks) quiescent episode in 2007. We find no evidence in the present data that the thermal properties of the crust, such as the heating rate and thermal conductivity, are different than those of non-pulsating neutron stars. Finding this neutron star so cold after its long outburst imposes interesting constraints on the heat capacity of the stellar core; these become even stronger if further cooling were to occur.

  18. IDENTIFICATION OF THE HIGH-ENERGY GAMMA-RAY SOURCE 3FGL J1544.6–1125 AS A TRANSITIONAL MILLISECOND PULSAR BINARY IN AN ACCRETING STATE

    SciTech Connect

    Bogdanov, Slavko; Halpern, Jules P.

    2015-04-20

    We present X-ray, ultraviolet, and optical observations of 1RXS J154439.4–112820, the most probable counterpart of the unassociated Fermi-LAT source 3FGL J1544.6–1125. The optical data reveal rapid variability, which is a feature of accreting systems. The X-rays exhibit large-amplitude variations in the form of fast switching (within ∼10 s) between two distinct flux levels that differ by a factor of ≈10. The detailed optical and X-ray behavior is virtually identical to that seen in the accretion-disk-dominated states of the transitional millisecond pulsar (MSP) binaries PSR J1023+0038 and XSS J12270–4859, which are also associated with γ-ray sources. Based on the available observational evidence, we conclude that 1RXS J154439.4–112820 and 3FGL J1544.6–1125 are the same object, with the X-rays arising from intermittent low-luminosity accretion onto an MSP and the γ-rays originating from an accretion-driven outflow. 1RXS J154439.4–112820 is only the fourth γ-ray-emitting low-mass X-ray binary system to be identified and is likely to sporadically undergo transformations to a non-accreting rotation-powered pulsar system.

  19. A Multiwavelength Study of the Pulsar PSR B1929+10 and Its X-Ray Trail

    NASA Astrophysics Data System (ADS)

    Becker, Werner; Kramer, Michael; Jessner, Axel; Taam, Ronald E.; Jia, Jian J.; Cheng, Kwong S.; Mignani, Roberto; Pellizzoni, Alberto; de Luca, Andrea; Słowikowska, Agnieszka; Caraveo, Patrizia A.

    2006-07-01

    We report on the emission properties of PSR B1929+10 and its putative trail from a multiwavelength study performed using optical, X-ray, and radio data. XMM-Newton observations confirm the existence of the diffuse emission with a trail morphology lying in a direction opposite to the transverse motion of the pulsar. The trail spectrum is nonthermal and produced by electron-synchrotron emission in the shock between the pulsar wind and the surrounding medium. Radio data from the Effelsberg 11 cm radio continuum survey show an elongated feature that roughly coincides with the X-ray trail. Three not fully resolved radio sources seen in the NVSS survey data at 1.4 GHz match with part of the elongated radio feature seen at 11 cm. The emission properties observed from PSR B1929+10 are in excellent agreement with a nonthermal, and thus magnetospheric-radiation-dominated, emission scenario. The pulsar's X-ray spectrum is best described by a single power-law model with a photon index of 2.72+0.12-0.09. A flux contribution from the thermal emission of heated polar caps of at most ~7% is inferred from a best-fitting composite Planckian and power-law spectral model. A pure thermal emission spectrum consisting of two Planckian spectra is regarded as unlikely. A broken power-law spectral model with Ebreak=0.83+0.05-0.03 keV and the photon indexes α1=1.12+0.02-0.03 and α2=2.48+0.08-0.07 can describe the optical and X-ray data entirely in terms of a nonthermal magnetospheric origin. The X-ray pulse profile observed in the 0.2-10 keV band is found to be markedly different from the broad sinusoidal pulse profile seen in the low statistic Röntgensatellit (ROSAT) data. Fitting Gaussians to the X-ray light curve indicates the possible existence of three pulse components. A small narrow pulse, characterized by energies greater than 1 keV, is found to lead the radio main pulse by ~20°. The fraction of pulsed photons in the 0.2-10 keV band is 32%+/-4%. For the subbands 0.2-1.0 and 1

  20. Observations of Accreting Pulsars with the FERMI-GBM

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, Colleen

    2012-01-01

    The Gamma-ray Burst Monitor (GBM) on-board Fermi comprises 12 NaI detectors spanning the 8-1000 keV band and 2 BGO detectors spanning the 100 keV to 40 MeV band. These detectors view the entire unocculted sky, providing long (approximately 40 ks/day) observations of accreting pulsars daily, which allow long-term monitoring of spin-frequencies and pulsed uxes via epoch-folded searches plus daily blind searches for new pulsars. Phase averaged uxes can be measured using the Earth occultation technique. In this talk I will present highlights of GBM accretion-powered pulsar monitoring such as the discovery of a torque reversal in 4U1626-67, a high-energy QPO in A0535+26, and evidence for a stable accretion disk in OAO 1657-415.

  1. Models of the hard X-ray spectrum of AM Herculis and implications for the accretion rate

    NASA Technical Reports Server (NTRS)

    Swank, J. H.; Fabian, A. C.; Ross, R. R.

    1983-01-01

    Phenomenological fits to the hard X-ray spectrum of AM Herculis left unexplained the high equivalent width (0.8 + or - 0.1 keV) of Fe K alpha emission. A purely thermal origin implies a much steeper spectrum than was observed. With Monte Carlo calculations, scattering and fluorescent line production in a cold or partially ionized accretion column of hard X-rays emitted at the base were investigated. The strength of the iron emission and the flat spectral continuum can be explained by the effects of fluorescence and absorption within the accretion column and the surface of the white dwarf on a thermal X-ray spectrum. Thomson optical depths across the column in the range 0.2 to 0.7 are acceptable. The accretion rate and gravitational power can be deduced from the optical depth across the column, if the column size is known, and, together with the observed hard X-ray and polarized light luminosities, imply a lower limit for the luminosity in the UV to soft X-ray range, for which the observations give model-dependent values. Estimates of the column size differ by a factor of 40. Small spot sizes and low luminosities would be consistent with the soft component being the expected reprocessed bremsstrahlung and cyclotron radiation, although the constraint of matching the spectrum confines one to solutions with fluxes exceeding 20% the Eddington limits.

  2. X-Ray Evidence for the Accretion Disc-Outflow Connection in 3C 111

    NASA Technical Reports Server (NTRS)

    Tombesi, Frank; Sambruna, R. M.; Reeves, J. N.; Reynolds, C. S.; Braito, V.

    2011-01-01

    We present the spectral analysis of three Suzaku X-ray Imaging Spectrometer observations of 3C III requested to monitor the predicted variability of its ultrafast outflow on approximately 7 d time-scales. We detect an ionized iron emission line in the first observation and a blueshifted absorption line in the second, when the flux is approximately 30 per cent higher. The location of the material is constrained at less than 0.006 pc from the variability. Detailed modelling supports an identification with ionized reflection off the accretion disc at approximately 20-100rg from the black hole and a highly ionized and massive ultrafast outflow with velocity approximately 0.1c, respectively. The outflow is most probably accelerated by radiation pressure, but additional magnetic thrust cannot be excluded. The measured high outflow rate and mechanical energy support the claims that disc outflows may have a significant feedback role. This work provides the first direct evidence for an accretion disc-outflow connection in a radio-loud active galactic nucleus, possibly linked also to the jet activity.

  3. X-ray and ultraviolet radiation from accreting white dwarfs. IV - Two-temperature treatment with electron thermal conduction

    NASA Technical Reports Server (NTRS)

    Imamura, J. N.; Durisen, R. H.; Lamb, D. Q.; Weast, G. J.

    1987-01-01

    Results are reported from two-temperature calculations of the structures and X-ray spectra of radiation shocks generated by accretion onto nonmagnetic white dwarfs. The approach was necessitated by the domination of bremsstrahlung in the emission region by Compton cooling. Features of the shock model, which includes steady, spherical infall of fully ionized plasma and dominance of the stand-off shock by collisional processes, are summarized. A maximum hard X-ray temperature of about 50 keV and a maximum hard X-ray luminosity of 2 x 10 to the 36th ergs/sec were obtained. The results prove that the bulk of accretion energy cannot be transported to the star by electron thermal conduction, provided that bremsstrahlung cooling is dominant over cyclotron cooling.

  4. Winds of Change: The Physics of Accretion, Ejection, and X-ray Variability in GRS1915+105

    NASA Astrophysics Data System (ADS)

    Neilsen, Joseph

    2013-04-01

    In the last twenty years, even as multiwavelength observations of black hole X-ray binaries have led to major advances, the microquasar GRS 1915+105 has continually challenged our understanding of the physics of accretion and ejection. With its relativistic jets, ionized winds, and myriad states of rapid, extreme variability, this remarkable black hole has been alternately seen as the black sheep of X-ray binaries and a Rosetta stone for black hole astrophysics. In this talk, I will present our efforts to use a decade of high-resolution X-ray spectroscopy of GRS 1915+105 to shed light on the processes that regulate its erratic behavior. I will highlight in particular the role of accretion disk winds on time scales ranging from seconds to years. Drawing on recent results, I will discuss the broader implications of these massive winds for the physics of inflows and outflows around black holes.

  5. Discovery of the Accretion-Powered Millisecond Pulsar SWIFT 51756.9-2508 with a Low-Mass Companion

    NASA Technical Reports Server (NTRS)

    Krimm, H.A.; Markwardt, C.B.; Deloye, C.J.; Romano, P.; Chakrabarty, S.; Campana. S.; Cummings, J.C.; Galloway, D.K.; Gehrels, N.; Hartman, J.M.; Kaaret, P.; Morgan, E.H.; Tueller, J

    2007-01-01

    We report on the discovery by the Swift Gamma-Ray Burst Explorer of the eighth known transient accretion-powered millisecond pulsar: SWIFT J1756.9-2508, as part of routine observations with the Swift Burst Alert Telescope hard X-ray transient monitor. The pulsar was subsequently observed by both the X-Ray Telescope on Swift and the Rossi X-Ray Timing Explorer Proportional Counter Array. It has a spin frequency of 182 Hz (5.5 ms) and an orbital period of 54.7 minutes. The minimum companion mass is between 0.0067 and 0.0086 Solar Mass, depending on the mass of the neutron star, and the upper limit on the mass is 0.030 Solar Mass (95% confidence level). Such a low mass is inconsistent with brown dwarf models. and comparison with white dwarf models suggests that the companion is a He-dominated donor whose thermal cooling has been at least modestly slowed by irradiation from the accretion flux. No X-ray bursts. dips, eclipses or quasi-periodic oscillations were detected. The current outburst lasted approx. 13 days and no earlier outbursts were found in archival data.

  6. ACCRETION DISK DYNAMO AS THE TRIGGER FOR X-RAY BINARY STATE TRANSITIONS

    SciTech Connect

    Begelman, Mitchell C.; Armitage, Philip J.; Reynolds, Christopher S.

    2015-08-20

    Magnetohydrodynamic accretion disk simulations suggest that much of the energy liberated by the magnetorotational instability (MRI) can be channeled into large-scale toroidal magnetic fields through dynamo action. Under certain conditions, this field can dominate over gas and radiation pressure in providing vertical support against gravity, even close to the midplane. Using a simple model for the creation of this field, its buoyant rise, and its coupling to the gas, we show how disks could be driven into this magnetically dominated state and deduce the resulting vertical pressure and density profiles. Applying an established criterion for MRI to operate in the presence of a toroidal field, we show that magnetically supported disks can have two distinct MRI-active regions, separated by a “dead zone” where local MRI is suppressed, but where magnetic energy continues to flow upward from the dynamo region below. We suggest that the relative strengths of the MRI zones, and the local poloidal flux, determine the spectral states of X-ray binaries. Specifically, “intermediate” and “hard” accretion states occur when MRI is triggered in the hot, upper zone of the corona, while disks in “soft” states do not develop the upper MRI zone. We discuss the conditions under which various transitions should take place and speculate on the relationship of dynamo activity to the various types of quasi-periodic oscillations that sometimes appear in the hard spectral components. The model also explains why luminous accretion disks in the “soft” state show no signs of the thermal/viscous instability predicted by standard α-models.

  7. Accretion Disk Dynamo as the Trigger for X-Ray Binary State Transitions

    NASA Astrophysics Data System (ADS)

    Begelman, Mitchell C.; Armitage, Philip J.; Reynolds, Christopher S.

    2015-08-01

    Magnetohydrodynamic accretion disk simulations suggest that much of the energy liberated by the magnetorotational instability (MRI) can be channeled into large-scale toroidal magnetic fields through dynamo action. Under certain conditions, this field can dominate over gas and radiation pressure in providing vertical support against gravity, even close to the midplane. Using a simple model for the creation of this field, its buoyant rise, and its coupling to the gas, we show how disks could be driven into this magnetically dominated state and deduce the resulting vertical pressure and density profiles. Applying an established criterion for MRI to operate in the presence of a toroidal field, we show that magnetically supported disks can have two distinct MRI-active regions, separated by a “dead zone” where local MRI is suppressed, but where magnetic energy continues to flow upward from the dynamo region below. We suggest that the relative strengths of the MRI zones, and the local poloidal flux, determine the spectral states of X-ray binaries. Specifically, “intermediate” and “hard” accretion states occur when MRI is triggered in the hot, upper zone of the corona, while disks in “soft” states do not develop the upper MRI zone. We discuss the conditions under which various transitions should take place and speculate on the relationship of dynamo activity to the various types of quasi-periodic oscillations that sometimes appear in the hard spectral components. The model also explains why luminous accretion disks in the “soft” state show no signs of the thermal/viscous instability predicted by standard α-models.

  8. X-Ray Analysis of the Proper Motion and Pulsar Wind Nebula for PSR J1741-2054

    NASA Technical Reports Server (NTRS)

    Auchettl, Katie; Slane, Patrick; Romani, Roger W.; Posselt, Bettina; Pavlov, George G.; Kargaltsev, Oleg; Ng, C-Y.; Temim, Tea; Weisskopf, Martin C.; Bykov, Andrei; Swartz, Douglas

    2015-01-01

    We obtained six observations of PSR J1741-2054 using the Chandra ACIS-S detector totaling approx.300 ks. By registering this new epoch of observations to an archival observation taken 3.2 yr earlier using X-ray point sources in the field of view, we have measured the pulsar proper motion at micron = 109 +/- 10 mas yr(exp. -1) in a direction consistent with the symmetry axis of the observed H(alpha) nebula. We investigated the inferred past trajectory of the pulsar but find no compelling association with OB associations in which the progenitor may have originated. We confirm previous measurements of the pulsar spectrum as an absorbed power law with photon index gamma = 2.68 +/- 0.04, plus a blackbody with an emission radius of (4.5(+3.2/-2.5))d(0.38) km, for a DM-estimated distance of 0.38d(0.38) kpc and a temperature of 61.7 +/- 3.0 eV. Emission from the compact nebula is well described by an absorbed power law model with a photon index of gamma = 1.67 +/- 0.06, while the diffuse emission seen as a trail extending northeast of the pulsar shows no evidence of synchrotron cooling. We also applied image deconvolution techniques to search for small-scale structures in the immediate vicinity of the pulsar, but found no conclusive evidence for such structures.

  9. PATCHY ACCRETION DISKS IN ULTRA-LUMINOUS X-RAY SOURCES

    SciTech Connect

    Miller, J. M.; Bachetti, M.; Barret, D.; Webb, N. A.; Harrison, F. A.; Walton, D. J.; Rana, V.; Fabian, A. C.

    2014-04-10

    The X-ray spectra of the most extreme ultra-luminous X-ray sources—those with L ≥ 10{sup 40} erg s{sup –1}—remain something of a mystery. Spectral roll-over in the 5-10 keV band was originally detected in the deepest XMM-Newton observations of the brightest sources; this is confirmed in subsequent NuSTAR spectra. This emission can be modeled via Comptonization, but with low electron temperatures (kT{sub e} ≅ 2 keV) and high optical depths (τ ≅ 10) that pose numerous difficulties. Moreover, evidence of cooler thermal emission that can be fit with thin disk models persists, even in fits to joint XMM-Newton and NuSTAR observations. Using NGC 1313 X-1 as a test case, we show that a patchy disk with a multiple temperature profile may provide an excellent description of such spectra. In principle, a number of patches within a cool disk might emit over a range of temperatures, but the data only require a two-temperature profile plus standard Comptonization, or three distinct blackbody components. A mechanism such as the photon bubble instability may naturally give rise to a patchy disk profile, and could give rise to super-Eddington luminosities. It is possible, then, that a patchy disk (rather than a disk with a standard single-temperature profile) might be a hallmark of accretion disks close to or above the Eddington limit. We discuss further tests of this picture and potential implications for sources such as narrow-line Seyfert-1 galaxies and other low-mass active galactic nuclei.

  10. Possible detection of a cyclotron resonance scattering feature in the X-ray pulsar 4U 1909+07

    SciTech Connect

    Jaisawal, Gaurava K.; Naik, Sachindra; Paul, Biswajit

    2013-12-10

    We present timing and broad band spectral studies of the high-mass X-ray binary pulsar 4U 1909+07 using data from Suzaku observations during 2010 November 2-3. The pulse period of the pulsar is estimated to be 604.11 ± 0.14 s. Pulsations are seen in the X-ray light curve up to ∼70 keV. The pulse profile is found to be strongly energy-dependent: a complex, multi-peaked structure at low energy becomes a simple single peak at higher energy. We found that the 1-70 keV pulse-averaged continuum can be fit by the sum of a blackbody and a partial covering Negative and Positive power law with Exponential cutoff model. A weak iron fluorescence emission line at 6.4 keV was detected in the spectrum. An absorption-like feature at ∼44 keV was clearly seen in the residuals of the spectral fitting, independent of the continuum model adopted. To check the possible presence of a cyclotron resonance scattering feature (CRSF) in the spectrum, we normalized the pulsar spectrum with the spectrum of the Crab Nebula. The resulting Crab ratio also showed a clear dip centered at ∼44 keV. We performed statistical tests on the residuals of the spectral fitting and also on the Crab spectral ratio to determine the significance of the absorption-like feature and identified it as a CRSF of the pulsar. We estimated the corresponding surface magnetic field of the pulsar to be 3.8 × 10{sup 12} G.

  11. An optical synchrotron nebula around the X-ray pulsar 0540 693 in the Large Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Chanan, G. A.; Helfand, D. J.; Reynolds, S. P.

    1984-12-01

    The discovery of extended optical continuum emission around the recently discovered 50 ms X-ray pulsar in the supernova remnant 0540 - 693 is reported. Exposures in blue and red broad-band filters made with the CTIO 4 m telescope and prime focus CCD show a center-brightened but clearly extended nebula about 4 arcsec in diameter (FWHM), while an image in an (O III) filter shows an 8 arcsec diameter shell (as reported earlier) which encloses the continuum source. The extinction-correction magnitudes B = 17.5 and I = 16.4 both correspond to flux densities which lie directly on the extrapolation of the observed X-ray power-law spectrum, suggesting that the emission from 10 to the 14.5 Hz to 10 to the 18th Hz is synchrotron radiation from a single population of particles. Line emission is shown to be only a small contaminant in the broad-band images. Thus the 0540 - 693 system is apparently a very close analog of the Crab Nebula. Any point source component in the former nebula must have B greater than 20; the Crab pulsar at this distance would have B approximately 23. The implications of the observations for the energetics of the pulsar/nebula system are discussed.

  12. An evolutionary channel towards the accreting millisecond pulsar SAX J1808.4-3658

    NASA Astrophysics Data System (ADS)

    Chen, Wen-Cong

    2017-02-01

    Recent timing analysis reveals that the orbital period of the first-discovered accreting millisecond pulsar SAX J1808.4-3658 is increasing at a rate dot{P}_orb=(3.89± 0.15)× 10^{-12} s s^{-1}, which is at least one order of magnitude higher than the value arising from the conservative mass transfer. An ejection of mass-loss rate of 10- 9 M⊙ yr- 1 from the donor star at the inner Lagrangian point during the quiescence state could interpret the observed orbital-period derivative. However, it is unknown whether this source can offer such a high mass-loss rate. In this work, we attempt to investigate an evolutionary channel towards SAX J1808.4-3658. Once the accretion disc becomes thermally and viscously unstable, the spin-down luminosity of the millisecond pulsar and the X-ray luminosity during outbursts are assumed to evaporate the donor star, and the resulting winds carry away the specific orbital angular momentum at the inner Lagrangian point. Our scenario could yield the observed orbital period, the orbital-period derivative, and the peak X-ray luminosity during outbursts. Low-mass X-ray binaries with a 1.0 M⊙ donor star, and an orbital period in the range of 0.8-1.5 d, may be the progenitor of SAX J1808.4-3658. Our numerical calculations propose that the current donor-star mass is 0.044 M⊙, which is approximately in agreement with the minimum mass of the donor star. In addition, our scenario can also account for the formation of black widows or the diamond planets like PSR J1719-1438.

  13. A Chandra look at the X-ray faint millisecond pulsars in the globular cluster NGC 6752

    NASA Astrophysics Data System (ADS)

    Forestell, L. M.; Heinke, C. O.; Cohn, H. N.; Lugger, P. M.; Sivakoff, G. R.; Bogdanov, S.; Cool, A. M.; Anderson, J.

    2014-06-01

    We combine new and archival Chandra observations of the globular cluster NGC 6752 to create a deeper X-ray source list, and study the faint radio millisecond pulsars (MSPs) of this cluster. We detect four of the five MSPs in NGC 6752, and present evidence for emission from the fifth. The X-rays from these MSPs are consistent with thermal emission from the neutron star surfaces, with significantly higher fitted blackbody temperatures than other globular cluster MSPs (though we cannot rule out contamination by non-thermal emission or other X-ray sources). NGC 6752 E is one of the lowest-LX MSPs known, with LX(0.3-8 keV) = 1.0^{+0.9}_{-0.5}× 10^{30} erg s-1. We check for optical counterparts of the three isolated MSPs in the core using new Hubble Space Telescope Advanced Camera for Surveys images, finding no plausible counterparts, which is consistent with their lack of binary companions. We compile measurements of LX and spin-down power for radio MSPs from the literature, including errors where feasible. We find no evidence that isolated MSPs have lower LX than MSPs in binary systems, omitting binary MSPs showing emission from intrabinary wind shocks. We find weak evidence for an inverse correlation between the estimated temperature of the MSP X-rays and the known MSP spin period, consistent with the predicted shrinking of the MSP polar cap size with increasing spin period.

  14. The slow X-ray pulsar SXP 1062 and associated supernova remnant in the Wing of the Small Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Oskinova, L. M.; Guerrero, M. A.; Hénault-Brunet, V.; Sun, W.; Chu, Y.-H.; Evans, C.; Gallagher, J. S.; Gruendl, R. A.; Reyes-Iturbide, J.

    2013-03-01

    SXP 1062 is an exceptional case of a young neutron star in a wind-fed high-mass X-ray binary associated with a supernova remnant. A unique combination of measured spin period, its derivative, luminosity and young age makes this source a key probe for the physics of accretion and neutron star evolution. Theoretical models proposed to explain the properties of SXP 1062 shall be tested with new data.

  15. Pulsar-Wind Nebulae and Magnetar Outflows: Observations at Radio, X-Ray, and Gamma-Ray Wavelengths

    NASA Astrophysics Data System (ADS)

    Reynolds, Stephen P.; Pavlov, George G.; Kargaltsev, Oleg; Klingler, Noel; Renaud, Matthieu; Mereghetti, Sandro

    2017-03-01

    We review observations of several classes of neutron-star-powered outflows: pulsar-wind nebulae (PWNe) inside shell supernova remnants (SNRs), PWNe interacting directly with interstellar medium (ISM), and magnetar-powered outflows. We describe radio, X-ray, and gamma-ray observations of PWNe, focusing first on integrated spectral-energy distributions (SEDs) and global spectral properties. High-resolution X-ray imaging of PWNe shows a bewildering array of morphologies, with jets, trails, and other structures. Several of the 23 so far identified magnetars show evidence for continuous or sporadic emission of material, sometimes associated with giant flares, and a few "magnetar-wind nebula" have been recently identified.

  16. A Compact X-Ray Source in the Radio Pulsar-wind Nebula G141.2+5.0

    NASA Astrophysics Data System (ADS)

    Reynolds, Stephen P.; Borkowski, Kazimierz J.

    2016-01-01

    We report the results of a 50 ks Chandra observation of the recently discovered radio object G141.2+5.0, presumed to be a pulsar-wind nebula. We find a moderately bright unresolved X-ray source that we designate CXOU J033712.8 615302 coincident with the central peak radio emission. An absorbed power-law fit to the 241 counts describes the data well, with absorbing column {N}H=6.7(4.0,9.7)× {10}21 cm-2 and photon index {{Γ }}=1.8(1.4,2.2). For a distance of 4 kpc, the unabsorbed luminosity between 0.5 and 8 keV is {1.7}-0.3+0.4× {10}32 erg s-1 (90% confidence intervals). Both LX and Γ are quite typical of pulsars in PWNe. No extended emission is seen; we estimate a conservative 3σ upper limit to the surface brightness of any X-ray PWN near the point source to be 3× {10}-17 erg cm-2 s-1 arcsec-2 between 0.5 and 8 keV, assuming the same spectrum as the point source; for a nebula of diameter 13\\prime\\prime , the flux limit is 6% of the flux of the point source. The steep radio spectrum of the PWN (α ˜ -0.7), if continued to the X-ray without a break, predicts {L}{{X}} {{(nebula)}}˜ 1× {10}33 erg s-1, so additional spectral steepening between radio and X-rays is required, as is true of all known PWNe. The high Galactic latitude gives a z-distance of 350 pc above the Galactic plane, quite unusual for a Population I object.

  17. UV And X-Ray Emission from Impacts of Fragmented Accretion Streams on Classical T Tauri Stars

    NASA Astrophysics Data System (ADS)

    Colombo, Salvatore; Orlando, Salvatore; Peres, Giovanni; Argiroffi, Costanza; Reale, Fabio

    2016-07-01

    According to the magnetoshperic accretion scenario, during their evo- lution, Classical T Tauri stars accrete material from their circumstellar disk. The accretion process is regulated by the stellar magnetic eld and produces hot and dense post-shocks on the stellar surface as a result of impacts of the downfalling material. The impact regions are expected to strongly radiate in UV and X-rays. Several lines of evidence support the magnetospheric accretion scenario, especially in optical and infrared bands. However several points still remain unclear as, for instance,where the complex-pro le UV lines originate, or whether and how UV and X-ray emission is produced in the same shock region. The analysis of a large solar eruption has shown that EUV excesses might be e ectively produced by the impact of dense fragments onto the stellar surface. Since a steady accretion stream does not reprouce observations, in this work we investi- gate the e ects of a fragmented accretion stream on the uxes and pro les of C IV and O VIII emission lines. To this end we model the impact of a fragmented accretion stream onto the chromosphere of a CTTS with 2D axysimmetric magneto-hydrodynamic simulations. Our model takes into account of the gravity, the stellar magnetic eld, the thermal conduction and the radiative cooling from an optically thin plasma. From the model results, we synthesize the UV and X-ray emission including the e ect of Doppler shift along the line of sight. We nd that a fragmented accretion stream produces complex pro les of UV emission lines which consists of multiple components with di erent Doppler shifts. Our model predicts line pro les that are consistent with those observed and explain their origin as due to the stream fragmentation.

  18. Improved reflection models of black hole accretion disks: Treating the angular distribution of X-rays

    SciTech Connect

    García, J.; Steiner, J. F.; McClintock, J. E.; Brenneman, L. E-mail: jsteiner@head.cfa.harvard.edu E-mail: lbrenneman@cfa.harvard.edu; and others

    2014-02-20

    X-ray reflection models are used to constrain the properties of the accretion disk, such as the degree of ionization of the gas and the elemental abundances. In combination with general relativistic ray tracing codes, additional parameters like the spin of the black hole and the inclination to the system can be determined. However, current reflection models used for such studies only provide angle-averaged solutions for the flux reflected at the surface of the disk. Moreover, the emission angle of the photons changes over the disk due to relativistic light bending. To overcome this simplification, we have constructed an angle-dependent reflection model with the XILLVER code and self-consistently connected it with the relativistic blurring code RELLINE. The new model, relxill, calculates the proper emission angle of the radiation at each point on the accretion disk and then takes the corresponding reflection spectrum into account. We show that the reflected spectra from illuminated disks follow a limb-brightening law highly dependent on the ionization of disk and yet different from the commonly assumed form I∝ln (1 + 1/μ). A detailed comparison with the angle-averaged model is carried out in order to determine the bias in the parameters obtained by fitting a typical relativistic reflection spectrum. These simulations reveal that although the spin and inclination are mildly affected, the Fe abundance can be overestimated by up to a factor of two when derived from angle-averaged models. The fit of the new model to the Suzaku observation of the Seyfert galaxy Ark 120 clearly shows a significant improvement in the constraint of the physical parameters, in particular by enhancing the accuracy in the inclination angle and the spin determinations.

  19. Glitch and pulsed flux increase in Anomalous X-ray Pulsar 1E 1048.1-5937.

    NASA Astrophysics Data System (ADS)

    Dib, R.; Kaspi, V. M.; Gavriil, F. P.; Woods, P. M.

    2007-04-01

    We report the detection of a sudden spin-up and pulsed flux increase in the 6.5-s anomalous X-ray pulsar 1E 1048.1-5937 in regular timing observations made with RXTE. The event, which occured between MJD 54181 (2007 March 22) and 54187 (2007 March 28), but most likely on MJD 54186 (2007 March 27) can be characterized by a fractional increase in the rotational frequency of magnitude (deltaNU/NU = 2.7+/-0.7 x 10-6).

  20. X-Ray and Optical Study of the Gamma-ray Source 3FGL J0838.8–2829: Identification of a Candidate Millisecond Pulsar Binary and an Asynchronous Polar

    NASA Astrophysics Data System (ADS)

    Halpern, Jules P.; Bogdanov, Slavko; Thorstensen, John R.

    2017-04-01

    We observed the field of the Fermi source 3FGL J0838.8‑2829 in optical and X-rays, initially motivated by the cataclysmic variable (CV) 1RXS J083842.1‑282723 that lies within its error circle. Several X-ray sources first classified as CVs have turned out to be γ-ray emitting millisecond pulsars (MSPs). We find that 1RXS J083842.1‑282723 is in fact an unusual CV, a stream-fed asynchronous polar in which accretion switches between magnetic poles (that are ≈120° apart) when the accretion rate is at minimum. High-amplitude X-ray modulation at periods of 94.8 ± 0.4 minutes and 14.7 ± 1.2 hr are seen. The former appears to be the spin period, while the latter is inferred to be one-third of the beat period between the spin and the orbit, implying an orbital period of 98.3 ± 0.5 minutes. We also measure an optical emission-line spectroscopic period of 98.413 ± 0.004 minutes, which is consistent with the orbital period inferred from the X-rays. In any case, this system is unlikely to be the γ-ray source. Instead, we find a fainter variable X-ray and optical source, XMMU J083850.38‑282756.8, that is modulated on a timescale of hours in addition to exhibiting occasional sharp flares. It resembles the black widow or redback pulsars that have been discovered as counterparts of Fermi sources, with the optical modulation due to heating of the photosphere of a low-mass companion star by, in this case, an as-yet undetected MSP. We propose XMMU J083850.38‑282756.8 as the MSP counterpart of 3FGL J0838.8‑2829.

  1. Accretion disk coronae of intermediate polar cataclysmic variables. 3D magnetohydrodynamic modelling and thermal X-ray emission

    NASA Astrophysics Data System (ADS)

    Barbera, E.; Orlando, S.; Peres, G.

    2017-04-01

    Context. Intermediate polar cataclysmic variables (IPCV) contain a magnetic, rotating white dwarf surrounded by a magnetically truncated accretion disk. To explain their strong flickering X-ray emission, accretion has been successfully taken into account. Nevertheless, observations suggest that accretion phenomena might not be the only process behind it. An intense flaring activity occurring on the surface of the disk may generate a corona, contribute to the thermal X-ray emission, and influence the system stability. Aims: Our purposes are: investigating the formation of an extended corona above the accretion disk, due to an intense flaring activity occurring on the disk surface; studying the effects of flares on the disk and stellar magnetosphere; assessing its contribution to the observed thermal X-ray flux. Methods: We have developed a 3D magnetohydrodynamic (MHD) model of a IPCV system. The model takes into account gravity, disk viscosity, thermal conduction, radiative losses, and coronal flare heating through heat injection at randomly chosen locations on the disk surface. To perform a parameter space exploration, several system conditions have been considered, with different magnetic field intensity and disk density values. From the results of the evolution of the model, we have synthesized the thermal X-ray emission. Results: The simulations show the formation of an extended corona, linking disk and star. The flaring activity is capable of strongly influencing the disk configuration and possibly its stability, effectively deforming the magnetic field lines. Hot plasma evaporation phenomena occur in the layer immediately above the disk. The flaring activity gives rise to a thermal X-ray emission in both the [ 0.1-2.0 ] keV and the [ 2.0-10 ] keV X-ray bands. Conclusions: An intense coronal activity occurring on the disk surface of an IPCV can affect the structure of the disk depending noticeably on the density of the disk and the magnetic field of the central

  2. Black hole accretion disks - Electrodynamic coupling of accretion-disk coronae and the partitioning of soft and hard X-ray emission

    NASA Technical Reports Server (NTRS)

    Kuperus, M.; Ionson, J. A.

    1985-01-01

    It is demonstrated that the observed large ratio of hard to soft X-ray emission and the bimodel behavior of black hole accreting X-ray sources such as Cygnus X-1 can be described in terms of a magnetically structured accretion disk corona which is electrodynamically coupled to the disk turbulent motions while the disk is thermodynamically coupled to the corona as described by a feedback parameter delta. The observed ratio of hard to soft X-ray emission is independent of the disk thickness, and weakly dependent of the disk parameter alpha relating the disk viscous stresses to the total pressure. Observed values of the luminosity ratio point towards strong differences of the feedback of the low state compared to the high state, in the sense that low state means small feedback (delta less than 0.2) and high state means strong feedback delta of about 0.5.

  3. Stronger Reflection from Black Hole Accretion Disks in Soft X-Ray States

    NASA Astrophysics Data System (ADS)

    Steiner, James F.; Remillard, Ronald A.; García, Javier A.; McClintock, Jeffrey E.

    2016-10-01

    We analyze 15,000 spectra of 29 stellar-mass black hole (BH) candidates collected over the 16 year mission lifetime of Rossi X-ray Timing Explorer using a simple phenomenological model. As these BHs vary widely in luminosity and progress through a sequence of spectral states, which we broadly refer to as hard and soft, we focus on two spectral components: the Compton power law and the reflection spectrum it generates by illuminating the accretion disk. Our proxy for the strength of reflection is the equivalent width of the Fe-K line as measured with respect to the power law. A key distinction of our work is that for all states we estimate the continuum under the line by excluding the thermal disk component and using only the component that is responsible for fluorescing the Fe-K line, namely, the Compton power law. We find that reflection is several times more pronounced (˜3) in soft compared to hard spectral states. This is most readily caused by the dilution of the Fe line amplitude from Compton scattering in the corona, which has a higher optical depth in hard states. Alternatively, this could be explained by a more compact corona in soft (compared to hard) states, which would result in a higher reflection fraction.

  4. The Crab Pulsar Observed by RXTE: Monitoring the X-Ray to Radio Delay for 16 Years

    NASA Technical Reports Server (NTRS)

    Rots, Arnold; Jahoda, Keith

    2012-01-01

    In 2004 we published the results of monitoring the Crab Pulsar by RXTE. At that time we determined that the primary pulse of the pulsar at X-ray energies precedes its radio counterpart by about 0.01 period in phase or approximately 330 micro seconds. However, we could not establish unambiguously whether the delay is in phase or due to a difference in pathlength. At this time we have twice the time baseline we had in 2004 and we present the same analysis, but now over a period of 16 years, which will represent almost the full mission and the best that will be available from RXTE. The full dataset shows that the phase delay has been decreasing faster than the pulse frequency over the 16 year baseline and that there are variations in the delay on a variety of timescales.

  5. Compact Stellar X-ray Sources

    NASA Astrophysics Data System (ADS)

    Lewin, Walter H. G.; van der Klis, Michiel

    2006-04-01

    1. Accreting neutron stars and black holes: a decade of discoveries D. Psaltis; 2. Rapid X-ray variability M. van der Klis; 3. New views of thermonuclear bursts T. Strohmayer and L. Bildsten; 4. Black hole binaries J. McClintock and R. Remillard; 5. Optical, ultraviolet and infrared observations of X-ray binaries P. Charles and M. Coe; 6. Fast X-ray transients and X-ray flashes J. Heise and J. in 't Zand; 7. Isolated neutron stars V. Kaspi, M. Roberts and A. Harding; 8. Globular cluster X-ray sources F. Verbunt and W. Lewin; 9. Jets from X-ray binaries R. Fender; 10. X-Rays from cataclysmic variables E. Kuulkers, A. Norton, A. Schwope and B. Warner; 11. Super soft sources P. Kahabka and E. van den Heuvel; 12. Compact stellar X-ray sources in normal galaxies G. Fabbiano and N. White; 13. Accretion in compact binaries A. King; 14. Soft gamma repeaters and anomalous X-ray pulsars: magnetar candidates P. Woods and C. Thompson; 15. Cosmic gamma-ray bursts, their afterglows, and their host galaxies K. Hurley, R. Sari and S. Djorgovski; 16. Formation and evolution of compact stellar X-ray sources T. Tauris and E. van den Heuvel.

  6. Compact Stellar X-ray Sources

    NASA Astrophysics Data System (ADS)

    Lewin, Walter; van der Klis, Michiel

    2010-11-01

    1. Accreting neutron stars and black holes: a decade of discoveries D. Psaltis; 2. Rapid X-ray variability M. van der Klis; 3. New views of thermonuclear bursts T. Strohmayer and L. Bildsten; 4. Black hole binaries J. McClintock and R. Remillard; 5. Optical, ultraviolet and infrared observations of X-ray binaries P. Charles and M. Coe; 6. Fast X-ray transients and X-ray flashes J. Heise and J. in 't Zand; 7. Isolated neutron stars V. Kaspi, M. Roberts and A. Harding; 8. Globular cluster X-ray sources F. Verbunt and W. Lewin; 9. Jets from X-ray binaries R. Fender; 10. X-Rays from cataclysmic variables E. Kuulkers, A. Norton, A. Schwope and B. Warner; 11. Super soft sources P. Kahabka and E. van den Heuvel; 12. Compact stellar X-ray sources in normal galaxies G. Fabbiano and N. White; 13. Accretion in compact binaries A. King; 14. Soft gamma repeaters and anomalous X-ray pulsars: magnetar candidates P. Woods and C. Thompson; 15. Cosmic gamma-ray bursts, their afterglows, and their host galaxies K. Hurley, R. Sari and S. Djorgovski; 16. Formation and evolution of compact stellar X-ray sources T. Tauris and E. van den Heuvel.

  7. SAX J1808.4-3658, an accreting millisecond pulsar shining in gamma rays?

    NASA Astrophysics Data System (ADS)

    de Oña Wilhelmi, E.; Papitto, A.; Li, J.; Rea, N.; Torres, D. F.; Burderi, L.; Di Salvo, T.; Iaria, R.; Riggio, A.; Sanna, A.

    2016-03-01

    We report the detection of a possible gamma-ray counterpart of the accreting millisecond pulsar SAX J1808.4-3658. The analysis of ˜6 yr of data from the Large Area Telescope on board the Fermi gamma-ray Space Telescope (Fermi-LAT) within a region of 15° radius around the position of the pulsar reveals a point gamma-ray source detected at a significance of ˜6σ (test statistic TS = 32), with a position compatible with that of SAX J1808.4-3658 within the 95 per cent confidence level. The energy flux in the energy range between 0.6 and 10 GeV amounts to (2.1 ± 0.5) × 10-12 erg cm-2 s-1 and the spectrum is represented well by a power-law function with photon index 2.1 ± 0.1. We searched for significant variation of the flux at the spin frequency of the pulsar and for orbital modulation, taking into account the trials due to the uncertainties in the position, the orbital motion of the pulsar and the intrinsic evolution of the pulsar spin. No significant deviation from a constant flux at any time-scale was found, preventing a firm identification via time variability. Nonetheless, the association of the LAT source as the gamma-ray counterpart of SAX J1808.4-3658 would match the emission expected from the millisecond pulsar, if it switches on as a rotation-powered source during X-ray quiescence.

  8. Strong Role of Non-stationary Accretion in Spectral Transitions of X-ray Binaries and Implications for Revealing the Accretion Geometry and Broadband Radiation Mechanisms

    NASA Astrophysics Data System (ADS)

    Yu, Wenfei; Yan, Zhen; Tang, Jing; Wu, Yuxiang

    Observations of spectral transitions from the hard state to the soft state in bright X-ray binaries show strong evidence that the rate-of-change of the mass accretion rate plays a dominant role in determining the luminosity at which the spectral transition occurs. This indicates that in many cases, especially accretion in transients during outbursts, the rate-of-change of the mass accretion rate is the primary parameter driving high energy phenomena. Although this goes beyond the scope of current stationary model of disk and jet, it tells us that it is the rate-of-change of the mass accretion rate that we need to trace observationally. Since state transition is a broadband phenomenon, multi-wavelength observations of spectral transitions of different rate-of-changes of mass accretion rate are expect to reveal the accretion geometry and broadband radiation mechanisms.

  9. X-ray jets from B2224+65: A Middle-aged Pulsar's New Trick

    NASA Astrophysics Data System (ADS)

    Wang, Q. Daniel

    2014-11-01

    B2224+65 is well known to have a very high proper motion and to be associated with the ``Guitar Nebula'' in the opposite direction of the motion. A jet-like X-ray feature, however, is offset from its proper motion direction by 118 degree. Furthermore, the X-ray luminosity and morphology of the feature changed significantly between three Chandra observations. We are carrying out a detailed measurements of the X-ray spectral variation with time and across the feature and are critically testing scenarios proposed to explain this enigmatic system. The study will also have strong implications for understanding somewhat similar linear nonthermal X-ray-emitting features that have been identified in the central 100 pc region of the Galaxy.

  10. DISCOVERY OF A FAINT X-RAY COUNTERPART AND A PARSEC-LONG X-RAY TAIL FOR THE MIDDLE-AGED, {gamma}-RAY-ONLY PULSAR PSR J0357+3205

    SciTech Connect

    De Luca, A.; Bignami, G. F.; Marelli, M.; Caraveo, P. A.; Mignani, R. P.; Hummel, W.; Collins, S.; Shearer, A.; Parkinson, P. M. Saz; Belfiore, A.

    2011-06-01

    The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope opened a new era for pulsar astronomy, detecting {gamma}-ray pulsations from more than 60 pulsars, {approx}40% of which are not seen at radio wavelengths. One of the most interesting sources discovered by LAT is PSR J0357+3205, a radio-quiet, middle-aged ({tau}{sub C} {approx} 0.5 Myr) pulsar standing out for its very low spin-down luminosity (E-dot{sub rot}{approx}6x10{sup 33} erg s{sup -1}), indeed the lowest among non-recycled {gamma}-ray pulsars. A deep X-ray observation with Chandra (0.5-10 keV), coupled with sensitive optical/infrared ground-based images of the field, allowed us to identify PSR J0357+3205 as a faint source with a soft spectrum, consistent with a purely non-thermal emission (photon index {Gamma} = 2.53 {+-} 0.25). The absorbing column (N{sub H} = 8 {+-} 4 x 10{sup 20} cm{sup -2}) is consistent with a distance of a few hundred parsecs. Moreover, the Chandra data unveiled a huge (9 arcmin long) extended feature apparently protruding from the pulsar. Its non-thermal X-ray spectrum points to synchrotron emission from energetic particles from the pulsar wind, possibly similar to other elongated X-ray tails associated with rotation-powered pulsars and explained as bow-shock pulsar wind nebulae (PWNe). However, energetic arguments as well as the peculiar morphology of the diffuse feature associated with PSR J0357+3205 make the bow-shock PWN interpretation rather challenging.

  11. Pulsator-like Spectra from Ultraluminous X-Ray Sources and the Search for More Ultraluminous Pulsars

    NASA Astrophysics Data System (ADS)

    Pintore, F.; Zampieri, L.; Stella, L.; Wolter, A.; Mereghetti, S.; Israel, G. L.

    2017-02-01

    Ultraluminous X-ray sources (ULXs) are a population of extragalactic objects whose luminosity exceeds the Eddington limit for a 10 M ⊙ black hole (BH). Their properties have been widely interpreted in terms of accreting stellar-mass or intermediate-mass BHs. However at least three neutron stars (NSs) have been recently identified in ULXs through the discovery of periodic pulsations. Motivated by these findings we studied the spectral properties of a sample of bright ULXs using a simple continuum model which was extensively used to fit the X-ray spectra of accreting magnetic NSs in the Galaxy. We found that such a model, consisting of a power-law with a high-energy exponential cut-off, fits most of the ULX spectra analyzed here very well, at a level comparable to that of models involving an accreting BH. On these grounds alone we suggest that other non-pulsating ULXs may host NSs. We also found that above 2 keV the spectrum of known pulsating ULXs is harder than that of the majority of the other ULXs of the sample, with only IC 342 X-1 and Ho IX X-1 displaying spectra of comparable hardness. We thus suggest that these two ULXs may host an accreting NS and encourage searches for periodic pulsations in the flux.

  12. X-ray and UV correlation in the quiescent emission of Cen X-4, evidence of accretion and reprocessing

    NASA Astrophysics Data System (ADS)

    Bernardini, F.; Cackett, E. M.; Brown, E. F.; D'Angelo, C.; Degenaar, N.; Miller, J. M.; Reynolds, M.; Wijnands, R.

    2014-01-01

    We conducted the first long-term (60 days), multiwavelength (optical, ultraviolet, and X-ray) simultaneous monitoring of Cen X-4 with daily Swift observations, with the goal of understanding variability in the low mass X-ray binary Cen X-4 during quiescence. We found Cen X-4 to be highly variable in all energy bands on timescales from days to months, with the strongest quiescent variability a factor of 22 drop in the X-ray count rate in only 4 days. The X-ray, UV and optical (V band) emission are correlated on timescales down to less than 110 s. The shape of the correlation is a power law with index γ about 0.2-0.6. The X-ray spectrum is well fitted by a hydrogen NS atmosphere (kT = 59 - 80 eV) and a power law (with spectral index Γ = 1.4 - 2.0), with the spectral shape remaining constant as the flux varies. Both components vary in tandem, with each responsible for about 50% of the total X-ray flux, implying that they are physically linked. We conclude that the X-rays are likely generated by matter accreting down to the NS surface. Moreover, based on the short timescale of the correlation, we also unambiguously demonstrate that the UV emission can not be due to either thermal emission from the stream impact point, or a standard optically thick, geometrically thin disc. The spectral energy distribution shows a small UV emitting region, too hot to arise from the accretion disk, that we identified as a hot spot on the companion star. Therefore, the UV emission is most likely produced by reprocessing from the companion star, indeed the vertical size of the disc is small and can only reprocess a marginal fraction of the X-ray emission. We also found the accretion disc in quiescence to likely be UV faint, with a minimal contribution to the whole UV flux.

  13. Magnetic jets from accretion disks : field structure and X-ray emission

    NASA Astrophysics Data System (ADS)

    Memola, Elisabetta

    2002-06-01

    . We also calculate the X-ray emission in the energy range 0.2--10.1,keV from a microquasar relativistic jet close to its source of 5 solar masses. In order to do it, we apply the jet flow parameters (densities, velocities, temperatures of each volume element along the collimating jet) derived in the literature from the relativistic magnetohydrodynamic equations. We obtain theoretical thermal X-ray spectra of the innermost jet as composition of the spectral contributions of the single volume elements along the jet. Since relativistic effects as Doppler shift and Doppler boosting due to the motion of jets toward us might be important, we investigate how the spectra are affected by them considering different inclinations of the line of sight to the jet axis. Emission lines of highly ionized iron are clearly visible in our spectra, probably also observed in the Galactic microquasars GRS 1915+105 and XTE J1748-288. The Doppler shift of the emission lines is always evident. Due to the chosen geometry of the magnetohydrodynamic jet, the inner X-ray emitting part is not yet collimated. Ergo, depending on the viewing angle, the Doppler boosting does not play a major role in the total spectra. This is the first time that X-ray spectra have been calculated from the numerical solution of a magnetohydrodynamic jet. Astrophysikalische Jets sind stark kollimierte Materieströmungen hoher Geschwindigkeit. Sie stehen im Zusammenhang mit einer Fülle verschiedener astrophysikalischer Objekte wie jungen Sternen, stellaren schwarzen Löchern ('Mikro-Quasare'), Galaxien mit aktivem Kern (AGN) und wahrscheinlich auch mit dem beobachteten intensiven Aufblitzen von Gamma-Strahlung (Gamma Ray Bursts). Insbesondere hat sich gezeigt, dass die Jets der Mikro-Quasare wahrscheinlich als kleinskalige Version der Jets der AGN anzusehen sind. Neben den Beobachtungen haben vor allem auch theoretische Überlegungen gezeigt, dass Magnetfelder bei der Jetentstehung, -beschleunigung und -kollimation eine

  14. Superorbital Periodic Modulation in Wind-Accretion High-Mass X-Ray Binaries from Swift Burst Alert Telescope Observations

    NASA Technical Reports Server (NTRS)

    Corbet, Robin H. D.; Krimm, Hans A.

    2013-01-01

    We report the discovery using data from the Swift-Burst Alert Telescope (BAT) of superorbital modulation in the wind-accretion supergiant high-mass X-ray binaries 4U 1909+07 (= X 1908+075), IGR J16418-4532, and IGR J16479-4514. Together with already known superorbital periodicities in 2S 0114+650 and IGR J16493-4348, the systems exhibit a monotonic relationship between superorbital and orbital periods. These systems include both supergiant fast X-ray transients and classical supergiant systems, and have a range of inclination angles. This suggests an underlying physical mechanism which is connected to the orbital period. In addition to these sources with clear detections of superorbital periods, IGR J16393-4643 (= AX J16390.4-4642) is identified as a system that may have superorbital modulation due to the coincidence of low-amplitude peaks in power spectra derived from BAT, Rossi X-Ray Timing Explorer Proportional Counter Array, and International Gamma-Ray Astrophysics Laboratory light curves. 1E 1145.1-6141 may also be worthy of further attention due to the amount of low-frequency modulation of its light curve. However, we find that the presence of superorbital modulation is not a universal feature of wind-accretion supergiant X-ray binaries.

  15. ON THE SPIN-DOWN AND MAGNETIC FIELD OF THE X-RAY PULSAR 1E 1207.4-5209

    SciTech Connect

    Halpern, J. P.; Gotthelf, E. V. E-mail: eric@astro.columbia.edu

    2011-06-01

    We analyze all of the archival X-ray timing data from the years 2000-2008 on the weakly magnetized central compact object (CCO) pulsar 1E 1207.4-5209 in an attempt to measure its dipole magnetic field strength via spin-down. because most of these observations were not planned for the purpose of phase-coherent timing, the resulting ephemeris is not unique, but is restricted to two comparably good timing solutions that correspond to B{sub s} = 9.9 x 10{sup 10} G or 2.4 x 10{sup 11} G, respectively, assuming dipole spin-down. One of these should be the correct value and the other one an alias. There are no spinning-up solutions. The smaller value of B{sub s} is close to the surface field of 8 x 10{sup 10} G that is measured independently from the unique absorption lines in the X-ray spectrum of 1E 1207.4-5209, assuming that the lowest-energy line at 0.7 keV is the electron-cyclotron fundamental. We suggest that 1E 1207.4-5209 has the strongest magnetic field among CCOs, which would account for the unique presence of its cyclotron absorption spectrum, while other CCOs likely have even weaker fields for which the cyclotron fundamental falls below the observable soft X-ray band.

  16. Superorbital Modulation and Orbital Parameters of the Eclipsing High-Mass X-ray Pulsar IGR J16493-4348

    NASA Astrophysics Data System (ADS)

    Pearlman, Aaron B.; Corbet, R.; Pottschmidt, K.

    2013-01-01

    Previous infrared studies of the X-ray pulsar IGR J16493-4348 classified the system as a supergiant high-mass X-ray binary (HMXB). A ~6.78 d orbital period was discovered from Swift Burst Alert Telescope (BAT) and Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA) Galactic Bulge scan observations. A coherent signal at ~20.07 d was also found using the PCA and BAT instruments, suggestive of superorbital behavior within the system. Using well-sampled PCA archival pointed data (2.5-25 keV) spanning 9.5 d, we find strong evidence for a pulse period at ~1093 s from pulse arrival time analysis and the power spectrum of the light curve after removal of low frequency noise. We present an eclipse model for the folded PCA scan and BAT 66-month snapshot light curves, which constrains the system's behavior during orbital transitions. Pulse arrival times are derived using the PCA pointed light curve, and circular and eccentric orbital solutions are provided. A 14.0 ± 2.3 M⊙ mass function is determined, which further confirms the designation of IGR J16493-4348 as a supergiant HMXB.

  17. A jet emission model to probe the dynamics of accretion and ejection coupling in black hole X-ray binaries

    NASA Astrophysics Data System (ADS)

    Malzac, Julien

    2016-07-01

    Compact jets are probably the most common form of jets in X-ray binaries and Active Galactic Nuclei. They seem to be present in all sources in the so-called hard X-ray spectral state. They are characterised by a nearly flat Spectral Energy Distribution (SED) extending from the radio to the infrared bands. This emission is usually interpreted as partially self absorbed synchrotron emission from relativistic leptons accelerated in the jet. The observed flat spectral shape requires energy dissipation and acceleration of particules over a wide range of distances along the jet. This distributed energy dissipation is likely to be powered by internal shocks caused by fluctuations of the outflow velocity. I will discuss such an internal shock model in the context of black hole binaries. I will show that internal shocks can produce the observed SEDs and also predict a strong, wavelength dependent, variability that resembles the observed one. The assumed velocity fluctuations of the jet must originate in the accretion flow. The model thus predicts a strong connection between the observable properties of the jet in the radio to IR bands, and the variability of the accretion flow as observed in X-rays. If the model is correct, this offers a unique possibility to probe the dynamics of the coupled accretion and ejection processes leading to the formation of compact jets.

  18. Super-eddington accretion in the ultraluminous x-ray source NGC 1313 X-2: An ephemeral feast

    SciTech Connect

    Weng, Shan-Shan; Zhang, Shuang-Nan; Zhao, Hai-Hui E-mail: zhangsn@ihep.ac.cn

    2014-01-10

    We investigate the X-ray spectrum, variability, and the surrounding ionized bubble of NGC 1313 X-2 to explore the physics of super-Eddington accretion. Beyond the Eddington luminosity, the accretion disk of NGC 1313 X-2 is truncated at a large radius (∼50 times the innermost stable circular orbit), and displays the similar evolution track with both luminous Galactic black-hole and neutron star X-ray binaries (XRBs). In super-critical accretion, the speed of radiatively driven outflows from the inner disk is mildly relativistic. Such ultra-fast outflows would be overionized and might produce weak Fe K absorption lines, which may be detected by the coming X-ray mission Astro-H. If NGC 1313 X-2 is a massive stellar XRB, the high luminosity indicates that an ephemeral feast is held in the source. That is, the source must be accreting at a hyper-Eddington mass rate to give the super-Eddington emission over ∼10{sup 4}-10{sup 5} yr. The expansion of the surrounding bubble nebula with a velocity of ∼100 km s{sup –1} might indicate that it has existed over ∼10{sup 6} yr and is inflated by the radiatively driven outflows from the transient with a duty cycle of activity of ∼ a few percent. Alternatively, if the surrounding bubble nebula is produced by line-driven winds, less energy is required than the radiatively driven outflow scenario, and the radius of the Strömgren radius agrees with the nebula size. Our results are in favor of the line-driven winds scenario, which can avoid the conflict between the short accretion age and the apparently much longer bubble age inferred from the expansion velocity in the nebula.

  19. Impacts of fragmented accretion streams onto classical T Tauri stars: UV and X-ray emission lines

    NASA Astrophysics Data System (ADS)

    Colombo, S.; Orlando, S.; Peres, G.; Argiroffi, C.; Reale, F.

    2016-10-01

    Context. The accretion process in classical T Tauri stars (CTTSs) can be studied through the analysis of some UV and X-ray emission lines which trace hot gas flows and act as diagnostics of the post-shock downfalling plasma. In the UV-band, where higher spectral resolution is available, these lines are characterized by rather complex profiles whose origin is still not clear. Aims: We investigate the origin of UV and X-ray emission at impact regions of density structured (fragmented) accretion streams. We study if and how the stream fragmentation and the resulting structure of the post-shock region determine the observed profiles of UV and X-ray emission lines. Methods: We modeled the impact of an accretion stream consisting of a series of dense blobs onto the chromosphere of a CTTS through two-dimensional (2D) magnetohydrodynamic (MHD) simulations. We explored different levels of stream fragmentation and accretion rates. From the model results, we synthesize C IV (1550 Å) and O VIII (18.97 Å) line profiles. Results: The impacts of accreting blobs onto the stellar chromosphere produce reverse shocks propagating through the blobs and shocked upflows. These upflows, in turn, hit and shock the subsequent downfalling fragments. As a result, several plasma components differing for the downfalling velocity, density, and temperature are present altoghether. The profiles of C IV doublet are characterized by two main components: one narrow and redshifted to speed ≈ 50 km s-1 and the other broader and consisting of subcomponents with redshift to speed in the range 200-400 km s-1. The profiles of O VIII lines appear more symmetric than C IV and are redshifted to speed ≈ 150 km s-1. Conclusions: Our model predicts profiles of C IV line remarkably similar to those observed and explains their origin in a natural way as due to stream fragmentation. Movies are available at http://www.aanda.org

  20. Detecting and timing a pulsed radio counterpart to the recently discovered high magnetic field X-ray pulsar PSR J1640-4631

    NASA Astrophysics Data System (ADS)

    Ferdman, Robert; Kaspi, Victoria; Gotthelf, Eric

    2014-04-01

    We propose to perform a directed search for a pulsed radio-emitting counterpart to the rotation-powered 206-ms X-ray pulsar PSR J1640-4631, recently discovered with the NuSTAR X-ray telescope. This source has a very large spin-down rate, and hence is an excellent and rare candidate for the measurement of the source's “braking index,” a fundamental test of the electromagnetic braking hypothesis. A braking index below 2, as has been recently measured for a similar pulsar, would provide further evidence of a connection between pulsars and magnetars. We request time to initially verify this pulsar’s radio detectability, and to perform coherent timing observations that would lead to the aforementioned braking index measurement. If the pulsar is not detected in the initial observations, we will inform the director to withdraw the timing observation portion of our request.

  1. High Spatial Resolution X-Ray Spectroscopy of the IC 443 Pulsar Wind Nebula and Environs

    NASA Astrophysics Data System (ADS)

    Swartz, Douglas A.; Pavlov, George G.; Clarke, Tracy; Castelletti, Gabriela; Zavlin, Vyacheslav E.; Bucciantini, Niccolò; Karovska, Margarita; van der Horst, Alexander J.; Yukita, Mihoko; Weisskopf, Martin C.

    2015-07-01

    Deep Chandra ACIS observations of the region around the putative pulsar, CXOU J061705.3+222127, in the supernova remnant (SNR) IC 443 reveal an ˜5″ radius ring-like structure surrounding the pulsar and a jet-like feature oriented roughly north-south across the ring and through the pulsar's location at 06h17m5.ˢ200 + 22°21‧27.″52 (J2000.0 coordinates). The observations further confirm that (1) the spectrum and flux of the central object are consistent with a rotation-powered pulsar, (2) the non-thermal spectrum and morphology of the surrounding nebula are consistent with a pulsar wind, and (3) the spectrum at greater distances is consistent with thermal emission from the SNR. The cometary shape of the nebula, suggesting motion toward the southwest, appears to be subsonic: There is no evidence either spectrally or morphologically for a bow shock or contact discontinuity; the nearly circular ring is not distorted by motion through the ambient medium; and the shape near the apex of the nebula is narrow. Comparing this observation with previous observations of the same target, we set a 99% confidence upper limit to the proper motion of CXOU J061705.3+222127 to be less than 44 mas yr-1 (310 km s-1 for a distance of 1.5 kpc), with the best-fit (but not statistically significant) projected direction toward the west.

  2. HIGH SPATIAL RESOLUTION X-RAY SPECTROSCOPY OF THE IC 443 PULSAR WIND NEBULA AND ENVIRONS

    SciTech Connect

    Swartz, Douglas A.; Zavlin, Vyacheslav E.; Pavlov, George G.; Clarke, Tracy; Castelletti, Gabriela; Bucciantini, Niccolò; Karovska, Margarita; Horst, Alexander J. van der; Yukita, Mihoko; Weisskopf, Martin C.

    2015-07-20

    Deep Chandra ACIS observations of the region around the putative pulsar, CXOU J061705.3+222127, in the supernova remnant (SNR) IC 443 reveal an ∼5″ radius ring-like structure surrounding the pulsar and a jet-like feature oriented roughly north–south across the ring and through the pulsar's location at 06{sup h}17{sup m}5.{sup s}200 + 22°21′27.″52 (J2000.0 coordinates). The observations further confirm that (1) the spectrum and flux of the central object are consistent with a rotation-powered pulsar, (2) the non-thermal spectrum and morphology of the surrounding nebula are consistent with a pulsar wind, and (3) the spectrum at greater distances is consistent with thermal emission from the SNR. The cometary shape of the nebula, suggesting motion toward the southwest, appears to be subsonic: There is no evidence either spectrally or morphologically for a bow shock or contact discontinuity; the nearly circular ring is not distorted by motion through the ambient medium; and the shape near the apex of the nebula is narrow. Comparing this observation with previous observations of the same target, we set a 99% confidence upper limit to the proper motion of CXOU J061705.3+222127 to be less than 44 mas yr{sup −1} (310 km s{sup −1} for a distance of 1.5 kpc), with the best-fit (but not statistically significant) projected direction toward the west.

  3. A broadband X-ray study of the Geminga pulsar with NuSTAR And XMM-Newton

    SciTech Connect

    Mori, Kaya; Gotthelf, Eric V.; Halpern, Jules P.; Beloborodov, Andrei M.; Hailey, Charles J.; Dufour, Francois; Kaspi, Victoria M.; An, Hongjun; Bachetti, Matteo; Boggs, Steven E.; Craig, William W.; Christensen, Finn E.; Harrison, Fiona A.; Kouveliotou, Chryssa; Pivovaroff, Michael J.; Stern, Daniel; Zhang, William W.

    2014-10-01

    We report on the first hard X-ray detection of the Geminga pulsar above 10 keV using a 150 ks observation with the Nuclear Spectroscopic Telescope Array (NuSTAR) observatory. The double-peaked pulse profile of non-thermal emission seen in the soft X-ray band persists at higher energies. Broadband phase-integrated spectra over the 0.2-20 keV band with NuSTAR and archival XMM-Newton data do not fit to a conventional two-component model of a blackbody plus power law, but instead exhibit spectral hardening above ∼5 keV. We find that two spectral models fit the data well: (1) a blackbody (kT {sub 1} ∼ 42 eV) with a broken power law (Γ{sub 1} ∼ 2.0, Γ{sub 2} ∼ 1.4 and E {sub break} ∼ 3.4 keV) and (2) two blackbody components (kT {sub 1} ∼ 44 eV and kT {sub 2} ∼ 195 eV) with a power-law component (Γ ∼ 1.7). In both cases, the extrapolation of the Rayleigh-Jeans tail of the thermal component is consistent with the UV data, while the non-thermal component overpredicts the near-infrared data, requiring a spectral flattening at E ∼ 0.05-0.5 keV. While strong phase variation of the power-law index is present below ∼5 keV, our phase-resolved spectroscopy with NuSTAR indicates that another hard non-thermal component with Γ ∼ 1.3 emerges above ∼5 keV. The spectral hardening in non-thermal X-ray emission as well as spectral flattening between the optical and X-ray bands argue against the conjecture that a single power law may account for multi-wavelength non-thermal spectra of middle-aged pulsars.

  4. X-ray and gamma-ray emission of Sagittarius A* as a wind-accreting black hole

    NASA Technical Reports Server (NTRS)

    Mastichiadis, A.; Ozernoy, L. M.

    1994-01-01

    If, as many believe, Sgr A* is a massive black hole at the Galactic center, one should expect it to be a source of X-ray and gamma-ray activity, behaving basically as a scaled-down active galactic nucleus. An unavoidable source of accretion is the wind from IRS 16, a nearby group of hot, massive stars. Since the density and velocity of the accreting matter are known from observations, the accretion rate is basically a function of the putative black hole mass, M(sub h), only; this value represents a reliable lower limit to a real rate, given the other possible sources of accreting matter. Based on this and on the theories about shock acceleration in active galactic nuclei, we have estimated the expected production of relativistic particles and their hard radiation. These values turn out to be a function of M(sub h) as well. Comparing our results with available X-ray and gamma-ray observations which show Sgr A* to have a relatively low activity level, we conclude tentatively that the putative black hole in the Galactic center cannot have a mass greater than approximately 6 x 10(exp 3) solar mass. This conclusion is consistent with the upper limits to the black hole mass found by different methods earlier, although much more work is needed to make calculations of shock acceleration around black holes more reliable.

  5. Puzzling accretion onto a black hole in the ultraluminous X-ray source M 101 ULX-1

    NASA Astrophysics Data System (ADS)

    Liu, Ji-Feng; Bregman, Joel N.; Bai, Yu; Justham, Stephen; Crowther, Paul

    2013-11-01

    There are two proposed explanations for ultraluminous X-ray sources (ULXs) with luminosities in excess of 1039 erg s-1. They could be intermediate-mass black holes (more than 100-1,000 solar masses, ) radiating at sub-maximal (sub-Eddington) rates, as in Galactic black-hole X-ray binaries but with larger, cooler accretion disks. Alternatively, they could be stellar-mass black holes radiating at Eddington or super-Eddington rates. On its discovery, M 101 ULX-1 had a luminosity of 3 × 1039 erg s-1 and a supersoft thermal disk spectrum with an exceptionally low temperature--uncomplicated by photons energized by a corona of hot electrons--more consistent with the expected appearance of an accreting intermediate-mass black hole. Here we report optical spectroscopic monitoring of M 101 ULX-1. We confirm the previous suggestion that the system contains a Wolf-Rayet star, and reveal that the orbital period is 8.2 days. The black hole has a minimum mass of 5, and more probably a mass of 20-30, but we argue that it is very unlikely to be an intermediate-mass black hole. Therefore, its exceptionally soft spectra at high Eddington ratios violate the expectations for accretion onto stellar-mass black holes. Accretion must occur from captured stellar wind, which has hitherto been thought to be so inefficient that it could not power an ultraluminous source.

  6. X-ray Emission from YSOs, Protostellar Jets, and Accretion Eruptive Variables

    NASA Astrophysics Data System (ADS)

    Stringfellow, Guy

    2010-10-01

    Imaging in X-rays has become an extremely useful tool to identify YSOs residing in star forming regions. X-ray emission is also being measured in eruptive young stars, the FUOr-EXOr type stars, and in protostellar jets. Recent deep near-IR imaging of the North American and Pelican nebulae in JHKs and narrowband emission lines of H2 and [FeII] have revealed one of the most active, richest star forming regions in the Galaxy. Within a single EPIC FOV lies dozens of resolved outflows, jets, clusters of YSOs, and even eruptive FUOR-EXOr stars currently undergoing outbursts. I propose to obtain XMM-Newton imaging of three regions rich in all three types of objects to render x-ray detections to assist with confirming the YSOs, and to measure the x-ray flux of the eruptive stars and shocked outflows.

  7. Circinus X-1: a Laboratory for Studying the Accretion Phenomenon in Compact Binary X-Ray Sources. Ph.D. Thesis - Maryland Univ.

    NASA Technical Reports Server (NTRS)

    Robinson-Saba, J. L.

    1983-01-01

    Observations of the binary X-ray source Circinus X-1 provide samples of a range of spectral and temporal behavior whose variety is thought to reflect a broad continuum of accretion conditions in an eccentric binary system. The data support an identification of three or more X-ray spectral components, probably associated with distinct emission regions.

  8. Multi-wavelength properties of IGR J05007-7047 (LXP 38.55) and identification as a Be X-ray binary pulsar in the LMC

    NASA Astrophysics Data System (ADS)

    Vasilopoulos, G.; Haberl, F.; Delvaux, C.; Sturm, R.; Udalski, A.

    2016-09-01

    We report on the results of a ˜40-d multi-wavelength monitoring of the Be X-ray binary system IGR J05007-7047 (LXP 38.55). During that period the system was monitored in the X-rays using the Swift telescope and in the optical with multiple instruments. When the X-ray luminosity exceeded 1036 erg s-1 we triggered an XMM-Newton ToO observation. Timing analysis of the photon events collected during the XMM-Newton observation reveals coherent X-ray pulsations with a period of 38.551(3) s (1σ), making it the 17th known high-mass X-ray binary pulsar in the LMC. During the outburst, the X-ray spectrum is fitted best with a model composed of an absorbed power law (Γ = 0.63) plus a high-temperature blackbody (kT ˜2 keV) component. By analysing ˜12 yr of available OGLE optical data we derived a 30.776(5) d optical period, confirming the previously reported X-ray period of the system as its orbital period. During our X-ray monitoring the system showed limited optical variability while its IR flux varied in phase with the X-ray luminosity, which implies the presence of a disc-like component adding cooler light to the spectral energy distribution of the system.

  9. X-ray orbital modulation of a white dwarf accreting from an L dwarf. The system SDSS J121209.31+013627.7

    NASA Astrophysics Data System (ADS)

    Stelzer, B.; de Martino, D.; Casewell, S. L.; Wynn, G. A.; Roy, M.

    2017-01-01

    In an XMM-Newton observation of the binary SDSS J121209.31+013627.7, consisting of a white dwarf and an L dwarf, we detect X-ray orbital modulation as proof of accretion from the substellar companion onto the magnetic white dwarf. We constrain the system geometry (inclination as well as magnetic and pole-cap angle) through modelling of the X-ray light curve, and we derive a mass accretion rate of 3.2 × 10-14M⊙/ yr from the X-ray luminosity ( 3 × 1029 erg/s). From X-ray studies of L dwarfs, a possible wind driven from a hypothesized corona on the substellar donor is orders of magnitude too weak to explain the observed accretion rate, while the radius of the L dwarf is comparable to its Roche lobe (0.1 R⊙), making Roche-lobe overflow the likely accretion mechanism in this system.

  10. A POPULATION OF ULTRALUMINOUS X-RAY SOURCES WITH AN ACCRETING NEUTRON STAR

    SciTech Connect

    Shao, Yong; Li, Xiang-Dong

    2015-04-01

    Most ultraluminous X-ray sources (ULXs) are believed to be X-ray binary systems, but previous observational and theoretical studies tend to prefer a black hole rather than a neutron star (NS) accretor. The recent discovery of 1.37 s pulsations from the ULX M82 X-2 has established its nature as a magnetized NS. In this work we model the formation history of NS ULXs in an M82- or Milky Way (MW)-like Galaxy, by use of both binary population synthesis and detailed binary evolution calculations. We find that the birth rate is around 10{sup −4} yr{sup −1} for the incipient X-ray binaries in both cases. We demonstrate the distribution of the ULX population in the donor mass–orbital period plane. Our results suggest that, compared with black hole X-ray binaries, NS X-ray binaries may significantly contribute to the ULX population, and high-mass and intermediate-mass X-ray binaries dominate the NS ULX population in M82- and MW-like Galaxies, respectively.

  11. Spectral and Temporal Properties of the Ultraluminous X-Ray Pulsar in M82 from 15 years of Chandra Observations and Analysis of the Pulsed Emission Using NuSTAR

    NASA Astrophysics Data System (ADS)

    Brightman, Murray; Harrison, Fiona; Walton, Dominic J.; Fuerst, Felix; Hornschemeier, Ann; Zezas, Andreas; Bachetti, Matteo; Grefenstette, Brian; Ptak, Andrew; Tendulkar, Shriharsh; Yukita, Mihoko

    2016-01-01

    The recent discovery by Bachetti et al. of a pulsar in M82 that can reach luminosities of up to 1040 erg s-1, a factor of ˜100 times the Eddington luminosity for a 1.4 M⊙ compact object, poses a challenge for accretion physics. In order to better understand the nature of this source and its duty cycle, and in light of several physical models that have been subsequently published, we conduct a spectral and temporal analysis of the 0.5-8 keV X-ray emission from this source from 15 years of Chandra observations. We analyze 19 ACIS observations where the point-spread function (PSF) of the pulsar is not contaminated by nearby sources. We fit the Chandra spectra of the pulsar with a power-law model and a disk blackbody model, subjected to interstellar absorption in M82. We carefully assess for the effect of pile-up in our observations, where four observations have a pile-up fraction of >10%, which we account for during spectral modeling with a convolution model. When fitted with a power-law model, the average photon index when the source is at high luminosity (LX > 1039 erg s-1) is Γ = 1.33 ± 0.15. For the disk blackbody model, the average temperature is Tin = 3.24 ± 0.65 keV, the spectral shape being consistent with other luminous X-ray pulsars. We also investigated the inclusion of a soft excess component and spectral break, finding that the spectra are also consistent with these features common to luminous X-ray pulsars. In addition, we present spectral analysis from NuSTAR over the 3-50 keV range where we have isolated the pulsed component. We find that the pulsed emission in this band is best fit by a power-law with a high-energy cutoff, where Γ = 0.6 ± 0.3 and {E}{{C}}={14}-3+5 keV. While the pulsar has previously been identified as a transient, we find from our longer-baseline study that it has been remarkably active over the 15-year period, where for 9/19 (47%) observations that we analyzed, the pulsar appears to be emitting at a luminosity in excess of

  12. Spectral and Temporal Properties of the Ultra-Luminous X-Ray Pulsar in M82 from 15 Years of Chandra Observations and Analysis of the Pulsed Emission Using NuSTAR

    NASA Technical Reports Server (NTRS)

    Brightman, Murray; Harrison, Fiona; Walton, Dominic J.; Fuerst, Felis; Zezas, Andreas; Bachetti, Matteo; Grefenstette, Brian; Ptak, Andrew; Tendulkar, Shriharsh; Yukita, Mihoko

    2016-01-01

    The recent discovery by Bachetti et al. of a pulsar in M82 that can reach luminosities of up to 10(exp 40) erg s(exp -1), a factor of approximately 100 times the Eddington luminosity for a 1.4 solar mass compact object, poses a challenge for accretion physics. In order to better understand the nature of this source and its duty cycle, and in light of several physical models that have been subsequently published, we conduct a spectral and temporal analysis of the 0.58 keV X-ray emission from this source from 15 years of Chandra observations. We analyze 19 ACIS observations where the point-spread function (PSF) of the pulsar is not contaminated by nearby sources. We fit the Chandra spectra of the pulsar with a power-law model and a disk blackbody model, subjected to interstellar absorption in M82. We carefully assess for the effect of pile-up in our observations, where four observations have a pile-up fraction of 10, which we account for during spectral modeling with a convolution model. When fitted with a power-law model, the average photon index when the source is at high luminosity (LX greater than 10(exp 39) erg s(exp -1) is equal to gamma 1.33 +/-.0.15. For the disk blackbody model, the average temperature is T(sub in) 3.24 +/- 0.65 keV, the spectral shape being consistent with other luminous X-ray pulsars. We also investigated the inclusion of a soft excess component and spectral break, finding that the spectra are also consistent with these features common to luminous X-ray pulsars. In addition, we present spectral analysis from NuSTAR over the 3-50 keV range where we have isolated the pulsed component. We find that the pulsed emission in this band is best fit by a power-law with a high-energy cutoff, where gamma is equal to 0.6 +/- 0.3 and E(sub C) is equal to 14(exp +5) (sub -3)) keV. While the pulsar has previously been identified as a transient, we find from our longer-baseline study that it has been remarkably active over the 15-year period, where for 9

  13. MAGNETIC DOMAINS IN MAGNETAR MATTER AS AN ENGINE FOR SOFT GAMMA-RAY REPEATERS AND ANOMALOUS X-RAY PULSARS

    SciTech Connect

    Suh, In-Saeng; Mathews, Grant J. E-mail: gmathews@nd.ed

    2010-07-10

    Magnetars have been suggested as the most promising site for the origin of observed soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars (AXPs). In this work, we investigate the possibility that SGRs and AXPs might be observational evidence for a magnetic phase separation in magnetars. We study magnetic domain formation as a new mechanism for SGRs and AXPs in which magnetar matter separates into phases containing different flux densities. We identify the parameter space in matter density and magnetic field strength at which there is an instability for magnetic domain formation. We conclude that such instabilities will likely occur in the deep outer crust for the magnetic Baym, Pethick, and Sutherland model and in the inner crust and core for magnetars described in the relativistic Hartree theory. Moreover, we estimate that the energy released by the onset of this instability is comparable with the energy emitted by SGRs.

  14. Tracing the incidence of X-ray AGN and their distribution of accretion rates across the galaxy population

    NASA Astrophysics Data System (ADS)

    Aird, James; Coil, Alison; Georgakakis, Antonis; Nandra, Kirpal

    2016-08-01

    X-ray selection provides a powerful method of identifying AGN across a variety of host galaxies and with a wide range of accretion rates. However, careful consideration of the underlying selection biases are vital to reveal the true underlying distribution of accretion rates and determine how the incidence of AGN is related to the properties of the galaxies that host them. I will present new measurements of the distribution of specific accretion rates (scaled relative to the total host galaxy mass, roughly tracing the Eddington ratio) within both star-forming and quiescent galaxy populations. We combine near-infrared selected samples of galaxies from the CANDELS/3D-HST and UltraVISTA surveys with deep Chandra X-ray data and use an advanced Bayesian technique to constrain the underlying distribution of specific accretion rates as a function of stellar mass and redshift. Our results reveal a broad distribution of accretion rates (reflecting long-term variability in the level of AGN fuelling) in both galaxy types. The probability of a star-forming galaxy hosting an AGN (above a fixed specific accretion rate) has a strong stellar mass dependence - revealing an intrinsically higher incidence of AGN in massive star-forming galaxies - and undergoes a stellar-mass-dependent evolution with redshift. The probability of a quiescent galaxy hosting an AGN is generally lower but does not depend on stellar mass and evolves differently with redshift. These results provide vital insights into the relationship between the growth of black hole and the physical properties of their host galaxies.

  15. The donor star of the X-ray pulsar X1908+075

    NASA Astrophysics Data System (ADS)

    Martínez-Núñez, S.; Sander, A.; Gímenez-García, A.; Gónzalez-Galán, A.; Torrejón, J. M.; Gónzalez-Fernández, C.; Hamann, W.-R.

    2015-06-01

    High-mass X-ray binaries consist of a massive donor star and a compact object. While several of those systems have been well studied in X-rays, little is known for most of the donor stars as they are often heavily obscured in the optical and ultraviolet regime. There is an opportunity to observe them at infrared wavelengths, however. The goal of this study is to obtain the stellar and wind parameters of the donor star in the X1908+075 high-mass X-ray binary system with a stellar atmosphere model to check whether previous studies from X-ray observations and spectral morphology lead to a sufficient description of the donor star. We obtained H- and K-band spectra of X1908+075 and analysed them with the Potsdam Wolf-Rayet (PoWR) model atmosphere code. For the first time, we calculated a stellar atmosphere model for the donor star, whose main parameters are: Mspec = 15 ± 6 M⊙, T∗ = 23-3+6 kK, log geff = 3.0 ± 0.2 and log L/L⊙ = 4.81 ± 0.25. The obtained parameters point towards an early B-type (B0-B3) star, probably in a supergiant phase. Moreover we determined a more accurate distance to the system of 4.85 ± 0.50 kpc than the previously reported value. Based on observations made with the William Herschel Telescope operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias.Appendix A is available in electronic form at http://www.aanda.org

  16. The 2005 Accretion Outburst in V1118 Ori: Evidence for A Spectral Change in X-rays

    NASA Astrophysics Data System (ADS)

    Audard, M.; Güdel, M.; Skinner, S. L.; Briggs, K. R.; Walter, F. M.; Stringfellow, G.; Hamilton, R. T.; Guinan, E. F.

    2005-12-01

    We present results from our X-ray monitoring campaign of the 2005 accretion outburst in the young low-mass star V1118 Ori. Optical and near-infrared photometry are presented as well. The X-ray data from early 2005 indicate that the X-ray flux and luminosity varied within a factor of two only, and were similar to the pre-outburst values measured in a serendipitous observation in 2002. Similarly, the hydrogen column density showed no evidence for significant excursions from the pre-outburst value of a few times 1021 cm-2. However, we observed a spectral change from a dominant hot plasma ( ˜ 25 MK) in 2002 and in January 2005 to a cooler plasma ( ˜ 8 MK) in February and March 2005. We argue that the closing in of the accretion disk during the outburst disrupted the hot magnetic loops high in the corona, whereas the lower cooler loops were less affected and became the dominant coronal component. We acknowledge support by NASA through Chandra award DD5-6029X and through XMM-Newton award NNG05GI96G to Columbia University. The Chandra X-ray Observatory Center is operated by the Smithsonian Astrophysical Observatory for and on behalf of the NASA under contract NAS8-03060. Based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. The PSI group acknowledges support from the Swiss National Science Foundation (grants 20-58827.99 and 20-66875.01). Stony Brook's participation in SMARTS is made possible by support from the offices of the Provost and the Vice President for Research. We thank J. Allyn Smith, P. McGehee, J. Espinoza, and D. Gonzalez for doing the observations with the SMARTS telescopes. We also thank H. Tannanbaum, N. Schartel, and the VLA TOO panel for granting time to observe V1118 Ori.

  17. Self-consistent models for Coulomb heated X-ray pulsar atmospheres

    NASA Technical Reports Server (NTRS)

    Harding, A.; Meszaros, S. P.; Kirk, J.; Galloway, D.

    1983-01-01

    Calculations of accreting magnetized neutron star atmospheres heated by the gradual deceleration of protons via Coulomb collisions are presented. Self consistent determinations of the temperature and density structure for different accretion rates are made by assuming hydrostatic equilibrium and energy balance, coupled with radiative transfer. The full radiative transfer in two polarizations, using magnetic cross sections but with cyclotron resonance effects treated approximately, is carried out in the inhomogeneous atmospheres.

  18. NUSTAR and SUZAKU X-ray spectroscopy of NGC 4151: Evidence for reflection from the inner accretion disk

    DOE PAGES

    Keck, M. L.; Brenneman, L. W.; Ballantyne, D. R.; ...

    2015-06-15

    We present X-ray timing and spectral analyses of simultaneous 150 ks Nuclear Spectroscopic Telescope Array (NuSTAR) and Suzaku X-ray observations of the Seyfert 1.5 galaxy NGC 4151. We disentangle the continuum emission, absorption, and reflection properties of the active galactic nucleus (AGN) by applying inner accretion disk reflection and absorption-dominated models. With a time-averaged spectral analysis, we find strong evidence for relativistic reflection from the inner accretion disk. We find that relativistic emission arises from a highly ionized inner accretion disk with a steep emissivity profile, which suggests an intense, compact illuminating source. We find a preliminary, near-maximal black hole spinmore » $$a\\gt 0.9$$ accounting for statistical and systematic modeling errors. We find a relatively moderate reflection fraction with respect to predictions for the lamp post geometry, in which the illuminating corona is modeled as a point source. Through a time-resolved spectral analysis, we find that modest coronal and inner disk reflection (IDR) flux variation drives the spectral variability during the observations. As a result, we discuss various physical scenarios for the IDR model and we find that a compact corona is consistent with the observed features.« less

  19. NuSTAR and Suzaku X-ray Spectroscopy of NGC 4151: Evidence for Reflection from the Inner Accretion Disk

    NASA Astrophysics Data System (ADS)

    Keck, M. L.; Brenneman, L. W.; Ballantyne, D. R.; Bauer, F.; Boggs, S. E.; Christensen, F. E.; Craig, W. W.; Dauser, T.; Elvis, M.; Fabian, A. C.; Fuerst, F.; García, J.; Grefenstette, B. W.; Hailey, C. J.; Harrison, F. A.; Madejski, G.; Marinucci, A.; Matt, G.; Reynolds, C. S.; Stern, D.; Walton, D. J.; Zoghbi, A.

    2015-06-01

    We present X-ray timing and spectral analyses of simultaneous 150 ks Nuclear Spectroscopic Telescope Array (NuSTAR) and Suzaku X-ray observations of the Seyfert 1.5 galaxy NGC 4151. We disentangle the continuum emission, absorption, and reflection properties of the active galactic nucleus (AGN) by applying inner accretion disk reflection and absorption-dominated models. With a time-averaged spectral analysis, we find strong evidence for relativistic reflection from the inner accretion disk. We find that relativistic emission arises from a highly ionized inner accretion disk with a steep emissivity profile, which suggests an intense, compact illuminating source. We find a preliminary, near-maximal black hole spin a\\gt 0.9 accounting for statistical and systematic modeling errors. We find a relatively moderate reflection fraction with respect to predictions for the lamp post geometry, in which the illuminating corona is modeled as a point source. Through a time-resolved spectral analysis, we find that modest coronal and inner disk reflection (IDR) flux variation drives the spectral variability during the observations. We discuss various physical scenarios for the IDR model and we find that a compact corona is consistent with the observed features.

  20. Application of the Ghosh & Lamb Relation to the Spin-up/down Behavior in the X-ray Binary Pulsar 4U 1626-67

    NASA Astrophysics Data System (ADS)

    Takagi, Toshihiro; Mihara, Tatehiro; Sugizaki, Mutsumi; Makishima, Kazuo; Morii, Mikio

    Using the relation proposed by Ghosh & Lamb (1979) between the pulse-period derivative and the X-ray luminosity in binary X-ray pulsars, we tried to constrain the mass and radius of a neutron star. To apply the relation to the binary X-ray pulsar 4U 1626-67, we compiled previous measurements of its period, period derivative, and flux, and added measurements with the MAXI/GSC onboard the International Space Station. The measured period derivative was tightly correlated with the flux, and the relation is successfully explained by the Ghosh & Lamb relation. We found that an assumed distance of, e.g., 8 kpc, gives a mass of 1.39-1.46 solar mass, and a radius as 11.9-12.0 km. This method thus provides a valuable tool to constrain these parameters, even though we need to precisely know the distance [2].

  1. Testing the Paradigm that Ultra-Luminous X-Ray Sources as a Class Represent Accreting Intermediate

    NASA Technical Reports Server (NTRS)

    Berghea, C. T.; Weaver, K. A.; Colbert, E. J. M.; Roberts, T. P.

    2008-01-01

    To test the idea that ultraluminous X-ray sources (ULXs) in external galaxies represent a class of accreting Intermediate-Mass Black Holes (IMBHs), we have undertaken a program to identify ULXs and a lower luminosity X-ray comparison sample with the highest quality data in the Chandra archive. We establish a general property of ULXs that the most X-ray luminous objects possess the fattest X-ray spectra (in the Chandra band pass). No prior sample studies have established the general hardening of ULX spectra with luminosity. This hardening occurs at the highest luminosities (absorbed luminosity > or equals 5x10(exp 39) ergs/s) and is in line with recent models arguing that ULXs are actually stellar-mass black holes. From spectral modeling, we show that the evidence originally taken to mean that ULXs are IMBHs - i.e., the "simple IMBH model" - is nowhere near as compelling when a large sample of ULXs is looked at properly. During the last couple of years, XMM-Newton spectroscopy of ULXs has to some large extent begun to negate the simple IMBH model based on fewer objects. We confirm and expand these results, which validates the XMM-Newton work in a broader sense with independent X-ray data. We find (1) that cool disk components are present with roughly equal probability and total flux fraction for any given ULX, regardless of luminosity, and (2) that cool disk components extend below the standard ULX luminosity cutoff of 10(exp 39) ergs/s, down to our sample limit of 10(exp 38:3) ergs/s. The fact that cool disk components are not correlated with luminosity damages the argument that cool disks indicate IMBHs in ULXs, for which a strong statistical support was never made.

  2. X-ray Analysis of the Pulsar Wind Nebula DA 495 and its Central Object

    NASA Astrophysics Data System (ADS)

    Karpova, A.; Zyuzin, D.; Danilenko, A.; Shibanov, Yu

    2016-11-01

    We report the results of a simultaneous analysis of the Chandra and XMM- Newton data on the pulsar wind nebula DA 495 and its central object, J1952.2+2925, which is presumably a pulsar. The J1952.2+2925 pure thermal spectrum can be equally well described either by the blackbody model with a temperature of 215 eV and an emitting area radius of 0.6 km or magnetized neutron star atmosphere models with temperatures of 80-90 eV. We also used the high temporal resolution XMM-Newton/EPIC-pn data to search for pulsations from J1952.2+2925. No pulsations were found so we set an upper limit for the pulsed fraction which is 40%. Using of the interstellar absorption-distance relation allowed us to estimate the distance to DA 495, which lies between 1 and 5 kpc.

  3. BROADBAND X-RAY IMAGING AND SPECTROSCOPY OF THE CRAB NEBULA AND PULSAR WITH NuSTAR

    SciTech Connect

    Madsen, Kristin K.; Harrison, Fiona; Grefenstette, Brian W.; Reynolds, Stephen; An, Hongjun; Boggs, Steven; Craig, William W.; Zoglauer, Andreas; Christensen, Finn E.; Fryer, Chris L.; Hailey, Charles J.; Nynka, Melania; Markwardt, Craig; Zhang, William; Stern, Daniel

    2015-03-01

    We present broadband (3-78 keV) NuSTAR X-ray imaging and spectroscopy of the Crab nebula and pulsar. We show that while the phase-averaged and spatially integrated nebula + pulsar spectrum is a power law in this energy band, spatially resolved spectroscopy of the nebula finds a break at ∼9 keV in the spectral photon index of the torus structure with a steepening characterized by ΔΓ ∼ 0.25. We also confirm a previously reported steepening in the pulsed spectrum, and quantify it with a broken power law with break energy at ∼12 keV and ΔΓ ∼ 0.27. We present spectral maps of the inner 100'' of the remnant and measure the size of the nebula as a function of energy in seven bands. These results find that the rate of shrinkage with energy of the torus size can be fitted by a power law with an index of γ = 0.094 ± 0.018, consistent with the predictions of Kennel and Coroniti. The change in size is more rapid in the NW direction, coinciding with the counter-jet where we find the index to be a factor of two larger. NuSTAR observed the Crab during the latter part of a γ-ray flare, but found no increase in flux in the 3-78 keV energy band.

  4. PSR J2022 plus 3842: An Energetic Radio and X-Ray Pulsar Associated with SNR G76.9 plus 1.0

    NASA Technical Reports Server (NTRS)

    Arzoumanian, Z.; Gotthelf, E. V.; Ransom, S. M.; Kothes, R.; Landecker, T. L.

    2010-01-01

    We present Chandra X-ray Observatory, Robert C. Byrd Green Bank Radio Telescope (GBT), and Rossi X-ray Timing Explorer (RXTE) observations directed toward the radio supernova remnant (SNR) G76.9+1.0. The Chandra investigation reveals a hard, unresolved X-ray source coincident with the midpoint of the double-lobed radio morphology and surrounded by faint, compact X-ray nebulosity. These features suggest that an energetic neutron star is powering a pulsar wind nebula (PWN) seen in synchrotron emission. Indeed, the spatial relationship of the X-ray and radio emissions is remarkably similar to the extended emission around the Vela pulsar. A follow-up pulsation search with the GBT uncovered a highly-dispersed (DM = 427 +/- 1 pc/cu cm) and highly-scattered pulsar with a period of 24 ms. Its subsequently measured spin-down rate implies a characteristic age T(sub c) = 8.9 kyr, making PSR J2022+3842 the most rapidly rotating young radio pulsar known. With a spin-down luminosity E = 1.2 x 10(exp 38) erg/s, it is the second-most energetic Galactic pulsar known, after the Crab pulsar. The 24-ms pulsations have also been detected in the RXTE observation; the combined Chandra and RXTE spectral fit suggests that the Chandra point-source emission is virtually 100% pulsed. The 2-16 keV spectrum of the narrow (0.06 cycles FWHM) pulse is well-fitted by an absorbed power-law model with column density N(sub H) = (1.7 +/- 0.5) x 10(exp 22)/sq cm and photon index Gamma = 1.0 +/- 0.2, strongly suggestive of magnetospheric emission. For an assumed distance of 10 kpc, the 2-10 keV luminosity of L(sub X) = 6.9 x 10(exp 33) erg/s suggests one of the lowest known X-ray conversion efficiencies L(sub X)/ E = 5.8 x 10(exp -5), similar to that of the Vela pulsar. Finally, the PWN around PSR J2022+3842 revealed by Chandra is also underluminous, with F(sub PWN)/ F(sub PSR) < or approx.1 in the 2-10 keV band, a further surprise given the pulsar's high spin-down luminosity.

  5. MAGNETOHYDRODYNAMIC MODELING OF THE ACCRETION SHOCKS IN CLASSICAL T TAURI STARS: THE ROLE OF LOCAL ABSORPTION IN THE X-RAY EMISSION

    SciTech Connect

    Bonito, R.; Argiroffi, C.; Peres, G.; Orlando, S.; Miceli, M.; Ibgui, L.; Matsakos, T.; Stehle, C.

    2014-11-10

    We investigate the properties of X-ray emission from accretion shocks in classical T Tauri stars (CTTSs), generated where the infalling material impacts the stellar surface. Both observations and models of the accretion process reveal several aspects that are still unclear: the observed X-ray luminosity in accretion shocks is below the predicted value, and the density versus temperature structure of the shocked plasma, with increasing densities at higher temperature, deduced from the observations, is at odds with that proposed in the current picture of accretion shocks. To address these open issues, we investigate whether a correct treatment of the local absorption by the surrounding medium is crucial to explain the observations. To this end, we describe the impact of an accretion stream on a CTTS by considering a magnetohydrodynamic model. From the model results, we synthesize the X-ray emission from the accretion shock by producing maps and spectra. We perform density and temperature diagnostics on the synthetic spectra, and we directly compare the results with observations. Our model shows that the X-ray fluxes inferred from the emerging spectra are lower than expected because of the complex local absorption by the optically thick material of the chromosphere and of the unperturbed stream. Moreover, our model, including the effects of local absorption, explains in a natural way the apparently puzzling pattern of density versus temperature observed in the X-ray emission from accretion shocks.

  6. HIGH-ENERGY X-RAYS FROM J174545.5-285829, THE CANNONBALL: A CANDIDATE PULSAR WIND NEBULA ASSOCIATED WITH Sgr A EAST

    SciTech Connect

    Nynka, Melania; Hailey, Charles J.; Mori, Kaya; Gotthelf, Eric V.; Zhang, Shuo; Baganoff, Frederick K.; Bauer, Franz E.; Boggs, Steven E.; Craig, William W.; Christensen, Finn E.; Harrison, Fiona A.; Hong, Jaesub; Perez, Kerstin M.; Stern, Daniel; Zhang, William W.

    2013-12-01

    We report the unambiguous detection of non-thermal X-ray emission up to 30 keV from the Cannonball, a few-arcsecond long diffuse X-ray feature near the Galactic Center, using the NuSTAR X-ray observatory. The Cannonball is a high-velocity (v {sub proj} ∼ 500 km s{sup –1}) pulsar candidate with a cometary pulsar wind nebula (PWN) located ∼2' north-east from Sgr A*, just outside the radio shell of the supernova remnant Sagittarius A (Sgr A) East. Its non-thermal X-ray spectrum, measured up to 30 keV, is well characterized by a Γ ∼ 1.6 power law, typical of a PWN, and has an X-ray luminosity of L(3-30 keV) = 1.3 × 10{sup 34} erg s{sup –1}. The spectral and spatial results derived from X-ray and radio data strongly suggest a runaway neutron star born in the Sgr A East supernova event. We do not find any pulsed signal from the Cannonball. The NuSTAR observations allow us to deduce the PWN magnetic field and show that it is consistent with the lower limit obtained from radio observations.

  7. High-Energy X-rays from J174545.5-285829, the Cannonball: a Candidate Pulsar Wind Nebula Associated with Sgr a East

    NASA Technical Reports Server (NTRS)

    Nynka, Melania; Hailey, Charles J.; Mori, Kaya; Baganoff, Frederick K.; Bauer, Franz E.; Boggs, Steven E.; Craig, William W.; Christensen, Finn E.; Gotthelf, Eric V.; Harrison, Fiona A.; Hong, Jaesub; Perez, Kerstin M.; Stern, Daniel; Zhang, Shuo; Zhang, William W.

    2013-01-01

    We report the unambiguous detection of non-thermal X-ray emission up to 30 keV from the Cannonball, a few arcsecond long diffuse X-ray feature near the Galactic Center, using the NuSTAR X-ray observatory. The Cannonball is a high-velocity (v(proj) approximately 500 km s(exp -1)) pulsar candidate with a cometary pulsar wind nebula (PWN) located approximately 2' north-east from Sgr A*, just outside the radio shell of the supernova remnant Sagittarius A (Sgr A) East. Its non-thermal X-ray spectrum, measured up to 30 keV, is well characterized by a Gamma is approximately 1.6 power law, typical of a PWN, and has an X-ray luminosity of L(3-30 keV) = 1.3 × 10(exp 34) erg s(exp -1). The spectral and spatial results derived from X-ray and radio data strongly suggest a runaway neutron star born in the Sgr A East supernova event. We do not find any pulsed signal from the Cannonball. The NuSTAR observations allow us to deduce the PWN magnetic field and show that it is consistent with the lower limit obtained from radio observations.

  8. Orbital Parameters and Spectroscopy of the Transient X-Ray Pulsar 4U 0115+63

    NASA Technical Reports Server (NTRS)

    Mueller, Sebastian; Obst,Maria; Kreykenbohm, Ingo; Fuerst, Felix; Kuehnel, Matthias; Wilms, Joern; Klochkov, Dmitry; Staubert, Ruediger; Santangelo, Andrea; Pottschmidt, Katja; Suchy, Slawomir; Rothschild, Richard E.; Caballero, Isabel; Schoenherr, Gabriele

    2011-01-01

    We report on an outburst of the high mass X-ray binary 4U 0115+63 with a pulse period of 3.6s in spring 2008 as observed with INTEGRAL and RXTE. By analyzing the lightcurves we derive an updated orbital- and pulse period ephemeris of the neutron star. We also study the pulse profile variations as a function of time and energy as well as the variability of the spectral parameters. We find clear evidence for at least three cyclotron line features. In agreement with previous observations of 4U 0115+63, we detect an anti-correlation between the luminosity and the fundamental cyclotron line energy.

  9. Torque Reversal and Spin-Down of the Accretion-Powered Pulsar 4U 1626-67

    NASA Technical Reports Server (NTRS)

    Chakrabarty, Deepto L.; Bildsten, L.; Grunsfeld, J. M.; Koh, D. T.; Prince, T. A.; Vaughan, B. A.; Finger, M. H.; Scott, D. M.; Wilson, R. B.

    1997-01-01

    Over 5 yr of hard X-ray (20-60 keV) monitoring of the 7.66 s accretion-powered pulsar 4U 1626-67 with the Compton Gamma Ray Observatory/BATSE large-area detectors has revealed that the neutron star is now steadily spinning down, in marked contrast to the steady spin-up and spin-down torques differ by only 15% with the neutron star spin changing on a timescale |v/v| approximately equals 5000 yr in both states. The current spin-down rate is itself decreasing on a timescale |v/v| approximately equals 26 yr. The long-term timing history shows small-amplitude variations on a 4000 day timescale, which are probably due to variations in the mass transfer rate. The pulsed 20-60 keV emission from 4U 1626-67 is well-fitted by a power-law spectrum with photon index gamma = 4.9 and a typical pulsed intensity of 1.5 x 10(exp -10) ergs cm (exp -2)s(exp -1). The low count rates with BATSE prohibited us from constraining the reported 42 minute binary orbit, but we can rule out long-period orbits in the range 2 days < or = P(orb) < or = 900 days. We compare the long-term torque behavior of 4U 1626-67 to other disk-fed accreting pulsars and discuss the implications of our results for the various theories of magnetic accretion torques. The abrupt change in the sign of the torque is difficult to reconcile with the extremely smooth spin-down now observed. The strength of the torque noise in 4U 1626-67, approximately 10(exp -22) Hz(exp 2)s(exp -2) Hz(exp -1), is the smallest ever measured for an accreting X-ray pulsar, and it is comparable to the timing noise seen in young radio pulsars. We close by pointing out that the core temperature and external torque (the two parameters potentially relevant to internal sources of timing noise) of an accreting neutron star are also comparable to those of young radio pulsars.

  10. The Reawakening of the Sleeping X-ray Pulsar XTE J1946+274

    NASA Technical Reports Server (NTRS)

    Mueller, Sebastian; Mueller, Sebastian; Kuechnel, Matthias; Fuerst, Felix; Kreykenbohm, Ingo; Sagredo, Macarena; Obst, Maria; Wilms, Joern; Caballero, Isabel; Potttschmidt, Katja; Ferrigno, Carlo; Rothschild, Richard E.

    2012-01-01

    We report on a series of outbursts of the high mass X-ray binary XTE 11946+274 in 2010/2011 as observed with INTEGRAL, RXTE, and Swift. We discuss possible mechanisms resulting in the extraordinary outburst behavior of this source. The X-ray spectra can be described by standard phenomenological models, enhanced by an absorption feature of unknown origin at about 10 keV and a narrow iron K alpha fluorescence line at 6.4keV, which are variable in flux and pulse phase. We find possible evidence for the presence of a cyclotron resonance scattering feature at about 25 keV at the 93% level. The presence of a strong cyclotron line at 35 keV seen in data from the source's 1998 outburst and confirmed by a reanalysis of these data can be excluded. This result indicates that the cyclotron line feature in XTE 11946+274 is variable between individual outbursts.

  11. GAMMA-RAY AND HARD X-RAY EMISSION FROM PULSAR-AIDED SUPERNOVAE AS A PROBE OF PARTICLE ACCELERATION IN EMBRYONIC PULSAR WIND NEBULAE

    SciTech Connect

    Murase, Kohta; Kashiyama, Kazumi; Kiuchi, Kenta; Bartos, Imre

    2015-05-20

    It has been suggested that some classes of luminous supernovae (SNe) and gamma-ray bursts (GRBs) are driven by newborn magnetars. Fast-rotating proto-neutron stars have also been of interest as potential sources of gravitational waves (GWs). We show that for a range of rotation periods and magnetic fields, hard X-rays and GeV gamma rays provide us with a promising probe of pulsar-aided SNe. It is observationally known that young pulsar wind nebulae (PWNe) in the Milky Way are very efficient lepton accelerators. We argue that, if embryonic PWNe satisfy similar conditions at early stages of SNe (in ∼1–10 months after the explosion), external inverse-Compton emission via upscatterings of SN photons is naturally expected in the GeV range as well as broadband synchrotron emission. To fully take into account the Klein–Nishina effect and two-photon annihilation process that are important at early times, we perform detailed calculations including electromagnetic cascades. Our results suggest that hard X-ray telescopes such as NuSTAR can observe such early PWN emission by follow-up observations in months to years. GeV gamma-rays may also be detected by Fermi for nearby SNe, which serve as counterparts of these GW sources. Detecting the signals will give us an interesting probe of particle acceleration at early times of PWNe, as well as clues to driving mechanisms of luminous SNe and GRBs. Since the Bethe–Heitler cross section is lower than the Thomson cross section, gamma rays would allow us to study subphotospheric dissipation. We encourage searches for high-energy emission from nearby SNe, especially SNe Ibc including super-luminous objects.

  12. Studies of the Origin of High-frequency Quasi-periodic Oscillations of Mass-accreting Black Holes in X-Ray Binaries with Next-generation X-Ray Telescopes

    NASA Astrophysics Data System (ADS)

    Beheshtipour, Banafsheh; Hoormann, Janie K.; Krawczynski, Henric

    2016-08-01

    Observations with RXTE (Rossi X-ray Timing Explorer) revealed the presence of high-frequency quasi-periodic oscillations (HFQPOs) of the X-ray flux from several accreting stellar-mass black holes. HFQPOs (and their counterparts at lower frequencies) may allow us to study general relativity in the regime of strong gravity. However, the observational evidence today does not yet allow us to distinguish between different HFQPO models. In this paper we use a general-relativistic ray-tracing code to investigate X-ray timing spectroscopy and polarization properties of HFQPOs in the orbiting Hotspot model. We study observational signatures for the particular case of the 166 Hz quasi-periodic oscillation (QPO) in the galactic binary GRS 1915+105. We conclude with a discussion of the observability of spectral signatures with a timing-spectroscopy experiment such as the LOFT (Large Observatory for X-ray Timing) and polarization signatures with space-borne X-ray polarimeters such as IXPE (Imaging X-ray Polarimetry Explorer), PolSTAR (Polarization Spectroscopic Telescope Array), PRAXyS(Polarimetry of Relativistic X-ray Sources), or XIPE (X-ray Imaging Polarimetry Explorer). A mission with high count rate such as LOFT would make it possible to get a QPO phase for each photon, enabling the study of the QPO-phase-resolved spectral shape and the correlation between this and the flux level. Owing to the short periods of the HFQPOs, first-generation X-ray polarimeters would not be able to assign a QPO phase to each photon. The study of QPO-phase-resolved polarization energy spectra would thus require simultaneous observations with a first-generation X-ray polarimeter and a LOFT-type mission.

  13. ELECTROMAGNETIC SPINDOWN OF A TRANSIENT ACCRETING MILLISECOND PULSAR DURING QUIESCENCE

    SciTech Connect

    Melatos, A.; Mastrano, A. E-mail: alpham@unimelb.edu.au

    2016-02-10

    The measured spindown rates in quiescence of the transient accreting millisecond pulsars IGR J00291+5934, XTE J1751–305, SAX J1808.4–3658, and Swift J1756.9–2508 have been used to estimate the magnetic moments of these objects assuming standard magnetic dipole braking. It is shown that this approach leads to an overestimate if the amount of residual accretion is enough to distort the magnetosphere away from a force-free configuration through magnetospheric mass loading or crushing, so that the lever arm of the braking torque migrates inside the light cylinder. We derive an alternative spindown formula and calculate the residual accretion rates where the formula is applicable. As a demonstration we apply the alternative spindown formula to produce updated magnetic moment estimates for the four objects above. We note that based on current uncertain observations of quiescent accretion rates, magnetospheric mass loading and crushing are neither firmly indicated nor ruled out in these four objects. Because quiescent accretion rates are not measured directly (only upper limits are placed), without more data it is impossible to be confident about whether the thresholds for magnetospheric mass loading or crushing are reached or not.

  14. Electromagnetic Spindown of a Transient Accreting Millisecond Pulsar During Quiescence

    NASA Astrophysics Data System (ADS)

    Melatos, A.; Mastrano, A.

    2016-02-01

    The measured spindown rates in quiescence of the transient accreting millisecond pulsars IGR J00291+5934, XTE J1751-305, SAX J1808.4-3658, and Swift J1756.9-2508 have been used to estimate the magnetic moments of these objects assuming standard magnetic dipole braking. It is shown that this approach leads to an overestimate if the amount of residual accretion is enough to distort the magnetosphere away from a force-free configuration through magnetospheric mass loading or crushing, so that the lever arm of the braking torque migrates inside the light cylinder. We derive an alternative spindown formula and calculate the residual accretion rates where the formula is applicable. As a demonstration we apply the alternative spindown formula to produce updated magnetic moment estimates for the four objects above. We note that based on current uncertain observations of quiescent accretion rates, magnetospheric mass loading and crushing are neither firmly indicated nor ruled out in these four objects. Because quiescent accretion rates are not measured directly (only upper limits are placed), without more data it is impossible to be confident about whether the thresholds for magnetospheric mass loading or crushing are reached or not.

  15. The Effect of Deep Hydrogen Burning in the Accreted Envelope of a Neutron Star on the Properties of X-Ray Bursts

    NASA Astrophysics Data System (ADS)

    Taam, Ronald E.; Woosley, S. E.; Lamb, D. Q.

    1996-03-01

    The thermal and compositional evolution of a neutron star has been numerically followed to determine the long-term properties of X-ray bursts produced by thermonuclear shell flashes in its accreted hydrogen-rich envelope. Uniform burning over the entire neutron star surface is assumed and mass accretion rates greater than 0. 1MEdd (where MEdd is the critical mass accretion rate for which the accretion luminosity is equal to the Eddington luminosity) are considered. Specific attention is focused on the consequences of electron capture initiated burning of hydrogen at high densities ( 107 g cm -3). The degree of heating associated with the burning of the residual hydrogen (i.e., the matter which is not completely processed in the outburst) is a function of the mass accretion rate and the composition of the accreted matter. Heating of the neutron star envelope is found to be more important for greater mass accretion rates and for greater residual hydrogen abundances. Because of the higher envelope temperatures, the resulting bursts are weaker and recur more frequently, for a given mass accretion rate, than in situations where the deep hydrogen burning does not occur. The mass accretion rate, which delineates strong X-ray bursts (where the ratio of the peak burst lumi- nosity to the quiescent level of emission is greater than 3) from weak X-ray bursts, lies in the range of 0.1-0.2times the Eddington value. Weak burst activity is found for accretion rates extending to about the Eddington limit provided that the helium content of the accreted matter is greater than 0.23. The implications of our results with regard to the absence of regular, periodic X-ray bursting activity in the bright low-mass X-ray binary sources are briefly discussed.

  16. Discovery of Radio Pulsations from the X-ray Pulsar JO205+6449 in Supernova Remnant 3C58 with the Green Bank Telescope

    NASA Technical Reports Server (NTRS)

    Camilo, F.; Stairs, I. H.; Lorimer, D. R.; Backer, D. C.; Ransom, S. M.; Klein, B.; Wielebinski, R.; Kramer, M.; McLaughlin, M. A.; Arzoumanian, Z.; White, Nicholas E. (Technical Monitor)

    2002-01-01

    We report the discovery with the 100m Green Bank Telescope of 65 ms radio pulsations from the X-ray pulsar J0205+6449 at the center of supernova remnant 3C58, making this possibly the youngest radio pulsar known. From our observations at frequencies of 820 and 1375 MHz, the free electron column density to USSR J0205+6449 is found to be 140.7 +/- 0.3/cc pc. The barycentric pulsar period P and P(dot) determined from a phase-coherent timing solution are consistent with the values previously measured from X-ray observations. The averaged radio profile of USSR J0205+6449 consists of one sharp pulse of width = 3 ms = 0.05 P. The pulsar is an exceedingly weak radio source, with pulse-averaged flux density in the 1400 MHz band of approximately 45 micro-Jy and a spectral index of approximately -2.1. Its radio luminosity of approximately 0.5 may kpc(exp 2) at 1400 MHz is lower than that of approximately 99% of known pulsar and is the lowest among known young pulsars.

  17. Puzzling accretion onto a black hole in the ultraluminous X-ray source M 101 ULX-1.

    PubMed

    Liu, Ji-Feng; Bregman, Joel N; Bai, Yu; Justham, Stephen; Crowther, Paul

    2013-11-28

    There are two proposed explanations for ultraluminous X-ray sources (ULXs) with luminosities in excess of 10(39) erg s(-1). They could be intermediate-mass black holes (more than 100-1,000 solar masses, M sun symbol) radiating at sub-maximal (sub-Eddington) rates, as in Galactic black-hole X-ray binaries but with larger, cooler accretion disks. Alternatively, they could be stellar-mass black holes radiating at Eddington or super-Eddington rates. On its discovery, M 101 ULX-1 had a luminosity of 3 × 10(39) erg s(-1) and a supersoft thermal disk spectrum with an exceptionally low temperature--uncomplicated by photons energized by a corona of hot electrons--more consistent with the expected appearance of an accreting intermediate-mass black hole. Here we report optical spectroscopic monitoring of M 101 ULX-1. We confirm the previous suggestion that the system contains a Wolf-Rayet star, and reveal that the orbital period is 8.2 days. The black hole has a minimum mass of 5 M sun symbol, and more probably a mass of 20 M sun symbol-30 M sun symbol, but we argue that it is very unlikely to be an intermediate-mass black hole. Therefore, its exceptionally soft spectra at high Eddington ratios violate the expectations for accretion onto stellar-mass black holes. Accretion must occur from captured stellar wind, which has hitherto been thought to be so inefficient that it could not power an ultraluminous source.

  18. Orbital parameters for the X-ray pulsar 1E1145-6141

    SciTech Connect

    Hutchings, J.B.; Crampton, D.; Cowley, A.P.; Thompson, I.B.

    1987-05-01

    Results are reported of spectroscopy of the B-star primary of the X-ray binary 1E1145-6141 obtained during the past five years. Since the period is longer than the individual observing runs, it is difficult to determine unambiguously, but the most probable orbital period is 10.756 days. A less likely possibility is 12.09 days. The orbital parameters are derived and used to show that the system contains a neutron star of mass 1.4 to 2.0 solar masses and a B2 supergiant of mass 10 to 18 solar masses. The orbital inclination is 45-65 deg, the mass ratio is 6-9, and the primary is undermassive for its type and luminosity. 8 references.

  19. The 2006-2007 Active Phase Of Anomalous X-Ray Pulsar 4U 0142+61: Radiative and Timing Changes, Bursts, and Burst Spectral Features

    NASA Technical Reports Server (NTRS)

    Gavril, Fotis P.; Dib, Rim; Kaspi, Victoria M.

    2009-01-01

    After at least 6 years of quiescence, Anomalous X-ray Pulsar (AXP) 4U 0142+61 entered an active phase in 2006 March that lasted several months and included six X-ray bursts as well as many changes in the persistent X-ray emission. The bursts, the first seen from this AXP in >11 years of Rossi X-ray Timing Explorer monitoring, all occurred in the interval between 2006 April 6 and 2007 February 7. The burst durations ranged from 8-3x10(exp 3)s. The first five burst spectra are well modeled by blackbodies, with temperatures kT approx. 2 - 6 keV. However, the sixth burst had a complicated spectrum that is well characterized by a blackbody plus three emission features whose amplitude varied throughout the burst. The most prominent feature was at 14.0 keV. Upon entry into the active phase the pulsar showed a significant change in pulse morphology and a likely timing glitch. The glitch had a total frequency jump of (1.9+/-0.4)x10(exp -7) Hz, which recovered with a decay time of 17+/-2 days by more than the initial jump, implying a net spin-down of the pulsar. We discuss these events in the context of the magnetar model.

  20. Accretion Properties of a Sample of Hard X-Ray (<60 keV) Selected Seyfert 1 Galaxies

    NASA Astrophysics Data System (ADS)

    Wang, J.; Mao, Y. F.; Wei, J. Y.

    2009-02-01

    We examine the accretion properties in a sample of 42 hard (3-60 keV) X-ray selected nearby broad-line active galactic nuclei (AGNs). The energy range in the sample is harder than that usually used in similar previous studies. These AGNs are mainly complied from the RXTE All Sky Survey, and complemented by the released INTEGRAL AGN catalog. The black hole masses, bolometric luminosities of AGN, and Eddington ratios are derived from their optical spectra in terms of the broad Hβ emission line. The tight correlation between the hard X-ray (3-20 keV) and bolometric/line luminosity is well identified in our sample. Also identified is a strong inverse Baldwin relationship of the Hβ emission line. In addition, all of these hard X-ray AGNs are biased toward luminous objects with a high Eddington ratio (mostly between 0.01 and 0.1) and a low column density (<1022 cm-2), which is most likely due to the selection effect of the surveys. The hard X-ray luminosity is consequently found to be strongly correlated with the black hole mass. We believe the sample completeness will be improved in the next few years by the ongoing Swift and the International Gamma-Ray Astrophysics Laboratory missions, and by the next advanced missions, such as NuSTAR, Simbol-X, and NeXT. Finally, the correlation between RFe (= optical Fe II/Hβ) and disk temperature as assessed by T vprop (L/L Edd)M -1 BH leads us to suggest that the strength of the Fe II emission is mainly determined by the shape of the ionizing spectrum.

  1. The Behavior of Accretion Disks in Low Mass X-ray Binaries: Disk Winds and Alpha Model

    NASA Astrophysics Data System (ADS)

    Bayless, Amanda J.

    2010-01-01

    This dissertation presents research on two low mass X-ray binaries. The eclipsing low-mass X-ray binary 4U 1822-371 is the prototypical accretion disk corona (ADC) system. We have obtained new time-resolved UV spectroscopy with the ACS/SBC on the Hubble Space Telescope and new V- and J-band photometry with the 1.3-m SMARTS telescope at CTIO. We show that the accretion disk in the system has a strong wind with projected velocities up to 4000 km/s as determined from the Doppler width of the C IV emission line. The broad and shallow eclipse indicates that the disk has a vertically-extended, optically-thick component at optical wavelengths. This component extends almost to the edge of the disk and has a height equal to 50% of the disk radius. As it has a low brightness temperature, we identify it as the optically-thick base of the disk wind. V1408 Aql (=4U 1957+115) is a low mass X-ray binary which continues to be a black hole candidate. We have new photometric data of this system from the Otto Struve 2.1-m telescope's high speed CCD photometer at McDonald Observatory. The light curve is largely sinusoidal which we model with two components: a constant light source from the disk and a sinusoidal modulation at the orbital period from the irradiated face of the companion star. This is a radical re-interpretation of the orbital light curve. We do not require a large or asymmetric disk rim to account for the modulation in the light curve. Thus, the orbital inclination is unconstrained in our new model, removing the foundation for any claims of the compact object being a black hole.

  2. The XMM-Newton Bright Survey sample of absorbed quasars: X-ray and accretion properties

    NASA Astrophysics Data System (ADS)

    Ballo, L.; Severgnini, P.; Della Ceca, R.; Caccianiga, A.; Vignali, C.; Carrera, F. J.; Corral, A.; Mateos, S.

    2014-11-01

    Although absorbed quasars are extremely important for our understanding of the energetics of the Universe, the main physical parameters of their central engines are still poorly known. In this work, we present and study a complete sample of 14 quasars (QSOs) that are absorbed in the X-rays (column density NH > 4 × 1021 cm-2 and X-ray luminosity L 2-10 keV > 1044 ergs-1; XQSO2) belonging to the XMM-Newton Bright Serendipitous Survey (XBS). From the analysis of their ultraviolet-to-mid-infrared spectral energy distribution, we can separate the nuclear emission from the host galaxy contribution, obtaining a measurement of the fundamental nuclear parameters, like the mass of the central supermassive black hole and the value of Eddington ratio, λ Edd. Comparing the properties of XQSO2s with those previously obtained for the X-ray unabsorbed QSOs in the XBS, we do not find any evidence that the two samples are drawn from different populations. In particular, the two samples span the same range in Eddington ratios, up to λ Edd ˜ 0.5; this implies that our XQSO2s populate the `forbidden region' in the so-called `effective Eddington limit paradigm'. A combination of low grain abundance, presence of stars inwards of the absorber, and/or anisotropy of the disc emission can explain this result.

  3. A search for X-ray emission from a nearby pulsar - PSR 1929 + 10

    NASA Technical Reports Server (NTRS)

    Alpar, A.; Brinkmann, W.; Oegelman, H.; Kiziloglu, U.; Pines, D.

    1987-01-01

    Observations of the radio pulsar PSR 1929 + 10 with the Exosat observatory are reported. A 2 sigma upper limit of 0.0005 cts/s was obtained in the 0.04-2.4 keV range, which translates into a luminosity upper limit of 2 x 10 to the 29th erg/s for a power-law source with photon number index 1-3, and a luminosity upper limit of 10 to the 30th erg/s corresponding to a temperature of 190,000 K for a blackbody with radius 10 km. The implications of these upper limits for various models and their compatibility with the positive detection of this source by the Einstein Observatory are discussed.

  4. X-RAY DETERMINATION OF THE VARIABLE RATE OF MASS ACCRETION ONTO TW HYDRAE

    SciTech Connect

    Brickhouse, N. S.; Cranmer, S. R.; Dupree, A. K.; Guenther, H. M.; Wolk, S. J.; Luna, G. J. M.

    2012-12-01

    Diagnostics of electron temperature (T{sub e} ), electron density (n{sub e} ), and hydrogen column density (N{sub H}) from the Chandra High Energy Transmission Grating spectrum of He-like Ne IX in TW Hydrae (TW Hya), in conjunction with a classical accretion model, allow us to infer the accretion rate onto the star directly from measurements of the accreting material. The new method introduces the use of the absorption of Ne IX lines as a measure of the column density of the intervening, accreting material. On average, the derived mass accretion rate for TW Hya is 1.5 Multiplication-Sign 10{sup -9} M{sub Sun} yr{sup -1}, for a stellar magnetic field strength of 600 G and a filling factor of 3.5%. Three individual Chandra exposures show statistically significant differences in the Ne IX line ratios, indicating changes in N{sub H}, T{sub e} , and n{sub e} by factors of 0.28, 1.6, and 1.3, respectively. In exposures separated by 2.7 days, the observations reported here suggest a five-fold reduction in the accretion rate. This powerful new technique promises to substantially improve our understanding of the accretion process in young stars.

  5. DISCOVERY OF {gamma}-RAY PULSATION AND X-RAY EMISSION FROM THE BLACK WIDOW PULSAR PSR J2051-0827

    SciTech Connect

    Wu, J. H. K.; Kong, A. K. H.; Huang, R. H. H.; Tam, P. H. T.; Takata, J.; Wu, E. M. H.; Cheng, K. S. E-mail: akong@phys.nthu.edu.tw

    2012-04-01

    We report the discovery of pulsed {gamma}-ray emission and X-ray emission from the black widow millisecond pulsar PSR J2051-0827 by using the data from the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope and the Advanced CCD Imaging Spectrometer array on the Chandra X-Ray Observatory. Using three years of LAT data, PSR J2051-0827 is clearly detected in {gamma}-rays with a significance of {approx}8{sigma} in the 0.2-20 GeV band. The 200 MeV-20 GeV {gamma}-ray spectrum of PSR J2051-0827 can be modeled by a simple power law with a photon index of 2.46 {+-} 0.15. Significant ({approx}5{sigma}) {gamma}-ray pulsations at the radio period were detected. PSR J2051-0827 was also detected in soft (0.3-7 keV) X-ray with Chandra. By comparing the observed {gamma}-rays and X-rays with theoretical models, we suggest that the {gamma}-ray emission is from the outer gap while the X-rays can be from intra-binary shock and pulsar magnetospheric synchrotron emissions.

  6. Durability of the accretion disk of millisecond pulsars.

    PubMed

    Michel, F C; Dessler, A J

    1985-05-24

    Pulsars with pulsation periods in the millisecond range are thought to be neutron stars that have acquired an extraordinarily short spin period through the accretion of stellar material spiraling down onto the neutron star from a nearby companion. Nearly all the angular momentum and most of the mass of the companion star is transferred to the neutron star. During this process, wherein the neutron star consumes its companion, it is required that a disk of stellar material be formed around the neutron star. In conventional models it is supposed that the disk is somehow lost when the accretion phase is finished, so that only the rapidly spinning neutron star remains. However, it is possible that, after the accretion phase, a residual disk remains in stable orbit around the neutron star. The end result of such an accretion process is an object that looks much like a miniature (about 100 kilometers), heavy version of Saturn: a central object (the neutron star) surrounded by a durable disk.

  7. The Accretion-Ejection Mechanisms in X-ray Binaries: an Unified View

    SciTech Connect

    Petrucci, P. O.; Foellmi, C.; Ferreira, J.; Henri, G.; Belmont, R.; Malzac, J.

    2009-05-11

    We present a new keplerian accretion disc solution, the so-called Jet Emitting Disc (JED hereafter), which is part of global self-consistent disc-jet MHD structure. In our framework, a large scale, organized vertical magnetic field is threading the JED giving birth, when conditions are met, to stationnary self-collimated non relativistic jets. The main condition is that the magnetic pressure P{sub mag} must be of the order of the total pressure P{sub tot} in the JED and a direct consequence is a jet torque largely dominating the viscuous torque. This in turn implies an accretion velocity of the order of the sound speed and then a density much lower than a standard accretion disc. Moreover, most of the accretion power P{sub acc} being extracted by the jet, only part of it (<50%) is liberated in the JED as heating power.

  8. X-RAYING AN ACCRETION DISK IN REALTIME: THE EVOLUTION OF IONIZED REFLECTION DURING A SUPERBURST FROM 4U 1636-536

    SciTech Connect

    Keek, L.; Ballantyne, D. R.; Kuulkers, E.; Strohmayer, T. E.

    2014-12-20

    When a thermonuclear X-ray burst ignites on an accreting neutron star, the accretion disk undergoes sudden strong X-ray illumination, which can drive a range of processes in the disk. Observations of superbursts, with durations of several hours, provide the best opportunity to study these processes and to probe accretion physics. Using detailed models of X-ray reflection, we perform time resolved spectroscopy of the superburst observed from 4U 1636-536 in 2001 with the Rossi X-Ray Timing Explorer. The spectra are consistent with a blackbody reflecting off a photoionized accretion disk, with the ionization state dropping with time. The evolution of the reflection fraction indicates that the initial reflection occurs from a part of the disk at larger radius, subsequently transitioning to reflection from an inner region of the disk. Even though this superburst did not reach the Eddington limit, we find that a strong local absorber develops during the superburst. Including this event, only two superbursts have been observed by an instrument with sufficient collecting area to allow for this analysis. It highlights the exciting opportunity for future X-ray observatories to investigate the processes in accretion disks when illuminated by superbursts.

  9. High-resolution X-ray spectroscopy of the X-ray burster and 11 Hz pulsar IGR J17480-2446

    NASA Astrophysics Data System (ADS)

    Canizares, Claude

    2013-09-01

    The detection and identification of photospheric absorption lines from a neutron star would allow measurement of their gravitational redshift and hence the neutron star compactness. In principle, the line shape would allow unique determination of M and R. X-ray bursters are, in most respects, the ideal targets for this search, but most rotate so rapidly that any lines are too broadened to detect. However, the recently discovered X-ray burster Terzan 5 X-2 spins at only 11 Hz, 20x slower than the next slowest rotator. We propose a TOO observation with HETGS to search for narrow lines of ionized Fe when this X-ray transient next becomes active. This is the best chance ever to detect a narrow atomic line in a neutron star.

  10. High-resolution X-ray spectroscopy of the X-ray burster and 11 Hz pulsar IGR J17480-2446

    NASA Astrophysics Data System (ADS)

    Canizares, Claude

    2014-09-01

    The detection and identification of photospheric absorption lines from a neutron star would allow measurement of their gravitational redshift and hence the neutron star compactness. In principle, the line shape would allow unique determination of M and R. X-ray bursters are, in most respects, the ideal targets for this search, but most rotate so rapidly that any lines are too broadened to detect. However, the recently discovered X-ray burster Terzan 5 X-2 spins at only 11 Hz, 20x slower than the next slowest rotator. We propose a TOO observation with HETGS to search for narrow lines of ionized Fe when this X-ray transient next becomes active. This is the best chance ever to detect a narrow atomic line in a neutron star.

  11. REVEALING THE STRUCTURE OF AN ACCRETION DISK THROUGH ENERGY-DEPENDENT X-RAY MICROLENSING

    SciTech Connect

    Chartas, G.; Moore, D.; Kochanek, C. S.; Mosquera, A. M.; Blackburne, J. A.; Dai, X.

    2012-10-01

    We present results from monitoring observations of the gravitationally lensed quasar RX J1131-1231 performed with the Chandra X-Ray Observatory. The X-ray observations were planned with relatively long exposures that allowed a search for energy-dependent microlensing in the soft (0.2-2 keV) and hard (2-10 keV) light curves of the images of RX J1131-1231. We detect significant microlensing in the X-ray light curves of images A and D, and energy-dependent microlensing of image D. The magnification of the soft band appears to be larger than that in the hard band by a factor of {approx}1.3 when image D becomes more magnified. This can be explained by the difference between a compact, softer-spectrum corona that is producing a more extended, harder spectrum reflection component off the disk. This is supported by the evolution of the fluorescent iron line in image D over three consecutive time-averaged phases of the light curve. In the first period, an Fe line at E = 6.35{sup +0.14}{sub -0.14} keV is detected (at >99% confidence). In the second period, two Fe lines are detected, one at E = 5.50{sup +0.03}{sub -0.08} keV (detected at >99% confidence) and another at E = 6.04{sup +0.10}{sub -0.07} keV (marginally detected at >90% confidence), and in the third period, a broadened Fe line at 6.42{sup +0.16}{sub -0.14} keV is detected (at >99% confidence). This evolution of the Fe line profile during the microlensing event is consistent with the line distortion expected when a caustic passes over the inner disk where the shape of the fluorescent Fe line is distorted by general relativistic and Doppler effects.

  12. Neutron star crustal plate tectonics. I. Magnetic dipole evolution in millisecond pulsars and low-mass X-ray binaries

    SciTech Connect

    Ruderman, M. )

    1991-01-01

    Crust lattices in spinning-up or spinning-down neutron stars have growing shear stresses caused by neutron superfluid vortex lines pinned to lattice nuclei. For the most rapidly spinning stars, this stress will break and move the crust before vortex unpinning occurs. In spinning-down neutron stars, crustal plates will move an equatorial subduction zone in which the plates are forced into the stellar core below the crust. The opposite plate motion occurs in spinning-up stars. Magnetic fields which pass through the crust or have sources in it move with the crust. Spun-up neutron stars in accreting low-mass X-ray binaries LMXBs should then have almost axially symmetric magnetic fields. Spun-down ones with very weak magnetic fields should have external magnetic fields which enter and leave the neutron star surface only near its equator. The lowest field millisecond radiopulsars seem to be orthogonal rotators implying that they have not previously been spun-up in LMXBs but are neutron stars initially formed with periods near 0.001 s that subsequently spin down to their present periods. Accretion-induced white dwarf collapse is then the most plausible genesis for them. 29 refs.

  13. FORMATION OF BINARY MILLISECOND PULSARS BY ACCRETION-INDUCED COLLAPSE OF WHITE DWARFS UNDER WIND-DRIVEN EVOLUTION

    SciTech Connect

    Ablimit, Iminhaji; Li, Xiang-Dong

    2015-02-20

    Accretion-induced collapse (AIC) of massive white dwarfs (WDs) has been proposed to be an important channel to form binary millisecond pulsars (MSPs). Recent investigations on thermal timescale mass transfer in WD binaries demonstrate that the resultant MSPs are likely to have relatively wide orbit periods (≳ 10 days). Here we calculate the evolution of WD binaries taking into account the excited wind from the companion star induced by X-ray irradiation of the accreting WD, which may drive rapid mass transfer even when the companion star is less massive than the WD. This scenario can naturally explain the formation of the strong-field neutron star in the low-mass X-ray binary 4U 1822–37. After AIC the mass transfer resumes when the companion star refills its Roche lobe, and the neutron star is recycled owing to mass accretion. A large fraction of the binaries will evolve to become binary MSPs with an He WD companion, with the orbital periods distributed between ≳ 0.1 days and ≲ 30 days, while some of them may follow the cataclysmic variable-like evolution toward very short orbits. If we instead assume that the newborn neutron star appears as an MSP and that part of its rotational energy is used to ablate its companion star, the binaries may also evolve to be the redback-like systems.

  14. PULSE AMPLITUDE DEPENDS ON kHz QPO FREQUENCY IN THE ACCRETING MILLISECOND PULSAR SAX J1808.4-3658

    SciTech Connect

    Bult, Peter; Van der Klis, Michiel

    2015-01-10

    We study the relation between the 300-700 Hz upper kHz quasi-periodic oscillation (QPO) and the 401 Hz coherent pulsations across all outbursts of the accreting millisecond X-ray pulsar SAX J1808.4-3658 observed with the Rossi X-ray Timing Explorer. We find that the pulse amplitude systematically changes by a factor of ∼2 when the upper kHz QPO frequency passes through 401 Hz: it halves when the QPO moves to above the spin frequency and doubles again on the way back. This establishes for the first time the existence of a direct effect of kHz QPOs on the millisecond pulsations and provides a new clue to the origin of the upper kHz QPO. We discuss several scenarios and conclude that while more complex explanations can not formally be excluded, our result strongly suggests that the QPO is produced by azimuthal motion at the inner edge of the accretion disk, most likely orbital motion. Depending on whether this azimuthal motion is faster or slower than the spin, the plasma then interacts differently with the neutron-star magnetic field. The most straightforward interpretation involves magnetospheric centrifugal inhibition of the accretion flow that sets in when the upper kHz QPO becomes slower than the spin.

  15. Correlated X-ray/ultraviolet/optical variability and the nature of accretion disc in the bare Seyfert 1 galaxy Fairall 9

    NASA Astrophysics Data System (ADS)

    Pal, Main; Dewangan, Gulab C.; Connolly, S. D.; Misra, Ranjeev

    2017-04-01

    We study the multiwavelength variability of the bare Seyfert 1 galaxy Fairall 9 using Swift monitoring observations consisting of 165 usable pointings spanning nearly two years and covering six ultraviolet (UV)/optical bands and X-rays. Fairall 9 is highly variable in all bands though the variability amplitude decreases from X-ray to optical bands. The variations in the X-ray and UV/optical bands are strongly correlated. Our reverberation mapping analysis using the JAVALIN tool shows that the variation in the UV/optical bands lag behind the variations in the X-ray band by ∼2-10 d. These lag measurements strongly suggest that the optical/UV variations are mainly caused by variations in the X-rays, and the origin of most of the optical/UV emission is X-ray reprocessing. The observed lags are found to vary as τ ∝ λ1.36 ± 0.13, consistent with the prediction, τ ∝ λ4/3, for X-ray reprocessing in a standard accretion disc. However, the predicted lags for a standard accretion disc with X-ray reprocessing using the black hole mass (MBH ∼ 2.6 × 108 M⊙) estimated from the reverberation mapping of broad emission lines and the accretion rate relative to the Eddington rate (dot{m_E}=0.02) are shorter than the observed lags. These observations suggest that the accretion disc in Fairall 9 is larger than that predicted by the standard disc model, and confirm similar findings in a few other Seyfert 1 galaxies such as NGC 5548.

  16. A WHITE DWARF MERGER AS PROGENITOR OF THE ANOMALOUS X-RAY PULSAR 4U 0142+61?

    SciTech Connect

    Rueda, J. A.; Boshkayev, K.; Izzo, L.; Ruffini, R.; Loren-Aguilar, P.; Kuelebi, B.; Aznar-Siguan, G.; Garcia-Berro, E. E-mail: enrique.garcia-berro@upc.edu

    2013-08-01

    It has been recently proposed that massive, fast-rotating, highly magnetized white dwarfs could describe the observational properties of some of soft gamma-ray repeaters and anomalous X-ray pulsars (AXPs). Moreover, it has also been shown that high-field magnetic white dwarfs can be the outcome of white dwarf binary mergers. The products of these mergers consist of a hot central white dwarf surrounded by a rapidly rotating disk. Here we show that the merger of a double degenerate system can explain the characteristics of the peculiar AXP 4U 0142+61. This scenario accounts for the observed infrared excess. We also show that the observed properties of 4U 0142+6 are consistent with an approximately 1.2 M{sub Sun} white dwarf, remnant of the coalescence of an original system made of two white dwarfs of masses 0.6 M{sub Sun} and 1.0 M{sub Sun }. Finally, we infer a post-merging age {tau}{sub WD} Almost-Equal-To 64 kyr and a magnetic field B Almost-Equal-To 2 Multiplication-Sign 10{sup 8} G. Evidence for such a magnetic field may come from the possible detection of the electron cyclotron absorption feature observed between the B and V bands at Almost-Equal-To 10{sup 15} Hz in the spectrum of 4U 0142+61.

  17. Chaotic and stochastic processes in the accretion flows of the black hole X-ray binaries revealed by recurrence analysis

    NASA Astrophysics Data System (ADS)

    Suková, Petra; Grzedzielski, Mikolaj; Janiuk, Agnieszka

    2016-02-01

    Aims: Both the well known microquasar GRS 1915+105, as well as its recently discovered analogue, IGR J17091-3624, exhibit variability that is characteristic of a deterministic chaotic system. Their specific kind of quasi-periodic flares that are observed in some states is intrinsically connected with the global structure of the accretion flow, which are governed by the nonlinear hydrodynamics. One plausible mechanism that is proposed to explain this kind of variability is the thermal-viscous instability that operates in the accretion disk. The purely stochastic variability that occurs because of turbulent conditions in the plasma, is quantified by the power density spectra and appears in practically all types of sources and their spectral states. Methods: We pose a question as to whether these two microquasars are one of a kind, or if the traces of deterministic chaos, and hence the accretion disk instability, may also be hidden in the observed variability of other sources. We focus on the black hole X-ray binaries that accrete at a high rate and are, therefore, theoretically prone to the development of radiation pressure-induced instability. To study the nonlinear behaviour of the X-ray sources and distinguish between the chaotic and stochastic nature of their emission, we propose a novel method, which is based on recurrence analysis. Widely known in other fields of physics, this powerful method is used here for the first time in an astrophysical context. We estimate the indications of deterministic chaos quantitatively, such as the Rényi's entropy for the observed time series, and we compare them with surrogate data. Results: Using the observational data collected by the RXTE satellite, we reveal the oscillations pattern and the observable properties of six black hole systems. For five of them, we confirm the signatures of deterministic chaos being the driver of their observed variability. Conclusions: We test the method and confirm the deterministic nature of

  18. GAMMA-RAY OBSERVATIONS OF THE Be/PULSAR BINARY 1A 0535+262 DURING A GIANT X-RAY OUTBURST

    SciTech Connect

    Acciari, V. A.; Benbow, W.; Aliu, E.; Araya, M.; Cui, W.; Finley, J. P.; Arlen, T.; Aune, T.; Beilicke, M.; Buckley, J. H.; Bugaev, V.; Dickherber, R.; Bradbury, S. M.; Byrum, K.; Cannon, A.; Collins-Hughes, E.; Cesarini, A.; Ciupik, L.; Duke, C.; Falcone, A. E-mail: cui@purdue.edu

    2011-06-01

    Giant X-ray outbursts, with luminosities of about 10{sup 37} erg s{sup -1}, are observed roughly every five years from the nearby Be/pulsar binary 1A 0535+262. In this article, we present observations of the source with VERITAS at very high energies (VHEs; E >100 GeV) triggered by the X-ray outburst in 2009 December. The observations started shortly after the onset of the outburst and provided comprehensive coverage of the episode, as well as the 111 day binary orbit. No VHE emission is evident at any time. We also examined data from the contemporaneous observations of 1A 0535+262 with the Fermi/Large Area Telescope at high-energy photons (E > 0.1 GeV) and failed to detect the source at GeV energies. The X-ray continua measured with the Swift/X-Ray Telescope and the RXTE/PCA can be well described by the combination of blackbody and Comptonized emission from thermal electrons. Therefore, the gamma-ray and X-ray observations suggest the absence of a significant population of non-thermal particles in the system. This distinguishes 1A 0535+262 from those Be X-ray binaries (such as PSR B1259-63 and LS I +61{sup 0}303) that have been detected at GeV-TeV energies. We discuss the implications of the results on theoretical models.

  19. The X-Ray Structure and Spectrum of the Pulsar Wind Nebula Surrounding PSR B1853+01 in W44

    NASA Technical Reports Server (NTRS)

    Petre, R.; Kuntz, K. D.; Shelton, R. L.; White, Nicholas E. (Technical Monitor)

    2001-01-01

    We present the result of a Chandra ACIS observation of the pulsar PSR B1853+01 and its associated pulsar wind nebula (PWN), embedded within the supernova remnant W44. A hard band ACIS map cleanly distinguishes the PWN from the thermal emission of W44. The nebula is extended in the north-south direction, with an extent about half that of the radio emission. Morphological differences between the X-ray and radio images are apparent. Spectral fitting reveals a clear difference in spectral index between the hard emission from PSR B1853+01 (Gamma approx. 1.4) and the extended nebula (Gamma approx. 2.2). The more accurate values for the X-ray flux and spectral index are used refine estimates for PWN parameters, including magnetic field strength, the average Lorentz factor gamma of the particles in the wind, the magnetization parameter sigma, and the ratio k of electrons to other particles.

  20. THE LONGEST TIMESCALE X-RAY VARIABILITY REVEALS EVIDENCE FOR ACTIVE GALACTIC NUCLEI IN THE HIGH ACCRETION STATE

    SciTech Connect

    Zhang Youhong

    2011-01-01

    The All Sky Monitor (ASM) on board the Rossi X-ray Timing Explorer has continuously monitored a number of active galactic nuclei (AGNs) with similar sampling rates for 14 years, from 1996 January to 2009 December. Utilizing the archival ASM data of 27 AGNs, we calculate the normalized excess variances of the 300-day binned X-ray light curves on the longest timescale (between 300 days and 14 years) explored so far. The observed variance appears to be independent of AGN black-hole mass and bolometric luminosity. According to the scaling relation of black-hole mass (and bolometric luminosity) from galactic black hole X-ray binaries (GBHs) to AGNs, the break timescales that correspond to the break frequencies detected in the power spectral density (PSD) of our AGNs are larger than the binsize (300 days) of the ASM light curves. As a result, the singly broken power-law (soft-state) PSD predicts the variance to be independent of mass and luminosity. Nevertheless, the doubly broken power-law (hard-state) PSD predicts, with the widely accepted ratio of the two break frequencies, that the variance increases with increasing mass and decreases with increasing luminosity. Therefore, the independence of the observed variance on mass and luminosity suggests that AGNs should have soft-state PSDs. Taking into account the scaling of the break timescale with mass and luminosity synchronously, the observed variances are also more consistent with the soft-state than the hard-state PSD predictions. With the averaged variance of AGNs and the soft-state PSD assumption, we obtain a universal PSD amplitude of 0.030 {+-} 0.022. By analogy with the GBH PSDs in the high/soft state, the longest timescale variability supports the standpoint that AGNs are scaled-up GBHs in the high accretion state, as already implied by the direct PSD analysis.

  1. Pulse Phase Dependence of Low Energy Emission Lines in an X-ray pulsar 4U 1626-67 during its spin-up and spin-down phase

    NASA Astrophysics Data System (ADS)

    Beri, Aru; Paul, Biswajit; Dewangan, Gulab Chand

    2016-07-01

    We will present the results obtained from the new observation of an ultra-compact X-ray binary pulsar 4U 1626-67, carried out with the XMM-Newton observatory. 4U 1626-67, a unique accretion powered pulsar underwent two torque reversals since its discovery in 1977. Pulse phase resolved spectroscopy of this source performed using the data from the XMM-Newton observatory during its spin-down phase revealed the dependence of the emission lines on the pulse phase. O VII emission line at 0.569 keV showed the maximum variation by factor of 4. These variations were interpreted due to warps in the accretion disk (Beri et al. 2015). Radiation pressure induced warping is also believed to be the cause for spin-down. In light of this possible explanation for spin-down torque reversal we expect different line variability during the spin-up phase. We will discuss the implications of the results obtained after performing pulse phase resolved spectroscopy using data from the EPIC-pn during the current spin-up phase. Detailed study of the prominent Neon and Oxygen line complexes with the high resolution Reflection Grating Spectrometer (RGS) on-board XMM-Newton will also be presented.

  2. Long-term timing and glitch characteristics of anomalous X-ray pulsar 1RXS J170849.0–400910

    SciTech Connect

    Muş, Sinem Şaşmaz; Göğüş, Ersin

    2013-12-01

    We present the results of our detailed timing studies of an anomalous X-ray pulsar, 1RXS J170849.0–400910, using Rossi X-ray Timing Explorer (RXTE) observations spanning over ∼6 yr from 2005 until the end of the RXTE mission. We constructed the long-term spin characteristics of the source and investigated the time and energy dependence of the pulse profile and pulsed count rates. We find that the pulse profile and pulsed count rates in the 2-10 keV band do not show any significant variations in ∼6 yr. 1RXS J170849.0–400910 has been the most frequently glitching anomalous X-ray pulsar: three spin-up glitches and three candidate glitches were observed prior to 2005. Our extensive search for glitches later in the timeline resulted in no unambiguous glitches, though we identified two glitch candidates (with Δν/ν ∼ 10{sup –6}) in two data gaps: a strong candidate around MJD 55532 and another one around MJD 54819, which is slightly less robust. We discuss our results in the context of pulsar glitch models and expectancy of glitches within the vortex unpinning model.

  3. The Peculiar Galactic Center Neutron Star X-Ray Binary XMM J174457-2850.3

    NASA Technical Reports Server (NTRS)

    Degenaar, N.; Wijnands, R.; Reynolds, M. T.; Miller, J. M.; Altamirano, D.; Kennea, J.; Gehrels, N.; Haggard, D.; Ponti, G.

    2014-01-01

    The recent discovery of a milli-second radio pulsar experiencing an accretion outburst similar to those seen in low mass X-ray binaries, has opened up a new opportunity to investigate the evolutionary link between these two different neutron star manifestations. The remarkable X-ray variability and hard X-ray spectrum of this object can potentially serve as a template to search for other X-ray binary radio pulsar transitional objects. Here we demonstrate that the transient X-ray source XMM J174457-2850.3 near the Galactic center displays similar X-ray properties. We report on the detection of an energetic thermonuclear burst with an estimated duration of 2 hr and a radiated energy output of 5E40 erg, which unambiguously demonstrates that the source harbors an accreting neutron star. It has a quiescent X-ray luminosity of Lx5E32 ergs and exhibits occasional accretion outbursts during which it brightens to Lx1E35-1E36 ergs for a few weeks (2-10 keV). However, the source often lingers in between outburst and quiescence at Lx1E33-1E34 ergs. This unusual X-ray flux behavior and its relatively hard X-ray spectrum, a power law with an index of 1.4, could possibly be explained in terms of the interaction between the accretion flow and the magnetic field of the neutron star.

  4. Properties of a B0 I stellar wind and interstellar grains derived from Ginga observations of the binary X-ray pulsar 4U 1538-52

    NASA Technical Reports Server (NTRS)

    Clark, George W.; Woo, Jonathan W.; Nagase, Fumiaki

    1994-01-01

    From measurements of the X-ray eclipse phenomena of the binary X-ray pulsar 4U 1538-52, we derive properties of the stellar wind of its B0 I companion, QV Nor, and a constraint on models of interstellar grains. Estimates of the wind density as a function of the distance from the center of QV Nor are obtained from an analysis of the variation of X-ray attenuation during an eclipse egress. A Monte Carlo computation of the absorption and scattering of X-rays in the X-ray-ionized wind accounts for approximately two-thirds of the spectrum of X-rays with energies above 4.5 keV observed during the eclipse. Our upper limit on R(sub XV) is 0.06/mag, which implies that the X-ray scattering efficiency of interstellar dust is less than expected for solid grains with a size distribution of the form n(sub g)(a) approximately a(exp -3.5) in the range from 0.005 to 0.25 microns and composed of silicate (R(sub XV) = 0.22/mag) or a silicate-graphite mixture (R(sub XV) = 0.11/mag) as derived from the calculations of Martin & Rouleau (1991). This lends support to the idea (Mathis & Whiffen 1989) that interstellar grains are 'fluffy' aggregates with an average bulk density less than that of their constitutent particles. Such aggregates would have a smaller ratio of X-ray scattering efficiency to optical extinction efficiency compared with solid grains of the same material.

  5. The Accreting Black Hole Swift J1753.5-0127 from Radio to Hard X-Ray

    NASA Astrophysics Data System (ADS)

    Tomsick, John A.; Rahoui, Farid; Kolehmainen, Mari; Miller-Jones, James; Fürst, Felix; Yamaoka, Kazutaka; Akitaya, Hiroshi; Corbel, Stéphane; Coriat, Mickael; Done, Chris; Gandhi, Poshak; Harrison, Fiona A.; Huang, Kuiyun; Kaaret, Philip; Kalemci, Emrah; Kanda, Yuka; Migliari, Simone; Miller, Jon M.; Moritani, Yuki; Stern, Daniel; Uemura, Makoto; Urata, Yuji

    2015-07-01

    We report on multiwavelength measurements of the accreting black hole Swift J1753.5-0127 in the hard state at low luminosity (L ˜ 2.7 × 1036 erg s-1 assuming a distance of d = 3 kpc) in 2014 April. The radio emission is optically thick synchrotron, presumably from a compact jet. We take advantage of the low extinction (E(B-V)=0.45 from earlier work) and model the near-IR to UV emission with a multitemperature disk model. Assuming a black hole mass of MBH = 5 M⊙ and a system inclination of i = 40°, the fits imply an inner radius for the disk of Rin/Rg > 212d3(MBH/5 M⊙)-1, where Rg is the gravitational radius of the black hole and d3 is the distance to the source in units of 3 kpc. The outer radius is Rout/Rg=90,000 d3(MBH/5 M⊙)-1, which corresponds to 6.6 × 1010 d3 cm, consistent with the expected size of the disk given previous measurements of the size of the companion's Roche lobe. The 0.5-240 keV energy spectrum measured by Swift/X-ray Telescope (XRT), Suzaku (XIS, PIN, and GSO), and Nuclear Spectroscopic Telescope Array is relatively well characterized by an absorbed power law with a photon index of Γ = 1.722 ± 0.003 (90% confidence error), but a significant improvement is seen when a second continuum component is added. Reflection is a possibility, but no iron line is detected, implying a low iron abundance. We are able to fit the entire (radio to 240 keV) spectral energy distribution (SED) with a multitemperature disk component, a Comptonization component, and a broken power law, representing the emission from the compact jet. The broken power law cannot significantly contribute to the soft X-ray emission, and this may be related to why Swift J1753.5-0127 is an outlier in the radio/X-ray correlation. The broken power law (i.e., the jet) might dominate above 20 keV, which would constrain the break frequency to be between 2.4 × 1010 and 3.6 × 1012 Hz. Although the fits to the full SED do not include significant thermal emission in the X-ray band

  6. Discovery of a 105-ms X-ray Pulsar in Kesteven-79: On the Nature of Compact Central Objects in Supernova Remnants

    NASA Technical Reports Server (NTRS)

    Gotthelf, E. V.; Halpern, J. P.; Seward, F. D.

    2005-01-01

    We report the discovery of 105-ms X-ray pulsations from the compact central object (CCO) in the supernova remnant \\snr\\ using data acquired with the {\\it Newton X-Ray Multi-Mirror Mission). Using two observations of the pulsar taken 6-days apart we derive an upper limit on its spin-down rate of $\\dot P < 9 \\times 10"{-14}$-s-${-l)$,a nd find no evidence for binary orbital motion. The implied energy loss rate is $\\dot E < 3 \\times 10A{36)$-ergs-s$A{-1)$, polar magnetic field strength is $B-{\\rm p) < 3 \\times 10A{12)$-G, and spin-down age is $\\tau > 18.5$-kyr. The latter exceeds the remnant's estimated age, suggesting that the pulsar was born spinning near its current period. The X-ray spectrum of \\psr\\ is best characterized as a blackbody of temperature $kT {BB) =, 0.43\\pm0.02$ keV, radius $R-{BB) \\approx 1.3$-km, and $I{\\rm bol) = 5.2 \\times 10A{33)$ ergs-sSA{-1)$ at $d = 7.1$-kpc. The sinusoidal light curve is modulated with a pulsed fraction of $>45\\%$, suggestive of a small hot spot on the surface of the rotating neutron star. The lack of a discernible pulsar wind nebula is consistent with an interpretation of \\psr\\ as a rotation-powered pulsar whose spin-down luminosity falls below the empirical threshold for generating bright wind nebulae, $\\dot E-{\\rm c) = 4 \\times 10A{36)$-ergs-sSA{-I)$. The age discrepancy suggests that its $\\dot E$ has always been below $\\dot E c$, perhaps a distinguishing property of the CCOs. Alternatively, the X-ray spectrum of \\psr\\ suggests a low-luminosity AXP, but the weak inferred $B-{\\rm p)$ field is incompatible with a magnetar theory of its X-ray luminosity. The ordinary spin parameters discovered from \\psr\\ highlight the inability of existing theories to explain the high luminosities and temperatures of CCO thermal X-ray spectra.

  7. X-ray measurement of the spin-down of CalverA: A radio- and gamma-ray-quiet pulsar

    SciTech Connect

    Halpern, J. P.; Bogdanov, S.; Gotthelf, E. V.

    2013-12-01

    We measure spin-down of the 59 ms X-ray pulsar Calvera by comparing the XMM-Newton discovery data from 2009 with new Chandra timing observations taken in 2013. Its period derivative is P-dot =(3.19± 0.08)×10{sup −15}, which corresponds to spin-down luminosity E-dot =6.1×10{sup 35} erg s{sup –1}, characteristic age τ{sub c}≡P/2 P-dot =2.9×10{sup 5} yr, and surface dipole magnetic field strength B{sub s} = 4.4 × 10{sup 11} G. These values rule out a mildly recycled pulsar, but Calvera could be an orphaned central compact object (anti-magnetar), with a magnetic field that was initially buried by supernova debris and is now reemerging and approaching normal strength. We also performed unsuccessful searches for high-energy γ-rays from Calvera in both imaging and timing of >100 MeV Fermi photons. Even though the distance to Calvera is uncertain by an order of magnitude, an upper limit of d < 2 kpc inferred from X-ray spectra implies a γ-ray luminosity limit of <3.3 × 10{sup 32} erg s{sup –1}, which is less than that of any pulsar of comparable E-dot . Calvera shares some properties with PSR J1740+1000, a young radio pulsar that we show by virtue of its lack of proper motion was born outside of the Galactic disk. As an energetic, high-Galactic-latitude pulsar, Calvera is unique in being undetected in both radio and γ-rays to faint limits, which should place interesting constraints on models for particle acceleration and beam patterns in pulsar magnetospheres.

  8. XMM-Newton observations of UW CrB: detection of X-ray bursts and evidence for accretion disc evolution

    NASA Astrophysics Data System (ADS)

    Hakala, Pasi; Ramsay, Gavin; Muhli, Panu; Charles, Phil; Hannikainen, Diana; Mukai, Koji; Vilhu, Osmi

    2005-01-01

    UW CrB (MS 1603+2600) is a peculiar short-period X-ray binary that exhibits extraordinary optical behaviour. The shape of the optical light curve of the system changes drastically from night to night, without any changes in overall brightness. Here we report X-ray observations of UW CrB obtained with XMM-Newton. We find evidence for several X-ray bursts, confirming a neutron star primary. This considerably strengthens the case that UW CrB is an accretion disc corona system located at a distance of at least 5-7 kpc (3-5 kpc above the Galactic plane). The X-ray and Optical Monitor (ultraviolet-optical) light curves show remarkable shape variation from one observing run to another, which we suggest are due to large-scale variations in the accretion disc shape resulting from a warp that periodically obscures the optical and soft X-ray emission. This is also supported by the changes in phase-resolved X-ray spectra.

  9. Timing of the accreting millisecond pulsar SAX J1748.9-2021 during its 2015 outburst

    NASA Astrophysics Data System (ADS)

    Sanna, A.; Burderi, L.; Riggio, A.; Pintore, F.; Di Salvo, T.; Gambino, A. F.; Iaria, R.; Matranga, M.; Scarano, F.

    2016-06-01

    We report on the timing analysis of the 2015 outburst of the intermittent accreting millisecond X-ray pulsar SAX J1748.9-2021 observed on March 4 by the X-ray satellite XMM-Newton. By phase connecting the time of arrivals of the observed pulses, we derived the best-fitting orbital solution for the 2015 outburst. We investigated the energy pulse profile dependence finding that the pulse fractional amplitude increases with energy while no significant time lags are detected. Moreover, we investigated the previous outbursts from this source, finding previously undetected pulsations in some intervals during the 2010 outburst of the source. Comparing the updated set of orbital parameters, in particular the value of the time of passage from the ascending node, with the orbital solutions reported from the previous outbursts, we estimated for the first time the orbital period derivative corresponding with dot{P}_{orb}=(1.1± 0.3)× 10^{-10} s s-1. We note that this value is significant at 3.5σ confidence level, because of significant fluctuations with respect to the parabolic trend and more observations are needed in order to confirm the finding. Assuming the reliability of the result, we suggest that the large value of the orbital-period derivative can be explained as a result of a highly non-conservative mass transfer driven by emission of gravitational waves, which implies the ejection of matter from a region close to the inner Lagrangian point. We also discuss possible alternative explanations.

  10. EXOSAT guest observer program. Binary parameters of the X-ray Pulsar 4U1626-67

    NASA Technical Reports Server (NTRS)

    Mcclintock, Jeffrey E.

    1987-01-01

    The pulsing X-ray source 4U1626-67 is an accreting neutron star in a binary system with a very low mass companion. The source was observed with EXOSAT continuously for 23 hr on 30 to 31 March 1986 UT. These observations allowed the setting of a stringent upper limit on the projected semimajor axis of the orbit of the neutron star of approx. 10 light msec for the 2485-s orbital period found by Middleditch et al., and a limit of approx. 13 light msec for any other plausible orbital period. The corresponding upper limit on the mass function for the 2485-s orbital period is 1.3 x 0.000001 solar mass. It was concluded that if the orbital inclination angle, i, equals 90 deg, then the optical companion star has a mass greater than 0.02 solar mass. However, it was found that a companion star mass greater than 0.06 solar mass is required if gravitational radiation is responsible for driving the mass transfer in this system. Only for i less than 16 deg can a companion star mass this large be accommodated by the limits set on the orbital amplitude. Also presented are results on the flaring activity in 4U1626-67 on time scales of approx. 1000 s, the energy dependent pulse profiles, and the pulse period history over the past decade.

  11. The 2006-2007 Active Phase of Anomalous X-Ray Pulsar 4U 0142+61: Radiative and Timing Changes, Bursts,and Burst Spectral Features

    NASA Technical Reports Server (NTRS)

    Gavriil, Fotis P.; Dib, Rim; Kaspi, Victoria M.

    2011-01-01

    After at least 6 years of quiescence, Anomalous X-ray Pulsar (AXP) 4U 0142+61 entered an active phase in 2006 March that lasted several months and included six X-ray bursts as well as many changes in the persistent X-ray emission. The bursts, the first seen from this AXP in > 11 years of Rossi X-ray Timing Explorer monitoring, all occurred in the interval between 2006 April 6 and 2007 February 7. The burst durations ranged from 0.4 - 1.8 x 10(exp 3) s. The first five burst spectra are well modeled by blackbodies, with temperatures kT approx 2 - 9 keV. However, the sixth burst had a complicated spectrum that is well characterized by a blackbody plus two emission features whose amplitude varied throughout the burst. The most prominent feature was at 14.0 keV. Upon entry into the active phase the pulsar showed a significant change in pulse morphology and a likely timing glitch. The glitch had a total frequency jump of (1.9+/-0.4) x 10(exp -7) Hz, which recovered with a decay time of 17+/-2 days by more than the initial jump, implying a net spin-down of the pulsar. Within the framework of the magnetar model, the net spin-down of the star could be explained by regions of the superfluid that rotate. slower than the rest. The bursts, flux enhancements, and pulse morphology changes can be explained as arising from crustal deformations due to stresses imposed by the highly twisted internal magnetic field. However, unlike other AXP outbursts, we cannot account for a major twist being implanted in the magnetosphere.

  12. Reprocessing of Soft X-ray Emission Lines in Black Hole Accretion Disks

    SciTech Connect

    Mauche, C W; Liedahl, D A; Mathiesen, B F; Jimenez-Garate, M A; Raymond, J C

    2003-10-17

    By means of a Monte Carlo code that accounts for Compton scattering and photoabsorption followed by recombination, we have investigated the radiation transfer of Ly{alpha}, He{alpha}, and recombination continua photons of H- and He-like C, N, O, and Ne produced in the photoionized atmosphere of a relativistic black hole accretion disk. We find that photoelectric opacity causes significant attenuation of photons with energies above the O VIII K-edge; that the conversion efficiencies of these photons into lower-energy lines and recombination continua are high; and that accounting for this reprocessing significantly (by factors of 21% to 105%) increases the flux of the Ly{alpha} and He{alpha} emission lines of H- and He-like C and O escaping the disk atmosphere.

  13. X-ray Reflected Spectra from Accretion Disk Models. III. A Complete Grid of Ionized Reflection Calculations

    NASA Technical Reports Server (NTRS)

    Garcia, J.; Dauser, T.; Reynolds, C. S.; Kallman, T. R.; McClintock, J. E.; Wilms, J.; Ekmann, W.

    2013-01-01

    We present a new and complete library of synthetic spectra for modeling the component of emission that is reflected from an illuminated accretion disk. The spectra were computed using an updated version of our code xillver that incorporates new routines and a richer atomic data base. We offer in the form of a table model an extensive grid of reflection models that cover a wide range of parameters. Each individual model is characterized by the photon index Gamma of the illuminating radiation, the ionization parameter zeta at the surface of the disk (i.e., the ratio of the X-ray flux to the gas density), and the iron abundance A(sub Fe) relative to the solar value. The ranges of the parameters covered are: 1.2 <= Gamma <= 3.4, 1 <= zeta <= 104, and 0.5 <= A(sub Fe) <= 10. These ranges capture the physical conditions typically inferred from observations of active galactic nuclei, and also stellar-mass black holes in the hard state. This library is intended for use when the thermal disk flux is faint compared to the incident power-law flux. The models are expected to provide an accurate description of the Fe K emission line, which is the crucial spectral feature used to measure black hole spin. A total of 720 reflection spectra are provided in a single FITS file suitable for the analysis of X-ray observations via the atable model in xspec. Detailed comparisons with previous reflection models illustrate the improvements incorporated in this version of xillver.

  14. X-RAY REFLECTED SPECTRA FROM ACCRETION DISK MODELS. III. A COMPLETE GRID OF IONIZED REFLECTION CALCULATIONS

    SciTech Connect

    Garcia, J.; McClintock, J. E.; Dauser, T.; Wilms, J.; Eikmann, W.; Reynolds, C. S.; Kallman, T. R. E-mail: jem@cfa.harvard.edu E-mail: thomas.dauser@sternwarte.uni-erlangen.de E-mail: wiebke.eikmann@sternwarte.uni-erlangen.de

    2013-05-10

    We present a new and complete library of synthetic spectra for modeling the component of emission that is reflected from an illuminated accretion disk. The spectra were computed using an updated version of our code XILLVER that incorporates new routines and a richer atomic database. We offer in the form of a table model an extensive grid of reflection models that cover a wide range of parameters. Each individual model is characterized by the photon index {Gamma} of the illuminating radiation, the ionization parameter {xi} at the surface of the disk (i.e., the ratio of the X-ray flux to the gas density), and the iron abundance A{sub Fe} relative to the solar value. The ranges of the parameters covered are 1.2 {<=} {Gamma} {<=} 3.4, 1 {<=} {xi} {<=} 10{sup 4}, and 0.5 {<=} A{sub Fe} {<=} 10. These ranges capture the physical conditions typically inferred from observations of active galactic nuclei, and also stellar-mass black holes in the hard state. This library is intended for use when the thermal disk flux is faint compared to the incident power-law flux. The models are expected to provide an accurate description of the Fe K emission line, which is the crucial spectral feature used to measure black hole spin. A total of 720 reflection spectra are provided in a single FITS file (http://hea-www.cfa.harvard.edu/{approx}javier/xillver/) suitable for the analysis of X-ray observations via the atable model in XSPEC. Detailed comparisons with previous reflection models illustrate the improvements incorporated in this version of XILLVER.

  15. Swift-XRT confirms the renewed X-ray activity of the Bursting Pulsar "GRO J1744-28"

    NASA Astrophysics Data System (ADS)

    Sanna, A.; D'Ai, A.; Bozzo, E.; Riggio, A.; Pintore, F.; Burderi, L.; Di Salvo, T.; Iaria, R.

    2017-02-01

    Triggered by the X-ray enhancement reported by INTEGRAL on 2017, Feb. 13 at a position compatible with the X-ray binary GRO J1744-28 (Atel #10073), a 1 ks observation with Swift-XRT was promptly carried out. Swift-XRT, operated in Window Timing mode, detected a bright X-ray source with mean count rate of approximately 3 cts/s.

  16. X-RAY OBSERVATIONS OF THE SUPERNOVA REMNANT CTB 87 (G74.9+1.2): AN EVOLVED PULSAR WIND NEBULA

    SciTech Connect

    Matheson, H.; Safi-Harb, S.; Kothes, R. E-mail: samar@physics.umanitoba.ca

    2013-09-01

    Pulsar wind nebulae (PWNe) studies with the Chandra X-Ray Observatory have opened a new window to address the physics of pulsar winds, zoom on their interaction with their hosting supernova remnant (SNR) and interstellar medium, and identify their powering engines. We here present a new 70 ks, plus an archived 18 ks, Chandra ACIS observation of the SNR CTB 87 (G74.9+1.2), classified as a PWN with unusual radio properties and poorly studied in X-rays. We find that the peak of the X-ray emission is clearly offset from the peak of the radio emission by {approx}100'' and located at the southeastern edge of the radio nebula. We detect a point source-the putative pulsar-at the peak of the X-ray emission and study its spectrum separately from the PWN. This new point source, CXOU J201609.2+371110, is surrounded by a compact nebula displaying a torus-like structure and possibly a jet. A more extended diffuse nebula is offset from the radio nebula, extending from the point source to the northwest for {approx}250''. The spectra of the point source, compact nebula, and extended diffuse nebula are all well described by a power-law model with a photon index of 1.1 (0.7-1.6), 1.2 (0.9-1.4), and 1.7 (1.5-1.8), respectively, for a column density N{sub H} = 1.38 (1.21-1.57) Multiplication-Sign 10{sup 22} cm{sup -2} (90% confidence). The total X-ray luminosity of the source is {approx}1.6 Multiplication-Sign 10{sup 34} erg s{sup -1} at an assumed distance of 6.1 kpc, with {approx}2% and 6% contribution from the point source and compact nebula, respectively. The observed properties suggest that CTB 87 is an evolved ({approx}5-28 kyr) PWN, with the extended radio emission likely a ''relic'' PWN, as in Vela-X and G327.1-1.1. To date, however, there is no evidence for thermal X-ray emission from this SNR, and the SNR shell is still missing, suggesting expansion into a low-density medium (n{sub 0} < 0.2 D{sup -1/2}{sub 6.1} cm{sup -3}), likely caused by a stellar wind bubble blown by the

  17. An X-ray Pulsar with a Superstrong Magnetic Field in the Soft Gamma-Ray Repeater SGR1806-20

    NASA Technical Reports Server (NTRS)

    Kouveliotou, C.; Dieters, S.; Strohmayer, T.; vanParadijs, J.; Fishman, G. J.; Meegan, C. A.; Hurley, K.; Kommers, J.; Smith, I.; Frail, D.; Murakami, T.

    1998-01-01

    Soft gamma-ray repeaters (SGRs) emit multiple, brief (approximately O.1 s) intense outbursts of low-energy gamma-rays. They are extremely rare; three are known in our galaxy and one in the Large Magellanic Cloud. Two SGRs are associated with young supernova remnants (SNRs), and therefore most probably with neutron stars, but it remains a puzzle why SGRs are so different from 'normal' radio pulsars. Here we report the discovery of pulsations in the persistent X-ray flux of SGR1806-20, with a period of 7.47 s and a spindown rate of 2.6 x 10(exp -3) s/yr. We argue that the spindown is due to magnetic dipole emission and find that the pulsar age and (dipolar) magnetic field strength are approximately 1500 years and 8 x 10(exp 14) gauss, respectively. Our observations demonstrate the existence of 'magnetars', neutron stars with magnetic fields about 100 times stronger than those of radio pulsars, and support earlier suggestions that SGR bursts are caused by neutron-star 'crust-quakes' produced by magnetic stresses. The 'magnetar' birth rate is about one per millenium, a substantial fraction of that of radio pulsars. Thus our results may explain why some SNRs have no radio pulsars.

  18. GRAVITATIONAL-WAVE SPIN-DOWN AND STALLING LOWER LIMITS ON THE ELECTRICAL RESISTIVITY OF THE ACCRETED MOUNTAIN IN A MILLISECOND PULSAR

    SciTech Connect

    Vigelius, M.; Melatos, A.

    2010-07-01

    The electrical resistivity of the accreted mountain in a millisecond pulsar is limited by the observed spin-down rate of binary radio millisecond pulsars (BRMSPs) and the spins and X-ray fluxes of accreting millisecond pulsars (AMSPs). We find {eta}{>=}10{sup -28} s ({tau}{sub SD}/1 Gyr){sup -0.8} (where {tau}{sub SD} is the spin-down age) for BRMSPs and {eta}{>=}10{sup -25} s ( M-dot{sub a}/ M-dot{sub E}){sup 0.6} (where M-dot{sub a} and M-dot{sub E} are the actual and Eddington accretion rates) for AMSPs. These limits are inferred assuming that the mountain attains a steady state, where matter diffuses resistively across magnetic flux surfaces but is replenished at an equal rate by infalling material. The mountain then relaxes further resistively after accretion ceases. The BRMSP spin-down limit approaches the theoretical electron-impurity resistivity at temperatures {approx_gt}10{sup 5} K for an impurity concentration of {approx}0.1, while the AMSP stalling limit falls 2 orders of magnitude below the theoretical electron-phonon resistivity for temperatures above 10{sup 8} K. Hence, BRMSP observations are already challenging theoretical resistivity calculations in a useful way. Next-generation gravitational-wave interferometers will constrain {eta} at a level that will be competitive with electromagnetic observations.

  19. A numerical investigation of wind accretion in persistent Supergiant X-ray Binaries I - Structure of the flow at the orbital scale

    NASA Astrophysics Data System (ADS)

    El Mellah, I.; Casse, F.

    2017-01-01

    Classical Supergiant X-ray Binaries host a neutron star orbiting a supergiant OB star and display persistent X-ray luminosities of 1035 to 1037 erg· s-1. The stellar wind from the massive companion is believed to be the main source of matter accreted by the compact object. With this first paper, we introduce a ballistic model to evaluate the influence of the orbital effects on the structure of the accelerating winds which participate to the accretion process. Thanks to the parametrization we retained and the numerical pipeline we designed, we can investigate the supersonic flow and the subsequent observables as a function of a reduced set of characteristic numbers and scales. We show that the shape of the permanent flow is entirely determined by the mass ratio, the filling factor, the Eddington factor and the α-force multiplier which drives the stellar wind acceleration. Provided scales such as the orbital period are known, we can trace back the observables to evaluate the mass accretion rates, the accretion mechanism, the shearing of the inflow and the stellar parameters. We discuss the likelihood of wind-formed accretion discs around the accretors in each case and confront our model to three persistent Supergiant X-ray Binaries (Vela X-1, IGR J18027-2016, XTE J1855-026).

  20. Variations of cyclotron line energy with luminosity in accreting X-ray pulsars

    SciTech Connect

    Nishimura, Osamu

    2014-01-20

    I develop a new model for changes of cyclotron line energy with luminosity based on changes in polar cap dimensions and the direction of photon propagation as well as a shock height. In X0115+63 and V0332+53, the fundamental cyclotron line energy has been observed to decrease with increasing luminosity. This phenomenon has been interpreted as a change of a shock height with luminosity. However, the rates of the observed changes are quite different, in which the line energy in V0332+53 varies slowly with luminosity compared with that in X0115+63. I demonstrate that a new model successfully reproduces the changes of the fundamental cyclotron line energies with luminosity in both X0115+63 and V0332+53. On the other hand, the cyclotron line energies in Her X–1, GX301–2, and GX304–1 were reported to increase with increasing luminosity. I discuss the positive correlation between the cyclotron line energy and luminosity based on changes in a beam pattern for Her X–1, GX301–2, and GX304–1. In addition, I discuss how a switch of the predominant, observed emission region from pole1 to pole2 influences cyclotron line energy for GX304–1 and A0535+26.

  1. The 2015 outburst of the accretion-powered pulsar IGR J00291+5934: INTEGRAL and Swift observations

    NASA Astrophysics Data System (ADS)

    De Falco, V.; Kuiper, L.; Bozzo, E.; Galloway, D. K.; Poutanen, J.; Ferrigno, C.; Stella, L.; Falanga, M.

    2017-03-01

    The pulsar IGR J00291+5934 is the fastest-known accretion-powered X-ray pulsar, discovered during a transient outburst in 2004. In this paper, we report on INTEGRAL and Swift observations during the 2015 outburst, which lasts for 25 d. The source has not been observed in outburst since 2008, suggesting that the long-term accretion rate has decreased by a factor of two since discovery. The averaged broad-band (0.1-250 keV) persistent spectrum in 2015 is well described by a thermal Comptonization model with a column density of NH ≈ 4 × 1021 cm-2, a plasma temperature of kTe ≈ 50 keV, and a Thomson optical depth of τT ≈ 1. Pulsations at the known spin period of the source are detected in the INTEGRAL data up to the 150 keV energy band. We also report on the discovery of the first thermonuclear burst observed from IGR J00291+5934, which lasts around 7 min and occurs at a persistent emission level corresponding to roughly 1.6% of the Eddington accretion rate. The properties of the burst suggest it is powered primarily by helium ignited at a depth of yign ≈ 1.5 × 109 g cm-2 following the exhaustion by steady burning of the accreted hydrogen. The Swift/BAT data from the first 20 s of the burst provide indications of a photospheric radius expansion phase. Assuming this is the case, we infer a source distance of d = 4.2 ± 0.5 kpc.

  2. NuSTAR observations of the X-ray pulsar LMC X-4: A constraint on the magnetic field and tomography of the system in the fluorescent iron line

    NASA Astrophysics Data System (ADS)

    Shtykovsky, A. E.; Lutovinov, A. A.; Arefiev, V. A.; Molkov, S. V.; Tsygankov, S. S.; Revnivtsev, M. G.

    2017-03-01

    We present the results of the spectral and timing analysis of the X-ray pulsar LMC X-4 based on data from the NuSTAR observatory in the broad X-ray energy range 3-79 keV. Along with a detailed analysis of the source's averaged spectrum, high-precision spectra corresponding to different phases of the neutron star spin cycle have been obtained for the first time. The Comptonization model is shown to describe best the source's spectrum, and the evolution of its parameters as a function of the pulse phase has been traced. For all spectra (the averaged and phase-resolved ones) in the energy range 5-55 keV we have searched for the cyclotron absorption line. The derived upper limit on the optical depth of the cyclotron line τ 0.15 (3 σ) points to the absence of this feature in the given energy range, which provides a constraint on the magnetic field of the neutron star: B <3 × 1011 or >6.5 × 1012 G. The latter constraint is consistent with the magnetic field estimate obtained by analyzing the pulsar's power spectrum, B ≅ 3 × 1013 G. Based on our analysis of the phase-resolved spectra, we have determined the delay between the emission peaks and the equivalent width of the fluorescent iron line. This delay depends on the orbital phase and is apparently associated with the travel time of photons between the emitting regions in the vicinity of the neutron star and the region where the flux is reflected (presumably in the inflowing stream or at the place of interaction between the stream and the outer edge of the accretion disk).

  3. The effects of high density on the X-ray spectrum reflected from accretion discs around black holes

    NASA Astrophysics Data System (ADS)

    García, Javier A.; Fabian, Andrew C.; Kallman, Timothy R.; Dauser, Thomas; Parker, Michael L.; McClintock, Jeffrey E.; Steiner, James F.; Wilms, Jörn

    2016-10-01

    Current models of the spectrum of X-rays reflected from accretion discs around black holes and other compact objects are commonly calculated assuming that the density of the disc atmosphere is constant within several Thomson depths from the irradiated surface. An important simplifying assumption of these models is that the ionization structure of the gas is completely specified by a single, fixed value of the ionization parameter ξ, which is the ratio of the incident flux to the gas density. The density is typically fixed at ne = 1015 cm-3. Motivated by observations, we consider higher densities in the calculation of the reflected spectrum. We show by computing model spectra for ne ≳ 1017 cm-3 that high-density effects significantly modify reflection spectra. The main effect is to boost the thermal continuum at energies ≲ 2 keV. We discuss the implications of these results for interpreting observations of both active galactic nuclei and black hole binaries. We also discuss the limitations of our models imposed by the quality of the atomic data currently available.

  4. THE STRUCTURE OF THE ACCRETION DISK IN THE ACCRETION DISK CORONA X-RAY BINARY 4U 1822-371 AT OPTICAL AND ULTRAVIOLET WAVELENGTHS

    SciTech Connect

    Bayless, Amanda J.; Robinson, Edward L.; Cornell, Mark E.; Hynes, Robert I.; Ashcraft, Teresa A.

    2010-01-20

    The eclipsing low-mass X-ray binary 4U 1822-371 is the prototypical accretion disk corona (ADC) system. We have obtained new time-resolved UV spectroscopy of 4U 1822-371 with the Advanced Camera for Surveys/Solar Blind Channel on the Hubble Space Telescope and new V- and J-band photometry with the 1.3 m SMARTS telescope at Cerro Tololo Inter-American Observatory. We use the new data to construct its UV/optical spectral energy distribution and its orbital light curve in the UV, V, and J bands. We derive an improved ephemeris for the optical eclipses and confirm that the orbital period is changing rapidly, indicating extremely high rates of mass flow in the system, and we show that the accretion disk in the system has a strong wind with projected velocities up to 4000 km s{sup -1}. We show that the disk has a vertically extended, optically thick component at optical wavelengths. This component extends almost to the edge of the disk and has a height equal to approx0.5 of the disk radius. As it has a low brightness temperature, we identify it as the optically thick base of a disk wind, not as the optical counterpart of the ADC. Like previous models of 4U 1822-371, ours needs a tall obscuring wall near the edge of the accretion disk, but we interpret the wall as a layer of cooler material at the base of the disk wind, not as a tall, luminous disk rim.

  5. The SAS-3 X-ray observatory

    NASA Technical Reports Server (NTRS)

    Mayer, W. F.

    1975-01-01

    The experiment section of the Small Astronomy Satellite-3 (SAS-3) launched in May 1975 is an X-ray observatory intended to determine the location of bright X-ray sources to an accuracy of 15 arc-seconds; to study a selected set of sources over a wide energy range, from 0.1 to 55 keV, while performing very specific measurements of the spectra and time variability of known X-ray sources; and to monitor the sky continuously for X-ray novae, flares, and unexpected phenomena. The improvements in SAS-3 spacecraft include a clock accurate to 1 part in 10 billion, rotatable solar panels, a programmable data format, and improved nutation damper, a delayed command system, improved magnetic trim and azimuth control systems. These improvements enable SAS-3 to perform three-axis stabilized observations of any point on the celestial sphere at any time of the year. The description of the experiment section and the SAS-3 operation is followed by a synopsis of scientific results obtained from the observations of X-ray sources, such as Vela X-1 (supposed to be an accreting neutron star), a transient source of hard X-ray (less than 36 min in duration) detected by SAS-3, the Crab Nebula pulsar, the Perseus cluster of galaxies, and the Vela supernova remnant.

  6. X-Ray Observations of the Supernova Remnant CTB 87 (G74.9+1.2): An Evolved Pulsar Wind Nebula

    NASA Astrophysics Data System (ADS)

    Matheson, H.; Safi-Harb, S.; Kothes, R.

    2013-09-01

    Pulsar wind nebulae (PWNe) studies with the Chandra X-Ray Observatory have opened a new window to address the physics of pulsar winds, zoom on their interaction with their hosting supernova remnant (SNR) and interstellar medium, and identify their powering engines. We here present a new 70 ks, plus an archived 18 ks, Chandra ACIS observation of the SNR CTB 87 (G74.9+1.2), classified as a PWN with unusual radio properties and poorly studied in X-rays. We find that the peak of the X-ray emission is clearly offset from the peak of the radio emission by ~100'' and located at the southeastern edge of the radio nebula. We detect a point source—the putative pulsar—at the peak of the X-ray emission and study its spectrum separately from the PWN. This new point source, CXOU J201609.2+371110, is surrounded by a compact nebula displaying a torus-like structure and possibly a jet. A more extended diffuse nebula is offset from the radio nebula, extending from the point source to the northwest for ~250''. The spectra of the point source, compact nebula, and extended diffuse nebula are all well described by a power-law model with a photon index of 1.1 (0.7-1.6), 1.2 (0.9-1.4), and 1.7 (1.5-1.8), respectively, for a column density N H = 1.38 (1.21-1.57) × 1022 cm-2 (90% confidence). The total X-ray luminosity of the source is ~1.6 × 1034 erg s-1 at an assumed distance of 6.1 kpc, with ~2% and 6% contribution from the point source and compact nebula, respectively. The observed properties suggest that CTB 87 is an evolved (~5-28 kyr) PWN, with the extended radio emission likely a "relic" PWN, as in Vela-X and G327.1-1.1. To date, however, there is no evidence for thermal X-ray emission from this SNR, and the SNR shell is still missing, suggesting expansion into a low-density medium (n_0 < 0.2 D^{-1/2}_{6.1} cm-3), likely caused by a stellar wind bubble blown by the progenitor star.

  7. Photometry of slow X-ray pulsars. II - The 13.9 minute period of X Persei

    NASA Technical Reports Server (NTRS)

    Margon, B.; Thorstensen, J. R.; Bowyer, S.; Mason, K. O.; White, N. E.; Sanford, P. W.; Parkes, G.; Stone, R. P. S.; Bailey, J.

    1977-01-01

    Results are presented for time-resolved narrow-band photometry and spectrophotometry of X Per performed in an unsuccessful effort to confirm previously reported observations of 13.9-min pulsations in the intensity of the He II line at 4686 A. No features that are synchronous with a 13.9-min period are found in the optical data, and simultaneous X-ray observations of 3U 0352+30 are reported which show that a strong 13.9-min X-ray modulation was present during the optical photometry. Some implications of the X-ray periodicities observed for X Per are considered.

  8. DEEP X-RAY OBSERVATIONS OF