High-energy X-ray production in a boundary layer of an accreting neutron star

1991 ◽  
Vol 373 ◽  
pp. 222 ◽  
Author(s):  
Tomoyuki Hanawa
Keyword(s):  
Boundary Layer ◽  
Neutron Star ◽  
High Energy ◽  
X Ray

A study of the hard X-ray spectral tails in Scorpius X-1 using RXTE observations

2020 ◽  
Vol 500 (1) ◽  
pp. 772-785
Author(s):  
G Q Ding ◽  
T T Chen ◽  
J L Qu
Keyword(s):  
Boundary Layer ◽  
Neutron Star ◽  
High Energy ◽  
Alternative Mechanism ◽  
Horizontal Branch ◽  
X Ray ◽  
Bulk Motion ◽  
Normal Branch ◽  
Specific Position ◽  
Proportional Counter Array

ABSTRACT Using all the data of the High Energy X-ray Timing Experiment (HEXTE) on board the Rossi X-ray Timing Explorer for Scorpius X-1 from 1996 February to 2012 January, we systematically search for hard X-ray tails in the X-ray spectra in 20–220 keV and, together with the data of the Proportional Counter Array (PCA), investigate the evolution of the detected hard X-ray tails along the Z-track on its hardness-intensity diagram (HID). The hard X-ray tails are detected in 30 observations and their presence is not confined to a specific position on the HID. Our analysis suggests that from the horizontal branch (HB), through the normal branch (NB), to the flaring branch (FB) on the HID, the hard X-ray tail becomes hard and its flux decreases. Jointly fitting the PCA+HEXTE spectra in 3–220 keV, it is found that the Bulk-Motion Comptonization (BMC) could be an alternative mechanism for producing the hard X-ray tails on the HB and the NB of this source. The temperature of the seed photons for the BMC spans in the range of ∼(2.4–2.6) keV, indicating that the seed photons might come from the surface of the neutron star (NS) or the boundary layer and, therefore, the BMC process could take place around the NS or in the boundary layer. Some possible mechanisms for producing the hard X-ray tails on the FB are given.

scholarly journals The Nature of the Compact Object in the Hard X-Ray Source 4U2206+54

2004 ◽  
Vol 194 ◽  
pp. 208-208
Author(s):  
J. M. Torrejón ◽  
I. Kreykenbohni ◽  
A. Orr ◽  
L. Titarchuk ◽  
I. Negueruela
Keyword(s):  
Neutron Star ◽  
Accretion Disk ◽  
Compact Object ◽  
High Energy ◽  
Energy Data ◽  
X Ray ◽  
Hot Plasma ◽  
Cyclotron Line ◽  
First Time

We present an analysis of archival RXTE and BeppoSAX data of the X-ray source 4U2206+54. For the first time, high energy data (≥ 30 keV) is analyzed. The data is well described by comptonization models in which seed photons with temperatures between 1.1 keV arid 1.5 keV are comptonized by a hot plasma at 50 keV thereby producing a hard tail which extends up to 100 keV. From luminosity arguments it is shown that the area of the soft photons source must be small (r ≈ 1 km) and that the presence of an accretion disk in this system is unlikely. Here we report on the possible existence of a cyclotron line around 30 keV . The presence of a neutron star in the system is strongly favored by the available data.

scholarly journals Accretion heated atmospheres of X-ray bursting neutron stars

2018 ◽  
Vol 619 ◽  
pp. A114 ◽  
Author(s):  
V. F. Suleimanov ◽  
J. Poutanen ◽  
K. Werner
Keyword(s):  
Neutron Star ◽  
Model Atmosphere ◽  
High Energy ◽  
Energy Dissipation Rate ◽  
Chemical Compositions ◽  
Type I ◽  
Coulomb Interactions ◽  
Spectral Evolution ◽  
X Ray ◽  
High Energy Tail

Some thermonuclear (type I) X-ray bursts at the neutron star surfaces in low-mass X-ray binaries take place during hard persistent states of the systems. Spectral evolution of these bursts is well described by the atmosphere model of a passively cooling neutron star when the burst luminosity is high enough. The observed spectral evolution deviates from the model predictions when the burst luminosity drops below a critical value of 20–70% of the maximum luminosity. The amplitude of the deviations and the critical luminosity correlate with the persistent luminosity, which leads us to suggest that these deviations are induced by the additional heating of the accreted particles. We present a method for computation of the neutron star atmosphere models heated by accreted particles assuming that their energy is released via Coulomb interactions with electrons. We computed the temperature structures and the emergent spectra of the atmospheres of various chemical compositions and investigate the dependence of the results on the velocity of accreted particles, their temperature and the penetration angle. We show that the heated atmosphere develops two different regions. The upper one is the hot (20–100 keV) corona-like surface layer cooled by Compton scattering, and the deeper, almost isothermal optically thick region with a temperature of a few keV. The emergent spectra correspondingly have two components: a blackbody with the temperature close to that of the isothermal region and a hard Comptonized component (a power law with an exponential decay). Their relative contribution depends on the ratio of the energy dissipation rate of the accreted particles to the intrinsic flux from the neutron star surface. These spectra deviate strongly from those of undisturbed, passively cooling neutron star atmospheres, with the main differences being the presence of a high-energy tail and a strong excess in the low-energy part of the spectrum. They also lack the iron absorption edge, which is visible in the spectra of undisturbed low-luminosity atmospheres with solar chemical composition. Using the computed spectra, we obtained the dependences of the dilution and color-correction factors as functions of relative luminosities for pure helium and solar abundance atmospheres. We show that the helium model atmosphere heated by accretion corresponding to 5% of the Eddington luminosity describes well the late stages of the X-ray bursts in 4U 1820−30.

scholarly journals IGR J17503–2636: a candidate supergiant fast X-ray transient

2019 ◽  
Vol 624 ◽  
pp. A142 ◽  
Author(s):  
C. Ferrigno ◽  
E. Bozzo ◽  
A. Sanna ◽  
G. K. Jaisawal ◽  
J. M. Girard ◽  
...  
Keyword(s):  
Spectral Analysis ◽  
Neutron Star ◽  
Energy Distribution ◽  
Power Law ◽  
Spectral Energy Distribution ◽  
High Energy ◽  
Spectral Energy ◽  
X Ray ◽  
Broad Feature

The object IGR J17503–2636 is a hard X-ray transient discovered by INTEGRAL on 2018 August 11. This was the first ever reported X-ray emission from this source. Following the discovery, follow-up observations were carried out with Swift, Chandra, NICER, and NuSTAR. Here we report on the analysis of all of these X-ray data and the results obtained. Based on the fast variability in the X-ray domain, the spectral energy distribution in the 0.5–80 keV energy range, and the reported association with a highly reddened OB supergiant at ∼10 kpc, we conclude that IGR J17503–2636 is most likely a relatively faint new member of the supergiant fast X-ray transients. Spectral analysis of the NuSTAR data revealed a broad feature in addition to the typical power-law with exponential roll-over at high energy. This can be modeled either in emission or as a cyclotron scattering feature in absorption. If confirmed by future observations, this feature would indicate that IGR J17503–2636 hosts a strongly magnetized neutron star with B ∼ 2 × 1012 G.

scholarly journals Discovery of X-ray pulsations in the Be/X-ray binary IGR J06074+2205

2018 ◽  
Vol 613 ◽  
pp. A52 ◽  
Author(s):  
P. Reig ◽  
A. Zezas
Keyword(s):  
Neutron Star ◽  
Model Fitting ◽  
High Energy ◽  
X Rays ◽  
Energy Bands ◽  
X Ray ◽  
Be Star ◽  
Best Fitting ◽  
Open Question ◽  
Star Surface

Context. IGR J06074+2205 is a poorly studied X-ray source with a Be star companion. It has been proposed to belong to the group of Be/X-ray binaries (BeXBs). In BeXBs, accretion onto the neutron star occurs via the transfer of material from the Be star’s circumstellar disk. Thus, in the absence of the disk, no X-ray should be detected. Aims. The main goal of this work is to study the quiescent X-ray emission of IGR J06074+2205 during a disk-loss episode. Methods. We obtained light curves at different energy bands and a spectrum covering the energy range 0.4–12 keV. We used Fourier analysis to study the aperiodic variability and epoch folding methods to study the periodic variability. Model fitting to the energy spectrum allowed us to identify the possible physical processes that generated the X-rays. Results. We show that at the time of the XMM-Newton observation, the decretion disk around the Be star had vanished. Still, accretion appears as the source of energy that powers the high-energy radiation in IGR J06074+2205. We report the discovery of X-ray pulsations with a pulse period of 373.2 s and a pulse fraction of ~50%. The 0.4–12 keV spectrum is well described by an absorbed power law and blackbody components with the best fitting parameters: NH = (6.2 ± 0.5) × 1021 cm−2, kTbb = 1.16 ± 0.03 keV, and Γ = 1.5 ± 0.1. The absorbed X-ray luminosity is LX = 1.4 × 1034 erg s−1 assuming a distance of 4.5 kpc. Conclusions. The detection of X-ray pulsations confirms the nature of IGR J06074+2205 as a BeXB. We discuss various scenarios to explain the quiescent X-ray emission of this pulsar. We rule out cooling of the neutron star surface and magnetospheric emission and conclude that accretion is the most likely scenario. The origin of the accreted material remains an open question.

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