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 Neutron star QPOs from oscillating, precessing hot, thick flow

2019 ◽  
Vol 491 (3) ◽  
pp. 3245-3250
Author(s):  
P Chris Fragile
Keyword(s):  
Neutron Star ◽  
Low Frequency ◽  
Outer Radius ◽  
Horizontal Branch ◽  
X Ray ◽  
Best Fitting ◽  
Low Mass ◽  
The Moment ◽  
X Ray Binaries ◽  
Simultaneous Oscillation

ABSTRACT Across black hole (BH) and neutron star (NS) low-mass X-ray binaries (LMXBs), there appears to be some correlation between certain high- and low-frequency quasi-periodic oscillations (QPOs). In a previous paper, we showed that for BH LMXBs, this could be explained by the simultaneous oscillation and precession of a hot, thick, torus-like corona. In the current work, we extend this idea to NS LMXBs by associating the horizontal branch oscillations (HBOs) with precession and the upper-kiloHertz (ukHz) QPO with vertical epicyclic motion. For the Atoll source 4U 1608-52, the model can match many distinct, simultaneous observations of the HBO and ukHz QPO by varying the inner and outer radius of the torus, while maintaining fixed values for the mass (MNS) and spin (a*) of the NS. The best-fitting values are MNS = 1.38 ± 0.03 M⊙ and a* = 0.325 ± 0.005. By combining these constraints with the measured spin frequency, we are able to obtain an estimate for the moment of inertia of INS = 1.40 ± 0.02 × 1045 g cm2, which places constraints on the equation of state. The model is unable to fit the lower-kHz QPO, but evidence suggests that QPO may be associated with the boundary layer between the accretion flow and the NS surface, which is not treated in this work.

scholarly journals The X-Ray Timing Explorer

1990 ◽  
Vol 123 ◽  
pp. 89-110
Author(s):  
H. V. Bradt ◽  
A. M. Levine ◽  
E. H. Morgan ◽  
R. A. Remillard ◽  
J. H. Swank ◽  
...  
Keyword(s):  
Neutron Star ◽  
Neutron Stars ◽  
Active Galactic Nuclei ◽  
High Throughput ◽  
Proportional Counter ◽  
Galactic Nuclei ◽  
X Ray ◽  
Sky Monitor ◽  
Proportional Counter Array ◽  
Millisecond Timing

AbstractThe capabilities of the X-ray Timing Explorer (XTE) are described with particular attention paid to current scientific problems it will address from galactic neutron star systems to active galactic nuclei. It features a low-background continuous 2-200 keV response with large apertures (a 0.63-m2 proportional counter array and a 0.16-m2 dual rocking NaI/CsI scintillation array). Rapid response (in hours) to temporal phenomena, e.g. transients, is obtained by virtue of a scanning all-sky monitor and rapid maneuverability. XTE will carry out detailed energy-resolved studies of phenomena close to neutron stars (e.g. QPO’s) because of its sub-millisecond timing (to 10 μs), its high telemetry rates (to 256 kb/s), and the high throughput of its data system (to ≳ 2 × 105 c s−1).

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 Prospects for Coordinated Observations with XTE

1995 ◽  
Vol 12 (2) ◽  
pp. 219-226 ◽  
Author(s):  
A. B. Giles ◽  
K. Jahoda ◽  
J. H. Swank ◽  
W. Zhang
Keyword(s):  
High Energy ◽  
High Time Resolution ◽  
Massachusetts Institute Of Technology ◽  
Large Area ◽  
X Ray ◽  
Transient Sources ◽  
Sky Monitor ◽  
Institute Of Technology ◽  
Proportional Counter Array ◽  
The University

AbstractThe X-ray Timing Explorer (XTE) is a NASA satellite designed to perform high-time-resolution studies of known X-ray sources. The two main experiments are a large-area proportional counter array (PCA) from the Goddard Space Flight Center (GSFC) and a high-energy X-ray timing experiment (HEXTE) from the University of California at San Diego (UCSD). The PCA data is processed by an electronic data system (EDS) built by the Massachusetts Institute of Technology (MIT) that performs many parallel processing analysis functions for on-board evaluation and data compression. MIT also provide an all-sky monitor (ASM) experiment so that XTE can be slewed rapidly to new transient sources. The spacecraft provides a mean science telemetry rate for the PCA of ~20 kilobits per second (kbps), with bursts to 256 kbps for durations of 30 minutes. Photons are tagged to 1 μs and absolute timing should be better than 100 μs. XTE is due for launch in late August 1995 and the first NASA Research Announcement (NRA) is due out in January 1995. This paper summarises XTE’s performance and then discusses the interactive and flexible operations of the satellite and some of the science it can do. These features should make XTE a productive spacecraft for coordinated observation programs.

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.

Sign in / Sign up

Export Citation Format

Share Document