scholarly journals Study of the reflection spectrum of the bright atoll source GX 3 + 1 with NuSTAR

2019 ◽  
Vol 487 (4) ◽  
pp. 5441-5449
Author(s):  
Aditya S Mondal ◽  
G C Dewangan ◽  
B Raychaudhuri
Keyword(s):  
Boundary Layer ◽  
Accretion Rate ◽  
Broad Band ◽  
X Ray ◽  
Upper Limit ◽  
Reflection Model ◽  
Single Temperature ◽  
Low Mass ◽  
October 17 ◽  
Spectral State

ABSTRACT We report on the NuSTAR observation of the atoll type neutron star (NS) low-mass X-ray binary GX 3 + 1 performed on 2017 October 17. The source was found in a soft X-ray spectral state with 3–70 keV luminosity of LX ∼ 3 × 1037 erg s−1 (${\sim } 16{{\ \rm per\ cent}}$ of the Eddington luminosity), assuming a distance of 6 kpc. A positive correlation between intensity and hardness ratio suggests that the source was in the banana branch during this observation. The broad-band 3–70 keV NuSTAR spectral data can be described by a two-component continuum model consisting of a disc blackbody (kTdisc ∼ 1.8 keV) and a single temperature blackbody model (kTbb ∼ 2.7 keV). The spectrum shows a clear and robust indication of relativistic reflection from the inner disc which is modelled with a self-consistent relativistic reflection model. The accretion disc is viewed at an inclination of i ≃ 22°–26° and extended close to the NS, down to $R_\text{in}=(1.2\!-\!1.8) R_\text{ISCO}\:(\simeq 6.1\!-\!9.1\, R_{\mathrm{ g}}\: \text{or}\: 14\!-\!20.5$ km) which allows an upper limit on the NS radius (≤13.5 km). Based on the measured flux and the mass accretion rate, the maximum radial extension for the boundary layer is estimated to be ∼6.3 Rg from the NS surface. However, if the disc is not truncated by the boundary layer but by the magnetosphere, an estimated upper limit on the polar magnetic field would be of B ≤ 6 × 108 G.

scholarly journals On the disc reflection spectroscopy of NS LMXB Serpens X-1: analysis of a recent NuSTAR observation

2020 ◽  
Vol 494 (3) ◽  
pp. 3177-3185
Author(s):  
Aditya S Mondal ◽  
G C Dewangan ◽  
B Raychaudhuri
Keyword(s):  
Boundary Layer ◽  
Continuum Model ◽  
Broad Band ◽  
Iron Line ◽  
X Ray ◽  
Reflection Model ◽  
Single Temperature ◽  
Back Scattering ◽  
Low Mass ◽  
Spectral State

ABSTRACT We present NuSTAR observation of the atoll type neutron star (NS) low-mass X-ray binary (LMXB) Serpens X-1 (Ser X-1) performed on 2018 February 17. We observed Ser X-1 in a soft X-ray spectral state with 3–79 keV luminosity of LX ∼ 0.4 × 1038 erg s−1 (${\sim}23{{\ \rm per\ cent}}$ of the Eddington luminosity), assuming a distance of 7.7 kpc. A positive correlation between intensity and hardness ratio suggests that the source was in the banana branch during this observation. The broad-band 3–30 keV NuSTAR energy spectrum can be well described either by a three-component continuum model consisting of a disc blackbody, a single temperature blackbody, and a power law or by a two-component continuum model consisting of a disc blackbody and a Comptonization component. A broad iron line ∼5–8 keV and the Compton back-scattering hump peaking at ∼10–20 keV band are clearly detected in the X-ray spectrum. These features are best interpreted by a self-consistent relativistic reflection model. Fits with relativistically blurred disc reflection model suggests that the inner disc radius Rin is truncated prior to the ISCO at (1.9–2.5) RISCO (${\simeq}11.4\!-\!15\, R_{g}\: \text{or}\: 26\!-\!34$ km) and the accretion disc is viewed at a low inclination of i ≃ 16°−20°. The disc is likely to be truncated either by a boundary layer or by the magnetosphere. Based on the measured flux and the mass accretion rate, the maximum radial extension for the boundary layer is estimated to be ∼6.4 Rg from the NS surface. The truncated inner disc in association with pressure from a magnetic field sets an upper limit of B ≤ 1.9 × 109 G.

scholarly journals Broad-band spectral energy distribution of the X-ray transient Swift J1745−26 from outburst to quiescence

2020 ◽  
Vol 637 ◽  
pp. A2
Author(s):  
Sylvain Chaty ◽  
Francis Fortin ◽  
Alicia López-Oramas
Keyword(s):  
Energy Distribution ◽  
Light Curve ◽  
Spectral Energy Distribution ◽  
Broad Band ◽  
Spectral Energy ◽  
X Ray ◽  
Upper Limit ◽  
Spectral Break ◽  
Hard State ◽  
Low Mass

Aims. We aim to analyse our study of the X-ray transient Swift J1745−26, using observations obtained from its outburst in September 2012, up to its decay towards quiescence in March 2013. Methods. We obtained optical and infrared observations, through override programme at ESO/VLT with FORS2 and ISAAC instruments, and added archival optical (VLT/VIRCAM), radio and X-ray (Swift) observations, to build the light curve and the broad-band spectral energy distribution (SED) of Swift J1745−26. Results. We show that, during its outburst and also during its decay towards quiescence, Swift J1745−26 SED can be adjusted, from infrared up to X-rays, by the sum of both a viscous irradiated multi-colour black body emitted by an accretion disc, and a synchrotron power law at high energy. In the radio domain, the SED arises from synchrotron emission from the jet. While our SED fitting confirms that the source remained in the low/hard state during its outburst, we determine an X-ray spectral break at frequency 3.1 ≤ νbreak ≤ 3.4 × 1014 Hz, and a radio spectral break at 1012 Hz ≤ νbreak ≤ 1013 Hz. We also show that the system is compatible with an absorption AV of ∼7.69 mag, lies within a distance interval of D ∼ [2.6 − 4.8] kpc with an upper limit of orbital period Porb = 11.3 h, and that the companion star is a late spectral type in the range K0–M0 V, confirming that the system is a low-mass X-ray binary. We finally plot the position of Swift J1745−26 on an optical-infrared – X-ray luminosity diagram: its localisation on this diagram is consistent with the source staying in the low-hard state during outburst and decay phases. Conclusions. By using new observations obtained at ESO/VLT with FORS2 and ISAAC, and adding archival optical (VLT/VIRCAM), radio and X-ray (Swift) observations, we built the light curve and the broad-band SED of Swift J1745−26, and we plotted its position on an optical-infrared – X-ray luminosity diagram. By fitting the SED, we characterized the emission of the source from infrared, via optical, up to X-ray domain, we determined the position of both the radio and X-ray spectral breaks, we confirmed that it remained in the low-hard state during outburst and decay phases, and we derived its absorption, distance interval, orbital period upper limit, and the late-type nature of companion star, confirming Swift J1745−26 is a low-mass X-ray binary.

scholarly journals A broad-band look of the accreting millisecond X-ray pulsar SAX J1748.9−2021 using AstroSat and XMM–Newton

2020 ◽  
Vol 492 (3) ◽  
pp. 4361-4368 ◽  
Author(s):  
Rahul Sharma ◽  
Aru Beri ◽  
Andrea Sanna ◽  
Anjan Dutta
Keyword(s):  
Timing Analysis ◽  
Broad Band ◽  
Energy Bands ◽  
Large Area ◽  
Pulse Profile ◽  
Time Resolved ◽  
X Ray ◽  
Reflection Model ◽  
Single Temperature ◽  
Energy Pulse

ABSTRACT SAX J1748.9−2021 is a transient accretion powered millisecond X-ray pulsar located in the globular cluster NGC 6440. We report on the spectral and timing analysis of SAX J1748.9−2021 performed on AstroSat data taken during its faint and short outburst of 2017. We derived the best-fitting orbital solution for the 2017 outburst and obtained an average local spin frequency of 442.361098(3) Hz. The pulse profile obtained from 3 to 7 and 7 to 20 keV energy bands suggest constant fractional amplitude ∼0.5 per cent for fundamental component, contrary to previously observed energy pulse profile dependence. Our AstroSat observations revealed the source to be in a hard spectral state. The 1–50 keV spectrum from SXT (Soft X-ray Telescope) and LAXPC (Large Area X-ray Proportional Counter) on-board AstroSat can be well described with a single temperature blackbody and thermal Comptonization. Moreover, we found that the combined spectra from XMM–Newton (EPIC-PN) and AstroSat (SXT + LAXPC) indicated the presence of reflection features in the form of iron (Fe Kα) line that we modelled with the reflection model xillvercp. One of the two X-ray burst observed during the AstroSat/LAXPC observation showed hard X-ray emission (>30 keV) due to Compton up-scattering of thermal photons by the hot corona. Time-resolved analysis performed on the bursts revealed complex evolution in emission radius of blackbody for second burst suggestive of mild photospheric radius expansion.

scholarly journals A stochastic propagation model to the energy dependent rapid temporal behaviour of Cygnus X-1 as observed by AstroSat in the hard state

2019 ◽  
Vol 486 (2) ◽  
pp. 2964-2975 ◽  
Author(s):  
Bari Maqbool ◽  
Sneha Prakash Mudambi ◽  
R Misra ◽  
J S Yadav ◽  
S B Gudennavar ◽  
...  
Keyword(s):  
Time Lag ◽  
Broad Band ◽  
Propagation Model ◽  
Large Area ◽  
Temporal Behaviour ◽  
X Ray ◽  
Single Temperature ◽  
Hard State ◽  
Band Spectra ◽  
Energy Dependent

Abstract We report the results from analysis of six observations of Cygnus X-1 by Large Area X-ray Proportional Counter (LAXPC) and Soft X-ray Telescope (SXT) onboard AstroSat, when the source was in the hard spectral state as revealed by the broad-band spectra. The spectra obtained from all the observations can be described by a single-temperature Comptonizing region with disc and reflection components. The event mode data from LAXPC provides unprecedented energy dependent fractional root mean square (rms) and time-lag at different frequencies which we fit with empirical functions. We invoke a fluctuation propagation model for a simple geometry of a truncated disc with a hot inner region. Unlike other propagation models, the hard X-ray emission (>4 keV) is assumed to be from the hot inner disc by a single-temperature thermal Comptonization process. The fluctuations first cause a variation in the temperature of the truncated disc and then the temperature of the inner disc after a frequency dependent time delay. We find that the model can explain the energy dependent rms and time-lag at different frequencies.

scholarly journals A broad-band X-ray spectral study of the Seyfert 1 galaxy ESO 141–G055 with XMM–Newton and NuSTAR

2020 ◽  
Vol 497 (4) ◽  
pp. 4213-4221
Author(s):  
Ritesh Ghosh ◽  
Sibasish Laha
Keyword(s):  
Black Hole ◽  
Spectral Study ◽  
Column Density ◽  
Broad Band ◽  
Accretion Disc ◽  
Physical Models ◽  
X Ray ◽  
Reflection Model ◽  
Ionization Parameter

ABSTRACT We have extensively studied the broad--band X-ray spectra of the source ESO 141–G055 using all available XMM–Newton and NuSTAR observations. We detect a prominent soft excess below $2\rm \, \, {\rm keV}$, a narrow Fe line, and a Compton hump ($\gt 10\rm \, \, {\rm keV}$). The origin of the soft excess is still debated. We used two models to describe the soft excess: the blurred reflection from the ionized accretion disc and the intrinsic thermal Comptonization model. We find that both of these models explain the soft excess equally well. We confirm that we do not detect any broad Fe line in the X-ray spectra of this source, although both the physical models prefer a maximally spinning black hole scenario (a > 0.96). This may mean that either the broad Fe line is absent or blurred beyond detection. The Eddington rate of the source is estimated to be $\lambda _{\rm \, Edd}\sim 0.31$. In the reflection model, the Compton hump has a contribution from both ionized and neutral reflection components. The neutral reflector which simultaneously describes the narrow Fe K α and the Compton hump has a column density of $N_{\rm H} \ge 7\times 10^{24} \, \rm cm^{-2}$. In addition, we detect a partially covering ionized absorption with ionization parameter $\log \xi /\rm \, erg\, cm\, s^{-1}$  = $0.1^{+0.1}_{-0.1}$ and column density $N_{\rm H} =20.6^{+1.0}_{-1.0}\times 10^{22} \, \rm cm^{-2}$ with a covering factor of $0.21^{+0.01}_{-0.01}$.

scholarly journals New ASCA Observations of two Anomalous X-ray Pulsars

2000 ◽  
Vol 177 ◽  
pp. 695-698 ◽  
Author(s):  
B. Paul ◽  
M. Kawasaki ◽  
T. Dotani ◽  
F. Nagase
Keyword(s):  
Accretion Rate ◽  
Accretion Disc ◽  
Spectral Shape ◽  
Energy Spectra ◽  
Pulse Profile ◽  
X Ray ◽  
Low Mass ◽  
Low X ◽  
Star Surface ◽  
Made In

AbstractNewASCAobservations of two anomalous X-ray pulsars (AXP) 4U 0142+61 and 1E 1048.1-5937, made in 1998, when compared to earlier observations in 1994 show remarkable stability in the intensity, spectral shape and pulse profile. The energy spectra consist of two components, a power-law and a blackbody emission from the neutron star surface. In IE 1048.1-5937, we have identified three epochs with different spin-down rates and discuss its implications for the magnetar hypothesis of the AXPs. We also note that the spin-down rate and its variations in IE 1048.1-5937 are much larger than what normally can be produced by an accretion disc with very low mass accretion rate corresponding to its low X-ray luminosity.

scholarly journals X-ray Emission from Hot DA White Dwarfs; EXOSAT Results, and Implications for Atmospheric Models

1989 ◽  
Vol 114 ◽  
pp. 198-201
Author(s):  
Frits Paerels ◽  
John Heise
Keyword(s):  
Systematic Uncertainty ◽  
Effective Temperature ◽  
White Dwarfs ◽  
Current Model ◽  
Broad Band ◽  
Model Calculations ◽  
X Ray ◽  
Transmission Grating ◽  
Upper Limit ◽  
Optical Flux

AbstractWe present the observations of the photospheric X-ray spectra of hot DA white dwarfs, obtained with the 500 lines mm−1 Transmission Grating Spectrometer on EXOSAT. These spectra cover the full soft X-ray band, at high wavelength resolution and statistical quality. They allow us to do an accurate measurement of the photospheric parameters, particularly of effective temperature and chemical composition of the atmosphere.We consider the case of HZ 43 in some detail. Model atmospheric spectra that satisfy all measured absolute optical, UV and X-ray fluxes turn out not to fit the shape of the measured X-ray spectrum. However, from a comparison of model spectra calculated with different model atmospheres codes we infer the existence of a 15% systematic uncertainty in the model fluxes at the shortest wavelengths (λ < 100 Å) in current model calculations. This can explain the fitting problem. Since the systematic uncertainty in the models is larger than the statistical uncertainty in the shape of the measured X-ray spectrum of HZ 43, we cannot at present use this measured shape to derive the effective temperature and gravity. We revert to broad band photometry, using the measured integrated soft X-ray flux and the optical flux, to determine Te = 45,000 – 54,000K, R/R⊙ = 0.0140 – 0.0165. From the absence of the He II Ly edge at 227 Å in the measured spectrum, we set a upper limit on the photospheric helium abundance of He/H = 1.0 × 10−5; this upper limit is independent of the uncertainties in the model calculations mentioned above.

scholarly journals A spectral study of the black hole X-ray binary MAXI J1820+070 with AstroSat and NuSTAR

2020 ◽  
Vol 498 (4) ◽  
pp. 5873-5884
Author(s):  
Sudip Chakraborty ◽  
Nilam Navale ◽  
Ajay Ratheesh ◽  
Sudip Bhattacharyya
Keyword(s):  
Black Hole ◽  
Broad Band ◽  
X Ray ◽  
Reflection Model ◽  
Temporal Features ◽  
Source State ◽  
Hard State ◽  
Independent Observations ◽  
Best Fitting ◽  
Fitting Model

ABSTRACT MAXI J1820+070 is a newly discovered transient black hole X-ray binary, which showed several spectral and temporal features. In this work, we analyse the broad-band X-ray spectra from all three simultaneously observing X-ray instruments onboard AstroSat, as well as contemporaneous X-ray spectra from NuSTAR, observed during the hard state of MAXI J1820+070 in 2018 March. Implementing a combination of multicolour disc model, relativistic blurred reflection model relxilllpcp, and a distant reflection in the form of xillvercp, we achieve reasonable and consistent fits for AstroSat and NuSTAR spectra. The best-fitting model suggests a low temperature disc (kTin ∼ 0.3 keV), iron overabundance (AFe ∼ 4–5 solar), a short lamp-post corona height (h ≲ 8Rg), and a high corona temperature (kTe ∼ 115–150 keV). Addition of a second Comptonization component leads to a significantly better fit, with the kTe of the second Comptonization component being ∼14–18 keV. Our results from independent observations with two different satellites in a similar source state indicate an inhomogeneous corona, with decreasing temperature attributed to increasing height. Besides, utilizing the broader energy coverage of AstroSat, we estimate the black hole mass to be 6.7–13.9 M⊙, consistent with independent measurements reported in the literature.

scholarly journals Radio and X-ray monitoring of the accreting millisecond X-ray pulsar IGR J17591−2342 in outburst

2019 ◽  
Vol 492 (1) ◽  
pp. 1091-1101 ◽  
Author(s):  
N V Gusinskaia ◽  
T D Russell ◽  
J W T Hessels ◽  
S Bogdanov ◽  
N Degenaar ◽  
...  
Keyword(s):  
Large Scatter ◽  
Millisecond Pulsar ◽  
Radio Luminosity ◽  
Correlation Index ◽  
X Ray ◽  
Wide Range ◽  
Low Mass ◽  
Green Bank Telescope ◽  
Spectral State ◽  
Rule Out

ABSTRACT IGR J17591−2342 is a new accreting millisecond X-ray pulsar that was recently discovered in outburst in 2018. Early observations revealed that the source’s radio emission is brighter than that of any other known neutron star low-mass X-ray binary (NS–LMXB) at comparable X-ray luminosity, and assuming its likely ≳6 kpc distance. It is comparably radio bright to black hole LMXBs at similar X-ray luminosities. In this work, we present the results of our extensive radio and X-ray monitoring campaign of the 2018 outburst of IGR J17591−2342. In total, we collected 10 quasi-simultaneous radio (VLA, ATCA) and X-ray (Swift–XRT) observations, which make IGR J17591−2342 one of the best-sampled NS–LMXBs. We use these to fit a power-law correlation index $\beta = 0.37^{+0.42}_{-0.40}$ between observed radio and X-ray luminosities (LR ∝ LXβ). However, our monitoring revealed a large scatter in IGR J17591−2342’s radio luminosity (at a similar X-ray luminosity, LX ∼1036 erg s−1, and spectral state), with LR ∼ 4 × 1029 erg s−1 during the first three reported observations, and up to a factor of 4 lower LR during later radio observations. None the less, the average radio luminosity of IGR J17591−2342 is still one of the highest among NS–LMXBs, and we discuss possible reasons for the wide range of radio luminosities observed in such systems during outburst. We found no evidence for radio pulsations from IGR J17591−2342 in our Green Bank Telescope observations performed shortly after the source returned to quiescence. None the less, we cannot rule out that IGR J17591−2342 becomes a radio millisecond pulsar during quiescence.

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