Timing and spectral studies of the transient X-ray pulsar GX 304−1 during an outburst (original) (raw)
Related papers
arXiv (Cornell University), 2020
We made a detailed study of the timing and spectral properties of the X-ray pulsar 1A 0535+262 during the recent giant outburst in 2020 November and December. The flux of the pulsar reached a record value of ∼12.5 Crab as observed by Swift/BAT (15-50 keV) and the corresponding mass accretion rate was ∼ 6.67 × 10 17 g s −1 near the peak of the outburst. There was a transition from the subcritical to the supercritical accretion regime which allows exploring different properties of the source in the supercritical regime. A q-like feature was detected in the hardness-intensity diagram during the outburst. We observed high variability and strong energy dependence of pulse profiles during the outburst. Cyclotron Resonant Scattering Feature (CRSF) was detected at ∼ 44 keV from the NuSTAR energy spectrum in the subcritical regime and the corresponding magnetic field was ≃ 4.9 × 10 12 G. The energy of the CRSF was shifted towards lower energy in the supercritical regime. The luminosity dependence of the CRSF was studied and during the supercritical regime, a negative correlation was observed between the line energy and luminosity. The critical luminosity was ∼ 6 × 10 37 erg s −1 above which a state transition occurred. A reversal of correlation between the photon index and luminosity was observed near the critical luminosity. The NuSTAR spectra can be described by a composite model with two continuum components, a blackbody emission, cutoff power law, and a discrete component to account for the iron emission line at 6.4 keV. An additional cyclotron absorption feature was included in the model.
Monthly Notices of the Royal Astronomical Society, 2022
We made a detailed study of the timing and spectral properties of the X-ray pulsar 1A 0535+262 during the recent giant outburst in 2020 November and December. The flux of the pulsar reached a record value of ∼12.5 Crab as observed by Swift/BAT (15-50 keV) and the corresponding mass accretion rate was ∼ 6.67 × 10 17 g s −1 near the peak of the outburst. There was a transition from the subcritical to the supercritical accretion regime which allows exploring different properties of the source in the supercritical regime. A q-like feature was detected in the hardness-intensity diagram during the outburst. We observed high variability and strong energy dependence of pulse profiles during the outburst. Cyclotron Resonant Scattering Feature (CRSF) was detected at ∼ 44 keV from the NuSTAR energy spectrum in the subcritical regime and the corresponding magnetic field was ≃ 4.9 × 10 12 G. The energy of the CRSF was shifted towards lower energy in the supercritical regime. The luminosity dependence of the CRSF was studied and during the supercritical regime, a negative correlation was observed between the line energy and luminosity. The critical luminosity was ∼ 6 × 10 37 erg s −1 above which a state transition occurred. A reversal of correlation between the photon index and luminosity was observed near the critical luminosity. The NuSTAR spectra can be described by a composite model with two continuum components, a blackbody emission, cutoff power law, and a discrete component to account for the iron emission line at 6.4 keV. An additional cyclotron absorption feature was included in the model.
TIMING AND SPECTRAL PROPERTIES OF Be/X-RAY PULSAR EXO 2030+375 DURING A TYPE I OUTBURST
The Astrophysical Journal, 2013
We present results from a study of broadband timing and spectral properties of EXO 2030+375 using a Suzaku observation. Pulsations with a period of 41.41 s and strong energy-dependent pulse profiles were clearly detected up to 100 keV. Narrow dips are seen in the profiles up to ∼70 keV. The presence of prominent dips at several phases in the profiles up to such high energy ranges was not seen before. At higher energies, these dips gradually disappeared and the profile appeared to be single-peaked. The 1.0-200.0 keV broadband spectrum is found to be well described by a partial covering high-energy cutoff power-law model. Several low-energy emission lines are also detected in the pulsar spectrum. We fitted the spectrum using neutral as well as partially ionized absorbers along with the above continuum model yielding similar parameter values. The partial covering with a partially ionized absorber resulted in a marginally better fit. The spectral fitting did not require any cyclotron feature in the best-fit model. To investigate the changes in spectral parameters at dips, we carried out pulse-phase-resolved spectroscopy. During the dips, the value of the additional column density was estimated to be high compared to other pulse phases. While using a partially ionized absorber, the value of the ionization parameter is also higher at the dips. This may be the reason for the presence of dips up to higher energies. No other spectral parameters show any systematic variation with pulse phases of the pulsar.
RXTE-PCA observations of 1A 1118−61: timing and spectral studies during an outburst
Monthly Notices of the Royal Astronomical Society, 2011
We report detailed timing and spectral analysis of RXTE-PCA data obtained from observations during the outburst of a transient X-ray pulsar 1A 1118-61 in January 2009. The pulse profile showed significant evolution during the outburst and also significant energy dependence − a double peaked profile upto 10 keV and a single peak at higher energy. We have also detected quasi-periodic oscillations (QPO) at 0.07-0.09 Hz. The rms value of the QPO is 5.2 % and it shows a significant energy dependence with highest rms of 7% at 9 keV. The QPO frequency changed from 0.09 Hz to 0.07 Hz within 10 days. The magnetic field strength calculated using the QPO frequency and the X-ray luminosity is in agreement with the magnetic field strength measured from the energy of the cyclotron absorption feature detected in this source. The 3-30 keV energy spectrum over the 2009 outburst of 1A 1118-61 can be well fitted with a partial covering power-law model with a high energy cutoff and an iron fluorescence line emission. The pulse phase resolved spectral analysis shows that the partial covering and high energy cutoff model parameters have significant changes with the pulse phase.
Overview of an extensive multi-wavelength study of GX 339−4 during the 2010 outburst
Astronomy & Astrophysics, 2011
The microquasar GX 339−4 experienced a new outburst in 2010: it was observed simultaneously at various wavelengths from radio up to soft γ-rays. We focused on observations that are quasi-simultaneous with those made with the INTEGRAL and RXTE satellites: these were collected in 2010 March-April during our INTEGRAL Target of Opportunity program, and during some of the other INTEGRAL observing programs with GX 339−4 in the field-of-view. X-ray transients are extreme systems that often harbour a black hole, and are known to emit throughout the whole electromagnetic spectrum when in outburst. The goals of our program are to understand the evolution of the physical processes close to the black hole and to study the connections between the accretion and ejection. We analysed radio, NIR, optical, UV, X-ray and soft γ-ray observations. We studied the source evolution in detail by producing light curves, hardness-intensity diagrams and spectra. We fitted the broadband data with phenomenological, then physical, models to study the emission coming from the distinct components. Based on the energy spectra, the source evolved from the canonical hard state to the canonical soft state. The source showed X-ray spectral variations that were correlated with changes in radio, NIR and optical emission. The bolometric flux increased from 0.8 to 2.9 ×10 −8 erg cm −2 s −1 while the relative flux and contribution of the hot medium globally decreased. Reprocessing in the disc was likely to be strong at the end of our observations. The source showed a behaviour similar to that of previous outbursts, with some small deviations in the hard X-rays parameters' evolution. The radio, NIR and optical emission from jets was detected, and seen to fade as the source softened. The results are discussed within the context of disc and jet models.
Very high energy γ-ray emission from X-ray transients during major outbursts
Astronomy and Astrophysics, 2007
Context. Some high mass X-ray binaries (HMXB) have been recently confirmed as γ-ray sources by ground based Cherenkov telescopes. In this work, we discuss the γ-ray emission from X-ray transient sources formed by a Be star and a highly magnetized neutron star. This kind of systems can produce variable hadronic γ-ray emission through the mechanism proposed by Cheng and Ruderman, where a proton beam accelerated in the pulsar magnetosphere impacts the transient accretion disk. We choose as case of study the best known system of this class: A0535+26. Aims. We aim at making quantitative predictions about the very high-energy radiation generated in Be-X ray binary systems with strongly magnetized neutron stars. Methods. We study the gamma-ray emission generated during a major X-ray outburst of a HMXB adopting for the model the parameters of A0535+26. The emerging photon signal from the disk is determined by the grammage of the disk that modulates the optical depth. The electromagnetic cascades initiated by photons absorbed in the disk are explored, making use of the so-called "Approximation A" to solve the cascade equations. Very high energy photons induce Inverse Compton cascades in the photon field of the massive star. We implemented Monte Carlo simulations of these cascades, in order to estimate the characteristics of the resulting spectrum. Results. TeV emission should be detectable by Cherenkov telescopes during a major X-ray outburst of a binary formed by a Be star and a highly magnetized neutron star. The γ-ray light curve is found to evolve in anti-correlation with the X-ray signal.
Monitoring Supergiant Fast X‐Ray Transients with Swift . I. Behavior Outside Outbursts
The Astrophysical Journal
IGR J16479−4514 is a Supergiant Fast X-ray Transient (SFXT), a new class of High Mass X-ray Binaries, whose number is rapidly growing thanks to the INTEGRAL observations of the Galactic plane. It was regularly monitored with Swift/XRT since November 2007, to study the quiescent emission, the outburst properties and their recurrence. A new bright outburst, reaching fluxes above 10 −9 erg cm −2 s −1 , was caught by the Swift/BAT. Swift immediately re-pointed at the target with the narrow-field instruments so that, for the first time, an outburst from a SFXT where a periodicity in the outburst recurrence is unknown could be observed simultaneously in the 0.2-150 keV energy band. The X-ray emission is highly variable and spans almost four orders of magnitude in count rate during the Swift/XRT observations covering a few days before and after the bright peak. The X-ray spectrum in outburst is hard and highly absorbed. The power-law fit resulted in a photon index of 0.98±0.07, and in an absorbing column density of ∼5×10 22 cm −2 . These observations demonstrate that in this source (similarly to what was observed during the 2007 outburst from the periodic SFXT IGR J11215−5952), the accretion phase lasts much longer than a few hours.
Monthly Notices of the Royal Astronomical Society, 2010
After a long quiescence of three decades, the transient X-ray pulsar 4U 1901+03 became highly active in 2003 February. From the analysis of a large number of Rossi X-ray Timing Explorer/Proportional Counter Array (RXTE/PCA) observations of this source, we report here the detection of X-ray flares, a broadening of the pulse frequency feature and Quasi Periodic Oscillations (QPOs). The X-ray flares showed spectral changes, had a duration of 100 s-300 s, and were more frequent and stronger during the peak of the outburst. In most of the observations during the outburst we also detected a broadening of the pulse frequency peak. We have also found intensity dependent changes in the pulse profile at very short timescales. This reveals a coupling between the periodic and the low frequency aperiodic variabilities. In addition, near the end of the outburst we have detected a strong QPO feature centered at ∼0.135 Hz. The QPO feature is broad with a quality factor of 3.3 and with an rms value of 18.5±3.1%. Using the QPO frequency and the X-ray luminosity during the QPO detection period we estimated the magnetic field strength of the neutron star as 0.31×10 12 G which is consistent with the value inferred earlier under the assumption of spin equilibrium.
2000
The transient X-ray pulsar Cepheus X-4 underwent its latest outburst in 1997, during July-August, which lasted for about 30 days. The Pointed mode Proportional Counters (PPCs) of the Indian X-ray Astronomy Experiment (IXAE) on board IRS-P3 satellite observed the source in its declining phase during 1997 July 28 to July 30. The timing analysis of the data confirms the 66 seconds pulsation of the neutron star. The Xray pulse profile obtained in two energy bands between 2 and 18 keV, shows energy dependent variations. The pulse profile obtained by us in the declining phase of the outburst when the X-ray luminosity of the source was about 6×10 35 ergs s −1 , is distinctly different from the one observed with the RXTE in the earlier phase of the outburst. It is found that near the end of the outburst, the relative strength of the two pulses of the double-pulse profile got reversed and the inter-pulse became more dominant compared to the main pulse. The observations can be interpreted in terms of a luminosity dependent emission profile of the pulsar, where depending on the pulsar geometry with respect to line of sight, one of the emission patterns, either a pencil-beam or a fan-beam, becomes more dominant. This is due to the changes in the pulsar magneto-sphere below a specific luminosity, which may cause relative changes in accretion process onto the two poles of the neutron star.