Probing the Cyclotron line characteristics of 4U 1538-522 using AstroSat-LAXPC
Abstract
We report the first report on cyclotron line studies with the LAXPC instrument onboard AstroSat of the high-mass X-ray binary pulsar 4U 1538-52. During the observation of source that spanned about 1 d with a net exposure of 50 ks, the source X-ray flux remained constant. Pulse profile is double peaked in low-energy range and has a single peak in high-energy range, the transition taking place around the cyclotron line energy of the source. Cyclotron scattering feature (CRSF) is detected at ∼22 keV with a very high significance in phase-averaged spectrum. It is one of the highest signal to noise ratio detections of CRSF for this source. We performed detailed pulse-phase-resolved spectral analysis with 10 independent phase bins. We report the results of pulse-phase-resolved spectroscopy of the continuum and CRSF parameters. The cyclotron line parameters show pulse phase dependence over the entire phase with a CRSF energy variation of {∼ }13{{ per cent}}, which is in agreement with previous studies. We also confirm the increase in the centroid energy of the CRSF observed between the 1996-2004 (RXTE) and the 2012 (Suzaku) observations, reinforcing that the increase was a long-term change.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- March 2019
- DOI:
- 10.1093/mnrasl/sly234
- arXiv:
- arXiv:1812.06609
- Bibcode:
- 2019MNRAS.484L...1V
- Keywords:
-
- binaries : general;
- radiation mechanism : non-thermal;
- (stars:) pulsars : general;
- (stars:) pulsars : individual : 4U 1538-522;
- X-rays : stars;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 6 pages, 7 figures, Accepted for publication in MNRAS Letter