Studies of Cepheus X-4 during the 2018 Outburst Observed with AstroSat
| Autor: | H. M. Antia, K. Mukerjee |
|---|---|
| Rok vydání: | 2021 |
| Předmět: |
High Energy Astrophysical Phenomena (astro-ph.HE)
High Energy Physics - Theory Physics Astrophysics::High Energy Astrophysical Phenomena FOS: Physical sciences Astronomy and Astrophysics Astrophysics::Cosmology and Extragalactic Astrophysics Astrophysics High Energy Physics - Experiment High Energy Physics - Experiment (hep-ex) High Energy Physics - Theory (hep-th) Space and Planetary Science Astrophysics - High Energy Astrophysical Phenomena Astrophysics - Instrumentation and Methods for Astrophysics Instrumentation and Methods for Astrophysics (astro-ph.IM) Astrophysics::Galaxy Astrophysics |
| Zdroj: | The Astrophysical Journal. 920:139 |
| ISSN: | 1538-4357 0004-637X |
| DOI: | 10.3847/1538-4357/ac11f1 |
| Popis: | We present timing and spectral results of 2018 outburst of Cepheus X-4, observed twice by AstroSat at luminosity of $2.04 \times 10^{37}$ erg s$^{-1}$ and $1.02 \times 10^{37}$ erg s$^{-1}$ respectively. The light curves showed strong pulsation and co-related X-ray intensity variation in SXT (0.5--8.0 keV) and LAXPC (3--60 keV) energy bands. Spin-period and spin-down rate of the pulsar were determined from two observations as $65.35080\pm0.00014$ s , $(-2.10\pm0.8)\times10^{-12}$ Hz s$^{-1}$ at an epoch MJD 58301.61850 and $65.35290\pm0.00017$ s, $(-1.6\pm0.8)\times10^{-12}$ Hz s$^{-1}$ for an epoch MJD 58307.40211. Pulse-shape studies with AstroSat showed energy and intensity dependent variations. The pulsar showed an overall continuous spin-down, over 30 years at an average-rate of $(-2.455\pm0.004)\times10^{-14}$ Hz s$^{-1}$, attributed to propeller-effect in the subsonic-regime of the pulsar, in addition to variations during its outburst activities. Spectra between 0.7--55 keV energy band were well fitted by two continuum models, an absorbed compTT-model and an absorbed power-law with a Fermi-Dirac cutoff (FD-cutoff) model with a black-body. These were combined with an iron-emission line and a cyclotron absorption line. The prominent cyclotron resonance scattering features with a peak absorption energy of $30.48^{+0.33}_{-0.34}$ keV and $30.68^{+0.45}_{-0.44}$ keV for FD-cutoff-model and $30.46^{+0.32}_{-0.28}$ keV and $30.30^{+0.36}_{-0.34}$ keV for compTT-model were detected during two AstroSat observations. These when compared with earlier results, showed long term stability of its average value of $30.23 \pm 0.22$ keV. The pulsar showed pulse-phase as well as luminosity dependent variations in cyclotron-line energy and width and in plasma optical-depth of its spectral continuum. 25 pages, 18 figures, 3 tables, Accepted for Publication in The Astrophysical Journal |
| Databáze: | OpenAIRE |
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