AstroSat and MAXI view of the Black Hole binary 4U 1630-472 during 2016 and 2018 Outbursts

Abstract

We present an in-depth spectral and timing analysis of the Black Hole binary 4U 1630-472 during 2016 and 2018 outbursts as observed by \textit{AstroSat} and \textit{MAXI}. The extensive coverage of the outbursts with \textit{MAXI} is used to obtain the Hardness Intensity Diagram (HID). The source follows a `c'-shaped profile in agreement with earlier findings. Based on the HIDs of previous outbursts, we attempt to track the evolution of the source during a `super'-outburst and `mini'-outbursts. We model the broadband energy spectra ($0.7-20.0$ keV) of \textit{AstroSat} observations of both outbursts using phenomenological and physical models. No Keplerian disc signature is observed at the beginning of 2016 outburst. However, the disc appears within a few hours after which it remains prominent with temperature ($T_{in}$) $\sim$ 1.3 keV and increase in photon index ($\Gamma$) from 1.8 to 2.0, whereas the source was at a disc dominant state throughout the \textit{AstroSat} campaign of 2018 outburst. Based on the HIDs and spectral properties, we classify the outbursts into three different states - the `canonical' hard and soft states along with an intermediate state. Evolution of rms along different states is seen although no Quasi-periodic Oscillations (QPOs) are detected. We fit the observed spectra using a dynamical accretion model and estimate the accretion parameters. Mass of the black hole is estimated using inner disc radius, bolometric luminosity and two component flow model to be $3-9$ $M_{\odot }$. Finally, we discuss the possible implications of our findings.

16 pages, 11 figures, Accepted for publication in MNRAS, typos fixed and figures updated

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Cited by in corpus (7)

• AstroSat and MAXI view of Cygnus X-1: Signature of an `extreme' soft nature
• AstroSat view of IGR J17091-3624 and GRS 1915+105: decoding the 'pulse' in the 'Heartbeat State'
• Revealing the nature of the transient source MAXI J0637-430 through spectro-temporal analysis
• Accretion Scenario of MAXI J1820+070 during 2018 Outbursts with Multi-mission Observations
• A Machine Learning approach for classification of accretion states of Black hole binaries
• Review the possible advective disk structures around a black hole with two-type gas inflows
• On the origin of core radio emissions from black hole sources in the realm of relativistic shocked accretion flow