Temporal variation in the coronal radius parameter in a jetted tidal disruption event: Swift J1644+57

Abstract

Tidal disruption events are exotic astrophysical phenomena where matter from a star or the interstellar medium is captured by a supermassive black hole. The process liberates enormous energy, within a few months to a year timescale, enough to detect dormant black holes in near as well as the farthest galaxies. We revisit the long-term spectral variabilities associated with the jetted tidal disruption event Swift J1644+57 by exploring the archival X-ray data obtained with the Swift X-ray Telescope and the XMM-Newton observatory. Our analysis reveals that the spectral indices decrease nonmonotonically as Swift J1644+57 evolves with time. We also find that the soft (0.3–1.5 keV) and hard (1.5–10 keV) X-ray photon counts are highly correlated with a maximum correlation coefficient of 0.95 and peak at zero lag. Moreover, the soft and hard band variabilities obtained from XMM-Newton observations are highly correlated with a Pearson cross-correlation coefficient of 0.96. This indicates that the soft and hard X-ray photons are emitted from the same site, which is most likely a Compton cloud, i.e., the corona. Assuming the hard X-ray photons originate from the corona, we find that the coronal parameter undergoes rapid expansion during the early phases when accompanied by a relativistic jet launching and subsequently evolves toward a state of saturation with minor fluctuations in the latter stages. The temporal variation in the coronal radius parameter (Rcor) is consistent with a simple theoretical conjecture. We also discuss the application of our analytical outcomes to other jetted and nonjetted tidal disruption events.