Temporal Variation of the Coronal Radius Parameter in a Jetted Tidal Disruption Event: Swift J1644+57

TL;DR

This study analyzes long-term X-ray spectral variability in a jetted tidal disruption event, revealing correlated soft and hard X-ray emissions and a dynamic coronal radius consistent with theoretical models.

Contribution

It provides new insights into the evolution of the coronal radius parameter in a TDE, linking spectral variability to physical changes in the corona during jet launching.

Findings

Spectral indices decrease non-monotonically over time.

Soft and hard X-ray counts are highly correlated with zero lag.

Coronal radius expands rapidly early on and then saturates.

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 \source~by exploring the archival X-ray data obtained with Swift/XRT and XMM-Newton observatories. Our analysis reveals that the spectral indices decrease non-monotonically as \source~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 {\it 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 of the coronal radius parameter ($R_{cor}$) is consistent with a simple theoretical conjecture. We also discuss the application of our analytical outcomes to other jetted and non-jetted tidal disruption events.