Tidal disruption event (TDE) — the incident in which a star becomes too close to a supermassive black hole (SMBH) so that it is tidally disrupted — provides an effective means of revealing the otherwise invisible SMBHs in normal galaxies. Conventionally, the search of TDE is carried out in UV and soft X-ray wavebands, where most of the emission is coming from, but photons in these bands are subject to extinction and this contributes a major uncertainty in the TDE research. Recently, it is realized that the interaction between the debris of a disrupted star with the surrounding ISM inevitably produces a large amount of cosmic rays, and eventually results in a long-lasting gamma-ray glow as the cosmic rays propagate in the host galaxy. Such a gamma-ray signature provides an alternative tool to probe TDE, which is less affected by extinction. In this talk, I will outline the properties of this gamma-ray signature. In particular, I will present the results from our recent studies of the interaction of stellar debris with molecular clouds, which are expect to exist in large amount close to SMBHs. The subsequent gamma-ray emission is much stronger than what is expected in the case of a smooth ISM, and such a gamma-ray source potentially could be detected by Fermi and H.E.S.S., and mostly likely by the future Cherenkov Telescopes Array (CTA) out to a distance of tens of Mpc. Our work also has profound implications for the search of other gamma-ray sources, such as starbursts, pulsars, and dark-matter annihilation, which will be briefly discussed towards the end of the talk.

Bio: Dr. Xian Chen received his Ph.D in 2010 from Peking University (PKU) under the supervision of Prof. Fukun Liu (PKU) and Prof. Piero Madau (UC Santa Cruz). After that he became a postdoc fellow at the Kavli Institute for Astronomy and Astrophysics at Peking University,  and two years later moved to Germany to work as a postdoc researcher at the Max-Planck Institute for Gravitational Physics (Albert Einstein Institute). He is currently an EMBIGGEN postdoc fellow at the Institute