Title：Tidal disruption events in the multi-wavelength era

　　Speaker：Wenbin Lu (University of Texas at Austin)

　　Time：May 24 (Tuesday), 10:00am

　　Place：Room 502, Astronomy Building

　　Abstract：Most galaxies harbor weakly- or non-active central super-massive black holes (BHs). Roughly once every 10^4 - 10^5 years in each galaxy, a star enters the BH's tidal disruption radius within which the tidal force of the BH exceeds the star's self gravity, and hence the star gets tidally disrupted. In these tidal disruption events (TDEs), the stellar debris feeds a burst of super-Eddington accretion that generates a bright flare of electromagnetic radiation. In the recent decade or so, several dozen such flares have been discovered by transient surveys in various wavelengths from gamma/X-ray to UV and optical. In addition, the discoveries of Sw J1644+57 and Sw J2058+05 showed that the TDE accretion disk can launch relativistic jets. TDEs offer a new window for studying many astrophysical puzzles, such as super-Eddington MHD accretion physics, population of non-active super-massive BHs, radiation mechanism of relativistic jets, etc.

　　I'll talk about some recent/on-going work with my advisor and collaborators. (1) We studied the physical mechanisms responsible for the bright gamma/X-ray emission from jetted TDEs, taking into account the multi-wavelength data from Sw J1644+57. We found that the gamma/X-ray is most likely the synchrotron emission from electrons continuously accelerated by magnetic reconnection, although external inverse-Compton emission is also a viable mechanism. (2) A typical TDE emits about 10^51 - 10^52 erg of UV/optical energy, which will be absorbed by pc-scale dust at the galactic center. Dust grains will re-radiate this energy in the mid-IR at a luminosity of 10^42 - 10^43 erg/s. Observations and applications of this mid-IR component will be discussed. (3) If the massive dark objects at galactic centers are not black holes and hence don't have event horizons hiding particles' kinetic energy, the in-falling stellar debris will form a luminous envelope. Non-detection of the envelope's radiation provides one of the strongest proofs on the existence of the event horizon.

欢迎各位老师、同学参加！

                                             南京大学天文与空间科学学院