X-ray Tidal Disruption Events Discovered from the XMM-Newton Pointed Observations

Stars wandering too close to massive black holes (BHs) can be tidally disrupted and subsequently accreted, leading to spectacular multiwavelength flares. Such tidal disruption events (TDEs) provide a unique way to find and study otherwise dormant massive BHs in dense stellar environments such as galactic nuclei and star clusters. Very few TDEs have been found, especially in X-rays (only ~30). Here I report our discovery of two very important subclasses of TDEs from intensive search over the XMM-Newton X-ray source catalog: super-Eddington accreting events and off-nuclear events associated with intermediate-mass BHs in star clusters. For super-Eddington accreting TDEs, I will focus on a well sampled super-long (>12 years, vs. ~1 year for typical events) luminous X-ray flare from the nuclear region of a dwarf starburst galaxy. This event displayed unique quasi-soft X-ray spectra signaling super-Eddington accretion, which is also supported by later dramatic transition to the thermal state of much softer X-ray spectra. Our discovery of two other events of similar super-Eddington accretion spectral characteristics suggests a new, super-Eddington accreting class of TDEs is emerging. For off-nuclear TDEs, I will focus on a luminous soft X-ray outburst from a massive star cluster on the outskirts of a large S0 galaxy. It demonstrates that one of the most effective means to detect intermediate-mass BHs that are still very rare is through X-ray flares from TDEs in star clusters.

Dacheng Lin (University of New Hampshire)
KIAA, 1st meeting room
Wed, 2018-11-07 12:00 to 13:00