No X-rays from the position of the candidate tidal disruption flare AT2019gte--perhaps another ASASSN-15lh like event?
ATel #12904; Dheeraj Pasham (MIT), and Thomas Wevers (U. Cambridge)
on 2 Jul 2019; 16:42 UT
Credential Certification: Dheeraj Pasham (drreddy@mit.edu)
Subjects: X-ray, AGN, Black Hole, Transient, Tidal Disruption Event
The optical transient AT2019gte was discovered on 31th May 2019 by the Zwicky Transient Facility. Based on its spatial coincidence with the nucleus of a galaxy at z=0.086 and the emergence of broad optical emission lines, it was tentatively classified as being a tidal disruption flare (ATEL#12857).
We observed the transient with the Swift/XRT and detect no X-rays above the background. We derive a 3-sigma upper limit of 7e-3 counts/sec in the 0.3-8 keV band. Assuming a soft thermal spectrum with a temperature of 0.1 keV, this corresponds to an unabsorbed flux of 2.2e-13 erg/s/cm^2. At a redshift of 0.086, this corresponds to a luminosity upper limit of 4e42 erg/sec.
Using the absorption lines from the archival SDSS spectrum and the M-sigma relation from Ferrarese & Ford (2005), we estimate its black hole mass to be 2.8(+4.4,-1.8)x10^8 solar masses. This value is in excess of the Hills mass for the disruption of a Solar-type star (which would be swallowed behind the event horizon), indicating either a star more massive than solar and/or a non-zero spin for the supermassive black hole. If the TDE nature can be confirmed, this could be similar to the case of ASASSN-15lh whose origin has been highly debated.
Follow up observations are encouraged. We thank the Swift ToO team for promptly responding to our ToO request.
