Swift discovers X-rays from the newly discovered tidal disruption flare candidate AT2019dsg
ATel #12777; Dheeraj Pasham (MIT), Ron Remillard (MIT) and Thomas Wevers (U. Cambridge)
on 18 May 2019; 17:52 UT
Credential Certification: Dheeraj Pasham (drreddy@mit.edu)
Subjects: X-ray, Black Hole, Transient, Tidal Disruption Event
The optical transient AT2019dsg was discovered on 4th April 2019 by the Zwicky Transient Facility. A follow-up optical spectrum revealed a blue continuum superposed with both narrow Balmer emission lines (from the host galaxy, at z=0.051) as well as a broad He II 4686 emission feature and potentially a broad H-alpha feature (ATEL#12752). Spatial coincidence with the nucleus of a galaxy combined with the blue optical spectrum and broad emission features suggest the source could be a tidal disruption flare (TDF) candidate.
Neil Gehrels Swift Observatory made 2 ks of exposure starting at 04:09:46 UTC on 2019-05-17. A point source with a mean X-ray (0.3-8.0 keV) count rate of 0.055+-0.005 counts/sec was detected at a position consistent with the optical coordinates (https://wis-tns.weizmann.ac.il/object/2019dsg). We extracted the X-ray spectrum and modeled it with a blackbody modified by galactic absorption (phabs*zashift(bbodyrad) in XSPEC). Fixing the absorbing column at the Galactic value of 0.065e22 cm**-2, the best-fit blackbody temperature is 0.06+-0.01 keV. The inferred size of the X-ray photosphere is 4.2(+3.3,-1.4)e11 cms, and the implied unabsorbed flux is 4e-12 ergs/cm**2/s. This corresponds to a model luminosity of 2.5e43 erg/sec which is similar to several previous X-ray bright TDFs in early phases of evolution.
We have requested for additional Swift (XRT+UVOT) observations and encourage follow-up observations of this rare X-ray bright TDF candidate.
We thank the Neil Gehrels Swift Observatory ToO team for approving the observation request.
