Swift UVOT Measurement of ROTSE3 J115649.1+542726, a Possible Tidal Disruption Event ?
ATel #1524; S. Gezari (JHU), J. P. Halpern (Columbia U.)
on 15 May 2008; 02:29 UT
Credential Certification: Jules Halpern (jules@astro.columbia.edu)
Subjects: Ultra-Violet, X-ray, Quasar, Transient
The magnitude 18 optical transient ROTSE3 J115649.1+542726, described
as a possible AGN at z=1.02 by Yuan et al. 2008 (ATel #1515),
was observed with Swift at our request beginning on 2008 May 14 00:10 UT.
Strong detections were obtained in all six UVOT filters covering 170-600 nm.
The spectral energy distribution (see link below), including the Palomar g,r,i
magnitudes reported in ATel #1515, is consistent with a ~2.5e4 K blackbody
in the rest frame at z=1.02. Apparent deviations from a blackbody
may be due to emission lines. The bolometric luminosity is ~2.3e46 erg/s,
corrected for Galactic extinction E(B-V) = 0.012.
A total exposure of 4764 s was obtained with the Swift XRT.
There is no X-ray detection. The upper limit corresponds
to F(0.5-10 keV)<3.2e-14 erg/cm2/s for a power law of photon index 2,
or L(0.5-10 keV)<1.8e44 erg/s at z=1.02.
In view of the large amplitude (~5 magnitudes), soft spectrum,
and slow evolution of this flare,
it is a candidate for a stellar tidal disruption
(cf., Gezari et al. 2008, ApJ, 676, 944)
around a ~1.8e8 solar mass black hole, now accreting
a significant fraction of a solar mass
through a thin disk at the Eddington limit.
Further monitoring observations with Swift are planned.
Spectral Energy Distribution