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ATEL # 1524; S. Gezari (JHU), J. P. Halpern (Columbia U.)
on 15 May 2008; 2:29 UT
Password Certification: Jules Halpern (firstname.lastname@example.org)
Subjects: Ultra-Violet, X-ray, Quasars, Transients
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