Gezari, Suvi and Heckman, Tim and Cenko, S. Bradley and Eracleous, Michael and Forster, Karl and Gonçalves, Thiago S. and Martin, D. Chris and Morrissey, Patrick and Neff, Susan G. and Seibert, Mark and Schiminovich, David and Wyder, Ted K. (2009) Luminous Thermal Flares from Quiescent Supermassive Black Holes. Astrophysical Journal, 698 (2). pp. 1367-1379. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20090827-112314953
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A dormant supermassive black hole lurking in the center of a galaxy will be revealed when a star passes close enough to be torn apart by tidal forces, and a flare of electromagnetic radiation is emitted when the bound fraction of the stellar debris falls back onto the black hole and is accreted. Although the tidal disruption of a star is a rare event in a galaxy,≈10^(–4) yr^(–1), observational candidates have emerged in all-sky X-ray and deep ultraviolet (UV) surveys in the form of luminous UV/X-ray flares from otherwise quiescent galaxies. Here we present the third candidate tidal disruption event discovered in the Galaxy Evolution Explorer (GALEX) Deep Imaging Survey: a 1.6 × 10^(43) erg s^(–1) UV/optical flare from a star-forming galaxy at z = 0.1855. The UV/optical spectral energy distribution (SED) during the peak of the flare measured by GALEX and Palomar Large Field Camera imaging can be modeled as a single temperature blackbody with T_(bb) = 1.7 × 10^5 K and a bolometric luminosity of 3 × 10^(45) erg s^(–1), assuming an internal extinction with E(B – V)_(gas) = 0.3. The Chandra upper limit on the X-ray luminosity during the peak of the flare, L_X (2 – 10 keV)<10^(41) erg s^(–1), is 2 orders of magnitude fainter than expected from the ratios of UV to X-ray flux density observed in active galaxies. We compare the light curves and broadband properties of all three tidal disruption candidates discovered by GALEX, and find that (1) the light curves are well fitted by the power-law decline expected for the fallback of debris from a tidally disrupted solar-type star and (2) the UV/optical SEDs can be attributed to thermal emission from an envelope of debris located at roughly 10 times the tidal disruption radius of a ≈10^7 M_☉ central black hole. We use the observed peak absolute optical magnitudes of the flares (–17.5>M_g > – 18.9) to predict the detection capabilities of upcoming optical synoptic surveys.
|Additional Information:||© 2009. The American Astronomical Society. Received 2008 December 15; accepted 2009 April 14; published 2009 May 29. We thank the anonymous referee for their helpful comments. S.G. was supported by NASA through Hubble Fellowship grant HST-HF-01219.01-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555, and in part by Chandra grant G07- 8112X. We gratefully acknowledge NASA’s support for construction, operation, and science analysis for the GALEX mission, developed in cooperation with Centre National d’Etudes Spatiales of France and the Korean Ministry of Science and Technology. Some of the data presented were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA. The Observatory was make possible by the generous financial support of the W. M. Keck Foundation. The analysis pipeline used to reduce the DEIMOS data was developed at UC Berkeley with support from NSF grant AST- 0071048. The Hobby-Eberly Telescope (HET) is a joint project of the University of Texas at Austin, the Pennsylvania State University, Stanford University, Ludwig-Maximillians-Universität München, and Georg-August-Universität Göttingen. The HET is named in honor of its principal benefactors,William P. Hobby and Robert E. Eberly. The Marcario Low-Resolution Spectrograph is named for Mike Marcario of High Lonesome Optics, who fabricated several optics for the instrument but died before its completion; it is a joint project of the Hobby–Eberly Telescope partnership and the Instituto de Astronomía de la Universidad Nacional Autόnoma de México.|
|Group:||Space Radiation Laboratory|
|Subject Keywords:||black hole physics; galaxies: nuclei; ultraviolet: ISM; X-rays: galaxies|
|Official Citation:||Luminous Thermal Flares from Quiescent Supermassive Black Holes Suvi Gezari, Tim Heckman, S. Bradley Cenko, Michael Eracleous, Karl Forster, Thiago S. Gonçalves, D. Chris Martin, Patrick Morrissey, Susan G. Neff, Mark Seibert, David Schiminovich, and Ted K. Wyder 2009 ApJ 698 1367-1379 doi: 10.1088/0004-637X/698/2/1367|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||11 Sep 2009 22:21|
|Last Modified:||04 Mar 2013 18:00|
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