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GRB060218 as a Tidal Disruption of a White Dwarf by an Intermediate Mass Black Hole

Shcherbakov, Roman V. and Pe'er, Asaf and Reynolds, Christopher S. and Haas, Roland and Bode, Tanja and Laguna, Pablo (2013) GRB060218 as a Tidal Disruption of a White Dwarf by an Intermediate Mass Black Hole. Astrophysical Journal, 769 (2). Art. No. 85. ISSN 0004-637X.

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The highly unusual pair of a gamma-ray burst (GRB) GRB060218 and an associated supernova, SN2006aj, has puzzled theorists for years. A supernova shock breakout and a jet from a newborn stellar mass compact object have been proposed to explain this pair's multiwavelength signature. Alternatively, we propose that the source is naturally explained by another channel: the tidal disruption of a white dwarf (WD) by an intermediate-mass black hole (IMBH). This tidal disruption is accompanied by a tidal pinching, which leads to the ignition of a WD and a supernova. Some debris falls back onto the IMBH, forms a disk, which quickly amplifies the magnetic field, and launches a jet. We successfully fit soft X-ray spectra with the Comptonized blackbody emission from a jet photosphere. The optical/UV emission is consistent with self-absorbed synchrotron emission from the expanding jet front. The temporal dependence of the accretion rate Ṁ(t)in a tidal disruption provides a good fit to the soft X-ray light curve. The IMBH mass is found to be about 10^4 M_☉ in three independent estimates: (1) fitting the tidal disruption Ṁ(t) to the soft X-ray light curve, (2) computing the jet base radius in a jet photospheric emission model, and (3) inferring the mass of the central black hole based on the host dwarf galaxy's stellar mass. The position of the supernova is consistent with the center of the host galaxy, while the low supernova ejecta mass is consistent with that of a WD. The high expected rate of tidal disruptions in dwarf galaxies is consistent with one source observed by the Swift satellite over several years at a distance of 150 Mpc measured for GRB060218. Encounters with WDs provide much fuel for the growth of IMBHs.

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Additional Information:© 2013 The American Astronomical Society. Received 2012 December 13; accepted 2013 March 18; published 2013 May 7. The authors are thankful to Nathaniel Bulter, John Cannizzo, Coleman Miller, Ramesh Narayan, Eve Ostriker, Enrico Ramirez-Ruiz, and Leslie Sage for useful discussions and comments. Special thanks to Abderahmen Zoghbi for advice on temporal analysis, Ranjan Vasudevan for general help with XSPEC, and Demosthenes Kazanas and Jonathan McKinney for discussions of the generation of a large-scale magnetic field. We thank the anonymous referee for insightful comments which helped to improve the manuscript. R.V.S. is supported by NASA Hubble Fellowship grant HST-HF-51298.01, P.L. is supported by NSF grants 1212433, 1205864, 0941417, 0903973, 0855423, and 0903973. C.S.R. thanks NASA for support under Astrophysics Theory Program (ATP) grant NNX10AE41G.
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NASA Hubble Fellowship grantHST-HF-51298.01
NASA Astrophysics Theory Program (ATP)NNX10AE41G
Subject Keywords:accretion, accretion disks; black hole physics – radiation mechanisms: general; supernovae: general; X-rays: bursts; X-rays: individual (GRB060218)
Record Number:CaltechAUTHORS:20130307-144356891
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Official Citation:GRB060218 as a Tidal Disruption of a White Dwarf by an Intermediate-mass Black Hole Roman V. Shcherbakov et al. 2013 ApJ 769 85
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37388
Deposited By: JoAnn Boyd
Deposited On:27 Mar 2013 18:34
Last Modified:19 Jul 2013 20:05

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