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X-Rays from the Location of the Double-humped Transient ASASSN-15lh

Margutti, R. and Metzger, B. D. and Chornock, R. and Milisavljevic, D. and Berger, E. and Blanchard, P. K. and Guidorzi, C. and Migliori, G. and Kamble, A. and Lunnan, R. and Nicholl, M. and Coppejans, D. L. and Dall’Osso, S. and Drout, M. R. and Perna, R. and Sbarufatti, B. (2017) X-Rays from the Location of the Double-humped Transient ASASSN-15lh. Astrophysical Journal, 836 (1). Art. No. 25. ISSN 0004-637X. PMCID PMC5619250.

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We present the detection of persistent soft X-ray radiation with L_x ~ 10^(41)-10^(42) erg s^(-1) at the location of the extremely luminous, double-humped transient ASASSN-15lh as revealed by Chandra and Swift. We interpret this finding in the context of observations from our multiwavelength campaign, which revealed the presence of weak narrow nebular emission features from the host-galaxy nucleus and clear differences with respect to superluminous supernova optical spectra. Significant UV flux variability on short timescales detected at the time of the rebrightening disfavors the shock interaction scenario as the source of energy powering the long-lived UV emission, while deep radio limits exclude the presence of relativistic jets propagating into a low-density environment. We propose a model where the extreme luminosity and double-peaked temporal structure of ASASSN-15lh is powered by a central source of ionizing radiation that produces a sudden change in the ejecta opacity at later times. As a result, UV radiation can more easily escape, producing the second bump in the light curve. We discuss different interpretations for the intrinsic nature of the ionizing source. We conclude that, if the X-ray source is physically associated with the optical–UV transient, then ASASSN-15lh most likely represents the tidal disruption of a main-sequence star by the most massive spinning black hole detected to date. In this case, ASASSN-15lh and similar events discovered in the future would constitute the most direct probes of very massive, dormant, spinning, supermassive black holes in galaxies. Future monitoring of the X-rays may allow us to distinguish between the supernova hypothesis and the hypothesis of a tidal disruption event.

Item Type:Article
Related URLs:
URLURL TypeDescription CentralArticle Paper
Margutti, R.0000-0003-4768-7586
Metzger, B. D.0000-0002-4670-7509
Chornock, R.0000-0002-7706-5668
Milisavljevic, D.0000-0002-0763-3885
Berger, E.0000-0002-9392-9681
Guidorzi, C.0000-0001-6869-0835
Migliori, G.0000-0003-0216-8053
Kamble, A.0000-0003-0861-5168
Lunnan, R.0000-0001-9454-4639
Nicholl, M.0000-0002-2555-3192
Coppejans, D. L.0000-0001-5126-6237
Drout, M. R.0000-0001-7081-0082
Additional Information:© 2017 The American Astronomical Society. Received 2016 September 27; revised 2016 November 27; accepted 2016 November 28; published 2017 February 6. We thank the referee for constructive criticism and suggestions that improved the quality of this work. R.M. acknowledges partial support from the James Arthur Fellowship at NYU during the completion of this project and the Research Corporation for Science Advancement. B.D.M. gratefully acknowledges support from the NSF (AST-1410950, AST-1615084), NASA Astrophysics Theory Program (NNX16AB30G), the Alfred P. Sloan Foundation, and the Research Corporation for Science Advancement. G.M. acknowledges the financial support from the UnivEarthS Labex program of Sorbonne Paris Cité (ANR10LABX0023 and ANR11IDEX000502). The scientific results reported in this article are based on observations made by the Chandra X-ray Observatory under program GO 17500103, PI Margutti, observations IDs 17879, 17880, 17881, 17882. This paper includes data gathered with the 6.5 meter Magellan Telescopes located at Las Campanas Observatory, Chile. Facility: Magellan:Clay.
Funding AgencyGrant Number
New York University (NYU)UNSPECIFIED
Research CorporationUNSPECIFIED
Alfred P. Sloan FoundationUNSPECIFIED
Agence Nationale pour la Recherche (ANR)ANR10LABX0023
Agence Nationale pour la Recherche (ANR)ANR11IDEX000502
Subject Keywords:supernovae: individual (ASASSN-15lh)
Issue or Number:1
PubMed Central ID:PMC5619250
Record Number:CaltechAUTHORS:20170206-103036074
Persistent URL:
Official Citation:R. Margutti et al 2017 ApJ 836 25
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:74072
Deposited By: Tony Diaz
Deposited On:06 Feb 2017 20:36
Last Modified:15 Apr 2020 22:40

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