J/ApJ/836/25 Swift UVOT light curves of ASASSN-15lh (Margutti+, 2017)
X-rays from the location of the double-humped transient ASASSN-15lh.
Margutti R., Metzger B.D., Chornock R., Milisavljevic D., Berger E.,
Blanchard P.K., Guidorzi C., Migliori G., Kamble A., Lunnan R., Nicholl M.,
Coppejans D.L., Dall'Osso S., Drout M.R., Perna R., Sbarufatti B.
<Astrophys. J., 836, 25-25 (2017)>
=2017ApJ...836...25M 2017ApJ...836...25M (SIMBAD/NED BibCode)
ADC_Keywords: Photometry, ultraviolet ; Photometry, UBV ; Supernovae
Keywords: supernovae: individual: ASASSN-15lh
Abstract:
We present the detection of persistent soft X-ray radiation with
Lx∼1041-1042erg/s 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.
Description:
We obtained four epochs of deep X-ray observations of ASASSN-15lh with
the Chandra X-ray Observatory (CXO) on 2015 November 12 (exposure of
10ks), 2015 December 13 (10ks), 2016 February 20 (40ks), and 2016
August 19 (30 ks, PI Margutti), corresponding to δt=129.4d,
δt=154.6, δt=210.5d, and δt=357.8d rest-frame since
optical maximum light, which occurred on 2015 June 5.
We reprocessed all the X-ray data collected by the Swift-XRT and all
the Swift-UVOT observations obtained from 2015 June 24 until 2016 July
22.
A partial collection of the Swift-UVOT photometry of ASASSN-15lh has
already been presented by Dong+ (2016Sci...351..257D 2016Sci...351..257D), Godoy-Rivera+
(2017MNRAS.466.1428G 2017MNRAS.466.1428G), Brown+ (2016, J/ApJ/828/3), and Leloudas+
(2016NatAs...1E...2L 2016NatAs...1E...2L). Here we update the observations and focus on
the presence of significant temporal variability that appears at the
time of the rebrightening.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
22 02 15.45 -61 39 34.6 ASASSN-15lh = SN 2015L
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 119 75 Swift UVOT photometry
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See also:
B/chandra : The Chandra Archive Log (CXC, 1999-2014)
B/xmm : XMM-Newton Log (XMM-Newton Science Operation Center, 2012)
B/sn : Asiago Supernova Catalogue (Barbon et al., 1999-)
VIII/76 : Leiden/Argentine/Bonn (LAB) Survey of Galactic HI (Kalberla+ 2005)
J/AJ/137/4517 : UVOT light curves of supernovae (Brown+, 2009)
J/MNRAS/412/1419 : Nearby supernova rates (Leaman+, 2011)
J/ApJ/746/156 : Radio afterglow observations of GRBs (Chandra+, 2012)
J/MNRAS/428/729 : GRB Swift X-ray light curves analysis (Margutti+, 2013)
J/ApJ/794/23 : Pan-STARRS1 transients optical photometry (Drout+, 2014)
J/ApJ/828/3 : Swift obs. of the superluminous SNI ASASSN-15lh (Brown+, 2016)
J/ApJ/817/103 : Swift/XRT LC of Swift J164449.3+573451 (Mangano+, 2016)
J/ApJ/830/13 : Host-galaxy NUV-NIR data of superluminous SNe (Perley+, 2016)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 8 F8.2 d MJD-v ? Observation date, Modified Julian Date, vmag
10- 14 F5.2 mag vmag [16.8/19]? Swift/UVOT v band Vega magnitude
16- 19 F4.2 mag e_vmag [0.07/0.6]? Uncertainty in vmag
21- 28 F8.2 d MJD-b ? Observation date, Modified Julian Date, bmag
30- 34 F5.2 mag bmag [16.7/19.5]? Swift/UVOT b band Vega magnitude
36- 39 F4.2 mag e_bmag [0.04/0.3]? Uncertainty in bmag
41- 48 F8.2 d MJD-u ? Observation date, Modified Julian Date, umag
50- 54 F5.2 mag umag [15.3/18]? Swift/UVOT u band Vega magnitude
56- 59 F4.2 mag e_umag [0.03/0.2]? Uncertainty in umag
61- 68 F8.2 d MJD-w1 ? Observation date, Modified Julian Date, w1mag
70- 74 F5.2 mag w1mag [15.2/18]? Swift/UVOT w1 band Vega magnitude
76- 79 F4.2 mag e_w1mag [0.04/0.2]? Uncertainty in w1mag
81- 88 F8.2 d MJD-w2 ? Observation date, Modified Julian Date, w2mag
90- 94 F5.2 mag w2mag [15.6/18.5]? Swift/UVOT w2 band Vega magnitude
96- 99 F4.2 mag e_w2mag [0.04/0.2]? Uncertainty in w2mag
101-108 F8.2 d MJD-m2 ? Observation date, Modified Julian Date, m2mag
110-114 F5.2 mag m2mag [15.2/18.3]? Swift/UVOT m2 band Vega magnitude
116-119 F4.2 mag e_m2mag [0.04/0.2]? Uncertainty in m2mag
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 07-Sep-2017