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12-20-2019
Evidence for Late-stage Eruptive Mass Loss in the Progenitor to Evidence for Late-stage Eruptive Mass Loss in the Progenitor to
SN2018gep, a Broad-lined Ic Supernova: Pre-explosion Emission SN2018gep, a Broad-lined Ic Supernova: Pre-explosion Emission
and a Rapidly Rising Luminous Transient and a Rapidly Rising Luminous Transient
Anna Y.Q. Ho
California Institute of Technology
Daniel A. Goldstein
California Institute of Technology
Steve Schulze
Weizmann Institute of Science Israel
David K. Khatami
University of California, Berkeley
Daniel A. Perley
Liverpool John Moores University
See next page for additional authors
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Recommended Citation Recommended Citation
Ho, A., Goldstein, D., Schulze, S., Khatami, D., Perley, D., Ergon, M., Gal-Yam, A., Corsi, A., Andreoni, I.,
Barbarino, C., Bellm, E., Blagorodnova, N., Bright, J., Burns, E., Cenko, S., Cunningham, V., De, K., Dekany, R.,
Dugas, A., Fender, R., Fransson, C., Fremling, C., Goldstein, A., Graham, M., Hale, D., Horesh, A., Hung, T.,
Kasliwal, M., M. Kuin, N., Kulkarni, S., Kupfer, T., Lunnan, R., & Masci, F. (2019). Evidence for Late-stage
Eruptive Mass Loss in the Progenitor to SN2018gep, a Broad-lined Ic Supernova: Pre-explosion Emission
and a Rapidly Rising Luminous Transient.
Astrophysical Journal, 887
(2) https://doi.org/10.3847/
1538-4357/ab55ec
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Authors Authors
Anna Y.Q. Ho, Daniel A. Goldstein, Steve Schulze, David K. Khatami, Daniel A. Perley, Mattias Ergon,
Avishay Gal-Yam, Alessandra Corsi, Igor Andreoni, Cristina Barbarino, Eric C. Bellm, Nadia Blagorodnova,
Joe S. Bright, E. Burns, S. Bradley Cenko, Virginia Cunningham, Kishalay De, Richard Dekany, Alison Dugas,
Rob P. Fender, Claes Fransson, Christoffer Fremling, Adam Goldstein, Matthew J. Graham, David Hale,
Assaf Horesh, Tiara Hung, Mansi M. Kasliwal, N. Paul M. Kuin, S. R. Kulkarni, Thomas Kupfer, Ragnhild
Lunnan, and Frank J. Masci
This article is available at LSU Digital Commons: https://digitalcommons.lsu.edu/physics_astronomy_pubs/566
PDF hosted at the Radboud Repository of the Radboud University
Nijmegen
The following full text is a publisher's version.
For additional information about this publication click this link.
https://hdl.handle.net/2066/215850
Please be advised that this information was generated on 2021-10-13 and may be subject to
change.
Evidence for Late-stage Eruptive Mass Loss in the Progenitor to SN2018gep, a Broad-
lined Ic Supernova: Pre-explosion Emission and a Rapidly Rising Luminous Transient
Anna Y. Q. Ho
1
, Daniel A. Goldstein
1,27
, Steve Schulze
2
, David K. Khatami
3
, Daniel A. Perley
4
, Mattias Ergon
5
,
Avishay Gal-Yam
2
, Alessandra Corsi
6
, Igor Andreoni
1
, Cristina Barbarino
5
, Eric C. Bellm
7
, Nadia Blagorodnova
8
,
Joe S. Bright
9
, E. Burns
10
, S. Bradley Cenko
11,12
, Virginia Cunningham
13
, Kishalay De
1
, Richard Dekany
14
,
Alison Dugas
1
, Rob P. Fender
9
, Claes Fransson
5
, Christoffer Fremling
15
, Adam Goldstein
16
, Matthew J. Graham
15
,
David Hale
14
, Assaf Horesh
17
, Tiara Hung
18
, Mansi M. Kasliwal
1
, N. Paul M. Kuin
19
, S. R. Kulkarni
1
, Thomas Kupfer
20
,
Ragnhild Lunnan
5
, Frank J. Masci
21
, Chow-Choong Ngeow
22
, Peter E. Nugent
23
, Eran O. Ofek
2
,
Maria T. Patterson
7
, Glen Petitpas
24
, Ben Rusholme
21
, Hanna Sai
25
, Itai Sfaradi
17
, David L. Shupe
21
, Jesper Sollerman
5
,
Maayane T. Soumagnac
2
, Yutaro Tachibana
26
, Francesco Taddia
5
, Richard Walters
1
, Xiaofeng Wang
25
, Yuhan Yao
1
, and
Xinhan Zhang
25
1
Cahill Center for Astrophysics, California Institute of Technology, MC 249-17, 1200 E California Boulevard, Pasadena, CA 91125, USA
2
Department of Particle Physics and Astrophysics, Weizmann Institute of Science, 234 Herzl Street, 76100 Rehovot, Israel
3
Department of Astronomy, University of California, Berkeley, CA 94720, USA
4
Astrophysics Research Institute, Liverpool John Moores University, IC2, Liverpool Science Park, 146 Brownlow Hill, Liverpool L3 5RF, UK
5
The Oskar Klein Centre & Department of Astronomy, Stockholm University, AlbaNova, SE-106 91 Stockholm, Sweden
6
Department of Physics and Astronomy, Texas Tech University, Box 1051, Lubbock, TX 79409-1051, USA
7
DIRAC Institute, Department of Astronomy, University of Washington, 3910 15th Avenue NE, Seattle, WA 98195, USA
8
Department of Astrophysics /IMAPP, Radboud University, Nijmegen, The Netherlands
9
Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
10
NASA Postdoctoral Program Fellow, Goddard Space Flight Center, Greenbelt, MD 20771, USA
11
Astrophysics Science Division, NASA Goddard Space Flight Center, Mail Code 661, Greenbelt, MD 20771, USA
12
Joint Space-Science Institute, University of Maryland, College Park, MD 20742, USA
13
Astronomy Department, University of Maryland, College Park, MD 20742, USA
14
Caltech Optical Observatories, California Institute of Technology, MC 11-17, 1200 E. California Boulevard, Pasadena, CA 91125, USA
15
Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
16
Science and Technology Institute, Universities Space Research Association, Huntsville, AL 35805, USA
17
Racah Institute of Physics, Hebrew University, Jerusalem 91904, Israel
18
Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA
19
Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
20
Kavli Institute for Theoretical Physics, University of California, Santa Barbara, CA 93106, USA
21
IPAC, California Institute of Technology, 1200 E. California Boulevard, Pasadena, CA 91125, USA
22
Graduate Institute of Astronomy, National Central University, 32001, Taiwan
23
Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA
24
Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
25
Physics Department/Tsinghua Center for Astrophysics, Tsinghua University; Beijing, 100084, Peopleʼs Republic of China
26
Department of Physics, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551, Japan
Received 2019 April 24; revised 2019 September 17; accepted 2019 October 1; published 2019 December 18
Abstract
We present detailed observations of ZTF18abukavn (SN2018gep), discovered in high-cadence data from the
Zwicky Transient Facility as a rapidly rising (1.4 ± 0.1 mag hr
−1
) and luminous (
=-M 20
g,peak
mag) transient. It
is spectroscopically classi fied as a broad-lined stripped-envelope supernova (Ic-BL SN). The high peak luminosity
(
´
-
L
310ergs
bol
44 1
), the short rise time (
=t 3days
rise
in g band), and the blue colors at peak (
~-gr 0.4–
)
all resemble the high-redshift Ic-BL iPTF16asu, as well as several other unclassified fast transients. The early
discovery of SN2018gep (within an hour of shock breakout) enabled an intensive spectroscopic campaign,
including the highest-temperature (
T 40,000 K
eff
) spectra of a stripped-envelope SN. A retrospective search
revealed luminous (
~»-MM 14
gr
mag) emission in the days to weeks before explosion, the first definitive
detection of precursor emission for a Ic-BL. We find a limit on the isotropic gamma-ray energy release
<´
g
E
4.9 10 erg
,iso
48
, a limit on X-ray emission
<
-
L
10 erg s
X
40 1
, and a limit on radio emission
n
n
-
L 10 erg s
37 1
. Taken together, we find that the early (
<
10 days
) data are best explained by shock
breakout in a massive shell of dense circumstellar material (0.02
M
) at large radii (
´
3
10 c
m
14
) that was ejected
in eruptive pre-explosion mass-loss episodes. The late-time (
>10 days
) light curve requires an additional energy
source, which could be the radioactive decay of Ni-56.
Key words: methods: observational – shock waves – stars: mass-loss – supernovae: individual – surveys
Supporting material: machine-readable tables
The Astrophysical Journal, 887:169 (24pp), 2019 December 20 https://doi.org/10.3847/1538-4357/ab55ec
© 2019. The American Astronomical Society. All rights reserved.
27
Hubble Fellow.
1
1. Introduction
Recent discoveries by optical time-domain surveys challenge
our understanding of how energy is deposited and transported in
stellar explosions (Kasen 2017). For example, over 50 transients
have been discovered with rise times and peak luminosities too
rapid and too high, respectively, to be explained by radioactive
decay (Poznanski et al. 2010; Drout et al. 2014; Arcavi et al.
2016; Shivvers et al. 2016;Tanakaetal.2016; Pursiainen et al.
2018;Restetal.2018). Possible powering mechanisms include
interaction with extended circumstellar material (CSM; Chevalier
& Irwin 2011), and energy injection from a long-lived central
engine (Kasen & Bildsten 2010; Woosley 2010; Kasen et al.
2016). These models have been difficult to test because the
majority of fast-luminous transients have been discovered post
facto and located at cosmological distances (z∼0.1).
The discovery of iPTF16asu (Wang et al. 2017; Whitesides
et al. 2017) in the intermediate Palomar Transient Factory (iPTF;
Law et al. 2009) showed that at least some of these fast-luminous
transients are energetic (
10 erg
52
) high-velocity (“broad-lined”;
v20,000 km
-
s
1
) stripped-envelope (Ic) supernovae (Ic-BL
SNe). The light curve of iPTF16asu was unusual among Ic-BL
SNe in being inconsistent with
Ni
56
-decay (Cano 2013;Taddia
et al. 2019). Suggested power sources include energy injection by
a magnetar, ejecta-CSM interaction, cooling-envelope emission,
and an engine-driven explosion similar to low-luminosity
gamma-ray bursts—or some combination thereof. Unfortunately,
the high redshift (z=0.187) precluded a definitive conclusion.
Today, optical surveys such as ATLAS (Tonry et al. 2018)
and the Zwicky Transient Facility (ZTF; Bellm et al. 2019a;
Graham et al. 2019) have the areal coverage to discover rare
transients nearby, as well as the cadence to discover transients
when they are young (
<
1day
). For example, the recent
discovery of AT2018cow at 60 Mpc(Smartt et al. 2018;
Prentice et al. 2018) represented an unprecedented opportunity
to study a fast-luminous optical transient up close, in detail, and
in real time. Despite an intense multiwavelength observing
campaign, the nature of AT2018cow remains unknown—
possibilities include an engine-powered stellar explosion
(Prentice et al. 2018; Ho et al. 2019; Margutti et al. 2019;
Perley et al. 2019), the tidal disruption of a white dwarf by an
intermediate-mass black hole (Kuin et al. 2019; Perley et al.
2019), and an electron capture SN (Lyutikov & Toonen 2019).
Regardless of the origin, it is clear that the explosion took place
within dense material (Ho et al. 2019; Margutti et al. 2019;
Perley et al. 2019) confined to
10 c
m
16
(Ho et al. 2019).
Here we present SN2018gep, discovered as a rapidly rising
(1.4 ± 0.1 mag
-
hr
1
) and luminous (
=-M 20
g,peak
) transient in
high-cadence data from ZTF (Ho et al. 2018c). The high inferred
velocities (>20,000 km
-
s
1
), the spectroscopic evolution from a
blue continuum to a Ic-BL SN (Costantin et al. 2018),andthe
rapid rise (
=t 3days
rise
in g band) to high peak luminosity
(
´
-
L
310ergs
bol
44 1
) all suggest that SN2018gep is a low-
redshift (z=0.0315 4) analog to iPTF16asu. The early discovery
enabled an intensive follow-up campaign within the first day of the
explosion, including the highest-temperature (
T
eff
40,000 K)
spectra of a stripped-envelope SN to date. A retrospective search in
ZTF data revealed the first definitive detection of pre-explosion
activity in a Ic-BL.
The structure of the paper is as follows. We present our radio
through X-ray data in Section 2. In Section 3 we outline basic
properties of the explosion and its host galaxy. In Section 4 we
attribute the power source for the light curve to shock breakout
in extended CSM. In Section 5 we compare SN2018gep to
unidentified fast-luminous transients at high redshift. Finally, in
Section 6 we summarize our findings and look to the future.
Throughout the paper, absolute times are reported in UTC and
relative times are reported with respect to t
0
, which is defined in
Section 2.1. We assume a standard ΛCDM cosmology (Planck
Collaboration et al. 2016).
2. Observations
2.1. ZTF Discovery
ZTF observing time is divided between several different
surveys, conducted using a custom mosaic camera (Dekany
et al. 2016) on the 48 inch Samuel Oschin Telescope (P48) at
Palomar Observatory. See Bellm et al. (2019a) for an overview
of the observing system, Bellm et al. (2019b) for a description
of the surveys and scheduler, and Masci et al. (2019) for details
of the image processing system.
Every 5σ point-source detection is saved as an “alert.” Alerts
are distributed in avro format (Patterson et al. 2019) and can be
filtered based on a machine learning–based real-bogus metric
(Duev et al. 2019; Mahabal et al. 2019), light-curve properties,
and host characteristics (including a star-galaxy classifier;
Tachibana & Miller 2018). The ZTF collaboration uses a web-
based system called the GROWTH marshal (Kasliwal et al.
2019) to identify and keep track of transients of interest.
ZTF18abukavn was discovered in an image obtained at UT
2018 September 9 03:55:18 (start of exposure) as part of the
ZTF extragalactic high-cadence partnership survey, which
covers 1725 deg
2
in six visits (3g,3r) per night (Bellm et al.
2019b). The discovery magnitude was
=
r
20.5 0.3 mag
,
and the source position was measured to be
a = 16 43 48.22
hm
s
,
d
=+41 02 43. 4
dm
s
(J2000), coincident with a compact galaxy
(Figure 1) at
=
z
0.0315
4
or
»
d
143 Mpc
. As described in
Section 2.3, the redshift was unknown at the time of discovery;
we measured it from narrow galaxy emission lines in our
follow-up spectra. The host redshift along with key observa-
tional properties of the transient are listed in Table 1.
As shown in Figure 2, the source brightened by over two
magnitudes within the first three hours. These early detections
passed a filter written in the GROWTH marshal that was
Figure 1. The position of SN2018gep (white crosshairs) in its host galaxy.
Images from the Canada–Fra nce–Hawaii Telescope Legacy Survey (2004–2012),
combined using the prescription in Lupton et al. (2004).
2
The Astrophysical Journal, 887:169 (24pp), 2019 December 20 Ho et al.
