J/ApJ/922/247 ZTF photometric measurements of AT 2018lqh (Ofek+, 2021)
AT 2018lqh and the nature of the emerging population of day-scale duration
optical transients.
Ofek E.O., Adams S.M., Waxman E., Sharon A., Kushnir D., Horesh A., Ho A.,
Kasliwal M.M., Yaron O., Gal-Yam A., Kulkarni S.R., Bellm E., Masci F.,
Shupe D., Dekany R., Graham M., Riddle R., Duev D., Andreoni I.,
Mahabal A., Drake A.
<Astrophys. J., 922, 247 (2021)>
=2021ApJ...922..247O 2021ApJ...922..247O
ADC_Keywords: Transient; Photometry; Optical
Keywords: Supernovae ; Burst astrophysics ; Neutron stars
Abstract:
We report on the discovery of AT 2018lqh (ZTF 18abfzgpl)-a rapidly
evolving extragalactic transient in a star-forming host at 242Mpc. The
transient g-band light curve's duration above a half-maximum light is
about 2.1 days, where 0.4/1.7 days are spent on the rise/decay,
respectively. The estimated bolometric light curve of this object
peaked at about 7x1042erg/s --roughly 7 times brighter than the
neutron star (NS)-- NS merger event AT 2017gfo. We show that this
event can be explained by an explosion with a fast (v∼0.08c) low-mass
(∼0.07M☉) ejecta, composed mostly of radioactive elements. For
example, ejecta dominated by 56Ni with a timescale of t0∼1.6d for
the ejecta to become optically thin for γ-rays fits the data
well. Such a scenario requires burning at densities that are typically
found in the envelopes of neutron stars or the cores of white dwarfs.
A combination of circumstellar material (CSM) interaction power at
early times and shock cooling at late times is consistent with the
photometric observations, but the observed spectrum of the event may
pose some challenges for this scenario. We argue that the observations
are not consistent with a shock breakout from a stellar envelope,
while a model involving a low-mass ejecta ramming into low-mass CSM
cannot explain both the early- and late-time observations.
Description:
The Zwicky Transient Facility (ZTF) is a sky survey utilizing the
48-inch (P48) Schmidt telescope on Mount Palomar, equipped with a
47deg2 camera. One of its programs entailed the scanning of about
1500deg2, at least three times per night. The ZTF project also
utilizes the Palomar 60 inch (P60) telescope, equipped with the
Spectroscopic Energy Distribution Machine and Rainbow camera.
AT 2018lqh was first automatically detected by ZTF on 2018 July 12
(JD2458311.6850).
In addition to the ZTF photometry, we obtained Keck/LRIS BVRI imaging
of the source on 2018 September 10 and 2019 March 7 (61d and 239d
after ts, respectively).
A few hours after the first detection, we obtained a spectrum (at
JD2458311.9389; 1.6d after ts) of the event using the Low Resolution
Imaging Spectrograph (LRIS) mounted on the Keck I 10m telescope.
See Section 2.2.
We observed the field of AT 2018lqh using the AMI Large Array (AMI-LA)
radio telescope at a central frequency of 15.5GHz (5GHz bandwidth)
with a synthesized beam size of ∼30". Overall, we carried out six
AMI-LA observations starting on 2018 December 19, about 160 days after
optical detection, and up to 2019 February 15.
Following the results from the AMI-LA observation, we undertook a
radio observation of AT 2018lqh at a higher angular resolution using
the Jansky Very Large Array (JVLA) under the director discretionary
time program 19A-452. The VLA observations were carried out on
2019-February-14 (218 days after ts), in both 5GHz (C band) and 13GHz
(Ku band).
The Ku-band observation resulted in a null detection with a 3σ
limit of 36uJy. A null detection was also the result of the C-band
observations with a 3σ limit of 21uJy, although a weak (∼35uJy)
point source was detected approximately 3" away from the optical
position of AT 2018lqh. See Section 2.3.
On 2019 February 11 (215 days after ts), we obtained a 9574s
integration of the source using Swift-XRT. See Section 2.4.
Throughout the paper, we assume the light curve and spectrum were
affected by a Galactic extinction with a reddening of EB-V=0.019mag
(Schlegel+ 1998ApJ...500..525S 1998ApJ...500..525S) and assume an extinction law with
RV=3.08 (Cardelli+ 1989ApJ...345..245C 1989ApJ...345..245C ; see Section 2.2).
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
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16 06 04.47 +36 52 16.5 AT 2018lqh = ZTF18abfzgpl
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 45 663 ZTF photometric measurements of AT 2018lqh
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See also:
J/ApJ/763/42 : X-ray emission from 28 SNe (IIn, Ibn or SLSN-I) (Ofek+, 2013)
J/ApJ/768/47 : Swift/XRT 0.2-10keV observations of SN2009ip (Ofek+, 2013)
J/other/Nat/494.65 : SN 2010mc outburst before explosion (Ofek+, 2013)
J/ApJ/794/23 : Pan-STARRS1 transients optical photometry (Drout+, 2014)
J/ApJ/788/154 : Palomar Transient Factory SNe IIn photometry (Ofek+, 2014)
J/ApJ/789/104 : SNe IIn observations and properties (Ofek+, 2014)
J/ApJ/781/42 : Optical photometry of SN 2010jl (Ofek+, 2014)
J/ApJ/819/35 : Light curves of 4 transients from PTF & SNLS (Arcavi+, 2016)
J/MNRAS/481/894 : Rapidly evolving transients in the DES (Pursiainen+, 2018)
J/A+A/631/A147 : Transient processing and analysis using AMPEL (Nordin+, 2019)
J/ApJ/912/46 : ZTF Type II supernovae with follow-up obs. (Bruch+, 2021)
J/ApJ/907/99 : Pre-explosion light curve of 227 SNe (Strotjohann+, 2021)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 9 F9.4 d JD [8222.9/8569.1] Julian Date; JD-2450000
11 I1 --- Band [1/3] Bandpass used in observation (1)
13- 19 F7.2 ct Count [-336/279] Counts in subtracted image
21- 26 F6.2 ct e_Count [15/180] Error in Count
28- 33 F6.3 mag ZP [25.66/26.33] Photometric zero point; AB mag
35- 39 F5.2 mag mag [20.21/30.04] Apparent AB magnitude Band;
sinh-mag/Luptitudes
41- 45 F5.2 --- S/N [0/13.7] Signal-to-Noise of measurements
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Note (1): Band 1 and 2 are g and r, respectively.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 31-Mar-2023