ZTF21aakruew
GCN Circular 29508
Subject
ZTF21aakruew/AT2021cwd: ZTF and LT discovery of a hostless, red, and rapidly fading optical transient
Date
2021-02-14T00:31:34Z (4 years ago)
From
Anna Ho at UC Berkeley <annayqho@berkeley.edu>
Yuhan Yao (Caltech), Daniel Perley (LJMU), Anna Ho (UCB) on behalf of the
Zwicky Transient Facility (ZTF) collaboration:
We report the discovery two nights ago of the fast optical transient
ZTF21aakruew/AT2021cwd in Zwicky Transient Facility (ZTF, Bellm et al.
2019, Graham et al. 2019) data at coordinates (J2000):
RA = 10:24:42.16 (156.17566 deg)
Dec = +11:36:40.98 (+11.61138 deg)
ZTF21aakruew was first detected at g=19.64+/-0.10 mag in an image obtained
at 2021-02-12 08:52.4 UT as part of the 2-day cadence public survey, and
passed a filter designed to find fast transients (Ho et al. 2020, ApJ, 905,
2). The most recent upper limit was one night prior: r > 20.93 mag on
2021-02-11 07:59.6 UT in an image obtained for reference construction.
Liverpool Telescope (LT) follow-up photometry showed that the source faded
by ~2.1 mag in r-band in the next 0.9 days. The transient was most recently
detected in an LT image on 2021-02-13 22:49 UT at r = 22.42 +/- 0.21 mag.
The color appears to be red, with g-r~0.9 on 2021-02-13 and low extinction
along the line of sight (E(B-V)=0.04 mag; Planck Collaboration et al.,
2015).
There do not appear to be any reported GRBs consistent with the position of
ZTF21aakruew during the interval between the last non-detection and the
first detection. No counterpart is visible in deep Legacy Survey
pre-imaging (>24 mag; Dey et al. 2019, ApJ, 157, 5).
We encourage spectroscopic classification and multi-wavelength follow-up of
ZTF21aakruew.
ZTF is supported by the National Science Foundation under Grant No.
AST-2034437 and a collaboration including Caltech, IPAC, the Weizmann
Institute for Science, the Oskar Klein Center at Stockholm University, the
University of Maryland, Deutsches Elektronen-Synchrotron and Humboldt
University, the TANGO Consortium of Taiwan, the University of Wisconsin at
Milwaukee, Trinity College Dublin, Lawrence Livermore National
Laboratories, and IN2P3, France. Operations are conducted by COO, IPAC, and
UW. Alert distribution service provided by DIRAC@UW (Patterson et al.
2019). Alert database searches are performed using Kowalski (Duev et al.
2019).
GCN Circular 29528
Subject
ZTF21aakruew/AT2021cwd: GROND observations
Date
2021-02-18T12:18:01Z (4 years ago)
Edited On
2025-04-09T18:45:13Z (2 months ago)
From
Ana Nicuesa at TLS Tautenburg <ana@tls-tautenburg.de>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Tyler Barna at University of Minnesota <tylerpbarna@gmail.com>
A. Nicuesa Guelbenzu and S. Klose (both TLS Tautenburg) report:
We observed the field of the optical transient ZTF21aakruew/AT2021cwd (Yao
et al., GCN 29508) that was located inside the error box of GRB 210212B
(Svinkin et al., GCN 29511) with GROND (Greiner et al. 2008, PASP 120,
405) mounted at the 2.2m MPG telescope at the ESO La Silla Observatory
(Chile).
Observations were performed at 5:00 UT (midtime) on February 15, 2021,
about 3.1 days after the GRB 210212B trigger. They were executed at an
average seeing of 1.15 arcsec and at an average airmass of 1.3.
The optical transient is detected in the optical but not in the NIR bands.
Based on a 33 min exposure in g'r'i'z' and 30 min in JHK, and we measure
the following preliminary AB magnitudes and upper limits (3 sigma):
g' = 24.16 +/- 0.14,
r' = 23.63 +/- 0.12,
i' = 23.41 +/- 0.21,
z' > 23.3,
J > 21.7,
H > 21.1,
K > 18.1,
calibrated against SDSS and 2MASS field stars. The observed r'-band
magnitude is formally consistent with the observations reported by
Pozanenko et al. (GCN 29512).
After correction for Galactic extinction (E(B-V)=0.04 mag; Ho et al., GCN
29508), the data are in agreement with an SED that follows a power law. We
consider this as evidence that the transient was indeed afterglow light,
confirming its suggested association with GRB 210212B (Svinkin et al., GCN
29511; Svinkin et al., GCN 29514).
We thank R. Lechaume (PUC) for performing the observations.