[vsnet-grb-info 26195] GRB200826A: Zwicky Transient Facility Identifies Optical Afterglow Candidate of a Fermi Short GRB (Trigger 620108997)

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  28295
SUBJECT: GRB200826A: Zwicky Transient Facility Identifies Optical Afterglow Candidate of a Fermi Short GRB (Trigger 620108997)
DATE:    20/08/27 16:42:00 GMT
FROM:    Tomas Ahumada at U. of Maryland  <tahumada at astro.umd.edu>

Tomas Ahumada (UMD), Shreya Anand (Caltech), Robert Stein (DESY), Harsh
Kumar (IITB), Ana Sagues Carracedo (OKC), Igor Andreoni (Caltech), Michael
Coughlin (UMN), Leo Singer (NASA/GSFC), Mansi Kasliwal (Caltech), Daniel
Perley (LJMU), Brad Cenko (NASA/GSFC), Varun Bhalerao (IITB), David Kaplan
(UWM) on behalf of the Zwicky Transient Facility (ZTF) and Global Relay of
Observatories Watching Transients Happen (GROWTH) collaborations

We continued a second night of monitoring the localization region of the
short GRB200826A (Fermi trigger 620108997; GCN 28284, 28287) with the
Zwicky Transient Facility (first night summary in Sagues Carracedo et al.
GCN 28293). Each exposure was 600s, reaching a g-band median depth of 22.3
mag and r-band median depth of 22.3 mag. IPN also triangulated this GRB
(Hurley et al. GCN 28291). Our total coverage was >99% of the joint
Fermi-IPN localization.

We followed standard candidate vetting procedures. We identify the
following compelling candidate for the optical afterglow:

+-------------------------------------------------------------------------------------------------+
| ZTF Name      | IAU Name  | RA (deg)  | DEC (deg)   | Filter | Mag   |
MagErr |MJD              |
+---------------+-----------+-----------+-------------+--------+-------+--------+-----------------+
| ZTF20abwysqy  | AT2020scz | 6.7855741 | +34.0273043 |   g    | 20.86 |
0.04   | 2459087.9181366 |
+---------------+-----------+-----------+-------------+--------+-------+--------+-----------------+

ZTF20abwysqy faded by >1.7 mag in 22.5 hours in the g-band. We ran forced
photometry and we obtained the following light curve:

+----------+--------+-------+--------+--------+
Time (Hrs) | Filter | Mag   | MagErr | Limmag |
+----------+--------+-------+--------+--------+
|    5.07  | g      | 20.86 | 0.048  | 22.50  |
|    5.53  | r      | 20.70 | 0.050  | 22.28  |
|    6.67  | g      | 20.96 | 0.168  | 21.24  |
|    27.5  | g      | -     | -      | 22.53  |
|    29.1  | r      | -     | -      | 21.31  |
|    30.9  | g      | -     | -      | 21.21  |
+----------+--------+-------+--------+--------+

ZTF20abwysqy is spatially coincident with X-ray Source 3 reported by the
Neil Gehrels Swift Observatory (GCN 28290,
https://www.swift.ac.uk/xrt_products/TILED_GRB00093/) with a separation of
2" from the XRT position that has an uncertainty of 2.7". It also has a
faint underlying galaxy counterpart within 0.35" (Legacy Survey (LS) DR8
photometric redshift z = 0.714 +- 0.137 and LS DR8 r-mag = 22.55). We
strongly encourage multi-wavelength follow-up.


ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; IPAC,
USA, WIS, Israel; OKC, Sweden; JSI/UMd, USA; U Washington, USA; DESY,
Germany; MOST, Taiwan; UW Milwaukee, USA; LANL USA; Tokyo Tech, Japan;
IITB, India; IIA, India; LJMU, UK; TTU, USA; SDSU, USA and USyd, Australia.
ZTF acknowledges the generous support of the NSF under AST MSIP Grant No
1440341.
GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949.
Alert distribution service provided by DIRAC at UW (Patterson et al. 2019).
Alert database searches are done by AMPEL (Nordin et al. 2019) and Kowalski
(Duev et al. 2019).


-- 
Tomás Ahumada (he/his)
Ph.D. Student
Department of Astronomy
University of Maryland, College Park
NASA <tomas.f.ahumdamena at nasa.gov> Goddard Space Flight Center, Code 661
B.Sc. Astronomy, Pontificia Universidad Católica de Chile