[vsnet-grb-info 26627] GRB200826A: GMOS-N detection of a supernova bump

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  28727
SUBJECT: GRB200826A: GMOS-N detection of a supernova bump
DATE:    20/10/21 18:40:54 GMT
FROM:    Tomas Ahumada at U. of Maryland  <tahumada at astro.umd.edu>

Tomas Ahumada (UMD), Leo Singer (NASA GSFC), Harsh Kumar (IITB), and Simeon
Reusch (DESY) report on behalf of the ZTF and GROWTH collaborations:

We imaged position of ZTF20abwysqy/AT2020scz (Ahumada et al. GCN 28295),
the afterglow of GRB 200826A (GCN 28284) with the Gemini Multi-Object
Spectrograph (GMOS-N) mounted on the Gemini-North 8-meter telescope on
Mauna Kea, on 2020-09-23 and 2020-10-10.

Each epoch consisted of 14 r- and i- band 200s exposures. We reduced and
co-added the images from each epoch using DRAGONS, a Python-based data
reduction platform provided by the Gemini Observatory. We subtracted the
coadded images of the two epochs using HOTPANTS. A source is detected on
2020-09-23 at the position of the afterglow with i = 23.9 AB mag and r >
23.5 AB mag.

At host galaxy's redshift of z = 0.7481 (GCN 28319) and assuming Planck
2015 cosmological parameters, the absolute magnitude of the GMOS-N
detection is M_i = -19.5 AB mag. At this time, a kilonova would have an
absolute magnitude of M_i >~ -14.5 AB mag whereas a SN1998bw-like supernova
would have an absolute magnitude of M_i ~ -19 AB mag. Since the GMOS-N
detection is consistent with a supernova but not a kilonova, we conclude
that GRB 200826A was powered by a collapsar rather than a neutron star
merger.

We thank the Gemini Observatory Director for awarding this observing time
and the Gemini staff for help with planning and for executing the
observations.
-- 
Tomas Ahumada (he/him)
Ph.D. Student
Department of Astronomy
University of Maryland, College Park
NASA Goddard Space Flight Center, Code 661
B.Sc. Astronomy, Pontificia Universidad Católica de Chile