[vsnet-grb-info 26926] GRB 200826A: GMOS-N detected source magnitude (Correction)

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  29029
SUBJECT: GRB 200826A: GMOS-N detected source magnitude (Correction)
DATE:    20/12/11 23:06:21 GMT
FROM:    Tomas Ahumada at U. of Maryland  <tahumada at astro.umd.edu>

Tomas Ahumada (UMD), Harsh Kumar (IITB), Christoffer Fremling (Caltech),
Leo Singer (NASA GSFC) report on behalf of the ZTF and GROWTH
collaborations:

Reanalysing the data used in Ahumada et al. GCN 28727, we provide a revised
magnitude of the source detected in the Gemini Multi-Object Spectrograph
(GMOS-N) i-band image of ZTF20abwysqy/AT2020scz (Ahumada et al. GCN 28295).

We imaged the region of GRB 200826A (GCN 28284) with GMOS-N, mounted on the
Gemini-North 8-meter telescope on Mauna Kea, on three nights: 2020-09-23
(2459115.9675 mjd), 2020-10-10 (2459133.8039 mjd) and 2020-11-08
(2459167.9342 mjd). 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 using HOTPANTS and PyZOGY
independently. We now present the revised magnitudes using a zero-point
calculated using 23 stars in the field from the SDSS catalog. We apologize
for any possible confusion caused by the erroneously reported photometry in
GCN 28727.

In the 2020-09-23 images, a source is detected at the position of the
afterglow with i = 25.49 +- 0.15 mag, but not in r-band up to r > 25.6 AB
mag. In the 2020-10-10 images, we do not detect a transient in either
filter up to a 5-sigma limit of i > 25.4 mag and r > 25.5 mag.

At the 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 = -17.9 AB mag.

We thank the Gemini Observatory Director for awarding this observing time
and the Gemini staff for help with planning and executing the observations.

-- 
Tomas Ahumada (he/him)
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