TITLE:   GCN CIRCULAR
NUMBER:  28026
SUBJECT: GRB 200623A: MMT observations at XRT Source #3
DATE:    20/06/24 21:47:34 GMT
FROM:    Jillian Rastinejad at Northwestern Univ.  <jillianrastinejad2024@u.northwestern.edu>

J. Rastinejad, Y. Dong, W. Fong, K. Paterson, and A. Rouco Escorial (Northwestern) report:

"We observed the location of the short-duration GRB 200623A at the position of XRT source #3 (Tohuvavohu et al. GCN 28023) within the GRB localization (Fermi GBM Team GCN 28011, DeLaunay et al. GCN 28013) with the MMTCam mounted on the MMT 6.5-meter telescope on Mount Hopkins, Arizona. We acquired 18 x 120-sec observations in the r-band at a mid-time of 2020 June 24.18 UT (25.03 hrs post-burst). The observations have a mean airmass of 1.11, seeing of 1.36", and were taken in thin clouds.

In the vicinity of the XRT Source #3 position, we detect several sources that are also apparent in SDSS and Pan-STARRs imaging. We find the brightest nearby galaxy, SDSS J160758.62+532842.2 (D’Avanzo et al. GCN 28021) to be consistent with the catalogued magnitude in SDSS (Alam et al. 2015). At the position of the XRT source, the 3-sigma limiting magnitude within the error circle is r > 23.1 AB magnitude, calibrated to SDSS and not corrected for Galactic Extinction. We note that our imaging was not deep enough to detect the faint source found by D’Avanzo et al. (GCN 28021).

Further observations are planned. We thank the MMT staff for their assistance with planning and executing these observations."

[GCN OPS NOTE(24jun20): Per author's request, "GRB 200624A: " was added to the SUBJECT field of the circular.]