[vsnet-grb-info 25936] GRB 200623A: Further MMTCam Observations of XRT Source #3

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  28036
SUBJECT: GRB 200623A: Further MMTCam Observations of XRT Source #3
DATE:    20/06/27 23:23:16 GMT
FROM:    Wen-fai Fong at Northwestern U  <wfong at northwestern.edu>

W. Fong (Northwestern) reports:

"We re-visited the location of XRT source #3 of the short GRB 200623A (Fermi-GBM Collab. et al., GCN 28011; DeLaunay et al., GCN 28013; Tohuvavohu et al., GCN 28023) with the MMT/MMTCam at a mid-time of 2020 June 26.176 UT (3.04 days post-burst and 2.0 days after our initial observations: Rastinejad et al., GCN 28026). We acquired 21x120-sec of r-band imaging in 0.88" seeing, and the 3-sigma depth of our image is 24.4 AB mag.

Upon inspection of the XRT source #3 position (90% confidence), we detect the faint optical source first reported in TNG observations (D'Avanzo et al.; GCN 28021) with r = 24.3 +/- 0.3 mag, at the same flux level as previous detections. In addition to a few catalogued sources, we report on an additional source toward the Eastern edge of the XRT position and in the wings of the bright star, with RA = 16:07:59.64, Dec = +53:28:43.6 (J2000) and r~22.2 AB mag. This source was marginally detected in our previous set of imaging although partially blended with the bright star, and it is not possible to discern at present whether this source is point-like or extended in nature. Finally, we do not detect the extended LBT source at the center of the XRT position (Rossi and D'Avanzo et al., GCN 28034), likely due to lack of sensitivity.

We perform image subtraction relative to our previous epoch, and do not detect any significant residuals. Thus, we find no evidence for significant variability in or around the XRT source #3 position, enabling a limit of r > 23.0 AB mag at 25.03 hrs post-burst on optical afterglow emission associated with this XRT candidate (c.f., Rastinejad et al., GCN 28026).

We thank Nelson Caldwell and Michael Calkins at the MMT for the rapid scheduling and execution of these observations."