TITLE: GCN CIRCULAR NUMBER: 36746 SUBJECT: GRB240615A: Gemini-North observations of the BAT and XRT positions DATE: 24/06/24 19:59:01 GMT FROM: Jillian Rastinejad at Northwestern Univ. jillianrastinejad2024@u.northwestern.edu

Jillian Rastinejad, Wen-fai Fong and Charles D. Kilpatrick (Northwestern) report on behalf of a larger collaboration:

We observed the location of the short-duration GRB 240615A (Fermi GBM Team GCN 36671, DeLaunay et al. GCN 36672, Frederiks et al. GCN 36677, Tan et al. GCN 36682) with the 5.5 arcminute square field of view Gemini Multi-Object Spectrograph (GMOS) mounted on Gemini-North (PI: Fong). We obtained two epochs of i-band imaging, each consisting of two pointings, at 2.8 and 4.8 days post-burst. Our first pointing was centered at R.A. = 21:44:39.51, Decl. = 38:35:31.2 (J2000), the approximate intersection of the IPN and BAT localizations (DeLaunay et al. GCN 36672, Kozyrev et al. GCN 36726). The second pointing was centered on XRT Source 1 (Page et al. GCN 36683). Observations were taken at a median airmass of 1.1 and in <0.8'' seeing. We perform image subtraction between the two epochs using HOTPANTS (Becker et al. 2015). Following visual inspection, we do not detect a clear optical afterglow in either pointing, though we note the presence of several residuals from saturated stars in the first pointing. Calibrated to Pan-STARRS1, we place an upper limit on an optical afterglow within these pointings at 2.8 days post-burst of i > 25.7 AB mag, not corrected for Galactic extinction.

Our observations covered the location of the optical Source 1 reported in Busmann et al. GCN 36706. We detect the source in both epochs. We do not obtain a significant residual at the position of the source following image subtraction.

We thank Aaron Tohuvavohu for helpful communication on the burst pointings and Jennifer Andrews and Kristin Chiboucas for the rapid planning and execution of these observations.

View this GCN Circular online at https://gcn.nasa.gov/circulars/36746. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...