{
  "circularId": 37454,
  "submitter": "Gregory Paek at Seoul National University <gregorypaek94@gmail.com>",
  "bibcode": "2024GCN.37454....1P",
  "subject": "GRB 240825A: 7DT Optical Upper Limit",
  "createdOn": 1726051082611,
  "eventId": "GRB 240825A",
  "format": "text/plain",
  "body": "Gregory S.H. Paek (SNU ARC/SNU), Myungshin Im (SNU ARC/SNU), Hyeonho Choi (SNU ARC/SNU), Seo-Won Chang (SNU ARC/SNU), and Ji Hoon Kim (SNU ARC/SNU) report on behalf of the 7-Dimensional Telescope collaboration\n\nWe searched for the bright optical counterpart of the gamma-ray burst, GRB240825A (Fermi GBM team, GCN 37273; Gupta et al., GCN 37274) using the 7-Dimensional Telescopes (7DT). Approximately 10 hours following the initial detection (2024-08-25T15:53:00 UTC), we targeted the UVOT coordinate (Gupta et al., GCN 37274). Observations were made with nine 7DT units in medium-band filters, denoted as m400, m425, then through m825, in which the numeric values indicate their central wavelengths in nanometers. Each filter has a bandwidth of 25nm. In the preliminary result, no significant signal was found. Photometric flux calibration was performed using synthetic photometries derived from the Gaia DR3 XP catalog (Gaia Collaboration et al. 2022) within the AB magnitude system. The first unit of 7DT (m400 and m425 filters) temporarily experienced an electronic issue with the camera, resulting in relatively low sensitivity.\n\n------\nFilter Date-obs[UT] Exp.time[s] Depth(5sigma)\nm400 2024-08-26T01:54:47 300 15.415\nm425 2024-08-26T02:00:23 300 17.851\nm450 2024-08-26T01:54:43 300 19.651\nm475 2024-08-26T02:00:09 300 19.790\nm500 2024-08-26T01:54:42 300 19.952\nm525 2024-08-26T02:00:07 300 19.883\nm550 2024-08-26T01:54:43 300 19.304\nm575 2024-08-26T02:00:10 300 19.456\nm600 2024-08-26T01:54:48 300 19.313\nm625 2024-08-26T02:00:21 300 18.892\nm650 2024-08-26T01:54:44 300 19.068\nm675 2024-08-26T02:00:09 300 19.156\nm700 2024-08-26T01:54:39 300 19.041\nm725 2024-08-26T02:00:02 300 18.658\nm750 2024-08-26T01:54:48 300 18.258\nm775 2024-08-26T02:00:14 300 17.792\nm850 2024-08-26T01:54:46 300 17.067\nm875 2024-08-26T02:00:11 300 16.834\n\nThe 7-Dimensional Telescope (7DT), comprising 20 wide-field telescopes equipped with 40 medium-bandwidth (~25nm) filters located in Chile, aims to detect optical counterparts of GW sources and conduct the 7-Dimensional Sky Survey (7DS) of the Southern Hemisphere. Further information about the 7DT is available at http://gwuniverse.snu.ac.kr/.",
  "submittedHow": "web"
}