{
  "subject": "Swift Trigger 1232755: likely consistent with noise and not astrophysical",
  "submittedHow": "email",
  "bibcode": "2024GCN.36612....1B",
  "createdOn": 1717507113945,
  "submitter": "Amy <yarleen@gmail.com>",
  "circularId": 36612,
  "body": "A. P. Beardmore (U Leicester), A. A. Breeveld (UCL-MSSL), A. Y. Lien (U\nTampa), D. M. Palmer (LANL) and T. M. Parsotan (GSFC) report on behalf of\nthe Neil Gehrels Swift Observatory Team:\n\nUsing the full data set from recent downlinks, we report further ground\ndata analysis for Swift trigger 1232755 (initially called GRB240603B;\nBeardmore  et al. GCN Circ. 36604).\n\nThe BAT analysis uses data from T-239 s to T+963 s. There are several very\nnoisy detectors during this time interval. Further ground analysis after\nremoving the contributions from these noisy detectors shows an image\nsignificance of 7.5 sigma and a small bump in the BAT mask-weighted light\ncurve from ~T0 to ~T+0.5 s. However, since there are many active noisy\ndetectors around this time, we also see higher chances of getting\ndetections above 7 sigma. Thus, the signal is likely to be consistent with\nthe larger noise fluctuation.\n\nSwift performed a follow-up observation of the trigger, with XRT collecting\n1.1 ks of Photon Counting (PC) mode data between T0+3.3 ks and T0+4.6 ks.\nNo X-ray sources were detected within 296 arcsec of the initially reported\nBAT position. The 3-sigma upper limit in the field ranges from ~0.005 to\n~0.007 ct s^-1, corresponding to a 0.3-10 keV observed flux of 2.1e-13 to\n2.7e-13 erg cm^-2 s^-1 (assuming a typical GRB spectrum).\n\nAdditionally, no optical afterglow consistent with the BAT position is\ndetected in the initial UVOT exposures. Preliminary 3-sigma upper limits\nusing the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc.\n1358, 373) for the initial exposures are:\n\nFilter         T_start(s) T_stop(s)  Exp(s)   Mag\n\nwhite          4758       4958       197      >20.2\nb              4553       4753       197      >19.6\nu              4347       4547       197      >19.2\nv              3733       3932       197      >18.7\nuvw1           4143       4342       197      >19.2\nuvw2           3528       5102       332      >19.6\nuvm2           3939       4137       197      >19.2\n\nThe increased detector noise visible in BAT and the absence of any X-ray\nand optical afterglow detection, suggest this trigger did not have an\nastrophysical origin and is consistent with noise fluctuations.\n"
}