{
  "createdOn": 1741590251732,
  "format": "text/markdown",
  "submitter": "Yue Wang <m18509381757@163.com>",
  "eventId": "GRB 250309B",
  "subject": "GRB 250309B / IceCube-250309A: GECAM-B observations",
  "submittedHow": "web",
  "body": "Yue Wang, Jia-Cong Liu, Jin-Peng Zhang, Chen-Wei Wang, Wen-Jun Tan, Wang-Chen Xue, Shao-Lin Xiong (IHEP), report on behalf of the GECAM team:\n\nGECAM-B was triggered on-ground by a long burst, GRB 250309B, at 2025-03-09T07:38:31.050 UTC (T0), which was also observed by Fermi/GBM (McDermott et al., GCN  39642). \n\nAccording to GECAM-B light curve, this burst mainly consists of multiple pulses with a duration (T90) of about 6.74 (+/-0.15) sec (50-300 keV). The GECAM-B light curve of GRB 250309B could be found at: \nhttps://www.bursthub.cn//admin/static/gecamgrb250309B.png\n\nThe GECAM-B localization of GRB 250309B is consistent with the Fermi/GBM localization of this burst (McDermott et al., GCN  39642) and the position of optical counterpart AT 2025dws (Stein et al., GCN 39639) as well as the IceCube-250309A (The IceCube Collaboration, GCN 39631). Thus, we confirm that GRB 250309B is spatially and temporally coincident with IceCube-250309A.\n\nThe time-integrated spectrum of GRB 250309B from T0-1.0 s to T0+6.0 s is best fitted by \na cutoff-powerlaw function with Epeak = 109.3 +/- 6.8 keV and alpha = -1.00 +/- 0.27. The event fluence (10-1000 keV) in this time interval is (7.65 +/- 0.56)E-06 erg/cm^2.\n\nWith the measured redshift z=1.898 (D. B. Malesani et al., GCN 39647), we calculate the isotropic energy Eiso is (7.4 ± 0.8)x10^52 erg. Then we note that GRB 250309B is well consistent with Type II GRBs in the 'Amati' relation diagram, as shown at:\nhttps://www.bursthub.cn//admin/static/grb250309B_amati.png\n\nFurther, we note that there is no GECAM-B trigger just around the event time of IceCube-250309A (2025-03-09 at 07:36:04.75 UT, The IceCube Collaboration, GCN 39631). We implemented a targeted search [1] for burst activities from T0-330 s to T0-30 s embracing this IceCube event, but identified no candidate above 3 sigma. \n\nThus, we calculated the upper limit of a potential precursor of GRB 250309B which is simultaneously associated with IceCube-250309A. Considering three typical GRB spectral models (i.e. soft, normal and hard Band functions), three timescales and the center region of GRB localization (RA= 211.07, Dec = -10.73), the 3 sigma upper limits of the potential GRB precursor energy flux (15 keV-5000 keV, in units of 10^-7 erg/s/cm^2) are reported below:\n\n|Timescale (s)|Soft|Normal|Hard|\n| ------------ | ------------ | ------------ | ------------ |\n|0.1|3.86|3.92|6.33|\n|1  |1.22|1.24|2.00|\n|10 |0.38|0.39|0.63|\n\nWe note that these results are preliminary. Refined analysis will be reported.\n\nGravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission originally consists of two microsatellites (GECAM-A and GECAM-B) launched in Dec. 2020. As the third member of GECAM constellation, GECAM-C was launched onboard SATech-01 experimental satellite in July 2022. GECAM mission is funded by the Chinese Academy of Sciences (CAS).",
  "bibcode": "2025GCN.39648....1W",
  "circularId": 39648
}