{
  "bibcode": "2026GCN.44203....1G",
  "submittedHow": "web",
  "format": "text/plain",
  "eventId": "GRB 260330B",
  "body": "S. Guillot, G. X. Lan (IRAP), D. Turpin, A. Saccardi (CEA/Irfu), report on behalf of the SVOM and EP collaborations:\n\n\nEP-FXT performed two follow-up observations of the SVOM/ECLAIRs-detected burst GRB 260330B (SVOM/sb26033003; Lan et al., GCN 44157), also detected as a sub-threshold event by Fermi/GBM (Trigg et al., GCN 44159). The first epoch started on 2026-03-31 at 16:39:42 UT, approximately 26.3 hours after the SVOM trigger, with a total exposure time of 3174 s. The second exposure started on 2026-04-02 at 19:48:54 UT, i.e., 77.5 hours after the SVOM trigger, with a total exposure time of 3200 s.\n\nThree uncataloged sources are detected within the ECLAIRs error circle in the first epoch:\n\nSource 1: EPF_J165032.7+365028 at RA, Dec (J2000) = 252.6363, 36.8413 with Fx=(1.20+/-0.32)e-13 erg/sec/cm2 from the FXT-B telescope.\n\nSource 2: EPF_J165010.3+364729 at RA, Dec (J2000) = 252.5430, 36.7914 with Fx=(2.40+/-0.43)e-13 erg/sec/cm2 from the FXT-B telescope.\n\nSource 3: EPF_J164951.2+365709 at RA, Dec (J2000) = 252.4635 36.9525 with Fx=(1.96+/-0.41)e-13 erg/sec/cm2 from the FXT-B telescope.\n\nAll three sources detected by EP/FXT during the first visit are detected in the second epoch data set. However, in the second epoch EPF_J165032.7+365028 has faded by a factor ~4, down to a flux of (4.0 +/- 2.3)e-14 erg/sec/cm2, while the flux of the other sources remained constant within their uncertainties.\n\nThe fading behavior of this X-ray source confirms it as the afterglow of GRB 260330B, localized at RA, Dec (J2000) = 252.6363, 36.8413 with an error radius of 10 arcsec.\n\nAll fluxes are calculated in the 0.5-10 keV range with 1-sigma uncertainties.\n\n​​Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics).\n",
  "circularId": 44203,
  "createdOn": 1775211960527,
  "subject": "GRB 260330B: EP-FXT follow-up and identification of candidate afterglow",
  "submitter": "SVOM_group <svomgroup@bao.ac.cn>"
}