TITLE: GCN CIRCULAR NUMBER: 39652 SUBJECT: IPN triangulation of GRB 250309B DATE: 25/03/10 13:17:34 GMT FROM: Dmitry Svinkin at Ioffe Institute svinkin@mail.ioffe.ru
A.S. Kozyrev, D.V. Golovin, M.L. Litvak, I.G. Mitrofanov, and A.B. Sanin on behalf of the HEND/Mars Odyssey team,
D. Svinkin, D. Frederiks, A. Lysenko, A. Ridnaia, and T. Cline on behalf of the Konus-Wind team,
A. Goldstein, M. S. Briggs, C. Wilson-Hodge, and E. Burns on behalf of the Fermi GBM team,
and
W. Boynton, C. Fellows, K. Harshman, H. Enos, R. Starr, and A.S. Gardner on on behalf of the GRS-Odyssey GRB team, report:
The long-duration GRB 250309B (Fermi-GBM BALROG localization: Preis and Greiner, GCN 39629; Fermi-GBM detection: The Fermi GBM team, GCN 39635; McDermott et al., GCN 39642; GECAM-B detection: Wang et al., GCN 39648) was detected by Fermi (GBM trigger 763198715), Konus-Wind, Mars-Odyssey (HEND), and GECAM-B at about 27510 s UT (07:38:30).
We have triangulated it to a preliminary, 3 sigma error box whose coordinates are: ------------------------------- RA(2000), deg Dec(2000), deg ------------------------------ Center: 208.8101 -12.9141 Corners: 204.1541 -23.3442 204.3621 -23.0319 213.4312 -2.9483 213.5345 -2.5970 ------------------------------- The error box area is 1.3 sq. deg, and its maximum dimension is 23 deg (the minimum one is 3.5 arcmin). The Sun distance was 135 deg.
This localization may be improved.
The IPN localization is consistent with, but reduces the area of, the final Fermi-GBM (GCN 39635) and BALROG (GCN 39629) localizations.
A triangulation map and HEALPix FITS file are posted at http://www.ioffe.ru/LEA/GRBs/GRB250309_T27513/IPN/ The HEALPix triangulation map is the multi-order HEALPix in units of probability density.
The localization of IceCube-250309A (IceCube Collaboration, GCN 39631) is inconsistent with the IPN localization. The optical transient ZTF25aaitvjt/AT2025dws (Stein et al., GCN 39639) is inside the IPN box, which further strengthen the interpretation of transient as the burst afterglow.
The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular.
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