TITLE: GCN CIRCULAR NUMBER: 40809 SUBJECT: IPN triangulation of GRB 250620С (long/bright) DATE: 25/06/22 09:58:12 GMT FROM: Dmitry Svinkin at Ioffe Institute dmitrysvinkin@gmail.com

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

S. Barthelmy, J. Cummings, H. Krimm, D. Palmer, A. Tohuvavohu, and J. DeLaunay on behalf of the Swift-BAT team, report:

The bright long-duration GRB 250620C (Fermi-GBM detection: The Fermi GBM team, GCN 40794; Mukherjee, GCN 40799; SVOM-GRM detection: Wang et al., GCN 40807) was detected by Fermi (GBM trigger 772128434), Swift (BAT), Konus-Wind, and SVOM (GRM) at about 58030 s UT (16:07:10). The burst was outside the coded field of view of the BAT.

We have triangulated it to a preliminary, 3 sigma error box whose area is 17.6 sq. deg, and its maximum dimension is 25.5 deg (the minimum one is 51.0 arcmin). The Sun distance was ~50 deg.

This localization may be improved.

The IPN localization is consistent with, but reduces the area of, the Fermi-GBM (GCN 40794) and BALROG (https://grb.mpe.mpg.de/grb/GRB250620672/?data_version=tte_v00) localizations.

A triangulation map and HEALPix FITS file are posted at http://www.ioffe.ru/LEA/GRBs/GRB250620_T58026/IPN The HEALPix triangulation map is the multi-order HEALPix in units of probability density.

The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular.

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