GRB 210925B

K. Hurley, on behalf of the IPN,

I. G. Mitrofanov, D. V. Golovin, A. S. Kozyrev, M. L. Litvak,
and A. B. Sanin, on behalf of the HEND-Odyssey GRB team,

A. Ridnaia, S. Golenetskii, D. Frederiks, D. Svinkin,
A. Lysenko, and T. Cline on behalf of the Konus-Wind team,

A. Goldstein, M. S. Briggs, and C. Wilson-Hodge
on behalf of the Fermi-GBM team,

A. von Kienlin, X. Zhang, A. Rau, V. Savchenko, E. Bozzo,
and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team,

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

W. Boynton, C. Fellows, K. Harshman, H. Enos, and R. Starr,
on behalf of the GRS-Odyssey GRB team, report:

The long-duration GRB 210925B
was detected by Fermi (GBM trigger 654225613), Konus-Wind,
Mars-Odyssey (HEND), INTEGRAL (SPI-ACS), and Swift-BAT
at about 4809 s UT (01:20:09).
The burst was outside the coded field of view of the BAT.

We have triangulated it to a preliminary, 3 sigma error box
whose coordinates are:
 ---------------------------------------------
  RA(2000), deg                 Dec(2000), deg
 ---------------------------------------------
 Center:
   48.817 (03h 15m 16s) -52.863 (-52d 51' 45")
 Corners:
   47.551 (03h 10m 12s) -53.723 (-53d 43' 21")
   50.006 (03h 20m 01s) -52.058 (-52d 03' 29")
   50.027 (03h 20m 06s) -51.978 (-51d 58' 41")
   47.579 (03h 10m 19s) -53.644 (-53d 38' 39")
 ---------------------------------------------
The error box area is 335 sq. arcmin, and its maximum
dimension is 2.3 deg (the minimum one is 2.5 arcmin).
The Sun distance was 113 deg.

This box may be improved.

A triangulation map is posted at
http://www.ioffe.ru/LEA/GRBs/GRB210925_T04810/IPN/

The time history and spectrum will be given in forthcoming GCN Circulars.

V. Prasad (IUCAA), P. Sawant (IUCAA), G. Waratkar (IITB), A. Vibhute
(IUCAA), V. Bhalerao (IITB), D. Bhattacharya (IUCAA), A. R. Rao
(IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat
CZTI collaboration: 

Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al.,
2021, JApA, 42, 73) showed detection of a long GRB 210925B for which the
IPN triangulation (Hurley et al., GCN 30890
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 ) was reported. 

The source was clearly detected in the 20-200 keV energy range. The
light curve showed multiple peaks of emission with the strongest peak at
2021-09-25 01:20:09.75 UT. The measured peak count rate associated with
the burst is 887 (+190, -97) cts/s above the background in the combined
data of four quadrants, with a total of 1482 (+214, -230) cts. The local
mean background count rate was 471 (+5, -9) cts/s. Using cumulative
rates, we measure a T90 of 6.3 (+1.9, -2.0) s. 

It was also clearly detected in the CsI anticoincidence (Veto) detector
in the 100-500 keV energy range. 

CZTI GRB detections are reported regularly on the payload site at
http://astrosat.iucaa.in/czti/?q=grb. CZTI is built by a TIFR-led
consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC,
and PRL. The Indian Space Research Organisation funded, managed, and
facilitated the project.