GRB 260504A
GCN Circular 44453
Subject
Fermi GRB 260504A: Global MASTER-Net observations report
Date
2026-05-04T09:46:26Z (6 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via
email
V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko,
G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU),
O.Gress, N.Budnev (ISU),
C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A.Sosnovskij (CrAO),
A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity),
D.Buckley (SAAO),
R.Rebolo (The Instituto de Astrofisica de Canarias),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)
MASTER-OAFA robotic telescope [1] located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 260504A ( Fermi GBM team, GCN 44452) errorbox 578 sec after notice time and 612 sec after trigger time at 2026-05-04 09:23:10 UT, with upper limit up to 16.5 mag. The observations began at zenith distance = 79 deg. The sun altitude is -22.5 deg.
The galactic latitude b = 5 deg., longitude l = 86 deg.
Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3291732
We obtain a following upper limits.
Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
672 | 2026-05-04 09:23:10 | MASTER-OAFA | (20h 30m 50.42s , +46d 55m 36.5s) | C | 120 | 16.4 |
813 | 2026-05-04 09:25:16 | MASTER-OAFA | (20h 30m 48.57s , +46d 55m 44.3s) | C | 150 | 16.1 |
924 | 2026-05-04 09:27:52 | MASTER-OAFA | (20h 30m 47.07s , +46d 55m 48.4s) | C | 60 | 16.4 |
990 | 2026-05-04 09:28:58 | MASTER-OAFA | (20h 30m 46.11s , +46d 55m 50.2s) | C | 60 | 16.5 |
1056 | 2026-05-04 09:30:03 | MASTER-OAFA | (20h 30m 45.24s , +46d 55m 54.1s) | C | 60 | 16.4 |
Filter C is a clear (unfiltred) band.
The observation and reduction will continue.
The message may be cited.
[1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp.
http : // www.pereplet.ru/lipunov/625.html
GCN Circular 44452
Subject
GRB 260504A: Fermi GBM Final Real-time Localization
Date
2026-05-04T09:21:13Z (6 days ago)
From
Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply@GIOC.nsstc.nasa.gov>
Via
email
The Fermi GBM team reports the detection of a likely LONG GRB
At 09:12:58 UT on 4 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260504A (trigger 799578783.057988 / 260504384).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 308.8, Dec = 48.4 (J2000 degrees, equivalent to J2000 20h 35m, 48d 23'), with a statistical uncertainty of 5.0 degrees.
The angle from the Fermi LAT boresight is 44.0 degrees.
The skymap can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260504384/quicklook/glg_skymap_all_bn260504384.png
The HEALPix FITS file, including the estimated localization systematic, can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260504384/quicklook/glg_healpix_all_bn260504384.fit
The GBM light curve can be found here:
https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260504384/quicklook/glg_lc_medres34_bn260504384.gif