GCN Circular 44455

Subject
SVOM GRB 260504B: MASTER-OAFA optical observations
Event
GRB 260504B
Date
2026-05-04T10:30:53Z (5 days ago)
From
Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov@xray.sai.msu.ru>
Via

F.Podesta, M.J. Segura, C.Francile, R.Podesta, E. Gonzalez (OAFA, SJNU),
A.Kuznetsov, V.Lipunov, I.Panchenko, P.Balanutsa, G.Antipov, N.Tiurina, K.Zhirkov, E.Gorbovskoy,
V.Senik, A.Chasovnikov, Ya.Kechin, V.Topolev, D.Vlasenko,A.Sankovich, I.Gorbunov (Lomonosov MSU),
N.Budnev, O.Gress (ISU),
D.Buckley (SAAO),
A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory),
A. Gabovich  (Blagoveschensk Educational StateUniversity)
R.Rebolo (The Instituto de Astrofisica de Canarias),
L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez,A.R.Corella,
J.Tanori, L. Villalobos, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)

MASTER-OAFA robotic telescope of MASTER Global Robotic Net [1-4]
was pointed to the SVOM GRB260504.40 (trigger No 1777887197,23h 24m 54.98s, -80d 21m 09.7s, R=0.0491, Saccardi et al. GCN 44454Loading...
 
  )
errorbox 434 sec after trigger time at 2026-05-04 09:40:30 UT, with upper limit up to  19.7 mag.
The observations began at zenith distance = 54 deg.
The sun  altitude  was -18.8 deg.

The galactic latitude b = -36 deg., longitude l = 307 deg.


Real time updated cover map and OT discovered available here:
https://master.sai.msu.ru/site/master2/observ.php?id=3291780

MASTER upper limits:

Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment

     489 | 2026-05-04 09:40:30 |         MASTER-OAFA | (23h 23m 41.35s , -81d 33m 14.0s) |   C |   110 | 18.9 |
     634 | 2026-05-04 09:40:30 |         MASTER-OAFA | (23h 23m 41.33s , -81d 33m 14.1s) |   C |   400 | 19.7 |  Coadd
     615 | 2026-05-04 09:42:26 |         MASTER-OAFA | (23h 23m 41.51s , -81d 33m 07.2s) |   C |   130 | 19.1 |
     767 | 2026-05-04 09:44:43 |         MASTER-OAFA | (23h 23m 41.18s , -81d 33m 00.8s) |   C |   160 | 19.2 |
     883 | 2026-05-04 09:47:29 |         MASTER-OAFA | (23h 23m 40.81s , -81d 32m 56.0s) |   C |    60 | 18.8 |
     943 | 2026-05-04 09:47:29 |         MASTER-OAFA | (23h 23m 40.80s , -81d 32m 56.1s) |   C |   180 | 19.5 |  Coadd
     948 | 2026-05-04 09:48:35 |         MASTER-OAFA | (23h 23m 40.67s , -81d 32m 53.0s) |   C |    60 | 18.8 |
    1014 | 2026-05-04 09:49:40 |         MASTER-OAFA | (23h 23m 40.42s , -81d 32m 50.2s) |   C |    60 | 18.8 |
    1080 | 2026-05-04 09:50:46 |         MASTER-OAFA | (23h 23m 40.47s , -81d 32m 47.6s) |   C |    60 | 18.9 |
    1140 | 2026-05-04 09:50:46 |         MASTER-OAFA | (23h 23m 40.46s , -81d 32m 47.6s) |   C |   180 | 19.6 |  Coadd
    1145 | 2026-05-04 09:51:51 |         MASTER-OAFA | (23h 23m 40.03s , -81d 32m 44.5s) |   C |    60 | 18.7 |
    1211 | 2026-05-04 09:52:57 |         MASTER-OAFA | (23h 23m 39.95s , -81d 32m 41.8s) |   C |    60 | 18.8 |
    1277 | 2026-05-04 09:54:03 |         MASTER-OAFA | (23h 23m 39.77s , -81d 32m 39.0s) |   C |    60 | 18.8 |
    1342 | 2026-05-04 09:55:09 |         MASTER-OAFA | (23h 23m 39.54s , -81d 32m 36.0s) |   C |    60 | 18.7 |
    1408 | 2026-05-04 09:56:14 |         MASTER-OAFA | (23h 23m 39.36s , -81d 32m 33.3s) |   C |    60 | 18.7 |
    1474 | 2026-05-04 09:57:21 |         MASTER-OAFA | (23h 23m 39.24s , -81d 32m 30.3s) |   C |    60 | 18.8 |
    1540 | 2026-05-04 09:58:26 |         MASTER-OAFA | (23h 23m 39.00s , -81d 32m 27.3s) |   C |    60 | 18.9 |
Filter C is a clear (unfiltred) band.



Observation and reduction will continue.

[1] Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L
[2] Lipunov et al. 2022, Universe, Vol. 8(5), id.271
[3] Lipunov et a. 2019, ARep, vol.63, 293
[4] Lipunov et al. 2023, Astronomical Robotic Networks and Operative Multichanel
Astrophysics,Lomonosov MSU PRESS, 591pp.
 http://www.pereplet.ru/lipunov/625.html#625