GRB 260916A

GRB 260916A: MAXI/GSC detection

M. Uenishi (Ehime U.), M. Nakajima (Nihon U.), Y. Kawakubo (AGU), 
H. Negoro, K. Saito, T. Yokoyama, M. Wada (Nihon U.),
T. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN),
T. Sakamoto, M. Serino, S. Sugita, H. Hiramatsu, A. Yoshida (AGU),
Y. Tsuboi, Y. Ishihara, H. Ogaki (Chuo U.),
M. Shidatsu, C. Kang, T. Usuki, S. Yatsuzuka, H. Aoe (Ehime U.),
I. Takahashi, Y. Yatsu (Science Tokyo),
S. Nakahira, S. Ueno, H. Tomida, M. Kurihara (JAXA),
Y. Ueda, K. Fujiwara, S. Kobayashi (Kyoto U.),
M. Yamauchi, M. Nishio, C. Hiraizumi (Miyazaki U.),
K. Yamaoka (Nagoya U.),
M. Sugizaki (Kanazawa U.),
W. Iwakiri (Chiba U.),
T. Kawamuro (Osaka U.),
S. Yamada (Tohoku U),
S. Ogawa (TUS)
report on behalf of the MAXI team:

The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient 
source at 08:51:44 UT on 16 September 2026.
Assuming that the source flux was constant over the transit,
we obtain the source position at
(R.A., Dec) = (17.811 deg, -26.193 deg) = (01 11 14, -26 11 34) (J2000)
with a statistical 90% C.L. elliptical error region
with long and short radii of 0.19 deg and 0.18 deg, respectively.
The roll angle of long axis from the north direction is 42.0 deg counterclockwise.
There is an additional systematic uncertainty of 0.1 deg (90% containment radius).
The X-ray flux averaged over the scan was 165 +- 26 mCrab
(4.0-10.0keV, 1 sigma error).
Without assumptions on the source constancy, we obtain a rectangular error
box for the transient source with the following corners:
(17.868, -25.913) deg = (01 11 28, -25 54 46) (J2000)
(17.539, -26.135) deg = (01 10 09, -26 08 06) (J2000)
(17.867, -26.526) deg = (01 11 28, -26 31 33) (J2000)
(18.196, -26.303) deg = (01 12 47, -26 18 10) (J2000)
There was no significant excess flux in the previous transit at 07:18 UT 
with an upper limit of 20 mCrab.

M. Segura,  F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA)

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 (Lomonosov MSU)

D.Buckley (SAAO),

A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity)
A.Sosnovskij (Lomonosov MSU)

A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory)

L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez,
A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory)

R.Rebolo (The Instituto de Astrofisica de Canarias)

O.Gress, N.Budnev(ISU)


MASTER-OAFA robotic telescope  [1]  located in Argentina (OAFA observatory of San Juan National University) started inspect of the MAXI GRB260916.37 (trigger No 299299081,01h 10m 41.04s , -26d 15m 07.2s, R=1) errorbox 2813 sec after trigger time at 2026-09-16 09:38:52 UT, with upper limit up to  20.0 mag. Observations started at twilight.  The observations began at zenith distance = 46 deg. The sun  altitude  is -12.5 deg. 

The galactic latitude b = -85 deg., longitude l = 201 deg.


Real time updated cover map and OT discovered available here: 
https://master.sai.msu.ru/site/master2/observ.php?id=3505122

We obtain a following upper limits.  

Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________

    2844 | 2026-09-16 09:38:52 |         MASTER-OAFA | (01h 09m 59.35s , -26d 20m 14.8s) |   C |    60 | 19.5 |        
    2904 | 2026-09-16 09:38:52 |         MASTER-OAFA | (01h 09m 59.35s , -26d 20m 14.8s) |   C |   180 | 20.0 |  Coadd 
    2909 | 2026-09-16 09:39:58 |         MASTER-OAFA | (01h 09m 59.38s , -26d 20m 15.0s) |   C |    60 | 19.2 |        
    2975 | 2026-09-16 09:41:03 |         MASTER-OAFA | (01h 09m 59.43s , -26d 20m 15.6s) |   C |    60 | 19.2 |        
    3040 | 2026-09-16 09:42:09 |         MASTER-OAFA | (01h 09m 59.46s , -26d 20m 16.0s) |   C |    60 | 19.0 |        
    3100 | 2026-09-16 09:42:09 |         MASTER-OAFA | (01h 09m 59.45s , -26d 20m 16.0s) |   C |   180 | 19.5 |  Coadd 
    3106 | 2026-09-16 09:43:14 |         MASTER-OAFA | (01h 09m 59.49s , -26d 20m 16.3s) |   C |    60 | 19.0 |        
    3172 | 2026-09-16 09:44:20 |         MASTER-OAFA | (01h 09m 59.46s , -26d 20m 16.8s) |   C |    60 | 18.6 |        
    3238 | 2026-09-16 09:45:26 |         MASTER-OAFA | (01h 09m 59.50s , -26d 20m 17.7s) |   C |    60 | 18.6 |        
    3304 | 2026-09-16 09:46:32 |         MASTER-OAFA | (01h 09m 59.55s , -26d 20m 18.1s) |   C |    60 | 18.5 |        
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