Back

GCN Circular 40992

Subject

GRB 250706B: SVOM/VT optical observation

Event

GRB 250706B

Date

2025-07-06T18:45:55Z (2 days ago)

Edited On

2025-07-07T13:29:29Z (19 hours ago)

From

SVOM_group <svomgroup@bao.ac.cn>

Edited By

Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of SVOM_group <svomgroup@bao.ac.cn>

Via

Web form

J. Palmerio (CEA), L. P. Xin, Y. L. Qiu, C. Wu, H. L. Li, Z. H. Yao, Y. N. Ma, X. H. Han, Y. Xu, J. Wang, P. P. Zhang, W. J. Xie, Y. J. Xiao, H. B. Cai, L. Lan, J. S. Deng, J. Y. Wei (NAOC) report on behalf of the SVOM/VT team

After the trigger by SVOM/ECLAIRs at 2025-07-06T17:06:04 UTC (T0), SVOM performed an automatic slew on the burst location (Palmerio et al., GCN 40989Loading...
 
 ). SVOM/VT began observing the field at 2025-07-06T17:10:48, 283.83 seconds after T0, in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously.

From a preliminary analysis of the 1-bit subimage and source list downloaded via VHF network, at least one credible candidate is identified, the details of which are presented below.

VT_ID 50:
  This candidate was flagged as un uncatalogued source whose magnitude varied with 3 sigma significance.
  The position of this candidate is R.A., Dec. 41.2311, -50.0612 degrees, corresponding to:
  R.A. (J2000) = 2h44m55.5s
  Dec. (J2000) = -50d03m40.4s
  with an uncertainty of 1 arcsec.
  
  This location is within the R90 uncertainty region of the SVOM/MXT onboard localization.
  This location is consistent with the optical afterglow reported by Zhu et al. (GCN 40991Loading...
 
 ).

  The source was detected in both VT_R and VT_B, and was fading between the first 2 VT observing sequences. The candidate's magnitudes are:
  
  | date-obs (UTC)       | mid-time    | exposure  | band  | mag(AB)       |
  | -------------------- | ----------- | --------- | ----- | ------------- |
  | 2025-07-06T17:10:48  | 7.23 min    | 6*50 sec  | VT_B  | 14.90 ± 0.01  |
  | 2025-07-06T17:10:48  | 7.23 min    | 6*50 sec  | VT_R  | 14.48 ± 0.01  |
  | 2025-07-06T17:15:48  | 12.23 min   | 6*50 sec  | VT_B  | 15.17 ± 0.01  |
  | 2025-07-06T17:15:48  | 12.23 min   | 6*50 sec  | VT_R  | 14.65 ± 0.01  |

  Magnitudes were not corrected for dust extinction.
  
  Given the VT colour of the counterpart, it might be a low redshift gamma-ray burst.


The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe.
SVOM/VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.

The SVOM/VT point of contact for this burst is Jesse Palmerio: palmerio@cea.fr.