sb25072103
GCN Circular 41144
Subject
SVOM J195836+32283/sb25072103: Second VT observation
Date
2025-07-23T16:24:40Z (a month ago)
From
Liping Xin at NAOC, SVOM <xlp@nao.cas.cn>
Via
Web form
L. P. Xin, Y. L. Qiu, C. Wu, H. L. Li, Z. H. Yao, 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, D.H. Zhao (NAOC), J. Palmerio (CEA) report on behalf of the SVOM team:
SVOM/VT performed a second ToO observation for the galactic transient SVOM J195836+32283 (sb25072103) (Gotz et al., GCN 41131) detected by SVOM/MXT. The VT conducted observations between July 22, 2025, 11:23:37 UT and 15:18:41 UT, from 26.7 hours 30.6 hours after trigger time in the VT_B (400-650 nm) and VT_R (650-1000 nm) channels simultaneously.
For the optical source identified in VT observation (Gotz et al., GCN 41131), its brightness was 22.2+/-0.3 mag in our second observations. No apparent variability was detected compared to the first VT observation.
Given the constant brightness in our twice observations, it is likely that this object is the extended source as noticed by Mo et al. (GCN 41138) and Eyles-Ferris et al. (GCN 41143).
The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC),CAS.
GCN Circular 41143
Subject
SVOM J195836+32283/sb25072103: Liverpool Telescope detection of an extended source
Date
2025-07-23T14:57:46Z (a month ago)
From
Rob Eyles-Ferris at U of Leicester <raje1@leicester.ac.uk>
Via
Web form
R. A. J. Eyles-Ferris and N. Habeeb (U of Leicester) report on behalf of a larger collaboration:
We observed the field of the SVOM transient SVOM J195836+32283 / sb25072103 (Götz et al., GCN 41131) with the 2m Liverpool Telescope using the IO:O instrument. We obtained 6x150s exposures in each of the SDSS g’, r’, i’ and z’ filters starting at 23:43:39 UT on 2025-07-22, approximately 41 hours after the ECLAIRs trigger.
No sources consistent with the SVOM/VT position are identified in the g’ or r’ images and we obtain 3-sigma upper limits of g’ > 22.7 and r’ > 22.9 calibrated to Pan-STARRS and not corrected for Galactic extinction.
In the i’ and z’ images, we do identify a source, the morphology of which is inconsistent with a single point source. Instead, it appears to be extended, consistent with the suggestion of Mo et al. (GCN 41138), or may be a combination of several components. We measure i’ = 22.9 +/- 0.3 and z’ = 21.9 +/- 0.2 for the source, again calibrated to Pan-STARRS and not corrected for Galactic extinction. The relative contributions of the transient and possible host to this flux are currently unknown and we encourage further observations of this source.
GCN Circular 41139
Subject
SVOM J195836+32283/sb25072103: Swift XRT/UVOT upper limits
Date
2025-07-23T12:34:20Z (a month ago)
From
noelklin@umbc.edu
Via
Web form
Noel Klingler (NASA-GSFC / UMBC / CRESST II), Brendan O'Connor (CMU), and Alexander Lange (GWU) report:
Swift has performed follow-up observations of SVOM J195836+32283 / sb25072103 (Götz et al; GCN Circ. 41131) between 2025-07-22T14:24:46 and 2025-07-22T14:40:52, which corresponds to 106.9 ks and 107.9 ks post-trigger.
The XRT collected 956 s of data. No counts (0.3-10 keV) are detected within a 25 arcsecond radius of the SVOM/MXT position (19h 58m 36s, +32° 28’ 20”).
The UVOT collected 950 s of data in the U-band. No source is seen at the position obtained by SVOM/VT (19h 58m 36.29s, +32° 28’ 25.7”); the 3 sigma limiting magnitude (AB) is 21.55.
GCN Circular 41138
Subject
SVOM J195836+32283/sb25072103: NIR observations with WINTER
Date
2025-07-23T01:26:48Z (a month ago)
From
Geoffrey Mo at MIT <gmo@mit.edu>
Via
Web form
Geoffrey Mo (MIT), Tomas Ahumada (Caltech), Viraj Karambelkar (Caltech), Benjamin Schneider (LAM), Robert Stein (UMD), Danielle Frostig (CfA), Nathan Lourie (MIT), Robert Simcoe (MIT), and Mansi Kasliwal (Caltech) report:
We observed the field of SVOM J195836+32283 (Götz et al., GCN 41131) in the near-infrared J and Hs bands with the Palomar 1-m telescope, equipped with the 1.2-square degree WINTER camera (Lourie et al. 2020, Frostig et al. 2024).
Observations began at 2025-07-22T03:36:20 UTC in the J band and 2025-07-22T04:09:09 in the Hs band (~19 hours after the SVOM trigger), consisting of 15 x 120 s and 30 x 60 s exposures respectively. The images were processed using the WINTER data reduction pipeline implemented with mirar (https://github.com/winter-telescope/mirar, https://doi.org/10.5281/zenodo.13352565).
We do not detect any source at the SVOM/VT optical candidate location (Götz et al., GCN 41131). We obtain the following 5-sigma upper limits: J ~ 18.1 mag, Hs ~ 18.4 mag (AB).
We note the presence of a faint, unresolved, possibly extended source at the position of the SVOM/VT candidate in archival UKIRT UKIDSS J, H, and K-band imaging (Lawrence et al., 2007). We encourage further observations in the IR.
WINTER (Wide-field INfrared Transient ExploreR) is a partnership between MIT and Caltech, housed at Palomar Observatory, and funded by NSF MRI, NSF AAG, the David and Lucile Packard Foundation, and the MIT Kavli Institute for Astrophysics and Space Research.
GCN Circular 41131
Subject
The SVOM alert sb25072103 is not due to a GRB, but to a new galactic transient SVOM J195836+32283.
Date
2025-07-21T17:00:16Z (a month ago)
From
Diego Gotz at CEA <diego.gotz@cea.fr>
Via
Web form
D. Götz, N. Dagoneau, A. Saccardi (CEA), D. Zhao, Y. Ma, L. Xin (NAOC), J.-L. Atteia (IRAP) on behalf of the SVOM collaboration report:
The SVOM alert sb25072103 (08:43:10 UTC) is not due to a GRB, but most probably to a new galactic transient source. The ECLAIRs alert was initially identified as a trigger from the known galactic High Mass X-ray Binary, 4U 1954+31. SVOM slewed to the source location, and, due to Earth occultation, MXT and VT could not observe the field right away.
As soon as MXT started the observation, about one hour later, at 09:32:37 UTC, its on board software detected an uncatalogued source in its field of view, not consistent with the position of 4U 1954+31. The MXT observation continued until 11:47:43 UTC.
Subsequent analysis of the entire MXT X-band data showed that the source was not fading and, on the contrary, increased its flux by a factor about two over the entire duration of the observation. In addition the source presents a thermal spectrum, compatible with a black body of temperature ~0.2 keV. Based on these properties and on its position in the galactic plane (l=69.03, b= 1.6) we can exclude that this alert is due to a GRB, and we propose to classify this source as a new galactic transient, SVOM J195836+32283.
The J2000 X-ray coordinates are:
R.A. = 19h 58m 36s
Dec. = +32° 28’ 20”
with a 90% c.l. error radius of 30 arc sec (18 arc sec of statistical error).
The MXT error region was in the VT field of view during the SVOM second orbit. A faint uncatalogued optical source was detected within the MXT error region in VT_R band with a brightness of 22.2+/-0.4 mag, compared to the PanSTARRS images at the following J2000 coordinates
R.A. = 19h 58m 36.29s
Dec. = +32° 28’ 25.7”
with an error of 0.5 arc sec.
The VT images were obtained between 11:11:09 and 11:42:49 UTC with an effective exposure time of 20x100 seconds. The VT magnitude is not corrected for the Galactic extinction on the line of sight.
This source lies at 6 arc seconds from the MXT position, and we suggest that it might be the counterpart of the X-ray source.
Follow-up observations at other wavelengths are encouraged.
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/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. SVOM/VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS.