sb25021804
GCN Circular 39363
Subject
SVOM/sb25021804: SVOM detection of a long X-ray transient
Date
2025-02-18T15:56:15Z (3 months ago)
From
Stéphane Schanne at CEA Paris-Saclay/IRFU <s.schanne@cea.fr>
Via
Web form
C.-W. Wang, W.-J. Tan (IHEP), D. Turpin, S. Schanne, N. Dagoneau (CEA)
report on behalf of the SVOM mission team:
The SVOM/ECLAIRs telescope triggered and located a long duration soft X-ray transient (SVOM burst-id sb25021804) starting at 2025-02-18T07:20:27 UTC (Tb).
The following trigger information was received on the ground with low-latency by the SVOM VHF Alert Network.
The burst was detected by the Image Trigger (IMT) and only 1 alert was produced with a signal-to-noise ratio of 7.56 in the 5-8 keV energy band over a time window of 22 minutes starting at Tb. The sub-image transmitted shows a clean point-like source.
The localization of the alert is R.A., Dec = 195.020, 28.078 degrees:
RA (J2000) = 13h00m04.93s
Dec (J2000) = 28d04m39.02s
with a 90% C.L. radius of 10.4 arcmin (including systematic error of 2 arcmin added in quadrature).
We notice that this error-box contains several X-ray sources which could produce such a transient,
including 4 AGNs and the ULX-candidate labelled "[SRW2012] Src. 6" in Simbad, located at 9.2 arcmin distance.
This trigger did not reach the slew threshold, hence no automatic slew was performed. A SVOM ToO has been scheduled and a Swift XRT ToO has been requested.
The Space 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.
The Burst Advocate (BA) on shift for this burst is Chen-Wei Wang (IHEP) : cwwang@ihep.ac.cn
Please contact the BA by email if you require additional information regarding the SVOM follow-up of this burst.
GCN Circular 39364
Subject
Transient SVOM/sb25021804: COLIBRÍ/DDRAGO Optical Upper Limits on the Optical Counterpart
Date
2025-02-18T16:18:24Z (3 months ago)
From
Alan Watson at UNAM <alan@astro.unam.mx>
Via
Web form
Antonio de Ugarte Postigo (LAM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), and Benjamin Schneider (LAM) report:
We imaged the field of SVOM trigger sb25021804 (Wang et al., GCN 39363) with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico.
The coordinates of this trigger are about 6 arcmin north of the galaxy NGC 4889, the brightest galaxy in the Coma Cluster (Abell 1656). The uncertainty radius is 10.4 arcmin, and so includes much of the central region of the cluster.
We observed from 2025-02-18 09:44 UTC to 11:51 UTC (2.71 to 4.52 hours after the trigger) and obtained 53 minutes of exposure in the i filter through patchy clouds and with high winds. The data were coadded with custom software and analyzed in STDWeb/STDPipe (Karpov 2021), with photometric calibration against Pan-STARRS DR1 and image subtraction against Pan-STARRS DR2. Our photometry is not corrected for Galactic extinction.
Our image reaches an AB 5-sigma limiting magnitude of
i > 21.7
We have performed image subtraction and see no obvious counterpart. The detection of a counterpart with Swift/XRT or SVOM/MXT would facilitate searches for a faint counterpart.
We warmly thank the COLIBRÍ and DDRAGO engineering teams and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir.
GCN Circular 39372
Subject
SVOM/sb25021804: QSO variability in Liverpool Telescope observations
Date
2025-02-19T11:37:18Z (3 months ago)
From
Rob Eyles-Ferris at U of Leicester <raje1@leicester.ac.uk>
Via
Web form
R. A. J. Eyles-Ferris, P. T. O’Brien and R. L. C. Starling (U of Leicester) report on behalf of a larger collaboration:
We observed the field of the SVOM/ECLAIRs transient sb25021804 (Wang et al., GCN 39363) in four pointings covering ~87% of the error area using the IO:O on the 2m Liverpool Telescope. We obtained 4x150s exposures per pointing in the SDSS g’ filter starting at 2025-02-19 04:59:09 UT, approximately 21.7 hours after the SVOM/ECLAIRs detection.
We performed image subtraction on the stacked images using reference images from Pan-STARRS. We identify a residual at RA, Dec 195.044, 28.130 which corresponds to the X-ray bright QSO WISEA J130010.60+280749.7, about 3.4 arcmin from the SVOM ECLAIRs position reported by Wang et al., GCN 39363. We performed PSF photometry on the stacked image and find g’ = 20.09 +/- 0.11 calibrated to Pan-STARRS and not corrected for Galactic extinction. This is ~0.5 mag brighter than the magnitude catalogued in Pan-STARRS DR2 and we suggest sb25021804 is related to this variability.
We find no other obvious residuals in the subtracted images to a 3-sigma limiting magnitude of ~21.5.
GCN Circular 39374
Subject
SVOM/sb25021804: COLIBRÍ/DDRAGO Confirmation of Variability
Date
2025-02-19T14:04:46Z (3 months ago)
From
Alan Watson at UNAM <alan@astro.unam.mx>
Via
Web form
Damien Dornic (CPPM), Antonio de Ugarte Postigo (LAM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Dalya Akl (AUS), Camila Angulo (UNAM), Sarah Antier (OCA), Jean-Luc Atteia (IRAP), Rosa L. Becerra (U Roma), Nathaniel R. Butler (ASU), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), and Benjamin Schneider (LAM) report:
We imaged the field of SVOM/ECLAIRs trigger sb25021804 (Wang et al., GCN 39363) with the DDRAGO wide-field imager on the COLIBRÍ telescope at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir in Mexico.
We observed from 2025-02-19 06:23 to 09:00 UTC (23.1 to 25.7 hours after the trigger) and obtained 100 minutes of exposure in the r filter. The data were coadded with custom software and analyzed in STDWeb/STDPipe (Karpov 2021), with photometric calibration against Pan-STARRS DR1. Our photometry is in the AB system and is not corrected for Galactic extinction.
For the X-ray bright QSO WISEA J130010.60+280749.7, suggested by Eyles-Ferris et al. (GCN Circ. 39372) as a possible counterpart of the ECLAIRs source, we measure a magnitude of
r = 19.95 +/- 0.01
In our observation on the previous night, reported in de Ugarte Postigo et al. (GCN Circ. 39364), we measure
i = 19.98 +/- 0.04
Our magnitudes are about 0.3 magnitudes above the mean magnitudes reported in SDSS DR6 and PanSTARRS DR1. This confirms the excess reported by Eyles-Ferris et al. (GCN Circ. 39372) and strengthens their suggestion that this QSO might be related to the SVOM trigger.
We warmly thank the COLIBRÍ and DDRAGO engineering teams and the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir.