sb25061218

J. Rodriguez, T. Sadibekova, B. Cordier, N. Dagoneau (CEA), U. Jacob (LUPM)
on behalf of the SVOM mission team.

At 2025-06-12T20:36:00 UTC (T0), SVOM/ECLAIRs triggered and located the X-ray transient sb25061218 (SVOM burst-id sb25061218).

The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network.

The burst was only detected by the Image Trigger (IMT), which produced a sequence of 1 alert. IMT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 7.01 in the [8-120] keV energy band over a time window of 81.92 seconds starting at 2025-06-12T20:34:38.

The localization of the best alert is R.A., Dec. 198.5028, 54.6582 degrees:
R.A. (J2000) = 13h14m00.67s
Dec. (J2000) = 54d39m29.47s
 with a 90% confidence level (C.L.) radius of 11.16 arcmin (including systematic error of 2 arcmin added in quadrature).

This burst was also detected by SVOM/GRM with a significance of 5.80.
Due to the detection significance being below the slew threshold, no immediate slew was performed on this 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. ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. 

The Burst Advocate (BA) on shift for this alert is Jerome Rodriguez: jerome.rodriguez@cea.fr.
Please contact the BA by email if you require additional information.

P.A. Evans (U. Leicester), J.A. Kennea (PSU), E. Ambrosi  (INAF-IASFPA) , A.P.
Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB), R. Brivio (INAF-OAB), D.N.
Burrows (PSU), S. Campana (INAF-OAB), M. Capalbi (INAF-OAR), A. D'Ai (INAF-IASFPA),
P. D'Avanzo (INAF-OAB), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), M. Ferro
(INAF-OAB), A. Melandri (INAF-OAR), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), M. Perri (SSDC & INAF-OAR), C. Salvaggio (INAF-OAB), T. Sbarrato
(INAF-OAB), B. Sbarufatti (INAF-OAB), M.A. Williams (PSU) report on behalf of the
Swift-XRT team:

Swift-XRT has performed follow-up observations of the SVOM/ECLAIRs-detected source
sb25061218, collecting 1.7 ks of Photon Counting (PC) mode data between T0+5.9 ks
and T0+7.7 ks after the trigger. We have detected 2 sources. These have been
automatically classified as follows:
  * 0 likely counterparts
  * 0 candidate counterparts
  * 2 uncatalogued X-ray sources
  * 0 known X-ray sources

Uncatalogued X-ray sources
--------------------------

  Source 1 (SWIFT J131445.9+544759):
  ==================================
    RA (J2000.0):  198.6914  =	13h 14m 45.94s
    Dec (J2000.0): +54.7999  =	+54d 47' 59.6"
    Error:	   11.2 (arcsec, radius, 90% confidence).
    Detect flag:   GOOD
    Distance:	   10.7 arcmin from the SVOM/ECLAIRs position.
    Mean rate:	   (9.8 [+3.7, -3.0])e-3 ct s^-1
    Mean flux:	   (4.8 [+1.8, -1.4])e-13 erg cm^-2 s^-1
    Peak rate:	   (9.8 [+3.7, -3.0])e-3 ct s^-1
    Peak flux:	   (4.8 [+1.8, -1.4])e-13 erg cm^-2 s^-1
    ECF:	   4.85e-11 erg cm^-2 ct^-1, assuming NH=2.15e+20 cm^-2,
		   gamma=1.50; determined from a spectral fit.
    XMM UL:	   2.1e-12 erg cm^-2 s^-1, (0.3-10 keV)
	 so the source is 10.0-sigma above this 3-sigma upper limit.
    There is no evidence for fading.
    A SIMBAD object `[VV2006] J131446.6+544804' is 6.6" away.

  Source 2 (SWIFT J131433.3+544329):
  ==================================
    RA (J2000.0):  198.6390  =	13h 14m 33.36s
    Dec (J2000.0): +54.7249  =	+54d 43' 29.6"
    Error:	   9.7 (arcsec, radius, 90% confidence).
    Detect flag:   GOOD
    Distance:	   6.2 arcmin from the SVOM/ECLAIRs position.
    Mean rate:	   (5.9 [+2.8, -2.1])e-3 ct s^-1
    Mean flux:	   (1.01 [+0.47, -0.37])e-13 erg cm^-2 s^-1
    Peak rate:	   (5.9 [+2.8, -2.1])e-3 ct s^-1
    Peak flux:	   (1.01 [+0.47, -0.37])e-13 erg cm^-2 s^-1
    ECF:	   1.71e-11 erg cm^-2 ct^-1, assuming NH=1.76e+22 cm^-2,
		   gamma=7.90; determined from a spectral fit.
    XMM UL:	   2.4e-12 erg cm^-2 s^-1, (0.3-10 keV)
	 so the source is 54.2-sigma above this 3-sigma upper limit.
    There is no evidence for fading.
    A SIMBAD object `SDSS J131433.74+544331.8' is 3.9" away.
    There is 1 2MASS object within the source's 3-sigma error radius.

All fluxes are 0.3-10 keV, observed. For all flux conversions and comparisons with
catalogues and upper limits  from other missions, we assumed a power-law spectrum
with NH=3x10^20 cm^-2 and photon index (Gamma)=1.7 unless otherwise stated.

The results of the XRT-team automatic analysis of the XRT observations, including a
position-specific upper limit calculator, are available at
https://www.swift.ac.uk/SVOM.

This circular is an official product of the Swift-XRT team.

Alan M. Watson (UNAM), Rosa L. Becerra (U Roma), Enrique Moreno Méndez (UNAM), Sarah Antier (OCA), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Fredd Alvarez (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (AUS), Nathaniel R. Butler (ASU) , Damien Dornic (CPPM), Jean-Grégoire Ducoin (CPPM), Francis Fortin (IRAP), Noémie Globus (UNAM), Kin Ocelotl López (UNAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), and Jerome Rodriguez (CEA):

We imaged the field of the SVOM X-ray transient sb25061218 (Rodriguez et al., GCN 40712
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 ) using the DDRAGO wide-field imager on the SVOM/COLIBRÍ (FM-GFT) telescope. We observed from 2025-06-13 06:18 to 10:34 UTC (from 9.7 to 14.0 hours after the trigger) and obtained 112 minutes of exposure in the i filter.

The data were reduced and coadded with the COLIBRÍ pipeline and analyzed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the Pan-STARRS DR1 catalog, is on the AB scale, and is not corrected for Galactic extinction.

In the stacked image, we do not detect any new source within the ECLAIRs source region reported by Rodriguez et al. (GCN 40712
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 ) to a formal 10-sigma limit of:

i > 23.0,

although we note that this is roughly the 50% completion limit of the Pan-STARRS DR1 catalog used to identify new sources.

We also performed image subtraction against Pan-STARRS DR2 at the position of the two XRT sources 1 and 2 reported by Evans et al. (GCN Circ. 40721
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 ) and see no evidence for optical counterparts to the same limit.

We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams.

COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico.

C. Adami (LAM/Pytheas/AMU), B. Schneider (LAM), S. Basa (LAM/OHP/Pytheas/AMU), E. Le Floc'h (CEA/Irfu), M. Dennefeld (IAP/Sorbonne U.), J. L. Atteia (IRAP), J. Rodriguez (CEA), F. Cangemi (APC), A. Coleiro (APC), Y. Degot-Longui (Pytheas/OHP), J. Balcaen (Pytheas/OHP), report on behalf of a larger collaboration:

We observed the field of the SVOM sb25061218 X-ray transient (Rodriguez et al., GCN 40712
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 ) using the T120cm and the T193cm equipped with the MISTRAL spectro-imager at Observatoire de Haute-Provence (France). 

Our T120 observations consisted of multiple epochs from 2025-06-12T22:07 to 2025-06-13T00:46 UT (from 1.52 to 4.17 hr after the trigger) in r-band and covered both uncatalogued X-ray sources seen with Swift/XRT (Evans et al. GCN 40721
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 ). We examined the sources visible at the XRT #1 and #2 positions and noted a rebrightening of ~0.3 mag of the SIMBAD object [VV2006] J131446.6+544804 compared to SDSS (r = 18.66 +/- 0.02) and PanStarrs (r = 18.65 +/- 0.01) surveys, possibly associated with the XRT source #1.

The magnitudes derived for that source (measured with STDWeb/STDPipe tools (Karpov 2025)) are:
date-obs (UT) | exposure time (min) | band, mag (AB) | mag err
2025-06-12T22:07 | 12min | r | 18.33 | 0.02
2025-06-12T22:36 | 12min | r | 18.29 | 0.04
2025-06-12T23:54 | 4min | r | 18.35 | 0.03
2025-06-13T00:46 | 8min | r | 18.36 | 0.03

On 2025-06-13 starting at 20:27 UT (23.85 hr after the trigger), we re-observed the object [VV2006] J131446.6+544804 with the spectro-imager MISTRAL. We obtained 1 minute of observation in r-band and measured a magnitude of r = 18.37 +/- 0.07, consistent with the T120 measurements on 2025-06-12. We also obtained 1 hour of spectroscopic observations using the MISTRAL blue mode with a spectral resolution of ~700 under moderately good conditions. When compared to the SDSS public spectrum, a preliminary analysis of the spectrum shows a flux increase of the Fe II complex between ~6600 AA and ~7000 AA. This increase is roughly consistent with the r-band magnitude variation observed by the T120 and MISTRAL.

Our observations suggest that the Swift/XRT source #1 is the X-ray counterpart to [VV2006] J131446.6+544804 source, a known QSO at z~ 0.49. The X-ray detection of this source is the first reported to our knowledge and may indicate that the SVOM trigger is also associated with this event. This object being radio-quiet (2.9 mJy at 1.4GHz, NVSS) without typical lines of TDEs, and the observed r-band magnitudes being nearly constant after the initial increase suggest a likely association with an accretion event onto the central black hole of this QSO and would disfavor a GRB nature of this event. 

We encourage further observations of [VV2006] J131446.6+544804.

We acknowledge the excellent support from Observatoire de Haute-Provence and in particular the students and professors from the summer camp OHP 2025 (Institut Origines) and the SOPHIE observer, Xavier Delfosse.