SVOM detection of either the high-energy counterpart to the Quasar [VV2006] J131446.6+544804, a new X-ray transient (SVOM J13140+5439), or a GRB

ATel #17236; J. Rodriguez (CEA, France), C. Adami (LAM/Pytheas/AMU, F), J. L. Atteia (IRAP, F), F. Cangemi (APC, F), A. Coleiro (APC, F), B. Cordier (CEA, F), T. Sadibekova, (CEA, F), B. Schneider (LAM, F), U. Jacob (LUPM, F), W. Xie (NAOC, C), L. Zhang (IHEP, C)
on 19 Jun 2025; 12:08 UT
Credential Certification: Jerome Rodriguez (jrodriguez@cea.fr)

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On 2025-06-12T20:36:00 UTC (hereafter T0), SVOM/ECLAIRs triggered and located an X-ray transient (SVOM burst-id sb25061218) at R.A.(J2000)= 13h14m00.67s and Dec.(J2000)=54d39m29.47s (+/-11.16 arcmin @ 90% confidence, Rodriguez et al. GCN 40712).

During the observation of the event (exposure time = 80s), the estimated average count rate is about 81 cts/s in the 4-120 keV energy band. A preliminary analysis of the (4-120 keV) ECLAIRs data shows the source has a power law like spectrum with a hard photon index Γ=1.5 +/-0.3 (90%) and a 4-120 keV flux of about 1e-8 erg/s/cm2.

In the X-rays, Swift observed the field between T0+5.9ks and T0+7.7ks. Two previously uncatalogued X-ray sources were detected with XRT within the ECLAIRs error box (Evans et al. GCN 40721). Both sources have very low 0.3-10 keV fluxes: ~5e-13 erg/s/cm2 and 1e-13 erg/s/cm2 for sources 1 and 2, respectively.

In Optical, the field was observed with various facilities. No sources were detected down to a 10-σ limit of i>23 with SVOM/Colibri between about T0+10hrs and T0+14hrs (Watson et al. GCN 40724).

On the other hand, Adami et al (GCN 40779) report the detection of a source within the XRT error box of source 1 at the OHP T120 telescope between T0+1.52hrs and T0+4.17hrs with r~18.3. The optical object is consistent with the quasar [VV2006] J131446.6+544804 (at z=0.48968), although with a 0.3 mag increase in r-band compared to standard optical catalogues. Their observations lead them to associate Swift source n1 to [VV2006] J131446.6+544804 (Adami et al., GCN 40779), while ruling out a GRB nature for this event.

The increase of the Optical flux two hours after the SVOM trigger renders the association of the SVOM trigger and the QSO tempting and possible, and in this case the SVOM trigger source would thus be the high-energy counterpart to [VV2006] J131446.6+544804 and Swift source n1, while in a period of enhanced multi-wavelength activity.

While the association of Swift source n1 with the quasar is very likely, the large differences of X-ray fluxes between SVOM and Swift are however puzzling in the context of transient QSO emission. We, thus, do not exclude that the SVOM trigger is a new unrelated X-ray transient source (SVOM J13140+5439), or a real GRB coincident by chance with a flare from [VV2006] J131446.6+544804. Under the latter interpretation, sb25061218 would be a rare example of an X-ray dark GRB.

Multi-wavelength follow-up of the field is encouraged.

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. ECLAIRs was developed jointly by APC, CEA, CNES and IRAP. MXT has been developed jointly by CNES, CEA, IJCLab, University of Leicester and MPE.