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New SVOM observations of 1ES 1959+650 during its current X-ray high state

ATel #16978; A. Foisseau (APC, France), F. Cangemi (APC, F), A. Coleiro (APC, F), P. Maggi (ObAS, F), C. Lachaud (APC, F), Z.-H. Yao (NAOC, China), S. Komossa (MPIfR, Germany), D. Grupe (NKU, USA) ; SVOM JSWG: J.-Y. Wei (NAOC, C), B. Cordier (CEA, F), S.-N. Zhang (IHEP, C), S. Basa (LAM, F), A. Claret (CEA, F), Z.-G. Dai (USTC, C), F. Daigne (IAP, F), J.-S. Deng (NAOC, C), O. Godet (IRAP, F), A. Goldwurm (APC, F), D. Götz (CEA, F), X.-H. Han (NAOC, C), E.-W. Liang (GXU, C), Y.-L. Qiu (NAOC, C), S. Vergani (Obs. Paris, F), J. Wang (NAOC, C), C. Wu (NAOC, C), L.-P. Xin (NAOC, C), S.-L. Xiong (IHEP, C), B. Zhang (UNLV, USA)
on 15 Jan 2025; 12:44 UT
Credential Certification: Floriane Cangemi (cangemi@apc.in2p3.fr)

Subjects: Optical, X-ray, AGN, Blazar

We report on the SVOM observational campaign targeting the TeV blazar 1ES 1959+650 (RA = 19h59min59.85s, DEC = +65°08’54.65”), detected in a high X-ray flux state on December 6 by SVOM (ATel #16935). Follow-up observations were carried out by Swift (ATel #16941, #16955) and MAGIC (ATel #16939). Also, IceCube searched for an excess of neutrino coming from the direction of the source (ATel #16959) and found that the data were consistent with the atmospheric background expectations.

The joint SVOM/MXT and SVOM/ECLAIRs spectra can be well fitted (chi2_red < 1.35) with an absorbed log-parabola with a fixed N_H = 0.101e22 cm-2 (galactic value). We retrieve the following integrated absorbed fluxes in the range [0.5-20] keV with the associated error at the confidence level of 1 sigma :

December 06 : F = 2.03(+0.04,-0.03) e-09 erg/cm2/s
December 11 : F = 1.01(+0.03,-0.04) e-09 erg/cm2/s
December 13 : F = 7.23(+0.43,-0.44) e-10 erg/cm2/s
December 15 : F = 1.77(+0.05,-0.05) e-09 erg/cm2/s
December 16 : F = 2.94(+0.05,-0.04) e-09 erg/cm2/s
December 18 : F = 9.18(+0.19,-0.26) e-10 erg/cm2/s
December 19 : F = 1.48(+0.03,-0.04) e-09 erg/cm2/s
December 22 : F = 1.78(+0.07,-0.08) e-09 erg/cm2/s
December 23 : F = 1.32(+0.04,-0.05) e-09 erg/cm2/s
December 26 : F = 6.91(+0.32,-0.14) e-10 erg/cm2/s


This confirms that the source was going through an outburst during all the period of observations with the highest flux state recorded around December the 16th, 2024. The 0.5-10 keV fluxes obtained with MXT are consistent with the Swift-XRT fluxes (see ATel #16941 and #16955). Moreover, the spectral evolution was found to be “harder-when-brighter” in the 0.5-10 keV energy range as expected for this type of source.

Finally, observations with the VT telescope onboard SVOM were conducted on December 6 and December 26, 2024. On December 6, we measured a magnitude of B = 14.712 +/- 0.005, and R = 14.120 +/- 0.004. On December 26, the magnitudes were B = 14.655 +/- 0.042 and R = 14.057 +/- 0.037. The magnitude in the B band reported by XRT (ATel #16955) shows a slight increase in the flux in the optical band between December 14 and December 26.

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.