X-ray outburst of the TeV blazar 1ES 1959+650 observed by SVOM
ATel #16935; A. Coleiro (APC, France), P. Maggi (ObAS, F), D. Götz (CEA, F), F. Cangemi (APC, F), A. Foisseau (APC, F), S. Le Stum (APC, F), S. Schanne (CEA, F.) SVOM JSWG: J.-Y. Wei (NAOC, China), B. Cordier (CEA, F), Shuang-Nan Zhang (IHEP, C), S. Basa (LAM, F), O. Godet (IRAP, F), A. Claret (CEA, F), Z.-G. Dai (USTC, C), F. Daigne (IAP, F), J.-S. Deng (NAOC, C), A. Goldwurm (APC, F), X.-H. Han (NAOC, C), C. Lachaud (APC, F), E.-W. Liang (GXU, C), Y.-L. Qiu (NAOC, C), S. Vergani (Obs. Paris, F), J. Wang (NAOC, C), C. Wu (NAOC, F), L-.P. Xin (NAOC, C), B. Zhang (UNLV, C)
on 7 Dec 2024; 10:57 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Floriane Cangemi (cangemi@apc.in2p3.fr)
X-ray outburst of the TeV blazar 1ES 1959+650 observed by SVOM
On Friday December 6th at 15:08:48 UT (Tb), the on-board trigger software of the SVOM/ECLAIRs telescope (currently in its commissioning phase, instrument energy range 4-150 keV), detected and localized a long duration soft X-ray transient at RA, Dec = 300.202 deg, 65.182 deg (J2000) with 9.3 arcmin uncertainty radius in the 5-8 keV energy band during a 22 min exposure starting at Tb (best alert with SNR=9.3, see GCN 38450); another alert with SNR=7.2 was produced in 5-8 keV during 11 min starting at 15:14:15, the sub-image transmitted in near real-time over the SVOM VHF network showed a clear point-like source not present in the onboard source catalog.
Following this detection, SVOM/MXT (0.2-10 keV) performed a ToO observation of the source starting at 16:47:41 UT for an exposure time of 3.6 ks. A single source was detected in the image at coordinates R.A. = 20h 00mm 03ss DEC. = +65 deg 09mm 07ss (J2000) with an uncertainty of 25 arc sec at 90% c.l. (systematic+statistical). This position lies at 22 arcsec from the BL Lac blazar 1ES 1959+650 (GCN 38452).
These observations hence suggest that 1ES 1959+650 is currently exhibiting a major X-ray outburst.
A preliminary spectral analysis of the SVOM/ECLAIRs data (775 s of exposure) shows that the source is significantly detected up to ~20 keV. The 4-20 keV spectrum is well fitted by a power-law model (chi-square = 2.33 / 4 dof) with a photon index of 2.3 (-0.4; +0.5). The integrated flux in the 4-20 keV band is 6.4(-3.6 +1.2)e-10 erg/cm^2/s . Extrapolating to the 14-195 keV band, we find that the integrated flux is approximately 16 times higher than the average flux of 3.7e-11 erg/s/cm^2 reported in the Swift/BAT 157-month catalogue.
The SVOM/MXT spectrum is well fitted (chi-square = 321 / 260 dof) by a single absorbed power-law with a photon index of 1.97+/-0.05, and absorption column density of (0.17+/-0.1)e22 atoms/cm^2. The 0.5-10 keV flux is (1.77+/-0.03)e-9 erg/s/cm^2 which looks well above the usual unabsorbed 0.3-10 keV fluxes of 5.76e-11 -- 5.39e-10 erg/s/cm^2 (see https://pos.sissa.it/233/142/pdf).
Further multi-wavelength follow-up observations are encouraged to investigate the evolution of the source.
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.
