INTEGRAL detection of RS Oph in outburst at hard X-rays

ATel #14855; C. Ferrigno, V. Savchenko, E. Bozzo (ISDC/University of Geneva, CH), P. Thalhammer (Remeis-Observatory & ECAP, FAU Erlangen-Nuernberg), J. J.E. Kajava, C. Sánchez-Fernández (ESAC/ESA, Spain), A. Domingo (CAB/CSIC-INTA, Spain), L. Ducci (IAAT, Germany), L. Sidoli, A. Paizis (INAF-IASF Milano, Italy), J. Chenevez (DTU Space, Denmark), J. Wilms (Remeis-Observatory & ECAP, FAU Erlangen-Nuernberg), E. Kuulkers (ESTEC/ESA, The Netherlands)
on 12 Aug 2021; 21:37 UT
Credential Certification: Carlo Ferrigno (Carlo.Ferrigno@unige.ch)

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A new outburst of the Recurrent Nova RS Ophiuchi (RS Oph) was detected on 2021- 08-08 (ATels #14834, #14838, #14840, #14844, #14845, #14846, #14848, #14849, #14850, #14852), 15 years after its previous outburst in 2006 (ATel #737). The Galactic center region is regularly monitored by INTEGRAL and the source was in the field of view of the IBIS/ISGRI imager (28 –1000 keV) during the observations performed from 2021-08-07 17:04 UTC to 21-08-08 21:30 and from 2021-08-10 14:27 UTC to 2021-08-11 05:10 UTC. It was also within the smaller field of view of the JEM-X monitor (3-25 keV) from 2021-08-10 14:28 UTC to 2021-08-10 21:30 UTC.

RS Oph was marginally detected (6 σ) in the 28-40 keV IBIS/ISGRI energy band at a level of about 10 mCrab and firmly detected (37 sigma) by JEM-X at a level of 49±2 mCrab (3-10 keV) and 47±7 mCrab (10-25 keV). The JEM-X light curve does not show any significant variation during the observation.

We fit the combined preliminary spectrum built using all the available JEM-X (12 ks) and IBIS/ISGRI (65 ks) data. The emission is well described (reduced χ² of 1.3 with 17 degrees of freedom) by an absorbed collisional equilibrium plasma model (mekal in Xspec) with a temperature kT=8.4±1.0 keV and an equivalent hydrogen column density below 2x10²² cm^-2 (at 3 σ). The 3-20 and 20-100 keV fluxes are 1.1e-10 ergs/cm²/s and 7.2e-11 ergs/cm²/s, respectively. These results are based on a preliminary energy calibration of the JEM-X camera and should be used with caution.

We also extracted the data provided by the Optical Monitoring Camera (OMC) onboard INTEGRAL. Due to the current source brightness, (Vmag=5.5), the available OMC images are saturated.

INTEGRAL will continue monitoring the Galactic Center region for the next month. RS Oph will be often in the field of view of its instruments.