INTEGRAL indication of enhanced non-thermal emission by eta Carinae
ATel #13347; C. Ferrigno (ISDC/UNIGE, CH), M. F. Corcoran (NASA/GSFC & CUA, USA), K. Hamaguchi (NASA/GSFC & UMBC, USA) , S. J. Sturner (NASA/GSFC & UMBC, USA), E. Kuulkers (ESTEC/ESA, NL), E. Bozzo, V. Sachenko (ISDC/UNIGE, CH), L. Ducci (IAAT, Germany)
on 13 Dec 2019; 16:23 UT
Credential Certification: Carlo Ferrigno (Carlo.Ferrigno@unige.ch)
Subjects: X-ray, Gamma Ray, Binary, Star, Variables
Referred to by ATel #: 13368
INTEGRAL performed a target-of-opportunity observation of the colliding wind binary eta Carinae from 2019-12-06 13:10:19 to 2019-12-07 09:28:36 (UTC). This was after the report of an X-ray flare seen by NICER (ATel #13327) and the enhanced gamma-ray emission by AGILE (ATel #13329). The IBIS/ISGRI imager marginally detected the source in the 28-40 keV energy band exploiting a net exposure of 41 ks, while the JEM-X monitor made a robust detection in the 3-10 keV band (net exposure of 46 ks). The combined JEM-X and IBIS/ISGRI spectrum can be fit in XSPEC with a model consisting of absorbed thermal emission (phabs*APEC ) below 10 keV in Xspec and non-thermal (powerlaw) emission above 10 keV. The reduced chi squared is 1.2 for 15 d.o.f.. The best-fit spectral parameters are:
n_H =36 (25-47) 1e22 cm^-2; kT = 0.9 (0.8-1.1) keV; Apec_norm = 42 (8-163); Photon Index = 2.2 (1.5-2.8); Flux (17-80 keV) =6 (4-8) 1e-11 erg/s/cm^2;
where the numbers in parentheses are the 1-sigma parameter ranges.
The 2-10 keV flux is consistent with the NICER 2-10 keV flux of 2.3e-10 ergs/cm2/s on 2019-12-09. Nominally, the 17-80 keV non-thermal flux is larger than the average orbital flux reported by Leyder et al. (2010, A&A 524, A59) and Hamaguchi et al. (2018, ApJ 795:119), although our flux estimate is still compatible with the earlier ones at the 2 sigma level. Longer INTEGRAL observations are needed to verify that the flux enhancement is significant.
Based on RXTE and Swift monitoring from previous cycles, eta Carinae is expected to start undergoing strong variations in its 2-10 keV band flux up to the decline to X-ray minimum. X-ray minimum is expected to occur on 13 February 2020. Multiwavelength observations prior to the X-ray minimum are encouraged.
