GX 339-4: INTEGRAL observations in the bright hard state
ATel #14440; C. Ferrigno (ISDC, UNIGE), V. Grinberg (IAAT), E. Bozzo (ISDC, UNIGE), V. Savchenko (ISDC, UNIGE), L. Ducci (IAAT), J. Wilms (ECAP/FAU), P. Thalhammer (ECAP FAU), J. Rodriguez (CEA Saclay)
on 5 Mar 2021; 18:19 UT
Credential Certification: Victoria Grinberg (grinberg@astro.uni-tuebingen.de)
Subjects: X-ray, Black Hole, Transient
The black hole X-ray binary GX 339-4 has entered a new outburst in January 2021 (see also ATels #14336, #14351,#14352, #14354, #14367, #14384, #14400, #14419). Here, we are reporting on serendipitous monitoring of the source with INTEGRAL as it stalls in the hard state.
INTEGRAL observed GX 339-4 during the Galactic Plane Scan and Galactic Center observations from 2021-01-17 to 2021-03-03 for a total exposure of 129 ks. We have no observations before 16 February. From 17 to 27 January, the source increased steadily in its 20-100 keV flux. Since then, the increase stalled and the 20-100 keV flux is stable between 5 and 6x 10^{-9} erg/s/cm^2. We modelled the spectrum during each satellite revolution using a power-law with exponential high-energy roll-over at energy ~50 keV and hard X-ray photon index ~1.
Additional soft coverage from 16 to 20 February using the JEM-X instruments allows us to detect possible contributions of a soft component that can be modelled with a (multicolor)black body.
As of the last INTEGRAL observation on 2021-03-03, the source is not showing any indication of decrease in hard X-rays that would be indicative of a true source transition or of the end of a failed outburst. INTEGRAL will observe the Galactic Center region again on 2021-03-08. We encourage further monitoring of the source.
