INTEGRAL detects high-energy > 200 keV emission of Swift 1727.8-1613

ATel #16238; F. Cangemi (UPC/APC), T. Bouchet (CEA-Saclay/DAP-AIM), S. E. Motta (INAF), P.-O. Petrucci (Grenoble University/IPAG)
on 12 Sep 2023; 07:40 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Floriane Cangemi (cangemi@apc.in2p3.fr)

Tweet

Since the MAXI/GSC detection on the 25th of august (Atel #16205) of Swift 1727.8-1613, the black hole candidate has been regularly monitored at all wavelengths, with various instruments (e.g., ATELs #16225, #16230, #16231, #16232, #16235), including INTEGRAL (e.g., ATEL #16217). The most recent observations show that the source is extremely bright with a 30-100 keV flux reaching 6 Crabs. After an initial period of flux increase, the last 5 observations made on 2023-08-30, 2023-09-01, 2023-09-05, 2023-09-07 and 2023-19-10 show that source is currently plateauing at hard-X-ray. The 30-100 keV IBIS spectrum varies little from one observation to another and can be modeled with a cut-off powerlaw with slope 2.2 +/-0.3 and cutoff energy 40 +/- 10 keV. Although, the source behaviour is typical of a black hole hard state and over these five last observations, we note that the photon index is slighly softer than usually observed in black hole hard state. Swift J1727.8-1613 is also detected in all 5 five observations with IBIS in the 200-600 keV at a significance level of ~10 sigma. The overall 30-600 keV spectra need an additional power law component to the cutoff powerlaw to be well represented (reduced chi squared 50.09/31 for the last observation). This extra hard tail has a photon index of 1.8 +/- 0.5 and a 200-600 keV flux of 5e-9 ergs/cm2/s. Note that the data analysed are near real time and not definitive; the results should then be taken with caution. All the analysis have been done with the latest version of the INTEGRAL data reduction software and calibrations (OSA 11.2). The next INTEGRAL ToO observation is planned for the 2023-09-13 03:16:41.