INTEGRAL confirms the detection of renewed activity from the NS transient H 1658-298

INTEGRAL observed the Galactic Center Region between (UT) 2015-08-22 05:26 and 18:44. Enhanced X-ray emission was detected by the Joint European Monitor for X-rays (JEM-X) in the 3-10 keV band, (15 mCrab; 9-sigma significance) at the following position: (R.A., Dec) = (255.5284, -29.94175) = (17 02 06.82, -29 56 30.3) (J2000); 0.4 arc min 90% confidence limit.

These coordinates are consistent with those of the optical counterpart of H 1658-298: (R.A., Dec) = (17 02 06.5, -29 56 44.1; J2000, Liu et al., 2007 A&A, 469, 807), and thus confirm the system as the origin of the MAXI trigger on Aug 21 (see ATel #7943). The source spectrum extracted from the JEM-X data (effective exposure time 10.7 ksec) can be fit by a power-law model with photon index 2.9+/-0.5.

The flux estimated from the spectral fit is 2.8E-10 erg/cm^2/s (3-10 keV). H 1658-298 was marginally detected in hard X-rays (~6.8 mCrab, 4.5-sigma significance in the 20-40 keV energy band) by IBIS, the Imager Onboard the INTEGRAL Satellite. H 1658-298 is a known X-ray burster. Therefore we have searched for Type-I burst activity in the JEM-X data during these observations, but no indications of burst activity have been found.

We note here that the last outburst from this system was detected in 1999 April and lasted for ~2.5 years. It is likely we are at the onset of a similar outburst. Further INTEGRAL observations of the Galactic Center field are foreseen in the coming time, from August 26. Multi-wavelength observations of H 1658-298 are encouraged.