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INTEGRAL observation of the on-going outburst from Swift J1658.2-4242

ATel #11336; L. Ducci (IAAT, Germany; ISDC, Switzerland), E. Bozzo, C. Ferrigno, V. Savchenko (ISDC, Switzerland), E. Kuulkers (ESA/ESTEC, The Netherlands)
on 22 Feb 2018; 16:44 UT
Credential Certification: E. Bozzo (enrico.bozzo@unige.ch)

Subjects: X-ray, Black Hole, Transient

Referred to by ATel #: 11358, 11375

The new X-ray and radio transient source Swift J1658.2-4242 (GCN #22416, #22417, #22419; ATel #11306, #11307, #11310, #11311, #11318, #11321, #11322, #11334) has been recently observed by INTEGRAL, from 2018 February 20 at 14:04 to 2018 February 22 at 15:03:12 (UTC), during a monitoring dedicated to this source.

We report the results from a preliminary data analysis of these data. Swift J1658.2-4242 is detected in the IBIS/ISGRI mosaic (based on data from 2018 February 20 at 14:04 to February 22 at 02:22, UTC; exposure time 125 ks) at a significance of 121 sigma in the 20-40 keV energy range and about 46 sigma in the 40-80 keV energy range. The corresponding fluxes estimated from the IBIS/ISGRI mosaics are 100+/-1 mCrab and 67+/-1 mCrab, respectively.

Swift J1658.2-4242 is also detected in the JEM-X mosaics (same observations used for the ISGRI mosaics, see above) at a significance of 59 sigma in the 3-10 keV energy range and about 37 sigma in the 10-20 keV energy range. The corresponding fluxes calculated from the JEM-X mosaics are 100+/-2 mCrab and 115+/-3 mCrab, respectively.

We measured the fluxes of Swift J1658.2-4242 in mCrab, using the most recently available calibration observation of the Crab carried out during the satellite revolution 1921 (from 2018 February 17 at 22:39 to 2018 February 18 at 11:59, UTC).

The average JEM-X + ISGRI spectrum (3-100 keV) can be reasonably well described (chi2_red=1.5, 24 d.o.f.) by an absorbed power law with photon index 2.61+/-0.04 (we fixed the absorption column density at N_H=1.3E23 cm^-2, as previously reported in the ATel #11321). Uncertainties are given at 68% c.l. The estimated flux from the spectral fit is about 3.6E-9 ergs/cm^2/s in the energy range 3 - 100 keV.

A more detailed spectral analysis will be carried on the consolidated INTEGRAL data.

We are grateful to the INTEGRAL team for rapidly planning the requested observation.