INTEGRAL observation of the Galactic transient Swift J174510.8-262411

ATel #4381; I. Vovk, C. Ferrigno, E. Bozzo (ISDC, Switzerland) S. P. Drave (Univ. of Southampton, UK), C. Sanchez, E. Kuulkers (ESAC/ESA, Spain), A. Bazzano, M. Del Santo, M. Fiocchi, L. Natalucci, A. Tarana (IAPS/INAF, Italy), I. Caballero, D. Goetz (CEA Saclay, France), J. Chenevez (DTU, Denmark), P. den Hartog (Stanford University HEPL/KIPAC, USA), L. Kuiper (SRON, The Netherlands), K. Watanabe (Florida Gulf Coast University, USA)
on 17 Sep 2012; 16:44 UT
Credential Certification: Carlo Ferrigno (Carlo.Ferrigno@unige.ch)

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During the INTEGRAL observations in direction of IGR J17544-2619 and the Galactic bulge performed from 2012-09-16T01:15 to 2012-09-17 05:34 UTC, a bright new transient is detected at coordinates RA=266.29,Dec=-26.40 with a 0.6 arcmin, 90% c.l. confinement radius. The location of the INTEGRAL source is consistent with the newly discovered transient Swift J174510.8-262411 (GCN #13774, GCN #13775, ATEL #4380).

The average broad band 5-500 keV JEM-X (61.6 ks) plus IBIS/ISGRI (63.9 ks) spectrum can be well fit by a power-law with exponential cut-off at high energy: Γ=1.29±0.04, E_cut=(122±10) keV (χ²=0.9 for 19 d.o.f., 1% systematic uncertainty). The 5-100 keV flux is (8.3±0.3)×10^-9 erg/s/cm². No significant features appear in the 3-35 keV JEM-X light curve (time bins 2 s-10 min).

The source presents a monotonically increasing flux in all bands: the continuous coverage by IBIS/ISGRI shows that the 20-40 keV flux at the beginning of the observation was 63±4 mCrab and reached 617±26 mCrab at its end. By comparing the corresponding rise in the harder 40-80 keV band from 78±5 to 805±40 mCrab and performing a linear fit to the hardness ratio, we found significant evidence (~8σ c.l.) of a spectral softening with time.

On the base of the rapid flux increase, the high value of the energy cut-off and the absence of thermonuclear bursts, we argue that Swift J174510.8-262411 might be a new black-hole transient.

Further observations at all wavelengths are encouraged to unveil the nature of this source.

We thank the INTEGRAL Galactic bulge monitoring group for their collaboration.