Swift J174510.8-262411 in the hard intermediate state

ATel #4450; T. Belloni (INAF-OAB, Italy), M. Cadolle Bel (ESAC, Spain), P. Casella (INAF-OAR, Italy), A. Castro-Tirado (IAA-CSIC, Spain), S. Corbel (CEA, France), M. Del Santo (IAPS, Italy), E. Gallo (Univ. Michigan, USA), V. Grinberg (Univ. Erlangen, Germany), J. Homan (MIT, USA), E. Kalemci (Sabanci Univ, Turkey), J. M. Miller (Univ. Michigan, USA), J. Miller-Jones (Curtin Univ, Australia), S. Motta (ESAC, Spain), T. Muñoz-Darias (Univ. Southampton, UK), M. Nowak (MIT, USA), K. Pottschmidt (NASA-GSFC, USA), J. Rodriguez (CEA, France), D. Russell (IAC, Spain), J. Tomsick (Univ. California Berkeley, USA), J. Wilms (Univ. Erlangen, Germany)
on 3 Oct 2012; 10:50 UT
Credential Certification: Tomaso Belloni (belloni@merate.mi.astro.it)

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We have been monitoring densely the bright transient Swift J174510.8-262411 (previous X-ray reports include ATel #4381,#4383,#4393,#4401,#4436) with INTEGRAL and Swift. The IBIS 20-150 keV light curve showed a flux increase between 2012 Sep 16 (MJD 56186) and Sep 17 (MJD 56187) and, after a time gap in the observations, a decrease from Sep 18 (MJD 56188.7) until Sep 28 (MJD 56198), after which it has remained constant. The IBIS spectrum softened monotonically through this period. A fit with a power law with a high-energy cutoff showed the photon index increasing from 1.3 to 2.24, while the cutoff energy increased marginally from 97 (-10,+31) keV to 145 (-19,+24). The 20-200 keV flux decreased from 1.5 10e-8 to 8.6 10e-9 erg/cm^2/s. In the same period, the Swift/XRT 0.6-10 keV rate has been steadily increasing (see ATel 4436). A QPO accompanied by band-limited noise is present in the power spectra of all XRT observations, with the frequency being strongly correlated with flux. It has increased from 0.25 Hz in the first observation (2012 Sep 18 19:03-22:18 UT, MJD 56188.8) to 2.4 Hz in the latest available observation (MJD 56202.3, 2012 October 2 7:09-7:28 UT). The energy spectrum on Oct 1 (MJD 56201) showed a slightly steeper spectrum than the last one reported in ATel #4436. The energy spectra and the power density spectra (along with the radio detections reported in ATel #4394,#4410) clearly indicate that in the first part of the campaign the source was brightening both in the hard and soft band and was in the low-hard state (LHS). This was followed by a transition to the hard intermediate state (HIMS), in which the source is currently still found. A further state transition to the soft-intermediate state is expected, which has been associated to relativistic jet ejections in other black-hole X-ray binaries, although it is difficult to predict when this will happen. Observations at all wavelengths are encouraged. We would like to thank the Swift and the INTEGRAL ISOC and ISDC Teams for making these observations possible.