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IGR J19140+0951 simultaneously observed with INTEGRAL, Swift and RXTE

ATel #800; J. Rodriguez (CEA/AIM Saclay, France), V. Beckmann (NASA/GSFC/UMBC, USA), D. C Hannikainen (Obs. of Helsinki, Finland), F. Lebrun (CEA/APC, France), S. E. Shaw (Univ. of Southampton, UK), D. Willis (MPE Garching, Germany)
on 28 Apr 2006; 14:19 UT
Credential Certification: Jerome Rodriguez (jrodriguez@cea.fr)

Subjects: X-ray, Gamma Ray, Black Hole, Neutron Star, Transient, Pulsar

The INTEGRAL source IGR J19140+0951 (Hannikainen et al. 2004, A&A, 423, L17) has been simultaneously targeted with INTEGRAL, Swift, and RXTE on April 26-27 2006, for 21, ~7, and ~7 ks respectively.

The source is not detected by INTEGRAL/ISGRI with a 20-40 keV 3-sigma upper limit of 4.5 mCrab, indicating that the source was in a faint luminosity state. The Swift XRT image shows a single, although dim, point source at a position consistent with that of IGR J19140+0951, from which a spectrum was extracted. Given the faintness of the source, seen in the Swift data, we further corrected the RXTE/PCA data for the emission of the Galactic Ridge at the position of IGR J19140+0951, using Valinia & Marshall 1998 (ApJ 505, 134).

All spectra have been rebinned so as to have a minimum of 20 counts per channel. A simple absorbed powerlaw gives a reasonable representation of the Swift/XRT and RXTE/PCA spectrum between 1 and 18 keV. The value of the absorption is 9.1(-3.0 +3.5) 1022 cm-2(errors are at the 90% level), the power law photon index Gamma=1.7 (+-0.3). Note that a multiplicative constant has been included to account for uncertainties in the instrumental cross calibrations. If set to 1.0 for PCA the value obtained for Swift is 0.77, which may suggest that the PCA spectrum still suffers from contamination by the Galactic Ridge emission.

The 1-20 flux is 1.54 x10-11 erg/s/cm2 (Swift normalization), and the 1-20 keV unabsorbed flux is 2.47 x10-11 erg/s/cm2. This is the faintest flux at which this source has ever been detected, in particular it is about 5 times fainter than the dimmest observation published so far (Rodriguez et al. 2005, A&A, 432, 235), and about 150 times fainter than the brightest state of the source seen with INTEGRAL. This gives a lower limit on the amplitudes of the X-ray emission that this source can show.

Finally the large absorption column density, its variation with time, the large amplitude of the variations of the X-ray flux of the source suggest that IGR J19140+0951 is truly another member of the class of heavily absorbed source revealed by INTEGRAL, similar to e.g. IGR J16320-4751.

We will continue our high energy monitoring campaign on this source in the future.

The authors acknowledge the great efforts of the INTEGRAL, RXTE and Swift planners in allowing us to have strictly simultaneous pointings with the three satellites.