The ongoing outbursts of Aql X-1 and Ginga 1843+009 as seen with INTEGRAL/IBIS-ISGRI

Our INTEGRAL monitoring campaign of GRS 1915+105 allows the Aquila region of the sky to be nicely covered with the IBIS telescope. During our last observation, on March 18, 2009 (11h-16h45 UTC), both the LMXB Aql X-1 was clearly detected with the ISGRI camera at 17.5 sigma, 8.6 sigma, 6.6 sigma in the 18-40 keV, 40-80 keV, and 80-150 keV energy ranges respectively.

This confirms the renewal activity of Aql X-1 mentioned in ATel #1970. The 18-300 keV ISGRI spectrum is well fitted by a power law with an index Gamma=2.0±0.2 (Red chi=1.10 for 16 dof). The 20-200 keV flux is 1.22E-9 erg/s/cm2. Adding a cut-off in any of its forms (highecut*po or cutoffpl), or replacing the simple model by thermal Comptonization (comptt) does not improve the fit.

This clearly shows the absence of any cut-off in the energy range considered for the fit. We remark that the spectral parameters are compatible with those obtained with INTEGRAL during the decay of the 2007 October outburst when a possible transition back to a hard state had been seen(ATel #1229). The flux we obtain here is, however about twice the value of the October 2007 one.

The Swift/BAT light curve shows the source may have reached a plateau at hard X-rays.