INTEGRAL Galactic Bulge monitoring: transient activity from KS 1741-293, MXB 1730-335, and IGR J17498-2921

As part of its regular monitoring of the Galactic Bulge (see ATel #438) INTEGRAL observed this region of the sky on September 13, 2011, between UTC 9:14:50 and 12:56:26. Both the JEM-X and the IBIS/ISGRI instruments detect the transient neutron star low-mass X-ray binary KS 1741-293 at the following flux levels: JEM-X: 6 +/-3 mCrab (3-10 keV) and 14 +/-6 mCrab (10-25 keV) ISGRI: 11 +/-2 mCrab (18-40 keV) and 13 +/-2 mCrab (40-100 keV) We note that the activity of this source already started two weeks ago as has been reported by Linares et al. (ATel #3632) and Barthelmy et al. (GCN #12319) using Swift data.

No X-ray burst is detected during the INTEGRAL observation. We also report on renewed activity (see, e.g., ATel #1398) from the Rapid Burster (MXB 1730-335) with the following fluxes: JEM-X: 139 +/-18 mCrab (3-10 keV) and 63 +/-20 mCrab (10-25 keV) ISGRI: 10 +/-2mCrab (18-40 keV) and 5 sigma upper limit of 10 mCrab (40-100 keV) A series of 15 type II bursts is detected when the source was inside the JEM-X field of view, with an average burst recurrence time of about four minutes.

The new transient source IGR J17498-2921 (see, e.g., ATels #3551, #3556, #3558, #3568, #3606) is only marginally detected by JEM-X in the 3-10 keV range at a flux level of 5 +/-3 mCrab and a 6 sigma upper limit of 2 mCrab between 10-25 keV. IBIS/ISGRI does not detect the source with 5 sigma upper limits of about 3 and 10 mCrab in the above quoted energy bands.

This indicates the source is fading back to quiescence. The next observation of the Galactic Bulge by INTEGRAL is planned for September 16, 2011.