Transient X-ray burster KS 1741-293 active again

ATel #4840; E. Kuulkers (ESA/ESAC, Spain), J. Alfonso-Garzon (CAB/INTA-CSIC, Spain), V. Beckmann (APC, France), T. Bird (Southampton, UK), S. Brandt, J. Chenevez (DTU Space, Denmark), T. Courvoisier (ISDC, Switzerland), M. Del Santo (INAF/IASF-Roma, Italy), A. Domingo (CAB/INTA-CSIC, Spain), K. Ebisawa (ISAS, Japan), P. Jonker (SRON, The Netherlands), P. Kretschmar (ESA/ESAC, Spain), C. Markwardt (GSFC, USA), T. Oosterbroek (ESA/ESTEC, The Netherlands), A. Paizis (INAF-IASF, Italy), K. Pottschmidt (UMBC/NASA GSFC, USA), C. Sanchez-Fernandez (ESA/ESAC, Spain) & R. Wijnands (UvA, The Netherlands)
on 25 Feb 2013; 14:28 UT
Credential Certification: Erik Kuulkers (ekuulker@rssd.esa.int)

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The transient X-ray burster KS 1741-293 (e.g., ATel #1531, #2465, #3632, #3646) has become active again. During observations as part of the INTEGRAL Galactic bulge monitoring program (see ATel #438) on (UT) 22 February 2013 15:22-19:04 and 24 February 07:04-10:45, the source brightened from 16+/-2 to 22+/-2 mCrab and 13+/-2 to 17+/-2 mCrab in the IBIS/ISGRI 18-40 and 40-100 keV bands, respectively. On 12 February it was seen in the 18-40 keV band with a flux of 8+/-2 mCrab, but with a low significance of 3.9, while it was undetected in the 40-100 keV bands (upper limit of ~10 mCrab; 6 sigma).

On 22 Feb the source was detected by JEM-X at 10+/-2 (3-10 keV) and 14+/-4 mCrab (10-25 keV), while it was not detected on 12 Feb (3 sigma upper limits of ~3 and ~8 mCrab, respectively). For the observation on 24 February we can only infer upper limits of ~15 and ~20 mCrab (3-10 keV and 10-25 keV, respectively, 3 sigma).

During the two observations on 22 and 24 February JEM-X observed one Type I X-ray burst. It started near UT 22 February 18:36:12, had a peak rate of about 0.3 Crab (3-25 keV), and an exponential decay time scale of about 8 sec.

The hardness of the source in this active state is similar to that seen during INTEGRAL Galactic bulge monitoring program observations performed in September 2011 (ATel #3646), but different to that seen in similar observations performed in March 2010 (ATel #2465). We encourage follow-up observations of this source at all wavelengths.

INTEGRAL Galactic bulge monitoring program