1 National Space Institute, Technical University of Denmark2 Astrophysics, National Space Institute, Technical University of Denmark3 European Space Astronomy Centre and European Space Agency4 University of Geneva5 National Institute for Astrophysics6 Florida Gulf Coast University
The neutron star, recurrent X-ray transients XTE J1709-267 (=RX J1709.5-2639) and XTE J1739-285, both of which are known X-ray bursters, were detected in outburst during INTEGRAL observations of the Galactic Center region (PI, J. Wilms), carried out between (UT) 2012 August 08, 07:18 - 19:05. XTE J1709-267 was seen by JEM-X at the 54-sigma level in the 3-10 keV band, with an average flux of 141 +/- 3 mCrab, and at the 27-sigma level in the 10-25 keV band, with an average flux of 61 +/- 7 mCrab. The effective JEM-X exposure time was 4 ks. XTE J1709-267 was only marginally detected by ISGRI in the 20-40 keV band. We estimate a rough flux of ~8 mCrab (5 sigma) for an effective ISGRI exposure time of 21 ks. A preliminary spectral fit to the JEM-X data is consistent with an absorbed disk blackbody model of temperature ~2.2 keV. The onset of this outburst was also detected by MAXI http://maxi.riken.jp/top/index.php?cid=1&jname=J1709-266 This new outburst from XTE J1709-267 occurs 2 years after the previous period of activity of the source, reported by MAXI/GSC (ATEL #2729), and is consistent with a outburst recurrence time of 2-3 years, claimed in ATel #1302. XTE J1739-285 was seen by JEM-X at the 9-sigma level in the 3-10 keV band, with an average flux of 16 +/- 2 mCrab, and at the 8-sigma level in the 10-25 keV band, with an average flux of 16 +/- 4 mCrab, for an effective exposure time of 10 ks. A weak (short) type-I X-ray burst was detected during these observations. The source flux in the 20-40 keV band was below the ISGRI sensitivity limit. The last outburst from XTE J1739-285, reported by INTEGRAL (ATel #734) was detected in 2006. XTE J1709-267 and XTE J1739-285 will be observed regularly by INTEGRAL in the coming weeks during Galactic Center and Galactic Bulge monitoring observations.