INTEGRAL sees transient activity in the Galactic Bulge: XTE J1751-305 and GRS 1741.9-2853 in outburst

Jérôme Chenevez, E. Kuulkers, V. Beckmann, A. Bird, Søren Kristian Brandt, A. Domingo, K. Ebisawa, P. Jonker, P. Kretschmar, C. Markwardt, T. Oosterbroek, A. Paizis, D. Risquez, C. Sanchez-Fernandez, S. Shaw, R. Wijnands

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Abstract

INTEGRAL monitoring observations of the Galactic Bulge (e.g. ATels #438 and #1944) have been performed between 2009 Oct 7th 20:29 and 8th 00:11 (UTC) during which transient activity from a few known sources has been recorded with respect to an observation 6 days earlier. The transient low-mass X-ray binary and known X-ray burster GRS 1741.9-2853 (e.g. Cocchi et al. A&A 346, L45, 1999) is detected by INTEGRAL/JEM-X at an average flux of about 58 mCrab (9.3E-10 erg/cm2/s) and 25 mCrab (2.75E-10 erg/cm2/s) in 3-10 keV and 10-25 keV, respectively. The source showed strong variations with a maximum at 92 +/- 12 mCrab (3-10 keV) and 37 +/-11 mCrab (10-25 keV) during one pointing between 2009 Oct 7 21:01 and 21:31 (UTC), and another at 46 +/- 2 mCrab (3-10 keV) and 13 +/- 4 mCrab (10-25 keV) during a pointing between 23:09 and 23:39 (UTC). At other times the source intensity stayed below 10 mCrab and 4 mCrab in above-mentioned energy ranges. IBIS/ISGRI did also detect GRS 1741.9-2853 with an average intensity of about 10 mCrab and significance of 6.1 sigma in the 18-40 keV range. The accreting millisecond X-ray pulsar XTE J1751-305 (e.g. Markwardt et al. ApJ 575, L21, 2002) is detected with JEM-X at 15 +/- 6 mCrab (3-10 keV) and 22 +/- 10 mCrab (10-25 keV), and with IBIS/ISGRI at 9 +/- 2mCrab (18-40 keV) and 14 +/- 3mCrab (40-100 keV). The source was not detected in the previous Bulge observation with 3-sigma upper limits of 4 mCrab and 2 mCrab in the same respective JEM-X energy bands. On the other hand, the closeby and recently discovered accreting millisecond X-ray pulsar IGR J17511-3057 (e.g. ATels #2196-2199) has dimmed to below the INTEGRAL detection levels, whereas it was still detected 6 days earlier at about 12 mCrab averaged over the above-mentioned energy bands. The 3-sigma upper limits are now about 5 mCrab and about 2 mCrab between 3-10 keV and 10-25 keV, respectively. We further notice that none of the X-ray bursters in the close source pair SLX 1744-299/300 is significantly detected in JEM-X with 3-sigma upper limits of about 6 mCrab (3-10 keV) and about 3 mCrab (10-25 keV). This seems to indicate an unusual change in their spectral state, for the pair is simultaneously detected by IBIS/ISGRI at 16.5 mCrab with a significance of 10.6 sigma (18-40 keV), while it was 8 mCrab (6 sigma significance), and 20 mCrab in average for JEM-X, in the previous observation. The next INTEGRAL Galactic Bulge observation is planned for 2009 October 16th.
Original languageEnglish
JournalThe Astronomer´s Telegram
Volume#2235
Publication statusPublished - 2009

Keywords

  • Transients
  • Binaries
  • X-ray
  • Neutron Stars
  • Request for Observations

Cite this

Chenevez, J., Kuulkers, E., Beckmann, V., Bird, A., Brandt, S. K., Domingo, A., Ebisawa, K., Jonker, P., Kretschmar, P., Markwardt, C., Oosterbroek, T., Paizis, A., Risquez, D., Sanchez-Fernandez, C., Shaw, S., & Wijnands, R. (2009). INTEGRAL sees transient activity in the Galactic Bulge: XTE J1751-305 and GRS 1741.9-2853 in outburst. The Astronomer´s Telegram, #2235. http://www.astronomerstelegram.org/?read=2235