Astronomy and Astrophysics, volume 466, 595-618 (2007/5-1)
The INTEGRAL Galactic bulge monitoring program: the first 1.5 years.
KUULKERS E., SHAW S.E., PAIZIS A., CHENEVEZ J., BRANDT S., COURVOISIER T.J.-L., DOMINGO A., EBISAWA K., KRETSCHMAR P., MARKWARDT C.B., MOWLAVI N., OOSTERBROEK T., ORR A., RISQUEZ D., SANCHEZ-FERNANDEZ C. and WIJNANDS R.
Abstract (from CDS):
The Galactic bulge region is a rich host of variable high-energy point sources. Since 2005, February 17 we are monitoring the source activity in the Galactic bulge region regularly and frequently, i.e., about every three days, with the instruments onboard INTEGRAL. Thanks to the large field of view, the imaging capabilities and the sensitivity at hard X-rays, we are able to present for the first time a detailed homogeneous (hard) X-ray view of a sample of 76 sources in the Galactic bulge region. We describe the successful monitoring program and show the first results from the start of the monitoring up to 2006, April 21, i.e., for a period of about one and a half year, during three visibility seasons. We focus on the short (hour), medium (month) and long-term (year) variability in the hard X-ray bands, i.e., 20-60keV and 60-150keV. When available, we discuss the simultaneous observations in the soft X-ray, 3-10keV and 10-25keV, bands. Almost all the sources in the Galactic bulge region we detect in the 20-60keV and 60-150keV bands are variable. During the last two and a half weeks of the third visibility season most of the known persistent (hard) X-ray sources in the Galactic Center region were not detected. Of our sample of sources, per visibility season we detect 32/33 sources in the 20-60keV band and 8/9 sources in the 60-150keV band above a signal to noise of 7. On average, we find per visibility season one active bright (>100mCrab, 20-60keV) black-hole candidate X-ray transient and three active weaker (≲25mCrab, 20-60keV) neutron star X-ray transients. Most of the time a clear anti-correlation can be seen between the soft and hard X-ray emission in some of the X-ray bursters. Hard X-ray flares or outbursts in X-ray bursters, which have a duration of the order of weeks are accompanied by soft X-ray drops. On the other hand, hard X-ray drops can be accompanied by soft X-ray flares/outbursts. During the course of our program we found a number of new sources, IGRJ17354-3255, IGR17453-2853, IGRJ17454-2703, IGRJ17456-2901b, IGRJ17536-2339, and IGRJ17541-2252. We report here on some of the high-energy properties of these sources. The high-energy light curves of all the sources in the field of view, and the high-energy images of the region, are made available through the WWW, as soon as possible after the observations have been performed, at http://isdc.unige.ch/Science/BULGE/
accretion, accretion disks - binaries: close - binaries: general - stars: neutron - Galaxy: bulge - X-rays: binaries
Table 1: H1 732-322 is a probable misprint for H 1743-322. SLX 1744-229 is a probable misprint for SLX 1744-299.
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