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تسجيل مستخدم جديدThe INTEGRAL Galactic bulge monitoring program: the first 1.5 years
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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 this region about every three days with 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 for a period of about one and a half year. We focus on the short (hour), medium (month) and long-term (year) variability in the 20-60 keV and 60-150 keV bands. When available, we discuss the simultaneous observations in the 3-10 keV and 10-25 keV bands. Per visibility season we detect 32/33 sources in the 20-60 keV band and 8/9 sources in the 60-150 keV band. On average, we find per visibility season one active bright (>~100 mCrab, 20-60 keV) black-hole candidate X-ray transient and three active weaker (<~25 mCrab, 20-60 keV) 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. We found a number of new sources, IGR J17354-3255, IGR 17453-2853, IGR J17454-2703, IGR J17456-2901b, IGR J17536-2339, and IGR J17541-2252. 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 at http://isdc.unige.ch/Science/BULGE/.
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The Galactic Bulge region is a rich host of variable high-energy point sources. These sources include bright and relatively faint X-ray transients, X-ray bursters, persistent neutron star and black-hole candidate binaries, X-ray pulsars, etc.. We hav
e a program to monitor the Galactic Bulge region regularly and frequently with the gamma-ray observatory INTEGRAL. As a service to the scientific community the high-energy light curves of all the active sources as well as images of the region are made available through the WWW. We show the first results of this exciting new program.
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[Abridged] When WFC3 is installed on HST, the community will have powerful new tools for investigating resolved stellar populations. The WFC3 Galactic Bulge Treasury program will obtain deep imaging on 4 low-extinction fields. These non-proprietary d
ata will enable a variety of science investigations not possible with previous data sets. To aid in planning for the use of these data and for future proposals, we provide an introduction to the program, its photometric system, and the associated calibration effort. The observing strategy is based upon a new 5-band photometric system spanning the UV, optical, and near-infrared. With these broad bands, one can construct reddening-free indices of Teff and [Fe/H]. Besides the 4 bulge fields, the program will target 6 fields in well-studied star clusters, spanning a wide range of [Fe/H]. The cluster data serve to calibrate the indices, provide population templates, and correct the transformation of isochrones into the WFC3 photometric system. The bulge data will shed light on the bulge formation history, and will also serve as population templates for other studies. One of the fields includes 12 candidate hosts of extrasolar planets. CMDs are the most popular tool for analyzing resolved stellar populations. However, due to degeneracies among Teff, [Fe/H], and reddening in traditional CMDs, it can be difficult to draw robust conclusions from the data. The 5-band system used for the bulge Treasury observations will provide indices that are roughly orthogonal in Teff and [Fe/H], and we argue that model fitting in an index-index diagram will make better use of the information than fitting separate CMDs. We provide simulations to show the expected data quality and the potential for differentiating between different star-formation histories.
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