Abstract
All-sky explorations by Fermi-LAT have revolutionized our view of the gamma-ray Universe. While its ongoing all-sky survey counts thousands of sources, essential issues related to the nature of unassociated sources call for more sensitive all-sky surveys at hard X-ray energies that allow for their identification. This latter energy band encodes the hard-tail of the thermal emission and the soft-tail of non-thermal emission thereby bridging the non-thermal and thermal emission mechanisms of gamma-ray sources. All-sky surveys at hard X-rays are best performed by current coded-mask telescopes Swift/BAT and INTEGRAL/IBIS. To boost the hard X-ray all-sky sensitivity, we have developed an ad hoc technique by combining photons from independent observations of BAT and IBIS. The resulting Swift-INTEGRAL X-ray (SIX) survey has an improved source-number density. This improvement is essential to enhance the positive hard X-ray - gamma-ray source matches. We present the results from the scientific link between the neighboring gamma-ray and hard X-ray bands in the context of galactic and extragalactic source classes of the second catalog Fermi Gamma-ray LAT (2FGL).
Highlights
Whenever a frequency range of the electromagnetic spectrum is newly accessed by observatories, the discovery space is huge
To address the limited sensitivity issue of coded-mask telescopes, we have developed a new and ad-hoc technique that consists in summing up the independent photons detected by the Burst Alert Telescope [19] of the Swift mission and the INTEGRAL Soft Gamma-Ray Imager [20] of the Imager on Board the INTEGRAL Satellite [21]
Finding the hard X-ray counterparts of the Fermi-LAT sources The first attempt to systematically associate Fermi-LAT sources to counterparts in the hard X-ray energy domain was performed in a detailed study by [23] using the INTEGRAL/IBIS survey alone
Summary
Whenever a frequency range of the electromagnetic spectrum is newly accessed by observatories, the discovery space is huge. Sophisticated association studies of the 2FGL at radio and IR frequencies show promising results for blazars on the extragalactic sky [5, 6], while the Galactic plane and other types of sources are barely accessible at these frequencies.
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