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INTEGRAL/IBIS 7-year All-Sky Hard X-Ray Survey. Part II: Catalog of Sources

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 نشر من قبل Roman Krivonos
 تاريخ النشر 2010
  مجال البحث فيزياء
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This paper is the second in a series devoted to the hard X-ray (17-60 keV) whole sky survey performed by the INTEGRAL observatory over seven years. Here we present a catalog of detected sources which includes 521 objects, 449 of which exceed a 5 sigma detection threshold on the time-averaged map of the sky, and 53 were detected in various subsamples of exposures. Among the identified sources with known and suspected nature, 262 are Galactic (101 low-mass X-ray binaries, 95 high-mass X-ray binaries, 36 cataclysmic variables, and 30 of other types) and 219 are extragalactic, including 214 active galactic nuclei (AGNs), 4 galaxy clusters, and galaxy ESO 389-G 002. The extragalactic (|b|>5 deg) and Galactic (|b|<5 deg) persistently detected source samples are of high identification completeness (respectively ~96% and ~94%) and valuable for population studies.



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This paper is the first in a series devoted to the hard X-ray whole sky survey performed by the INTEGRAL observatory over seven years. Here we present an improved method for image reconstruction with the IBIS coded mask telescope. The main improvemen ts are related to the suppression of systematic effects which strongly limit sensitivity in the region of the Galactic Plane (GP), especially in the crowded field of the Galactic Center (GC). We extended the IBIS/ISGRI background model to take into account the Galactic Ridge X-ray Emission (GRXE). To suppress residual systematic artifacts on a reconstructed sky image we applied nonparametric sky image filtering based on wavelet decomposition. The implemented modifications of the sky reconstruction method decrease the systematic noise in the ~20 Ms deep field of GC by ~44%, and practically remove it from the high-latitude sky images. New observational data sets, along with an improved reconstruction algorithm, allow us to conduct the hard X-ray survey with the best currently available minimal sensitivity 3.7E-12 erg/s/cm2 ~0.26 mCrab in the 17-60 keV band at a 5 sigma detection level. The survey covers 90% of the sky down to the flux limit of 6.2E-11 erg/s/cm2 (~4.32 mCrab) and 10% of the sky area down to the flux limit of 8.6E-12 erg/s/cm2 (~0.60 mCrab).
Context. The INTEGRAL observatory operating in a hard X-ray/gamma domain has gathered a large observational data set over nine years starting in 2003. Most of the observing time was dedicated to the Galactic source population study, making possible t he deepest Galactic survey in hard X-rays ever compiled. Aims. We aim to perform a Galactic survey that can be used as the basis of Galactic source population studies, and perform mapping of the Milky Way in hard X-rays over the maximum exposure available at |b|<17.5 deg. Methods. We used sky reconstruction algorithms especially developed for the high quality imaging of INTEGRAL/IBIS data. Results. We present sky images, sensitivity maps, and catalogs of detected sources in the three energy bands 17-60, 17-35, and 35-80 keV in the Galactic plane at |b|<17.5 deg. The total number of sources in the reference 17-60 keV band includes 402 objects exceeding a 4.7 sigma detection threshold on the nine-year time-averaged map. Among the identified sources with known and tentatively identified natures, 253 are Galactic objects (108 low-mass X-ray binaries, 82 high-mass X-ray binaries, 36 cataclysmic variables, and 27 are of other types), and 115 are extragalactic objects, including 112 active galactic nuclei (AGNs) and 3 galaxy clusters. The sample of Galactic sources with S/N>4.7 sigma has an identification completeness of ~92%, which is valuable for population studies. Since the survey is based on the nine-year sky maps, it is optimized for persistent sources and may be biased against finding transients.
We present results of an all-sky hard X-ray survey based on almost four years of observations with the IBIS telescope on board the INTEGRAL observatory. The dead time-corrected exposure of the survey is ~33 Ms. Approximately 12% and 80% of the sky ha ve been covered to limiting fluxes lower than 1 and 5 mCrab, respectively. Our catalog of detected sources includes 400 objects, 339 of which exceed a 5 sigma detection threshold on the time-averaged map of the sky and the rest were detected in various subsamples of exposures. Among the identified sources, 213 are Galactic (87 low-mass X-ray binaries, 74 high-mass X-ray binaries, 21 cataclysmic variables, 6 coronally active stars, and other types) and 136 are extragalactic, including 131 active galactic nuclei (AGNs) and 3 clusters of galaxies. We obtained number-flux functions for AGNs and Galactic sources. The logN-logS relation of AGNs (excluding blazars) is based on 69 sources with fluxes higher than S_lim=1.1 x 10^{-11} erg/s/cm^2 (~0.8 mCrab) in the 17-60 keV energy band. The cumulative number-flux function of AGNs located at Galactic latitudes $|b|>5^circ$, where the survey is characterized by high identification completeness, can be described by a power law with a slope of 1.62 +/- 0.15 and normalization of (5.7 +/- 0.7) x 10^{-3} sources per deg^2 at fluxes >1.43 x 10^{-11} erg/s/cm^2 (>1 mCrab). AGNs with fluxes higher than S_lim make up ~1% of the cosmic X-ray background at 17-60 keV. We present evidence of strong inhomogeneity in the spatial distribution of nearby (<70 Mpc) AGNs, which reflects the large-scale structure in the local Universe.
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