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    The Palermo BAT survey

    The 1st Palermo BAT catalogue

    We have performed a complete analysis of 39 months of BAT survey data in the 14-30, 14-70, 14-150 keV bands (Cusumano et al. 2010, A&A 510 A48). The data sample we used covers 90% of the sky down to a flux limit of 1.1 mCrab in the 14-150 keV band and 50% of the sky down to a flux limit of 0.8 mCrab. The minimum detection limiting flux is not fully uniform on the sky: the Galactic center and the ecliptic plane are characterized by a worse sensitivity due to high contamination from intense Galactic sources and to the observing constrains of the Swift spacecraft. The highest flux sensitivity is achieved near the ecliptic poles where a detection flux limit of about 1.1E-11 erg cm-2 s-1 is reached (~0.5 mCrab).

    Flusso limite

    Map of the 39-months survey limiting flux in the 14-150 keV band in galactic Aitoff projection, with the ecliptic coordinates grid superimposed. The scale on the colorbar is in mCrab.

    Our search yielded a list of 970 detections above a significance threshold of 4.8 standard deviations. We proceeded to the identification of the source counterparts using three strategies: cross-correlation with published hard X-ray catalogues, analysis of field observations of soft X-ray instruments, cross-correlation with the Simbad databases. Our all-sky map is shown in the Figure below. We derived a catalogue of 748 identified sources, 65% of which are extragalactic, while 25% are Galactic objects and 10% are already known X-ray or gamma ray emitters whose nature has not yet been determined. Our catalogue is by far more extended than the third ISGRI catalogue (amounting to ~500 sources, including transients; Bird et al. 2007) and the latest BAT survey catalogue published by the Swift-BAT team (154 AGNs from 9 months of data only; Tueller et al. 2008).

    Mappa sorgenti

    Map of the sources detected in the BAT survey data with BatImager. Different colors denote different object classes, as detailed in the legend. The size of the symbol is proportional to the source flux in the 14-150 keV band.

    By comparing the BAT source distribution with the third ISGRI catalogue we find a significant increase in the number of detected cataclysmic variable, and a dramatic improvement in the detection of extragalactic objects, both in the nearby Universe (normal galaxies, LINERs) and at higher distances (Seyfert galaxies, QSO, clusters of galaxies). This can be explained in part with the different pointing strategy of the two instruments. Sources in the Galactic plane not included in the ISGRI catalogue have been also detected. most of which identified as X-ray binaries.

    The Palermo BAT survey catalogue is available here

    Confronto ISGRI Galattiche

    Confronto ISGRI Galattiche Comparison between the sources in our catalog and those reported in the third ISGRI catalog. Top: Galactic sources. Bottom: Extragalactic sources.

    The remaining 220 unidentified sources detected with the BatImager in the 39-months all-sky map are uniformly distributed in the sky. From careful analysis of noise statistical fluctuations we expect between 23 and 69 spurious detections, corresponding to a fraction ranging from 10 to 30% of the sample of the 220 unidentified sources. We have started an identification campaign of these source candidates with Swift-XRT ( GI Cycle 5 )

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    Last Modified: February 9, 2012
    Edited by Valentina La Parola

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