The 105-Month Swift-BAT All-sky Hard X-Ray Survey

Abstract

We present the catalog of sources detected in the first 22 months of data from the hard X-ray survey (14-195 keV) conducted with the Burst Alert Telescope (BAT) coded mask imager on the Swift satellite. The catalog contains 461 sources detected above the 4.8σ level with BAT. High angular resolution X-ray data for every source from Swift-XRT or archival data have allowed associations to be made with known counterparts in other wavelength bands for over 97% of the detections, including the discovery of ∼30 galaxies previously unknown as active galactic nuclei and several new Galactic sources. A total of 266 of the sources are associated with Seyfert galaxies (median redshift z ∼ 0.03) or blazars, with the majority of the remaining sources associated with X-ray binaries in our Galaxy. This ongoing survey is the first uniform all-sky hard X-ray survey since HEAO-1 in 1977. Since the publication of the nine-month BAT survey we have increased the number of energy channels from four to eight and have substantially increased the number of sources with accurate average spectra. The BAT 22 month catalog is the product of the most sensitive all-sky survey in the hard X-ray band, with a detection sensitivity (4.8σ ) of 2.2 × 10 −11 erg cm −2 s −1 (1 mCrab) over most of the sky in the 14-195 keV band.

Hard X-ray properties of radio-selected blazars

“…In order to determine the number of common sources in the BAT 105-month source catalog and the MOJAVE-1 sample, the empirical relation of 90% error radius and signal strength is applied as a guideline (Oh et al 2018),…”

“…with the photon index Γ. Spectral fitting of the BAT spectra in the previous object catalogs (Tueller et al 2008;Baumgartner et al 2013;Oh et al 2018) made use of the χ 2 fitting statistic. Since this fitting statistic assumes Gaussian-distributed data with at least about 30 counts per energy bin, fitting of sources with lower numbers of counts is not feasible.…”

“…Within the uncertainty range of α Moj,BAT the log N-log S distribution for the hard X-ray data is not compatible with a regular Euclidean distribution. For comparison we also show the log N-log S distribution of the beamed AGN sub-sample of the 105-month Swift/BAT source catalog (Oh et al 2018), indicated Additionally, we fit the MOJAVE-1 log N-log S distribution of available VLBI radio flux density data from Lister et al (2015), using median flux density values. The observation time of the measurements spans 2008 -2012, reasonably close to the BAT survey time.…”

“…Previous all-sky surveys and studies at hard X-rays with the Swift/BAT instrument featured a moderately high significance cutoff at approximately 5 σ, effectively hiding a large number of blazars, and consequently leading to small sample sizes (see, e.g., Baumgartner et al 2013;Krivonos et al 2015). The 105-month BAT survey catalog (Oh et al 2018) counts 158 "beamed AGN", including blazars and flat-spectrum radio 2. Object samples 2.1.…”

“…The purpose of BAT, aside from GRB detection, is the monitoring of hard X-ray light curves for a list of transient and variable sources, as well as a continuous blind all-sky survey. The most recent catalog of galactic and extragalactic hard X-ray sources from Swift/BAT for the first 105 months of operation reaches a flux level of 7.24 · 10 −12 ergs −1 cm −2 over 50% of the sky and 8.40 · 10 −12 ergs −1 cm −2 over 90% of the sky at very uniformly distributed exposure times (Oh et al 2018).…”