The 157-month Swift-BAT All-Sky Hard X-Ray Survey

TL;DR

This paper presents the 157-month all-sky hard X-ray survey using Swift-BAT, cataloging 1888 sources with spectral and temporal data, and discusses the survey's sensitivity and new detections over an extended period.

Contribution

The study provides an updated, comprehensive catalog of X-ray sources from Swift-BAT with 4.5 additional years of data and improved calibration, including new detections and detailed source information.

Findings

Sensitivity of $8.83 imes 10^{-12}$ erg s$^{-1}$ cm$^{-2}$ for 90 h percentile sky

Detection of 256 new X-ray sources above $4.8\sigma$ threshold

Identification of systematic noise affecting sensitivity improvements

Abstract

The Burst Alert Telescope (BAT) onboard the Neil Gehrels Swift observatory has been serving as a survey instrument for the hard X-ray sky, and has detected thousands of X-ray sources (e.g., AGNs, X-ray binaries, etc). BAT monitors these X-ray sources and follows their light curves on time scales from minutes to years. In addition, BAT discovers hundreds of new X-ray sources in survey images stacked throughout the mission lifetime. We present the updated BAT survey catalog since the last published BAT 105 month survey catalog (Oh et al. 2018) with additional of 4.5 years of data until December 2017. Data since 2007 are reprocessed to include updated instrumental calibration. Analysis in this study shows that additional systematic noise can be seen in the 157-month mosaic images, resulting in decreases in the expected improvement in sensitivity and the number of new detections. The BAT 157-month survey reaches a sensitivity of $8.83 \times 10^{-12} \rm \ erg \ s^{-1} \ cm^{-2}$ for 90\% of the sky and $6.44 \times 10^{-12} \rm \ erg \ s^{-1} \ cm^{-2}$ for 10\% of the sky. This catalog includes spectra, monthly and snapshot light curves in eight energy bands (14-20, 20-24, 24-35, 35-50, 50-75, 75-100, 100-150, and 150-195 keV) for 1888 sources, including 256 new detections above the detection threshold of $4.8\sigma$. The light curves, spectra, and tables that summarize the information of the detected-sources are available in the online journal and in the catalog web page https://swift.gsfc.nasa.gov/results/bs157mon/.