The Swift/BAT Hard X-ray Transient Monitor

TL;DR

The Swift/BAT Hard X-ray Transient Monitor provides real-time sky coverage in 15-50 keV, detecting new and known X-ray transients, generating extensive light curves, and discovering 17 previously unknown sources over eight years.

Contribution

This paper details the methodology, data processing, and sensitivity analysis of the BAT transient monitor, highlighting its role in discovering 17 new X-ray sources and tracking over 900 sources.

Findings

Detected 245 sources, including 17 new ones.

Achieved a sensitivity of 5.3 mCrab for daily observations.

Monitored sources over eight years with detailed light curves.

Abstract

The Swift/Burst Alert Telescope (BAT) hard X-ray transient monitor provides near real-time coverage of the X-ray sky in the energy range 15-50 keV. The BAT observes 88% of the sky each day with a detection sensitivity of 5.3 mCrab for a full-day observation and a time resolution as fine as 64 seconds. The three main purposes of the monitor are (1) the discovery of new transient X-ray sources, (2) the detection of outbursts or other changes in the flux of known X-ray sources, and (3) the generation of light curves of more than 900 sources spanning over eight years. The primary interface for the BAT transient monitor is a public web page. Between 2005 February 12 and 2013 April 30, 245 sources have been detected in the monitor, 146 of them persistent and 99 detected only in outburst. Among these sources, 17 were previously unknown and were discovered in the transient monitor. In this paper, we discuss the methodology and the data processing and filtering for the BAT transient monitor and review its sensitivity and exposure. We provide a summary of the source detections and classify them according to the variability of their light curves. Finally, we review all new BAT monitor discoveries; for the new sources that are previously unpublished, we present basic data analysis and interpretations.