The RXTE All Sky Monitor: First Year of Performance

TL;DR

The RXTE All Sky Monitor has provided over a year of X-ray observations of celestial sources, detecting numerous sources and states, and offering valuable data for understanding X-ray binaries, active galactic nuclei, and transient phenomena.

Contribution

This paper presents the first-year performance data of the RXTE ASM, including source detections, light curve analysis, and insights into X-ray source behavior and outburst mechanisms.

Findings

109 sources detected, including 16 transients

Observed complex light curves and new emission states

Detected state changes in key X-ray binaries

Abstract

The RXTE All Sky Monitor provides a public database that includes more than one year of X-ray monitoring observations (2-12 keV) of X-ray binaries and a few active galactic nuclei. The instrument operates with a 40% duty cycle, and the exposures yield roughly 5 celestial scans per day. There have been 109 source detections, including 16 X-ray transients, the majority of which are recurrent cases. The two sources of relativistic radio jets have exhibited particularly complex light curves and new types of emission states. Progress has been achieved in understanding the outburst mechanism via the reported detection of an optical precursor to the April 1996 X-ray outburst in GRO J1655-40. The ASM has also detected state changes in both Cyg X-1 and Cyg X-3, leading to new constraints on the accretion disk geometry associated with the ``soft/high'' state. X-ray variations are seen in extragalactic nuclei, such as NGC4151 and Mkn501, providing new opportunities for multifrequency timing or spectral studies. The ASM archive empowers observers with the opportunity for state-dependent observing programs with RXTE and other instruments. The ASM also provides a long-term context for source behavior, and this knowledge may be crucial in shaping the interpretation of brief observations with other telescopes.