Multiwavelength Observations of LS I +61 303 with VERITAS, Swift and RXTE

TL;DR

This study presents long-term multiwavelength observations of the TeV binary LS I +61 303, revealing variability in TeV and X-ray emissions over multiple orbital cycles and exploring potential correlations between these bands.

Contribution

First comprehensive multiwavelength monitoring of LS I +61 303 combining VERITAS, Swift, and RXTE data over multiple orbital cycles.

Findings

Detected TeV emission with significance up to 8.8 sigma.

Observed flux variability in TeV and X-ray bands over orbital cycles.

Found marginal evidence for TeV emission outside of apastron.

Abstract

We present results from a long-term monitoring campaign on the TeV binary LSI +61 303 with VERITAS at energies above 500 GeV, and in the 2-10 keV hard X-ray bands with RXTE and Swift, sampling nine 26.5 day orbital cycles between September 2006 and February 2008. The binary was observed by VERITAS to be variable, with all integrated observations resulting in a detection at the 8.8 sigma (2006/2007) and 7.3 sigma (2007/2008) significance level for emission above 500 GeV. The source was detected during active periods with flux values ranging from 5 to 20% of the Crab Nebula, varying over the course of a single orbital cycle. Additionally, the observations conducted in the 2007-2008 observing season show marginal evidence (at the 3.6 sigma significance level) for TeV emission outside of the apastron passage of the compact object around the Be star. Contemporaneous hard X-ray observations with RXTE and Swift show large variability with flux values typically varying between 0.5 and 3.0*10^-11 ergs cm^-2 s^-1 over a single orbital cycle. The contemporaneous X-ray and TeV data are examined and it is shown that the TeV sampling is not dense enough to detect a correlation between the two bands.