Simultaneous H.E.S.S. and RXTE observations of the microquasars GRS 1915+105, Circinus X-1 and V4641 Sgr

TL;DR

This study conducted simultaneous H.E.S.S. and RXTE observations of three microquasars to search for gamma-ray flaring events, providing upper limits on their very-high-energy gamma-ray flux and enhancing understanding of their emission mechanisms.

Contribution

It presents the first simultaneous gamma-ray and X-ray observations of GRS 1915+105, Circinus X-1, and V4641 Sgr, setting upper limits on their VHE gamma-ray emission.

Findings

No significant gamma-ray emission detected during observations.

Established upper limits on VHE gamma-ray flux for each microquasar.

Provided detailed X-ray spectral analysis and source state classification.

Abstract

Microquasars, Galactic binary systems showing extended and variable radio emission, are potential gamma-ray emitters. Indications of gamma-ray transient episodes have been reported in at least two systems, Cyg X-1 and Cyg X-3. The identification of additional gamma-ray emitting microquasars is key for a better understanding of these systems. Very-high-energy gamma-ray emission from microquasars has been predicted to happen during periods of transient outbursts potentially connected with the formation of a jet-like outflow. Contemporaneous observations using the H.E.S.S. telescope array and the RXTE satellite were obtained on three microquasars: GRS 1915+105, Circinus X-1 and V4641 Sgr with the aim of detecting a broadband flaring event in the very-high-energy gamma-ray and X-ray bands. We report here on the analysis of these data for each system, including a detailed X-ray analysis assessing the location of the sources in a hardness-intensity diagram during the observations. Finally we discuss the derived upper limits on their very-high-energy gamma-ray flux.