A giant radio flare from Cygnus X-3 with associated Gamma-ray emission

TL;DR

This study reports on multi-wavelength observations of Cygnus X-3, linking gamma-ray emission to jet activity and state transitions, revealing that gamma-ray activity is associated with specific accretion states and jet formation.

Contribution

It provides the first detailed correlation between gamma-ray emission and radio/X-ray states in Cygnus X-3, highlighting the connection between accretion processes, jet activity, and high-energy emission.

Findings

Gamma-ray emission correlates with giant radio flares.

Gamma rays are absent during the radio-quenched state.

Gamma-ray activity occurs during state transitions, not only giant flares.

Abstract

With frequent flaring activity of its relativistic jets, Cygnus X-3 is one of the most active microquasars and is the only Galactic black hole candidate with confirmed high energy Gamma-ray emission, thanks to detections by Fermi/LAT and AGILE. In 2011, Cygnus X-3 was observed to transit to a soft X-ray state, which is known to be associated with high-energy Gamma-ray emission. We present the results of a multi-wavelength campaign covering a quenched state, when radio emission from Cygnus X-3 is at its weakest and the X-ray spectrum is very soft. A giant (~ 20 Jy) optically thin radio flare marks the end of the quenched state, accompanied by rising non-thermal hard X-rays. Fermi/LAT observations (E >100 MeV) reveal renewed Gamma-ray activity associated with this giant radio flare, suggesting a common origin for all non-thermal components. In addition, current observations unambiguously show that the Gamma-ray emission is not exclusively related to the rare giant radio flares. A 3-week period of Gamma-ray emission is also detected when Cygnus X-3 was weakly flaring in radio, right before transition to the radio quenched state. No Gamma rays are observed during the ~ one-month long quenched state, when the radio flux is weakest. Our results suggest transitions into and out of the ultrasoft X-ray (radio quenched) state trigger Gamma-ray emission, implying a connection to the accretion process, and also that the Gamma-ray activity is related to the level of radio flux (and possibly shock formation), strengthening the connection to the relativistic jets.