X-ray, Optical and Infrared Observations of GX 339-4 During Its 2011 Decay

TL;DR

This study presents multiwavelength observations of GX 339-4 during its 2011 outburst decay, revealing state transitions, a rebrightening event, and jet-related spectral features, enhancing understanding of black hole transient behaviors.

Contribution

It provides detailed multiwavelength data and analysis of the spectral energy distribution and jet emission during the decay, highlighting the evolution of the source from soft-intermediate to hard state.

Findings

Rebrightening observed in optical and infrared bands 12 days after state transition.

Flat spectral slopes in SEDs suggest jet emission dominates during rebrightening.

Fluctuations with the binary period detected during the rising phase of rebrightening.

Abstract

We report multiwavelength observations of the black hole transient GX 339-4 during its outburst decay in 2011 using the data from RXTE, Swift and SMARTS. Based on the X-ray spectral, temporal, and the optical/infrared (OIR) properties, the source evolved from the soft-intermediate to the hard state. Twelve days after the start of the transition towards the hard state, a rebrightening was observed simultaneously in the optical and the infrared bands. Spectral energy distributions (SED) were created from observations at the start, and close to the peak of the rebrightening. The excess OIR emission above the smooth exponential decay yields flat spectral slopes for these SEDs. Assuming that the excess is from a compact jet, we discuss the possible locations of the spectral break that mark the transition from optically thick to optically thin synchrotron components. Only during the rising part of the rebrightening, we detected fluctuations with the binary period of the system. We discuss a scenario that includes irradiation of the disk in the intermediate state, irradiation of the secondary star during OIR rise and jet emission dominating during the peak to explain the entire evolution of the OIR light curve.