Following the 2008 outburst decay of the black hole candidate H1743-322 in X-ray and radio

TL;DR

This study presents multi-wavelength observations of the 2008 outburst decay of black hole candidate H1743-322, revealing unique radio-X-ray correlation behavior, flaring activity, and insights into jet and accretion processes.

Contribution

It provides the first detailed analysis of radio and X-ray decay, showing a lower radio-X-ray correlation index and evidence for shocks in the jet, advancing understanding of black hole outburst physics.

Findings

Radio-X-ray correlation index ~0.18, lower than typical values.

Detection of optically thin radio flares during decay.

No significant change in X-ray spectral index during decay.

Abstract

In this Paper we report on radio (VLA and ATCA) and X-ray (RXTE, Chandra and Swift) observations of the outburst decay of the transient black hole candidate H1743-322 in early 2008. We find that the X-ray light curve followed an exponential decay, leveling off towards its quiescent level. The exponential decay timescale is ~4 days and the quiescent flux corresponds to a luminosity of 3x10^32 (d/7.5 kpc)^2 erg/s. This together with the relation between quiescent X-ray luminosity and orbital period reported in the literature suggests that H1743-322 has an orbital period longer than ~10 hours. Both the radio and X-ray light curve show evidence for flares. The radio - X-ray correlation can be well described by a power-law with index ~0.18. This is much lower than the index of 0.6-0.7 found for the decay of several black hole transients before. The radio spectral index measured during one of the radio flares while the source is in the low-hard state, is -0.5+-0.15, which indicates that the radio emission is optically thin. This is unlike what has been found before in black hole sources in the low-hard state. We attribute the radio flares and the low index for the radio - X-ray correlation to the presence of shocks downstream the jet flow, triggered by ejection events earlier in the outburst. We find no evidence for a change in X-ray power law spectral index during the decay, although the relatively high extinction of N_H =2.3x10^22 cm^-2 limits the detected number of soft photons and thus the accuracy of the spectral fits.