Disentangling the NIR/optical emission of the black hole XTE J1650-500 during outburst

TL;DR

This study investigates the origins of NIR/optical emission in the black hole candidate XTE J1650-500 during outburst, revealing multiple emission sources including reprocessing and a weak jet, and highlighting its unique outlier status in NIR/optical correlations.

Contribution

It provides the first detailed analysis of NIR/optical emission mechanisms in XTE J1650-500, combining photometric, timing, and spectral data to disentangle emission sources.

Findings

NIR/optical flux arises from multiple emission mechanisms.

The jet in XTE J1650-500 is weaker than in similar sources.

XTE J1650-500 is an outlier in NIR/optical--X-ray correlation.

Abstract

While the sources of X-ray and radio emission in the different states of low-mass X-ray binaries are relatively well understood, the origin of the near-infrared (NIR) and optical emission is more often debated. It is likely that the NIR/optical flux originates from an amalgam of different emission regions, because it occurs at the intersecting wavelengths of multiple processes. We aim to identify the NIR/optical emission region(s) of one such low-mass X-ray binary and black hole candidate, XTE J1650-500, via photometric, timing, and spectral analyses. We present unique NIR/optical images and spectra, obtained with the ESO-New Technology Telescope, during the peak of the 2001 outburst of XTE J1650-500. The data suggest that the NIR/optical flux is due to a combination of emission mechanisms including a significant contribution from X-ray reprocessing and, at early times in the hard state, a relativistic jet that is NIR/radio dim compared to similar sources.The jet of XTE J1650-500 is relatively weak compared to that of other black hole low-mass X-ray binaries, possibly because we observe as it is being "turned off" or quenched at the state transition. While there are several outliers to the radio--X-ray correlation of the hard state of low-mass X-ray binaries, XTE J1650-500 is the first example of an outlier to the NIR/optical--X-ray correlation.