Limits on the quiescent radio emission from the black hole binaries GRO J1655-40 and XTE J1550-564

TL;DR

This study sets upper limits on radio emissions from two black hole binaries in quiescence, suggesting they are relatively radio quiet at low luminosities and extending the known X-ray:radio correlation to quiescent states.

Contribution

First to provide radio flux upper limits for GRO J1655-40 and XTE J1550-564 in quiescence, indicating their radio quiet nature at low luminosities.

Findings

Neither system was detected in radio observations.

Black hole binaries are relatively radio quiet at low luminosities.

The X-ray:radio correlation extends to quiescent states.

Abstract

We present the results of radio observations of the black hole binaries GRO J1655-40 and XTE J1550-564 in quiescence, with the upgraded Australia Telescope Compact Array. Neither system was detected. Radio flux density upper limits (3 sigma) of 26 micro Jy (at 5.5 GHz), 47 micro Jy (at 9 GHz) for GRO J1655-40, and 1.4 mJy (at 1.75 GHz), 27 micro Jy (at 5.5 GHz), 47 micro Jy (at 9 GHz) for XTE J1550-564 were measured. In conjunction with quasi-simultaneous Chandra X-ray observations (in the case of GRO J1655-40) and Faulkes Telescope optical observations (XTE J1550-564) we find that these systems provide the first evidence of relatively `radio quiet' black hole binaries at low luminosities; indicating that the scatter observed in the hard state X-ray:radio correlation at higher luminosities may also extend towards quiescent levels.