Radio detections during two state transitions of the intermediate-mass black hole HLX-1

Abstract

Relativistic jets are streams of plasma moving at appreciable fractions of the speed of light. They have been observed from stellar-mass black holes (∼3 to 20 solar masses, M⊙) as well as supermassive black holes (∼106 to 109 M⊙) found in the centers of most galaxies. Jets should also be produced by intermediate-mass black holes (∼102 to 105 M⊙), although evidence for this third class of black hole has, until recently, been weak. We report the detection of transient radio emission at the location of the intermediate-mass black hole candidate ESO 243-49 HLX-1, which is consistent with a discrete jet ejection event. These observations also allow us to refine the mass estimate of the black hole to be between ∼9 × 103 M⊙ and ∼9 × 104 M⊙.