Radio emission from the X-ray pulsar Her X-1: a jet launched by a strong magnetic field neutron star?

TL;DR

This paper reports the first detection of radio emission from the X-ray pulsar Her X-1, suggesting the presence of a jet, which has implications for understanding jet formation in strongly magnetized neutron stars.

Contribution

It presents the discovery of radio emission from Her X-1 and discusses the potential origin of this emission as a jet, a novel finding for this type of neutron star.

Findings

Radio emission detected at 9 GHz with flux density of 38.7 μJy.

Jet origin is consistent with observed radio properties, ruling out other mechanisms.

Implications for jet formation in strongly magnetized neutron stars.

Abstract

Her X-1 is an accreting neutron star in an intermediate-mass X-ray binary. Like low-mass X-ray binaries (LMXBs), it accretes via Roche-lobe overflow, but similar to many high-mass X-ray binaries containing a neutron star, Her X-1 has a strong magnetic field and slow spin. Here, we present the discovery of radio emission from Her X-1 with the Very Large Array. During the radio observation, the central X-ray source was partially obscured by a warped disk. We measure a radio flux density of $38.7 \pm 4.8$ $\mu$Jy at $9$ GHz but can not constrain the spectral shape. We discuss possible origins of the radio emission, and conclude that coherent emission, a stellar wind, shocks and a propeller outflow are all unlikely explanations. A jet, as seen in LMXBs, is consistent with the observed radio properties. We consider the implications of the presence of a jet in Her X-1 on jet formation mechanisms and on the launcing of jets by neutron stars with strong magnetic fields.