The generalized hardness-intensity diagram for black hole and neutron star X-ray binaries

TL;DR

This paper generalizes the hardness-intensity diagram for X-ray binaries, explaining differences in jet and wind behaviors between black holes and neutron stars through accretion dynamics and scale invariance.

Contribution

It introduces a unified framework connecting jet and wind phenomena in X-ray binaries, incorporating neutron star specifics and scale invariance.

Findings

Black hole X-ray binaries suppress jets in soft states

Neutron stars can have co-existing jets and winds in soft states

Neutron stars are analogs of FRII quasars at small scales

Abstract

Over the past half century, X-ray and radio observations of accreting neutron stars and stellar mass black holes have yielded a rich observational picture with common features including state transitions and jet formation, but also sharp differences. While black hole X-ray binaries overwhelmingly suppress jets in so-called soft states, accreting neutron stars are less restrictive, with a soft state wind observed in some sources to co-exist with a jet. We propose an explanation for these differences that leads to a generalization of a foundational element, the hardness-intensity diagram of Fender et al (2004). The inverse relation between jets and winds fits into a picture that connects to prograde accretion while the possibility of counterrotation between accretion disk and compact object accounts for observed differences in accreting neutron stars. This picture comes with a surprising twist, which is that neutron stars embody the small-scale analog of FRII quasars, an idea that allows us to complete the scale invariant picture for the jet-disk connection.