Irradiation effect and binary radio pulsars with giant companions

TL;DR

This study explores how irradiation influences the evolution and properties of binary radio pulsars with giant star companions, expanding the potential parameter space and suggesting the existence of submillisecond pulsars with such companions.

Contribution

It introduces a detailed binary evolution model considering irradiation effects, revealing expanded parameter space and potential for submillisecond pulsars with giant companions.

Findings

Irradiation significantly expands the parameter space for binary pulsars with giant companions.

Strong irradiation can lead to the formation of submillisecond pulsars with giant companions.

The correlation between binary timescale and irradiation efficiency was demonstrated.

Abstract

Pulsars are neutron stars that rotate rapidly. Most of the pulsars in binary systems tend to spin faster than those in isolation. According to binary evolution theory, radio pulsars in binary systems can have various types of companion stars. However, binary radio pulsars with giant stars, helium stars, and black holes as companions are lacking so far. We aim to investigate the possible parameter space of binary radio pulsars with giant companions. We used the MESA stellar evolution code to consider the effect of irradiation in binary evolution and evolved a series of binary models. We present the potential physical properties of binary radio pulsars with giant star companions in the framework of the classical recycling scenario and the irradiation model. We found that the parameter space of binary radio pulsars with giant companions can be greatly expanded by the effect of irradiation. Moreover, when irradiation is strong enough, submillisecond pulsars might be accompanied by giant companion stars. We also demonstrate a correlation between the timescale of the binary system as a low-mass X-ray binary and the irradiation efficiency. The birthrate problem between millisecond pulsars and low-mass X-ray binaries might not be resolved by the irradiation effect. A more detailed binary population synthesis is necessary. Our findings may offer guidance for observers that wish to locate binary radio pulsars with giant companions or submillisecond pulsars.