Diagnosing pulsar winds in black-widow, redback, and other binary millisecond pulsar systems

TL;DR

This paper investigates how pulsar winds heat companion stars in binary systems, using simulations and observations to infer particle energies in the pulsar wind based on temperature variations.

Contribution

It introduces a method to diagnose pulsar wind particle energies by analyzing temperature modulations in binary systems, applying it to specific cases.

Findings

Deep heating requires particles > 100 TeV in some systems.

Temperature differences can be maintained with particles around 100 MeV.

Observational evidence constrains pulsar wind particle energies.

Abstract

Binary systems composed of a recycled millisecond pulsar and a stellar companion in close orbit could be excellent sites to diagnose pulsar winds. In such systems, the pulsar outflow irradiates and heats up the companion atmosphere, which can lead to the observation of strong day/night modulations in temperature. We demonstrate with particle shower simulations that the particle energy of the wind affects the heating depth in the atmosphere: the wind heat can be deposited above or below the photosphere, leading to different signatures in the observed spectra. We apply our method to four specific systems: We find that systems with cool night side companions showing strong temperature variations can give interesting lower limits on the particle energy in the winds. In particular, if the companion night side of PSR B1957+20 were to be suddenly irradiated, deep heating would only take place if particles with energy > 100 TeV were present. Observational evidence of deep heating in this system thus suggests that i) such particles exist in the pulsar wind and/or ii) binary evolution non-trivially takes the companion to the observed temperature asymmetry. Besides, the observed temperature difference can be maintained only with particle energies of the order of 100 MeV.