2FGL J1653.6-0159: A New Low in Evaporating Pulsar Binary Periods

TL;DR

This paper reports the discovery of a binary system with the shortest known orbital period for an evaporating pulsar binary, providing insights into pulsar companion interactions and system properties.

Contribution

It identifies a new record-low orbital period binary system associated with a Fermi gamma-ray source, expanding understanding of pulsar binary evolution.

Findings

Orbital period of 75 minutes, the shortest for such systems.

High radial velocity amplitude indicating a massive companion.

Presence of hard emission possibly from complex system interactions.

Abstract

We have identified an optical binary with orbital period P_b=4488s as the probable counterpart of the Fermi source 2FGL J1653.6-0159. Although pulsations have not yet been detected, the source properties are consistent with an evaporating millisecond pulsar binary; this P_b=75min is the record low for a spin-powered system. The heated side of the companion shows coherent radial velocity variations, with amplitude K=666.9+/-7.5 km/s for a large mass function of f(M)=1.60+/-0.05 M_sun. This heating suggests a pulsar luminosity ~3x10^34 erg/s. The colors and spectra show additional hard emission dominating at binary minimum. Its origin is, at present, unclear. This system is similar to PSR J1311-3430, with a low mass H-depleted companion, a dense shrouding wind and, likely, a large pulsar mass.