Optical Counterparts of Two Fermi Millisecond Pulsars: PSR J1301+0833 and PSR J1628-3205

TL;DR

This study identified and characterized optical companions of two millisecond pulsars, revealing their heating effects, orbital parameters, and companion star properties through light curve analysis.

Contribution

First optical identification and detailed light curve analysis of companions to two Fermi-discovered millisecond pulsars, providing insights into their system parameters.

Findings

PSR J1301+0833's companion is strongly heated and varies significantly.

PSR J1628-3205's companion shows ellipsoidal variations and long-term brightness changes.

Modeling constrains the system's inclination, companion mass, and temperature.

Abstract

Using the 1.3m and 2.4m telescopes of the MDM Observatory, we identified the close companions of two eclipsing millisecond radio pulsars discovered by the Green Bank Telescope in searches of Fermi Gamma-ray Space Telescope sources, and measured their light curves. PSR J1301+0833 is a black widow pulsar in a 6.5 hr orbit whose companion star is strongly heated on the side facing the pulsar. It varies from R = 21.8 to R > 24 around the orbit. PSR J1628-3205 is a "redback," a nearly Roche-lobe filling system in a 5.0 hr orbit whose optical modulation in the range 19.0 < R < 19.4 is dominated by strong ellipsoidal variations, indicating a large orbital inclination angle. PSR J1628-3205 also shows evidence for a long-term variation of about 0.2 mag, and an asymmetric temperature distribution possibly due to either off-center heating by the pulsar wind, or large starspots. Modelling of its light curve restricts the inclination angle to i > 55 degrees, the mass of the companion to 0.16 < M_c < 0.30 M_sun, and the effective temperature to 3560 < T_eff < 4670 K. As is the case for several redbacks, the companion of PSR J1628-3205 is less dense and hotter than a main-sequence star of the same mass.