A Search for Very High-Energy Gamma Rays from the Missing Link Binary Pulsar J1023+0038 with VERITAS

TL;DR

This study used VERITAS to search for very high-energy gamma rays from the binary pulsar J1023+0038 before and after its state change, setting upper limits that inform the magnetic field conditions in its shock region.

Contribution

First gamma-ray search for J1023+0038 with VERITAS before and after state change, constraining shock magnetic fields based on non-detections.

Findings

No significant gamma-ray detection above 100 GeV.

Upper limits constrain the shock magnetic field to >2 G before state change.

Upper limits constrain the shock magnetic field to >10 G after state change.

Abstract

The binary millisecond radio pulsar PSR J1023+0038 exhibits many characteristics similar to the gamma-ray binary system PSR B1259--63/LS 2883, making it an ideal candidate for the study of high-energy non-thermal emission. It has been the subject of multi-wavelength campaigns following the disappearance of the pulsed radio emission in 2013 June, which revealed the appearance of an accretion disk around the neutron star. We present the results of very high-energy gamma-ray observations carried out by VERITAS before and after this change of state. Searches for steady and pulsed emission of both data sets yield no significant gamma-ray signal above 100 GeV, and upper limits are given for both a steady and pulsed gamma-ray flux. These upper limits are used to constrain the magnetic field strength in the shock region of the PSR J1023+0038 system. Assuming that very high-energy gamma rays are produced via an inverse-Compton mechanism in the shock region, we constrain the shock magnetic field to be greater than $\sim$2 G before the disappearance of the radio pulsar and greater than $\sim$10 G afterwards.