Simultaneous radio and X-ray observations of the transitional millisecond pulsar candidate 3FGL J1544.6-1125

TL;DR

This study presents simultaneous radio and X-ray observations of the tMSP candidate 3FGL J1544.6-1125, revealing an anti-correlation similar to known tMSPs, aiding understanding of their emission mechanisms.

Contribution

First simultaneous radio and X-ray observations of 3FGL J1544.6-1125, demonstrating anti-correlated emission patterns akin to other tMSPs, despite its greater distance.

Findings

Radio and X-ray emissions are anti-correlated in 3FGL J1544.6-1125.

The system shows variability in radio and X-ray on short timescales.

Results support models of tMSP emission mechanisms.

Abstract

Transitional millisecond pulsars (tMSPs) are neutron-star systems that alternate between a rotation-powered radio millisecond pulsar state and an accretion-disk-dominated low-mass X-ray binary (LMXB)-like state on multi-year timescales. During the LMXB-like state, the X-ray emission from tMSPs switches between "low" and "high" X-ray brightness modes on a timescale of seconds to minutes (or longer), while the radio emission shows variability on timescales of roughly minutes. Coordinated VLA and Chandra observations of the nearby tMSP PSR J1023+0038 uncovered a clear anti-correlation between radio and X-ray luminosities such that the radio emission consistently peaks during the X-ray low modes. In addition, there are sometimes also radio/X-ray flares that show no obvious correlation. In this paper, we present simultaneous radio and X-ray observations of a promising tMSP candidate system, 3FGL J1544.6-1125, which shows optical, gamma-ray, and X-ray phenomena similar to PSR J1023+0038, but which is challenging to study because of its greater distance. Using simultaneous VLA and Chandra observations we find that the radio and X-ray emission are consistent with being anti-correlated in a manner similar to PSR J1023+0038. We discuss how our results help in understanding the origin of bright radio emission from tMSPs. The greater sensitivity of upcoming telescopes like the Square Kilometre Array will be crucial for studying the correlated radio/X-ray phenomena of tMSP systems.