The MAVERIC survey: A transitional millisecond pulsar candidate in Terzan 5

TL;DR

This paper presents evidence that Terzan 5 CX1 is a transitional millisecond pulsar candidate, showing state changes consistent with known transitional pulsars, based on multi-wavelength observations over 14 years.

Contribution

It identifies a new transitional millisecond pulsar candidate in Terzan 5 through combined X-ray and radio data analysis, highlighting its state transitions.

Findings

CX1 exhibits two brightness states with distinct X-ray properties.

Spectral and variability analysis aligns CX1 with known transitional millisecond pulsars.

Potential for detecting CX1 as a radio pulsar in existing timing data.

Abstract

Transitional millisecond pulsars are accreting millisecond pulsars that switch between accreting X-ray binary and millisecond radio pulsar states. Only a handful of these objects have been identified so far. Terzan 5 CX1 is a variable hard X-ray source in the globular cluster Terzan 5. In this paper, we identify a radio counterpart to CX1 in deep Very Large Array radio continuum data. Chandra observations over the last fourteen years indicate that CX1 shows two brightness states: in 2003 and 2016 the source was the brightest X-ray source in the cluster (at L$_X \sim 10^{33}$ erg s$^{-1}$), while in many intermediate observations, its luminosity was almost an order of magnitude lower. We analyze all available X-ray data of CX1, showing that the two states are consistent with the spectral and variability properties observed for the X-ray active and radio pulsar states of known transitional millisecond pulsars. Finally, we discuss the prospects for the detection of CX1 as a radio pulsar in existing timing data.