Evolutionary implications of a magnetar interpretation for GLEAM-X J162759.5-523504.3

TL;DR

This paper critically examines the magnetar hypothesis for GLEAM-X J162759.5-523504.3, suggesting it could be the most magnetized neutron star, with implications for its magnetic field, age, and cooling mechanisms.

Contribution

It provides a detailed analysis of the magnetar interpretation, including magnetic field estimates, birth conditions, and observational constraints, advancing understanding of ultra-magnetized neutron stars.

Findings

Magnetic field likely exceeds 10^{16} G.

Star's age estimated around 10,000 years.

Cooling consistent with direct Urca process.

Abstract

The radio pulsar GLEAM-X J162759.5-523504.3 has an extremely long spin period ($P = 1091.17\, \mbox{s}$), and yet seemingly continues to spin down rapidly ($\dot{P} < 1.2 \times 10^{-9}\, \mbox{ss}^{-1}$). The magnetic field strength that is implied, if the source is a neutron star undergoing magnetic dipole braking, could exceed $10^{16}\,\mbox{G}$. This object may therefore be the most magnetised neutron star observed to date. In this paper, a critical analysis of a magnetar interpretation for the source is provided. (i) A minimum polar magnetic field strength of $B \sim 5 \times 10^{15}\,\mbox{G}$ appears to be necessary for the star to activate as a radio pulsar, based on conventional `death valley' assumptions. (ii) Back-extrapolation from magnetic braking and Hall-plastic-Ohm decay suggests that a large angular momentum reservoir was available at birth to support intense field amplification. (iii) The observational absence of X-rays constrains the star's field strength and age, as the competition between heating from field decay and Urca cooling implies a surface luminosity as a function of time. If the object is an isolated, young ($\sim 10\, \mbox{kyr}$) magnetar with a present-day field strength of $B \gtrsim 10^{16}\,\mbox{G}$, the upper limit ($\approx 10^{30}\, \mbox{erg s}^{-1}$) set on its thermal luminosity suggests it is cooling via a direct Urca mechanism.