# Spin frequency evolution and pulse profile variations of the recently re-activated radio magnetar XTE J1810-197

## TL;DR

This study monitors the re-activated radio magnetar XTE J1810-197, revealing increased spin-down rate, smooth pulse profile evolution, and stable periodic structures across multiple radio frequencies over 48 days.

## Contribution

First detailed timing and pulse profile analysis of XTE J1810-197 after its recent radio re-activation, highlighting new spin-down behavior and stable pulse periodicity.

## Key findings

- Spin frequency derivative increased by 2.6 times.
- Pulse profiles evolved smoothly over time.
- Detected stable ~50-ms periodicity across frequencies.

## Abstract

After spending almost a decade in a radio-quiet state, the Anomalous X-ray Pulsar XTE J1810-197 turned back on in early December 2018. We have observed this radio magnetar at 1.5 GHz with ~daily cadence since the first detection of radio re-activation on 8 December 2018. In this paper, we report on the current timing properties of XTE J1810-197 and find that the magnitude of the spin frequency derivative has increased by a factor of 2.6 over our 48-day data set. We compare our results with the spin-down evolution reported during its previous active phase in the radio band. We also present total intensity pulse profiles at five different observing frequencies between 1.5 and 8.4 GHz, collected with the Lovell and the Effelsberg telescopes. The profile evolution in our data set is less erratic than what was reported during the previous active phase, and can be seen varying smoothly between observations. Profiles observed immediately after the outburst show the presence of at least five cycles of a very stable ~50-ms periodicity in the main pulse component that lasts for at least tens of days. This remarkable structure is seen across the full range of observing frequencies.