Radio spectrum of the AXP J1810-197 and of its profile components

TL;DR

This study presents multi-frequency radio observations of the magnetar AXP J1810-197, revealing its spectral evolution, flux density decrease, and pulse profile changes over time, providing insights into its transient radio emission behavior.

Contribution

First detailed spectral and temporal analysis of the radio-emitting magnetar AXP J1810-197 across multiple frequencies over several months.

Findings

Flux density decreased by a factor of 10 over 8 months

Disappearance of one main pulse component observed

Spectral index showed large fluctuations over time

Abstract

As part of a European Pulsar Network (EPN) multi-telescope observing campaign, we performed simultaneous multi-frequency observations at 1.4, 4.9 and 8.4 GHz during July 2006 and quasi-simultaneous multi-frequency observations from Decem- ber 2006 until July 2007 at 2.7, 4.9, 8.4, 14.6 and 32 GHz, in order to obtain flux density measurements and spectral features of the 5.5-sec radio-emitting magnetar AXP J1810-197. We monitored the spectral evolution of its pulse shape which consists of a main pulse (MP) and an interpulse (IP). We present the flux density spectrum of the average profile and of the separate pulse components of this first-known radio-emitting transient anomalous X-ray pulsar. We observe a decrease of the flux density by a factor of 10 within 8 months and follow the disappearance of one of the two main components. Although the spectrum is generally flat, we observe large fluctuations of the spectral index with time. For that reason we have made some measurements of modulation indices for individual pulses in order to also investigate the origin of these fluctuations.