| Abstract : | Magnetars constitute one of the exotic parts of the neutron star population. Discovered via their high energy emission, magnetars exhibit persistent but highly variable X-ray emission, very high magnetic fields, young ages, and transient radio emission. The detection of radio emission provided the observational link between the magnetars and pulsars, and also firmly ruled out the alternative accretion based models for the former's X-ray emission. The radio emission, observed only from a handful of magnetars so far, typically follows an X-ray outburst, and is transient in nature. Moreover, unlike the normal radio pulsars, the average radio emission properties of magnetars are highly variable. XTE J1810-197 was the first-ever magnetar which was found to emit transient radio emission. Using our monitoring observations since its recent transition into the only second known radio outburst phase in late 2018, we have uncovered several interesting properties. Particularly, monitoring over more than 800 days has uncovered a gradually evolving radio spectrum as well as the emission beam-size of the magnetar. Such an evolution, seen for the first time, has important implications for the emission processes responsible for radio emission from magnetars as well as for a potential presence of a magnetar wind nebulae. Another particularly noteworthy finding is that the magnetar emits narrow bursts of emission with, likely intrinsic, spectral structures. These structures might indicate a phenomenological link with the repeating fast radio burst (FRBs) and giant pulses from the Crab pulsar, which also show interesting but even more detailed frequency structures. I will present these findings and discuss them in the context of emission components known from pulsars, FRBs and magnetars. |
