Magnetars: a short review and some sparse considerations

Abstract

We currently know about 30 magnetars: seemingly isolated neutron stars whose properties can be (in part) comprehended only acknowledging that they are endowed with magnetic fields of complex morphology and exceptional intensity-at least in some components of the field structure. Although magnetars represent only a small percentage of the known isolated neutron stars, there are almost certainly many more of them, since most magnetars were discovered in transitory phases called outbursts, during which they are particularly noticeable. In outburst, in fact, a magnetar can be brighter in X-rays by orders of magnitude and usually emit powerful bursts of hard-X/soft-gamma-ray photons that can be detected almost everywhere in the Galaxy with all-sky monitors such as those on board the Fermi satellite or the Neil Gehrels Swift Observatory. Magnetars command great attention because the large progress that has been made in their understanding is proving fundamental to fathom the whole population of isolated neutron stars, and because, due to their extreme properties, they are relevant for a vast range of different astrophysical topics, from the study of gamma-ray bursts and superluminous supernovae, to ultraluminous X-ray sources, fast radio bursts, and even to sources of gravitational waves. Several excellent reviews with different focuses were published on magnetars in the last few years: among others, Israel and Dall'Osso (2011); Rea and Turolla and Esposito (2013);Mereghetti et al. (2015); Turolla et al.

Upgraded antennas for pulsar observations in the Argentine Institute of Radio astronomy

“…These are characterized by energetic winds, intense radiation, and a decaying magnetic field on scales from days to months. For a recent overview of the observational properties of magnetars we refer to Esposito et al (2018) and, for its physical modeling, to Turolla et al (2015).…”

“…Another characteristic feature of magnetars is that their pulses do not stabilize in shape, as opposed to regular pulsars that reach stability after average of a few hundred pulses (although they might switch between a few kind of them on minutes to hours scales). Also, magnetars can be very bright (reaching 10 Jy in the L-band) in radio and also have an on-off-on behaviour (Esposito et al 2018).…”

Large polar caps for twisted magnetosphere of magnetars

“…The outburst observations of magnetars are very diverse and rich (Esposito et al 2018;Coti Zelati et al 2018). The above calculations for XTE J1810−197 is only one example.…”

“…Magnetars may be young and high magnetic field neutron stars (Duncan & Thompson 1992;Kaspi & Beloborodov 2017). Observationally, they show various kinds of activities: bursts (including giant flares), outbursts, and variation of timing properties (Esposito et al 2018). During the outburst, the magnetar persistent X-ray luminosity may be enhanced and decays subsequently.…”

“…During the outburst, the magnetar persistent X-ray luminosity may be enhanced and decays subsequently. During the outburst decay phase, the magnetar may show a shrinking hot spot, appearance of radio emission and subsequent cessation, decreasing torque, softening X-ray spectra, and simple pulse profile etc (Coti Zelati et al 2018;Esposito et al 2018). The physical reason accounting for the magnetar activities may be that magnetars have twisted magnetic fields (Thompson et al 2002).…”