Strongly magnetized pulsars: explosive events and evolution

Well before the radio discovery of pulsars offered the first observational confirmation for their existence (Hewish et al., 1968), it had been suggested that neutron stars might be endowed with very strong magnetic fields of $10^{10}$-$10^{14}$G (Hoyle et al., 1964; Pacini, 1967). It is because of their magnetic fields that these otherwise small ed inert, cooling dead stars emit radio pulses and shine in various part of the electromagnetic spectrum. But the presence of a strong magnetic field has more subtle and sometimes dramatic consequences: In the last decades of observations indeed, evidence mounted that it is likely the magnetic field that makes of an isolated neutron star what it is among the different observational manifestations in which they come. The contribution of the magnetic field to the energy budget of the neutron star can be comparable or even exceed the available kinetic energy. The most magnetised neutron stars in particular, the magnetars, exhibit an amazing assortment of explosive events, underlining the importance of their magnetic field in their lives. In this chapter we review the recent observational and theoretical achievements, which not only confirmed the importance of the magnetic field in the evolution of neutron stars, but also provide a promising unification scheme for the different observational manifestations in which they appear. We focus on the role of their magnetic field as an energy source behind their persistent emission, but also its critical role in explosive events.Comment: Review commissioned for publication in the White Book of "NewCompStar" European COST Action MP1304, 43 pages, 8 figure

Observations of the magnetars 4U 0142+61 and 1E 2259+586 with the MAGIC telescopes (Research Note)

Context. Magnetars are an extreme, highly magnetized class of isolated neutron stars whose large X-ray luminosity is believed to be driven by their high magnetic field. Aims. We study for the first time the possible very high energy gamma-ray emission above 100 GeV from magnetars, observing the sources 4U 0142+ 61 and 1E 2259+586. Methods. We observed the two sources with atmospheric Cherenkov telescopes in the very high energy range (E > 100 GeV). 4U0142+61 was observed with the MAGIC I telescope in 2008 for about 25 h and 1E 2259+586 was observed with the MAGIC stereoscopic system in 2010 for about 14 h. The data were analyzed with the standard MAGIC analysis software. Results. Neither magnetar was detected. Upper limits to the differential and integral flux above 200 GeV were computed using the Rolke algorithm. We obtain integral upper limits to the flux of 1.52 x 10(-12) cm(-2) s(-1) and 2.7 x 10(-12) cm(-2) s(-1) with a confidence level of 95% for 4U 0142+ 61 and 1E 2259+586, respectively. The resulting differential upper limits are presented together with X-ray data and upper limits in the GeV energy range