Magnetar giant flares near and far

Giant flares are the most energetic manifestation of magnetars, isolated neutron stars powered mainly by magnetic energy. They provide us the best evidence for magnetic fields as high as 10^15 Gauss in these highly variable neutron stars. Soon after the discovery of the first giant flare in the Large Magellanic Cloud  more than forty years ago, it was realized that these powerful events reaching peak luminosity up to 10e47 erg/s could be detected up to distances of several tens of mega-parsecs, at least during their initial phase lasting less than one second. Although these events are difficult to distinguish from the much more frequent short gamma-ray bursts, a few candidates were proposed and different estimates of their relevance in the short GRB population were derived. In recent years, the small sample of (candidate) extragalactic  magnetar giant flares has nearly doubled thanks to the precise localization of 231115A in the starburst galaxy M82, and with the discovery of other candidates such as 200415A and 180128A in NGC 253 or 070222 in M83. The most recent addition is 241107A, another short burst well localized with INTEGRAL and  possibly associated with the galaxy PGC 86046. Thanks to this increased sample it is now possible to derive tighter constraints on the rate of occurrence of giant flares. Since these flares involve a significant fraction of the available magnetic energy, constraining their rate of occurrence is important to understand the evolution and dissipation  of magnetic fields in these extreme neutron stars.

Sandro Mereghetti – INAF, Istituto di Astrofisica Spaziale e Fisica cosmica di Milano

Sandro Mereghetti, Research Director at INAF/IASF-Milano, has given important contributions to the study of high-energy sources containing relativistic compact objects, in particular highly magnetised neutron stars. He also participated in the development of space missions for X and gamma-ray astronomy. In this context, he developed the IBAS system for the rapid localisation of the GRBs detected by INTEGRAL that led to the identification of the first magnetar burst associated to a fast radio burst and to the discovery of a magnetar giantflare in the M82 starburst galaxy.