The peculiar bursting behavior of magnetars and its implications

High energetic sudden flares lasting from few fraction of a second to 100s of seconds are observed from magnetars – neutron stars that exhibit the most extreme magnetic fields in the universe. Such bursts are proposed to originate from sudden fracturing of the neutron star crust due to build up magnetic stress or from magnetic reconnection in a highly magnetized environment. The burst properties vary widely from repetitive short bursts to super-Eddington giant flares. Extended emission phases with intensity clearly above the pre-burst level are observed following the intermediate bursts from a number of magnetar sources. The spectral and temporal properties during these episodes are distinctly different from the magnetar persistent emission. The duration and the energetics of the extended tail phase, when compared against that of the burst, vary extensively between different events. We detected extended tail emission phases following several bursts from two magnetar sources 4U 0142+61 and SGR J1550-5418. In a number of cases, we observed a sudden enhancement of the pulsation amplitude in conjunction with bursts and a cooling behavior during the tail. We propose that an inefficiently radiating trapped fireball formed during the burst, which can heat up the stellar surface, is able to explain the tail emission properties  and its energetics. Transient absorption and emission line features were also detected during the tail episodes. Such lines possibly arise from the proton/ion cyclotron resonance process which can be a valuable tool for probing the complex magnetic field of magnetars.