Spectrotemporal Studies Of Magnetar Bursts And Their Origin Through Crustal Yielding

One of the most distinctive features of magnetars − the highly magnetized neutronstars − is their recurring emission of brief yet highly luminous bursts in hard Xrays/soft γ-rays. Once an active episode begins, a few to thousands of such burstscan occur over timescales from days to months. The temporal clustering of these recurrentbursts suggests an underlying mechanism triggering multiple bursts in rapidsuccession, which is likely crucial for understanding the processes driving magnetaractivity. In this thesis, we investigate the “triggering” mechanism of short magnetarbursts by modeling repetitive burst behavior through crustal interactions and employinga cellular automaton model for the magnetar crust. Our simulations, basedon physically motivated criteria, successfully reproduce burst clustering. Additionally,the durations and energetics of active episodes in our simulations agree wellwith observational data. Based on our results, we discuss the potential physicalmechanisms underlying burst clusters observed in numerous magnetars, as well asthe reactivations of an individual magnetar.We also investigate how the “triggered” system generates radiation (bursts) and howthis radiation evolves within the magnetosphere via time-resolved spectral analysisof 51 bright bursts from the magnetar SGR J1935+2154. Unlike conventional studiesin the literature, we follow a two-step approach to probe true spectral evolution. Foreach burst, we first extract spectral information from overlapping time segments, fitthem with three continuum models, and employ a machine-learning-based clusteringalgorithm to identify time segments that provide the largest spectral variationsduring each burst. We then extract spectra from those non-overlapping (clustered)time segments and fit them again with the three models: the exponential cutoffpower-law model, the sum of two blackbody functions, and the model consideringthe emission of a modified black body undergoing resonant cyclotron scattering,which is applied systematically at this scale for the first time. Our novel techniqueallowed us to establish the genuine spectral evolution of magnetar bursts. We discussthe implications of our results and compare their collective behavior with theave