BROADBAND SPECTRAL INVESTIGATIONS OF MAGNETAR BURSTS
Physics, MSc. Thesis, 2017
Prof. Dr. Ersin Gogus (Thesis Advisor), Prof. Dr. M. Ali Alpar,
Assoc. Prof. Tolga Guver
Date & Time: 11th, May 2017 – 11:00 AM
Place: FENS L067
Keywords : Magnetars, X-rays, Bursts, Spectral Analysis
Magnetars are neutron stars whose variety of energetic emission mechanisms are thought to be governed by the decay of their extremely strong magnetic fields (B ~ 1014- 1015 G). Studies on radiative magnetar behavior promise insight into emission mechanisms in highly magnetized regions as well as the formation, evolution and structure of neutron stars. In this thesis, we present our broadband (2-250 keV) spectral analysis of 42, 125 and 221 bursts from magnetar sources SGR J1550-5418, SGR 1900+14 and SGR 1806-20, respectively, detected with the Rossi X-ray Timing Explorer (RXTE) mission. We find that 258 out of 388 bursts examined provided better fit statistics when fitted with the Comptonized emission model while 28 were better fitted with a sum of two blackbody functions. We performed numerical simulations to further constrain the best fitting model for each burst spectrum, and found that 69 out of 102 burst spectra with well-constrained parameters are significantly better described by the Comptonized model when the true emission mechanism is Comptonization. We also found that 66 out of 102 these burst spectra are better described with the the sum of two modified blackbody models, which is employed in X-ray spectral modeling for the first time here, than the sum of two blackbody and sum of blackbody and power law models. We also show a significant correlation between burst emission area and blackbody temperatures when blackbody+blackbody fits are employed. We expand on the physical interpretation of these models and discuss our results in the framework of strongly magnetized neutron star case.