arXiv subjects

Mustafa Demirer

Publications and source records attributed to Mustafa Demirer.

3 recordsLinked to original sources

arXiv2026

17 Yr of Magnetar Bursts Observed with the Fermi Gamma-ray Burst Monitor

The Fermi Gamma-ray Burst Monitor (GBM) has been in operation for over 17 years, during which it has observed more than a thousand bursts from soft gamma repeaters (SGRs), also known as magnetars. Serving as a laboratory for extreme physics, magnetars are a sub-family of neutron stars characterized by extreme magnetic field strength, observed through a combination of persistent and short transient emission across the electromagnetic spectrum. We present the comprehensive GBM catalog of SGR short bursts which supersedes the 5-year catalog of Collazzi et al. 2015. The new catalog contains 1254 SGR short bursts observed over 17 years, providing the longest uninterrupted, high-sensitivity all-sky monitoring of magnetar bursts with unprecedented spectral and temporal resolution. Our catalog contains bursts from 17 unique Galactic sources, with major contributions by bursts from SGR J1935+2154 and SGR J1550-5418. We present overall characteristics of these bursts, such as the durations, spectral parameters for various photon models, fluxes, as well as their comparison with recently published catalogs of other missions and the previous GBM magnetar catalog. The machine readable catalog, as well as burst spectra and response files are made publicly available for the community.

astro-ph.HE↗

arXiv2025

Detailed Time Resolved Spectral and Temporal Investigations of SGR J1550-5418 Bursts Detected with Fermi/Gamma-ray Burst Monitor

We have conducted a time-resolved spectral analysis of magnetar bursts originating from SGR J1550-5418. Our analysis utilizes a two-step methodology for temporal segmentation of the data. We first generated and fitted overlapping time segments. Subsequently, we obtained non-overlapping time segments with varying lengths based on their spectral evolution patterns, employing a machine learning algorithm called k-means clustering. For the fitting process, we employed three distinct models, namely a modified blackbody (MBB-RCS), a double blackbody (BB+BB), and a power law with an exponential cut-off (COMPT) model. We found that nearly all of the time segments fit well with the COMPT model. Both the average peak energy in the ${\nu}$F${\nu}$ spectra (Epeak) and Photon Index parameters follow a Gaussian distribution with the means ${\sim}$30 keV and -0.5, respectively. Furthermore, there is a strong positive correlation between the cooler and hotter temperature parameters of the BB+BB model, and both two parameters show a Gaussian distribution with peaks ${\sim}$4 keV and 12 keV, respectively. Additionally, we found that the distribution of the temperature parameter of the MBB-RCS model can be fitted with a skewed Gaussian function with a peak ${\sim}$9-10 keV. Lastly, we searched for quasiperiodic spectral oscillations (QPSOs) in the hardness ratio evolution of the bursts. We identified five potential QPSO candidates at frequencies ranging from ${\sim}$15 Hz to ${\sim}$68 Hz. We discuss and compare these results with previous studies.

astro-ph.HE↗

arXiv2024

Concise Spectrotemporal Studies of Magnetar SGR J1935+2154 Bursts

SGR J1935+2154 has truly been the most prolific magnetar over the last decade: It has been entering into burst active episodes once every 1-2 years since its discovery in 2014, it emitted the first Galactic fast radio burst associated with an X-ray burst in 2020, and has emitted hundreds of energetic short bursts. Here, we present the time-resolved spectral analysis of 51 bright bursts from SGR J1935+2154. Unlike conventional time-resolved X-ray spectroscopic studies in the literature, we follow a two-step approach to probe true spectral evolution. For each burst, we first extract spectral information from overlapping time segments, fit them with three continuum models, and employ a machine learning based clustering algorithm to identify time segments that provide the largest spectral variations during each burst. We then extract spectra from those non-overlapping (clustered) time segments and fit them again with the three models: the cutoff power-law model, the sum of two blackbody functions, and the model considering the emission of a modified black body undergoing resonant cyclotron scattering, which is applied systematically at this scale for the first time. Our novel technique allowed us to establish the genuine spectral evolution of magnetar bursts. We discuss the implications of our results and compare their collective behavior with the average burst properties of other magnetars.

astro-ph.HE↗