Mete Uzuner | Searcharxiv

arXiv2026

An 11-Year Catalog of Gamma-Ray Transients: A Comprehensive Search with Fermi Gamma-ray Burst Monitor Data

The Gamma-ray Burst Monitor (GBM) on board Fermi Gamma-ray Space Telescope has produced the largest database of all-sky observations in gamma rays with its continuous data with high time and energy resolutions. These data contain a wealth of unidentified transient events that did not trigger the detectors for various reasons. We conducted extensive searches to identify such untriggered transient events observed with GBM in 11 years (July 2010 - June 2021). In particular, we employed four different search modes with various energy ranges (mainly below 300 keV) and time resolutions (from 8 ms to 2 s), utilizing three statistical methods (signal-to-noise ratio, Poisson, and Bayesian statistics), each with different effectiveness in identifying specific classes of transients. Moreover, we developed algorithms for known-event flagging as well as unknown-event classification for our candidate events found in the searches. In this paper, we present our search methodologies, event flagging and classification algorithms and the resulting comprehensive event catalog. The catalog contains more than a million events in total, including known events such as gamma-ray bursts, soft-gamma repeater bursts, galactic X-ray source activities, terrestrial gamma flashes, and solar flares. For each candidate event, the catalog presents the event time, detection significance, event duration, hardness ratios, known-event flagging results, and classification probabilities. Our short-transient catalog significantly expands the currently-existing list of known events and complements the GBM trigger catalog. The event database with filtering capabilities is also publicly available at https://magnetars.sabanciuniv.edu/gbm, which allows users to retrieve event information based on their input queries along with the event lightcurves.

astro-ph.HE↗

arXiv2025

Searching for quasi-periodicities in short transients: the curious case of GRB 230307A

Gamma-ray bursts (GRBs) are the most powerful explosions in the Universe; their energy release reache s us from the end of the re-ionization era, making them invaluable cosmological probes. GRB 230307A i s the second-brightest GRB ever observed in the 56 years of observations since the discovery of the phenomenon in 1967. Follow-up observations of the event at longer wavelengths revealed a lanthanide-ri ch kilonova with long-lasting X-ray emission immediately following the prompt gamma-rays. Moreover, t he gamma-ray light curve of GRB 230307A collected with INTEGRAL's SPectrometer of INTEGRAL AntiCoincidence Shield (SPI-ACS) and Fermi's Gamma-Ray Burst Monitor (GBM). We use Fourier analysis, wavelets and Gaussian Processes to search for periodic and quasi-periodic oscillations (QPOs) in the prompt gamma-ray emission of GRB 230307A. We critically assess all three methods in terms of their robustness for detections of QPOs in fast transients such as GRBs. Our analyses reveal QPOs at a frequency of $\sim 1.2$ Hz (0.82s period) near the burst's peak emission phase, consistent across instruments and detection methods. We also identify a second, less significant QPO at $\sim 2.9$ Hz (0.34s) nearly simultaneously. We hypothesise that the two QPOs originate from the transition epoch at the end of the jet acceleration phase. These QPOs re present plasma circulation periods in vorticity about the jet axis carried outwards to the prompt radiation zone at much larger radii. They are sampled by colliding structures (e.g., shocks) in the spinning jet, possibly marking the evolution of plasma rotation during the final stages of the progenitor neutron star coalescence event.

astro-ph.HE↗