Ersin Göğüş

Magnetar short bursts (SBs) are hard X-ray transients of durations 0.01–1 s peaking at ∼10–100 keV and are prime targets for new high-energy missions and polarimeters. The recent association of SBs with bright radio bursts in SGR 1935+2154 has broadened interest in SB physics. We present new advanced fireball models combining general relativistic light bending, polarized transport in magnetized photospheres, magnetic photon-splitting attenuation, and magnetospheric vacuum birefringence. These models also have relevance to trapped fireballs in magnetar giant flare pulsating tails. We adopt confined flux-tube geometries consistent with adiabatic fireballs, anisotropic/polarized emergent intensities to produce spectra and polarizations, and energy–time Stokes impulse responses. We predict that most fireballs are highly linearly polarized, especially when vacuum birefringence is important. There is rich potential for diagnostics: coexisting direct and lensed delayed images, gaps by occultation of the neutron star surface, and Shapiro+Rømer delay with temporal caustics. These effects can imprint spin-phase dependence of the spectral and polarization character of bursts. Predicted signatures depend strongly on viewing geometry, fireball configuration, and photon-splitting assumptions, yielding large variance in model high-energy spectral shapes and cutoffs, and energy-dependent polarization. The models can reproduce established double-blackbody SB spectral phenomenology, and we find that the unusual 2020 April radio-associated SB from SGR 1935+2154 is broadly consistent with a footpoint close to the magnetic pole, and possibly near pole-on viewing geometry. Our models motivate reverberation-style analyses for SBs and suggest that high-quality data might constrain source geometry, burst crustal footpoints, and, potentially, neutron star masses and radii.

The Fermi Gamma-ray Burst Monitor (GBM) has been in operation for over 17 yr, during which it has observed more than 1000 bursts from soft gamma repeaters (SGRs), also known as magnetars. Serving as a laboratory for extreme physics, magnetars are a subfamily 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 yr catalog of A. C. Collazzi et al. The new catalog contains 1254 SGR short bursts observed over 17 yr, 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, and 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.

The magnetar 1E 1841–045 exhibited a new active episode starting on 2024 August 20, marked by X-ray bursts and enhanced persistent emission. Using data from the Einstein Probe (EP), we report on the timing and spectral results following the onset of this outburst. The pulse profile displays a multipeaked structure, with notable phase shifts in the secondary peak. Energy-resolved pulse profile analysis indicates a transition in the dominant peak of the pulse profile above 5.8 keV. The 0.5–10 keV X-ray spectrum is well modeled by a combined blackbody and power-law (BB+PL) model, showing a ∼20% flux increase following the outburst. Phase-resolved spectroscopy indicates a correlation between BB temperature and pulse profile intensity, along with spectral hardening at a specific pulse phase. The high spatial resolution of EP enables effective separation of the supernova remnant emission, which is crucial for measuring the intrinsic pulse emission of the source. These findings underscore the intricate relationship between magnetar outbursts, pulse profile evolution, and spectral characteristics.

The Gamma-ray Burst Monitor (GBM) on board the 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 by GBM during the 11 yr period of 2010 July–2021 June. 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.

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.

Context. We investigated the James Webb Space Telescope photometric color classification of mid-infrared (MIR) selected galaxies at high redshifts, toward cosmic noon. Aims. The aim of the present work is to obtain a z -dependent mid-infrared (MIR) photometric galaxy classification tool based on broad spectral emission and absorption lines using the JWST Mid-Infrared Instrument (MIRI) and its broadband filters. Methods. We used the largest Spitzer MIR spectral database to obtain synthetic photometry in the JWST/MIRI filters. We formed MIRI filter combinations to trace the strong polycyclic aromatic hydrocarbon (PAH) emission features and the 9.7 μm silicate feature in seven redshift windows from z = 0.25 − 2.10. Results. We present z -dependent MIRI color–color plots that separate active galactic nuclei (AGN), star-forming galaxies (SFGs), and silicate absorption-dominated galaxies up to z ∼ 2. We applied the photometric MIR colors to the largest (∼34 arcmin ² ) MIRI survey called the Systematic Mid-infrared Instrument Legacy Extragalactic Survey (SMILES), to identify AGN, SFGs, and Si-absorption dominated galaxies out to substantial redshifts. Our JWST/MIRI SFGs sample includes galaxies with total IR luminosities of 10 ^9.2 ∼ 10 ^11.9 L _⊙ at 0.9 ≤ z < 1.57. The majority of them are consistent with the z ∼ 1 main sequence. We also identified the first examples of z ∼ 1 galaxies with deep silicate absorption.

We present new results for the hot Jupiters HAT-P-16b, TOI-1516b, and TOI-2046b, based on photometric observations collected using both space- and ground-based facilities. Ground-based data were collected in the 2020–2024 time span with the 0.6 m telescope (ADYU60) located at the Adiyaman University Application and Research Center (Adiyaman, Türkiye) and the 1.0 m telescope at the Türkiye National Observatory (TUG, Türkiye). Through a combination of fits to our ground-based data, the midtransit times data from TESS, and additional data taken from the literature, we present an updated linear ephemeris for each system. Transit timing variations (TTVs) were analyzed using linear, orbital decay, and apsidal precession models. The resulting BIC(ΔBIC) values indicate that the orbital decay model is statistically favored for HAT-P-16b and TOI-1516b, while the constant period model is preferred for TOI-2046b. False alarm probabilities (FAPs) were computed to assess the significance of any periodic signals. TOI-1516b displays a strong TTV signal with a FAP (of 0.0001) well below the 0.01 threshold, suggesting a likely dynamical origin that warrants further investigation. The higher FAP value (0.0055) for HAT-P-16b suggests that the case of a possible presence of an additional body in the system is less convincing. In contrast, the much higher FAP value (0.0196) for TOI-2046b implies that there are no statistically significant TTVs.

GRB 250702B is an exceptional transient that produced multiple episodes of luminous gamma-ray radiation lasting for >25 ks, placing it among the class of ultralong gamma-ray bursts (GRBs). However, unlike any known GRB, the Einstein Probe detected soft-X-ray emission up to 24 hr before the gamma-ray triggers. We present comprehensive X-ray observations of the transient’s “afterglow” obtained with the Neil Gehrels Swift Observatory, the Nuclear Spectroscopic Telescope Array, and the Chandra X-ray Observatory between 0.5 and 65 days (observer frame) after the initial high-energy trigger. The X-ray emission decays steeply as ∼ t ^−1.9 and shows short-timescale X-ray variability (Δ T / T < 0.03) in both Swift and NuSTAR, consistent with flares superposed on an external shock continuum. Serendipitous detections by the Swift Burst Alert Telescope out to ∼0.3 days and continued NuSTAR variability to ∼2 days imply sustained central engine activity; including the early Einstein Probe X-ray detections, the required engine duration is ≳3 days. Afterglow modeling favors the combination of forward- and reverse-shock emission in a windlike ( k ≈ 2) environment. These properties, especially the long-lived engine and early soft-X-ray emission, are difficult to reconcile with a collapsar origin, and GRB 250702B does not fit neatly with canonical ultralong GRBs or relativistic tidal disruption events (TDEs). A “hybrid” scenario, in which a star is disrupted by a stellar-mass black hole (a micro-TDE), provides a plausible explanation, although a relativistic TDE from an intermediate-mass black hole remains viable.

Context. Gamma-ray bursts (GRBs) are the most powerful explosions in the Universe; their energy release reaches us from the end of the re-ionisation era, making them invaluable cosmological probes. GRB 230307A is 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 have revealed a lanthanide-rich kilonova with long-lasting X-ray emission immediately following the prompt gamma-rays. Moreover, the gamma-ray light curve of GRB 230307A exhibits high amplitude variability, especially within the first 15 s. Aims. We performed a timing analysis of the prompt emission of GRB 230307A collected with INTEGRAL’s SPectrometer of INTEGRAL AntiCoincidence Shield (SPI-ACS) and Fermi’s Gamma-Ray Burst Monitor (GBM). Methods. We used Fourier analysis, wavelets, and Gaussian processes. We critically assessed all three methods in terms of their robustness for detections of quasi-periodic oscillations (QPOs) in fast transients such as GRBs. Results. Our analyses reveal QPOs at a frequency of ∼1.2 Hz (0.82 s period) near the burst’s peak emission phase, consistent across instruments and detection methods. We also identify a second, less significant QPO at ∼2.9 Hz (0.34 s) nearly simultaneously. We hypothesise that the two QPOs originate from the transition epoch at the end of the jet acceleration phase. These QPOs represent 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.