In this study, we report partly simultaneous XMM-Newton and NuSTAR observations of the bursting, dipping low mass X-ray binary, 4U 1323-62 obtained in 2024. 4U 1323-62 is one of the well-known persistent bursters, with bursts occurring roughly every three hours. It is also one of the few sources for which the orbital period is known, and shows dips in X-rays. In this paper, we report the detection of 12 unique bursts with XMM-Newton and NuSTAR, 6 of them observed jointly. We detected two double burst events, one with the NuSTAR and another one observed with both missions. During our observations we detected 10 X-ray dips with a periodicity of 2.942 hours, in line with previous measurements. We also present the results of the time resolved X-ray spectral analysis of the bursts and show the limits on the cooling of the corona heated by the burst emission. We also found a $0.898+/- 0.017 Hz quasi-periodic oscillation (QPO) during the non-bursting and non-dipping times confirming previous detections.

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 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 similar to 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 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.

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, and 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 April 2020 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 magnetar SGR J1935+2154 entered a new active episode on 2022 October 10, with X-ray bursts and enhanced persistent emission. At the tail of a high burst rate interval, lasting several hours, radio bursts were detected, revealing the connection between the X-ray activities and radio emissions. We analyzed observations of SGR J1935+2154 for nearly 3 months, using data from the Neutron Star Interior Composition Explorer. We report the timing and spectral results following the onset of this outburst. In general, the X-ray flux of the persistent emission decays exponentially. While a flare is evident on the light curve, a fast radio burst (FRB) was detected immediately following the peak of this flare. We found a phase jump in the pulse profile, with a deviation of a 0.16 ± 0.03 phase, which is related to the glitch. The spectra are well fit with the combination of a blackbody and a power-law (PL) model. The decay of the outburst is dominated by the drop in the nonthermal component, which also leads to an increase in thermal proportion. The photon index of the PL is inversely correlated with both the unabsorbed flux and the burst rate. We find that unlike the large variety of the persistent emission around FRB 221014, the X-ray properties are very stable when FRBs 221021 and 221201 happened. These results manifest the connection between the glitch, phase jump, X-ray burst, and radio burst, crucial for studying the mutation in twisted magnetic fields and constraining the trigger mechanism of radio bursts.

Energetic bursts from strongly magnetized neutron stars, known as magnetars, are typically detected in clusters. Once an active episode begins, anywhere from a few to thousands of hard X-ray bursts can occur over durations ranging from days to months. The temporal clustering of these recurrent bursts during an active episode suggests an underlying mechanism that triggers multiple bursts in rapid succession. These burst clusters are likely crucial for understanding the processes driving magnetar activity. In this study, we investigate the repetitive short X-ray burst behavior of magnetars through crustal interactions, employing the cellular automaton model for the magnetar crust proposed by S. K. Lander. Our simulations, based on physically motivated criteria, successfully reproduce burst clustering. Additionally, the durations and energetics of active episodes in our simulations agree well with observational data. We discuss the potential physical mechanisms underlying burst clusters observed in numerous magnetars, as well as the reactivations of an individual magnetar.

We present a comprehensive multiwavelength analysis of GRB 240825A, a bright gamma-ray burst (GRB) detected by Fermi and Swift, with a prompt duration (T_ 90 4 sec in 50-300 keV) near the boundary separating short and long GRBs, prompting a detailed investigation into its classification and progenitor. Using classical prompt metrics (duration, minimum variability timescale (MVT), lag, and spectral hardness) and modern classification techniques (machine-learning (ML) based t-SNE, support vector machine, energy-hardness-duration, and ε≡ E_γ,iso,52 / E_p,z,2^5/3), we find GRB 240825A exhibits hybrid characteristics. The short MVT (13.830 ± 1.574 ms), rest-frame duration, and ML-based classification indicate a merger-like or ambiguous nature, while its energetics and position on the Amati relation favor a collapsar origin. We conducted deep optical and NIR photometric and spectroscopic late-time search for an associated supernova (SN)/kilonova (KN) and the host galaxy using 10.4 m GTC and 8.4 m binocular LBT telescopes. No bright SN (like SN 1998bw) is detected down to stringent limits (e.g., m_r > 26.1 mag at 17.59 days), despite a redshift of z = 0.659 measured from GTC spectroscopy. Host galaxy SED modeling with Prospector indicates a massive, dusty, and star-forming galaxy-typical of collapsar GRB hosts, though with low sSFR and large offset. We compare these findings with hybrid events like GRB 211211A, GRB 230307A, GRB 200826A, including SNe-GRBs, and conclude that GRB 240825A likely originated from a massive star collapse, with the associated supernova obscured by a dusty host environment or low luminosity SN with absolute magnitude M_V fainter than -18.0. This study emphasizes the need for multiwavelength follow-up and a multi-layered classification to determine GRB progenitors.

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 similar to 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 similar to 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.

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 nonoverlapping 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 cutoff (COMPT) model. We found that nearly all of the time segments fit well with the COMPT model. Both the average peak energy in the νF _ν spectra ( E _peak ) and photon index parameters follow a Gaussian distribution with means ∼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 parameters show a Gaussian distribution with peaks ∼4 and 12 keV, respectively. Additionally, we found that the distribution of the temperature parameter of the MBB-RCS model can be fit with a skewed Gaussian function with a peak ∼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 ∼15 to ∼68 Hz. We discuss and compare these results with previous studies.

In this study, we test whether the power law slopes (alpha(F)) for fluxes (F), and (alpha(E)) for energies (E) are universal in their size distributions, N(F)proportional to F-alpha F and N(E)proportional to E-alpha E, in astrophysical observations of galactic, extragalactic, and black hole systems. This is a test of fundamental importance for self-organized criticality (SOC) systems. The test decides whether (i) power laws are a natural consequence of the scale-freeness and inherent universality of SOC systems, or (ii) if they depend on more complex physical scaling laws. The former criterion allows quantitative predictions of the power-law-like size distributions, while the latter criterion requires individual physical modeling for each SOC variable and data set. Our statistical test, carried out with 61 published data sets, is consistent with the former option, which implies that observed power laws can simply be derived from the scale-freeness and do not require specific physical models to understand their statistical distributions. The observations show a mean and standard deviation of alpha(F) = 1.78 +/- 0.29 for SOC fluxes and alpha(E) = 1.66 +/- 0.22 for SOC fluences, and thus are consistent with the prediction of the fractal-diffusive SOC model, with alpha(F) = 1.80 and alpha(E) = 1.67.

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 mu m 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 similar to 2. We applied the photometric MIR colors to the largest (similar to 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) similar to 10(11.9) L-circle dot at 0.9 <= z < 1.57. The majority of them are consistent with the z similar to 1 main sequence. We also identified the first examples of z similar to 1 galaxies with deep silicate absorption.

We analyze a wide set of historical magnetar burst observations detected with five different instruments, calibrating these to the energy range of Fermi-GBM observations for consistency. We find a striking correlation between a magnetar’s characteristic age and both its typical burst energy and its burst activity level. Arguing that this bursting behavior also correlates with true age, we interpret it as the result of a reducing high-stress volume of the crust in an aging magnetar: Previous giant flares cause relaxation of large regions of its crust and inhibit burst clustering, while the reducing burst energy reflects the progressively shallower region of the crust where Hall drift can build stresses effectively, as the field decays through the range ∼10 ^12 –10 ^13 G. Low-energy bursts from very young magnetars may represent failures of weak regions of the crust that have only recently solidified.

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.

We present the results obtained from timing and spectral studies of 15 thermonuclear X-ray bursts from 4U 1820-30 observed with the Neutron Star Interior Composition Explorer (NICER) during its 5 yr of observations between 2017 and 2022. All bursts showed clear signs of photospheric radius expansion (PRE), where the neutron star (NS) photosphere expanded more than 50 km above the surface. One of the bursts produced a superexpansion with a blackbody emission radius of 902 km for the first time with NICER. We searched for burst oscillations in all 15 bursts and found evidence of a coherent oscillation at 716 Hz in a burst, with a 2.9 sigma detection level based on Monte Carlo simulations. If confirmed with future observations, 4U 1820-30 would become the fastest-spinning NS known in X-ray binary systems. The fractional rms amplitude of the candidate burst oscillation was found to be 5.8% in the energy range of 3-10 keV. Following the variable persistent model from burst time-resolved spectroscopy, an anticorrelation is seen between the maximum scaling factor value and the (preburst) persistent flux. We detected a low value of ionization at the peak of each burst based on reflection modeling of burst spectra. A partially interacting inner accretion disk or a weakly ionized outer disk may cause the observed ionization dip during the PRE phase.

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.

Cüce Eliptik Galaksiler (dwarf elliptical galaxies, dEs), galaksi kümeleri içinde çok sayıda ve baskın tür olarak bulunurlar. Bu çalışmada çözümlenmemiş küçük yıldız sistemlerinin yıldız popülasyonu çalışmaları için kullanılacak yeni bir yüksek çözünürlüklü tayfsal indeksler setini tanımlayıp, bunları kullanarak, Fornax galaksi kümesinde bulunan 8 dEs yıldız popülasyonlarının ayrıntılı bir incelemesini sunuyoruz. Bu çalışmada 11 elemente ait 23 yeni çizgi indeksi tanımlanmıştır. Gözlem verileri Sidney-Avusturalya Gözlemevinde bulunan 3.9m çapa sahip AAT’ye takılı olan Çoklu-Obje İntegral Alan Tayfmetresi (SAMI) ile elde edilmiştir. Sekiz dE’nin yeni yüksek çözünürlüklü indeks sistemimizde ölçülen çizgi kuvvetleri, yıldız popülasyon modelleri yardımıyla analiz edilmiştir. Bu kadar çok sayıda elemente ait bolluk oranı vekilleri, daha önce Yerel Grup dışındaki cüce eliptik galaksiler için hiç çalışılmamıştır. Sonuçlar, Yerel Grup'taki çözümlenmiş yıldızların bolluk oranları ve daha büyük erken tip galaksilerin integral ışığından alınan indekslerle karşılaştırılır. Tüm galaksilerimizin, Samanyolu diskiyle tutarlı bir bolluk oranları modeli gösterdiğini, yüksek kütleli emsallerine kıyasla yavaş oluşumun göstergesi olduğu bulunmuştur.

Magnetars are a special subset of the isolated neutron star family, with X-ray and radio emission mainly powered by the decay of their immense magnetic fields. Many attributes of magnetars remain poorly understood: spin-down glitches or the sudden reductions in the star’s angular momentum, radio bursts reminiscent of extragalactic fast radio bursts (FRBs) and transient pulsed radio emission lasting months to years. Here we unveil the detection of a large spin-down glitch event (fractional change in spin frequency $$| {{\Delta }}\nu /\nu | =5.{8}_{-1.6}^{+2.6}\times 1{0}^{-6}$$ ) from the magnetar SGR 1935+2154 on 5 October 2020 (±1 day). We find no change to the source-persistent surface thermal or magnetospheric X-ray behaviour, nor is there evidence of strong X-ray bursting activity. Yet, in the subsequent days, the magnetar emitted three FRB-like radio bursts followed by a month-long episode of pulsed radio emission. Given the rarity of spin-down glitches and radio signals from magnetars, their approximate synchronicity suggests an association, providing pivotal clues to their origin and triggering mechanisms with ramifications to the broader magnetar and FRB populations. We postulate that impulsive crustal plasma shedding close to the magnetic pole generates a wind that combs out magnetic field lines, rapidly reducing the star’s angular momentum while temporarily altering the magnetospheric field geometry to permit the pair creation needed to precipitate radio emission. An abrupt slow-down in a magnetar’s rotation rate (a ‘glitch’) may be related to the subsequent emission of three radio bursts (resembling fast radio bursts) and a month-long episode of pulsed radio emission.

Bileşenlerinden biri Kara delik (KD) olan Düşük kütleli X-ışın çiftlerinin (LMXB'lerin), ani parlamalara uğradıklarında sergiledikleri farklı yığılma süreçleri ile ilişkili tayfsal evreler ve geçişler gösterdikleri yaygın olarak kabul edilmektedir. Kompakt bileşeni bir nötron yıldızı (NY) olan LMXB'lerin de, KD-LMXB'lere benzer tayfsal evre geçişleri sergiledikleri bilinmektedir. Bu çalışmada, parlama profili q-eğri yapısı gösteren 9 tane KD ve NY-LMXB' nin zamansal analiz sonuçları sunulmaktadır. Çalışma kapsamında RXTE arşiv verileri kullanılarak kaynakların tayfsal evreleri ile ilişkili olan minimal zaman ölçeği (MTS) elde edilmiştir. KD ve NY kaynaklarında meydana gelen tayfsal değişimleri izlemede MTS'nin öneminin ileri boyutta araştırılması için kaynakların evre geçişlerine özgü diğer parametreler olan ışıma şiddeti, RMS değişkenliği ve sertlik oranları ile karşılaştırılmıştır.

In this study, we explore the dynamical stability of magnetar bursts within the context of the chaos-randomness phase space for the first time, aiming to uncover unique behaviors compared to various astrophysical transients, including fast radio bursts (FRBs). We analyze burst energy time series data from active magnetar sources SGR J1550-5418 and SGR J1935+2154, focusing on burst arrival time and energy differences between consecutive events. We find a distinct separation in the time domain, where magnetar bursts exhibit significantly lower randomness compared to FRBs, solar flares, and earthquakes, with a slightly higher degree of chaos. In the energy domain, magnetar bursts exhibit a broad consistency with other phenomena, primarily due to the wide distribution of chaos-randomness observed across different bursts and sources. Intriguingly, contrary to expectations from the FRB-magnetar connection, the arrival time patterns of magnetar bursts in our analysis do not exhibit significant proximity to repeating FRBs in the chaos-randomness plane. This finding may challenge the hypothesis that FRBs are associated with typical magnetar bursts but indirectly supports the evidence that FRBs may primarily be linked to special magnetar bursts like peculiar X-ray bursts from SGR J1935+2154 observed simultaneously with Galactic FRB 200428.