Searcharxiv⌕ Search

arXiv subjects

Lajos G. Balazs

Publications and source records attributed to Lajos G. Balazs.

13 recordsLinked to original sources
arXiv2026

Correlation between X-ray and gamma data of Swift measurements

Several studies over the last two decades have used canonical correlation analysis (CCA) to study the relationships between main γ-ray (e.g. fluence, peak flux, and duration) and main X-ray (flux, decay and spectral index, and hydrogen column density) data from gamma-ray bursts (GRBs). In this paper, we revisit this approach using a much larger dataset to identify potential new insights into these relationships. We used CCA to investigate the interrelationship of the aforementioned gamma-ray and X-ray parameters. Using the derived canonical variables, we calculated their correlations (canonical loadings) with the original data. Consistently with previous research, the analysis revealed that gamma-ray fluence and X-ray flux have the strongest correlation, while the X-ray decay index and spectral index have a lower contribution. Interestingly, our analysis of a much larger dataset reveals that the HI column density makes a significant contribution to the overall correlation. This finding, in the context of the collapsar model for long GRBs, could be interpreted as an indication that the progenitor star ejected an HI envelope during the GRB.

astro-ph.HE↗
arXiv2026

Gamma-Ray Bursts and Optical Brightness: Insights from Swift Satellite

During the examination of optical properties of gamma-ray bursts (GRBs) measured during the life of the Neil Gehrels Swift Observatory satellite, significant discoveries were made. While the satellite measures gamma, X-ray, and optical data simultaneously, in many cases, only an upper limit is established in the optical domain. Hence, survival analysis, a.k.a. dependability modelling, was necessary, serving as a tool for studying samples where some cases are bound only by the upper limit, as mentioned earlier. This method is used to analyse datasets that may have upper or lower bounds rather than precise observations, but nevertheless contain relevant information. It was previously established that the duration, gamma fluence, and peak flux all have a substantial effect on the optical brightness distribution, probably due to the energy of the beam from the GRB's central engine. However, after analysing more than 200 data points, we no longer see this association. This disagreement shows that the previously reported impact may not be as significant as previously derived, needing more research to better understand the underlying processes that determine the optical brightness in connection to gamma-ray properties.

astro-ph.HE↗
arXiv2026

Spheroidal Resampling Analysis of High-Redshift Gamma-Ray Burst Spatial Densities

Gamma-ray bursts (GRBs) are bright transient sources that can be observed at high redshift. They can therefore be used as tracers of the distant large-scale structure, although the GRB redshift sample is sparse and affected by strong selection effects. We analyze the three-dimensional distribution of 542 GRBs with spectroscopic redshifts. The method extends our earlier spherical-window search by replacing spherical counting volumes with axisymmetric spheroids. The angular positions of the observed GRBs are kept fixed in the Monte-Carlo null samples, while the redshifts are shuffled within each Galactic hemisphere. In the Northern Galactic hemisphere, the overdensity associated with the Hercules--Corona Borealis Great Wall remains significant for a range of spheroidal shapes. This supports the stability of the previously reported signal and shows that it is not only a consequence of using spherical counting volumes. In the Southern Galactic hemisphere, the same method finds no structure with comparable significance. A small candidate grouping is present, but its significance is only marginal, and it is sensitive to the small number of events. We conclude that spheroidal resampling is a useful check of GRB overdensity searches, but the physical nature of any candidate structure still requires confirmation with independent tracers such as galaxy or quasar samples.

astro-ph.CO↗
arXiv2026

Reanalysing large-scale structure using an updated gamma-ray burst spatial density approach

In the past few decades, large universal structures have been found that challenge the homogeneity and isotropy expected in standard cosmological models. This study examines burst clustering in both galactic hemispheres using a recently developed methodology, using spheres in 3D space for testing regularities. Using our new method in both hemisphere we find only one deviation from isotropy. A small one in the Southern and a huge one in the Northern hemisphere. This itself suggests that the two deviations do not likely to come from statistical fluctuation. The northern huge group contains app. 125 gamma-ray bursts (GRBs) corresponds with the so - called Hercules-Corona Borealis Great Wall. The southern group contains 4-5 GRBs locating very close to each other. Two of them (GRB050822 and GRB050318) are close not just in redshift and the angular position but they are very close in observing time (5 months). We concluded that the third important result of this work that this method could not find other overdensity deviation from homogeneity in the GRBs spatial distribution. We have shown that the large-scale density increase in the spatial distribution of gamma-ray bursts does not necessarily violate the cosmological principle.

astro-ph.CO↗
arXiv2025

Scanning the Universe for Large-Scale Structures using Gamma-Ray Bursts

In the past few decades, large universal structures have been found that challenge the homogeneity and isotropy expected in standard cosmological models. The largest of these, identified as the Hercules-Corona Borealis Great Wall, was found in 2014 in the northern galactic hemisphere in the redshift range of 1.6 < z < 2.1. Subsequent studies used an increasing gamma-ray burst database to show that the cluster was unlikely to have been caused by statistical sampling uncertainties. This study re-examines burst clustering in the northern galactic hemisphere using a recently developed methodology. Evidence is provided that the Hercules-Corona Borealis Great Wall cluster is larger than previously thought, with members potentially spanning the redshift range of 0.33 < z < 2.43. The extension of this cluster's size does not appear to have been due to statistical variations or sampling biases.

astro-ph.CO↗
arXiv2023

Mapping the Universe with Gamma-Ray Bursts

We explore large-scale cosmic structure using the spatial distribution of 542 gamma-ray bursts (GRBs) having accurately measured positions and spectroscopic redshifts. Prominent cosmological clusters are identified in both the northern and southern galactic hemispheres (avoiding extinction effects in the plane of the Milky Way) using the Bootstrap Point-Radius method. The Northern Galactic hemisphere contains a significant group of four GRBs in the redshift range 0.59 < z < 0.62 (with a Bootstrap probability of p = 0.012) along with the previously-identified Hercules-Corona Borealis GreatWall (in the revised redshift range 0.9 < z < 2.1, p = 0.017). The Southern Galactic hemisphere contains the previously-identified Giant GRB Ring (p = 0.022) along with another possible cluster of 7 - 9 GRBs at 1.179 < z < 1.444 (p = 0.031). Additionally, both the Hercules-Corona Borealis Great Wall and the Giant GRB Ring have become more prominent as the GRB sample size has grown. The approach used here underscores the potential value of GRB clustering as a probe of large-scale cosmic structure, complementary to galaxy and quasar clustering. Because of the vast scale on which GRB clustering provides valuable insights, it is important that optical GRB monitoring continue so that additional spectroscopic redshift measurements should be obtained.

astro-ph.CO↗
arXiv2023

Some statistical remarks on GRBs jointly detected by Fermi and Swift satellites

We made statistical analysis of the Fermi GBM and Swift BAT observational material, accumulated over 15 years. We studied how GRB parameters (T$_{90}$ duration, fluence, peak flux) that were observed by only one satellite differ from those observed by both. In the latter case, it was possible to directly compare the values of the parameters that both satellites measured. The GRBs measured by both satellites were identified using the knn() k-nearest neighbour algorithm in the FNN library of the R statistical package. In the parameter space we determined the direction in which the jointly detected GRBs differ most from those detected by only one of the instruments using the lda() in MASS library of R. To get the strength of the relationship between the parameters obtained from the GBM and BAT, a canonical correlation was performed using the cc() procedure in the CCA library in R. The GBM and BAT T$_{90}$ distributions were fitted with a linear combination of lognormal functions. The optimal number of such functions required for fit is two for GBM and three for BAT. Contrary to the widely accepted view, we found that the number of lognormal functions required for fitting the observed distribution of GRB durations does not allow us to deduce the number of central engine types responsible for GRBs.

astro-ph.HE↗
arXiv2017

The AKARI FIS catalogue of YSOs and extragalactic objects

The point sources in the Bright Source Catalogue of the AKARI Far-Infrared Surveyor (FIS) were classified based on their FIR and mid-IR fluxes and colours into young stellar object (YSO) and extragalactic source types using Quadratic Discriminant Analysis method (QDA) and Support Vector Machines (SVM). The reliability of the selection of YSO candidates is high, and the number of known YSO candidates were increased significantly, that we demonstrate in the case of the nearby open cluster IC348. Our results show that we can separate galactic and extragalactic AKARI point sources in the multidimensional space of FIR fluxes and colours with high reliability, however, differentiating among the extragalactic sub-types needs further information.

astro-ph.GA↗
arXiv2017

Foreground of GRBs from AKARI FIS data

A significant number of the parameters of a gamma-ray burst (GRB) and its host galaxy are calculated from the afterglow. There are various methods obtaining extinction values for the necessary correction for galactic foreground. These are: galaxy counts, from HI 21 cm surveys, from spectroscopic measurements and colors of nearby Galactic stars, or using extinction maps calculated from infrared surveys towards the GRB. We demonstrate that AKARI Far-Infrared Surveyor sky surface brightness maps are useful uncovering the fine structure of the galactic foreground of GRBs. Galactic cirrus structures of a number of GRBs are calculated with a 2 arcminute resolution, and the results are compared to that of other methods.

astro-ph.GA↗
arXiv2012

Cosmology with Gamma-Ray Bursts Using k-correction

In the case of Gamma-Ray Bursts with measured redshift, we can calculate the k-correction to get the fluence and energy that were actually produced in the comoving system of the GRB. To achieve this we have to use well-fitted parameters of a GRB spectrum, available in the GCN database. The output of the calculations is the comoving isotropic energy E_iso, but this is not the endpoint: this data can be useful for estimating the ΩM parameter of the Universe and for making a GRB Hubble diagram using Amati's relation.

astro-ph.HE↗
arXiv2012

GRB duration distribution considering the position of the Fermi

The Fermi satellite has a particular motion during its flight which enables it to catch the gamma-ray bursts mostly well. The side-effect of this favourable feature is that the lightcurves of the GBM detectors are stressed by rapidly and extremely varying background. Before this data is processed, it needs to be separated from the background. The commonly used methods were useless for most cases of Fermi, so we developed a new technique based on the motion and orientation of the satellite. The background-free lightcurve can be used to perform statistical surveys, hence we showed the efficiency of our background-filtering method presenting a statistical analysis known from the literature.

astro-ph.HE↗
arXiv2005

A Gamma-Ray Bursts' Fluence-Duration Correlation

We present an analysis indicating that there is a correlation between the fluences and the durations of gamma-ray bursts, and provide arguments that this reflects a correlation between the total emitted energies and the intrinsic durations. For the short (long) bursts the total emitted energies are roughly proportional to the first (second) power of the intrinsic duration. This difference in the energy-duration relationship is statistically significant, and may provide an interesting constraint on models aiming to explain the short and long gamma-ray bursts.

astro-ph↗