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Recent space-borne and ground-based observations provide photometric measurements as time series. The effect of interstellar dust extinction in the near-infrared range is only 10% of that measured in the V band. However, the sensitivity of the light curve shape to the physical parameters in the near-infrared is much lower. So, interpreting these types of data sets requires new approaches like the different large-scale surveys, which create similar problems with big data. Using a selected data set, we provide a method for applying routines implemented in R to extract most information of measurements to determine physical parameters, which can also be used in automatic classification schemes and pipeline processing. We made a multivariate classification of 131 Cepheid light curves (LC) in J, H, and K colors, where all the LCs were represented in 20D parameter space in these colors separately. Performing a Principal Component Analysis (PCA), we got an orthogonal coordinate system and squared Euclidean distances between LCs, with 6 significant eigenvalues, reducing the 20-dimension to 6. We also estimated the optimal number of partitions of similar objects and found it to be equal to 7 in each color; their dependence on the period, absolute magnitude, amplitude, and metallicity are also discussed. We computed the Spearman rank correlations, showing that periods and absolute magnitudes correlate with the first three PCs significantly. The first two PC are also found to have a relationship with the amplitude, but the metallicity effects are only marginal. The method shown can be generalized and implemented in unsupervised classification schemes and analysis of mixed and biased samples. The analysis of our Classical Cepheid near-infrared LC sample showed that the J, H, K curves are insufficient for determination of stellar metallicity, with mass being the key factor shaping them., Comment: Accepted in New Astronomy, 16 Pages, 18 Figures

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., Comment: 11 pages, 15 figures, submitted to MNRAS

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., Comment: Submitted to MNRAS

Detecting the thermal emission from double neutron star merger events is a challenging task because of the quick fading of the observed flux. In order to create an efficient observing strategy for their observing method it is crucial to know their intrinsic rate. Unfortunately, the numerous models existing today predict this rate on a vary wide range. Hence, our goal in this paper is to investigate the effect of different level of approximations on the relative rate predictions. Also, we study the effect of distinct ejecta mass lay-outs on the light curve. We find that the ratio of the expected kilonova detections of the spherical to axisymmetrical models is 6:1 (or 2:1, depending on the input parameter set applied in our work). Nevertheless, the light curve shape is only slightly affected by the various ejecta alignments. This means that different ejecta layouts can produce light curves with similar shapes making it a challenging task to infer the structure of the matter outflow. Thus, we conclude that the uncertainty in the rate predictions arising from the various ejecta mass distribution models is negligible compared to the errors present in other input parameters (e.g. binary neutron star merger rate). In addition, we show that up to moderate redshifts (z < 0.2) the redshift distribution type (observed or uniform in volume) does not affect the expected relative rate estimations., Comment: Published in MNRAS

Studying the GRBs' gamma-ray spectra may reveal some physical information of Gamma-ray Bursts. The Fermi satellite observed more than two thousand GRBs. The FERMIGBRST catalog contains GRB parameters (peak energy, spectral indices, intensity) estimated for both the total emission (fluence), and the emission during the interval of the peak flux. We found a relationship with linear discriminant analysis between the spectral categories and the model independent physical data. We compared the Swift and Fermi spectral types. We found a connection between the Fermi fluence spectra and the Swift spectra but the result of the peak flux spectra can be disputable. We found that those GRBs which were observed by both Swift and Fermi can similarly discriminate as the complete Fermi sample. We concluded that the common observation probably did not mean any trace of selection effects in the spectral behavior of GRBs., Comment: arXiv admin note: text overlap with arXiv:1712.00389

Statistical studies of gamma-ray burst (GRB) spectra may result in important information on the physics of GRBs. The Fermi GBM catalog contains GRB parameters (peak energy, spectral indices, intensity) estimated fitting the gamma-ray SED of the total emission (fluence, flnc), and during the time of the peak flux pflx. Using contingency tables we studied the relationship of the models best fitting pflx and flnc time intervals. Our analysis revealed an ordering of the spectra into a power law - Comptonized - smoothly broken power law - Band series. This result was further supported by a correspondence analysis (CA) of the pflx and flnc spectra categorical variables. We performed a linear discriminant analysis (LDA) to find a relationship between categorical (spectral) and model independent physical data. LDA resulted in highly significant physical differences among the spectral types, that is more pronounced in the case of the pflx spectra, than for the flnc spectra. We interpreted this difference as caused by the temporal variation of the spectrum during the outburst. This spectral variability is confirmed by the differences in the low energy spectral index and peak energy, between the pflx and flnc spectra. We found that the synchrotron radiation is significant in GBM spectra. The mean low energy spectral index is close to the canonical value of {\alpha} = -2/3 during the peak flux. However, $\alpha$ is ~ -0.9 for the spectra of the fluences. We interpret this difference as showing that the effect of cooling is important only for the fluence spectra., Comment: Manuscript accepted for publication in MNRAS

We studied some statistical properties of the spatial point process displayed by GRBs of known redshift. To find ring like point patterns we developed an algorithm and defined parameters to characterize the level of compactness and regularity of the rings found in this procedure. Applying this algorithm to the GRB sample we identified three more ring like point patterns. Although, they had the same regularity but much less level of compactness than the original GRB ring. Assuming a stochastic independence of the angular and radial positions of the GRBs we obtained 1502 additional samples, altogether 542222 data points, by bootstrapping the original one. None of these data points participated in rings having similar level of compactness and regularity as the original one. Using an appropriate kernel we estimated the joint probability density of the angular and radial variables of the GRBs. Performing MCMC simulations we obtained 1502 new samples, altogether 542222 data points. Among these data points only three represented ring like patterns having similar parameters as the original one. By defining a new statistical variable we tested the independence of the angular and radial variables of the GRBs. We concluded that despite the existence of local irregularities in the GRBs' spatial distribution (e.g. the GGR) one can not reject the Cosmological Principle, based on their spatial distribution as a whole. We pointed out the large scale spatial pattern of the GRB activity does not necessarily re ects the large scale distribution of the cosmic matter., Comment: 13 pages, 9 figures. Accepted for publication in MNRAS

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.

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.

Gamma-ray bursts can be divided into three groups: short-, intermediate and long-duration bursts. While the progenitors of the short and long ones are relatively known, the progenitor objects of the intermediate-duration bursts are generally unknown, however, recent statistical studies suggest, that they should be related to the long-duration bursts. In this work we investigate whether there is a differ- ence between the global parameters of the X-ray flashes and intermediate-duration group of gamma-ray bursts. The statistical tests do not show any significant discrepancy regarding most of the parameters, except the BAT photon index, which is only a consequence of the defintion of the X-ray flashes., Comment: 9 pages, 10 figures, submitted to Astronomische Nachrichten

We demonstrate the use of the AKARI survey photometric data in the study of galactic star formation. Our aim was to select young stellar objects (YSOs) in the AKARI FIS catalogue. We used AKARI Far-Infrared Surveyor and Wide-field Infrared Survey Explorer data to derive mid- and far-infrared colours of YSOs. Classification schemes based on Quadratic Discriminant Analysis have been given for YSOs. The training catalogue for QDA was the whole sky selection of previously known YSOs (i.e. listed in SIMBAD). A new catalogue of AKARI FIS YSO candidates including 44001 sources has been prepared. Reliability of the classification is over 90% as tested in comparison to known YSOs. As much as 76% of our YSO candidates are from previously uncatalogued type. The vast majority of these sources are Class I and II types according to the Lada classification. The distribution of AKARI FIS YSOs' is well correlated with that of the galactic ISM. Local over densities were found on infrared loops and towards the cold clumps detected by Planck., Comment: This paper has been withdrawn by the author due to critical errors in references and in tables description

We present results from an Halpha emission-line survey in a one square degree area centered on the Orion Nebula Cluster, obtained with the Wide Field Grism Spectrograph-2 on the 2.2-meter telescope of the University of Hawaii. We identified 587 stars with Halpha emission, 99 of which, located mainly in the outer regions of the observed area, have not appeared in previous Halpha surveys. We determined the equivalent width (EW) of the line, and based on it classified 372 stars as classical T Tauri stars (CTTS) and 187 as weak line T Tauri stars (WTTS). Simultaneous r', i' photometry indicates a limiting magnitude of r' ~ 20 mag, but the sample is incomplete at r' > 17 mag. The surface distribution of the Halpha emission stars reveals a clustered and a dispersed population, the former consisting of younger and more massive young stars than the latter. Comparison of the derived EWs with those found in the literature indicates variability of the Halpha line. We found that the typical amplitudes of the variability are not greater than a factor 2-3 in the most cases. We identified a subgroup of low-EW stars with infrared signatures indicative of optically thick accretion disks. We studied the correlations between the equivalent width and other properties of the stars. Based on literature data we examined several properties of our CTTS and WTTS subsamples and found significant differences in mid-infrared color indices, average rotational periods, and spectral energy distribution characteristics of the subsamples., Comment: accepted for ApJS

We present a method for determining the background of Fermi GBM GRBs using the satellite positional information and a physical model. Since the polynomial fitting method typically used for GRBs is generally only indicative of the background over relatively short timescales, this method is particularly useful in the cases of long GRBs or those which have Autonomous Repoint Request (ARR) and a background with much variability on short timescales. We give a Direction Dependent Background Fitting (DDBF) method for separating the motion effects from the real data and calculate the duration (T90 and T50, as well as confidence intervals) of the nine example bursts, from which two resulted an ARR. We also summarize the features of our method and compare it qualitatively with the official GBM Catalogue. Our background filtering method uses a model based on the physical information of the satellite position. Therefore, it has many advantages compared to previous methods. It can fit long background intervals, remove all the features caused by the rocking behaviour of the satellite, and search for long emissions or not-triggered events. Furthermore, many part of the fitting have now been automatised, and the method have been shown to work for both Sky Survey mode and ARR mode data. Future work will provide a burst catalogue with DDBF., Comment: 16 pages, 28 figures

The Fermi Gamma-ray Burst Monitor (GBM) detects gamma-rays in the energy range 8 keV - 40 MeV. We developed a new background fitting process of these data, based on the motion of the satellite. Here we summarize this method, called Direction Dependent Background Fitting (DDBF), regarding the GBM triggered catalog. We also give some preliminary results and compare the duration parameters with the 2-years Fermi Burst Catalog., Comment: 2012 Fermi Symposium proceedings - eConf C121028

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 {\Omega}M parameter of the Universe and for making a GRB Hubble diagram using Amati's relation., Comment: 4 pages, 6 figures. Presented as a talk on the conference '7th INTEGRAL/BART Workshop 14 -18 April 2010, Karlovy Vary, Czech Republic'. Published in Acta Polytechnica

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., Comment: 4 pages, 6 figures. Presented as a poster on the conference '8th INTEGRAL/BART Workshop, 26-29 April 2011, Karlovy Vary, Czech Republic'. Accepted to Acta Polytechnica

Swift satellite measurements contributed substantially to the gamma-ray burst (GRB) redshift observations through fast slewing to the source of the GRBs. Still, a large number of bursts are without redshift. We study the celestial distribution of bursts with various methods and compare them to a random catalog using Monte-Carlo simulations. We find an anisotropy in the distribution of the intermediate class of bursts and find that the short and long population are distributed isotropically., Comment: 3 pages, 2 figures, appeared in The Ancient Universe With Gamma-Ray Bursts. AIP Conference Proceedings, Volume 1279, pp. 457-459 (2010)

Recently the anisotropy of the short gamma-ray bursts detected by BATSE was announced (Vavrek et al. 2008). The impact of this discovery on cosmology is discussed. It is shown that the anisotropy found may cause the breakdown of the cosmological principle., Comment: 4 pages, 1 figure. Published in Proceedings of the 6th INTEGRAL/BART Workshop, 26-29 March, 2009; Karlovy Vary

Two classes of gamma-ray bursts have been identified in the BATSE catalogs characterized by durations shorter and longer than about 2 seconds. There are, however, some indications for the existence of a third one. Swift satellite detectors have different spectral sensitivity than pre-Swift ones for gamma-ray bursts. Therefore it is worth to reanalyze the durations and their distribution and also the classification of GRBs. In this paper we are going to analyze the bursts' duration distribution and also the duration-hardness bivariate distribution, published in The First BAT Catalog, whether it contains two, three or maybe more groups. Similarly to the BATSE data, to explain the BAT GRBs duration distribution three components are needed. Although, the relative frequencies of the groups are different than they were in the BATSE GRB sample, the difference in the instrument spectral sensitivities can explain this bias in a natural way. This means theoretical models may have to explain three different type of gamma-ray bursts., Comment: GAMMA-RAY BURST: Sixth Huntsville Symposium. AIP Conference Proceedings, Volume 1133, pp. 412-414 (2009)

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., Comment: In Gamma-Ray Burst in the Afterglow Era. Springer. ed by E. Costa, F. Frontera, and J. Hjorth