L. G. Balázs

Eötvös Loránd University, Budapeŝto, Budapest, Hungary

Are you L. G. Balázs?

Claim your profile

Publications (153)155.55 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Astronomische Nachrichten 07/2014; 334(9). · 1.40 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) has observed more than 80,000 solar energetic events since its launch on February $12^{\rm th}$, 2002. Using this large sample of observed flares, we studied the spatio-temporal relationship between succeeding flares. Our results show that the statistical relationship between the temporal and spatial differences of succeeding flares can be described as a power law of the form $R(t)\sim t^p$ with $p=0.327\pm 0.007$. We discuss the possible interpretations of this result as a characteristic function of a supposed underlying physics. Different scenarios are considered to explain this relation, including the case where the connectivity between succeeding events is realised through a shock wave in the post Sedov-Taylor phase or where the spatial and temporal relationship between flares is supposed to be provided by an expanding flare area in the sub-diffusive regime. Furthermore, we cannot exclude the possibility that the physical process behind the statistical relationship is the reordering of the magnetic field by the flare or it is due to some unknown processes.
    03/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: We demonstrate the use of the AKARI all-sky survey photometric data in the study of galactic star formation. Our aim was to select young stellar objects (YSOs) in the AKARI Far-Infrared Surveyor (FIS) Bright Source Catalogue. We used AKARI/FIS and Wide-field Infrared Survey Explorer (WISE) data to derive mid- and far-infrared colors of YSOs. Classification schemes based on quadratic discriminant analysis (QDA) have been given for YSOs and the training catalog for QDA was the whole-sky selection of previously known YSOs (i.e., listed in the SIMBAD database). A new catalog of AKARI FIS YSO candidates including 44001 sources has been prepared; the 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 types. 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.
    01/2014; 66(1).
  • [Show abstract] [Hide abstract]
    ABSTRACT: We observed the ONC, centered on the Trapezium, with the Wide Field Grism Spectrograph-2 (WFGS2) installed on the University of Hawaii 2.2m telescope, on the five nights of 2010 December 31, 2011 January 2, 2011 January 25, 2011 February 27, and 2011 October 16. We covered an area of almost 1deg2 centered on RAJ2000=5:35:16.4 and DEJ2000=-5:23:25 with a mosaic of 25 overlapping fields. We used a 300line/mm grism blazed at 6500Å and providing a dispersion of 3.8Å/pixel and a resolving power of 820. The Hα filter had a 500Å passband centered near 6515Å. Direct images of each field of the mosaic with the same instrument were obtained through r' and i' filters immediately before the spectroscopic exposures. One exposure was taken at each position and in each filter with integration time of 60s. (3 data files).
    VizieR Online Data Catalog. 11/2013;
  • Source
    Dataset: 1204.1222
  • [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    09/2013;
  • J. Kóbori, Z. Bagoly, L. G. Balázs, I. Horváth
    [Show abstract] [Hide abstract]
    ABSTRACT: We investigated the main prompt and afterglow emission parameters of gamma-ray bursts detected by the Burst Alert Telescope (BAT) and X-Ray Telescope installed on the Swift satellite. Our aim was to look for differences or connections between the different types of gamma-ray bursts, so we compared the BAT fluences, 1-sec peak photon fluxes, photon indices, XRT early fluxes, initial temporal decay and spectral indices. We found that there might be a connection between the XRT initial decay index and XRT early flux/BAT photon index. Using statistical tools we also determined that beside the duration and hardness ratios, the means of the \gamma- and X-ray--fluences and the \gamma-ray photon index differ significantly between the three types of bursts.
    09/2013;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    The Astrophysical Journal Supplement Series 08/2013; 208(2). · 16.24 Impact Factor
  • Source
    L. G. Balazs, I. Horvath, Z. Bagoly, J. Kobori
    [Show abstract] [Hide abstract]
    ABSTRACT: We studied the distribution of the GRBs, observed by the Fermi satellite, in the multidimensional parameter space consisting of the duration, Fluence, Peak flux and Peak energy (if it was available). About 10% of the Fermi bursts was observed also by the Swift satellite. We did not find significant differences between the Peak flux and Peak energy of GRBs observed and not observed also by the Swift satellite. In contrast, those GRBs detected also by the Swift satellite had significantly greater Fluence and duration. We did a similar study for the GRBs detected by the Swift satellite. About 30% percent of these bursts was also measured by the Fermi satellite. We found a significant difference in the Fluence, Peak flux and Photon index but none in duration. These differences may be accounted for the different construction and observing strategy of the Fermi and Swift satellites.
    07/2013;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Gamma-Ray Bursts (GRBs) are the most powerful cosmic explosions since the Big Bang, and thus act as signposts throughout the distant Universe. Over the last 2 decades, these ultra-luminous cosmological explosions have been transformed from a mere curiosity to essential tools for the study of high-redshift stars and galaxies, early structure formation and the evolution of chemical elements. In the future, GRBs will likely provide a powerful probe of the epoch of reionisation of the Universe, constrain the properties of the first generation of stars, and play an important role in the revolution of multi-messenger astronomy by associating neutrinos or gravitational wave (GW) signals with GRBs. Here, we describe the next steps needed to advance the GRB field, as well as the potential of GRBs for studying the Early Universe and their role in the up-coming multi-messenger revolution.
    06/2013;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    Astronomy and Astrophysics 06/2013; · 5.08 Impact Factor
  • Source
    Dataset: 447aa23
  • [Show abstract] [Hide abstract]
    ABSTRACT: The Swift satellite made a real break through with measuring simultaneously the gamma X-ray and optical data of GRBs, effectively. Although, the satellite measures the gamma, X-ray and optical properties almost in the same time a significant fractions of GRBs remain undetected in the optical domain. In a large number of cases only an upper bound is obtained. Survival analysis is a tool for studying samples where a part of the cases has only an upper (lower) limit. The obtained survival function may depend on some other variables. The Cox regression is a way to study these dependencies. We studied the dependence of the optical brightness (obtained by the UVOT) on the gamma and X-ray properties, measured by the BAT and XRT on board of the Swift satellite. We showed that the gamma peak flux has the greatest impact on the afterglow's optical brightness while the gamma photon index and the X-ray flux do not. This effect probably originates in the energetics of the jet launched from the central engine of the GRB which triggers the afterglow.
    03/2013;
  • [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    03/2013;
  • [Show abstract] [Hide abstract]
    ABSTRACT: It is remarkable that the long gamma-ray bursts, as objects connected with the supernovae - i.e. with the end of the massive stars, trace the star formation rate. This connection is discussed in this contribution. The presentation is in essence a recapitulation of the article Mészáros A. et al. A&A, 2006, 455, 785.
    Proceedings of the International Astronomical Union 03/2013; 8(S292):334-334.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Physical parameters were derived for 100 young stellar objects in the TAPO region.
    Proceedings of the International Astronomical Union 03/2013; 8(S292):64-64.
  • [Show abstract] [Hide abstract]
    ABSTRACT: We revealed a statistically significant clustering in the all sky distribution of AKARI-WISE young stellar objects with large groups of elongated and bush types.
    Proceedings of the International Astronomical Union 03/2013; 8(S292):113-113.
  • [Show abstract] [Hide abstract]
    ABSTRACT: The Fermi GBM Catalog has been recently published. Previous classification analyses of the BATSE, RHESSI, BeppoSAX, and Swift databases found three types of gamma-ray bursts. Now we analyzed the GBM catalog to classify the GRBs. PCA and Multiclustering analysis revealed three groups. Validation of these groups, in terms of the observed variables, shows that one of the groups coincides with the short GRBs. The other two groups split the long class into a bright and dim part, as defined by the peak flux. Additional analysis is needed to determine whether this splitting is only a mathematical byproduct of the analysis or has some real physical meaning.
    Gamma-Ray Bursts 2012 Conference (GRB 2012), Munich, Germany; 05/2012
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: 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.
    04/2012;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Up to 24 Feb 2012 Swift has triggered on 638 GRBs. In this work we use the pattern of the missing gamma, X-ray and optical data measured by BAT, XRT, UVOT and ground based measurements of the redshift, collected for the Swift GRBs ([1]). Using the Boolean factor analysis of multivariate statistical methods we studied the missing data patterns of the gamma, X-ray and optical observed quantities of GRBs. We found that the measured gamma properties have some impact on the missing data in the X-ray and optical domains. The missing data pattern depends, however, on random effects as well.
    Proceedings of the Gamma-Ray Bursts 2012 Conference (GRB 2012).; 01/2012

Publication Stats

253 Citations
155.55 Total Impact Points

Institutions

  • 2004–2014
    • Eötvös Loránd University
      • • Department of Astronomy
      • • Department of Physics of Complex Systems
      Budapeŝto, Budapest, Hungary
  • 1987–2013
    • Konkoly Observatory
      Budapeŝto, Budapest, Hungary
  • 2009
    • Alfréd Rényi Institute of Mathematics
      Budapeŝto, Budapest, Hungary
  • 2006–2009
    • The Budapest Observatory
      Budapeŝto, Budapest, Hungary
  • 1993–2000
    • Hungarian Academy of Sciences
      • • MTA Research Centre for Astronomy and Earth Sciences
      • • Institute for Soil Science and Agricultural Chemistry
      Budapeŝto, Budapest, Hungary
  • 1998
    • Pennsylvania State University
      • Department of Astronomy and Astrophysics
      University Park, Maryland, United States