- ID:
- ivo://CDS.VizieR/J/MNRAS/407/2075
- Title:
- Gamma-ray bursts spectral peak estimator
- Short Name:
- J/MNRAS/407/2075
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Simple hardness ratios are found to be a good estimator for the spectral peak energy in gamma-ray bursts (GRBs). Specifically, a high correlation strength is found between the nuFnu peak in the spectrum of Burst and Transient Source Experiment (BATSE) GRBs, Ep,obs and the hardness of GRBs, inline image, as defined by the fluences in channels 3 and 4, divided by the combined fluences in channels 1 and 2 of the BATSE Large Area Detectors (LADs). The correlation is independent of the type of the burst, whether long-duration GRB (LGRB) or short-duration (SGRB) and remains almost linear over the wide range of the BATSE energy window (20-2000KeV). Based on Bayes theorem and Markov Chain Monte Carlo techniques, we also present multivariate analyses of the observational data while accounting for data truncation and sample incompleteness. Prediction intervals for the proposed inline image relation are derived. Results and further simulations are used to compute Ep,obs estimates for nearly the entire BATSE catalogue: 2130 GRBs.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/PAZh/35/10
- Title:
- Gamma-ray bursts with known redshifts
- Short Name:
- J/PAZh/35/10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Observational parameters of the optical and gamma-ray emissions from 58 gamma-ray bursts (GRBs) with discovered afterglows and known redshifts are analyzed. The distributions of these parameters and pair correlations between them are studied. Approximately half of the objects exhibit a relatively slow decrease in the optical flux at initial afterglow phases (with a power-law index in the decay law {alpha}<1). Correlations have been found between the luminosities, energies, and durations of the optical and gamma-ray emissions, which can be explained by the presence of universal features in the light curves. A correlation of the peak luminosity for afterglows with the redshift and an anticorrelation of their durations with the redshift have been found for the first time. Against the background of a weak z dependence of the total afterglow energy, this effect can be explained by cosmological evolution of the GRB environment, which determines the rate of optical energy release.
- ID:
- ivo://CDS.VizieR/J/other/RAA/13.259
- Title:
- {gamma}-ray Doppler factor for Fermi blazars
- Short Name:
- J/other/RAA/13.2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Observations suggest that gamma-ray loud blazars are strongly beamed. The Fermi mission has detected many of blazars, which provide us with a good opportunity to investigate the emission mechanism and the beaming effect in the gamma-ray region. We compiled the X-ray observations for 138 Fermi blazars (54 flat spectrum radio quasars, 36 low-peaked BL Lacertae objects, and 48 high-peaked BL Lacertae objects) and calculated their Doppler factors, {delta}_{gamma}. It is interesting that the calculated Doppler factors, {delta}_{gamma}, are strongly correlated with the gamma-ray luminosity.
- ID:
- ivo://CDS.VizieR/J/ApJ/894/88
- Title:
- {gamma}-ray emission of star-forming galaxies
- Short Name:
- J/ApJ/894/88
- Date:
- 19 Jan 2022 13:04:51
- Publisher:
- CDS
- Description:
- A majority of the {gamma}-ray emission from star-forming galaxies is generated by the interaction of high-energy cosmic rays with the interstellar gas and radiation fields. Star-forming galaxies are expected to contribute to both the extragalactic {gamma}-ray background and the IceCube astrophysical neutrino flux. Using roughly 10yr of {gamma}-ray data taken by the Fermi Large Area Telescope, in this study we constrain the {gamma}-ray properties of star-forming galaxies. We report the detection of 11 bona fide {gamma}-ray-emitting galaxies and 2 candidates. Moreover, we show that the cumulative {gamma}-ray emission of below-threshold galaxies is also significantly detected at ~5{sigma} confidence. The {gamma}-ray luminosity of resolved and unresolved galaxies is found to correlate with the total (8-1000{mu}m) infrared luminosity as previously determined. Above 1GeV, the spectral energy distribution of resolved and unresolved galaxies is found to be compatible with a power law with a photon index of ~2.2-2.3. Finally, we find that star-forming galaxies account for roughly 5% and 3% of the extragalactic {gamma}-ray background and the IceCube neutrino flux, respectively.
- ID:
- ivo://CDS.VizieR/J/ApJ/722/520
- Title:
- Gamma-ray light curves of Fermi blazars
- Short Name:
- J/ApJ/722/520
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This paper presents light curves as well as the first systematic characterization of variability of the 106 objects in the high-confidence Fermi Large Area Telescope Bright AGN Sample (LBAS). Weekly light curves of this sample, obtained during the first 11 months of the Fermi survey (2008 August 4-2009 July 4), are tested for variability and their properties are quantified through autocorrelation function and structure function analysis. For the brightest sources, 3 or 4 day binned light curves are extracted in order to determine power density spectra (PDSs) and to fit the temporal structure of major flares. More than 50% of the sources are found to be variable with high significance, where high states do not exceed 1/4 of the total observation range. Variation amplitudes are larger for flat spectrum radio quasars and low/intermediate synchrotron frequency peaked BL Lac objects. Autocorrelation timescales derived from weekly light curves vary from four to a dozen of weeks.
- ID:
- ivo://CDS.VizieR/J/ApJ/726/16
- Title:
- {gamma}-ray loud blazars
- Short Name:
- J/ApJ/726/16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The radio properties of blazars detected by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope have been observed as part of the VLBA Imaging and Polarimetry Survey. This large, flux-limited sample of active galactic nuclei (AGNs) provides insights into the mechanism that produces strong {gamma}-ray emission. At lower flux levels, radio flux density does not directly correlate with {gamma}-ray flux. We find that the LAT-detected BL Lac objects tend to be similar to the non-LAT BL Lac objects, but that the LAT-detected FSRQs are often significantly different from the non-LAT FSRQs. The differences between the {gamma}-ray loud and quiet FSRQs can be explained by Doppler boosting; these objects appear to require larger Doppler factors than those of the BL Lac objects. It is possible that the {gamma}-ray loud FSRQs are fundamentally different from the {gamma}-ray quiet FSRQs. Strong polarization at the base of the jet appears to be a signature for {gamma}-ray loud AGNs.
- ID:
- ivo://CDS.VizieR/J/MNRAS/442/1693
- Title:
- Gamma-ray-loud blazars optical polarization
- Short Name:
- J/MNRAS/442/1693
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present first results from RoboPol, a novel-design optical polarimeter operating at the Skinakas Observatory in Crete. The data, taken during the 2013 May-June commissioning of the instrument, constitute a single-epoch linear polarization survey of a sample of gamma-ray-loud blazars, defined according to unbiased and objective selection criteria, easily reproducible in simulations, as well as a comparison sample of, otherwise similar, gamma-ray-quiet blazars. As such, the results of this survey are appropriate for both phenomenological population studies and for tests of theoretical population models. We have measured polarization fractions as low as 0.015 down to Rmag of 17 and as low as 0.035 down to 18mag. The hypothesis that the polarization fractions of gamma-ray-loud and gamma-ray-quiet blazars are drawn from the same distribution is rejected at the 3{sigma} level. We therefore conclude that gamma-ray-loud and gamma-ray-quiet sources have different optical polarization properties. This is the first time this statistical difference is demonstrated in optical wavelengths. The polarization fraction distributions of both samples are well described by exponential distributions with averages of <p>=6.4^+0.9^_-0.8_x10^-2^ for gamma-ray-loud blazars, and <p>=3.2^+2.0^_-1.1_x10^-2^ for gamma-ray-quiet blazars. The most probable value for the difference of the means is 3.4^+1.5^_-2.0_x10^-2^. The distribution of polarization angles is statistically consistent with being uniform.
- ID:
- ivo://CDS.VizieR/J/A+A/598/A134
- Title:
- {gamma}-ray signature in WHSP blazars (1BIGB)
- Short Name:
- J/A+A/598/A134
- Date:
- 04 Feb 2022 00:00:12
- Publisher:
- CDS
- Description:
- A direct search of {gamma}-ray emission centered on multifrequency selected candidates is a valuable complementary approach to the standard search adopted in current {gamma}-ray Fermi-LAT catalogs. Our sources are part of the 2WHSP sample that was assembled with the aim of providing targets for Imaging Atmospheric Cherenkov Telescopes (IACT). A likelihood analysis based on their known position enabled us to detect 150 {gamma}-ray excess signals that have not yet been reported in previous {gamma}-ray catalogs (1FGL, 2FGL, 3FGL). By identifying new sources, we solve a fraction of the extragalactic isotropic {gamma}-ray background (IGRB) composition, improving the description of the {gamma}-ray sky. We perform data reduction with the Fermi Science Tools using positions from 400 high synchrotron peaked (HSP) blazars as seeds of tentative {gamma}-ray sources; none of them have counterparts from previous 1FGL, 2FGL and 3FGL catalogs. Our candidates are part of the 2WHSP sample (currently the largest set of HSP blazars). We focus on HSPs characterized by bright synchrotron component with peak flux {nu}f_({nu})_>=10^-12.1^erg/cm^2^/s, testing the hypothesis of having a {gamma}-ray source in correspondence to the WHSP positions. Our likelihood analysis considers the 0.3-500GeV energy band, integrating over 7.2yr of Fermi-LAT observation and making use of the Pass 8 data release. From the 400 candidates tested, a total of 150 2WHSPs showed excess {gamma}-ray signature: 85 high-significance detections with test statistic (TS)>25, and 65 lower-significance detections with TS between 10 to 25. We assume a power law spectrum in the 0.3-500GeV band and list the spectrum parameters describing all 150 new {gamma}-ray sources. We study the {gamma}-ray photon spectral index distribution, the likelihood of detection according to the synchrotron peak brightness (figure of merit parameter), and plot the measured {gamma}-ray LogN-LogS of HSP blazars, also discussing the portion of the IGRB that has been resolved by the present work. We also report on four cases where we could resolve source confusion and find counterparts for unassociated 3FGL sources with the help of high-energy TS maps together with multifrequency data. The 150 new {gamma}-ray sources are named with the acronym 1BIGB for the first version of the Brazil ICRANet Gamma-ray Blazar catalog, in reference to the cooperation agreement supporting this work.
- ID:
- ivo://CDS.VizieR/J/other/RAA/18.56
- Title:
- gamma-ray spectrum for Fermi blazars
- Short Name:
- J/other/RAA/18.5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The curvature of the {gamma}-ray spectrum in blazars may reflect the intrinsic distribution of emitting electrons, which will further give some information on the possible acceleration and cooling processes in the emitting region. The {gamma}-ray spectra of Fermi blazars are normally fitted either by a single power-law (PL) or a log-normal (call Logarithmic Parabola, LP) form. The possible reason for this difference is not clear. We statistically explore this issue based on the different observational properties of 1419 Fermi blazars in the 3LAC Clean Sample.We find that the {gamma}-ray flux (100MeV-100GeV) and variability index follow bimodal distributions for PL and LP blazars, where the {gamma}-ray flux and variability index show a positive correlation. However, the distributions of {gamma}-ray luminosity and redshift follow a unimodal distribution. Our results suggest that the bimodal distribution of {gamma}-ray fluxes for LP and PL blazars may not be intrinsic and all blazars may have an intrinsically curved {gamma}-ray spectrum, and the PL spectrum is just caused by the fitting effect due to less photons.
- ID:
- ivo://CDS.VizieR/J/ApJ/794/82
- Title:
- GeV gamma-ray bursts with the ARGO-YBJ detector
- Short Name:
- J/ApJ/794/82
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The search for gamma-ray burst (GRB) emission in the energy range of 1-100 GeV in coincidence with the satellite detection has been carried out using the Astrophysical Radiation with Ground-based Observatory at YangBaJing (ARGO-YBJ) experiment. The high-altitude location (4300 m a.s.l.), the large active surface (~6700 m^2^ of Resistive Plate Chambers), the wide field of view (~2 sr, limited only by the atmospheric absorption), and the high duty cycle (>86%) make the ARGO-YBJ experiment particularly suitable to detect short and unexpected events like GRBs. With the scaler mode technique, i.e., counting all the particles hitting the detector with no measurement of the primary energy and arrival direction, the minimum threshold of ~1 GeV can be reached, overlapping the direct measurements carried out by satellites. During the experiment lifetime from 2004 December 17 to 2013 February 7, a total of 206 GRBs occurring within the ARGO-YBJ field of view (zenith angle {theta}<=45{deg}) have been analyzed. This is the largest sample of GRBs investigated with a ground-based detector. Two light curve models have been assumed and since in both cases no significant excess has been found, the corresponding fluence upper limits in the 1-100 GeV energy region have been derived, with values as low as 10^-5^ erg/cm2. The analysis of a subset of 24 GRBs with known redshift has been used to constrain the fluence extrapolation to the GeV region together with possible cutoffs under different assumptions on the spectrum.
