- ID:
- ivo://CDS.VizieR/J/ApJS/238/13
- Title:
- Spectral and timing results of 1ES 1959+650
- Short Name:
- J/ApJS/238/13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the detailed timing and spectral results obtained during the Swift observations of the TeV-detected blazar 1ES 1959+650 in 2016 August-2017 November. The source continued its trend of gradually enhancing X-ray flaring activity in the 0.3-10keV energy range, starting in 2015 August, and a new highest historical brightness state was recorded twice. A long-term high state was superimposed by both weak and strong flares, and we detected 32 instances of intraday X-ray flux variability, including several occasions of extremely fast fluctuations with fractional amplitudes of 5.4%-7.5% within 1ks exposures. The 0.3-10keV spectra generally showed a best fit with the log-parabolic model, yielding a very wide range of the curvature parameter b and the photon index at 1keV. The position of the synchrotron SED peak Ep showed an extreme variability on various timescales between energies less than 0.1keV and 7.7+/-0.7keV, with 25% of the spectra peaking at hard X-rays. In 2017 May-November, the source mostly showed lower spectral curvature and an anticorrelation b-Ep, expected in the case of efficient stochastic acceleration of X-ray-emitting electrons. The 0.3-100GeV and optical-UV fluxes also attained their highest historical values in this period, although the latter showed an anticorrelation with the 0.3-10keV emission, which is explained by the stochastic acceleration of electrons with a narrow initial energy distribution, having an average energy significantly higher than the equilibrium energy.
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- ID:
- ivo://CDS.VizieR/J/ApJS/166/298
- Title:
- Spectral catalog of bright BATSE gamma-ray bursts
- Short Name:
- J/ApJS/166/298
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a systematic spectral analysis of 350 bright gamma-ray bursts (GRBs) observed with the Burst and Transient Source Experiment (BATSE; 30keV-2MeV) with high temporal and spectral resolution. Our sample was selected from the complete set of 2704 BATSE GRBs based on their energy fluence or peak photon flux values to assure good statistics and included 17 short GRBs. To obtain well-constrained spectral parameters, several photon models were used to fit each spectrum.
- ID:
- ivo://CDS.VizieR/J/ApJS/224/26
- Title:
- Spectral energy distributions of Roma BZCAT blazars
- Short Name:
- J/ApJS/224/26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We combined multi-wavelength data for blazars from the Roma-BZCAT catalog and analyzed hundreds of X-ray spectra. We present the fluxes and spectral energy distributions (SEDs), in 12 frequency bands from radio to {gamma}-rays, for a final sample of 2214 blazars. Using a model-independent statistical approach, we looked for systematic trends in the SEDs; the most significant trends involved the radio luminosities and X-ray spectral indices of the blazars. We used a principal component analysis (PCA) to determine the basis vectors of the blazar SEDs and, in order to maximize the size of the sample, imputed missing fluxes using the K-nearest neighbors method. Using more than an order of magnitude more data than was available when Fossati et al. first reported trends of SED shape with blazar luminosity, we confirmed the anti-correlation between radio luminosity and synchrotron peak frequency, although with greater scatter than was seen in the smaller sample. The same trend can be seen between bolometric luminosity and synchrotron peak frequency. Finally, we used all of the available blazar data to determine an empirical SED description that depends only on the radio luminosity at 1.4GHz and the redshift. We verified that this statistically significant relation was not a result of the luminosity-luminosity correlations that are natural in flux-limited samples (i.e., where the correlation is actually caused by the redshift rather than the luminosity).
- ID:
- ivo://CDS.VizieR/J/ApJ/756/44
- Title:
- Spectral lags and counts of the RHESSI GRBs
- Short Name:
- J/ApJ/756/44
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A sample of 427 gamma-ray bursts (GRBs) from a database (2002 February-2008 April) of the RHESSI satellite is analyzed statistically. The spectral lags and peak-count rates, which have been calculated for the first time in this paper, are studied, completing an earlier analysis of durations and hardness ratios. The analysis of the RHESSI database has already inferred the existence of a third group with intermediate duration, apart from the so-called short and long groups. The first aim of this article is to discuss the properties of these intermediate-duration bursts in terms of peak-count rates and spectral lags. The second aim is to discuss the number of GRB groups using another statistical method and by also employing the peak-count rates and spectral lags. The standard parametric (model-based clustering) and non-parametric (K-means clustering) statistical tests together with the Kolmogorov-Smirnov and Anderson-Darling tests are used. Two new results are obtained. (1) The intermediate-duration group has properties similar to those of the group of short bursts. Intermediate and long groups appear to be different. (2) The intermediate-duration GRBs in the RHESSI and Swift databases seem to be represented by different phenomena.
- ID:
- ivo://CDS.VizieR/J/A+A/573/A81
- Title:
- Spectral properties of energetic GRBs
- Short Name:
- J/A+A/573/A81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the time-resolved spectral properties of energetic gamma-ray bursts (GRBs) with good high-energy photon statistics observed by the Gamma-Ray Burst Monitor (GBM) onboard the Fermi Gamma-Ray Space Telescope. We aim to constrain in detail the spectral properties of GRB prompt emission on a time-resolved basis and to discuss the theoretical implications of the fitting results in the context of various prompt emission models. Our sample comprises eight GRBs observed by the Fermi GBM in its first five years of mission, with 1keV-1MeV fluence f>1.0x10^-4^erg/cm2 and a signal-to-noise ratio level of S/N>=10.0 above 900keV. We performed a time-resolved spectral analysis using a variable temporal binning technique according to optimal S/N criteria, resulting in a total of 299 time-resolved spectra. We performed Band function fits to all spectra and obtained the distributions for the low-energy power-law index {alpha}, the high-energy power-law index {beta}, the peak energy in the observed {nu}F_{nu}_ spectrum E_p_, and the difference between the low- and high-energy power-law indices {Delta}s={alpha}-{beta}. We also applied a physically motivated synchrotron model, which is a triple power-law with constrained power-law indices and a blackbody component, to test the prompt emission for consistency with a synchrotron origin and obtain the distributions for the two break energies E_b,1_ and E_b,2_, the middle segment power-law index {beta}, and the Planck function temperature kT.
- ID:
- ivo://CDS.VizieR/J/A+A/530/A21
- Title:
- Spectral properties of 438 GRBs
- Short Name:
- J/A+A/530/A21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of the spectral analysis of the public data of 438 gamma ray bursts (GRBs) detected by the Fermi Gamma ray Burst Monitor (GBM) up to March 2010. For 432 bursts we could fit the time-integrated spectrum. In 318 cases we could reliably constrain the peak energy E^obs^_peak_ of their {nu}F{nu} spectrum by analyzing their time-integrated spectrum between 8keV and 35MeV. Eighty percent of these spectra are fitted by a power-law with an exponential cutoff, and the remaining with the Band function. Among these 318 GRBs, 274 belong to the long GRB class and 44 to the short.
- ID:
- ivo://CDS.VizieR/J/ApJ/832/108
- Title:
- Spectral properties of Type Ic & Ic-bl SNe
- Short Name:
- J/ApJ/832/108
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first systematic investigation of spectral properties of 17 Type Ic Supernovae (SNe Ic), 10 broad-lined SNe Ic (SNe Ic-bl) without observed gamma-ray bursts (GRBs), and 11 SNe Ic-bl with GRBs (SN-GRBs) as a function of time in order to probe their explosion conditions and progenitors. Using a number of novel methods, we analyze a total of 407 spectra, which were drawn from published spectra of individual SNe as well as from the densely time-sampled spectra of Modjaz+ (2014, J/AJ/147/99). In order to quantify the diversity of the SN spectra as a function of SN subtype, we construct average spectra of SNe Ic, SNe Ic-bl without GRBs, and SNe Ic-bl with GRBs. We find that SN 1994I is not a typical SN Ic, contrasting the general view, while the spectra of SN 1998bw/GRB 980425 are representative of mean spectra of SNe Ic-bl. We measure the ejecta absorption and width velocities using a new method described here and find that SNe Ic-bl with GRBs, on average, have quantifiably higher absorption velocities, as well as broader line widths than SNe without observed GRBs. In addition, we search for correlations between SN-GRB spectral properties and the energies of their accompanying GRBs. Finally, we show that the absence of clear He lines in optical spectra of SNe Ic-bl, and in particular of SN-GRBs, is not due to them being too smeared-out due to the high velocities present in the ejecta. This implies that the progenitor stars of SN-GRBs are probably free of the He-layer, in addition to being H-free, which puts strong constraints on the stellar evolutionary paths needed to produce such SN-GRB progenitors at the observed low metallicities.
- ID:
- ivo://CDS.VizieR/J/ApJ/764/135
- Title:
- Spectroscopic redshifts of BL Lac objects
- Short Name:
- J/ApJ/764/135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on spectroscopic observations covering most of the 475 BL Lacs in the second Fermi Large Area Telescope (LAT) catalog of active galactic nuclei (AGNs). Including archival measurements (correcting several erroneous literature values) we now have spectroscopic redshifts for 44% of the BL Lacs. We establish firm lower redshift limits via intervening absorption systems and statistical lower limits via searches for host galaxies for an additional 51% of the sample leaving only 5% of the BL Lacs unconstrained. The new redshifts raise the median spectroscopic {overline}{Z} from 0.23 to 0.33 and include redshifts as large as z=2.471. Spectroscopic redshift minima from intervening absorbers have {overline}{Z}, showing a substantial fraction at large z and arguing against strong negative evolution. We find that detected BL Lac hosts are bright ellipticals with black hole masses M_{bullet}_~10^8.5^-10^9^, substantially larger than the mean of optical AGNs and LAT Flat Spectrum Radio Quasar samples. A slow increase in M_{bullet}_ with z may be due to selection bias. We find that the power-law dominance of the optical spectrum extends to extreme values, but this does not strongly correlate with the {gamma}-ray properties, suggesting that strong beaming is the primary cause of the range in continuum dominance.
- ID:
- ivo://CDS.VizieR/J/A+A/484/783
- Title:
- Spectroscopy of 7 INTEGRAL X-ray sources
- Short Name:
- J/A+A/484/783
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The INTEGRAL hard X-ray observatory has revealed an emerging population of highly obscured X-ray binary systems through multi-wavelength observations. Previous studies have shown that many of these sources are high-mass X-ray binaries hosting neutron stars orbiting around luminous and evolved companion stars. To better understand this newly-discovered population, we have selected a sample of sources for which an accurate localisation is available to identify the stellar counterpart and reveal the nature of the companion star and of the binary system.
- ID:
- ivo://CDS.VizieR/J/PAZh/36/744
- Title:
- SPI-ACS/INTEGRAL short gamma-ray bursts
- Short Name:
- J/PAZh/36/744
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The short duration (T90<2s) gamma-ray bursts (GRBs) detected in the SPI-ACS experiment onboard the INTEGRAL observatory are investigated. Averaged light curves have been constructed for various groups of events, including short GRBs and unidentified short events. Extended emission has been found in the averaged light curves of both short GRBs and unidentified short events. It is shown that the fraction of the short GRBs in the total number of SPI-ACS GRBs can range from 30 to 45%, which is considerably larger than has been thought previously.
