- ID:
- ivo://CDS.VizieR/J/ApJS/135/155
- Title:
- Radio identification of 3EG EGRET sources
- Short Name:
- J/ApJS/135/155
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The method of Mattox et al. (1996ApJ...461..396M) for identifying EGRET sources with 5GHz radio sources has been applied to the 3EG EGRET catalog of Hartman et al. (1999, Cat. <J/ApJS/123/79>). Complete results are tabulated. We tabulate separately 46 EGRET sources with radio identifications which we expect to have a high probability of being correct. We suggest that these sources are appropriate for most studies of the properties of {gamma}-ray blazars as a class. All but one of these 46 sources were classified by Hartman et al. (1999, Cat. <J/ApJS/123/79>) as high-confidence identifications; and the additional source was classified by Hartman et al. (1999, Cat. <J/ApJS/123/79>) as a plausible identification. We also tabulate separately 37 additional "plausible identifications of EGRET sources with radio sources." These less secure possibilities include the remaining 21 "high-confidence identifications" of Hartman et al. (1999, Cat. <J/ApJS/123/79>), three of the 27 "lower confidence potential blazar identifications" of Hartman et al. (1999, Cat. <J/ApJS/123/79>), and an additional 15 plausible identifications which have not been suggested previously. Many of these sources require new radio and optical observations to establish them as blazars. We suggest that the 23 "lower-confidence potential blazar identifications" of Hartman et al. (1999, Cat. <J/ApJS/123/79>) which we do not find plausible should not be used in studies of the properties of the EGRET blazars. For this analysis, we have made elliptical fits to the 95% confidence contours of the position uncertainty regions of the 3EG sources.
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- ID:
- ivo://CDS.VizieR/J/ApJ/481/95
- Title:
- Radio identification of EGRET sources
- Short Name:
- J/ApJ/481/95
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a method to assess the reliability of the identification of EGRET sources with extragalactic radio sources. We verify that EGRET is detecting the blazar class of active galactic nuclei (AGNs). However many published identifications are found to be questionable. We provide a table of 42 blazars that we expect to be robust identifications of EGRET sources. This includes one previously unidentified EGRET source, the lensed AGN PKS 1830-210, near the direction of the Galactic center. We provide the best available positions for 16 more radio sources that are also potential identifications for previously unidentified EGRET sources. All high Galactic latitude EGRET sources (|b|>3) that demonstrate significant variability can be identified with flat-spectrum radio sources. This suggests that EGRET is not detecting any type of AGN other than blazars. This identification method has been used to establish with 99.998% confidence that the peak gamma-ray flux of a blazar is correlated with its average 5GHz radio flux. An even better correlation is seen between gamma-ray flux and the 2.29GHz flux density measured with VLBI at the base of the radio jet. Also, using high-confidence identifications, we find that the radio sources identified with EGRET sources have greater correlated VLBI flux densities than the parent population of flat radio spectrum sources.
- ID:
- ivo://CDS.VizieR/J/A+A/596/A45
- Title:
- Radio light curves of 8 AGN
- Short Name:
- J/A+A/596/A45
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To fully exploit the scientific potential of the Fermi mission for the physics of active galactic nuclei (AGN), we initiated the F-GAMMA programme. Between 2007 and 2015 the F-GAMMA was the prime provider of complementary multi-frequency monitoring in the radio regime. Aims. We quantify the radio variability of {gamma}-ray blazars. We investigate its dependence on source class and examine whether the radio variability is related to the {gamma}-ray loudness. Finally, we assess the validity of a putative correlation between the two bands. Methods. The F-GAMMA performed monthly monitoring of a sample of about 60 sources at up to twelve radio frequencies between 2.64 and 228.39GHz. We perform a time series analysis on the first 2.5-yr data set to obtain variability parameters. A maximum likelihood analysis is used to assess the significance of a correlation between radio and {gamma}-ray fluxes. We present light curves and spectra (coherent within ten days) obtained with the Effelsberg 100m and IRAM 30m telescopes. All sources are variable across all frequency bands with amplitudes increasing with frequency up to rest frame frequencies of around 60-80GHz as expected by shock-in-jet models. Compared to flat-spectrum radio quasars (FSRQs), BL Lacertae objects (BL Lacs) show systematically lower variability amplitudes, brightness temperatures, and Doppler factors at lower frequencies, while the difference vanishes towards higher ones. The time scales appear similar for the two classes. The distribution of spectral indices appears flatter or more inverted at higher frequencies for BL Lacs. Evolving synchrotron self-absorbed components can naturally account for the observed spectral variability. We find that the Fermi-detected sources show larger variability amplitudes, brightness temperatures, and Doppler factors than non-detected ones. Flux densities at 86.2 and 142.3GHz correlate with 1GeV fluxes at a significance level better than 3{sigma}, implying that {gamma} rays are produced very close to the mm-band emission region.
- ID:
- ivo://CDS.VizieR/J/A+AS/131/11
- Title:
- Radio sources related to gamma-ray emission
- Short Name:
- J/A+AS/131/11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Table 2 lists the individual flux density measurements for 47 radio sources as observed with the Effelsberg 100-m telescope.
- ID:
- ivo://CDS.VizieR/J/ApJ/884/121
- Title:
- Radio to UV observations of GRB 181201A
- Short Name:
- J/ApJ/884/121
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present comprehensive multiwavelength radio to X-ray observations of GRB 181201A spanning from ~150s to ~163days after the burst, comprising the first joint ALMA-VLA-GMRT observations of a gamma-ray burst (GRB) afterglow. The radio and millimeter-band data reveal a distinct signature at ~3.9days, which we interpret as reverse-shock (RS) emission. Our observations present the first time that a single radio- frequency spectral energy distribution can be decomposed directly into RS and forward shock (FS) components. We perform detailed modeling of the full multiwavelength data set, using Markov Chain Monte Carlo sampling to construct the joint posterior density function of the underlying physical parameters describing the RS and FS synchrotron emission. We uncover and account for all discovered degeneracies in the model parameters. The joint RS-FS modeling reveals a weakly magnetized ({sigma}~3x10^-3^), mildly relativistic RS, from which we derive an initial bulk Lorentz factor of {Gamma}_0_~103 for the GRB jet. Our results support the hypothesis that low-density environments are conducive to the observability of RS emission. We compare our observations to other events with strong RS detections and find a likely observational bias selecting for longer lasting, nonrelativistic RSs. We present and begin to address new challenges in modeling posed by the present generation of comprehensive, multifrequency data sets.
- ID:
- ivo://CDS.VizieR/J/ApJ/654/L21
- Title:
- R-band light curves of GRB 060206 and GRB 060210
- Short Name:
- J/ApJ/654/L21
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on two z~4 gamma-ray bursts, GRB 060206 and GRB 060210, for which we have obtained well-sampled optical light curves. Both light curves show unusual behavior. GRB 060206 experienced a slow early decay, followed by a rapid increase in brightness by factor 2.5 about 1hr after the burst. Its afterglow then faded in a broken power-law fashion, with a smooth break at t_b_=0.6 days, but with additional, less dramatic bumps and wiggles. The afterglow of GRB 060210 is also unusual: the light curve was more or less flat between 60 and 300s after the burst, followed by a 70% increase at 600s after the burst, after which the light curve declined as a ~t^-1.3^ power law. We argue that anomalous optical afterglows are likely to be the norm and that such rapid optical variations should be seen in many bursts, given good enough sampling. Given that, some of the usual procedures, such as deriving the jet opening angle from fitting a smooth function to the optical light curve, might often have a poor statistical significance. We propose that the rapid rise at ~3000s in the optical for GRB 060206 and the optical bump at ~700s in GRB 060210 might be due to the turn-on of the external shock. The existence and timing of such features could provide us with valuable additional information about the bursts.
- ID:
- ivo://CDS.VizieR/J/ApJ/642/L99
- Title:
- R-band photometry of GRB 060206
- Short Name:
- J/ApJ/642/L99
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Rapid Telescopes for Optical Response (RAPTOR) system at Los Alamos National Laboratory observed GRB 060206 starting 48.1min after gamma-ray emission triggered the Burst Alert Telescope on board the Swift satellite. The afterglow light curve measured by RAPTOR shows a spectacular rebrightening by ~1mag about 1hr after the trigger and peaks at R~16.4mag. Shortly after the onset of the explosive rebrightening, the optical transient doubled its flux on a timescale of about 4min. The total R-band fluence received from GRB 060206 during this episode is 2.3x10^9^ergs/cm^2^. In the rest frame of the burst (z=4.045), this yields an isotropic equivalent energy release of E_iso_~0.7x10^50^ergs in just a narrow UV band, {lambda}~130{+/-}22nm. We discuss the implications of RAPTOR observations for untriggered searches for fast optical transients and studies of GRB environments at high redshift.
- ID:
- ivo://CDS.VizieR/J/ApJ/731/103
- Title:
- Redshift catalog for Swift long GRBs
- Short Name:
- J/ApJ/731/103
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog of the redshifts for most long-duration gamma-ray bursts (GRBs) by Swift from 2004 December 20 to 2008 July 23 (258 bursts in total). All available information is collected, including spectroscopic redshifts, photometric redshift limits, and redshifts calculated from various luminosity relations. Error bars for the redshifts derived from the luminosity relations are asymmetric, with tails extended to the high-redshift end, and this effect is evaluated by looking at the 30% of Swift bursts with spectroscopic redshifts. A simulation is performed to eliminate this asymmetric effect, and the resultant redshift distribution is deconvolved. We test and confirm this simulation on the sample of bursts with known spectroscopic redshifts and then apply it to the 70% of Swift bursts that do not have spectroscopic measures. A final intrinsic redshift distribution is then made for almost all Swift bursts, and the efficiency of the spectroscopic detections is evaluated. The efficiency of spectroscopic redshifts varies from near unity at low redshift to 0.5 at z=1, to near 0.3 at z=4, and to 0.1 at z=6. We also find that the fraction of GRBs with z>5 is ~10%, and this fraction is compared with simulations from a cosmological model.
- ID:
- ivo://CDS.VizieR/J/ApJ/780/73
- Title:
- Redshifts of BL Lac objects from Fermi
- Short Name:
- J/ApJ/780/73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Fermi has provided the largest sample of {gamma}-ray-selected blazars to date. In this work we use a uniformly selected set of 211 BL Lacertae (BL Lac) objects detected by Fermi during its first year of operation. We obtained redshift constraints for 206 out of the 211 BL Lac objects in our sample, making it the largest and most complete sample of BL Lac objects available in the literature. We use this sample to determine the luminosity function of BL Lac objects and its evolution with cosmic time. We find that for most BL Lac classes the evolution is positive, with a space density peaking at modest redshift (z{approx}1.2). Low-luminosity, high-synchrotron-peaked (HSP) BL Lac objects are an exception, showing strong negative evolution, with number density increasing for z<~0.5. Since this rise corresponds to a drop-off in the density of flat-spectrum radio quasars (FSRQs), a possible interpretation is that these HSPs represent an accretion-starved end state of an earlier merger-driven gas-rich phase. We additionally find that the known BL Lac correlation between luminosity and photon spectral index persists after correction for the substantial observational selection effects with implications for the so-called "blazar sequence." Finally, by estimating the beaming corrections to the luminosity function, we find that BL Lac objects have an average Lorentz factor of {gamma}=6.1_-0.8_^+1.1^, and that most are seen within 10{deg} of the jet axis.
- ID:
- ivo://CDS.VizieR/J/A+A/629/A131
- Title:
- Reduced X-shooter spectra of GRB 190114A
- Short Name:
- J/A+A/629/A131
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the detections of molecular hydrogen (H_2_), vibrationally-excited H_2_ (H_2_*), and neutral atomic carbon (CI), an efficient tracer of molecular gas, in two new afterglow spectra of GRBs 181020A (z=2.938) and 190114A (z=3.376), observed with X-shooter at the Very Large Telescope (VLT). Both host-galaxy absorption systems are characterized by strong damped Lyman-alpha absorbers (DLAs) and substantial amounts of molecular hydrogen with logN(HI,H_2_)=22.20+/-0.05, 20.40+/-0.04 (GRB 181020A) and logN(HI, H_2_)=22.15+/-0.05, 19.44+/-0.04 (GRB 190114A). The DLA metallicites, depletion levels, and dust extinctions are within the typical regimes probed by GRBs with [Zn/H]=-1.57+/-0.06, [Zn/Fe]=0.67+/-0.03, and AV=0.27+/-0.02mag (GRB 181020A) and [Zn/H]=-1.23+/-0.07, [Zn/Fe]=1.06+/-0.08, and AV=0.36+/-0.02mag (GRB 190114A). In addition, we examine the molecular gas content of all known H2-bearing GRB-DLAs and explore the physical conditions and characteristics required to simultaneously probe CI and H_2_*. We confirm that H2 is detected in all CI- and H2*-bearing GRB absorption systems, but that these rarer features are not necessarily detected in all GRB H2 absorbers. We find that a large molecular fraction of f_H2_>~10^-3^ is required for CI to be detected. The defining characteristic for H_2_* to be present is less clear, though a large H_2_ column density is an essential factor. We also find that the observed line profiles of the molecular-gas tracers are kinematically "cold", with small velocity offsets of {delta}v<20km/s from the bulk of the neutral absorbing gas. We then derive the H_2_ excitation temperatures of the molecular gas and find that they are relatively low with Tex~=100-300K, however, there could be evidence of warmer components populating the high-J H_2_ levels in GRBs 181020A and 190114A. Finally, we demonstrate that even though the X-shooter GRB afterglow campaign has been successful in recovering several H2-bearing GRB-host absorbers, this sample is still hampered by a significant dust bias excluding the most dust-obscured H_2_ absorbers from identification. CI and H_2_* could open a potential route to identify molecular gas even in low-metallicity or highly dust-obscured bursts, though they are only efficient tracers for the most H2-rich GRB-host absorption systems.
