- ID:
- ivo://CDS.VizieR/J/ApJS/247/16
- Title:
- Extreme high-frequency-peaked BL Lac objects
- Short Name:
- J/ApJS/247/16
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Extreme high-frequency-peaked BL Lac objects (EHBLs) are blazars that exhibit extremely energetic synchrotron emission. They also feature nonthermal gamma-ray emission whose peak lies in the very high-energy (VHE, E>100GeV) range, and in some sources exceeds 1TeV: this is the case for hard-TeV EHBLs such as 1ES 0229+200. With the aim of increasing the EHBL population, 10 targets were observed with the MAGIC telescopes from 2010 to 2017, for a total of 265hr of good-quality data. The data were complemented by coordinated Swift observations. The X-ray data analysis confirms that all but two sources are EHBLs. The sources show only a modest variability and a harder-when-brighter behavior, typical for this class of objects. At VHE gamma-rays, three new sources were detected and a hint of a signal was found for another new source. In each case, the intrinsic spectrum is compatible with the hypothesis of a hard-TeV nature of these EHBLs. The broadband spectral energy distributions (SEDs) of all sources are built and modeled in the framework of a single-zone, purely leptonic model. The VHE gamma-ray-detected sources were also interpreted with a spine-layer model and a proton synchrotron model. The three models provide a good description of the SEDs. However, the resulting parameters differ substantially in the three scenarios, in particular the magnetization parameter. This work presents the first mini catalog of VHE gamma-ray and multiwavelength observations of EHBLs.
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- ID:
- ivo://CDS.VizieR/J/A+A/557/A100
- Title:
- Fermi and Swift GRBs E_peak_-E_iso_ relation
- Short Name:
- J/A+A/557/A100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We used a sample of gamma-ray bursts (GRBs) detected by Fermi and Swift to reanalyze the correlation discovered by Amati et al. (2002A&A...390...81A) between E_pi_, the peak energy of the prompt GRB emission, and E_iso_, the energy released by the GRB assuming isotropic emission. This correlation has been disputed by various authors, and our aim is to assess whether it is an intrinsic GRB property or the consequence of selection effects. We constructed a sample of Fermi GRBs with homogeneous selection criteria, and we studied their distribution in the E_pi_-E_iso_ plane. Our sample is made of 43 GRBs with a redshift and 243 GRBs without a redshift. We show that GRBs with a redshift follow a broad E_pi_-E_iso_ relation, while GRBs without a redshift show several outliers. We use these samples to discuss the impact of selection effects associated with GRB detection and with redshift measurement.
- ID:
- ivo://CDS.VizieR/J/ApJ/835/L38
- Title:
- Fermi blazars with Doppler factors
- Short Name:
- J/ApJ/835/L38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Blazars are an extreme subclass of active galactic nuclei. Their rapid variability, luminous brightness, superluminal motion, and high and variable polarization are probably due to a beaming effect. However, this beaming factor (or Doppler factor) is very difficult to measure. Currently, a good way to estimate it is to use the timescale of their radio flares. In this Letter, we use multiwavelength data and Doppler factors reported in the literature for a sample of 86 flaring blazars detected by Fermi to compute their intrinsic multiwavelength data and intrinsic spectral energy distributions and investigate the correlations among observed and intrinsic data. Quite interestingly, intrinsic data show a positive correlation between luminosity and peak frequency, in contrast with the behavior of observed data, and a tighter correlation between {gamma}-ray luminosity and the lower-energy ones. For flaring blazars detected by Fermi, we conclude that (1) observed emissions are strongly beamed; (2) the anti-correlation between luminosity and peak frequency from the observed data is an apparent result, the correlation between intrinsic data being positive; and (3) intrinsic {gamma}-ray luminosity is strongly correlated with other intrinsic luminosities.
- ID:
- ivo://CDS.VizieR/J/MNRAS/441/1899
- Title:
- Fermi bright blazars
- Short Name:
- J/MNRAS/441/1899
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The exact location of the {gamma}-ray emitting region in blazars is still controversial. In order to attack this problem we present first results of a cross-correlation analysis between radio (11cm to 0.8mm wavelength, F-GAMMA programme) and {gamma}-ray (0.1-300GeV) ~3.5yr light curves of 54 Fermi-bright blazars. We perform a source stacking analysis and estimate significances and chance correlations using mixed source correlations.
- ID:
- ivo://CDS.VizieR/J/A+A/562/A64
- Title:
- Fermi detection of BL Lac objects
- Short Name:
- J/A+A/562/A64
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- By cross-correlating an archival sample of 170 BL Lacs with a 2 year Fermi/LAT AGN sample, we have compiled a sample of 100 BL Lacs with Fermi detection (FBLs) and a sample of 70 non-Fermi BL Lacs (NFBLs). We compared various parameters of FBLs with those of NFBLs, including the redshift, the low-frequency radio luminosity at 408MHz (L_408MHz_), the absolute magnitude of host galaxies (M_host_), the polarization fraction from the NVSS survey (P_NVSS_), the observed arcsecond scale radio core flux at 5GHz (F_core_), and the jet Doppler factor. All these parameters are directly measured or derived from available data in the literature. We found that the Doppler factor is on average greater in FBLs than in NFBLs, and the Fermi {gamma}-ray detection rate is higher in sources with higher Doppler factor. In contrast, there are no significant differences in terms of the intrinsic parameters of redshift, L_408MHz_, M_host_, and P_NVSS_. FBLs seem to have a higher probability of exhibiting measurable proper motion.
- ID:
- ivo://CDS.VizieR/J/ApJ/811/93
- Title:
- Fermi/GBM GRB minimum timescales
- Short Name:
- J/ApJ/811/93
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We constrain the minimum variability timescales for 938 gamma-ray bursts (GRBs) observed by the Fermi/Gamma-ray Burst Monitor instrument prior to 2012 July 11. The tightest constraints on progenitor radii derived from these timescales are obtained from light curves in the hardest energy channel. In the softer bands --or from measurements of the same GRBs in the hard X-rays from Swift-- we show that variability timescales tend to be a factor of two to three longer. Applying a survival analysis to account for detections and upper limits, we find median minimum timescale in the rest frame for long-duration and short-duration GRBs of 45 and 10ms, respectively. Less than 10% of GRBs show evidence for variability on timescales below 2ms. These shortest timescales require Lorentz factors >~400 and imply typical emission radii R~1x10^14^cm for long-duration GRBs and R~3x10^13^cm for short-duration GRBs. We discuss implications for the GRB fireball model and investigate whether or not GRB minimum timescales evolve with cosmic time.
- ID:
- ivo://CDS.VizieR/J/ApJS/254/35
- Title:
- Fermi GBM GRBs with multiple pulses
- Short Name:
- J/ApJS/254/35
- Date:
- 19 Jan 2022 13:11:51
- Publisher:
- CDS
- Description:
- Gamma-ray bursts (GRBs) are highly variable and exhibit strong spectral evolution. In particular, the emission properties vary from pulse to pulse in multipulse bursts. Here we present a time-resolved Bayesian spectral analysis of a compilation of GRB pulses observed by the Fermi/Gamma-ray Burst Monitor. The pulses are selected to have at least four time bins with a high statistical significance, which ensures that the spectral fits are well determined and spectral correlations can be established. The sample consists of 39 bursts, 117 pulses, and 1228 spectra. We confirm the general trend that pulses become softer over time, with mainly the low-energy power-law index {alpha} becoming smaller. A few exceptions to this trend exist, with the hardest pulse occurring at late times. The first pulse in a burst is clearly different from the later pulses; three-fourths of them violate the synchrotron line of death, while around half of them significantly prefer photospheric emission. These fractions decrease for subsequent pulses. We also find that in two-thirds of the pulses, the spectral parameters ({alpha} and peak energy) track the light-curve variations. This is a larger fraction compared to what is found in previous samples. In conclusion, emission compatible with the GRB photosphere is typically found close to the trigger time, while the chance of detecting synchrotron emission is greatest at late times. This allows for the coexistence of emission mechanisms at late times.
- ID:
- ivo://CDS.VizieR/J/ApJ/756/112
- Title:
- Fermi/GBM GRB time-resolved spectral analysis
- Short Name:
- J/ApJ/756/112
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a time-resolved spectral analysis of 51 long and 11 short bright gamma-ray bursts (GRBs) observed with the Fermi/Gamma-Ray Burst Monitor, paying special attention to E_p_ evolution within each burst. Among eight single-pulse long GRBs, five show an evolution from hard to soft, while three show intensity tracking. The multi-pulse long GRBs have more complicated patterns. Statistically, the hard-to-soft evolution pulses tend to be more asymmetric than the intensity-tracking ones, with a steeper rising wing than the falling wing. Short GRBs have E_p_ tracking intensity exclusively with the 16ms time-resolution analysis. We performed a simulation analysis and suggest that for at least some bursts, the late intensity-tracking pulses could be a consequence of overlapping hard-to-soft pulses. However, the fact that the intensity-tracking pattern exists in the first pulse of the multi-pulse long GRBs and some single-pulse GRBs, suggests that intensity tracking is an independent component, which may operate in some late pulses as well. For the GRBs with measured redshifts, we present a time-resolved E_p_-L_{gamma},iso_ correlation analysis and show that the scatter of the correlation is comparable to that of the global Amati/Yonetoku relation. We discuss the predictions of various radiation models regarding E_p_ evolution, as well as the possibility of a precessing jet in GRBs. The data pose a great challenge to each of these models, and hold the key to unveiling the physics behind GRB prompt emission.
- ID:
- ivo://CDS.VizieR/J/ApJ/806/52
- Title:
- 8 Fermi GRB afterglows follow-up
- Short Name:
- J/ApJ/806/52
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Fermi Gamma-ray Space Telescope has greatly expanded the number and energy window of observations of gamma-ray bursts (GRBs). However, the coarse localizations of tens to a hundred square degrees provided by the Fermi GRB Monitor instrument have posed a formidable obstacle to locating the bursts' host galaxies, measuring their redshifts, and tracking their panchromatic afterglows. We have built a target-of-opportunity (TOO) mode for the intermediate Palomar Transient Factory (iPTF) in order to perform targeted searches for Fermi afterglows. Here, we present the results of one year of this program: 8 afterglow discoveries out of 35 searches. Two of the bursts with detected afterglows (GRBs 130702A and 140606B) were at low redshift (z=0.145 and 0.384, respectively) and had spectroscopically confirmed broad-line Type Ic supernovae. We present our broadband follow-up including spectroscopy as well as X-ray, UV, optical, millimeter, and radio observations. We study possible selection effects in the context of the total Fermi and Swift GRB samples. We identify one new outlier on the Amati relation. We find that two bursts are consistent with a mildly relativistic shock breaking out from the progenitor star rather than the ultra-relativistic internal shock mechanism that powers standard cosmological bursts. Finally, in the context of the Zwicky Transient Facility, we discuss how we will continue to expand this effort to find optical counterparts of binary neutron star mergers that may soon be detected by Advanced LIGO and Virgo.
- ID:
- ivo://CDS.VizieR/J/ApJ/763/15
- Title:
- Fermi GRB analysis. III. T_90_ distributions
- Short Name:
- J/ApJ/763/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The durations (T_90_) of 315 gamma-ray bursts (GRBs) detected with Fermi/GBM (8-1000keV) up to 2011 September are calculated using the Bayesian Block method. We compare the T_90_ distributions between this sample and those derived from previous/current GRB missions. We show that the T_90_ distribution of this GRB sample is bimodal, with a statistical significance level comparable to those derived from the BeppoSAX/GRBM sample and the Swift/BAT sample, but lower than that derived from the CGRO/BATSE sample. The short-to-long GRB number ratio is also much lower than that derived from the BATSE sample, i.e., 1:6.5 versus 1:3. We measure T_90_ in several bands, i.e., 8-15, 15-25, 25-50, 50-100, 100-350, and 350-1000keV, to investigate the energy-dependence effect of the bimodal T_90_distribution. It is found that the bimodal feature is well observed in the 50-100 and 100-350keV bands, but is only marginally acceptable in the 25-50keV and 350-1000keV bands. The hypothesis of bimodality is confidently rejected in the 8-15 and 15-25keV bands. The T_90_distributions in these bands are roughly consistent with those observed by missions with similar energy bands. The parameter T_90_ as a function of energy follows {overline}{T}_90_{propto}E^-0.20+/-0.02^ for long GRBs. Considering the erratic X-ray and optical flares, the duration of a burst would be even longer for most GRBs. Our results, together with the observed extended emission of some short GRBs, indicate that the central engine activity timescale would be much longer than T_90_ for both long and short GRBs and the observed bimodal T_90_ distribution may be due to an instrumental selection effect.
