- ID:
- ivo://CDS.VizieR/J/A+A/623/A175
- Title:
- 2015 BL Lac VHE gamma-ray flare
- Short Name:
- J/A+A/623/A175
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The mechanisms producing fast variability of the {gamma}-ray emission in active galactic nuclei (AGNs) are under debate. The MAGIC telescopes detected a fast, very-high-energy (VHE, E>100GeV) {gamma}-ray flare from BL Lacertae on 2015 June 15. The flare had a maximum flux of (1.5+/-0.3)x10^-10^photons/cm^2^/s and halving time of 26+/-8min. The MAGIC observations were triggered by a high state in the optical and high-energy (HE, E>100MeV) {gamma}-ray bands. In this paper we present the MAGIC VHE {gamma}-ray data together with multi-wavelength data from radio, optical, X-rays, and HE {gamma} rays from 2015 May 1 to July 31. Well-sampled multi-wavelength data allow us to study the variability in detail and compare it to the other epochs when fast, VHE {gamma}-ray flares have been detected from this source. Interestingly, we find that the behaviour in radio, optical, X-rays, and HE {gamma}-rays is very similar to two other observed VHE {gamma}-ray flares. In particular, also during this flare there was an indication of rotation of the optical polarization angle and of activity at the 43GHz core. These repeating patterns indicate a connection between the three events. We also test modelling of the spectral energy distribution based on constraints from the light curves and VLBA observations, with two different geometrical setups of two-zone inverse Compton models. In addition we model the {gamma}-ray data with the star-jet interaction model. We find that all of the tested emission models are compatible with the fast VHE {gamma}-ray flare, but all have some tension with the multi-wavelength observations.
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Search Results
- ID:
- ivo://CDS.VizieR/J/AZh/84/1110
- Title:
- Brightness of SN 2006X
- Short Name:
- J/AZh/84/1110
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of observations over 2005-2006 years at the robotic telescope MASTER are presented. There are the first in the world observation of optical emission of GRB 050824 and GRB 060926 gamma-ray bursts. Our data combined with more later one gives the low of brightness drop t^-0.55+/-0.05^ for GRB 050824. We discovered optical flare for GRB 060926 around 500-700s. The power low spectral index (F_E_~E^-beta^) is equal beta=1.0+/-0.2. In the course of sky survey we have images of more than 90% possible sky. The virtual data-base and pipe-line was made. The limit to the orphan optical bursts rate is presented. We discovered 3 supernovae stars, they are the following: SN 2005bv (Ia-type) is the first one, opened from Russian territory, SN 2005ee is one of the most powerful among II-type supernovae, SN 2006ak (Ia-type). New method of the OT search after IPN-triangulation gamma-observation is proposed and tested.
- ID:
- ivo://CDS.VizieR/J/A+A/609/A112
- Title:
- Bulk Lorentz factors of gamma-ray bursts
- Short Name:
- J/A+A/609/A112
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Knowledge of the bulk Lorentz factor {Gamma}_0_ of gamma-ray bursts (GRBs) allows us to compute their comoving frame properties shedding light on their physics. Upon collisions with the circumburst matter, the fireball of a GRB starts to decelerate, producing a peak or a break (depending on the circumburst density profile) in the light curve of the afterglow. Considering all bursts with known redshift and with an early coverage of their emission, we find 67 GRBs (including one short event) with a peak in their optical or GeV light curves at a time t_p_. For another 106 GRBs we set an upper limit t_p_^UL^. The measure of t_p_ provides the bulk Lorentz factor {Gamma}_0_ of the fireball before deceleration. We show that t_p_ is due to the dynamics of the fireball deceleration and not to the passage of a characteristic frequency of the synchrotron spectrum across the optical band. Considering the t_p_ of 66 long GRBs and the 85 most constraining upper limits, we estimate {Gamma}_0_ or a lower limit {Gamma}_0_^LL^. Using censored data analysis methods, we reconstruct the most likely distribution of t_p_. All t_p_ are larger than the time T_p,{gamma}_ when the prompt {gamma}-ray emission peaks, and are much larger than the time T_ph_ when the fireball becomes transparent, that is, t_p_>T_p,{gamma}_>T_ph_. The reconstructed distribution of {Gamma}_0_ has median value ~300 (150) for a uniform (wind) circumburst density profile. In the comoving frame, long GRBs have typical isotropic energy, luminosity, and peak energy <E_iso_>=3(8)x10^50^erg, <L_iso_>=3(15)x10^47^erg/s, and <E_peak_>=1(2)keV in the homogeneous (wind) case. We confirm that the significant correlations between {Gamma}_0_ and the rest frame isotropic energy (E_iso_), luminosity (L_iso_), and peak energy (E_p_) are not due to selection effects. When combined, they lead to the observed E_p_-E_iso_ and E_p_-L_iso_ correlations. Finally, assuming a typical opening angle of 5 degrees, we derive the distribution of the jet baryon loading which is centered around a few 10^-6^M_{\sun}_.
- ID:
- ivo://CDS.VizieR/J/ApJ/787/66
- Title:
- Burst duration measurements for a GRB sample
- Short Name:
- J/ApJ/787/66
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Several gamma-ray bursts (GRBs) last much longer (~hours) in {gamma}-rays than typical long GRBs (~minutes), and it has recently been proposed that these "ultra-long GRBs" may form a distinct population, probably with a different (e.g., blue supergiant) progenitor than typical GRBs. However, Swift observations suggest that many GRBs have extended central engine activities manifested as flares and internal plateaus in X-rays. We perform a comprehensive study on a large sample of Swift GRBs with X-Ray Telescope observations to investigate GRB central engine activity duration and to determine whether ultra-long GRBs are unusual events. We define burst duration t_burst_ based on both {gamma}-ray and X-ray light curves rather than using {gamma}-ray observations alone. We find that t_burst_can be reliably measured in 343 GRBs. Within this "good" sample, 21.9% GRBs have t_burst_>~10^3^ s and 11.5% GRBs have t_burst_>~10^4^ s. There is an apparent bimodal distribution of t_burst_ in this sample. However, when we consider an "undetermined" sample (304 GRBs) with t_burst_ possibly falling in the gap between GRB duration T_90_ and the first X-ray observational time, as well as a selection effect against t_burst_ falling into the first Swift orbital "dead zone" due to observation constraints, the intrinsic underlying t_burst_ distribution is consistent with being a single component distribution. We found that the existing evidence for a separate ultra-long GRB population is inconclusive, and further multi-wavelength observations are needed to draw a firmer conclusion. We also discuss the theoretical implications of our results. In particular, the central engine activity duration of GRBs is generally much longer than the {gamma}-ray T_90_ duration and it does not even correlate with T_90_. It would be premature to make a direct connection between T_90_ and the size of the progenitor star.
- ID:
- ivo://CDS.VizieR/J/ApJ/691/723
- Title:
- BVIJHKs observations of GRB 080319B
- Short Name:
- J/ApJ/691/723
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The first gamma-ray burst (GRB) confirmed to be bright enough to be seen with the naked eye, GRB 080319B at redshift z=0.937, allowed for exquisite follow-up observations across the electromagnetic spectrum. We present our detailed optical and infrared (IR) observations of the afterglow, consisting of over 5000 images starting 51s after the GRB trigger, in concert with our own analysis of the Swift UVOT, Burst Alert Telescope (BAT), and XRT data. The event is extreme not only in observed properties but also intrinsically: it was the most luminous event ever recorded at optical and IR wavelengths and had an exceedingly high isotropic-equivalent energy release in {gamma}-rays. At early times, the afterglow evolution is broadly consistent with being reverse-shock dominated, but then is subsumed by a forward shock at around 1000s. The overall spectral energy distribution, spanning from ultraviolet through near-IR wavelengths, shows no evidence for a significant amount of dust extinction in the host frame. The afterglow evolution, however, is highly chromatic: starting at about 1000s the index shifts blueward before shifting back to the red at late times. In our deepest late-time observations, we find tentative evidence for an optical jet break and a luminous supernova. Finally, we examine the detectability of such events with current and future facilities and find that such an event could be detected in gamma rays by BAT out to z=10.7 (8{sigma}), while the nominal EXIST sensitivity would allow detection to z~32. At the K band, this source would have been easily detected with meter-class telescopes to z~17.
- ID:
- ivo://CDS.VizieR/J/PAZh/40/271
- Title:
- Catalog of short gamma-ray transients
- Short Name:
- J/PAZh/40/271
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyzed the data obtained by the SPI telescope onboard the INTEGRAL observatory to search for short transient events with a duration from 1 ms to a few tens of seconds. An algorithm for identifying gamma-ray events against the background of a large number of charged particle interactions with the detector has been developed. The classification of events was made. Apart from the events associated with cosmic gamma-ray bursts (GRBs) confirmed by other space experiments and the activity of known soft gamma repeaters (for example, SGR 1806-20), previously unreported GRBs have been found. GRB candidates and short gamma-ray events probably associated with the activity of known SGRs and AXPs have been selected. The spectral evolution of 28 bright GRBs from the catalog has been studied extensively. A new method for investigating the spectral evolution is proposed. The energy dependence of the spectral lag for bursts with a simple structure of their light curves and for individual pulses of multipulse events is shown to be described by a logarithmic function, lag~Alog(E). It has been established that the parameter A depends on the pulse duration, with the dependence being universal for all of the investigated GRBs. No negative spectral lags have been detected for bursts with a simple structure of their light curves.
- ID:
- ivo://CDS.VizieR/J/ApJS/175/97
- Title:
- CGRaBS: survey of {gamma}-ray blazar candidates
- Short Name:
- J/ApJS/175/97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We describe a uniform all-sky survey of bright blazars, selected primarily by their flat radio spectra, that is designed to provide a large catalog of likely {gamma}-ray active galactic nuclei (AGNs). The defined sample has 1625 targets with radio and X-ray properties similar to those of the EGRET blazars, spread uniformly across the |^b^|>10{deg} sky. We also report progress toward optical characterization of the sample; of objects with known R<23, 85% have been classified and 81% have measured redshifts. One goal of this program is to focus attention on the most interesting (e.g., high-redshift, high-luminosity, ...) sources for intensive multiwavelength study during the observations by the Large Area Telescope (LAT) on GLAST.
- ID:
- ivo://CDS.VizieR/J/ApJ/816/38
- Title:
- Chandra observations of 8 INTEGRAL sources
- Short Name:
- J/ApJ/816/38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on 0.3-10keV observations with the Chandra X-ray Observatory of eight hard X-ray sources discovered within 8{deg} of the Galactic plane by the International Gamma-ray Astrophysics Laboratory (INTEGRAL) satellite. The short (~5ks) Chandra observations of the IGR source fields have yielded very likely identifications of X-ray counterparts for three of the IGR sources: IGRJ14091-6108, IGRJ18088-2741, and IGRJ18381-0924. The first two have very hard spectra in the Chandra band that can be described by a power law with photon indices of {Gamma}=0.6+/-0.4 and -0.7_-0.3_^+0.4^, respectively (90% confidence errors are given), and both have a unique near-IR counterpart consistent with the Chandra position. IGR J14091-6108 also displays a strong iron line and a relatively low X-ray luminosity, and we argue that the most likely source type is a cataclysmic variable (CV), although we do not completely rule out the possibility of a high mass X-ray binary. IGR J18088-2741 has an optical counterpart with a previously measured 6.84hr periodicity, which may be the binary orbital period. We also detect five cycles of a possible 800-950s period in the Chandra light curve, which may be the compact object spin period. We suggest that IGR J18088-2741 is also most likely a CV. For IGR J18381-0924, the spectrum is intrinsically softer with {Gamma}=1.5_-0.4_^+0.5^, and it is moderately absorbed, N_H_=(4+/-1)x10^22^/cm2. There are two near-IR sources consistent with the Chandra position, and they are both classified as galaxies, making it likely that IGR J18381-0924 is an active galactic nucleus. For the other five IGR sources, we provide lists of nearby Chandra sources, which may be used along with further observations to identify the correct counterparts, and we discuss the implications of the low inferred Chandra count rates for these five sources.
- ID:
- ivo://CDS.VizieR/J/ApJ/615/897
- Title:
- Chandra X-Ray sources in the {gamma} Cyg Field
- Short Name:
- J/ApJ/615/897
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In search of the counterpart to the brightest unidentified gamma-ray source, 3EG J2020+4017 (2CG 078+2), we report on new X-ray and radio observations of the {gamma} Cygni field with the Chandra X-Ray Observatory and with the Green Bank Telescope (GBT). We also report on reanalysis of archival ROSAT data.
- ID:
- ivo://CDS.VizieR/J/ApJ/887/134
- Title:
- Classification of Fermi blazar cand. from the 4FGL
- Short Name:
- J/ApJ/887/134
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The recently published fourth Fermi Large Area Telescope source catalog (4FGL) reports 5065 gamma-ray sources in terms of direct observational gamma-ray properties. Among the sources, the largest population is the active galactic nuclei (AGNs), which consists of 3137 blazars, 42 radio galaxies, and 28 other AGNs. The blazar sample comprises 694 flat-spectrum radio quasars (FSRQs), 1131 BL Lac-type objects (BL Lacs), and 1312 blazar candidates of an unknown type (BCUs). The classification of blazars is difficult using optical spectroscopy given the limited knowledge with respect to their intrinsic properties, and the limited availability of astronomical observations. To overcome these challenges, machine-learning algorithms are being investigated as alternative approaches. Using the 4FGL catalog, a sample of 3137 Fermi blazars with 23 parameters is systematically selected. Three established supervised machine-learning algorithms (random forests (RFs), support vector machines (SVMs), artificial neural networks (ANNs)) are employed to general predictive models to classify the BCUs. We analyze the results for all of the different combinations of parameters. Interestingly, a previously reported trend the use of more parameters leading to higher accuracy is not found. Considering the least number of parameters used, combinations of eight, 12 or 10 parameters in the SVM, ANN, or RF generated models achieve the highest accuracy (Accuracy ~91.8%, or ~92.9%). Using the combined classification results from the optimal combinations of parameters, 724 BL Lac type candidates and 332 FSRQ type candidates are predicted; however, 256 remain without a clear prediction.
