scholarly journals Exploring the bulk of the BL Lacertae object population

2018 ◽  
Vol 618 ◽  
pp. A175
Author(s):  
F. D’Ammando ◽  
M. Giroletti ◽  
S. Rainó
Keyword(s):  
Radio Emission ◽  
Test Statistic ◽  
Large Area ◽  
Bl Lacertae ◽  
The Third ◽  
Long Baseline ◽  
Photon Index ◽  
Multi Wavelength ◽  
Doppler Factor ◽  
Bl Lacs

Aims. We are studying an unbiased sample of 42 nearby (z < 0.2) BL Lacertae objects with a multi-wavelength approach. The results of Very Long Baseline Interferometry observations were presented in the first paper of this series. In this paper, we study the γ-ray properties of the sample. Methods. We analyse data collected by the Fermi-Large Area Telescope (LAT) during its first 8.5 yr of operation in the energy range 0.1−300 GeV. Results. We reveal 23 sources with a test statistic greater than 25 (corresponding to ~4.6-σ) out of 42, with 3 sources not detected in the third LAT active galactic nucleus (AGN) catalogue, and fluxes between 3.5 × 10−10 and 7.4 × 10−8 ph cm−2 s−1. The majority of the sources have hard spectra (Γ ≤ 2), with only four having values in the range 2.1–2.4. The three newly detected sources have fluxes in the range between 0.54 × 10−9 and 1.35 × 10−9 ph cm−2 s−1 and photon index 1.7–1.9. Among the 23 LAT-detected sources, 19 are included in the third catalogue of hard Fermi-LAT sources, with a spectrum that connects relatively smoothly from 0.1 GeV to 2 TeV. LAT-detected BL Lacs are more luminous on parsec scales with respect to non-LAT-detected sources and have larger core dominance according to the unified models. Conclusions. The LAT-detected BL Lacs seem to be composed of a bulk of “classical” sources dominated by Doppler boosting and characterised by compact and bright radio emission as well as hard γ-ray spectra. Moreover, we have identified a possible population of low-luminosity BL Lacs not detected by LAT, lacking a VLBI core, and with a small Doppler factor. Furthermore, three LAT-detected sources show non-classical properties for γ-ray emitting BL Lacs (no evidence of relativistic jet, low Doppler factor in radio images, relatively low core dominance) and three other sources, while showing radio emission on parsec scales, are not detected in γ rays so far.

scholarly journals Outflow Angles and Bulk Lorentz Factors for Different Categories of AGN

1997 ◽  
Vol 163 ◽  
pp. 695-696 ◽  
Author(s):  
Erick. J. Guerra ◽  
Ruth A. Daly
Keyword(s):  
Lorentz Factor ◽  
Radio Galaxies ◽  
Line Of Sight ◽  
Radio Sources ◽  
Bl Lacertae Objects ◽  
Bl Lacertae ◽  
High Polarization ◽  
Inverse Compton ◽  
Doppler Factor ◽  
Bl Lacs

AbstractRelativistic outflows from AGN can be parameterized by θ, the angle subtended by the direction of the outflow and the line of sight to the observer, and γ, the bulk Lorentz factor of the outflow. The Doppler factor, δ, and the apparent speed in the plane of the sky, βapp, are combinations of θ and γ. The Doppler factor can be estimated using either the equipartition Doppler factor, δeq (Readhead 1994), or the inverse Compton Doppler factor, δIC. These Doppler factor estimates are combined with observed βapp to solve for θ and γ for different categories of AGN.Ghisellini et al. (1993) compute δIC for 105 compact radio sources, and Güijosa & Daly (1996) compute δeq for the same sample. Daly, Guerra, & Güijosa (1996) estimate θ and γ for the 43 sources that have βapp listed by Vermeulen & Cohen (1994) and δeq computed by Güijosa & Daly (1996).Solutions and errors for θ and γ are presented in Figures 1 and 2 using δeq and δIC respectively. Guerra & Daly (1996) discuss these estimates and errors in greater detail. These AGN fall into the following categories: BL Lacertae objects (BL Lacs), core-dominated high-polarization quasars (CDHPQ), core-dominated low-polarization quasars (CDLPQ), core-dominated quasars with no polarization information (CDQ(NPI)), lobe-dominated quasars (LDQ), and radio galaxies (RG).

scholarly journals Searching for Gamma-Ray Millisecond Pulsars: Selection of Candidates Revisited

Galaxies ◽  
2019 ◽  
Vol 7 (1) ◽  
pp. 31
Author(s):  
Xuejie Dai ◽  
Zhongxiang Wang ◽  
Jithesh Vadakkumthani
Keyword(s):  
Point Source ◽  
Gamma Ray ◽  
Previous Analysis ◽  
Test Statistic ◽  
Large Area ◽  
Millisecond Pulsars ◽  
Multi Wavelength ◽  
Γ Ray ◽  
Available Information ◽  
Selection Of

We are starting a project to find γ -ray millisecond pulsars (MSPs) among the unidentified sources detected by the Large Area Telescope (LAT) onboard the Fermi Gamma-Ray Space Telescope (Fermi), by radio observations. The selection of good candidates from analysis of the LAT data is an important part of the project. Given that there is more than 10 years worth of LAT data and the advent of the newly released LAT 8-year point source list (FL8Y), we have conducted a selection analysis, on the basis of our previous analysis, and report the results here. Setting the requirements for the unidentified sources in FL8Y of Galactic latitudes | b | > 5 ∘ and curvature significances >3 σ , there are 202 sources with detection signficances >6 σ . We select 57 relatively bright ones (detection significances >15 σ ) and analyze their 10.2 years of LAT data. Their variability is checked to exclude variable sources (likely blazars), test statistic maps are constructed to avoid contaminated sources, and curvature significances are re-obtained and compared to their γ -ray spectra to exclude non-significant sources. In the end, 48 candidates are found. Based on the available information, mostly from multi-wavelength studies, we discuss the possible nature of several of the candidates. Most of these candidates are currently being observed with the 65-meter Shanghai Tian Ma Radio Telescope.

NEW INSIGHT INTO GAMMA-RAY BLAZARS FROM THE FERMI-LAT

2010 ◽  
Vol 19 (06) ◽  
pp. 831-839 ◽  
Author(s):  
◽  
BENOIT LOTT
Keyword(s):  
Gamma Ray ◽  
High Energy ◽  
Test Statistic ◽  
Large Area ◽  
Bl Lac Objects ◽  
Spectrum Radio ◽  
Sky Survey ◽  
Bl Lac ◽  
Ngc 1275 ◽  
Bl Lacs

The first three months of sky-survey operation with the Large Area Telescope (LAT) on board the Fermi satellite revealed 132 bright sources at |b| > 10° with test statistic greater than 100 (corresponding to about 10σ). Two methods, based on the CGRaBS, CRATES and BZCat catalogs, indicated high-confidence associations of 106 of these sources with known AGNs. This sample is referred to as the LAT Bright AGN Sample (LBAS). It contains two radio galaxies, namely Centaurus A and NGC 1275, and 104 blazars consisting of 58 flat spectrum radio quasars (FSRQs), 42 BL Lac objects, and four blazars with unknown classification. Remarkably, the LBAS includes 10 high-energy-peaked BL Lacs. Only 33 of the sources, plus two at |b| < 10°, were previously detected with EGRET, probably due to variability. The analysis of the gamma-ray properties of the LBAS sources reveals that the average GeV spectra of BL Lac objects are significantly harder than the spectra of FSRQs. Other spectral and variability blazar properties are discussed. Some prominent Fermi-detected radiogalaxies are presented.

scholarly journals Classification of blazar candidates of uncertain type from the Fermi LAT 8-yr source catalogue with an artificial neural network

2020 ◽  
Vol 493 (2) ◽  
pp. 1926-1935 ◽  
Author(s):  
M Kovačević ◽  
G Chiaro ◽  
S Cutini ◽  
G Tosti
Keyword(s):  
Neural Network ◽  
Artificial Neural Network ◽  
Supervised Machine Learning ◽  
Large Area ◽  
Bl Lacertae ◽  
Spectrum Radio ◽  
Γ Ray ◽  
Artificial Neural ◽  
Bl Lacs

ABSTRACT The Fermi Large Area Telescope (LAT) has detected more than 5000 γ-ray sources in its first 8 yr of operation. More than 3000 of them are blazars. About 60 per cent of the Fermi-LAT blazars are classified as BL Lacertae objects (BL Lacs) or Flat Spectrum Radio Quasars (FSRQs), while the rest remain of uncertain type. The goal of this study was to classify those blazars of uncertain type, using a supervised machine learning method based on an artificial neural network, by comparing their properties to those of known γ-ray sources. Probabilities for each of 1329 uncertain blazars to be a BL Lac or FSRQ are obtained. Using 90 per cent precision metric, 801 can be classified as BL Lacs and 406 as FSRQs while 122 still remain unclassified. This approach is of interest because it gives a fast preliminary classification of uncertain blazars. We also explored how different selections of training and testing samples affect the classification and discuss the meaning of network outputs.

scholarly journals Very long baseline interferometry observation of the triple AGN candidate J0849+1114

2019 ◽  
Vol 630 ◽  
pp. L5 ◽  
Author(s):  
K. É. Gabányi ◽  
S. Frey ◽  
S. Satyapal ◽  
A. Constantin ◽  
R. W. Pfeifle
Keyword(s):  
High Resolution ◽  
Radio Emission ◽  
Active Galactic Nuclei ◽  
Very Long Baseline Interferometry ◽  
Galactic Nuclei ◽  
Long Baseline ◽  
Continuum Observation ◽  
The Hierarchical Structure ◽  
Multi Wavelength ◽  
Interferometric Observation

Context. In the hierarchical structure formation model, galaxies grow through various merging events. Numerical simulations indicate that mergers can enhance the activity of central supermassive black holes in galaxies. Aims. A system of three interacting galaxies, called J0849+1114, has recently been identified and multi-wavelength evidence of all three galaxies containing active galactic nuclei has recently been found. The system has substantial radio emission; we aim to investigate the origin of this radio emission with a high-resolution radio interferometric observation and to discover whether it is related to star formation or to one or more of the active galactic nuclei in the system. Methods. We performed high-resolution continuum observation of J0849+1114 with the European Very Long Baseline Interferometry Network at 1.7 GHz. Results. We detected one compact radio emitting source at the position of the easternmost nucleus. Its high brightness temperature and radio power indicate that the radio emission originates from a radio-emitting active galactic nucleus. Additionally, we found that significant amount of flux density is contained in ∼100 milliarcsec-scale feature related to the active nucleus.

scholarly journals Very Long Baseline Interferometry observations: the closest look at the cores of AGN

2013 ◽  
Vol 9 (S304) ◽  
pp. 71-77
Author(s):  
Marcello Giroletti ◽  
Rocco Lico ◽  
Kazuhiro Hada ◽  
Gabriele Giovannini
Keyword(s):  
Very Long Baseline Interferometry ◽  
High Energy ◽  
Physical Parameters ◽  
Long Baseline ◽  
Superluminal Motion ◽  
Multi Wavelength ◽  
Very High Energy ◽  
Doppler Factor ◽  
Jet Structure ◽  
Very High

AbstractVery Long Baseline Interferometry (VLBI) provides the highest angular resolution achievable in astronomy, reaching sub-milliarcsecond scales. For radio loud AGNs, this offers the unique opportunity to directly image and monitor the fine details of the jet structure, approaching the event horizon in the nearest and most supermassive black holes, like in M87. After a quick review of various VLBI facilities, we present results from recent VLBI monitoring projects on two remarkable radio and high energy sources: the radio galaxy M87 and the BL Lac object Mrk421. For the latter, we present a detailed analysis of the jet structure in total intensity and polarization through the whole 2011, during which a multi-wavelength campaign took place. We reveal flux density variability but no significant changes in the jet structure. In M87, we detect and follow the evolution of the core and of the jet feature HST-1; we reveal superluminal motion of components within HST-1, with a possible connection between ejection of new such components and the occurrence of very high energy flares. Estimates on the physical parameters for both sources are given (Doppler factor, viewing angle, magnetic field, etc.).

scholarly journals Diffuse γ-ray emission toward the massive star-forming region, W40

2020 ◽  
Vol 639 ◽  
pp. A80
Author(s):  
Xiao-Na Sun ◽  
Rui-Zhi Yang ◽  
Yun-Feng Liang ◽  
Fang-Kun Peng ◽  
Hai-Ming Zhang ◽  
...  
Keyword(s):  
Cosmic Ray ◽  
High Energy ◽  
Young Star ◽  
Gas Content ◽  
Large Area ◽  
Stellar Cluster ◽  
Production Region ◽  
Star Forming ◽  
Photon Index ◽  
Young Star Clusters

We report the detection of high-energy γ-ray signal towards the young star-forming region, W40. Using 10-yr Pass 8 data from the Fermi Large Area Telescope (Fermi-LAT), we extracted an extended γ-ray excess region with a significance of ~18σ. The radiation has a spectrum with a photon index of 2.49 ± 0.01. The spatial correlation with the ionized gas content favors the hadronic origin of the γ-ray emission. The total cosmic-ray (CR) proton energy in the γ-ray production region is estimated to be the order of 1047 erg. However, this could be a small fraction of the total energy released in cosmic rays (CRs) by local accelerators, presumably by massive stars, over the lifetime of the system. If so, W40, together with earlier detections of γ-rays from Cygnus cocoon, Westerlund 1, Westerlund 2, NGC 3603, and 30 Dor C, supports the hypothesis that young star clusters are effective CR factories. The unique aspect of this result is that the γ-ray emission is detected, for the first time, from a stellar cluster itself, rather than from the surrounding “cocoons”.

scholarly journals A possible radio signal of annihilating dark matter in the Abell 4038 cluster

2019 ◽  
Vol 495 (1) ◽  
pp. L124-L128 ◽  
Author(s):  
Man Ho Chan ◽  
Chak Man Lee
Keyword(s):  
Dark Matter ◽  
Cross Section ◽  
Radio Signal ◽  
Dark Matter Particle ◽  
Cosmic Ray ◽  
Annihilation Cross Section ◽  
Radio Continuum ◽  
Test Statistic ◽  
Large Area ◽  
Dark Matter Annihilation

ABSTRACT In the past decade, some telescopes [e.g. Fermi-Large Area Telescope (LAT), Alpha Magnetic Spectrometer(AMS), and Dark Matter Particle Explorer(DAMPE)] were launched to detect the signals of annihilating dark matter in our Galaxy. Although some excess of gamma-rays, antiprotons, and electrons/positrons have been reported and claimed as dark matter signals, the uncertainties of Galactic pulsars’ contributions are still too large to confirm the claims. In this Letter, we report a possible radio signal of annihilating dark matter manifested in the archival radio continuum spectral data of the Abell 4038 cluster. By assuming the thermal annihilation cross-section and comparing the dark matter annihilation model with the null hypothesis (cosmic ray emission without dark matter annihilation), we get very large test statistic values &gt;45 for four popular annihilation channels, which correspond to more than 6.5σ statistical preference. This provides a very strong evidence for the existence of annihilating dark matter. In particular, our results also support the recent claims of dark matter mass m ≈ 30–50 GeV annihilating via the bb̄ quark channel with the thermal annihilation cross-section.

VERITAS OBSERVATIONS OF RELATIVISTIC OUTFLOWS IN LOW- AND INTERMEDIATE-FREQUENCY-PEAKED BL LAC OBJECTS

2014 ◽  
Vol 28 ◽  
pp. 1460178
Author(s):  
◽  
HEIKE PROKOPH
Keyword(s):  
Gamma Ray ◽  
Intermediate Frequency ◽  
Bl Lac Objects ◽  
Bl Lacertae ◽  
Bl Lac ◽  
Bl Lacs ◽  
Gamma Ray Telescopes ◽  
Very High

The majority of blazars detected at very high energies (VHE; E > 100 GeV) are high-frequency-peaked BL Lac objects (HBLs). Low- and intermediate-frequency-peaked BL Lacs (LBLs/IBLs with synchrotron-peak frequencies in the infrared and optical regime) are generally more powerful, more luminous, and have a richer jet environment than HBLs. However, only a handful of these IBL and LBLs have been detected by ground-based gamma-ray telescopes, typically during high-flux states. The VERITAS array has been monitoring five known VHE LBLs/IBLs since 2009: 3C 66A, W Comae, PKS 1424+240, S5 0716+714 and BL Lacertae, with typical exposures of 5-10 hours per year. The results of these long-term observations are presented, including a bright, subhour-scale VHE flare of BL Lacertae in June 2011, the first low-state detections of 3C 66A and W Comae, and the detection and characterization of the IBL B2 1215+30.

scholarly journals Polarization VLBI Observations of a Complete Sample of Northern BL Lacertae Objects

1998 ◽  
Vol 164 ◽  
pp. 165-166
Author(s):  
A. B. Pushkarev ◽  
D. C. Gabuzda
Keyword(s):  
Magnetic Field ◽  
Radio Emission ◽  
Synchrotron Emission ◽  
Complete Sample ◽  
Bl Lacertae Objects ◽  
Bl Lacertae ◽  
Vlbi Observations ◽  
Core Components ◽  
Jet Structure ◽  
The Magnetic Field

AbstractThe polarization electric vectors in the VLBI jets of BL Lacertae objects are typically aligned with the jet structure. If the jet radio emission is optically thin synchrotron emission, this implies that the magnetic field is perpendicular to the jet, usually interpreted as a signature of shocks. The distribution of polarization position angles in the VLBI core components appears to be bimodal, with the polarization angles either aligned with or perpendicular to the jet direction. In order to study the origin of this characteristic polarization structure, we have made VLBI polarization observations of all 34 sources in the Kühr and Schmidt sample of BL Lacertae objects.

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