- ID:
- ivo://CDS.VizieR/J/A+A/390/39
- Title:
- HEGRA AIROBICC gamma radiation above 15 TeV
- Short Name:
- J/A+A/390/39
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Results of the search for gamma radiation above 15 TeV, using the AIROBICC air shower detector, from a set of 196 candidate point sources taken from different catalogs. For each object, the equatorial coordinates are provided, together with the number of signal events registered by the detector, the estimated background, the statistical significance of the excess (or defect) of events, the average energy threshold of the observation (in TeV), and the flux upper limit (at 90% confidence level) of gamma rays above this threshold.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/627/A100
- Title:
- HESS and Suzaku observations of Vela X
- Short Name:
- J/A+A/627/A100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Pulsar Wind Nebulae (PWNe) represent the most prominent population of Galactic very-high-energy gamma-ray sources and are thought to be an efficient source of leptonic cosmic rays. Vela X is a nearby middle-aged PWN, which shows bright X-ray and TeV gamma-ray emission toward an elongated structure called the cocoon. Since TeV emission is likely inverse-Compton emission of electrons, predominantly from interactions with the cosmic microwave background, while X-ray emission is synchrotron radiation of the same electrons, we aim to derive the properties of the relativistic particles and of magnetic fields with minimal modelling. We use data from the Suzaku XIS to derive the spectra from three compact regions in Vela X covering distances from 0.3pc to 4pc from the pulsar along the cocoon. We obtain gamma-ray spectra of the same regions from H.E.S.S. observations and fit a radiative model to the multi-wavelength spectra. The TeV electron spectra and magnetic field strengths are consistent within the uncertainties for the three regions, with energy densities of the order 10^-12^erg/cm^-3^. The data indicate the presence of a cutoff in the electron spectrum at energies of 100TeV and a magnetic field strength of 6G. Constraints on the presence of turbulent magnetic fields are weak. The pressure of TeV electrons and magnetic fields in the cocoon is dynamically negligible, requiring the presence of another dominant pressure component to balance the pulsar wind at the termination shock. Sub-TeV electrons cannot account completely for the missing pressure, that may be provided either by relativistic ions or from mixing of the ejecta with the pulsar wind. The electron spectra are consistent with expectations from transport scenarios dominated either by advection via the reverse shock or by diffusion, but for the latter the role of radiative losses near the termination shock needs to be further investigated in the light of the measured cutoff energies. Constraints on turbulent magnetic fields and the shape of the electron cutoff can be improved by spectral measurements in the energy range >~10keV.
- ID:
- ivo://CDS.VizieR/J/A+A/612/A1
- Title:
- H.E.S.S. Galactic Plane Survey
- Short Name:
- J/A+A/612/A1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of the most comprehensive survey of the Galactic plane in very high-energy (VHE) gamma-rays, including a public release of Galactic sky maps, a catalog of VHE sources, and the discovery of 16 new sources of VHE gamma-rays. The High Energy Spectroscopic System (H.E.S.S.) Galactic plane survey (HGPS) was a decade-long observation program carried out by the H.E.S.S. I array of Cherenkov telescopes in Namibia from 2004 to 2013. The observations amount to nearly 2700 h of quality-selected data, covering the Galactic plane at longitudes from l=250{deg} to 65{deg} and latitudes |b|<=3. In addition to the unprecedented spatial coverage, the HGPS also features a relatively high angular resolution (0.08{deg}~5-arcmin mean point spread function 68% containment radius), sensitivity (1.5% Crab flux for point-like sources), and energy range (0.2-100TeV). We constructed a catalog of VHE gamma-ray sources from the HGPS data set with a systematic procedure for both source detection and characterization of morphology and spectrum. We present this likelihood- based method in detail, including the introduction of a model component to account for unresolved, large-scale emission along the Galactic plane. In total, the resulting HGPS catalog contains 78 VHE sources, of which 14 are not reanalyzed here, for example, due to their complex morphology, namely shell-like sources and the Galactic center region. Where possible, we provide a firm identification of the VHE source or plausible associations with sources in other astronomical catalogs. We also studied the characteristics of the VHE sources with source parameter distributions. 16 new sources were previously unknown or unpublished, and we individually discuss their identifications or possible associations. We firmly identified 31 sources as pulsar wind nebulae (PWNe), supernova remnants (SNRs), composite SNRs, or gamma-ray binaries. Among the 47 sources not yet identified, most of them (36) have possible associations with cataloged objects, notably PWNe and energetic pulsars that could power VHE PWNe.
- ID:
- ivo://CDS.VizieR/J/A+A/612/A3
- Title:
- HESS Galactic supernova remnants
- Short Name:
- J/A+A/612/A3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Shell-type supernova remnants (SNRs) are considered prime candidates for the acceleration of Galactic cosmic rays (CRs) up to the knee of the CR spectrum at E~=3x10^15^eV. Our Milky Way galaxy hosts more than 350 SNRs discovered at radio wavelengths and at high energies, of which 220 fall into the H.E.S.S. Galactic Plane Survey (HGPS) region. Of those, only 50 SNRs are coincident with a H.E.S.S source and in 8 cases the very high-energy (VHE) emission is firmly identified as an SNR. The H.E.S.S. GPS provides us with a legacy for SNR population study in VHE {gamma}-rays and we use this rich data set to extract VHE flux upper limits from all undetected SNRs. Overall, the derived flux upper limits are not in contradiction with the canonical CR paradigm. Assuming this paradigm holds true, we can constrain typical ambient density values around shell-type SNRs to n<=7cm^-3^ and electron-to-proton energy fractions above 10TeV to {epsilon}_ep_<=5x10^-3^. Furthermore, comparisons of VHE with radio luminosities in non-interacting SNRs reveal a behaviour that is in agreement with the theory of magnetic field amplification at shell-type SNRs.
- ID:
- ivo://CDS.VizieR/J/A+A/621/A116
- Title:
- HESS J1825-137 particle transport
- Short Name:
- J/A+A/621/A116
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed view of the pulsar wind nebula (PWN) HESS J1825--137. We aim to constrain the mechanisms dominating the particle transport within the nebula, accounting for its anomalously large size and spectral characteristics. The nebula is studied using a deep exposure from over 12 years of H.E.S.S. I operation, together with data from H.E.S.S. II improving the low energy sensitivity. Enhanced energy- dependent morphological and spatially-resolved spectral analyses probe the Very High Energy (VHE, E>0.1TeV) gamma-ray properties of the nebula. The nebula emission is revealed to extend out to 1.5 degrees from the pulsar, ~1.5 times further than previously seen, making HESS J1825-137, with an intrinsic diameter of ~100pc, potentially the largest gamma-ray PWN currently known. Characterisation of the nebula's strongly energy-dependent morphology enables the particle transport mechanisms to be constrained. A dependence of the nebula extent with energy of R{prop.to} E^alpha^ with alpha=-0.29+/-0.04(stat)+/-0.05(sys) disfavours a pure diffusion scenario for particle transport within the nebula. The total gamma-ray flux of the nebula above 1~TeV is found to be (1.12+/-0.03(stat)+/-0.25(sys))x10^-11^cm^-2^s^-1^, corresponding to ~64% of the flux of the Crab Nebula. HESS J1825-137 is a PWN with clear energy-dependent morphology at VHE gamma-ray energies. This source is used as a laboratory to investigate particle transport within middle-aged PWNe. Deep observations of this highly spatially-extended PWN enable a spectral map of the region to be produced, providing insights into the spectral variation within the nebula.
- ID:
- ivo://CDS.VizieR/J/other/GCN/1070.1
- Title:
- HETE Trigger Information
- Short Name:
- J/other/GCN/1070
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- At 15:54:53.123 UT on 23 June, the HETE FREGATE and WXM instruments detected and localized an intense burst from SGR1806-20, a soft gamma-ray repeater. This event, disseminated in near real time as a GCN Alert (HETE BID_1566; see http://gcn.gsfc.nasa.gov/gcn/hete_grbs.html ), is the second burst localized from this source in the past week. (The first burst was reported in GCN Circular #1068). The coordinates (J2000) of the 23 June burst are: RA=272.1460{deg} (18:08:35.02), DE=-20.3658{deg} (-20:21:56) The error circle for this localization is 6 arcmin in radius. SGR1806-20 lies 3.1arcmin from the HETE position. The burst duration in the 8-40keV band was ~200ms, comprised of two peaks each <100ms in duration. A total of 2250 counts were detected during that interval, corresponding to a fluence of ~4x10^-7^ergs/cm^2^. The peak flux was >6x10^-6^erg/cm^2^/s (i.e. >200Crab-flux). Follow-up observations of this transient are encouraged. Additional information on this burst detection (including light curves), as well as for the HETE mission, will be available at: http://space.mit.edu/HETE/
- ID:
- ivo://CDS.VizieR/J/ApJ/897/177
- Title:
- 142 high-redshift blazars at the cosmic dawn
- Short Name:
- J/ApJ/897/177
- Date:
- 11 Mar 2022
- Publisher:
- CDS
- Description:
- The uncharted territory of the high-redshift (z>~3) universe holds the key to understanding the evolution of quasars. In an attempt to identify the most extreme members of the quasar population, that is, blazars, we have carried out a multiwavelength study of a large sample of radio-loud quasars beyond z=3. Our sample consists of nine {gamma}-ray-detected blazars and 133 candidate blazars selected based on the flatness of their soft X-ray spectra (0.3-10keV photon index <~1.75), including 15 with Nuclear Spectroscopic Telescope Array (NuSTAR) observations. The application of the likelihood profile stacking technique reveals that the high-redshift blazars are faint {gamma}-ray emitters with steep spectra. The high-redshift blazars host massive black holes (<logM_BH,M{odot}_>>9) and luminous accretion disks (<L_disk_>>10^46^erg/s). Their broadband spectral energy distributions are found to be dominated by high-energy radiation, indicating their jets are among the most luminous ones. Focusing on the sources exhibiting resolved X-ray jets (as observed with the Chandra satellite), we find the bulk Lorentz factor to be larger with respect to other z>3 blazars, indicating faster moving jets. We conclude that the presented list of high-redshift blazars may act as a reservoir for follow-up observations, such as with NuSTAR, to understand the evolution of relativistic jets at the dawn of the universe.
- ID:
- ivo://CDS.VizieR/J/ApJ/727/73
- Title:
- High S/N composite spectrum of GRB afterglows
- Short Name:
- J/ApJ/727/73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a composite spectrum of 60 long duration gamma-ray burst (GRB) afterglows with redshifts in the range 0.35<z<6.7 observed with low-resolution optical spectra. The composite spectrum covers the wavelength range 700-6600{AA} in the rest frame and has a mean signal-to-noise ratio of 150 per 1{AA} pixel and reaches a maximum of ~300 in the range 2500-3500{AA}. Equivalent widths are measured from metal absorption lines from the Ly{alpha} line to ~5200{AA}, and associated metal and hydrogen lines are identified between the Lyman break and Ly{alpha} line. The average transmission within the Lyman forest is consistent with that found along quasar lines of sight.
199. 3HSP blazars catalog
- ID:
- ivo://CDS.VizieR/J/A+A/632/A77
- Title:
- 3HSP blazars catalog
- Short Name:
- J/A+A/632/A77
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- High-synchrotron peaked blazars (HSPs or HBLs) play a central role in very high-energy (VHE) {gamma}-ray astronomy, and likely in neutrino astronomy. Currently, the largest compilation of HSP blazars, the 2WHSP sample, includes 1691 sources, but it is not complete in the radio or in the X-ray band. In order to provide a larger and more accurate set of HSP blazars that is useful for future statistical studies and to plan for VHE/TeV observations, we present the 3HSP catalogue, the largest sample of extreme and high-synchrotron peaked (EHSP; HSP) blazars and blazar candidates. We implemented several ways to improve the size and the completeness of the 2WHSP catalogue and reduced the selection biases to be taken into consideration in population studies. By discarding the IR constraint and relaxing the radio-IR and IR-X-ray slope criteria, we were able to select more sources with peak close to the 10^15^Hz threshold and objects where the host galaxy dominates the flux. The selection of extra sources now commences with a crossmatching between radio and X-ray surveys, applying a simple flux ratio cut. We also considered Fermi-LAT catalogues to find reasonable HSP-candidates that are detected in the {gamma}-ray band but are not included in X-ray or radio source catalogues. The new method, and the use of newly available multi-frequency data, allowed us to add 395 sources to the sample, to remove 73 2WHSP sources that were previously agged as uncertain and could not be confirmed as genuine HSP blazars, and to update parameters obtained by fitting the synchrotron component. The 3HSP catalogue includes 2013 sources, 88% of which with a redshift estimation, a much higher percentage than in any other list of HSP blazars. All new {gamma}-ray detections are described in the First and Second Brazil ICRANet {gamma}-ray blazar catalogues (1BIGB & 2BIGB) also taking into account the 4FGL list of {gamma}-ray sources published by the Fermi Large Area Telescope (Fermi-LAT) team. Moreover, the cross-matching between the 2WHSP, 2FHL HSP, and IceCube neutrino positions suggests that HSPs are likely counterparts of neutrino events, which implies the 3HSP catalogue is also useful in that respect. The 3HSP catalogue shows improved completeness compared to its predecessors, the 1WHSP and 2WHSP catalogues, and follows the track of their increasing relevance for VHE astronomy.
- ID:
- ivo://CDS.VizieR/J/ApJS/256/40
- Title:
- HST imaging survey of low-z Swift-BAT AGNs
- Short Name:
- J/ApJS/256/40
- Date:
- 03 Mar 2022 00:28:07
- Publisher:
- CDS
- Description:
- We present initial results from a Hubble Space Telescope snapshot imaging survey of the host galaxies of Swift-BAT active galactic nuclei (AGN) at z<0.1. The hard X-ray selection makes this sample relatively unbiased in terms of obscuration, compared to optical AGN selection methods. The high-resolution images of 154 target AGN enable us to investigate the detailed photometric structure of the host galaxies, such as the Hubble type and merging features. We find 48% and 44% of the sample to be hosted by early-type and late-type galaxies, respectively. The host galaxies of the remaining 8% of the sample are classified as peculiar galaxies because they are heavily disturbed. Only a minor fraction of host galaxies (18%-25%) exhibit merging features (e.g., tidal tails, shells, or major disturbance). The merging fraction increases strongly as a function of bolometric AGN luminosity, revealing that merging plays an important role in triggering luminous AGN in this sample. However, the merging fraction is weakly correlated with the Eddington ratio, suggesting that merging does not necessarily lead to an enhanced Eddington ratio. Type 1 and Type 2 AGN are almost indistinguishable in terms of their Hubble type distribution and merging fraction. However, the merging fraction of Type 2 AGN peaks at a lower bolometric luminosity compared with those of Type 1 AGN. This result may imply that the triggering mechanism and evolutionary stages of Type 1 and Type 2 AGN are not identical.
