- ID:
- ivo://CDS.VizieR/J/MNRAS/442/1693
- Title:
- Gamma-ray-loud blazars optical polarization
- Short Name:
- J/MNRAS/442/1693
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present first results from RoboPol, a novel-design optical polarimeter operating at the Skinakas Observatory in Crete. The data, taken during the 2013 May-June commissioning of the instrument, constitute a single-epoch linear polarization survey of a sample of gamma-ray-loud blazars, defined according to unbiased and objective selection criteria, easily reproducible in simulations, as well as a comparison sample of, otherwise similar, gamma-ray-quiet blazars. As such, the results of this survey are appropriate for both phenomenological population studies and for tests of theoretical population models. We have measured polarization fractions as low as 0.015 down to Rmag of 17 and as low as 0.035 down to 18mag. The hypothesis that the polarization fractions of gamma-ray-loud and gamma-ray-quiet blazars are drawn from the same distribution is rejected at the 3{sigma} level. We therefore conclude that gamma-ray-loud and gamma-ray-quiet sources have different optical polarization properties. This is the first time this statistical difference is demonstrated in optical wavelengths. The polarization fraction distributions of both samples are well described by exponential distributions with averages of <p>=6.4^+0.9^_-0.8_x10^-2^ for gamma-ray-loud blazars, and <p>=3.2^+2.0^_-1.1_x10^-2^ for gamma-ray-quiet blazars. The most probable value for the difference of the means is 3.4^+1.5^_-2.0_x10^-2^. The distribution of polarization angles is statistically consistent with being uniform.
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- ID:
- ivo://CDS.VizieR/J/A+A/598/A134
- Title:
- {gamma}-ray signature in WHSP blazars (1BIGB)
- Short Name:
- J/A+A/598/A134
- Date:
- 04 Feb 2022 00:00:12
- Publisher:
- CDS
- Description:
- A direct search of {gamma}-ray emission centered on multifrequency selected candidates is a valuable complementary approach to the standard search adopted in current {gamma}-ray Fermi-LAT catalogs. Our sources are part of the 2WHSP sample that was assembled with the aim of providing targets for Imaging Atmospheric Cherenkov Telescopes (IACT). A likelihood analysis based on their known position enabled us to detect 150 {gamma}-ray excess signals that have not yet been reported in previous {gamma}-ray catalogs (1FGL, 2FGL, 3FGL). By identifying new sources, we solve a fraction of the extragalactic isotropic {gamma}-ray background (IGRB) composition, improving the description of the {gamma}-ray sky. We perform data reduction with the Fermi Science Tools using positions from 400 high synchrotron peaked (HSP) blazars as seeds of tentative {gamma}-ray sources; none of them have counterparts from previous 1FGL, 2FGL and 3FGL catalogs. Our candidates are part of the 2WHSP sample (currently the largest set of HSP blazars). We focus on HSPs characterized by bright synchrotron component with peak flux {nu}f_({nu})_>=10^-12.1^erg/cm^2^/s, testing the hypothesis of having a {gamma}-ray source in correspondence to the WHSP positions. Our likelihood analysis considers the 0.3-500GeV energy band, integrating over 7.2yr of Fermi-LAT observation and making use of the Pass 8 data release. From the 400 candidates tested, a total of 150 2WHSPs showed excess {gamma}-ray signature: 85 high-significance detections with test statistic (TS)>25, and 65 lower-significance detections with TS between 10 to 25. We assume a power law spectrum in the 0.3-500GeV band and list the spectrum parameters describing all 150 new {gamma}-ray sources. We study the {gamma}-ray photon spectral index distribution, the likelihood of detection according to the synchrotron peak brightness (figure of merit parameter), and plot the measured {gamma}-ray LogN-LogS of HSP blazars, also discussing the portion of the IGRB that has been resolved by the present work. We also report on four cases where we could resolve source confusion and find counterparts for unassociated 3FGL sources with the help of high-energy TS maps together with multifrequency data. The 150 new {gamma}-ray sources are named with the acronym 1BIGB for the first version of the Brazil ICRANet Gamma-ray Blazar catalog, in reference to the cooperation agreement supporting this work.
- ID:
- ivo://CDS.VizieR/J/MNRAS/477/4749
- Title:
- gamma-rays in Fermi blazars
- Short Name:
- J/MNRAS/477/4749
- Date:
- 17 Jan 2022 00:27:10
- Publisher:
- CDS
- Description:
- The gamma-ray emission in broad-line blazars is generally explained as inverse Compton (IC) radiation of relativistic electrons in the jet scattering optical-UV photons from the broad-line region (BLR), the so-called BLR external Compton (EC) scenario. We test this scenario on the Fermi gamma-ray spectra of 106 broad-line blazars detected with the highest significance or largest BLR, by looking for cut-off signatures at high energies compatible with {gamma}-{gamma} interactions with BLR photons. We do not find evidence for the expected BLR absorption. For 2/3 of the sources, we can exclude any significant absorption ({tau}_max_<1), while for the remaining 1/3 the possible absorption is constrained to be 1.5-2 orders of magnitude lower than expected. This result holds also dividing the spectra in high- and low-flux states, and for powerful blazars with large BLR. Only 1 object out of 10 seems compatible with substantial attenuation ({tau}_max_>5). We conclude that for 9 out of 10 objects, the jet does not interact with BLR photons. Gamma-rays seem either produced outside the BLR most of the time, or the BLR is ~100 x larger than given by reverberation mapping. This means that (i) EC on BLR photons is disfavoured as the main gamma-ray mechanism, versus IC on IR photons from the torus or synchrotron self-Compton; (ii) the Fermi gamma-ray spectrum is mostly intrinsic, determined by the interaction of the particle distribution with the seed-photon spectrum; and (iii) without suppression by the BLR, broad-line blazars can become copious emitters above 100GeV, as demonstrated by 3C 454.3. We expect the CTA sky to be much richer of broad-line blazars than previously thought.
- ID:
- ivo://nasa.heasarc/mggammadet
- Title:
- Gamma-RaySourceDetailedCatalog(Macomb&Gehrels1999)
- Short Name:
- MGGAMMADET
- Date:
- 27 Sep 2024
- Publisher:
- NASA/GSFC HEASARC
- Description:
- This database table contains the slightly revised contents of the detailed Tables 2A - 2G from the General Gamma-Ray Source Catalog of Macomb & Gehrels (1999). It lists details of all known gamma-ray observations within the energy range from 50 keV to ~1 TeV for 314 discrete gamma-ray sources that were listed in Tables 2A - 2G of the published version of this catalog, including all 310 sources listed in the published Summary Table 1, together with 4 sources (2CG 054+01, A0620-00, GX 340+0, and H1822-000) that were listed only in Table 2 of the published catalog but were (presumably accidentally) omitted from Table 1. The positions for the sources in the present database were taken from Table 1 of the General Gamma-Ray Source Catalog. Thus, this table is essentially a compilation of gamma-ray observations of discrete sources as known to the authors as of early 1999. There is another HEASARC database table called the Gamma-Ray Source Summary Catalog (Macomb & Gehrels 1999) or MGGAMMACAT that contains the summary information on these sources that was given in Table 1 of the General Gamma-Ray Source Catalog. As noted above, this is a slightly revised version compared to the published Tables 2A - 2G. The known differences between the HEASARC and published versions are discussed in the HEASARC_Version section of the help documentation. This database table was created by the HEASARC in March 2002 based upon machine-readable versions of Tables 2A-2G of the Macomb & Gehrels (1999) General Gamma-Ray Source Catalog that were supplied by the authors. One duplicate entry was removed from this table in June 2019. This is a service provided by NASA HEASARC .
- ID:
- ivo://nasa.heasarc/mggammacat
- Title:
- Gamma-RaySourceSummaryCatalog(Macomb&Gehrels1999&2001)
- Short Name:
- M&GGamma-ray
- Date:
- 27 Sep 2024
- Publisher:
- NASA/GSFC HEASARC
- Description:
- This database table is a revised and updated version of the published General Gamma-Ray Source Catalog (Macomb & Gehrels 1999, ApJS, 120, 335). It contains all 309 gamma-ray point sources listed in Table 1 of the published version of this catalog; 4 gamma-ray point sources (2CG 054+01, A0620-00, GX 340+0, and H1822-000) added by the HEASARC that were listed in Table 2 of the published catalog but were (presumably accidentally) omitted from Table 1 of the published catalog; and 107 sources (106 sources from the 3rd Egret (3EG) catalog of Hartman et al. (1999, ApJS, 123, 79) and GEV J1732-3130) that were compiled by Macomb and Gehrels subsequent to their original publication (Macomb and Gehrels 2001, unpublished). Thus, the present database table is essentially a summary master list of all detected gamma-ray point sources as of circa 2000. There is another HEASARC database table called the Gamma-Ray Source Detailed Catalog (Macomb & Gehrels 1999 & 2001) or MGGAMMADET that contains detailed information on the gamma-ray properties of these sources such as fluxes and spectral indices and that is based on Tables 2A-2G of the Macomb & Gehrels paper. This database table was created by the HEASARC in March 2001 based on tables supplied to the HEASARC by the catalog authors which contained an updated version of Table 1 from the published paper. This is a service provided by NASA HEASARC .
- ID:
- ivo://CDS.VizieR/J/other/RAA/18.56
- Title:
- gamma-ray spectrum for Fermi blazars
- Short Name:
- J/other/RAA/18.5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The curvature of the {gamma}-ray spectrum in blazars may reflect the intrinsic distribution of emitting electrons, which will further give some information on the possible acceleration and cooling processes in the emitting region. The {gamma}-ray spectra of Fermi blazars are normally fitted either by a single power-law (PL) or a log-normal (call Logarithmic Parabola, LP) form. The possible reason for this difference is not clear. We statistically explore this issue based on the different observational properties of 1419 Fermi blazars in the 3LAC Clean Sample.We find that the {gamma}-ray flux (100MeV-100GeV) and variability index follow bimodal distributions for PL and LP blazars, where the {gamma}-ray flux and variability index show a positive correlation. However, the distributions of {gamma}-ray luminosity and redshift follow a unimodal distribution. Our results suggest that the bimodal distribution of {gamma}-ray fluxes for LP and PL blazars may not be intrinsic and all blazars may have an intrinsically curved {gamma}-ray spectrum, and the PL spectrum is just caused by the fitting effect due to less photons.
- ID:
- ivo://CDS.VizieR/J/ApJ/813/51
- Title:
- {gamma}-ray to IR study of the blazar CTA 102
- Short Name:
- J/ApJ/813/51
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We perform a multi-wavelength polarimetric study of the quasar CTA 102 during an extraordinarily bright {gamma}-ray outburst detected by the Fermi Large Area Telescope in 2012 September-October when the source reached a flux of F_>100MeV_=5.2+/-0.4x10^-6^photons/cm2/s. At the same time, the source displayed an unprecedented optical and near-infrared (near-IR) outburst. We study the evolution of the parsec-scale jet with ultra-high angular resolution through a sequence of 80 total and polarized intensity Very Long Baseline Array images at 43GHz, covering the observing period from 2007 June to 2014 June. We find that the {gamma}-ray outburst is coincident with flares at all the other frequencies and is related to the passage of a new superluminal knot through the radio core. The powerful {gamma}-ray emission is associated with a change in direction of the jet, which became oriented more closely to our line of sight ({theta}~1.2{deg}) during the ejection of the knot and the {gamma}-ray outburst. During the flare, the optical polarized emission displays intra-day variability and a clear clockwise rotation of electric vector position angles (EVPAs), which we associate with the path followed by the knot as it moves along helical magnetic field lines, although a random walk of the EVPA caused by a turbulent magnetic field cannot be ruled out. We locate the {gamma}-ray outburst a short distance downstream of the radio core, parsecs from the black hole. This suggests that synchrotron self-Compton scattering of NIR to ultraviolet photons is the probable mechanism for the {gamma}-ray production.
- ID:
- ivo://CDS.VizieR/J/A+A/394/187
- Title:
- {gamma} Ser & 101 Her elemental abundances
- Short Name:
- J/A+A/394/187
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Elemental abundances analysis of the superficially normal stars {gamma} Ser (F6 V) and 101 Herculis (A7 V) consistent with previous studies of this series using photographic region spectrograms obtained with Reticon and CCD detectors produced derived values that are generally solar except for Al which is very underabundant and the rare earths which do not have the solar pattern. Similar discrepancies from solar values are seen in other superficially normal stars of this series with similar temperatures. Our results for {gamma} Ser are in acceptable agreement with other recent studies based on different techniques and spectral regions.
- ID:
- ivo://CDS.VizieR/J/A+A/589/A70
- Title:
- Gamma Vel cluster membership and IMF
- Short Name:
- J/A+A/589/A70
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Understanding the properties of young open clusters, such as the Initial Mass Function (IMF), star formation history and dynamic evolution, is crucial to obtain reliable theoretical predictions of the mechanisms involved in the star formation process. We want to obtain a list, as complete as possible, of confirmed members of the young open cluster Gamma Velorum, with the aim of deriving general cluster properties such as the IMF. We used all available spectroscopic membership indicators within the Gaia-ESO public archive together with literature photometry and X-ray data and, for each method, we derived the most complete list of candidate cluster members. Then, we considered photometry, gravity and radial velocities as necessary conditions to select a subsample of candidates whose membership was confirmed by using the lithium and H{alpha} lines and X-rays as youth indicators. We found 242 confirmed and 4 possible cluster members for which we derived masses using very recent stellar evolutionary models. The cluster IMF in the mass range investigated in this study shows a slope of {alpha}=2.6+/-0.5 for 0.5<M/M_{sun}<1.3 and {alpha}=1.1+/-0.4 for 0.16<M/M_{sun}_<0.5 and is consistent with a standard IMF. The similarity of the IMF of the young population around gamma^2^ Vel to that in other star forming regions and the field suggests it may have formed through very similar processes.
- ID:
- ivo://CDS.VizieR/J/A+A/586/A67
- Title:
- G64-12 and G64-37 linelist and EWs
- Short Name:
- J/A+A/586/A67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Studies of extremely metal-poor stars indicate that chemical abundance ratios [X/Fe] have a root mean square scatter as low as 0.05dex (12%). It remains unclear whether this reflects observational uncertainties or intrinsic astrophysical scatter arising from physical conditions in the ISM at early times. We measure differential chemical abundance ratios in extremely metal-poor stars to investigate the limits of precision and to understand whether cosmic scatter or observational errors are dominant. We used high-resolution (R~95000) and high signal-to-noise (S/N=700 at 5000{AA}) HIRES/Keck spectra to determine high-precision differential abundances between two extremely metal-poor stars through a line-by-line differential approach. We determined stellar parameters for the star G64-37 with respect to the standard star G64-12. We performed EW measurements for the two stars for the lines recognized in both stars and performed spectral synthesis to study the carbon abundances. Results. The differential approach allowed us to obtain errors of {sigma}(Teff)=27K, {sigma}(logg)=0.06dex, {sigma}([Fe/H])=0.02dex and {sigma}(vt)=0.06km/s. We estimated relative chemical abundances with a precision as low as {sigma}([X/Fe])~0.01dex. The small uncertainties demonstrate that there are genuine abundance differences larger than the measurement errors. The observed Li difference cannot be explained by the difference in mass because the less massive star has more Li. It is possible to achieve an abundance precision around ~0.01-0.05dex for extremely metal-poor stars, which opens new windows on the study of the early chemical evolution of the Galaxy.