J/A+A/700/A229ivo://CDS.VizieR/J/A+A/700/A229doi:10.26093/cds/vizier/bc-nw/lccjCDSLainez M.Nievas-Rosillo M.Dominguez A.Contreras J.L.,Becerra Gonzalez J.Dinesh A.Paliya V.S.2026-08-03T06:56:34Z2025-08-20T08:33:52ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frbl-lacertae-objectsstellar-spectral-typesgamma-ray-astronomyExtreme high-synchrotron peaked blazars (EHSPs) are rare high-energy sources characterised by synchrotron peaks beyond 10^17^Hz in their spectral energy distributions (SEDs). Their extreme properties challenge conventional blazar emission models and provide a unique opportunity to test the limits of particle acceleration and emission mechanisms in relativistic jets. However, the number of identified EHSPs is still small, limiting comprehensive studies of their population and characteristics. This study aims to identify new EHSP candidates and characterise their emission properties, including synchrotron peak frequencies, Compton dominance, and jet environments. It also examines how EHSPs fit within the broader framework of the blazar sequence, providing insights into their role in the population of active galactic nuclei. A sample of 124 gamma-ray blazars is analysed, selected for their high synchrotron peak frequencies and gamma-ray emission properties, with a focus on sources showing low variability and good broadband data coverage. Their SEDs are constructed using archival multi-wavelength data from the SSDC SED Builder service, supplemented with recent Swift-UVOT, Swift-XRT, and Fermi-LAT observations. The SEDs are modelled with a one-zone synchrotron/synchrotron-self-Compton framework, classifying sources by synchrotron peak frequency. EHSP properties are compared to other blazar populations, and their detectability with the Cherenkov Telescope Array Observatory (CTAO) is assessed. We identify 66 new EHSP candidates, significantly expanding the known population. A clear correlation between synchrotron peak frequency and the magnetic-to-kinetic energy density ratio is found, with the most extreme EHSPs nearing equipartition. This indicates that as the synchrotron peak shifts to higher frequencies, the energy stored in the magnetic field becomes comparable to that of the relativistic electrons, suggesting a more balanced and energetically efficient jet environment in the most extreme blazars. Host galaxy emission is detected in many sources, but no significant differences are observed between elliptical and lenticular hosts. Finally, our analysis suggests that 9 high-synchrotron peaked/EHSPs could be observed by CTAO at >5{sigma} (20 at >3{sigma}) in 20-hour exposures, a feasible integration time for Imaging Atmospheric Cherenkov Telescopes, indicating that while the overall detection rate remains modest, a subset of these sources is within reach of next-generation very-high-energy gamma-ray instruments.2025A&A...700A.229Lhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/700/A229CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toIX/67 : Incremental Fermi LAT 4th source cat. (4FGL-DR3) (Fermi-LAT col., 2022)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/700/A229https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/700/A229http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/700/A229https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/700/A229https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/700/A229http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/700/A229GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/700/A229/tablec1 (Best-fit parameters of the 124 sources)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/700/A229/tablec1?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/700/A229/tablec1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/700/A229/tablec1?GETtext/xml+votable180.050000true0.8316683-52.79091190.0055555555555555566/29 717 1120 1203 2249 4040 4160 4642 4705 4882 5091 5872 6204 6348 6829 7641 8173 8258 8321 8595 9049 9762 9773 10154 10258 10810 11124 11253 11639 11778 12385 12433 12851 12902 15003 16015 16223 16606 16665 16696 16740 16806 17601 17994 18259 18513 19190 19870 20478 20489 20611 20736 21203 21454 21764 21792 21808 21879 22608 22823 23009 23011 23071 23085 23181 23208 23516 24641 24785 25061 25734 25760 25820 26074 26203 26571 26787 27631 27945 28199 29336 31698 32244 32262 32537 32596 33243 33865 34478 34617 34721 34900 34911 35330 35434 35594 35821 36137 36366 36471 36615 36910 38192 39467 40323 40353 43377 43422 43630 44213 44533 44539 45016 45289 45820 46142 46280 46442 47101 47425 47461 47479 47497 48100https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/700/A229?format=asciiGamma-raydefaultJ/A+A/700/A229/tablec1Best-fit parameters of the 124 sourcesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintSourceSource name given in the 4FGL cataloguemeta.id;meta.maincharBMagnetic field strengthGphys.atmol.collStrength;obs.fielddoubleR[1.0e+16] Radius of the emitting regioncmphys.size.radius;obs.fielddoubleRH[2.0e+18] Distance from the emitting region to the central black holecmpos.distancedoublethetaJet viewing angledegpos.posAngdoubleBulkFactor[20.0] Bulk Lorentz factor of the electrons in the jetstat.fit.paramfloatSimbadSimbad column added by the CDSmeta.ref.urlcharNElectron densitycm**-3phys.density;phys.electrondoublegmin[1000.0] Minimum Lorentz factor of the electron populationstat.fit.paramfloatgmaxMaximum Lorentz factor of the electron populationstat.fit.paramdoublegammabreakBreak Lorentz factorstat.fit.paramdoublep1Spectral slope of the lower energy electron populationmeta.crypticdoublep2Spectral slope of the higher energy electron populationmeta.crypticdoubleHostGalaxyBest-fit host galaxy modelmeta.id.parentcharTHostTemperature of the host galaxyKphys.temperaturedoublechisqChi square value of the fittingstat.fit.chi2double_RARight Ascension (J2000) from SIMBAD (not part of the original data)degpos.eq.ra;meta.main_DEDeclination (J2000) from SIMBAD (not part of the original data)degpos.eq.dec;meta.mainJ/A+A/700/A229/tablec2Synchrotron and inverse Compton peaks frequency, Compton dominance and energetic reportrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintSourceSource name given in the 4FGL cataloguemeta.id;meta.maincharnusyncpeakFrequency of the synchrotron peakHzem.freqdoublenuICpeakFrequency of the inverse Compton peakHzem.freqdoubleCDCompton dominancestat.fit.paramdoublejetLSyncJet luminosity due to the synchrotron component1e-07Wphys.luminositydoublejetLradJet luminosity associated with radiative mechanisms1e-07Wphys.luminositydoublejetLBJet luminosity due to the magnetic field1e-07Wphys.luminositydoublejetLkinJet luminosity due to the electrons1e-07Wphys.luminositydoublejetLtotTotal jet luminosity1e-07Wphys.luminositydoubleUB/UeRatio of magnetic to electron energy densityphys.density;arith.ratiodoubleJ/A+A/700/A229/table2CTAO expected detection significance and redshiftsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintSourceSource name given in the 4FGL cataloguemeta.id;meta.maincharCTAOsigniCTAO expected detection significancestat.fit.goodnessdoublezRedshift of the sourcesrc.redshiftfloatr_zReference of the redshift estimates (1)meta.ref;pos.framechar