J/A+A/700/A229 Multi-wavelength properties of EHSP blazars (Lainez+, 2025)
Exploring the most extreme gamma-ray blazars using broadband spectral energy
distributions.
Lainez M., Nievas-Rosillo M., Dominguez A., Contreras J.L.,
Becerra Gonzalez J., Dinesh A., Paliya V.S.
<Astron. Astrophys. 700, A229 (2025)>
=2025A&A...700A.229L 2025A&A...700A.229L (SIMBAD/NED BibCode)
ADC_Keywords: BL Lac objects ; Spectral types ; Gamma rays
Keywords: radiation mechanisms: non-thermal - galaxies: active -
BL Lacertae objects: general - galaxies: jets
Abstract:
Extreme high-synchrotron peaked blazars (EHSPs) are rare high-energy
sources characterised by synchrotron peaks beyond 1017Hz 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 >5σ (20 at >3σ) 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.
Description:
Best-fit parameters and energetic properties from spectral energy
distribution modeling of 124 gamma-ray sources using a one-zone
synchrotron self-Compton model, including synchrotron peak
frequencies, luminosities, and predicted CTAO detection significances.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablec1.dat 269 124 Best-fit parameters of the 124 sample sources
tablec2.dat 223 124 Synchrotron and inverse Compton peaks frequency,
Compton dominance and energetic report
table2.dat 53 124 CTAO expected detection significance and
redshifts
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See also:
IX/67 : Incremental Fermi LAT 4th source cat. (4FGL-DR3) (Fermi-LAT col., 2022)
Byte-by-byte Description of file: tablec1.dat
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Bytes Format Units Label Explanations
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1- 16 A16 --- Source Source name given in the 4FGL catalogue
18- 35 F18.16 G B Magnetic field strength
41- 47 E7.2 cm R [1.0e+16] Radius of the emitting region
53- 59 E7.2 cm RH [2.0e+18] Distance from the emitting region
to the central black hole
61- 79 F19.16 deg theta Jet viewing angle
81- 84 F4.1 --- BulkFactor [20.0] Bulk Lorentz factor of the electrons
in the jet
86- 91 F6.1 --- gmin [1000.0] Minimum Lorentz factor of the
electron population
93-113 F21.11 --- gmax Maximum Lorentz factor of the
electron population
115-138 F24.16 cm-3 N Electron density
140-163 F24.14 --- gammabreak Break Lorentz factor
165-182 F18.16 --- p1 Spectral slope of the
lower energy electron population
184-207 E24.16 --- p2 Spectral slope of the
higher energy electron population
209-225 A17 --- HostGalaxy Best-fit host galaxy model
227-244 F18.13 K THost Temperature of the host galaxy
246-269 F24.16 --- chisq Chi square value of the fitting
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Byte-by-byte Description of file: tablec2.dat
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Bytes Format Units Label Explanations
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1- 16 A16 --- Source Source name given in the 4FGL catalogue
18- 41 E24.16 Hz nusyncpeak Frequency of the synchrotron peak
43- 64 E22.16 Hz nuICpeak Frequency of the inverse Compton peak
66- 83 F18.16 --- CD Compton dominance
85-106 E22.16 10-7W jetLSync Jet luminosity due to the
synchrotron component
108-129 E22.16 10-7W jetLrad Jet luminosity associated with
radiative mechanisms
131-152 E22.16 10-7W jetLB Jet luminosity due to the magnetic field
154-175 E22.16 10-7W jetLkin Jet luminosity due to the electrons
177-198 E22.16 10-7W jetLtot Total jet luminosity
201-223 E23.16 --- UB/Ue Ratio of magnetic to electron energy density
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 16 A16 --- Source Source name given in the 4FGL catalogue
18- 36 F19.16 --- CTAOsigni CTAO expected detection significance
38- 42 F5.3 --- z Redshift of the source
44- 53 A10 --- r_z Reference of the redshift estimates (1)
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Note (1): References as follows:
3HSP = Chang et al., 2019A&A...632A..77C 2019A&A...632A..77C, Cat. J/A+A/632/A77
4LAC = Ajello et al., 2020ApJ...892..105A 2020ApJ...892..105A, Cat. J/ApJ/892/105,
2022ApJS..263...24A 2022ApJS..263...24A, Cat. J/ApJS/263/24
Goldoni+21 = Goldoni, 2021, Review of redshift values of bright AGNs
with hard spectra in 4LAC catalog
Paliya+21 = Paliya et al., 2021ApJS..253...46P 2021ApJS..253...46P, Cat. J/ApJS/253/46
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Acknowledgements:
Maria Lainez, malainez(at)ucm.es
(End) Patricia Vannier [CDS] 15-Jul-2025