https://doi.org/10.48550/arXiv.2502.11888 ================================================================================ Exploring the Most Extreme Gamma-Ray Blazars Using Broadband Spectral Energy Distributions M. Láinez, M. Nievas-Rosillo, A. Domínguez, J. L. Contreras, J. Becerra González, A. Dinesh, and V. S. Paliya ================================================================================ Keywords: Radiation mechanisms: non-thermal – Gamma rays: galaxies – Galaxies: jets – Galaxies: active – BL Lacertae objects: general Abstract: Extreme high-synchrotron peaked blazars (EHSPs) are rare high-energy sources characterised by synchrotron peaks beyond 1017 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. A sample of 124 γ-ray blazars is analysed, selected for their high synchrotron peak frequencies and γ-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. We identify 66 new EHSP candidates, significantly expanding the known population. Their synchrotron peak frequencies are statistically higher than in previous studies, and they exhibit low Compton dominance, consistent with environments lacking strong external photon fields. A clear correlation between synchrotron peak frequency and the magnetic-to-kinetic energy density ratio is found, with the most extreme EHSPs nearing equipartition. Our analysis suggests that 9 high-synchrotron peaked/EHSPs could be observed by the Cherenkov Telescope Array Observatory (CTAO) at >5σ (20 at >3σ) in 20-hour exposures, highlighting their potential to improve studies of extreme jet physics and cosmology. ================================================================================ Overview: This FITS file (`EHSP_blazars.fits`) contains data resulting from the broadband SED modeling performed for 124 blazars. File Structure: This FITS file consists of the following HDUs: | HDU Index | Type | Shape | Description | |-----------|--------------|-------------|------------------| | 1 | BinTableHDU | 124R x 15C | Best-fit parameters resulting from the SED modeling | | 2 | BinTableHDU | 124R x 10C | Other derived physical parameters and energetic report | | 3 | BinTableHDU | 124R x 4C | CTAO expected detection significance | | 4 | BinTableHDU | 124R x 6C | Multi-wavelength SED data used for the modeling | Description of table 1 (HDU 1): | Column Name | Data Type | Units | Description | |---------------|-----------|-------|-------------| | 'Source_Name' | bytes16 | - | Source name given in the 4FGL catalogue | | 'B' | float64 | G | Magnetic field strength | | 'R' | float64 | cm | Radius of the emitting region | | 'R_H' | float64 | cm | Distance from the emitting region to the central black hole | | 'theta' | float64 | deg | Jet viewing angle | | 'BulkFactor' | float64 | - | Bulk Lorentz factor of the electrons in the jet | | 'gmin' | float64 | - | Minimum Lorentz factor of the electron population | | 'gmax' | float64 | - | Maximum Lorentz factor of the electron population | | 'N' | float64 | 1/cm3 | Electron density | | 'gamma_break' | float64 | - | Break Lorentz factor | | 'p1' | float64 | - | Spectral slope of the lower energy electron population | | 'p2' | float64 | - | Spectral slope of the higher energy electron population | | 'Host_Galaxy' | bytes17 | - | Best-fit host galaxy model | | 'T_host' | float64 | K | Temperature of the host galaxy | | 'chisq' | float64 | - | Chi square value of the fitting | Description of table 2 (HDU 2): | Column Name | Data Type | Units | Description | |---------------|-----------|-------|-------------| | 'Source_Name' | bytes16 | - | Source name given in the 4FGL catalogue | | 'nu_sync_peak'| float64 | Hz | Frequency of the synchrotron peak | | 'nu_IC_peak' | float64 | Hz | Frequency of the inverse Compton peak | | 'CD' | float64 | - | Compton dominance | | 'jet_L_Sync' | float64 | erg/s | Jet luminosity due to the synchrotron component | | 'jet_L_rad' | float64 | erg/s | Jet luminosity associated with radiative mechanisms | | 'jet_L_B' | float64 | erg/s | Jet luminosity due to the magnetic field | | 'jet_L_kin' | float64 | erg/s | Jet luminosity due to the electrons | | 'jet_L_tot' | float64 | erg/s | Total jet luminosity | | 'UB/Ue' | float64 | - | Ratio of magnetic to electron energy density | Description of table 3 (HDU 3): | Column Name | Data Type | Units | Description | |---------------------|-----------|-------|-------------| | 'Source_Name' | bytes16 | - | Source name given in the 4FGL catalogue | | 'CTAO_significance' | float64 | - | CTAO expected detection significance | | 'Redshift' | float64 | - | Redshift of the source | | 'Redshift_reference'| bytes10 | - | Reference of the redshift estimate | Description of table 4 (HDU 4): | Column Name | Data Type | Units | Description | |-----------------|-----------|-------------|-------------| | 'Source_Name' | bytes16 | - | Source name given in the 4FGL catalogue | | 'log10nu' | float32 | Hz | log nu values used to reconstruct the broadband SED | | 'log10nuFnu' | float32 | erg/(cm2 s) | log nuFnu values used to reconstruct the broadband SED | | 'unc_log10nuFnu'| float32 | erg/(cm2 s) | Uncertainty in log10nuFnu | | 'UL' | bool | - | Upper limits | | 'instrument' | bytes37 | - | Instrument that took the corresponding SED data |