Testing the Blazar Sequence with Spectra of Recently Discovered Dim Blazars from the Fermi Unassociated Catalog

TL;DR

This study analyzes recently discovered dim blazars from the Fermi unassociated catalog, constructing their spectral energy distributions, and tests the blazar sequence predictions by comparing their physical properties with brighter blazars.

Contribution

It provides the first detailed spectral and physical analysis of a new dim blazar sample, extending blazar sequence tests to lower flux regimes.

Findings

Most new blazars are HSP BL Lac objects with higher synchrotron peaks.

New blazars exhibit smaller Lorentz factors and magnetic fields, consistent with blazar sequence.

They show slightly higher Compton dominance ratios, suggesting alternative emission mechanisms.

Abstract

Recent works have developed samples of blazars from among the Fermi-LAT unassociated sources via machine learning comparisons with known blazar samples. Continued analysis of these new blazars tests the predictions of the blazar sequence and enables more flux-complete samples of blazars as a population. Using Fermi, Swift, WISE, and archival radio data, we construct broadband spectral energy distributions for 106 recently identified blazars. Drawn from the unassociated 4FGL source sample, this new sample has a lower median flux than the overall sample of gamma-ray blazars. By measuring the synchrotron peak frequency, we compare our sample of new blazars with known blazars from the 4LAC catalog. We find that the bulk of the new blazars are similar to High-Synchrotron Peak (HSP) BL Lac objects, with a higher median synchrotron peak; the sample has a median $ log( {\nu}_{syn} /Hz ) = 15.5 $ via BLaST peak estimation, compared to $ log( {\nu}_{syn} /Hz ) = 14.2 $ for the 4LAC BL Lacs. Finally, we conduct synchrotron self-Compton (SSC) leptonic modeling, comparing fitted physical and phenomenological properties to brighter blazars. We find that the new blazars have smaller characteristic Lorentz factors ${\gamma}_{boost}$ and fitted magnetic fields $B$, in agreement with blazar sequence predictions. The new blazars have slightly higher Compton dominance ratios than expected, which may point to alternative emission models for these dim blazars. Our results extend the predictions of the blazar sequence to a sample of dimmer blazars, confirming the broad predictions of that theory.