Discerning Misclassified Flat-spectrum Radio Quasars from Low-frequency-peaked BL Lacertae Objects

Abstract A sample of 312 low-frequency-peaked BL Lacertae objects (LBLs) and 694 flat-spectrum radio quasars (FSRQs) with the parameters of both redshift and gamma-ray photon spectral index (Γ γ ) is compiled from the Fourth Catalog of Active Galactic Nuclei Data Release 2 from the Fermi Large Area Telescope (LAT). The multiwavelength data of the sample sources are downloaded from the Space Science Data Center, and then matched to the corresponding gamma-ray data from the Fermi-LAT Fourth Source Catalog Data Release 2. The synchrotron radiation peak frequency and Compton dominance (CD) parameters of the sources are obtained by using a log-parabolic model to fit the average-state multiwavelength spectral energy distribution. A support vector machine in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:msub> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>γ</mml:mi> </mml:mrow> </mml:msub> </mml:math> –Γ γ frame is utilized to delineate the optimal boundary between FSRQs and LBL sources. The 1 σ position of the Gaussian fitting on the histograms of the Γ γ , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:msubsup> <mml:mi>ν</mml:mi> <mml:mi>peak</mml:mi> <mml:mi>syn</mml:mi> </mml:msubsup> </mml:math> , and CD parameter distributions are also introduced. With this criterion, 25 FSRQ candidates are selected from LBL sample sources. The optical spectral identification result confirms that 8 out of 13 candidate sources available with the optical spectral data exhibit the relationship of EW &gt; 5 Å.