Properties of radio spectral index for Fermi blazars
Abstract
<p indent="0mm">Taking the blazars in Fermi/LAT (large area telescope) 4FGL-DR3 as a sample, the radio energy spectrum (log<italic>f</italic><sub><italic>ν</italic></sub>-log<italic>ν</italic>) was obtained. According to the distribution trend of scattered points, the energy spectrum was fitted with the primary, quadratic, or cubic curves, and the parameters of the 2347 blazars energy spectrum and its fitting curve were obtained. The radio spectrum indices at 9 frequencies, such as 0.05, 0.1, 0.5, 1.4, 5, 8, 15, 50, and <sc>150 GHz,</sc> are given according to the fitting results. The variation in the average spectral index with frequency and the correlation between the synchrotron spectral curvature and the radio spectral index are discussed. The results indicate that (1) the average radio spectral index changes in the range of −0.1–1, and the spectral index changes with the smallest amplitude (0–0.2) in the range of <sc>1–50 GHz;</sc> (2) at the same frequency, the average spectral index differs among subclasses of blazars, and <inline-formula content-type="pic" id="INLINE43"><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mover accent="true" other="0"><mml:mrow other="0"><mml:msub other="0"><mml:mi other="0">α</mml:mi><mml:mi other="1">ν</mml:mi></mml:msub></mml:mrow><mml:mo other="1" stretchy="true">¯</mml:mo></mml:mover><mml:mo stretchy="false">(</mml:mo><mml:mtext>BL</mml:mtext><mml:mo stretchy="false">)</mml:mo><mml:mo>></mml:mo><mml:mover accent="true" other="0"><mml:mrow other="0"><mml:msub other="0"><mml:mi other="0">α</mml:mi><mml:mi other="1">ν</mml:mi></mml:msub></mml:mrow><mml:mo other="1" stretchy="true">¯</mml:mo></mml:mover><mml:mo stretchy="false">(</mml:mo><mml:mtext>FSRQ</mml:mtext><mml:mo stretchy="false">)</mml:mo></mml:mrow></mml:math></inline-formula> and <inline-formula content-type="pic" id="INLINE44"><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mover accent="true" other="0"><mml:mrow other="0"><mml:msub other="0"><mml:mi other="0">α</mml:mi><mml:mi other="1">ν</mml:mi></mml:msub></mml:mrow><mml:mo other="1" stretchy="true">¯</mml:mo></mml:mover><mml:mo stretchy="false">(</mml:mo><mml:mtext>HBL</mml:mtext><mml:mo stretchy="false">)</mml:mo><mml:mo>></mml:mo><mml:mover accent="true" other="0"><mml:mrow other="0"><mml:msub other="0"><mml:mi other="0">α</mml:mi><mml:mi other="1">ν</mml:mi></mml:msub></mml:mrow><mml:mo other="1" stretchy="true">¯</mml:mo></mml:mover><mml:mo stretchy="false">(</mml:mo><mml:mtext>FSRQ</mml:mtext><mml:mo stretchy="false">)</mml:mo><mml:mo>></mml:mo><mml:mover accent="true" other="0"><mml:mrow other="0"><mml:msub other="0"><mml:mi other="0">α</mml:mi><mml:mi other="1">ν</mml:mi></mml:msub></mml:mrow><mml:mo other="1" stretchy="true">¯</mml:mo></mml:mover><mml:mo stretchy="false">(</mml:mo><mml:mtext>LBL</mml:mtext><mml:mo stretchy="false">)</mml:mo></mml:mrow></mml:math></inline-formula>; (3) with increasing frequency, the average spectral index first decreases and then increases, showing an open upward parabola; (4) according to the distribution trend of scattered points, the radio spectrum can be divided into three types (Λ, V, and S), comprising inner and outer jet radiation, but the two components in the Λ- and V-type sources may differ; (5) the synchrotron spectral curvature positively correlates with the radio spectral index, and the effect of radio radiation on the synchrotron radiation spectra of Low synchrotron peak BL Lacs (LBL), flat spectrum radio quasars (FSRQs), and high synchrotron peak BL Lacs (HBL) decreases in turn.</p>
