2019ApJ...885....8W

The spectral energy distribution of blazars around the synchrotron peak can be well described by the log-parabolic model that has three parameters: peak energy (E_p), peak luminosity (L_p), and the curvature parameter (b). It has been suggested that E_p shows relations with L_p and b in several sources, which can be used to constrain the physical properties of the emitting region and/or acceleration processes of the emitting particles. We systematically study the E_p-L_p and E_p-(1/b) relations for 14 BL Lac objects using the 3-25 keV RXTE/PCA and 0.3-10 keV Swift/XRT data. Most objects (9/14) exhibit positive E_p-L_p correlations, three sources show no correlation, and two sources display negative correlations. In addition, most targets (7/14) present no correlation between E_p and 1/b, five sources pose negative correlations, and two sources demonstrate positive correlations. 1ES 1959+650 displays two different E_p-L_p relations in 2002 and 2016. We also analyze E_p-L_p and E_p-(1/b) relations during flares lasting for several days. The E_p-L_p relation does not exhibit significant differences between flares, while the E_p-(1/b) relation varies from flare to flare. For the total sample, when L_p < 10⁴⁵ erg s^–1, there seems to be a positive E_p-L_p correlation. L_p and the slope of E_p-L_p relation present an anticorrelation, which indicates that the causes of spectral variations might be different between luminous and faint sources. E_p shows a positive correlation with the black hole mass. We discuss the implications of these results.