The BL Lac objects OQ 530 and S5 0716+714. Simultaneous observations in the X-rays, radio, optical and TeV bands

TL;DR

This study presents simultaneous multi-wavelength observations of two BL Lac objects, revealing their X-ray spectra are best described by a double power-law model consistent with synchrotron and inverse Compton emission, and interprets their spectral states within a unified blazar model.

Contribution

First simultaneous multi-band observations of OQ 530 and S5 0716+714, demonstrating spectral features and variability consistent with a homogeneous synchrotron and inverse Compton model.

Findings

X-ray spectra are better fitted by a double power-law model.

Spectral breaks at 0.3 and 1.5 keV indicate synchrotron and inverse Compton components.

Variability observed in S5 0716+714 supports the emission scenario.

Abstract

We present the results of the BeppoSAX observations of two BL Lacs, OQ 530 and S5 0716+714, as part of a ToO program for the simultaneous observation at radio, optical, X-ray and TeV energies. Both sources are detected in the LECS and MECS, with S5 0716+714 visible also in the PDS band, up to about 60 keV. The X-ray spectra of both sources are better fitted by a double power-law model, with a steep soft X-ray component flattening at harder energies, with breaks at 0.3 and 1.5 keV, respectively. The concave shape of the spectra in both objects is consistent with soft X-rays being produced by the synchrotron and harder X-rays by the inverse Compton processes. Also the X-ray variability properties confirm this scenario, in particular for S5 0716+714 our observation shows variations by about a factor 3 over one hour below 3 keV and no variability above. Their simultaneous broad band energy spectral distributions can be successfully interpreted within the frame of a homogeneous synchrotron and inverse Compton model, including a possible contribution from an external source of seed photons with the different spectral states of S5 0716+714 being reproduced by changing the injected power. The resulting parameters are fully consistent with the two sources being intermediate objects within the "sequence" scenario proposed for blazars.