The spectral energy distribution of AO 0235+164 during two active optical phases

Abstract

We investigate the spectral variability of the source AO 0235+164 during two active phases. We find that the peak frequencies in the Spectral Energy Distributions (SED) are variable with time within a range of an order of magnitude, which does not cause the source to make a transition from Low-energy peaked BL Lac objects to High-energy peaked BL Lac objects. The correlation of peak frequency and peak flux either for an individual outburst or the combination of several individual outbursts is significant. Our research reveals that in many physical properties AO 0235+164 is much closer to flat-spectrum radio quasars, rather than to High-energy peaked BL Lacs, which in turn implies that Comptonization of external radiation may play quite an important role in γ-ray emission. There are indications that the observed variability may be due to superposition of intrinsic and propagation effects, which is in agreement with the conclusion of Kraus et al. ([CITE]). We also explore the possible origin of the two outbursts and suggest that intrinsic variability, not including the shock effect, probably accounts for the two outbursts.