出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：We present the SED of three BL Lac objects with the peak of their synchrotron emission at very
low (≃ 1013 Hz) frequency, using ground-based radio (5 GHz) and optical-NIR data, UV and
X-ray data from Swift satellite. A log-parabolic fit was applied to the data around the peak region,
joined to a power-law in the radio. The sources showed a large flux variability, an increase of
the peak frequency and a flattening of the spectral shape at higher fluxes. A comparison of the
(log)shifts of the synchrotron peak and flux level of these LBL sources with that of an HBL one
(Mrk 421) indicates that the same physical mechanism originates the flux variability of these
objects, despite the large difference in peak frequency, and therefore physical parameters of the
jets.
