Long-term monitoring of PKS 0537-441 with Fermi-LAT and multiwavelength
  observations
  We report on multiwavelength observations of the blazar PKS 0537-441 (z =
0.896) obtained from microwaves through gamma rays by SMA, REM, ATOM, Swift and
Fermi during 2008 August-2010 April. Strong variability has been observed in
gamma rays, with two major flaring episodes (2009 July and 2010 March) and a
harder-when-brighter behaviour, quite common for FSRQs and
low-synchrotron-peaked BL Lacs, in 2010 March. In the same way the SED of the
source cannot be modelled by a simple synchrotron self-Compton model, as
opposed to many BL Lacs, but the addition of an external Compton component of
seed photons from a dust torus is needed. The 230 GHz light curve showed an
increase simultaneous with the gamma-ray one, indicating co-spatiality of the
mm and gamma-ray emission region likely at large distance from the central
engine. The low, average, and high activity SED of the source could be fit
changing only the electron distribution parameters, but two breaks in the
electron distribution are necessary. The ensuing extra spectral break, located
at NIR-optical frequencies, together with that in gamma rays seem to indicate a
common origin, most likely due to an intrinsic feature in the underlying
electron distribution. An overall correlation between the gamma-ray band with
the R-band and K-band has been observed with no significant time lag. On the
other hand, when inspecting the light curves on short time scales some
differences are evident. In particular, flaring activity has been detected in
NIR and optical bands with no evident gamma-ray counterparts in 2009 September
and November. Moderate variability has been observed in X-rays with no
correlation between flux and photon index. An increase of the detected X-ray
flux with no counter part at the other wavelengths has been observed in 2008
October, suggesting once more a complex correlation between the emission at
different energy bands.
