PKS 2005-489 at VHE: Four Years of Monitoring with HESS and Simultaneous
  Multi-wavelength Observations
  VHE observations of PKS 2005-489 were made with HESS from 2004 through 2007,
together with three simultaneous multi-wavelength campaigns performed with
XMM-Newton and RXTE in 2004 and 2005. A strong VHE signal, ~17sigma total, is
detected during the four years of HESS observations (90.3 hrs live time). The
integral flux above the average analysis threshold of 400 GeV is ~3% of the
Crab and varies weakly on time-scales from days to years. At X-ray energies the
flux is observed to vary by more than an order of magnitude between 2004 and
2005. Strong changes in the X-ray spectrum (DeltaGamma~0.7) are also observed,
which appear to be mirrored in the VHE band. The SED of PKS 2005-489,
constructed for the first time with contemporaneous data on both humps, shows
significant evolution. The large flux variations in the X-ray band, coupled
with weak or no variations in the VHE band and a similar spectral behavior,
suggest the emergence of a new, separate, harder emission component in
September 2005.
