  The nebula powered by the Vela pulsar is one of the best examples of an
evolved pulsar wind nebula, allowing to access the particle injection history
and the interaction with the supernova ejecta. We report on the INTEGRAL
discovery of extended emission above 18 keV from the Vela nebula. The northern
side has no known counterparts and it appears larger and more significant than
the southern one, which is in turn partially coincident with the cocoon, the
soft X-ray and TeV filament towards the center of the remnant. We also present
the spectrum of the Vela nebula in the 18-400 keV energy range as measured by
IBIS/ISGRI and SPI on board the INTEGRAL satellite. The apparent discrepancy
between IBIS/ISGRI, SPI, and previous measurements is understood in terms of
point spread function, supporting the hypothesis of a nebula more diffuse than
previously thought. A break at ~25 keV is found in the spectrum within 6' from
the pulsar after including the Suzaku XIS data. Interpreted as a cooling break,
this points out that the inner nebula is composed by electrons injected in the
last ~2000 years. Broad-band modeling also implies a magnetic field higher than
10 microGauss in this region. Finally, we discuss the nature of the northern
emission, which might be due to fresh particles injected after the passage of
the reverse shock.
