We present results from Chandra observations of NGC 5813 , the dominant central galaxy in a nearby galaxy group .
We focus on three main results .
1 ) The diffuse gas shows clear signatures from three distinct outbursts of the central AGN , with three pairs of roughly collinear cavities .
The inner two cavity pairs are associated with unambiguous elliptical shock fronts , with Mach numbers M \sim 1.7 and M \sim 1.5 for the inner and outer shocks , respectively .
2 ) The mean power of the two most recent outbursts differs by a factor of six , indicating that the mean jet power varies over long ( \sim 10 ^ { 7 } yr ) time scales .
3 ) The heating from the shocks alone is sufficient to balance radiative cooling of the gas within at least the central 10 kpc , allowing feedback to operate isotropically at small radii .