The Jet‐Disk Connection and Blazar Unification

We discuss the relation between the power carried by relativistic jets andthe nuclear power provided by accretion, for a group of blazars including FSRQsand BL Lac objects. They are characterized by good quality broad band X-raydata provided by the Beppo SAX satellite. The jet powers are estimated usingphysical parameters determined from uniformly modelling their spectral energydistributions (SEDs). Our analysis indicates that for Flat Spectrum RadioQuasars the total jet power is of the same order as the accretion power. Wesuggest that blazar jets are likely powered by energy extraction from a rapidlyspinning black hole through the magnetic field provided by the accretion disk.FSRQs must have large BH masses (10^8 - 10^9 solar masses) and high, nearEddington accretion rates. For BL Lac objects the jet luminosity is larger thanthe disk luminosity. This can be understood within the same scenario if BL Lacobjects have masses similar to FSRQ but accrete at largely subcritical rates,whereby the accretion disk radiates inefficiently. Thus the ``unification'' ofthe two classes into a single blazar population, previously proposed on thebasis of a spectral sequence governed by luminosity, finds a physical basis.Comment: 27 pages, 3 figures, ApJ in pres