Jet efficiencies and black hole spins in jetted quasars

Abstract

The mechanisms responsible for the production of relativistic jets from supermassive black holes (SMBHs) accreting at near-Eddington rates are not well understood. Simple theoretical expectations indicate that SMBHs in quasars accrete via thin discs which should produce at most very weak jets. This is contradicted by observations of powerful jets in flat-spectrum radio quasars (FSRQs). We use gamma-ray luminosities observed with the Fermi Large Area Telescope as a proxy of the jet power for a population of 154 FSRQs. Assuming typical quasar accretion rates and using black hole (BH) mass measurements from a variety of methods, we find a mean jet production efficiency of about 10 per cent for FSRQs, with values as high as 222 per cent. We find that this is consistent with FSRQs hosting moderately thin, magnetically arrested accretion discs around rapidly spinning BHs. Modelling our observations using general relativistic magnetohydrodynamic (GRMHD) simulations of jets from thin discs, we find an average lower limit of a* = 0.59 for the SMBH spins of FSRQs, with tendency for the spins to decrease as the BH mass increases. Our results are consistent with the merger-driven evolution of SMBHs. 3 per cent of the sample cannot be explained by current GRMHD models of jet production from Kerr BHs due to the high efficiencies. Along the way, we find a correlation between BH masses and Lγ which may be an useful mass estimator in blazar gamma-ray studies.

Introducing the NEWHORIZON simulation: Galaxy properties with resolved internal dynamics across cosmic time

“…MBH spin evolution with MBH mass for all MBH at redshift z = 0.25 (black markers), and the spin evolution history with mass for the six most massive MBH (coloured lines). Shown for comparison are observations from Reynolds (2013; grey triangles) andSoares & Nemmen (2020; grey crosses). MBHs experience a fast initial spin growth phase followed by a more stochastic evolution.…”

Powerful Jets from Radiatively Efficient Disks, a Decades-Old Unresolved Problem in High Energy Astrophysics

“…Ref. [30] report that it drops from 0.098 to 6 × 10 −4 , which is 163 times smaller. The basic question here is whether or not the disk thickness that is compatible with jet energetics, is also compatible with the required radiative efficiency.…”

“…Using gamma-ray luminosity from the Fermi Large Area Telescope as a proxy for jet powers, and independent measurements of black hole mass, Ref. [30] produce the best fit correlation between jet power and black hole mass from observations of 154 FSRQs. The ideas are built on the work of [31] who uncovered a correlation between gamma-ray luminosity L γ and total blazar jet power P jet given by…”

“…Ref. [30] have explored the blazar subclass of radio quasars (flat spectrum radio quasars (FSRQs), attempting to fit observations with simulations of disks in the context of moderately thin disks (those of [25]). We will explore this in the next section but the basic conclusion is the need for some missing ingredient that allows for both large jet and disk efficiency.…”

“…Ref. [30] show that 97% of their FSRQ sample satisfies jet energetics as a function of black hole mass (Equation ( 3)) for moderately thin disks (H/R = 0.13). If the radiative efficiency in such moderately thin disks is insufficient to explain the quasar-like spectrum, the success of equation ( 3) to the sample becomes moot.…”