Preheated advection-dominated accretion flow

Myeong Gu Park, Jeremiah P. Ostriker

Research output: Contribution to journalArticlepeer-review

38 Scopus citations

Abstract

The advection-dominated accretion flow (ADAF) has been quite successful in explaining a wide variety of accretion-powered astronomical sources. The physical characteristics of ADAF complement the classical thin disk flow quite nicely, and extensive work has been done on it. However, all high-temperature accretion solutions including ADAF are physically thick, so outgoing radiation interacts with the incoming flow. Thus, ADAF solutions share as much or more resemblance with classical spherical accretion flows as with disk flows. This interaction, which has been neglected by most authors, is primarily through the Compton heating process that will typically limit the steady solutions to L ≲ 10-2LEdd, where LEdd is the Eddington luminosity. We examine this interaction for the popular ADAF case, but similar conclusions, we expect, would apply for other high-temperature, geometrically thick disks as well. We study the global thermal nature of the flow, with special consideration given to various cooling and, especially, preheating by Comptonizing hot photons produced at smaller radii. We find that without allowance for Compton preheating a very restricted domain of ADAF solution is permitted and with Compton preheating included a new high-temperature PADAF branch appears in the solution space. In the absence of preheating, high-temperature flows do not exist when the mass accretion rate ṁ ≡ Ṁc2/LEdd ≳ 10-1.5. Below this mass accretion rate, a roughly conical region around the hole cannot sustain high-temperature ions and electrons for all flows having ṁ ≳ 10-4, which may lead to a funnel possibly filled with a tenuous hot outgoing wind. If the flow starts at large radii with the usual equilibrium temperature ∼104 K, the critical mass accretion rate is much lower, ṁ ∼ 10-3.7, above which level no self-consistent ADAF (without preheating) can exist. However, above this critical mass accretion rate, the flow can be self-consistently maintained at high temperature if Compton preheating is considered. These solutions constitute a new branch of solutions as in spherical accretion flows. High-temperature PADAF flows can exist above the critical mass accretion rate in addition to the usual cold thin disk solutions. We also find solutions where the flow near the equatorial plane accretes normally while the flow near the pole is overheated by Compton preheating, possibly becoming a polar wind, solutions which we designate WADAF.

Original languageEnglish
Pages (from-to)100-117
Number of pages18
JournalAstrophysical Journal
Volume549
Issue number1 PART 1
DOIs
StatePublished - 1 Mar 2001

Keywords

  • Accretion, accretion disks
  • Black hole physics
  • Quasars: general
  • X-rays: general

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