EXTENDED SCATTERING ENVELOPE IN THE Q2237+0305 QUASAR

Abstract

Purpose: Studying the accretion disc structure in the Q2237+0305 gravitationally lensed quasar in optical wavelengths; estimation of parameters of the matter accretion regime onto a central black hole. Design/methodology/approach: Measuring the time delays between the quasar brightness variations in two spectral ranges allows to obtain direct estimates of distances between the quasar’s zones, which radiate in the selected wavelengths (the reverberation mapping method). Findings: New estimates of the time delays between the Q2237+0305 light curves in the R and V spectral bands have been obtained from the observations of 2004, as well as more accurate estimates for the light curves of the 2005 season reported earlier. The time delay value averaged over the two years is ΔtR-V ≈ 6.7 ± 2.4 days in the observer’s coordinate system, or Δt̃R-V ≈ 2.49 ± 0.9 days in the rest frame. With this delay, a distance between the accretion disk annular zones responsible for the radiation in V and R is RR-RV = Δt̃R-V · c ≈ 6.46·1015 sm. This indicates an accretion disk size far exceeding that one predicted by the standard thin accretion disc model by Shakura and Sunyaev. In this work, a suggestion is checked that thus large disk size can be a consequence of a super-critical (super-Eddington) accretion regime considered in the classical work by Shakura and Sunyaev, where the supercritical accretion regime has been shown to results in formation of an extended optically thick scattering envelope on the disk periphery. Conclusions: Analytical expressions for the radius and temperature of such an envelope derived by Shakura and Sunyaev have been used in this work to calculate the RR and RV envelope dimensions in the R and V spectral bands expected from the super-critical accretion regime scenario in the Q2237+0305 quasar. The calculations have been made for three values of the black hole mass covering the whole range of the existing estimates for Q2237+0305, from MВH = 2·108 Mʘ to MВH = 20·108 Mʘ. The accretion rate was assumed to be ṁ = 17. The calculated envelope radii in spectral bands R and V are well consistent with the inter-band time delay value of 2.49 days obtained in the present work from the data of observations. Thus, it can be argued that the black hole in the Q2237+0305 quasar is accreting the matter in a moderately super-critical regime, which results in creating an extended optically thick scattering envelope, and this is just in this envelope that the reverberation responses examined in this work arise. Parameter α for the black hole- (efficiency of the angular momentum transport) is varying within 0.005 0.006 minimal mass, and from 0.029 to 0.033 for the maximal one, while parameter A (ratio of the energy losses in Compton scattering to those in free-free transitions) is within 50 to 100.

Keywords

• quasar
• black hole
• accretion disk
• reverberation mapping