Determination of the properties of the central engine in microlensed QSOs

Abstract

Abstract. We study a recently observed gravitational microlensing peak in the V-band light curve of Q2237+0305A using a relatively simple physical model, but one that is highly consistent with the data (the best-fit reduced χ 2 is very close to 1). The source quasar is assumed to be a Newtonian geometrically-thin and optically-thick accretion disk. The disk has an arbitrary orientation, and both blackbody and greybody emission spectra are considered. When the electron-photon scattering plays a role, the greybody spectrum will be a simplified version of the exact one. In our model, the microlensing variability results from the source crossing a caustic straight line. The main goal of our work is to estimate the black hole mass and the mass accretion rate in QSO 2237+0305 as well as to discuss the power and the weakness of the technique, some possible improvements, and future prospects from multifrequency monitoring of new microlensing peaks. We also put into perspective the new methodology and the results on the central engine in QSO 2237+0305. From the fitted microlensing parameters and reasonable dynamical/cosmological constraints, it is concluded that QSO 2237+0305 harbours a central massive black hole: 10 7 M < M < 6 × 10 8 M . While the information about the central dark mass is very interesting, the mass accretion rate is not so well constrained. The typical values of the disk luminosity/Eddington luminosity ratio are in the (1 − 20)ε range, where ε ≤ 1 is the emissivity relative to a blackbody and the highest L/L Edd ratio corresponds to the largest deflector motion. Therefore, in order to verify L/L Edd ≤ 1, a relatively small projected peculiar motion of the lens galaxy and a greybody emission seem to be favored.

Accurate photometric light curves of the lensed components of Q2237+0305 derived with an optimal image subtraction technique: Evidence for microlensing in image A

“…By applying this method to the V light curve of the lensed component A in the Einstein Cross, Lee et al (2005) have found that a torus source model may easily account for the observed light curve of component A, especially for the double peak present in the GLITP data. So far, Shalyapin et al (2002) and Goicoechea et al (2003) have also investigated this observed HAE in terms of a Newtonian geometrically thin and optically thick accretion disk. They used the same GLITP data, but the results derived from the PSF fitting photometry, not those obtained by the ISIS image subtraction technique presented in this paper.…”

Limits on the transverse velocity of the lensing galaxy in Q2237+0305 from the lack of strong microlensing variability

“…2. It is clear that whereas components A and C show a small but significant variability (see Shalyapin et al 2002 andGoicoechea et al 2003, for the interpretation of the variation in the component A as the peak of a high-magnification event), images B and D remain relative flat, showing no signs of strong microlensing during the monitoring period. As the expected time delays between the images are short (≤1 day, see Schneider et al 1988;Wambsganss & Paczyński 1994), intrinsic fluctuations would show up in all 4 images almost simultaneously.…”

Analytical Methods in Gravitational Microlensing

“…Nevertheless, it is convenient to have a representation of K cr in the form of expansion in powers of small parameter. Such an expansion can be fulfilled correctly after substitution of K cr into integral (36). On this way, starting from form (18), it is easy to show that to define K cr correctly, one must replace the term Θ(y 2 )(y 2 ) for any test function f (y).…”

“…On the other hand, a number of authors [4,16,[33][34][35][36][37][38][39] discussed delicate questions concerning determination a fine quasar structure from HAE. For example, the authors of [36] wrote that the GLITP data [28] on Q2237+0305 admit only accretion disc models (see also [4,39]). Obviously, the presence of an accretion disk in a central region of quasar is beyond any doubts, as well as the fact that the real appearance of the quasar core can be quite different from our simplified models.…”