Old Q0957+561 data & software:
► Simple FORTRAN programs to apply the d2 test (accurate and robust time delay measurements)
► Photos
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GRAVITATIONAL LENSES
INTERNATIONAL TIME PROJECT (GLITP) RESULTS
The GLITP data for QSO 2237+0305A-D in two optical bands (V and R) were derived from both a point-spread function (PSF) photometry and an image-subtraction (ISIS) photometry. A comparison (in terms of sampling, trends, errors,...) between the V-band GLITP records and the OGLE ones was also performed (details). The D component is flat on a long-timescale (time of sampling), and this indicates (apart from a conspiracy of the nature) that neither intrinsic nor microlensing long-timescale events are present in the faintest component. As there is no intrinsic variability (a long term), the GLITP data accurately trace the peak of a microlensing high magnification event (HME) in the A component, the wing of another HME in the C component, and two "flat" microlensing signals in the components B and D. Several GLITP members and collaborators hardly worked (and work) in several ways, and here, we present some results of the theoretical (interpretation) projects. More properly, the projects associated with the microlensing peak in the brightest component A and involving the GLUC group.
The structure of the compact source in QSO
2237+0305:
important advances and one doubt
important advances and one doubt
From the light curves of QSO 2237+0305A, we are deriving interesting results on the physical properties of the compact source in the quasar. As the observed microlensing peaks are highly asymmetric and correspond to a prominent fluctuation (observations by the OGLE team), they were associated with a microcaustic crossing event since were discovered. Considering that the peaks are caused by a microcaustic crossing, we obtained that the standard accretion disk (e.g., Shakura & Sunyaev 1973, A&A 24, 337) fits both the V-band and R-band observations with reduced chi-square values very close to 1 (Fig. 1). Moreover, using the standard disk model and a robust upper limit on the transverse galactic velocity (Wyithe et al. 1999, MNRAS 309, 261), it is also inferred that 90 per cent of the V-band and R-band luminosities are emitted from a region with radial size less than 1.2 × 10-2 pc (= 3.7 × 1016 cm, at 95% confidence level). Finally, the standard disk picture led to a relatively tight constraint on the dark mass in the heart of the quasar: it must be larger than 107 MSUN and smaller than 6 × 108 MSUN (Fig. 2). More details are included in the papers on the nature and size of the compact source, and the black hole mass and accretion rate.
As we see, the microcaustic crossing hypothesis lead to very reasonable results for the source structure, which are an "a posteriori" support for the initial hypothesis. However, do the microlensing peaks really correspond to a microcaustic crossing?, what is the probability of our "a priori" approach?, are there other kinds of events with significant probability?. Kochanek (2004, ApJ, in press) has studied the source trajectories that agree with the whole V-band OGLE light curves for QSO 2237+0305A-D. His results for the origin of the prominent feature in the A component are a bit disappointing, because the best trajectories in terms of chi-square cross over simple microfolds (i.e., they correspond to microcaustic crossings), but other relatively good trajectories pass through complex magnification zones (see Figs. 12-16 in Kochanek 2004). Several issues suggest that the Kochanek's conclusions about the nature of the microlensing peaks are preliminary ones, and at present, the GLUC group is carrying out a deep study about the origin of the OGLE-GLITP/QSO 2237+0305A event.
We and our collaborators are also working on a new scheme to study the nature of the central engine in a microlensed QSO. The compact emission regions could have different sizes in different optical wavelengths, and our framework permits to obtain the source size ratios when a special HME (e.g., a caustic crossing event, a two--dimensional maximum crossing event and so on) is produced in one of the QSO components. To infer the source size ratios, only cross-correlations between the brightness records in different optical bands are required. While the deconvolution method gets a richer information (1D intrinsic luminosity profiles), the new approach is free of the technical problems with complex inversion procedures. Using simulations related to VR GLITP data of QSO 2237+0305A, we are testing the ability of the scheme in the determination of the visible-to-red ratio q = RV/RR. Our synthetic light curves indicate that extremely accurate fluxes (with a few µJy uncertainties, or equivalently, a few milli-magnitudes errors) can lead to about 10% measurements of q. Taking into account the errors in the fluxes of QSO 2237+0305A from a normal ground-based telescope (of about 10 µJy, or equivalently, 10 mmag), it must be possible the achievement of smaller errors from the current superb-telescopes, and thus, an accurate determination of q.
QSO 2237+0305
OPTICAL MONITORING: Some years ago, the GLIP collaboration followed-up the VR variability of the four components of this quad, and the UC group was involved in different studies. Even today, the GLITP-OGLE event in the brightest component (A) represents the strongest evidence for an accretion disc (source) crossing a microcaustic (related to microlenses in the lensing galaxy): Gil-Merino et al. 2006, Udalski et al. 2006, Koptelova & Shimanovskaya 2005, Bogdanov & Cherepashchuk 2005, Goicoechea et al. 2003, Shalyapin et al. 2002, Alcalde et al. 2002. In the middle 2007, we started a new monitoring programme with the 2.0 m Liverpool Robotic Telescope, so that the global multiwavelength records of this emblematic system (OGLE curves in the V band, COSMOGRAIL monitoring, Maidanak brightness records, our curves, etc) will form a very rich database for different kinds of analyses.