A. Eigenbrod

Microlensing variability in the gravitationally lensed quasar QSO 2237+0305 = the Einstein Cross. II. Energy profile of the accretion disk

We present the continuation of our long-term spectroscopic monitoring of the gravitationally lensed quasar QSO 2237 + 0305. We investigate the chromatic variations observed in the UV/optical continuum of both quasar images A and B, and compare them with numerical simulations to infer the energy profile of the quasar accretion disk. Our procedure combines the microlensing ray-shooting technique with Bayesian analysis, and derives probability distributions for the source sizes as a function of wavelength. We find that the effective caustic crossing timescale is 4.0 +/- 1.0 months. Using a robust prior on the effective transverse velocity, we find that the source responsible for the UV/optical continuum has an energy profile well reproduced by a power-law R proportional to lambda(zeta) with zeta = 1.2 +/- 0.3, where R is the source size responsible for the emission at wavelength.. This is the first accurate, model-independent determination of the energy profile of a quasar accretion disk on such small scales.

Zooming into the broad line region of the gravitationally lensed quasar QSO 2237 + 0305 ≡ the Einstein Cross - III. Determination of the size and structure of the C iv and C iii] emitting regions using microlensing

Aims. We aim to use microlensing taking place in the lensed quasar QSO 2237+0305 to study the structure of the broad line region (BLR) and measure the size of the region emitting the C-IV and C-III] lines.

COSMOGRAIL: The COSmological MOnitoring of GRAvItational Lenses. I. How to sample the light curves of gravitationally lensed quasars to measure accurate time delays

We use numerical simulations to test a broad range of plausible observational strategies designed to measure the time delay between the images of gravitationally lensed quasars. Artificial quasar light curves are created along with Monte-Carlo simulations in order to determine the best temporal sampling to adopt when monitoring the photometric variations of systems with time delays between 5 and 120 days, i.e., always shorter than the visibility window across the year. Few and realistic assumptions are necessary on the quasar photometric variations (peak-to-peak amplitude and time-scale of the variations) and on the accuracy of the individual photometric points. The output of the simulations is the (statistical) relative error made on the time delay measurement, as a function of 1- the object visibility over the year; 2- the temporal sampling of the light curves; and 3- the time delay. Also investigated is the effect of long term microlensing variations which must be below the 5% level (either intrinsically or by subtraction) if the goal is to measure time delays with an accuracy of 1-2%. However, while microlensing increases the random error on the time delay, it does not significantly increase the systematic error, which is always a factor 5 to 10 smaller than the random error. Finally, it is shown that, when the time delay is comparable to the visibility window of the object, a logarithmic sampling can significantly improve the time delay determination. All results are presented in the form of compact plots to be used to optimize the observational strategy of future monitoring programs.

Microlensing variability in the gravitationally lensed quasar QSO 2237+0305 ≡ the Einstein Cross I. Spectrophotometric monitoring with the VLT

We present the results of the first long-term (2.2 years) spectroscopic monitoring of a gravitationally lensed quasar, namely the Einstein Cross QSO 2237+0305. The goal of this paper is to present the observational facts to be compared in follow-up papers with theoretical models to constrain the inner structure of the source quasar.We present the results of the first long-term (2.2 years) spectroscopic monitoring of a gravitationally lensed quasar, namely the Einstein Cross Q2237+0305. We spatially deconvolve deep VLT/FORS1 spectra to accurately separate the spectrum of the lensing galaxy from the spectra of the quasar images. Accurate cross-calibration of the observations at 31 epochs from October 2004 to December 2006 is carried out using foreground stars observed simultaneously with the quasar. The quasar spectra are further decomposed into a continuum component and several broad emission lines. We find prominent microlensing events in the quasar images A and B, while images C and D are almost quiescent on a timescale of a few months. The strongest variations are observed in the continuum, and their amplitude is larger in the blue than in the red, consistent with microlensing of an accretion disk. Variations in the intensity and profile of the broad emission lines are also reported, most prominently in the wings of the CIII] and in the center of the CIV emission lines. During a strong microlensing episode observed in quasar image A, the broad component of the CIII] is more magnified than the narrow component. In addition, the emission lines with higher ionization potentials are more magnified than the lines with lower ionization potentials, consistent with the stratification of the broad line region (BLR) infered from reverberation mapping observations.

GRB 050509b: the elusive optical/nIR/mm afterglow of a short-duration GRB

We present multiwavelength (optical/near infrared/millimetre) observations of a short duration gamma-ray burst detected by Swift (GRB 050509b) collected between 0 seconds and ~18.8 days after the event. No optical, near infrared or millimetre emission has been detected in spite of the well localised X-ray afterglow, confirming the elusiveness of the short duration events. We also discuss the possibility of the burst being located in a cluster of galaxies at

Spectroscopy of extended Lyα envelopes around z = 4.5 quasars

z = 0.225

Red giants in open clusters - XI. Membership, duplicity, and structure of NGC 2477

or beyond. In the former case, the spectral energy distribution of the neighbouring, potential host galaxy, favours a system harbouring an evolved dominant stellar population (age ~360 Myr), unlike most long duration GRB host galaxies observed so far, i.e. thus giving support to a compact binary merger origin. Any underlying supernova that could be associated with this particular event should have been at least 3 magnitudes fainter than the type Ib/c SN 1998bw and 2.3 mag fainter than a typical type Ia SN.

Redshifts and lens profile for the double quasar QJ 0158-4325

What are the frequency, shape, kinematics, and luminosity of Ly alpha envelopes surrounding radio-quiet quasars at high redshift, and is the luminosity of these envelopes related to that of the quasar or not? As a first step towards answering these questions, we have searched for Ly alpha envelopes around six radio-quiet quasars at z similar to 4.5, using deep spectra taken with the FORS2 spectrograph attached to the UT1 of the Very Large Telescope (VLT). Using the multi-slit mode allows us to observe several point spread function stars simultaneously with the quasar, and to remove the point-like emission from the quasar, unveiling the faint underlying Ly alpha envelope with unprecedented depth. An envelope is detected around four of the six quasars, which suggests that these envelopes are very frequent. Their diameter varies in the range 26 less than or similar to d less than or similar to 64 kpc, their surface brightness in the range 3 x 10(-19) less than or similar to mu less than or similar to 2 x 10(-17) erg s(-1) cm(-2) arcsec(-2), and their luminosity in the range 10(42) less than or similar to L(Ly alpha) less than or similar to 1044 erg s(-1). Their shape may be strongly asymmetric. The Ly alpha emission line full width at half maximum (FWHM) is 900 < FWHM < 2200 km s-1 and its luminosity correlates with that of the broad line region (BLR) of the quasar, with the notable exception of BR2237-0607, the brightest object in our sample. The same holds for the relation between the envelope Ly alpha luminosity and the ionizing luminosity of the quasar. While the deep slit spectroscopy presented in this paper is very efficient at detecting very faint Ly alpha envelopes, narrow-band imaging is now needed to measure accurately their spatial extent, radial luminosity profile, and total luminosity. These observables are crucial to help us discriminate between the three possible radiation processes responsible for the envelope emission: (i) cold accretion, (ii) fluorescence induced by the quasar, and (iii) scattering of the BLR photons by cool gas.

Microlensing variability in the gravitationally lensed quasar QSO

New, accurate radial velocities and photoelectric

2237+0305 \equiv

{\it UBV}