2 research outputs found
The dark halo of the main lens galaxy in QSO 0957+561
We present an analysis of infrared/optical/ultraviolet spectra of the two
images of the first gravitationally lensed quasar Q0957+561A, B. The Hubble
Space Telescope observations of Q0957+561A and Q0957+561B are separated in time
by the known time delay in this system, so we can directly deduce the flux
ratios. These flux ratios of images lead to important information on the dark
halo of the main lens galaxy (a giant elliptical at redshift z = 0.36). Our
measurements for the continuum are in good agreement with extinction in the
elliptical galaxy and a small fraction of mass in collapsed objects (no need
for gravitational microlensing). From the continuum and emission line ratios,
we also show evidence in favour of the existence of a network of compact dusty
clouds.Comment: 5 pages, 2 figures + 1 table, accepted for publication in MNRAS
Letters (more details at http://grupos.unican.es/glendama/
Around the Clock Observations of the Q0957+561 A,B Gravitationally Lensed Quasar II: Results for the second observing season
We report on an observing campaign in March 2001 to monitor the brightness of
the later arriving Q0957+561 B image in order to compare with the previously
published brightness observations of the (first arriving) A image. The 12
participating observatories provided 3543 image frames which we have analyzed
for brightness fluctuations. From our classical methods for time delay
determination, we find a 417.09 +/- 0.07 day time delay which should be free of
effects due to incomplete sampling. During the campaign period, the quasar
brightness was relatively constant and only small fluctuations were found; we
compare the structure function for the new data with structure function
estimates for the 1995--6 epoch, and show that the structure function is
statistically non-stationary. We also examine the data for any evidence of
correlated fluctuations at zero lag. We discuss the limits to our ability to
measure the cosmological time delay if the quasar's emitting surface is time
resolved, as seems likely.Comment: AAS LaTeX, 5 PostScript figure