183 research outputs found
New database for a sample of optically bright lensed quasars in the northern hemisphere
In the framework of the Gravitational LENses and DArk MAtter (GLENDAMA)
project, we present a database of nine gravitationally lensed quasars (GLQs)
that have two or four images brighter than = 20 mag and are located in the
northern hemisphere. This new database consists of a rich variety of follow-up
observations included in the GLENDAMA global archive, which is publicly
available online and contains 6557 processed astronomical frames of the nine
lens systems over the period 19992016. In addition to the GLQs, our archive
also incorporates binary quasars, accretion-dominated radio-loud quasars, and
other objects, where about 50% of the non-GLQs were observed as part of a
campaign to identify GLQ candidates. Most observations of GLQs correspond to an
ongoing long-term macro-programme with 210 m telescopes at the Roque de los
Muchachos Observatory, and these data provide information on the distribution
of dark matter at all scales. We outline some previous results from the
database, and we additionally obtain new results for several GLQs that update
the potential of the tool for astrophysical studies.Comment: Accepted to A&A; 32 pages. Tables 4-6, 8-11 and 13-16 are only
available in electronic form at the CDS and
https://grupos.unican.es/glendama/LQLM_results.ht
Short-timescale Fluctuations in the Difference Light Curves of QSO 0957+561A,B: Microlensing or Noise?
From optical R band data of the double quasar QSO 0957+561A,B, we made two
new difference light curves (about 330 days of overlap between the time-shifted
light curve for the A image and the magnitude-shifted light curve for the B
image). We observed noisy behaviours around the zero line and no
short-timescale events (with a duration of months), where the term event refers
to a prominent feature that may be due to microlensing or another source of
variability. Only one event lasting two weeks and rising - 33 mmag was found.
Measured constraints on the possible microlensing variability can be used to
obtain information on the granularity of the dark matter in the main lensing
galaxy and the size of the source. In addition, one can also test the ability
of the observational noise to cause the rms averages and the local features of
the difference signals. We focused on this last issue. The combined
photometries were related to a process consisting of an intrinsic signal plus a
Gaussian observational noise. The intrinsic signal has been assumed to be
either a smooth function (polynomial) or a smooth function plus a stationary
noise process or a correlated stationary process. Using these three pictures
without microlensing, we derived some models totally consistent with the
observations. We finally discussed the sensitivity of our telescope (at Teide
Observatory) to several classes of microlensing variability.Comment: MNRAS, in press (LaTeX, 14 pages, 22 eps figures
Optical and near-infrared observations of the GRB 970616 error box
We report on near-infrared and optical observations of the GRB 970616 error
box and of the X-ray sources discovered by ASCA and ROSAT in the region. No
optical transient was found either within the IPN band or in the X-ray error
boxes, similarly to other bursts, and we suggest that either considerable
intrinsic absorption was present (like GRB 970828) or that the optical
transient displayed a very fast decline (like GRB 980326 and GRB 980519).Comment: 2 pages with one encapsulated PostScript figure included. Uses
Astronomy & Astrophysics LaTeX macros. Accepted for publication in Astronomy
& Astrophysics Supplement Serie
ContribuciĂłn al conocimiento de los plecĂłpteros (Insecta : Plecoptera) en la cuenca del Ebro
Se presentan los resultados de las capturas de ninfas de algunas especies de plecĂłpteros (Insecta : Plecoptera) en diferentes rĂos de la cuenca del Ebro (España). Se han clasificado seis especies (Dinocras cephalotes, Perla bipunctata, Perla grandis, Perla marginata, Perlodes microcephalus, Taeniopteryx schienemundi) de las que se da el mapa de presencia en la cuenca del Ebro. En general estas especies se encontraron en tramos de cabecera y rĂos de montaña, donde la calidad del agua fue alta. Los requerimientos ambientales especĂficos de estos taxones y su sensibilidad a la alteraciĂłn del medio pueden ser responablesde esta localizaciĂłn
A Large Brightness Enhancement of the QSO 0957+561 A Component
We report an increase of more than 0.2 mag in the optical brightness of the
leading image (A) of the gravitational lens Q0957+561, detected during the
09/2000 -- 06/2001 monitoring campaign (2001 observing season). The brightening
is similar to or even greater than the largest change ever detected during the
20 years of monitoring of this system. We discuss two different provisional
explanations to this event: intrinsic source variability or microlensing
(either short timescale microlensing or cessation of the historical
microlensing). An exhaustive photometric monitoring of Q0957+561 is needed
until summer of 2002 and during 2003 to discriminate between these
possibilities.Comment: 13 pages including 3 figures and 1 table. Accepted for publication in
ApJ Let
GLITP Optical Monitoring of QSO 0957+561: VR Light Curves and Variability
The GLITP collaboration observed the first gravitational lens system (QSO
0957+561) from 2000 February 3 to 2000 March 31. The daily VR observations were
made with the 2.56-m Nordic Optical Telescope at Roque de los Muchachos
Observatory, La Palma (Spain). We have derived detailed and robust VR light
curves of the two components Q0957+561A and Q0957+561B. In spite of the
excellent sampling rate, we have not found evidence in favor of true daily
variability. With respect to variability on time-scales of several weeks, we
measure VR gradients of about -0.8 mmag/day in Q0957+561A and + 0.3 mmag/day in
Q0957+561B. The gradients are very probably originated in the far source, thus
adopting this reasonable hypothesis (intrinsic variability), we compare them to
the expected gradients during the evolution of a compact supernova remnant at
the redshift of the source quasar. The starburst scenario is roughly consistent
with some former events, but the new gradients do not seem to be caused by
supernova remnant activity.Comment: MNRAS, in press (21 pages, 11 figures
Spectroscopy of the Lens Galaxy of Q0957+561A,B. Implications of a possible central massive dark object
We present new long-slit William Herschel Telescope spectroscopic
observations of the lens galaxy G1 associated with the double-imaged QSO
0957+561A,B. The obtained central stellar velocity dispersion, sigma_l = 310
+/- 20 km/s, is in reasonable agreement with other measurements of this
dynamical parameter. Using all updated measurements of the stellar velocity
dispersion in the internal region of the galaxy (at angular separations < 1".5)
and a simple isotropic model, we discuss the mass of a possible central massive
dark object. It is found that the data of Falco et al. (1997) suggest the
existence of an extremely massive object of (0.5-2.1) x 10E10/h M_\odot (80%
confidence level), whereas the inclusion of very recent data (Tonry & Franx
1998, and this paper) substantially changes the results: the compact central
mass must be 6 x10E9/h M_\odot at the 90% confidence level. We note that,
taking into account all the available dynamical data, a compact nucleus with a
mass of 10E9/h M_\odot (best fit) cannot be ruled out.Comment: 20 pages, 10 figures ApJ, in pres
New VR magnification ratios of QSO 0957+561
We present VR magnification ratios of QSO 0957+561, which are inferred from
the GLITP light curves of Q0957+561A and new frames taken with the 2.56m Nordic
Optical Telescope about 14 months after the GLITP monitoring. From two
photometric approaches and a reasonable range for the time delay in the system
(415-430 days), we do not obtain achromatic optical continuum ratios, but
ratios depending on the wavelength. These new measurements are consistent with
differential extinction in the lens galaxy, the Lyman limit system, the damped
Ly-alpha system, or the host galaxy of the QSO. The possible values for the
differential extinction and the ratio of total to selective extinction in the V
band are reasonable. Moreover, crude probability arguments suggest that the ray
paths of the two components cross a similar dusty environment, including a
network of compact dust clouds and compact dust voids. As an alternative (in
fact, the usual interpretation of the old ratios), we also try to explain the
new ratios as caused by gravitational microlensing in the deflector. From
magnification maps for each of the gravitationally lensed images, using
different fractions of the surface mass density represented by the microlenses,
as well as different sizes and profiles of the V-band and R-band sources,
several synthetic distributions of V-band and R-band ratios are derived. In
some gravitational scenarios, there is an apparent disagreement between the
observed pair of ratios and the simulated distributions. However, several
microlensing pictures work well. To decide between either extinction, or
microlensing, or a mixed scenario (extinction + microlensing), new
observational and interpretation efforts are required.Comment: PS and PDF versions are created from the LaTeX file and 5 EPS
figures, two additional figues (Figs. 6 and 7) in JPEG format, scheduled for
the ApJ 20 January 2005 issu
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