A collection of images of lensed quasars from various sources.
Included are images from Maidanak Observatory
(ivo://org.gavo.dc/maidanak/res/rawframes/siap), Apache Point
Observatory, from the MiNDSTEp project
(ivo://org.gavo.dc/danish/red/q), and from the Liverpool Robotic
Telescope (ivo://org.gavo.dc/liverpool/res/rawframes/q).
This collection includes optical monitorings of gravitationally lensed
quasars. The frames can be used to make light curves of quasar images
and field objects. From quasar light curves, one may measure time
delays and flux ratios, analyse variability and chromaticity, etc.
These direct analyses/measurements are basic tools for different
astrophysical studies, e.g., expansion rate of the Universe, mechanism
of intrinsic variability in quasars, accretion disk structure,
supermassive black holes, dark halos of galaxies (dust, collapsed dark
matter, smoothly distributed dark matter,...)
This service queries the catalog of images from the LOFAR Two-metre
Sky Survey First Data Release (LoTSS-DR1). This data release contains
images and catalogs that characterise the low-frequency radio emission
in the region of the HETDEX Spring Field (right ascension 10h45m00s
to15h30m00s and declination 45◦00′00′′ to 57◦00′00′′). A total of
325,694 radio sources are detected in a region covering 424 square
degrees. The maps have a median sensitivity of 71 uJy/beam and a
resolution of 6 arcsec. Optical counterparts for 71% of the radio
sources have been identified and where possible photometric redshifts
for these sources have been derived.
This service provides cutouts from the images of the LOFAR Two-metre
Sky Survey First Data Release (LoTSS-DR1). This data release contains
images and catalogs that characterise the low-frequency radio emission
in the region of the HETDEX Spring Field (right ascension 10h45m00s
to15h30m00s and declination 45◦00′00′′ to 57◦00′00′′). A total of
325,694 radio sources are detected in a region covering 424 square
degrees. The maps have a median sensitivity of 71 uJy/beam and a
resolution of 6 arcsec. Optical counterparts for 71% of the radio
sources have been identified and where possible photometric redshifts
for these sources have been derived.
In this data release from the ongoing LOw-Frequency ARray (LOFAR)
Two-metre Sky Survey (LoTSS) we present 120-168 MHz images covering
27% of the northern sky. Our coverage is split into two regions
centred at approximately 12h45m +44°30′ and 1h00m +28°00′ and spanning
4178 and 1457 square degrees respectively. The images were derived
from 3,451 hrs (7.6 PB) of LOFAR High Band Antenna data which were
corrected for the direction-independent instrumental properties as
well as direction-dependent ionospheric distortions during extensive,
but fully automated, data processing. A catalogue of 4,395,448 radio
sources is derived from our total intensity (Stokes I) maps, where the
majority of these have never been detected at radio wavelengths
before. At 6′′ resolution, our full bandwidth Stokes I continuum maps
with a central frequency of 144 MHz have: a median rms sensitivity of
83 μ Jy/beam; a flux density scale accuracy of approximately 10%; an
astrometric accuracy of 0.2′′; and we estimate the point-source
completeness to be 90% at a peak brightness of 0.8 mJy/beam. By
creating three 16 MHz bandwidth images across the band we are able to
measure the in-band spectral index of many sources, albeit the error
on the derived spectral index is > ±0.2 which is a consequence of our
flux-density scale accuracy and small fractional bandwidth. Our
circular polarisation (Stokes V) 20′′ resolution 120-168 MHz continuum
images have a median rms sensitivity of 95 μ Jy/beam, and we estimate
a Stokes I to Stokes V leakage of 0.056%. Our linear polarisation
(Stokes Q and Stokes U) image cubes consist of 480 97.6 kHz wide
planes and have a median rms sensitivity per plane of 10.8mJy/beam at
4′ and 2.2mJy/beam at 20′′; we estimate the Stokes I to Stokes Q/U
leakage to be approximately 0.2%. Here we characterise and publicly
release our Stokes I, Q, U and V images in addition to the calibrated
uv-data to facilitate the thorough scientific exploitation of this
unique dataset. This service queries the Stokes I continuum mosaic
images.
This service queries the catalog of images from the LOFAR HBA Tier-1
preliminary data release (LoTSS-PDR). This data release contains
images and catalogs that characterise the low-frequency radio emission
in the region of the HETDEX Spring Field. In excess of 40,000 sources
are detected in the images that cover an area of over 350 square
degrees, have a resolution of 25 arcsec, and typical noise levels of
less than 0.5 mJy/beam.
This service provides cutouts from the images of the LOFAR HBA Tier-1
preliminary data release (LoTSS-PDR). This data release contains
images and catalogs that characterise the low-frequency radio emission
in the region of the HETDEX Spring Field. In excess of 40,000 sources
are detected in the images that cover an area of over 350 square
degrees, have a resolution of 25 arcsec, and typical noise levels of
less than 0.5 mJy/beam.
Reduced frames of lensed quasar observations from Maidanak
Observatory. See the referenceURL for details on the reduction
procedure and calibration data.
