2,433 research outputs found
A Synoptic, Multiwavelength Analysis of a Large Quasar Sample
We present variability and multi-wavelength photometric information for the
933 known quasars in the QUEST Variability Survey. These quasars are grouped
into variable and non-variable populations based on measured variability
confidence levels. In a time-limited synoptic survey, we detect an
anti-correlation between redshift and the likelihood of variability. Our
comparison of variability likelihood to radio, IR, and X-ray data is consistent
with earlier quasar studies. Using already-known quasars as a template, we
introduce a light curve morphology algorithm that provides an efficient method
for discriminating variable quasars from periodic variable objects in the
absence of spectroscopic information. The establishment of statistically robust
trends and efficient, non-spectroscopic selection algorithms will aid in quasar
identification and categorization in upcoming massive synoptic surveys.
Finally, we report on three interesting variable quasars, including variability
confirmation of the BL Lac candidate PKS 1222+037.Comment: AJ, accepted for publication 15 Dec 200
The 3-53 keV Spectrum of the Quasar 1508+5714: X-rays from z = 4.3
We present a high-quality X-ray spectrum in the 3--53 keV rest-frame band of
the radio-loud quasar 1508+5714, by far the brightest known X-ray source at z >
4. A simple power-law model with an absorption column density equal to the
Galactic value in the direction of the source provides an excellent and fully
adequate fit to the data; the measured power-law photon index Gamma = 1.42
(+0.13,-0.10). Upper limits to Fe K alpha line emission and Compton-reflection
components are derived. We offer evidence for both X-ray and radio variability
in this object and provide the first contemporaneous radio spectrum (alpha =
-0.25). The data are all consistent with a picture in which the emission from
this source is dominated by a relativistically beamed component in both the
X-ray and radio bands.Comment: 8 pages, TeX, 2 postscript figures; to appear in ApJ Letter
Optical monitoring of the z=4.40 quasar Q 2203+292
We report Cousins R-band monitoring of the high-redshift (z=4.40) radio quiet
quasar Q 2203+292 from May 1999 to October 2007. The quasar shows maximum
peak-to-peak light curve amplitude of ~0.3 mag during the time of our
monitoring, and ~0.9 mag when combined with older literature data. The rms of a
fit to the light curve with a constant is 0.08 mag and 0.2 mag, respectively.
The detected changes are at ~3-sigma level. The quasar was in a stable state
during the recent years and it might have undergone a brightening event in the
past. The structure function analysis concluded that the object shows
variability properties similar to those of the lower redshift quasars. We set a
lower limit to the Q 2203+292 broad line region mass of 0.3-0.4 M_odot.
Narrow-band imaging search for redshifted Ly_alpha from other emission line
objects at the same redshift shows no emission line objects in the quasar
vicinity.Comment: 9 pages, 8 figures, accepted for publication in MNRA
Navigating implementation dilemmas in technology-forcing policies: a comparative analysis of accelerated smart meter diffusion in the Netherlands, UK, Norway, and Portugal (2000-2019)
This paper addresses the implementation of technology-forcing policies in open-ended diffusion processes that involve companies and regulators as well as consumers and civil society actors. Mobilising insights from the societal embedding of technology framework and policy steering theories, we investigate two implementation dilemmas that relate to an overarching tension between flexibility (to enable technological learning and stakeholder engagement) and coordinated push (to focus actors and drive deployment): a) early or late formulation of initial targets, and b) technocratic or emergent-adaptive implementation styles. We investigate these dilemmas with four comparative case studies of smart electricity meters between 2000 to 2019, which diffused rapidly in the Netherlands, Norway, and Portugal, but decelerated in the UK. We relate these differences to policy choices, and identify two patterns for successful implementation of technology-forcing policies: a) start with early targets and a technocratic style, but make adjustments if there are substantial protests or technical problems, and b) start with an emergent-adaptive style and formulate and enforce targets later, once technical and social stabilisation has occurred
In-Flight Calibration of the Thermal Infrared Sensor (TIRS) on the Landsat Data Continuity Mission
Describe in-flight calibration for the Thermal Infrared Sensor (TIRS) (1) Overview of TIRS (2) On-orbit radiometric calibration (2a) Onboard calibrator (2b) Terrestrial sites (3) On-orbit geometric and spatial calibratio
Land and cryosphere products from Suomi NPP VIIRS: overview and status
[1] The Visible Infrared Imaging Radiometer Suite (VIIRS) instrument was launched in October 2011 as part of the Suomi National Polar-Orbiting Partnership (S-NPP). The VIIRS instrument was designed to improve upon the capabilities of the operational Advanced Very High Resolution Radiometer and provide observation continuity with NASA's Earth Observing System's Moderate Resolution Imaging Spectroradiometer (MODIS). Since the VIIRS first-light images were received in November 2011, NASA- and NOAA-funded scientists have been working to evaluate the instrument performance and generate land and cryosphere products to meet the needs of the NOAA operational users and the NASA science community. NOAA's focus has been on refining a suite of operational products known as Environmental Data Records (EDRs), which were developed according to project specifications under the National Polar-Orbiting Environmental Satellite System. The NASA S-NPP Science Team has focused on evaluating the EDRs for science use, developing and testing additional products to meet science data needs, and providing MODIS data product continuity. This paper presents to-date findings of the NASA Science Team's evaluation of the VIIRS land and cryosphere EDRs, specifically Surface Reflectance, Land Surface Temperature, Surface Albedo, Vegetation Indices, Surface Type, Active Fires, Snow Cover, Ice Surface Temperature, and Sea Ice Characterization. The study concludes that, for MODIS data product continuity and earth system science, an enhanced suite of land and cryosphere products and associated data system capabilities are needed beyond the EDRs currently available from the VIIRS
Observation of a low-lying neutron-unbound state in 19C
Proton removal reactions from a secondary 22N beam were utilized to populate
unbound states in neutron-rich carbon isotopes. Neutrons were measured with the
Modular Neutron Array (MoNA) in coincidence with carbon fragments. A resonance
with a decay energy of 76(14) keV was observed in the system 18C+n
corresponding to a state in 19C at an excitation energy of 653(95)keV. This
resonance could correspond to the first 5/2+ state which was recently
speculated to be unbound in order to describe 1n and 2n removal cross section
measurements from 20C.Comment: accepted for publication in Nucl. Phys.
- …