97,619 research outputs found
Deep Low-Frequency Radio Observations of the NOAO Bootes Field: I. Data Reduction and Catalog Construction
In this article we present deep, high-resolution radio interferometric
observations at 153 MHz to complement the extensively studied NOAO Bootes
field. We provide a description of the observations, data reduction and source
catalog construction. From our single pointing GMRT observation of ~12 hours we
obtain a high-resolution (26" x 22") image of ~11.3 square degrees, fully
covering the Bootes field region and beyond. The image has a central noise
level of ~1.0 mJy/beam, which rises to 2.0-2.5 mJy/beam at the field edge,
placing it amongst the deepest ~150 MHz surveys to date. The catalog of 598
extracted sources is estimated to be ~92 percent complete for >10 mJy sources,
while the estimated contamination with false detections is <1 percent. The low
RMS position uncertainty of 1.24" facilitates accurate matching against
catalogs at optical, infrared and other wavelengths. Differential source counts
are determined down to <~10 mJy. There is no evidence for flattening of the
counts towards lower flux densities as observed in deep radio surveys at higher
frequencies, suggesting that our catalog is dominated by the classical
radio-loud AGN population that explains the counts at higher flux densities.
Combination with available deep 1.4 GHz observations yields an accurate
determination of spectral indices for 417 sources down to the lowest 153 MHz
flux densities, of which 16 have ultra-steep spectra with spectral indices
below -1.3. We confirm that flattening of the median spectral index towards low
flux densities also occurs at this frequency. The detection fraction of the
radio sources in NIR Ks-band is found to drop with radio spectral index, which
is in agreement with the known correlation between spectral index and redshift
for brighter radio sources.Comment: 14 pages, 7 figures. Accepted for publication by A&A. Source catalog
will be available from CDS soo
Reviewing the Drivers and Challenges in RFID Implementation in the Pharmaceutical Supply Chain
Counterfeiting is a global phenomenon that poses a serious financial threat to the pharmaceutical industry and more importantly jeopardizes public safety and security. Different measures, including new laws and regulations, have been put in place to mitigate the threat and tighten control in the pharmaceuticals supply chain. However, it appears that the most promising countermeasure is track-and-trace technology such as electronic-pedigree (E-pedigree) with Radio Frequency Identification (RFID) technology. In this study we present a framework exploring the antecedents and consequences of RFID applications in the pharmaceutical supply chain. The framework proposes that counterfeiting and E-pedigree regulation will drive the implementation of RFID in the pharmaceutical supply chain, which in turn provides strategic and operational benefits that enable competitive advantage. Meanwhile, the implementation of RFID requires overcoming many operational, technical and financial challenges. The framework provides a springboard that future study can explore using empirical data
Where Will Consumers Find Privacy Protection From RFIDs?: A Case for Federal Legislation
With the birth of RFID technology, businesses gained the ability to tag products with practically invisible computer chips that relay information about consumer behavior to remote databases. Such tagging permits retailers and manufacturers to track the purchases, identities, and movements of their customers. In the absence of enforceable regulations, society risks being subjected to an unprecedented level of Orwellian surveillance. This iBrief addresses consumer privacy concerns stemming from the proliferation of RFID technology. It discusses why tort law, state legislation, FTC guidelines, and proposed regulations are insufficient methods to alleviate consumer privacy concerns and suggests amending various federal privacy laws, thereby prohibiting the underlying RFID tracking behavior
The Allen Telescope Array Pi GHz Sky Survey I. Survey Description and Static Catalog Results for the Bootes Field
The Pi GHz Sky Survey (PiGSS) is a key project of the Allen Telescope Array.
PiGSS is a 3.1 GHz survey of radio continuum emission in the extragalactic sky
with an emphasis on synoptic observations that measure the static and
time-variable properties of the sky. During the 2.5-year campaign, PiGSS will
twice observe ~250,000 radio sources in the 10,000 deg^2 region of the sky with
b > 30 deg to an rms sensitivity of ~1 mJy. Additionally, sub-regions of the
sky will be observed multiple times to characterize variability on time scales
of days to years. We present here observations of a 10 deg^2 region in the
Bootes constellation overlapping the NOAO Deep Wide Field Survey field. The
PiGSS image was constructed from 75 daily observations distributed over a
4-month period and has an rms flux density between 200 and 250 microJy. This
represents a deeper image by a factor of 4 to 8 than we will achieve over the
entire 10,000 deg^2. We provide flux densities, source sizes, and spectral
indices for the 425 sources detected in the image. We identify ~100$ new flat
spectrum radio sources; we project that when completed PiGSS will identify 10^4
flat spectrum sources. We identify one source that is a possible transient
radio source. This survey provides new limits on faint radio transients and
variables with characteristic durations of months.Comment: Accepted for publication in ApJ; revision submitted with extraneous
figure remove
The Allen Telescope Array Pi GHz Sky Survey I. Survey Description and Static Catalog Results for the Bootes Field
The Pi GHz Sky Survey (PiGSS) is a key project of the Allen Telescope Array.
PiGSS is a 3.1 GHz survey of radio continuum emission in the extragalactic sky
with an emphasis on synoptic observations that measure the static and
time-variable properties of the sky. During the 2.5-year campaign, PiGSS will
twice observe ~250,000 radio sources in the 10,000 deg^2 region of the sky with
b > 30 deg to an rms sensitivity of ~1 mJy. Additionally, sub-regions of the
sky will be observed multiple times to characterize variability on time scales
of days to years. We present here observations of a 10 deg^2 region in the
Bootes constellation overlapping the NOAO Deep Wide Field Survey field. The
PiGSS image was constructed from 75 daily observations distributed over a
4-month period and has an rms flux density between 200 and 250 microJy. This
represents a deeper image by a factor of 4 to 8 than we will achieve over the
entire 10,000 deg^2. We provide flux densities, source sizes, and spectral
indices for the 425 sources detected in the image. We identify ~100$ new flat
spectrum radio sources; we project that when completed PiGSS will identify 10^4
flat spectrum sources. We identify one source that is a possible transient
radio source. This survey provides new limits on faint radio transients and
variables with characteristic durations of months.Comment: Accepted for publication in ApJ; revision submitted with extraneous
figure remove
Radio Sources in the NCP Region Observed with the 21 Centimeter Array
We present a catalog of 624 radio sources detected around the North Celestial
Pole (NCP) with the 21 Centimeter Array (21CMA), a radio interferometer
dedicated to the statistical measurement of the epoch of reionization (EoR).
The data are taken from a 12 h observation made on 2013 April 13, with a
frequency coverage from 75 to 175 MHz and an angular resolution of ~ 4 arcmin.
The catalog includes flux densities at eight sub-bands across the 21CMA
bandwidth and provides the in-band spectral indices for the detected sources.
To reduce the complexity of interferometric imaging from the so-called "w" term
and ionospheric effects, the present analysis are restricted to the east-west
baselines within 1500 m only. The 624 radio sources are found within 5 degrees
around the NCP down to ~ 0.1 Jy. Our source counts are compared, and also
exhibit a good agreement, with deep low-frequency observations made recently
with the GMRT and MWA. In particular, for fainter radio sources below ~ 1 Jy,
we find a flattening trend of source counts towards lower frequencies. While
the thermal noise (~0.4 mJy) is well controlled to below the confusion limit,
the dynamical range (~10^4) and sensitivity of current 21CMA imaging is largely
limited by calibration and deconvolution errors, especially the grating lobes
of very bright sources, such as 3C061.1, in the NCP field which result from the
regular spacings of the 21CMA. We note that particular attention should be paid
to the extended sources, and their modeling and removals may constitute a large
technical challenge for current EoR experiments. Our analysis may serve as a
useful guide to design of next generation low-frequency interferometers like
the Square Kilometre Array.Comment: 16 pages, 21 figures, 7 tables, 1 machine readable table, accepted
for publication in Ap
J021659-044920: a relic giant radio galaxy at z ~ 1.3
We report the discovery of a relic Giant Radio Galaxy (GRG) J021659-044920 at
redshift that exhibits large-scale extended, nearly co-spatial,
radio and X-ray emission from radio lobes, but no detection of Active Galactic
Nuclei core, jets and hotspots. The total angular extent of the GRG at the
observed frame 0.325 GHz, using Giant Metrewave Radio Telescope observations is
found to be 2.4 arcmin, that corresponds to a total projected linear
size of 1.2 Mpc. The integrated radio spectrum between 0.240 and 1.4 GHz
shows high spectral curvature ( 1.19) with sharp steepening above
0.325 GHz, consistent with relic radio emission that is 8
10 yr old. The radio spectral index map between observed frame 0.325 and
1.4~GHz for the two lobes varies from 1.4 to 2.5 with the steepening trend from
outer-end to inner-end, indicating backflow of plasma in the lobes. The
extended X-ray emission characterized by an absorbed power-law with photon
index 1.86 favours inverse-Compton scattering of the Cosmic Microwave
Background (ICCMB) photons as the plausible origin. Using both X-ray and radio
fluxes under the assumption of ICCMB we estimate the magnetic field in the
lobes to be 3.3 G. The magnetic field estimate based on energy
equipartition is 3.5 G. Our work presents a case study of a rare
example of a GRG caught in dying phase in the distant Universe.Comment: 10 pages, 5 figures, 3 tables. Published in MNRAS. Corrected typos
and added a referenc
In search of dying radio sources in the local universe
Up till now very few dying sources were known, presumably because the dying
phase is short at centimeter wavelengths. We therefore have tried to improve
the statistics on sources that have ceased to be active, or are intermittently
active. The latter sources would partly consist of a fossil radio plasma left
over from an earlier phase of activity, plus a recently restarted core and
radio jets. Improving the statistics of dying sources will give us a better
handle on the evolution of radio sources, in particular the frequency and time
scales of radio activity. We have used the WENSS and NVSS surveys, in order to
find sources with steep spectral indices, associated with nearby elliptical
galaxies. In the cross correlation we presently used only unresolved sources,
with flux densities at 1.4 GHz larger than 10 mJy. The eleven candidates thus
obtained were observed with the VLA in various configurations, in order to
confirm the steepness of the spectra, and to check whether active structures
like flat-spectrum cores and jets are present, perhaps at low levels. We
estimated the duration of the active and relic phases by modelling the
integrated radio spectra using the standard models of spectral evolution. We
have found six dying sources and three restarted sources, while the remaining
two candidates remain unresolved also with the new VLA data and may be Compact
Steep Spectrum sources, with an unusually steep spectrum. The typical age of
the active phase, as derived by spectral fits, is in the range 10^7 - 10^8
years. For our sample of dying sources, the age of the relic phase is on
average shorter by an order of magnitude than the active phase.Comment: 21 pages, 17 figures, accepted by A&A. For a version with high
quality figures, see http://erg.ca.astro.it/preprints/dying2007
PKS 1502+106: a new and distant gamma-ray blazar in outburst discovered by the Fermi Large Area Telescope
The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope
discovered a rapid (about 5 days duration), high-energy (E >100 MeV) gamma-ray
outburst from a source identified with the blazar PKS 1502+106 (OR 103, S3
1502+10, z=1.839) starting on August 05, 2008 and followed by bright and
variable flux over the next few months. Results on the gamma-ray localization
and identification, as well as spectral and temporal behavior during the first
months of the Fermi all-sky survey are reported here in conjunction with a
multi-waveband characterization as a result of one of the first Fermi
multi-frequency campaigns. The campaign included a Swift ToO (followed up by
16-day observations on August 07-22, MJD 54685-54700), VLBA (within the MOJAVE
program), Owens Valley (OVRO) 40m, Effelsberg-100m, Metsahovi-14m, RATAN-600
and Kanata-Hiroshima radio/optical observations. Results from the analysis of
archival observations by INTEGRAL, XMM-Newton and Spitzer space telescopes are
reported for a more complete picture of this new gamma-ray blazar.Comment: 17 pages, 11 figures, accepted for The Astrophysical Journa
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