75 research outputs found
The Power of Jets: New Clues from Radio Circular Polarization and X-rays
Jets are ubiquitous in accreting black holes. Often ignored, they may be a
major contributor to the emitted spectral energy distribution for sub-Eddington
black holes. For example, recent observations of radio-to-X-ray correlations
and broad band spectra of X-ray binaries in the low/hard state can be explained
by a significant synchrotron contribution from jets also to their IR-to-X-ray
spectrum as proposed by Markoff, Falcke, Fender 2001. This model can also
explain state-transitions from low/hard to high/soft states. Relativistic
beaming of the jet X-ray emission could lead to the appearance of seemingly
Super-Eddington X-rays sources in other galaxies. We show that a simple
population synthesis model of X-ray binaries with relativistic beaming can well
explain the currently found distribution of off-nucleus X-ray point sources in
nearby galaxies. Specifically we suggest that the so-called ultra-luminous
X-ray sources (ULXs, also IXOs) could well be relativistically beamed
microblazars. The same model that can be used to explain X-ray binaries also
fits Low-Luminosity AGN (LLAGN) and especially Sgr A* in the Galactic Center.
The recent detection of significant circular polarization in AGN radio cores,
ranging from bright quasars down to low-luminosity AGN like M81*, Sgr A* and
even X-ray binaries, now places additional new constraints on the matter
contents of such jets. The emerging picture are powerful jets with a mix of hot
and cold matter, a net magnetic flux, and a stable magnetic north pole.Comment: to appear in: ``Lighthouses of the Universe'', Springer Verlag, ESO
Astrophysics Symposia, Eds: R.Sunyaev, M.Gilfanov, E.Churazov, LaTex, 8
pages, 5 figures, also available at
http://www.mpifr-bonn.mpg.de/staff/hfalcke/publications.html#lighthouse
Multiplexed characterization of rationally designed promoter architectures deconstructs combinatorial logic for IPTG-inducible systems
A crucial step towards engineering biological systems is the ability to precisely tune the genetic response to environmental stimuli. In the case of Escherichia coli inducible promoters, our incomplete understanding of the relationship between sequence composition and gene expression hinders our ability to predictably control transcriptional responses. Here, we profile the expression dynamics of 8269 rationally designed, IPTG-inducible promoters that collectively explore the individual and combinatorial effects of RNA polymerase and LacI repressor binding site strengths. We then fit a statistical mechanics model to measured expression that accurately models gene expression and reveals properties of theoretically optimal inducible promoters. Furthermore, we characterize three alternative promoter architectures and show that repositioning binding sites within promoters influences the types of combinatorial effects observed between promoter elements. In total, this approach enables us to deconstruct relationships between inducible promoter elements and discover practical insights for engineering inducible promoters with desirable characteristics
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 Twenty-centimeter Survey - A 690-Square-Degree, 12-Epoch Radio Dataset - I: Catalog and Long-Duration Transient Statistics
We present the Allen Telescope Array Twenty-centimeter Survey (ATATS), a
multi-epoch (12 visits), 690 square degree radio image and catalog at 1.4GHz.
The survey is designed to detect rare, very bright transients as well as to
verify the capabilities of the ATA to form large mosaics. The combined image
using data from all 12 ATATS epochs has RMS noise sigma = 3.94mJy / beam and
dynamic range 180, with a circular beam of 150 arcsec FWHM. It contains 4408
sources to a limiting sensitivity of S = 20 mJy / beam. We compare the catalog
generated from this 12-epoch combined image to the NRAO VLA Sky Survey (NVSS),
a legacy survey at the same frequency, and find that we can measure source
positions to better than ~20 arcsec. For sources above the ATATS completeness
limit, the median flux density is 97% of the median value for matched NVSS
sources, indicative of an accurate overall flux calibration. We examine the
effects of source confusion due to the effects of differing resolution between
ATATS and NVSS on our ability to compare flux densities. We detect no
transients at flux densities greater than 40 mJy in comparison with NVSS, and
place a 2-sigma upper limit on the transient rate for such sources of 0.004 per
square degree. These results suggest that the > 1 Jy transients reported by
Matsumura et al. (2009) may not be true transients, but rather variable sources
at their flux density threshold.Comment: 41 pages, 19 figures, ApJ accepted; corrected minor typo in Table
Radio imaging of the Subaru/XMM-Newton Deep Field - III. Evolution of the radio luminosity function beyond z=1
We present spectroscopic and eleven-band photometric redshifts for galaxies
in the 100-uJy Subaru/XMM-Newton Deep Field radio source sample. We find good
agreement between our redshift distribution and that predicted by the SKA
Simulated Skies project. We find no correlation between K-band magnitude and
radio flux, but show that sources with 1.4-GHz flux densities below ~1mJy are
fainter in the near-infrared than brighter radio sources at the same redshift,
and we discuss the implications of this result for spectroscopically-incomplete
samples where the K-z relation has been used to estimate redshifts. We use the
infrared--radio correlation to separate our sample into radio-loud and
radio-quiet objects and show that only radio-loud hosts have spectral energy
distributions consistent with predominantly old stellar populations, although
the fraction of objects displaying such properties is a decreasing function of
radio luminosity. We calculate the 1.4-GHz radio luminosity function (RLF) in
redshift bins to z=4 and find that the space density of radio sources increases
with lookback time to z~2, with a more rapid increase for more powerful
sources. We demonstrate that radio-loud and radio-quiet sources of the same
radio luminosity evolve very differently. Radio-quiet sources display strong
evolution to z~2 while radio-loud AGNs below the break in the radio luminosity
function evolve more modestly and show hints of a decline in their space
density at z>1, with this decline occurring later for lower-luminosity objects.
If the radio luminosities of these sources are a function of their black hole
spins then slowly-rotating black holes must have a plentiful fuel supply for
longer, perhaps because they have yet to encounter the major merger that will
spin them up and use the remaining gas in a major burst of star formation.Comment: Accepted for publication in MNRAS: 36 pages, including 13 pages of
figures to appear online only. In memory of Stev
The Allen Telescope Array
The Allen Telescope Array, originally called the One Hectare Telescope (1hT) [1] will be a large array radio telescope whose novel characteristics will be a wide field of view (3.5 deg-GHz HPBW), continuous frequency coverage of 0.5 - 11 GHz, four dual-linear polarization output bands of 100 MHz each, four beams in each band, two 100 MHz spectral correlators for two of the bands, and hardware for RFI mitigation built in. Its scientific motivation is for deep SETI searches and, at the same time, a variety of other radio astronomy projects, including transient (e.g. pulsar) studies, HI mapping of the Milky Way and nearby galaxies, Zeeman studies of the galactic magnetic field in a number of transitions, mapping of long chain molecules in molecular clouds, mapping of the decrement in the cosmic background radiation toward galaxy clusters, and observation of HI absorption toward quasars at redshifts up to z=2. The array is planned for 350 6.1-meter dishes giving a physical collecting area of about 10,000 square meters. The large number of components reduces the price with economies of scale. The front end receiver is a single cryogenically cooled MIMIC Low Noise Amplifier covering the whole band. The feed is a wide-band log periodic feed of novel design, and the reflector system is an offset Gregorian for minimum sidelobes and spillover. All preliminary and critical design reviews have been completed. Three complete antennas with feeds and receivers are under test, and an array of 33 antennas is under construction at the Hat Creek Radio Observatory for the end of 2004. The present plan is to have a total of about 200 antennas completed by the summer of 2006 and the balance of the array finished before the end of the decade
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
Supporting People With Type 2 Diabetes in the Effective Use of Their Medicine Through Mobile Health Technology Integrated With Clinical Care to Reduce Cardiovascular Risk : Protocol for an Effectiveness and Cost-effectiveness Randomized Controlled Trial
Funding Information: The Support Through Mobile Messaging and Digital Health Technology for Diabetes research team acknowledges the support of the National Institute for Health Research (NIHR) through the Clinical Research Networks. AF, LT, and RR have received support from the NIHR Oxford Biomedical Research Centre. RH received support from the NIHR Collaboration for Leadership in Applied Health Research and Care and North Thames at Bart's Health National Health Service (NHS) Trust. The views expressed are those of the authors and not necessarily those of the NHS, the NIHR, or the Department of Health. This paper presents independent research funded by the NIHR under its Program Grants for Applied Research as part of a wider program of work (RP-PG-1214-20003). The authors thank the personnel of the University of Oxford Primary Care and Vaccines Clinical Trials Collaborative for providing support in the conduct of the trial.Peer reviewedPublisher PD
Forgotten Plotlanders: Learning from the survival of lost informal housing in the UK.
Colin Ward’s discourses on the arcadian landscape of ‘plotlander’ housing are unique documentations of the anarchistic birth, life, and death of the last informal housing communities in the UK. Today the forgotten history of ‘plotlander’ housing documented by Ward can be re-read in the context of both the apparently never-ending ‘housing crisis’ in the UK, and the increasing awareness of the potential value of learning from comparable informal housing from the Global South. This papers observations of a previously unknown and forgotten plotlander site offers a chance to begin a new conversation regarding the positive potential of informal and alternative housing models in the UK and wider Westernised world
The Allen Telescope Array
The Allen Telescope Array, originally called the One Hectare Telescope (1hT) [1] will be a large array radio telescope whose novel characteristics will be a wide field of view (3.5 deg-GHz HPBW), continuous frequency coverage of 0.5 - 11 GHz, four dual-linear polarization output bands of 100 MHz each, four beams in each band, two 100 MHz spectral correlators for two of the bands, and hardware for RFI mitigation built in. Its scientific motivation is for deep SETI searches and, at the same time, a variety of other radio astronomy projects, including transient (e.g. pulsar) studies, HI mapping of the Milky Way and nearby galaxies, Zeeman studies of the galactic magnetic field in a number of transitions, mapping of long chain molecules in molecular clouds, mapping of the decrement in the cosmic background radiation toward galaxy clusters, and observation of HI absorption toward quasars at redshifts up to z=2. The array is planned for 350 6.1-meter dishes giving a physical collecting area of about 10,000 square meters. The large number of components reduces the price with economies of scale. The front end receiver is a single cryogenically cooled MIMIC Low Noise Amplifier covering the whole band. The feed is a wide-band log periodic feed of novel design, and the reflector system is an offset Gregorian for minimum sidelobes and spillover. All preliminary and critical design reviews have been completed. Three complete antennas with feeds and receivers are under test, and an array of 33 antennas is under construction at the Hat Creek Radio Observatory for the end of 2004. The present plan is to have a total of about 200 antennas completed by the summer of 2006 and the balance of the array finished before the end of the decade
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