62 research outputs found
Radio Luminosities and Classificatory Criteria of BL Lacertae Objects
Using the sample of radio selected BL Lacertae objects (RBLs) and X-ray
selected BL Lacertae objects (XBLs) presented by Sambruna et al. (1996), we
calculated the luminosities of radio, optical and X-ray of each source and made
the statistical analysis among the luminosities at different wave-bands,
broad-band spectral indices from radio to X-ray () and peak
frequencies (). Our results are as follows: (i) there is a positive
correlation between radio luminosity and and a
negative correlation between and . High-energy peak BL Lacs
(HBLs) and low-energy peak BL Lacs (LBLs) can be distinguished very well, the
dividing lines are probably those of (erg/sec) and
(or )0.75 for - plot and
those of (erg/sec) and for the
- plot; (ii) there is a weak positive correlation between
optical luminosity and and a negatively weak
correlation between and ; (iii) there is no correlation
between X-ray luminosity and or between and
. From our analysis, we find that synchrotron radiation is the main
X-ray radiation mechanism for HBLs while inverse Compton scattering for LBLs.Comment: 9 pages, 3 figures. Submitted to A&
Testing the blazar spectral sequence: X-ray selected blazars
We present simultaneous optical and X-ray data from Swift for a sample of
FSRQs selected from the EMSS survey. We present also a complete analysis of
Swift and INTEGRAL data on 4 blazars recently discussed as possibly challenging
the trends of the "blazar spectral sequence". The SEDs of all these objects are
modelled in terms of a general theoretical scheme leading to an estimate of the
jets' physical parameters. Our results show that, in the case of the EMSS broad
line blazars, X-ray selection does not lead to find sources with synchrotron
peaks in the UV/X-ray range, as was the case for X-ray selected BL Lacs.
Instead, for a wide range of radio powers all the sources with broad emission
lines show similar SEDs, with synchrotron components peaking below the
optical/UV range. Of the remaining 4 "anomalous" blazars, two highly luminous
sources with broad lines, claimed to possibly emit synchrotron X-rays, are
shown to be better described with IC models for their X-ray emission. For one
source with weak emission lines (a BL Lac object) a synchrotron peak in the
soft X-ray range is confirmed, while for the fourth source, exhibiting lines
typical of NLSy1s, no evidence of X-ray emission from a relativistic jet is
found. We reexamine the original "blazar spectral sequence" and suggest that
the photon ambient, in which the particle acceleration and emission occur, is
likely the main factor determining the shape of the blazar SED.Comment: 11 figures and 6 tables. Accepted for publication in MNRA
Optical and radio variability of the BL Lac object AO 0235+16: a possible 5-6 year periodicity
New optical and radio data on the BL Lacertae object AO 0235+16 have been
collected in the last four years by a wide international collaboration, which
confirm the intense activity of this source. The optical data also include the
results of the Whole Earth Blazar Telescope (WEBT) first-light campaign
organized in November 1997. The optical spectrum is observed to basically
steepen when the source gets fainter. We have investigated the existence of
typical variability time scales and of possible correlations between the
optical and radio emissions by means of visual inspection, Discrete Correlation
Function analysis, and Discrete Fourier Transform technique. The major radio
outbursts are found to repeat quasi-regularly with a periodicity of about 5.7
years; this period is also in agreement with the occurrence of some of the
major optical outbursts, but not all of them.Comment: to be published in A&
CMB Telescopes and Optical Systems
The cosmic microwave background radiation (CMB) is now firmly established as
a fundamental and essential probe of the geometry, constituents, and birth of
the Universe. The CMB is a potent observable because it can be measured with
precision and accuracy. Just as importantly, theoretical models of the Universe
can predict the characteristics of the CMB to high accuracy, and those
predictions can be directly compared to observations. There are multiple
aspects associated with making a precise measurement. In this review, we focus
on optical components for the instrumentation used to measure the CMB
polarization and temperature anisotropy. We begin with an overview of general
considerations for CMB observations and discuss common concepts used in the
community. We next consider a variety of alternatives available for a designer
of a CMB telescope. Our discussion is guided by the ground and balloon-based
instruments that have been implemented over the years. In the same vein, we
compare the arc-minute resolution Atacama Cosmology Telescope (ACT) and the
South Pole Telescope (SPT). CMB interferometers are presented briefly. We
conclude with a comparison of the four CMB satellites, Relikt, COBE, WMAP, and
Planck, to demonstrate a remarkable evolution in design, sensitivity,
resolution, and complexity over the past thirty years.Comment: To appear in: Planets, Stars and Stellar Systems (PSSS), Volume 1:
Telescopes and Instrumentatio
Disentangling the synchrotron and Inverse Compton variability in the X-ray emission of the intermediate BL Lac object S5 0716+71
The possibility to detect simultaneously in the X-ray band the synchrotron
and Inverse Compton (IC)emission of intermediate BL Lac objects offers the
unique opportunity to study contemporaneously the low- and high-energy tails of
the electron distribution in the jets of these sources. We attempted to
disentangle the X-ray spectral variability properties of both the low- and
high-energy ends of the synchrotron and Inverse Compton emission of the
intermediate BL Lac object S5 0716+71. We carried out spectral, temporal and
cross-correlation analyses of the data from a long XMM-Newton pointing of S5
0716+71 and we compared our findings with previous results from past X-ray
observations. Strong variability was detected during the XMM exposure.Both the
synchrotron and Inverse Compton components were found to vary on time scales of
hours, implying a size of the emitting region of R\la 0.7\delta /(1+z)
light-hours. The synchrotron emission was discovered to become dominant during
episodes of flaring activity, following a harder-when-brighter trend. Tight
correlations were observed between variations in different energy bands. Upper
limits on time lags between the soft and hard X-ray light curves are of the
order of a few hundred seconds.Comment: 14 pages, 9 figures, 5 tables, A&A in press, minor corrections to
match the version to be publishe
Characterizing wave- and current- induced bottom shear stress : U.S. middle Atlantic continental shelf
This paper is not subject to U.S. copyright. The definitive version was published in Continental Shelf Research 52 (2013): 73-86, doi:10.1016/j.csr.2012.10.012.Waves and currents create bottom shear stress, a force at the seabed that influences sediment texture distribution, micro-topography, habitat, and anthropogenic use. This paper presents a methodology for assessing the magnitude, variability, and driving mechanisms of bottom stress and resultant sediment mobility on regional scales using numerical model output. The analysis was applied to the Middle Atlantic Bight (MAB), off the U.S. East Coast, and identified a tidally-dominated shallow region with relatively high stress southeast of Massachusetts over Nantucket Shoals, where sediment mobility thresholds are exceeded over 50% of the time; a coastal band extending offshore to about 30 m water depth dominated by waves, where mobility occurs more than 20% of the time; and a quiescent low stress region southeast of Long Island, approximately coincident with an area of fine-grained sediments called the âMud Patchâ. The regional high in stress and mobility over Nantucket Shoals supports the hypothesis that fine grain sediment winnowed away in this region maintains the Mud Patch to the southwest. The analysis identified waves as the driving mechanism for stress throughout most of the MAB, excluding Nantucket Shoals and sheltered coastal bays where tides dominate; however, the relative dominance of low-frequency events varied regionally, and increased southward toward Cape Hatteras. The correlation between wave stress and local wind stress was lowest in the central MAB, indicating a relatively high contribution of swell to bottom stress in this area, rather than locally generated waves. Accurate prediction of the wave energy spectrum was critical to produce good estimates of bottom shear stress, which was sensitive to energy in the long period waves.P.S. Dalyander was supported by the U.S. Geological Survey Mendenhall Research Fellowship Program
Recommended from our members
Current state of the evidence on community treatments for people with complex emotional needs: a scoping review
Background
Improving the quality of care in community settings for people with âComplex Emotional Needsâ (CENâour preferred working term for services for people with a âpersonality disorderâ diagnosis or comparable needs) is recognised internationally as a priority. Plans to improve care should be rooted as far as possible in evidence. We aimed to take stock of the current state of such evidence, and identify significant gaps through a scoping review of published investigations of outcomes of community-based psychosocial interventions designed for CEN.
Methods
We conducted a scoping review with systematic searches. We searched six bibliographic databases, including forward and backward citation searching, and reference searching of relevant systematic reviews. We included studies using quantitative methods to test for effects on any clinical, social, and functioning outcomes from community-based interventions for people with CEN. The final search was conducted in November 2020.
Results
We included 226 papers in all (210 studies). Little relevant literature was published before 2000. Since then, publications per year and sample sizes have gradually increased, but most studies are relatively small, including many pilot or uncontrolled studies. Most studies focus on symptom and self-harm outcomes of various forms of specialist psychotherapy: most result in outcomes better than from inactive controls and similar to other specialist psychotherapies. We found large evidence gaps. Adaptation and testing of therapies for significant groups (e.g. people with comorbid psychosis, bipolar disorder, post-traumatic stress disorder, or substance misuse; older and younger groups; parents) have for the most part only reached a feasibility testing stage. We found little evidence regarding interventions to improve social aspects of peopleâs lives, peer support, or ways of designing effective services.
Conclusions
Compared with other longer term mental health problems that significantly impair functioning, the evidence base on how to provide high quality care for people with CEN is very limited. There is good evidence that people with CEN can be helped when specialist therapies are available and when they are able to engage with them. However, a much more methodologically robust and substantial literature addressing a much wider range of research questions is urgently needed to optimise treatment and support across this group
- âŠ