898 research outputs found
Photospheric Emission in the Joint GBM and Konus Prompt Spectra of GRB 120323A
GRB 120323A is a very intense short Gamma Ray Burst (GRB) detected
simultaneously during its prompt gamma-ray emission phase with the Gamma-ray
Burst Monitor (GBM) on board the Fermi Gamma-ray Space Telescope and the Konus
experiment on board the Wind satellite. GBM and Konus operate in the keV--MeV
regime, however, the GBM range is broader both toward the low and the high
parts of the gamma-ray spectrum. Analysis of such bright events provide a
unique opportunity to check the consistency of the data analysis as well as
cross-calibrate the two instruments. We performed time-integrated and coarse
time-resolved spectral analysis of GRB 120323A prompt emission. We conclude
that the analyses of GBM and Konus data are only consistent when using a
double-hump spectral shape for both data sets; in contrast, the single-hump of
the empirical Band function, traditionally used to fit GRB prompt emission
spectra, leads to significant discrepancies between GBM and Konus analysis
results. Our two-hump model is a combination of a thermal-like and a
non-thermal component. We interpret the first component as a natural
manifestation of the jet photospheric emission.Comment: 7 pages of article (3 figures and 1 table) + 3 pages of Appendix (3
figures). Submitted to ApJ on 2017 March 2
Anisotropies in the Diffuse Gamma-Ray Background Measured by the Fermi LAT
The contribution of unresolved sources to the diffuse gamma-ray background could induce anisotropies in this emission on small angular scales. We analyze the angular power spectrum of the diffuse emission measured by the Fermi LAT at Galactic latitudes absolute value of b > 30 deg in four energy bins spanning 1 to 50 GeV. At multipoles l >= 155, corresponding to angular scales approx 99.99% CL in the 1-2 GeV, 2- 5 GeV, and 5- 10 GeV energy bins, and at > 99% CL at 10-50 GeV. Within each energy bin the measured angular power takes approximately the same value at all multipoles l >= 155, suggesting that it originates from the contribution of one or more unclustered source populations. The amplitude of the angular power normalized to the mean intensity in each energy bin is consistent with a constant value at all energies, C(sub p) / (I)(exp 2) = 9.05 +/- 0.84 x 10(exp -6) sr, while the energy dependence of C(sub p) is consistent with the anisotropy arising from one or more source populations with power-law photon spectra with spectral index Gamma (sub s) = 2.40 +/- 0.07. We discuss the implications of the measured angular power for gamma-ray source populations that may provide a contribution to the diffuse gamma-ray background
Baker Street Wonderpass: evaluation of improvement works
Summary:
Baker Street Quarter Partnership identified the pedestrian subway under the Marylebone Road as an area that many of its members would like to see improved. Researchers from the Policy Studies Institute were commissioned to provide an impartial evaluation of improvement works that were carried out to transform the subway into the āBaker Street Wonderpassā.
The views of users were assessed through an online survey of Baker Street Quarter members (June 2015), pedestrian counting and face-to-face surveys both before the improvement works (July 2015) and after the Wonderpass had opened (February 2016). The pre-works surveys took place in July 2015, with 206 subway usersā answering a total of 12 questions. The post-works surveys took place in February 2016 with 163
subway users answering a total of 15 questions. The survey was supplemented by āvox-popā interviews.
Pedestrian counts before and after the improvement works show a very large increase in pedestrian traffic after the improvement works were completed. After the improvement works, morning usage increased by 153.8%, afternoon usage increasing by 27.8%, and evening usage increasing by 70.8%.
Survey results showed a substantial improvement in userās satisfaction with the lighting, cleanliness, overall appearance, safety, signage and visibility of the subway. The redevelopment of the subway and the opening of the Wonderpass have been a clear success. 83.9% of users said that the subway was āmuch betterā, and 98.4% of users said that they thought the subway was ābetterā or āmuch betterā after the improvement works.
Overall, the investment in the Marylebone Road underpass has greatly improved usage levels and user perceptions of the subway and some users stated that they used the subway solely to see the renovations and new displays. While users previously complained about the cleanliness, lighting and appearance of the subway, by February 2016 it has been successfully transformed into a much safer, cleaner, and more desirable āWonderpassā to cross Marylebon
Evidence for a Photospheric Component in the Prompt Emission of the Short GRB120323A and its Effects on the GRB Hardness-Luminosity Relation
The short GRB 120323A had the highest flux ever detected with the Fermi/GBM.
Here we study its remarkable spectral properties and their evolution using two
spectral models: (i) a single emission component scenario, where the spectrum
is modeled by the empirical Band function, and (ii) a two component scenario,
where thermal (Planck-like) emission is observed simultaneously with a
non-thermal component (a Band function). We find that the latter model fits the
integrated burst spectrum significantly better than the former, and that their
respective spectral parameters are dramatically different: when fit with a Band
function only, the Epeak of the event is unusually soft for a short GRB, while
adding a thermal component leads to more typical short GRB values. Our
time-resolved spectral analysis produces similar results. We argue here that
the two-component model is the preferred interpretation for GRB 120323A, based
on: (i) the values and evolution of the Band function parameters of the two
component scenario, which are more typical for a short GRB, and (ii) the
appearance in the data of a significant hardness-intensity correlation,
commonly found in GRBs, when we employee two-component model fits; the
correlation is non-existent in the Band-only fits. GRB 110721A, a long burst
with an intense photospheric emission, exhibits the exact same behavior. We
conclude that GRB 120323A has a strong photospheric emission contribution,
first time observed in a short GRB. Magnetic dissipation models are difficult
to reconcile with these results, which instead favor photospheric thermal
emission and fast cooling synchrotron radiation from internal shocks. Finally,
we derive a possibly universal hardness-luminosity relation in the source frame
using a larger set of GRBs L,i=(1.59+/-0.84).10^50 (Epeak,i)^(1.33+/-0.07)
erg/s), which could be used as a possible redshift estimator for cosmology.Comment: 27 pages, 13 figures, Accepted by ApJ (April, 7th 2013
A general scheme for modeling gamma-ray burst prompt emission
We describe a general method for modeling gamma-ray burst prompt emission. We
find that for the burst to be produced via the synchrotron process unphysical
conditions are required -- the distance of the source from the center of the
explosion () must be larger than cm and the source
Lorentz factor \gta 10^3; for such a high Lorentz factor the deceleration
radius () is less than even if the number density of particles
in the surrounding medium is as small as cm. The result,
, is in contradiction with the early x-ray and optical
afterglow data. The synchrotron-self-Compton (SSC) process fares much better.
There is a large solution space for a typical GRB prompt emission to be
produced via the SSC process. The prompt optical emission accompanying the
burst is found to be very bright (\lta 14 mag; for ) in the SSC
model, which exceeds the observed flux (or upper limit) for most GRBs.
Continuous acceleration of electrons can significantly reduce the optical flux
and bring it down to the observed limits. (Abridged)Comment: Published in MNRAS Jan 2008, 56 page
Development of a Moderated Online Intervention to Treat Social Anxiety in First-Episode Psychosis.
Background: It is well established that social anxiety disorder (SAD) is a significant clinical problem for individuals with a psychotic disorder. Comorbid social anxiety in individuals with psychosis has been associated with poorer premorbid functioning, increased depression, and a reduced quality of life. Cognitive behavior therapy (CBT) is recommended for people with psychosis as a first-line psychological treatment; however, its focus and evaluation primarily revolves around reducing psychotic symptoms and not necessarily targeting comorbid social anxiety symptoms. We developed a novel online social cognitive behavioral intervention (entitled EMBRACE) specifically designed to treat social anxiety symptoms in first episode psychosis (FEP). Methods: The key clinical and engagement features of the intervention were established through integrating evidence-based material derived from 1) CBT-based treatment models for SAD, 2) relevant literature findings related to psychosis and its clinical correlates (e.g., shame, social rank, and its relationship with social anxiety and paranoia), 3) feedback from youth focus groups in order to inform a user-centered intervention design, and 4) a highly multidisciplinary collaborative development approach to design therapy comics. Results: A detailed description of the final version of the 12-week online social intervention to treat social anxiety in FEP is presented. Conclusion: The EMBRACE intervention was designed to provide young people with the necessary skills and confidence to overcome social anxiety within a supportive, safe online space. By design, it allows young people the opportunity to practice their newly learnt skills to connect with others and in doing so, learn to embrace their true authentic selves
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