682 research outputs found
The afterglow of GRB050709 and the nature of the short-hard gamma-ray bursts
The final chapter in the long-standing mystery of the gamma-ray bursts (GRBs)
centres on the origin of the short-hard class, suspected on theoretical grounds
to result from the coalescence of neutron star or black hole binary systems.
Numerous searches for the afterglows of short-hard bursts have been made,
galvanized by the revolution in our understanding of long-duration GRBs that
followed the discovery in 1997 of their broadband (X-ray, optical, and radio)
afterglow emission. Here we present the discovery of the X-ray afterglow of a
short-hard burst whose accurate position allows us to unambiguously associate
it with a star-forming galaxy at redshift z=0.160, and whose optical lightcurve
definitively excludes a supernova association. Together with results from three
other recent short-hard bursts, this suggests that short-hard bursts release
much less energy than the long-duration GRBs. Models requiring young stellar
populations, such as magnetars and collapsars, are ruled out, while coalescing
degenerate binaries remain the most promising progenitor candidates.Comment: Nature in press (Oct 6 issue). 23 pages, 4 figure
An HST Study of the Supernovae Accompanying GRB 040924 and GRB 041006
We present the results from a {\it Hubble Space Telescope/ACS} study of the
supernovae associated with gamma-ray bursts 040924 () and 041006
(). We find evidence that both GRBs were associated with a SN
1998bw-like supernova dimmed by and magnitudes,
respectively, making GRB 040924 the faintest GRB-associated SN ever detected.
We study the luminosity dispersion in GRB/XRF-associated SNe and compare to
local Type Ibc supernovae from the literature. We find significant overlap
between the two samples, suggesting that GRB/XRF-associated SNe are not
necessarily more luminous nor produce more Ni than local SNe. Based on
the current (limited) datasets, we find that the two samples may share a
similar Ni production mechanism.Comment: ApJ accepted (in press). Revised version. High-resolution figures
available at http://www.astro.caltech.edu/~ams/GRB-SNe.htm
Population inversion of a NAHS mixture adsorbed into a cylindrical pore
A cylindrical nanopore immersed in a non-additive hard sphere binary fluid is
studied by means of integral equation theories and Monte Carlo simulations. It
is found that at low and intermediate values of the bulk total number density
the more concentrated bulk species is preferentially absorbed by the pore, as
expected. However, further increments of the bulk number density lead to an
abrupt population inversion in the confined fluid and an entropy driven
prewetting transition at the outside wall of the pore. These phenomena are a
function of the pore size, the non-additivity parameter, the bulk number
density, and particles relative number fraction. We discuss our results in
relation to the phase separation in the bulk.Comment: 7 pages, 8 Figure
A comprehensive study of GRB 070125, a most energetic gamma ray burst
We present a comprehensive multiwavelength analysis of the bright, long
duration gamma-ray burst GRB 070125, comprised of observations in -ray,
X-ray, optical, millimeter and centimeter wavebands. Simultaneous fits to the
optical and X-ray light curves favor a break on day 3.78, which we interpret as
the jet break from a collimated outflow. Independent fits to optical and X-ray
bands give similar results in the optical bands but shift the jet break to
around day 10 in the X-ray light curve. We show that for the physical
parameters derived for GRB 070125, inverse Compton scattering effects are
important throughout the afterglow evolution. While inverse Compton scattering
does not affect radio and optical bands, it may be a promising candidate to
delay the jet break in the X-ray band. Radio light curves show rapid flux
variations, which are interpreted as due to interstellar scintillation, and are
used to derive an upper limit of cm on the radius of the
fireball in the lateral expansion phase of the jet. Radio light curves and
spectra suggest a high synchrotron self absorption frequency indicative of the
afterglow shock wave moving in a dense medium. Our broadband modeling favors a
constant density profile for the circumburst medium over a wind-like profile
(). However, keeping in mind the uncertainty of the parameters, it is
difficult to unambiguously distinguish between the two density profiles. Our
broadband fits suggest that \event is a burst with high radiative efficiency
().Comment: 50 pages, 33 figures, sty file included, Appeared in 20 Aug 2008
edition of Astrophysical Journa
A New Population of High-Redshift Short-Duration Gamma-Ray Bursts
The redshift distribution of the short-duration gamma-ray bursts (GRBs) is a crucial, but currently fragmentary, clue to the nature of their progenitors. Here we present optical observations of nine short GRBs obtained with Gemini, Magellan, and the Hubble Space Telescope. We detect the afterglows and host galaxies of two short bursts, and host galaxies for two additional bursts with known optical afterglow positions, and five with X-ray positions (âČ6" radius). In eight of the nine cases we find that the most probable host galaxies are faint, R â 23-26.5 mag, and are therefore starkly different from the first few short GRB hosts with R â 17-22 mag and z âČ 0.5. Indeed, we measure spectroscopic redshifts of z â 0.4-1.1 for the four brightest hosts. A comparison to large field galaxy samples, as well as the hosts of long GRBs and previous short GRBs, indicates that the fainter hosts likely reside at z âł 1. Our most conservative limit is that at least half of the five hosts without a known redshift reside at z > 0.7 (97% confidence level), suggesting that about 1/3 to 2/3 of all short GRBs originate at higher redshifts than previously determined. This has two important implications: (1) we constrain the acceptable age distributions to a wide lognormal (Ï âł 1) with Ï* ~ 4-8 Gyr, or to a power law, P(Ï)α Ï^n, with -1 âČ n âČ 0; and (2) the inferred isotropic energies, E_Îł,iso ~ 10^50-10^52 ergs, are significantly larger than ~10^48-10^49 ergs for the low-redshift, short GRBs, indicating a large spread in energy release or jet opening angles. Finally, we reiterate the importance of short GRBs as potential gravitational-wave sources and find a conservative detection rate with the advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) of ~2-6 yr^-1
Comparison of Solution and Crystal Structures of PreQ1 Riboswitch Reveals Calcium-Induced Changes in Conformation and Dynamics
Meditation Awareness Training for individuals with fibromyalgia syndrome: an interpretative phenomenological analysis of participants' experiences
Fibromyalgia syndrome (FMS) is a complex and poorly understood psychosomatic pain disorder. The illness has been the subject of controversy, both in terms of the alleged lack of interest and capability of the medical community to understand and support patients with FMS, and the burden that such individuals place upon economic and healthcare re- sources. Due to the lack of convincing data for the effectiveness of extant pharmacological and non-pharmacological FMS treatments, a recent direction in FMS research has been the empirical investigation of mindfulness and other meditation-based approaches. The present qualitative study explored whether following participation in a mindfulness-based intervention, patients with FMS report experiencing changes in (i) how they experience and relate to their illness and (ii) their attitudes towards societal participation, work and unemployment. Ten individuals with FMS were randomly selected from the intervention arm of a randomised controlled trial (RCT) evaluating the effectiveness of a mindfulness-based intervention known as Meditation Awareness Training (MAT) for the treatment of FMS. Transcripts of semi-structured interviews were analysed using Interpretative Phenomenological Analysis, a robust and rigorous qualitative methodology for analysing sub jective experiences. Five super-ordinate themes emerged from the dataset: (i) reservations about participating,(ii) improvements in psychosomatic well-being,(iii) spiritual growth,(iv) awareness of impermanence and (v) increased sense of citizenship. MAT was experienced as both an acceptable and accessible intervention by individuals with FMS, and participants reported experiencing improvements in psychosocial functioning as well as an increased sense of societal responsibility. MAT appears to have utility for treating FMS and for changing the attitudes of some individuals with FMS towards community engagement and societal contribution
The Impact of Adolescent Chronic Pain on Functioning: Disentangling the Complex Role of Anxiety
A number of adolescents with chronic pain have clinically significant disability across physical, social, and academic activities, and pain severity only explains a portion of the variance in functioning. Thus, it is important to identify therapeutic options to improve adolescentsâ functioning. In contrast to studies with adults with chronic pain, research in pediatric pain has not consistently found anxiety to be a good predictor of pain-related disability. The present study evaluated pain, anxiety, and functioning in 222 adolescents with chronic pain. Results indicated that pain was consistently and linearly related to disability across measures of physical and social functioning, school attendance, and physician visits. The relation between anxiety and functioning was complex; increased anxiety was related to poorer physical and social functioning and was related to fewer physician visits, although it was not associated with school attendance. Additional analyses revealed that anxiety serves to moderate the relation between pain and functioning. Specifically, at high anxiety, pain was not related to functioning, but at low anxiety pain consistently predicted disability. In other words, highly anxious adolescents were functioning poorly regardless of the level of pain. The moderating role of anxiety highlights a number of research and clinical possibilities to explore with adolescents with chronic pain-related disability. Data suggest that high anxiety is associated with poor functioning irrespective of pain intensity. At low anxiety, higher pain predicted greater disability. Anxiety is important to assess when investigating potential reasons for pain-related disability
A Spectacular Radio Flare from XRF 050416a at 40 days and Implications for the Nature of X-ray Flashes
We present detailed optical, near-infrared, and radio observations of the
X-ray flash 050416a obtained with Palomar and Siding Springs Observatories as
well as HST and the VLA, placing this event among the best-studied X-ray
flashes to date. In addition, we present an optical spectrum from Keck LRIS
from which we measure the redshift of the burst, z=0.6528. At this redshift the
isotropic-equivalent prompt energy release was about 10^51 erg, and using a
standard afterglow synchrotron model we find that the blastwave kinetic energy
is a factor of 10 larger, E_K,iso ~ 10^52 erg. The lack of an observed jet
break to t ~ 20 days indicates that the opening angle is larger than 7 deg and
the total beaming-corrected relativistic energy is larger than 10^50 erg. We
further show that the burst produced a strong radio flare at t ~ 40 days
accompanied by an observed flattening in the X-ray band which we attribute to
an abrupt circumburst density jump or an episode of energy injection (either
from a refreshed shock or off-axis ejecta). Late-time observations with HST
show evidence for an associated supernova with peak optical luminosity roughly
comparable to that of SN 1998bw. Next, we show that the host galaxy of XRF
050416a is actively forming stars at a rate of at least 2 M_solar per year with
a luminosity of L_B ~ 0.5L* and metallicity of Z ~ 0.2-0.8 Z_solar. Finally, we
discuss the nature of XRF 050416a in the context of short-hard gamma-ray bursts
and under the framework of off-axis and dirty fireball models for X-ray
flashes.Comment: ApJ in press (accepted version; 40 pages, 7 figures, 4 tables
The afterglow and elliptical host galaxy of the short gamma-ray burst GRB 050724
Despite a rich phenomenology, gamma-ray bursts (GRBs) are divided into two
classes based on their duration and spectral hardness -- the long-soft and the
short-hard bursts. The discovery of afterglow emission from long GRBs was a
watershed event, pinpointing their origin to star forming galaxies, and hence
the death of massive stars, and indicating an energy release of about 10^51
erg. While theoretical arguments suggest that short GRBs are produced in the
coalescence of binary compact objects (neutron stars or black holes), the
progenitors, energetics, and environments of these events remain elusive
despite recent localizations. Here we report the discovery of the first radio
afterglow from a short burst, GRB 050724, which unambiguously associates it
with an elliptical galaxy at a redshift, z=0.257. We show that the burst is
powered by the same relativistic fireball mechanism as long GRBs, with the
ejecta possibly collimated in jets, but that the total energy release is
10-1000 times smaller. More importantly, the nature of the host galaxy
demonstrates that short GRBs arise from an old (>1 Gyr) stellar population,
strengthening earlier suggestions, and providing support for coalescing compact
object binaries as the progenitors.Comment: Accepted to Nature; revisions include broad-band afterglow mode
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