2,211 research outputs found
A Note on Frame Dragging
The measurement of spin effects in general relativity has recently taken
centre stage with the successfully launched Gravity Probe B experiment coming
toward an end, coupled with recently reported measurements using laser ranging.
Many accounts of these experiments have been in terms of frame-dragging. We
point out that this terminology has given rise to much confusion and that a
better description is in terms of spin-orbit and spin-spin effects. In
particular, we point out that the de Sitter precession (which has been mesured
to a high accuracy) is also a frame-dragging effect and provides an accurate
benchmark measurement of spin-orbit effects which GPB needs to emulate
The Giant Flare of December 27, 2004 from SGR 1806-20
The giant flare of December 27, 2004 from SGR 1806-20 represents one of the
most extraordinary events captured in over three decades of monitoring the
gamma-ray sky. One measure of the intensity of the main peak is its effect on
X- and gamma-ray instruments. RHESSI, an instrument designed to study the
brightest solar flares, was completely saturated for ~0.5 s following the start
of the main peak. A fortuitous alignment of SGR 1806-20 near the Sun at the
time of the giant flare, however, allowed RHESSI a unique view of the giant
flare event, including the precursor, the main peak decay, and the pulsed tail.
Since RHESSI was saturated during the main peak, we augment these observations
with Wind and RHESSI particle detector data in order to reconstruct the main
peak as well. Here we present detailed spectral analysis and evolution of the
giant flare. We report the novel detection of a relatively soft fast peak just
milliseconds before the main peak, whose timescale and sizescale indicate a
magnetospheric origin. We present the novel detection of emission extending up
to 17 MeV immediately following the main peak, perhaps revealing a
highly-extended corona driven by the hyper-Eddington luminosities. The spectral
evolution and pulse evolution during the tail are presented, demonstrating
significant magnetospheric twist and evolution during this phase. Blackbody
radii are derived for every stage of the flare, which show remarkable agreement
despite the range of luminosities and temperatures covered. Finally, we place
significant upper limits on afterglow emission in the hundreds of seconds
following the giant flare.Comment: 32 pages, 14 figures, submitted to Ap
RHESSI Spectral Fits of Swift GRBs
One of the challenges of the Swift era has been accurately determining Epeak
for the prompt GRB emission. RHESSI, which is sensitive from 30 keV to 17 MeV,
can extend spectral coverage above the Swift-BAT bandpass. Using the public
Swift data, we present results of joint spectral fits for 26 bursts co-observed
by RHESSI and Swift-BAT through May 2007. We compare these fits to estimates of
Epeak which rely on BAT data alone. A Bayesian Epeak estimator gives better
correspondence with our measured results than an estimator relying on
correlations with the Swift power law indices.Comment: 4 pages, 1 figure. To appear in the proceedings of Gamma Ray Bursts
2007, Santa Fe, New Mexico, November 5-9 200
The Compton hump and variable blue wing in the extreme low-flux NuSTAR observations of 1H0707-495
The Narrow-line Seyfert I galaxy, 1H0707-495, has been well observed in the
0.3-10 keV band, revealing a dramatic drop in flux in the iron K alpha band, a
strong soft excess, and short timescale reverberation lags associated with
these spectral features. In this paper, we present the first results of a deep
250 ks NuSTAR observation of 1H0707-495, which includes the first sensitive
observations above 10 keV. Even though the NuSTAR observations caught the
source in an extreme low-flux state, the Compton hump is still significantly
detected. NuSTAR, with its high effective area above 7 keV, clearly detects the
drop in flux in the iron K alpha band, and by comparing these observations with
archival XMM-Newton observations, we find that the energy of this drop
increases with increasing flux. We discuss possible explanations for this, the
most likely of which is that the drop in flux is the blue wing of the
relativistically broadened iron K alpha emission line. When the flux is low,
the coronal source height is low, thus enhancing the most gravitationally
redshifted emission.Comment: Submitted to MNRAS, comments are welcome. 9 pages, 5 figure
Observations of MCG-5-23-16 with Suzaku, XMM-Newton and NuSTAR: Disk tomography and Compton hump reverberation
MCG-5-23-16 is one of the first AGN where relativistic reverberation in the
iron K line originating in the vicinity of the supermassive black hole was
found, based on a short XMM-Newton observation. In this work, we present the
results from long X-ray observations using Suzaku, XMM-Newton and NuSTAR
designed to map the emission region using X-ray reverberation. A relativistic
iron line is detected in the lag spectra on three different time-scales,
allowing the emission from different regions around the black hole to be
separated. Using NuSTAR coverage of energies above 10 keV reveals a lag between
these energies and the primary continuum, which is detected for the first time
in an AGN. This lag is a result of the Compton reflection hump responding to
changes in the primary source in a manner similar to the response of the
relativistic iron K line.Comment: Accepted for Publication in Ap
Testing Lorentz Invariance with GRB021206
Since the discovery of the cosmological origin of GRBs there has been growing
interest in using these transient events to probe the quantum gravity energy
scale in the range 10^16--10^19 GeV, up to the Planck mass scale. This energy
scale can manifest itself through a measurable modification in the
electromagnetic radiation dispersion relation for high energy photons
originating from cosmological distances. We have used data from the gamma-ray
burst (GRB) of 6 December 2002 (GRB021206) to place an upper bound on the
energy dispersion of the speed of light. The limit on the first-order quantum
gravity effects derived from this single GRB indicate that the energy scale is
in excess of 1.8x10^17 GeV. We discuss a program to further constrain the
energy scale by systematically studying such GRBs.Comment: 10 pages, 3 figures, accepted for publication in ApJ
Impact of Technology on Meat Safety
Innovations and new technologies tend to create apprehension among consumers who are not familiar with the technologies and their mode of action. This case currently exists regarding the use of hormones, antibiotics and other feed additives in livestock production. The purpose of this fact sheet is to familiarize consumers with some of the products of technology that are currently utilized in the production of meat animals and to provide an evaluation of how these products impact the safety of meat and meat products
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