310 research outputs found
Optical afterglows of Gamma-Ray Bursts: peaks, plateaus, and possibilities
The optical light-curves of GRB afterglows display either peaks or plateaus.
We identify 16 afterglows of the former type, 17 of the latter, and 4 with
broad peaks, that could be of either type. The optical energy release of these
two classes is similar and is correlated with the GRB output, the correlation
being stronger for peaky afterglows, which suggests that the burst and
afterglow emissions of peaky afterglows are from the same relativistic ejecta
and that the optical emission of afterglows with plateaus arises more often
from ejecta that did not produce the burst emission.
Consequently, we propose that peaky optical afterglows are from impulsive
ejecta releases and that plateau optical afterglows originate from long-lived
engines, the break in the optical light-curve (peak or plateau end) marking the
onset of the entire outflow deceleration.
In the peak luminosity--peak time plane, the distribution of peaky afterglows
displays an edge with L_p \propto t_p^{-3}, which we attribute to variations
(among afterglows) in the ambient medium density. The fluxes and epochs of
optical plateau breaks follow a L_b \propto t_b^{-1} anticorrelation.
Sixty percent of 25 afterglows that were well-monitored in the optical and
X-rays show light-curves with comparable power-law decays indices and
achromatic breaks. The other 40 percent display three types of decoupled
behaviours: i) chromatic optical light-curve breaks (perhaps due to the peak of
the synchrotron spectrum crossing the optical), ii) X-ray flux decays faster
than in the optical (suggesting that the X-ray emission is from local
inverse-Compton scattering), and iii) chromatic X-ray light-curve breaks
(indicating that the X-ray emission is from external up-scattering).Comment: 11 pages, table with afterglows added, to appear in MNRA
A model for the UHE gamma-rays from Hercules X-1
An outburst of gamma rays with energies E gamma 10 to the 12th power eV was recently detected from the X-ray pulsar Hercules X-1. The outburst had a 3 minute duration and occurred at a time during the 35 day X-ray modulation that is associated with X-ray turnon. The gamma rays also have the same 1.24 second modulation that is observed at X-ray energies. Subsequently a 40 minute outburst was detected at E gamma 10 to the 14th power eV. The interaction of ultrahigh energy particles with a precessing accretion disk explain the observed gamma ray light curve. The constraints one can place on acceleration mechanisms and the possibility that the UHE particles are accelerated by shocks in an accretion flow are explained
Hard X‐ray polarimetry of solar flares with BATSE
We describe a technique for measuring the polarization of hard X‐rays from solar flares based on the angular distribution of that portion of the flux which is scattered off the top of the Earth’s atmosphere. The scattering cross section depends not only on the scatter angle itself, but on the orientation of the scatter angle with respect to the incident polarization vector. Consequently, the distribution of the observed albedo flux will depend on the direction and the polarization properties (i.e., the level of polarization and polarization angle) of the source. Since the albedo component can represent a relatively large fraction (up to 40%) of the direct source flux, there will generally be sufficient signal for making such a measurement. The sensitivity of this approach is therefore dictated by the effective area and the ability of a detector system to ‘image’ the albedo flux. The 4π coverage of the BATSE detectors on the Compton Gamma‐RayObservatory provides an opportunity to measure both the direct and the albedo flux from a given solar flare event. Although the BATSE design (with its large field‐of‐view for each detector) is not optimized for albedo polarimetry, we have nonetheless investigated the feasibility of this technique using BATSE data
Using BATSE to measure gamma-ray burst polarization
We describe a technique for measuring the polarization of hard x-rays from γ-ray bursts based on the angular distribution of that portion of the flux which is scattered off the top of the Earth’s atmosphere. The scattering cross section depends not only on the scatter angle itself, but on the orientation of the scatter angle with respect to the incident polarization vector. Consequently, the distribution of the observed albedo flux will depend on the direction and the polarization properties (i.e., the level of polarization and polarization angle) of the source. Although the BATSE design (with its large field-of-view for each detector) is not optimized for albedo polarimetry, we have nonetheless investigated the feasibility of this technique using BATSE data
Of Shining Knights and Cunning Pettifoggers: The Symbolic World of the Model Rules of Professional Conduct
This article offers a coherent ethical perspective on the American Bar Association (ABA) Model Rules of Professional Conduct. The legal profession bases its Model Rules on assumptions about lawyers, their clients and adversaries, the authority to which lawyers appeal, and the economy in which they practice. Citing in support every Model Rule, this article exposes the rich symbolic assumptions underlying the Rules and concludes that it is through this symbolic world that the Model Rules are best understood. This article includes a description of the normative economy on which the symbolic world of the Model Rules is based
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