3,223 research outputs found
Multiphotons and Photon-Jets
We discuss an extension of the Standard Model with a new vector-boson
decaying predominantly into a multi-photon final state through intermediate
light degrees of freedom. The model has a distinctive phase in which the
photons are collimated. As such, they would fail the isolation requirements of
standard multi-photon searches, but group naturally into a novel object, the
photon-jet. Once defined, the photon-jet object facilitates more inclusive
searches for similar phenomena. We present a concrete model, discuss
photon-jets more generally, and outline some strategies that may prove useful
when searching for such objects.Comment: 4 pages, 2 figure
PMN J0525-3343: soft X-ray spectral flattening in a blazar at z=4.4
We report optical, radio and X-ray observations of a new distant blazar, PMN
J0525-3343, at a redshift of 4.4. The X-ray spectrum measured from ASCA and
BeppoSAX flattens below a few keV, in a manner similar to the spectra of two
other z>4 blazars, GB 1428+4217 (z=4.72) reported by Boller et al and RXJ
1028.6-0844 (z=4.28) by Yuan et al. The spectrum is well fitted by a power-law
continuum which is either absorbed or breaks at a few keV. An intrinsic column
density corresponding to 2 x 10^23 H-atoms cm-2 at solar abundance is required
by the absorption model. This is however a million times greater than the
neutral hydrogen, or dust, column density implied by the optical spectrum,
which covers the rest-frame UV emission of the blazar nucleus. We discuss the
problems raised and suggest that, unless there is intrinsic flattening in the
spectral distribution of the particles/seed photons producing X-rays via
inverse Compton scattering, the most plausible solution is a warm absorber
close to the active nucleus.Comment: 7 pages, 7 figures; MNRAS, in pres
Isolation, characterization, and emendation of description of Angiococcus disciformis (Thaxter 1904) Jahn 1924 and proposal of a neotype strain
ESO Imaging Survey VII. Distant Cluster Candidates over 12 square degrees
In this paper the list of candidate clusters identified from the I-band data
of the ESO Imaging Survey (EIS) is completed using the images obtained over a
total area of about 12 square degrees. Together with the data reported earlier
the total I-band coverage of EIS is 17 square degrees, which has yielded a
sample of 252 cluster candidates in the redshift range 0.2 \lsim z \lsim 1.3.
This is the largest optically-selected sample currently available in the
Southern Hemisphere. It is also well distributed in the sky thus providing
targets for a variety of VLT programs nearly year round.Comment: 5 pages, 3 figures, submitted to Astronomy & Astrophysic
Image Coaddition with Temporally Varying Kernels
Large, multi-frequency imaging surveys, such as the Large Synaptic Survey
Telescope (LSST), need to do near-real time analysis of very large datasets.
This raises a host of statistical and computational problems where standard
methods do not work. In this paper, we study a proposed method for combining
stacks of images into a single summary image, sometimes referred to as a
template. This task is commonly referred to as image coaddition. In part, we
focus on a method proposed in previous work, which outlines a procedure for
combining stacks of images in an online fashion in the Fourier domain. We
evaluate this method by comparing it to two straightforward methods through the
use of various criteria and simulations. Note that the goal is not to propose
these comparison methods for use in their own right, but to ensure that
additional complexity also provides substantially improved performance
The racist bodily imaginary: the image of the body-in-pieces in (post)apartheid culture
This paper outlines a reoccurring motif within the racist imaginary of (post)apartheid culture: the black body-in-pieces. This disturbing visual idiom is approached from three conceptual perspectives. By linking ideas prevalent in Frantz Fanonâs description of colonial racism with psychoanalytic concepts such as Lacanâs notion of the corps morcelĂ©, the paper offers, firstly, an account of the black body-in-pieces as fantasmatic preoccupation of the (post)apartheid imaginary. The role of such images is approached, secondly, through the lens of affect theory which eschews a representational âreadingâ of such images in favour of attention to their asignifying intensities and the role they play in effectively constituting such bodies. Lastly, Judith Butlerâs discussion of war photography and the conditions of grievability introduces an ethical dimension to the discussion and helps draw attention to the unsavory relations of enjoyment occasioned by such images
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