49 research outputs found
Deconvolution of Images Taken with the Suzaku X-ray Imaging Spectrometer
We present a non-iterative method to deconvolve the spatial response function
or the point spread function (PSF) from images taken with the Suzaku X-ray
Imaging Spectrometer (XIS). The method is optimized for analyses of extended
sources with high photon statistics. Suzaku has four XIS detectors each with
its own X-ray CCD and X-Ray Telescope (XRT) and has been providing unique
opportunities in spatially-resolved spectroscopic analyses of extended objects.
The detectors, however, suffer from broad and position-dependent PSFs with
their typical half-power density (HPD) of about 110''. In the authors' view,
this shortcoming has been preventing the high collecting area and high spectral
resolution of Suzaku to be fully exploited. The present method is intended to
recover spatial resolution to ~15'' over a dynamic range around 1:100 in the
brightness without assuming any source model. Our deconvolution proceeds in two
steps: An XIS image is multiplied with the inverse response matrix calculated
from its PSF after rebinning CCD pixels to larger-size tiles (typically 6''x
6''); The inverted image is then adaptively smoothed to obtain the final
deconvolved image. The PSF is modeled on a ray-tracing program and an observed
point-source image. The deconvolution method has been applied to images of
Centaurus A, PSR B1509-58 and RCW 89 taken by one XIS (XIS-1). The results have
been compared with images obtained with Chandra to conclude that the spatial
resolution has been recovered to ~20'' down to regions where surface brightness
is about 1:50 of the brightest tile in the image. We believe the spatial
resolution and the dynamic range can be improved in the future with higher
fidelity PSF modeling and higher precision pointing information.Comment: 21 pages, accepted for publication in PASJ. A PS file with
original-quality figures is available at
http://www.slac.stanford.edu/~sugizaki/preprint/pasj3256/sugizaki_No3256.p
Studies of Cosmic Rays with GeV Gamma Rays
We describe the role of GeV gamma-ray observations with GLAST-LAT (Gamma-ray
Large Area Space Telescope - Large Area Telescope) in identifying interaction
sites of cosmic-ray proton (or hadrons) with interstellar medium (ISM). We
expect to detect gamma rays from neutral pion decays in high-density ISM
regions in the Galaxy, Large Magellanic Cloud, and other satellite galaxies.
These gamma-ray sources have been detected already with EGRET (Energetic Gamma
Ray Experiment Telescope) as extended sources (eg. LMC and Orion clouds) and
GLAST-LAT will detect many more with a higher spatial resolution and in a wider
spectral range. We have developed a novel image restoration technique based on
the Richardson-Lucy algorithm optimized for GLAST-LAT observation of extended
sources. Our algorithm calculates PSF (point spread function) for each event.
This step is very important for GLAST-LAT and EGRET image analysis since PSF
varies more than one order of magnitude from one gamma ray to another depending
on its energy as well as its impact point and angle in the instrument. The
GLAST-LAT and EGRET image analysis has to cope with Poisson fluctuation due to
low number of detected photons for most sources. Our technique incorporates
wavelet filtering to minimize effects due to the fluctuation. Preliminary
studies on some EGRET sources are presented, which shows potential of this
novel image restoration technique for the identification and characterisation
of extended gamma-ray sources.Comment: 9 pages, 6 figures, Invited Talk at International Workshop on
"Cosmic-Rays and High Energy Universe," Aoyama-Gakuin University, Shibuya,
Tokyo, Japan, March 5-6, 200
Studies of EGRET sources with a novel image restoration technique
We have developed an image restoration technique based on the Richardson-Lucy
algorithm optimized for GLAST-LAT image analysis. Our algorithm is original
since it utilizes the PSF (point spread function) that is calculated for each
event. This is critical for EGRET and GLAST-LAT image analysis since the PSF
depends on the energy and angle of incident gamma-rays and varies by more than
one order of magnitude. EGRET and GLAST-LAT image analysis also faces Poisson
noise due to low photon statistics. Our technique incorporates wavelet
filtering to minimize noise effects. We present studies of EGRET sources using
this novel image restoration technique for possible identification of extended
gamma-ray sources.Comment: 5 pages, 3 figures. Presented at First GLAST Symposium, Stanford
University, Stanford, CA, USA, February 5-8, 200
Parameterization of the Angular Distribution of Gamma Rays Produced by p-p Interaction in Astronomical Environment
We present the angular distribution of gamma rays produced by proton-proton
interactions in parameterized formulae to facilitate calculations in
astrophysical environments. The parameterization is derived from Monte Carlo
simulations of the up-to-date proton-proton interaction model by Kamae et al.
(2005) and its extension by Kamae et al. (2006). This model includes the
logarithmically rising inelastic cross section, the diffraction dissociation
process and Feynman scaling violation. The extension adds two baryon resonance
contributions: one representing the Delta(1232) and the other representing
multiple resonances around 1600 MeV/c^2. We demonstrate the use of the formulae
by calculating the predicted gamma-ray spectrum for two different cases: the
first is a pencil beam of protons following a power law and the second is a
fanned proton jet with a Gaussian intensity profile impinging on the
surrounding material. In both cases we find that the predicted gamma-ray
spectrum to be dependent on the viewing angle.Comment: 8 pages, 7 figures, figure 7 updated, accepted for publication in
ApJ, text updated to match changes by the editor, two refs updated from
preprints to full journal
Soft X-ray precursors of the non-thermal flares in blazars - theoretical predictions
Popular internal shock models, developed to explain production of high energy
flares in blazar jets, involve collisions between local overdensities of matter
being ejected by a central engine and moving along the jet with different
velocities. Prior to such collisions, the matter is relatively cold and
therefore does not produce intrinsic non-thermal radiation. However, due to
Comptonization of external radiation by cold electrons, the presence of such
matter should be apparent by prominent precursor soft X-ray flares, visible
prior to non-thermal -ray flares. In this paper we discuss the
predicted properties of such precursors and study the dependence of their
properties (luminosities and light curves) on kinematic parameters of
relativistic ejecta and on an angle of view. We demonstrate that the lack of
evidence for luminous soft X-ray precursors can be reconciled with our
predictions for their properties if acceleration and collimation of a jet takes
about three distance decades. We briefly discuss the severe constraints on the
internal shock models that would be imposed by a non-detection of such
precursors.Comment: 20 pages, 5 figures, accepted for publication in Ap
3-D Model of Broadband Emission from Supernova Remnants Undergoing Non-linear Diffusive Shock Acceleration
We present a 3-dimensional model of supernova remnants (SNRs) where the
hydrodynamical evolution of the remnant is modeled consistently with nonlinear
diffusive shock acceleration occuring at the outer blast wave. The model
includes particle escape and diffusion outside of the forward shock, and
particle interactions with arbitrary distributions of external ambient
material, such as molecular clouds. We include synchrotron emission and
cooling, bremsstrahlung radiation, neutral pion production, inverse-Compton
(IC), and Coulomb energy-loss. Boardband spectra have been calculated for
typical parameters including dense regions of gas external to a 1000 year old
SNR. In this paper, we describe the details of our model but do not attempt a
detailed fit to any specific remnant. We also do not include magnetic field
amplification (MFA), even though this effect may be important in some young
remnants. In this first presentation of the model we don't attempt a detailed
fit to any specific remnant. Our aim is to develop a flexible platform, which
can be generalized to include effects such as MFA, and which can be easily
adapted to various SNR environments, including Type Ia SNRs, which explode in a
constant density medium, and Type II SNRs, which explode in a pre-supernova
wind. When applied to a specific SNR, our model will predict cosmic-ray spectra
and multi-wavelength morphology in projected images for instruments with
varying spatial and spectral resolutions. We show examples of these spectra and
images and emphasize the importance of measurements in the hard X-ray, GeV, and
TeV gamma-ray bands for investigating key ingredients in the acceleration
mechanism, and for deducing whether or not TeV emission is produced by IC from
electrons or neutral pions from protons.Comment: 12 pages, 9 figures, accepted by Apj, 24 June 200