2,638 research outputs found
Suzaku observation of the unidentified VHE gamma-ray source HESS J1702-420
A deep X-ray observation of the unidentified very high energy (VHE) gamma-ray
source HESS J1702-420, for the first time, was carried out by Suzaku. No bright
sources were detected in the XIS field of view (FOV) except for two faint
point-like sources. The two sources, however, are considered not to be related
to HESS J1702-420, because their fluxes in the 2-10 keV band (~ 10^-14 erg s^-1
cm^-2) are ~ 3 orders of magnitude smaller than the VHE gamma-ray flux in the
1-10 TeV band (F_{TeV} = 3.1 x 10^-11 erg s^-1 cm^-2). We compared the energy
spectrum of diffuse emission, extracted from the entire XIS FOV with those from
nearby observations. If we consider the systematic error of background
subtraction, no significant diffuse emission was detected with an upper limit
of F_X <2.7 x 10^-12 erg s^-1 cm^-2 in the 2-10 keV band for an assumed
power-law spectrum of \Gamma=2.1 and a source size same as that in the VHE
band. The upper limit of the X-ray flux is twelve times as small as the VHE
gamma-ray flux. The large flux ratio (F_{TeV}/F_X) indicates that HESS
J1702-420 is another example of a "dark" particle accelerator. If we use a
simple one-zone leptonic model, in which VHE gamma-rays are produced through
inverse Compton scattering of the cosmic microwave background and interstellar
far-infrared emission, and the X-rays via the synchrotron mechanism, an upper
limit of the magnetic field (1.7 \mu G) is obtained from the flux ratio.
Because the magnetic field is weaker than the typical value in the Galactic
plane (3-10 \mu G), the simple one-zone model may not work for HESS J1702-420
and a significant fraction of the VHE gamma-rays may originate from protons.Comment: 7 pages, accepted for publication in PASJ (Suzaku and MAXI special
issue
Ultra-Fast Generation of Air Shower Images for Imaging Air Cherenkov Telescopes using Generative Adversarial Networks
For the analysis of data taken by Imaging Air Cherenkov Telescopes (IACTs), a
large number of air shower simulations are needed to derive the instrument
response. The simulations are very complex, involving computational and
memory-intensive calculations, and are usually performed repeatedly for
different observation intervals to take into account the varying optical
sensitivity of the instrument. The use of generative models based on deep
neural networks offers the prospect for memory-efficient storing of huge
simulation libraries and cost-effective generation of a large number of
simulations in an extremely short time. In this work, we use Wasserstein
Generative Adversarial Networks to generate photon showers for an IACT equipped
with the FlashCam design, which has more than pixels. Using
simulations of the H.E.S.S. experiment, we demonstrate the successful
generation of high-quality IACT images. The analysis includes a comprehensive
study of the generated image quality based on low-level observables and the
well-known Hillas parameters that describe the shower shape. We demonstrate for
the first time that the generated images have high fidelity with respect to
low-level observables, the Hillas parameters, their physical properties, as
well as their correlations. The found increase in generation speed in the order
of yields promising prospects for fast and memory-efficient simulations
of air showers for IACTs.Comment: 27 pages, 12 figure
A new population of very high-energy gamma-ray sources detected with H.E.S.S. in the inner part of the Milky Way
The H.E.S.S., experiment (High Energy Stereoscopic System) is an array of four imaging Cherenkov telescopes designed to detect gamma-rays in the energy domain above 100 GeV. The telescopes utilise the stereoscopic approach, in which particle showers in the atmosphere are observed by several telescopes simultaneously, connected by a central trigger system at the hardware level. This approach greatly reduces the background of the instrument and thereby allows one to decrease the energy threshold and improve the sensitivity of the system. The functionality and performance of the central trigger of H.E.S.S., is presented. Making use of the reduced energy threshold and the improved sensitivity, a survey of the inner part of the Milky way in very high energy gamma-rays, was conducted in 2004 with H.E.S.S. at an unprecedented sensitivity level. The Galactic plane between +- 30deg, in longitude and +-3deg, in latitude relative to the Galactic centre was observed for a total of 230 hours, reaching an average flux sensitivity of 3% of the Crab nebula at energies above 200 GeV. Fourteen new sources were detected at a significance level greater than 4 sigma in addition to three previously known sources in this area. Detailed spectral and morphological information for these new sources are provided, along with a discussion on possible counterparts in other wavelength bands. The distribution in galactic latitude of the detected sources appears to be consistent with a scale height in the galactic disc for the parent population of less than 100 parsec
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