7 research outputs found
Investigating a Deep Learning Method to Analyze Images from Multiple Gamma-ray Telescopes
Imaging atmospheric Cherenkov telescope (IACT) arrays record images from air
showers initiated by gamma rays entering the atmosphere, allowing astrophysical
sources to be observed at very high energies. To maximize IACT sensitivity,
gamma-ray showers must be efficiently distinguished from the dominant
background of cosmic-ray showers using images from multiple telescopes. A
combination of convolutional neural networks (CNNs) with a recurrent neural
network (RNN) has been proposed to perform this task. Using CTLearn, an open
source Python package using deep learning to analyze data from IACTs, with
simulated data from the upcoming Cherenkov Telescope Array (CTA), we implement
a CNN-RNN network and find no evidence that sorting telescope images by total
amplitude improves background rejection performance.Comment: 4 pages, 4 figures, Proceedings of the 2019 New York Scientific Data
Summit (NYSDS
Locating the most energetic electrons in Cassiopeia A
We present deep (2.4 Ms) observations of the Cassiopeia A supernova
remnant with {\it NuSTAR}, which operates in the 3--79 keV bandpass and is the
first instrument capable of spatially resolving the remnant above 15 keV. We
find that the emission is not entirely dominated by the forward shock nor by a
smooth "bright ring" at the reverse shock. Instead we find that the 15 keV
emission is dominated by knots near the center of the remnant and dimmer
filaments near the remnant's outer rim. These regions are fit with unbroken
power-laws in the 15--50 keV bandpass, though the central knots have a steeper
() spectrum than the outer filaments ().
We argue this difference implies that the central knots are located in the 3-D
interior of the remnant rather than at the outer rim of the remnant and seen in
the center due to projection effects. The morphology of 15 keV emission does
not follow that of the radio emission nor that of the low energy (12 keV)
X-rays, leaving the origin of the 15 keV emission as an open mystery. Even
at the forward shock front we find less steepening of the spectrum than
expected from an exponentially cut off electron distribution with a single
cutoff energy. Finally, we find that the GeV emission is not associated with
the bright features in the {\it NuSTAR} band while the TeV emission may be,
suggesting that both hadronic and leptonic emission mechanisms may be at work.Comment: 12 pages, 11 figures, accepted for publication in Ap
Strategies for the Follow-up of Gravitational Wave Transients with the Cherenkov Telescope Array
The observation of the electromagnetic counterpart of gravitational-wave (GW)
transient GW170817 demonstrated the potential in extracting astrophysical
information from multimessenger discoveries. The forthcoming deployment of the
first telescopes of the Cherenkov Telescope Array (CTA) observatory will
coincide with Advanced LIGO/Virgo's next observing run, O3, enabling the
monitoring of gamma-ray emission at E > 20 GeV, and thus particle acceleration,
from GW sources. CTA will not be greatly limited by the precision of GW
localization as it will be be capable of rapidly covering the GW error region
with sufficient sensitivity. We examine the current status of GW searches and
their follow-up effort, as well as the status of CTA, in order to identify some
of the general strategies that will enhance CTA's contribution to
multimessenger discoveries.Comment: 10 page
THE JUNE 2008 FLARE OF MARKARIAN 421 FROM OPTICAL TO TeV ENERGIES
We present optical, X-ray, high-energy ((sic) 30 GeV) and very high energy ((sic) 100 GeV; VHE) observations of the high-frequency peaked blazar Mrk 421 taken between 2008 May 24 and June 23. A high-energy gamma-ray signal was detected by AGILE with root TS = 4.5 between June 9 and 15, with F(E > 100 MeV) = 42(-12)(+14) x 10(-8) photons cm(-2) s(-1). This flaring state is brighter than the average flux observed by EGRET by a factor of similar to 3, but still consistent with the highest EGRET flux. In hard X-rays (20-60 keV) SuperAGILE resolved a five-day flare (June 9-15) peaking at similar to 55 mCrab. SuperAGILE, RXTE/ASM and Swift/BAT data show a correlated flaring structure between soft and hard X-rays. Hints of the same flaring behavior are also detected in the simultaneous optical data provided by the GASP-WEBT. A Swift/XRT observation near the flaring maximum revealed the highest 2-10 keV flux ever observed from this source, of 2.6 x 10(-9) erg cm(-2) s(-1) (i.e. > 100 mCrab). A peak synchrotron energy of similar to 3 keV was derived, higher than typical values of similar to 0.5-1 keV. VHE observations with MAGIC and VERITAS between June 6 and 8 showed the flux peaking in a bright state, well correlated with the X-rays. This extraordinary set of simultaneous data, covering a 12-decade spectral range, allowed for a deep analysis of the spectral energy distribution as well as of correlated light curves. The gamma-ray flare can be interpreted within the framework of the synchrotron self-Compton model in terms of a rapid acceleration of leptons in the jet
The High-Altitude water cherenkov (HAWC) observatory in México: The primary detector
The High-Altitude Water Cherenkov (HAWC) observatory is a second-generation continuously operated, wide field-of-view, TeV gamma-ray observatory. The HAWC observatory and its analysis techniques build on experience of the Milagro experiment in using ground-based water Cherenkov detectors for gamma-ray astronomy. HAWC is located on the Sierra Negra volcano in México at an elevation of 4100 meters above sea level. The completed HAWC observatory principal detector (HAWC) consists of 300 closely spaced water Cherenkov detectors, each equipped with four photomultiplier tubes to provide timing and charge information to reconstruct the extensive air shower energy and arrival direction. The HAWC observatory has been optimized to observe transient and steady emission from sources of gamma rays within an energy range from several hundred GeV to several hundred TeV. However, most of the air showers detected are initiated by cosmic rays, allowing studies of cosmic rays also to be performed. This paper describes the characteristics of the HAWC main array and its hardware.UCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Físic