30 research outputs found
The TeV Morphology of the Interacting Supernova Remnant IC 443
The middle-aged supernova remnant IC 443 is interacting with molecular gas in
its surroundings. -LAT has established that its gamma-ray emission at
low energies shows the "pion bump" that is characteristic of hadronic emission.
TeV emission was previously established by MAGIC and VERITAS at a site of
interaction between the shock front and a molecular cloud. VERITAS has
continued to observe IC 443 and can now resolve the emission on few-arcmin
scales. We will present results on the emission morphology and discuss possible
sources of the emission, including the shell of the remnant and other gaseous
structures in the vicinity.Comment: Submitted to Proceedings of the 34th International Cosmic Ray
Conference, The Hague, Netherlands, 30 July - 6 August, 201
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
Energetic Particles of Cosmic Accelerators I: Galactic Accelerators
The high-energy universe has revealed that energetic particles are ubiquitous in the cosmos and play a vital role in the cultivation of cosmic environments on all scales. Our pursuit of more than a century to uncover the origins and fate of these cosmic energetic particles has given rise to some of the most interesting and challenging questions in astrophysics. Energetic particles in our own galaxy, galactic cosmic rays (GCRs), engage in a complex interplay with the interstellar medium and magnetic fields in the galaxy, giving rise to many of its key characteristics. For instance, GCRs act in concert with galactic magnetic fields to support its disk against its own weight. GCR ionization and heating are essential ingredients in promoting and regulating the formation of stars and protostellar disks. GCR ionization also drives astrochemistry, leading to the build up of complex molecules in the interstellar medium. GCR transport throughout the galaxy generates and maintains turbulence in the interstellar medium, alters its multi-phase structure, and amplifies magnetic fields. GCRs could even launch galactic winds that enrich the circumgalactic medium and alter the structure and evolution of galactic disks. As crucial as they are for many of the varied phenomena in our galaxy, there is still much we do not understand about GCRs. While they have been linked to supernova remnants (SNRs), it remains unclear whether these objects can fully account for their entire population, particularly at the lower (approximately less than 1 GeV per nucleon) and higher (~PeV) ends of the spectrum. In fact, it is entirely possible that the SNRs that have been found to accelerate CRs merely re-accelerate them, leaving the origins of the original GCRs a mystery. The conditions for particle acceleration that make SNRs compelling source candidates are also likely to be present in sources such as protostellar jets, superbubbles, and colliding wind binaries (CWBs), but we have yet to ascertain their roles in producing GCRs. For that matter, key details of diffusive shock acceleration (DSA) have yet to be revealed, and it remains to be seen whether DSA can adequately explain particle acceleration in the cosmos. This White Paper is the first of a two-part series highlighting the most well-known high-energy cosmic accelerators and contributions that MeV gamma-ray astronomy will bring to understanding their energetic particle phenomena. For the case of GCRs, MeV astronomy will: 1) Search for fresh acceleration of GCRs in SNRs; 2) Test the DSA process, particularly in SNRs and CWBs; 3) Search for signs of CR acceleration in protostellar jets and superbubbles