Christopher M. Karwin
A5071481475- Astrophysics and Cosmic Phenomena
- Dark Matter and Cosmic Phenomena
- Gamma-ray bursts and supernovae
- Galaxies: Formation, Evolution, Phenomena
- Radio Astronomy Observations and Technology
- Particle Detector Development and Performance
- Neutrino Physics Research
- Astrophysical Phenomena and Observations
- Pulsars and Gravitational Waves Research
- Ionosphere and magnetosphere dynamics
- Cosmology and Gravitation Theories
- Radiation Therapy and Dosimetry
- Astrophysics and Star Formation Studies
- Atmospheric Ozone and Climate
- Particle physics theoretical and experimental studies
- Solar and Space Plasma Dynamics
- Astronomy and Astrophysical Research
- Atomic and Subatomic Physics Research
- Liquid Crystal Research Advancements
- Plant Reproductive Biology
- Radioactivity and Radon Measurements
- Atomic and Molecular Physics
- Stellar, planetary, and galactic studies
- Space Technology and Applications
- Nonlinear Dynamics and Pattern Formation
Clemson University
2021-2024
Goddard Space Flight Center
2023-2024
Stanford University
2019-2023
University of California, San Diego
2023
University of California, Berkeley
2023
University of Würzburg
2023
University of California, Irvine
2016-2023
Tohoku University
2023
Pennsylvania State University
2023
Kyoto University
2023
The Fermi Large Area Telescope (LAT) has provided the most detailed view to date of emission towards Galactic centre (GC) in high-energy gamma-rays. This paper describes analysis data taken during first 62 months mission energy range 1-100 GeV from a $15^\circ \times 15^\circ$ region about direction GC, and implications for interstellar emissions produced by cosmic ray (CR) particles interacting with gas radiation fields inner Galaxy point sources detected. Specialised models (IEMs) are...
We present an incremental version (4FGL-DR3, for Data Release 3) of the fourth Fermi-LAT catalog gamma-ray sources. Based on first twelve years science data in energy range from 50 MeV to 1 TeV, it contains 6658 The analysis improves that used 4FGL over eight data: more sources are fit with curved spectra, we introduce a robust spectral parameterization pulsars, and extend points TeV. parameters, distributions, associations updated all Light curves rebuilt yr intervals (not 2 month...
The Milky Way dwarf spheroidal satellite galaxies (dSphs) are particularly intriguing targets to search for gamma rays from weakly interacting massive particle dark matter (DM) annihilation or decay. They nearby, DM-dominated, and lack significant emission standard astrophysical processes. Previous studies using the Fermi-Large Area Telescope (LAT) of DM-induced dSphs have provided most robust stringent constraints on DM cross section mass. We report here an analysis over 14 years LAT data...
The center of the Milky Way is predicted to be brightest region $\ensuremath{\gamma}$-rays generated by self-annihilating dark matter particles. Excess emission about Galactic above predictions made for standard astrophysical processes has been observed in $\ensuremath{\gamma}$-ray data collected Fermi Large Area Telescope. It well described square a Navarro, Frenk, and White density distribution. Although other interpretations excess are plausible, possibility that it arises from...
The All-sky Medium Energy Gamma-ray Observatory eXplorer (AMEGO-X) is designed to identify and characterize gamma rays from extreme explosions accelerators. main science themes include: supermassive black holes their connections neutrinos cosmic rays; binary neutron star mergers the relativistic jets they produce; ray particle acceleration sources including Galactic supernovae; continuous monitoring of other astrophysical events over full sky in this important energy range. AMEGO-X will...
Abstract Recent observations of high-energy neutrinos by IceCube and gamma rays the Fermi Large Area Telescope (LAT) MAGIC telescope have suggested that are produced in gamma-ray opaque environments vicinity supermassive black holes. In this work, we present 20 MeV–1 TeV spectra three Seyfert galaxies whose nuclei predicted to be active neutrinos, NGC 4151, 4945, Circinus galaxy, using 14.4 yr LAT data. particular, find evidence sub-GeV excess emission can attributed from as was also seen...
An excess $\gamma$-ray signal toward the outer halo of M31 has recently been reported. Although other explanations are plausible, possibility that it arises from dark matter (DM) is valid. In this work we interpret in framework DM annihilation, using as our representative case WIMP annihilating to bottom quarks, and perform a detailed study systematic uncertainty $J$-factor for field. We find favors particle with mass $\sim$46-73 GeV. While well constrained, cross-section spans 2.5 orders...
Abstract The Compton Spectrometer and Imager balloon payload (COSI-Balloon) is a wide field-of-view gamma-ray telescope that operates in the 0.2–5 MeV bandpass. COSI-Balloon had successful 46 day flight 2016 during which instrument observed Crab Nebula, Cygnus X-1, Centaurus A. Using data collected by this flight, we present source flux extraction of signals from variable background environment produce images these background-dominated sources performing Richardson–Lucy deconvolutions. We...
Abstract Recent results from numerical simulations and models of galaxy formation suggest that recently discovered ultrafaint compact stellar systems (UFCSs) in the halo Milky Way (MW) may be some smallest faintest galaxies. If this is case, these would attractive targets for indirect searches weakly interacting massive particle dark matter (DM) annihilation due to their relative proximity high expected DM content. In study, we analyze 14.3 yr γ -ray data collected by Fermi-Large Area...
The Andromeda Galaxy is the closest spiral galaxy to us and has been subject of numerous studies. It harbors a massive dark matter (DM) halo which may span up ~600 kpc across comprises ~90% galaxy's total mass. This size translates into large diameter 42 degrees on sky for an M31-Milky Way (MW) distance 785 kpc, but its presumably low surface brightness makes it challenging detect with gamma-ray telescopes. Using 7.6 years Fermi Large Area Telescope (Fermi-LAT) observations, we make detailed...
Massive black holes at the centers of galaxies can launch powerful wide-angle winds that, if sustained over time, unbind gas from stellar bulges galaxies. These may be responsible for observed scaling relation between masses central and velocity dispersion stars in galactic bulges. Propagating through galaxy, wind should interact with interstellar medium creating a strong shock, similar to those supernovae explosions, which is able accelerate charged particles high energies. In this work we...
Indirect searches for dark matter through Standard Model products of its annihilation generally assume a cross-section which is dominated by term independent velocity ($s$-wave annihilation). However, in many DM models an $s$-wave absent or helicity suppressed. To reproduce the correct relic density these models, leading cross section proportional to squared ($p$-wave detection such $p$-wave difficult because average velocities galaxies today are orders magnitude slower than at time...
This white paper discusses the current landscape and prospects for experiments sensitive to particle dark matter processes producing photons cosmic rays. Much of gamma-ray sky remains unexplored on a level sensitivity that would enable discovery signal. Currently operating GeV-TeV observatories, such as Fermi-LAT, atmospheric Cherenkov telescopes, water detector arrays continue target several promising matter-rich environments within beyond Galaxy. Soon, new will explore, with increased...
Abstract In 2016, the Compton Spectrometer and Imager (COSI) had a successful 46 day flight on board NASA’s Super Pressure Balloon platform. this work, we report measurements of Galactic diffuse continuum emission (GDCE) observed toward inner Galaxy during flight, which in COSI energy band (0.2–5 MeV) is primarily generated from inverse radiation. Within uncertainties, find overall good agreement with previous INTEGRAL/SPI COMPTEL. Based these initial findings, discuss potential for further...
The Compton Spectrometer and Imager (COSI) is a NASA Small Explorer (SMEX) satellite mission in development with planned launch 2027. COSI wide-field gamma-ray telescope designed to survey the entire sky at 0.2-5 MeV. It provides imaging, spectroscopy, polarimetry of astrophysical sources, its germanium detectors provide excellent energy resolution for emission line measurements. Science goals include studies 0.511 MeV from antimatter annihilation Galaxy, mapping radioactive elements...
Abstract FR0 galaxies constitute the most abundant jet population in local Universe. With their compact structure, they are broadband photon emitters and have been proposed as multimessenger sources. Recently, these sources detected for first time γ rays. Using a revised catalog, we confirm that whole -ray emitters, also identify two significant For time, find correlation between 5 GHz core radio luminosity 1–800 GeV band, having 4.8 σ statistical significance. This is clear evidence...
Gamma-rays, the most energetic photons, carry information from far reaches of extragalactic space with minimal interaction or loss information. They bring messages about particle acceleration in environments so extreme they cannot be reproduced on earth for a closer look. Gamma-ray astrophysics is complementary collider work that physicists and astroparticle are often one same. instruments, especially Fermi Space Telescope, have been pivotal major multi-messenger discoveries over past...
Abstract Many star-forming galaxies and those hosting active galactic nuclei show evidence of massive outflows material in a variety phases including ionized, neutral atomic, molecular. Molecular particular have been the focus recent interest as they may be responsible for removing gas from galaxy, thereby suppressing star formation. As is ejected cores galaxies, interactions outflowing with interstellar medium can accelerate cosmic rays produce high-energy gamma rays. In this work, we...
The Andromeda galaxy is the closest spiral to us and has been subject of numerous studies. It harbors a massive dark matter halo which may span up ~600 kpc across comprises ~90% galaxy's total mass. This size translates into large diameter 42 degrees on sky for an M31-Milky Way (MW) distance 785 kpc, but its presumably low surface brightness makes it challenging detect with gamma-ray telescopes. Using 7.6 years Fermi Large Area Telescope (Fermi-LAT) observations, we make detailed study...
The phase-shift per unit-length of microwave radiation passing through a liquid crystal cell is calculated. By using twisted nematics, as compared to the standard homogeneous nematic crystal, increased over transition region. This has potential lower operating voltage and decrease size such phase shifters. In particular, shifts for produced by crystals K15, E7, E44 are It found that with large values elastic constant ratio K22/K11 have their performance most improved when twist introduced.
Cosmic Probes of Fundamental Physics take two primary forms: Very high energy particles (cosmic rays, neutrinos, and gamma rays) gravitational waves. Already today, these probes give access to fundamental physics not available by any other means, helping elucidate the underlying theory that completes Standard Model. The last decade has witnessed a revolution exciting discoveries such as detection high-energy neutrinos scope for major developments in next decades is dramatic, we detail this report.
A significant pointlike component from the small-scale (or discrete) structure in ${\mathrm{H}}_{2}$ interstellar gas might be present Fermi-LAT data, but modeling this emission relies on observations of rare tracers only available limited regions sky. Identifying contribution is important to discriminate $\ensuremath{\gamma}$-ray point sources gas, and better characterize extended sources. We design train convolutional neural networks predict where these do not exist, discuss impact...
AbstractThe phase-shift per unit-length (PSL) of microwave radiation is calculated when it passed through a cell containing twisted nematic liquid crystal (NLC) with weak anchoring energy at the boundaries. It shown that PSL induced by given applied voltage strongly increased as boundaries decreased. The effect therefore important to consider designing real devices, such phase shifters. calculation then extended treat supertwisted NLC cells and strong energy. effective permittivity may have...
The presence of an excess gamma-ray signal toward the Galactic center (GC) has now been well established, and is known as GC excess. Leading explanations for include mis-modeling diffuse emission along line sight, unresolved population millisecond pulsars, and/or annihilation dark matter (DM). Recently, evidence another reported outer halo M31. In this work we interpret signals from both M31 in framework DM annihilation, show that two spectra are consistent with a origin once J-factors taken...
The Andromeda Galaxy is the closest spiral galaxy to us and has been subject of numerous studies. It harbors a massive dark matter (DM) halo which may span up ~600 kpc across comprises ~90% galaxy's total mass. This size translates into large diameter 42 degrees on sky for an M31-Milky Way (MW) distance 785 kpc, but its presumably low surface brightness makes it challenging detect with gamma-ray telescopes. Using 7.6 years Fermi Large Area Telescope (Fermi-LAT) observations, we make detailed...