24 research outputs found
Characterizing the -ray Emission from FR0 Radio Galaxies
FR0 galaxies constitute the most abundant jet population in the local
Universe. With their compact jet structure, they are broadband photon emitters
and have been proposed as multi-messenger sources. Recently, these sources have
been detected for the first time in rays. Using a revised FR0 catalog,
we confirm that the FR0 population as a whole are -ray emitters, and we
also identify two significant sources. For the first time, we find a
correlation between the 5 GHz core radio luminosity and -ray luminosity
in the 1 - 800 GeV band, having a 4.5 statistical significance. This is
clear evidence that the jet emission mechanism is similar in nature for FR0s
and the well-studied canonical FR (FRI and FRII) radio galaxies. Furthermore,
we perform broadband SED modeling for the significantly detected sources as
well as the subthreshold source population using a one-zone SSC model. Within
the maximum jet power budget, our modeling shows that the detected gamma rays
from the jet can be explained as inverse Compton photons. To explain the
multi-wavelength observations for these galaxies, the modeling results
stipulate a low bulk Lorentz factor and a jet composition far from
equipartition, with the particle energy density dominating over the magnetic
field energy density.Comment: 24 pages, 9 figures, 2 tables. Submitted to the Astrophysical Journa
The All-sky Medium Energy Gamma-ray Observatory eXplorer (AMEGO-X) Mission Concept
The All-sky Medium Energy Gamma-ray Observatory eXplorer (AMEGO-X) is
designed to identify and characterize gamma rays from extreme explosions and
accelerators. The main science themes include: supermassive black holes and
their connections to neutrinos and cosmic rays; binary neutron star mergers and
the relativistic jets they produce; cosmic ray particle acceleration sources
including Galactic supernovae; and continuous monitoring of other astrophysical
events and sources over the full sky in this important energy range. AMEGO-X
will probe the medium energy gamma-ray band using a single instrument with
sensitivity up to an order of magnitude greater than previous telescopes in the
energy range 100 keV to 1 GeV that can be only realized in space. During its
three-year baseline mission, AMEGO-X will observe nearly the entire sky every
two orbits, building up a sensitive all-sky map of gamma-ray sources and
emission. AMEGO-X was submitted in the recent 2021 NASA MIDEX Announcement of
Opportunity.Comment: 23 pages, 16 figures, Published Journal of Astronomical Telescopes,
Instruments, and System
Fermi-LAT Observations of γ-Ray Emission toward the Outer Halo of M31
The Andromeda galaxy is the closest spiral galaxy to us and has been the subject of numerous studies. It harbors a massive dark matter halo, which may span up to ~600 kpc across and comprises ~90% of the galaxy's total mass. This halo size translates into a large diameter of 42° on the sky, for an M31-Milky Way (MW) distance of 785 kpc, but its presumably low surface brightness makes it challenging to detect with γ-ray telescopes. Using 7.6 yr of Fermi Large Area Telescope (Fermi-LAT) observations, we make a detailed study of the γ-ray emission between 1-100 GeV toward M31's outer halo, with a total field radius of 60° centered at M31, and perform an in-depth analysis of the systematic uncertainties related to the observations. We use the cosmic-ray propagation code GALPROP to construct specialized interstellar emission models to characterize the foreground γ-ray emission from the MW, including a self-consistent determination of the isotropic component. We find evidence for an extended excess that appears to be distinct from the conventional MW foreground, having a total radial extension upward of ~120-200 kpc from the center of M31. We discuss plausible interpretations of the excess emission, but emphasize that uncertainties in the MW foreground-and in particular, modeling of the H i-related components-have not been fully explored and may impact the results
Sub-GeV Gamma Rays from Nearby Seyfert Galaxies and Implications for Coronal Neutrino Emission
Recent observations of high-energy neutrinos by IceCube and gamma rays by the Fermi Large Area Telescope (LAT) and the MAGIC telescope have suggested that neutrinos are produced in gamma-ray opaque environments in the vicinity of supermassive black holes. In this work, we present 20 MeV–1 TeV spectra of three Seyfert galaxies whose nuclei are predicted to be active in neutrinos, NGC 4151, NGC 4945, and the Circinus galaxy, using 14.4 yr of Fermi LAT data. In particular, we find evidence of sub-GeV excess emission that can be attributed to gamma rays from NGC 4945, as was also seen in NGC 1068. These spectral features are consistent with predictions of the magnetically powered corona model, and we argue that NGC 4945 is among the brightest neutrino active galaxies detectable for KM3Net and Baikal-GVD. On the other hand, in contrast to other reported results, we do not detect gamma rays from NGC 4151, which constrains neutrino emission from the accretion shock model. Future neutrino detectors such as IceCube-Gen2 and MeV gamma - ray telescopes such as AMEGO-X will be crucial for discriminating among the theoretical models
Dark matter interpretation of the Fermi-LAT observation toward the Galactic Center
The center of the Milky Way is predicted to be the brightest region of
gamma-rays generated by self-annihilating dark matter particles. Excess
emission about the Galactic center above predictions made for standard
astrophysical processes has been observed in gamma-ray data collected by the
Fermi Large Area Telescope. It is well described by the square of an NFW dark
matter density distribution. Although other interpretations for the excess are
plausible, the possibility that it arises from annihilating dark matter is
valid. In this paper, we characterize the excess emission as annihilating dark
matter in the framework of an effective field theory. We consider the
possibility that the annihilation process is mediated by either pseudo-scalar
or vector interactions and constrain the coupling strength of these
interactions by fitting to the Fermi Large Area Telescope data for energies
1-100 GeV in the 15 x 15 degree region about the Galactic center using
self-consistently derived interstellar emission models and point source lists
for the region. The excess persists and its spectral characteristics favor a
dark matter particle with a mass in the range approximately from 50 to 190 (10
to 90) GeV and annihilation cross section approximately from 1E-26 to 4E-25
(6E-27 to 2E-25) cm^3/s for pseudo-scalar (vector) interactions. We map these
intervals into the corresponding WIMP-neutron scattering cross sections and
find that the allowed range lies well below current and projected direct
detection constraints for pseudo-scalar interactions, but are typically ruled
out for vector interactions
Improved Modeling of the Discrete Component of the Galactic Interstellar Gamma-ray Emission and Implications for the Fermi-LAT Galactic Center Excess
The aim of this work is to improve models for the gamma-ray discrete or
small-scale structure related to H2 interstellar gas. Reliably identifying this
contribution is important to disentangle gamma-ray point sources from
interstellar gas, and to better characterize extended gamma-ray signals.
Notably, the Fermi-LAT Galactic center (GC) excess, whose origin remains
unclear, might be smooth or point-like. If the data contain a point-like
contribution that is not adequately modeled, a smooth GC excess might be
erroneously deemed to be point-like. We improve models for the H2-related
gamma-ray discrete emission for a region along the
Galactic plane via H2 proxies better suited to trace these features. We find
that these are likely to contribute significantly to the gamma-ray Fermi-LAT
data in this region, and the brightest ones are likely associated with detected
Fermi-LAT sources, a compelling validation of this methodology. We discuss
prospects to extend this methodology to other regions of the sky and
implications for the characterization of the GC excess.Comment: Submitte
Deep Learning Models of the Discrete Component of the Galactic Interstellar Gamma-Ray Emission
A significant point-like component from the small scale (or discrete)
structure in the H2 interstellar gas might be present in the Fermi-LAT data,
but modeling this emission relies on observations of rare gas tracers only
available in limited regions of the sky. Identifying this contribution is
important to discriminate gamma-ray point sources from interstellar gas, and to
better characterize extended gamma-ray sources. We design and train
convolutional neural networks to predict this emission where observations of
these rare tracers do not exist and discuss the impact of this component on the
analysis of the Fermi-LAT data. In particular, we evaluate prospects to exploit
this methodology in the characterization of the Fermi-LAT Galactic center
excess through accurate modeling of point-like structures in the data to help
distinguish between a point-like or smooth nature for the excess. We show that
deep learning may be effectively employed to model the gamma-ray emission
traced by these rare H2 proxies within statistical significance in data-rich
regions, supporting prospects to employ these methods in yet unobserved
regions.Comment: Submitted. Companion paper to "Improved modeling of the discrete
component of the galactic interstellar gamma-ray emission and implications
for the Fermi--LAT galactic center excess