100 research outputs found
Exploring A Cosmic-Ray Origin of the Multi-wavelength Emission in M31
A recent detection of spatially extended gamma-ray emission in the central
region of the Andromeda galaxy (M31) has led to several possible explanations
being put forth, including dark matter annihilation and millisecond pulsars.
Another possibility is that the emission in M31 can be accounted for with a
purely astrophysical cosmic-ray (CR) scenario. This scenario would lead to a
rich multi-wavelength emission that can, in turn, be used to test it.
Relativistic cosmic-ray electrons (CRe) in magnetic fields produce radio
emission through synchrotron radiation, while X-rays and gamma rays are
produced through inverse Compton scattering. Additionally, collisions of
primary cosmic-ray protons (CRp) in the interstellar medium produce charged and
neutral pions that then decay into secondary CRe (detectable through radiative
processes) and gamma-rays. Here, we explore the viability of a CR origin for
multi-wavelength emission in M31, taking into consideration three scenarios: a
CR scenario dominated by primary CRe, one dominated by CRp and the resulting
secondary CRe and gamma rays from neutral pion decay, and a final case in which
both of these components exist simultaneously. We find that the multi-component
model is the most promising, and is able to fit the multi-wavelength spectrum
for a variety of astrophysical parameters consistent with previous studies of
M31 and of cosmic-ray physics. However, the CR power injection implied by our
models exceeds the estimated CR power injection from typical astrophysical
cosmic-ray sources such as supernovae.Comment: Accepted to Phys Rev D, 15 Pages, 9 figures, 4 tables, updated
figures/tables, added discussio
Multiwavelength Analysis of Dark Matter Annihilation and RX-DMFIT
Dark matter (DM) particles are predicted by several well motivated models to
yield Standard Model particles through self-annihilation that can potentially
be detected by astrophysical observations. In particular, the production of
charged particles from DM annihilation in astrophysical systems that contain
magnetic fields yields radio emission through synchrotron radiation and X-ray
emission through inverse Compton scattering of ambient photons. We introduce
RX-DMFIT, a tool used for calculating the expected secondary emission from DM
annihilation. RX-DMFIT includes a wide range of customizable astrophysical and
particle parameters and incorporates important astrophysics including the
diffusion of charged particles, relevant radiative energy losses, and magnetic
field modelling. We demonstrate the use and versatility of RX-DMFIT by
analyzing the potential radio and X-ray signals for a variety of DM particle
models and astrophysical environments including galaxy clusters, dwarf
spheroidal galaxies and normal galaxies. We then apply RX-DMFIT to a concrete
example using Segue I radio data to place constraints for a range of assumed DM
annihilation channels. For WIMP models with GeV and
assuming weak diffusion, we find that the the leptonic and
final states provide the strongest constraints, placing limits
on the DM particle cross-section well below the thermal relic cross-section,
while even for the channel we find limits close to the thermal relic
cross-section. Our analysis shows that radio emission provides a highly
competitive avenue for dark matter searches.Comment: 21 pages, 9 figures, 2 tables, corrections to figures, additional
text, accepted to JCA
Synchrotron Emission from Dark Matter Annihilation: Predictions for Constraints from Non-detections of Galaxy Clusters with New Radio Surveys
The annihilation of dark matter particles is expected to yield a broad
radiation spectrum via the production of Standard Model particles in
astrophysical environments. In particular, electrons and positrons from dark
matter annihilation produce synchrotron radiation in the presence of magnetic
fields. Galaxy clusters are the most massive collapsed structures in the
universe, and are known to host G-scale magnetic fields. They are
therefore ideal targets to search for, or to constrain the synchrotron signal
from dark matter annihilation. In this work we use the expected sensitivities
of several planned surveys from the next generation of radio telescopes to
predict the constraints on dark matter annihilation models which will be
achieved in the case of non-detections of diffuse radio emission from galaxy
clusters. Specifically, we consider the Tier 1 survey planned for the Low
Frequency Array (LOFAR) at 120 MHz, the EMU survey planned for the Australian
Square Kilometre Array Pathfinder (ASKAP) at 1.4 GHz, and planned surveys for
APERTIF at 1.4 GHz. We find that, for massive clusters and dark matter masses
GeV, the predicted limits on the annihilation cross section
would rule out vanilla thermal relic models for even the shallow LOFAR Tier 1,
ASKAP, and APERTIF surveys.Comment: accepted to ApJ; removal of LOFAR Tier 2 limits; other minor text
changes; conclusions largely unchange
A Multi-Wavelength Analysis of Annihilating Dark Matter as the Origin of the Gamma-Ray Emission from M31
[Abridged] Indirect detection of dark matter (DM) by multi-wavelength
astronomical observations provides a promising avenue for probing the particle
nature of DM. In the case of DM consisting of Weakly-Interacting Massive
Particles (WIMPs), self-annihilation ultimately produces observable products
including pairs and gamma rays. The gamma rays can be detected
directly, while the pairs can be detected by radio emission from
synchrotron radiation or X-rays and soft gamma rays from inverse Compton
scattering. An intriguing region to search for astrophysical signs of DM is the
Galactic center (GC) of the Milky Way, due in part to an observed excess of
gamma-rays that could be DM. A recent observation by the Fermi-LAT
collaboration of a similar excess in the central region of the Andromeda galaxy
(M31) leads us to explore the possibility of a DM-induced signal there as well.
We use the RX-DMFIT tool to perform a multi-frequency analysis of potential DM
annihilation emissions in M31. We consider WIMP models consistent with the GC
excess and calculate the expected emission across the electromagnetic spectrum
in comparison with available observational data from M31. We find that the
particle models that best fit the M31 excess favor lower masses than the GC
excess. The best fitting models are for a final state with
GeV and \left=2.6\times 10^{-26}
cms, as well as an evenly mixed final state
with GeV and \left=2.03\times 10^{-26}
cms. For conservative estimates of the diffusion and magnetic field
models the expected radio emissions appear to be in tension with currently
available data in the central region of M31, although this constraint has a
fairly strong dependence on the values chosen for parameters describing the
magnetic field strength and geometry.Comment: 11 pages, 7 figures, 2 tables, Added Table 2 and Figure 4, added
galactic center contours to Figure 3, split section VA, some changes to text,
Accepted to Phys. Rev
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