10 research outputs found
Particle Acceleration in Cosmic Sites - Astrophysics Issues in our Understanding of Cosmic Rays
Laboratory experiments to explore plasma conditions and stimulated particle
acceleration can illuminate aspects of the cosmic particle acceleration
process. Here we discuss the cosmic-ray candidate source object variety, and
what has been learned about their particle-acceleration characteristics. We
identify open issues as discussed among astrophysicists. -- The cosmic ray
differential intensity spectrum is a rather smooth power-law spectrum, with two
kinks at the "knee" (~10^15 eV) and at the "ankle" (~3 10^18 eV). It is unclear
if these kinks are related to boundaries between different dominating sources,
or rather related to characteristics of cosmic-ray propagation. We believe that
Galactic sources dominate up to 10^17 eV or even above, and the extragalactic
origin of cosmic rays at highest energies merges rather smoothly with Galactic
contributions throughout the 10^15--10^18 eV range. Pulsars and supernova
remnants are among the prime candidates for Galactic cosmic-ray production,
while nuclei of active galaxies are considered best candidates to produce
ultrahigh-energy cosmic rays of extragalactic origin. Acceleration processes
are related to shocks from violent ejections of matter from energetic sources
such as supernova explosions or matter accretion onto black holes. Details of
such acceleration are difficult, as relativistic particles modify the structure
of the shock, and simple approximations or perturbation calculations are
unsatisfactory. This is where laboratory plasma experiments are expected to
contribute, to enlighten the non-linear processes which occur under such
conditions.Comment: accepted for publication in EPJD, topical issue on Fundamental
physics and ultra-high laser fields. From review talk at "Extreme Light
Infrastructure" workshop, Sep 2008. Version-2 May 2009: adjust some wordings
and references at EPJD proofs stag
Radio Halos From Simulations And Hadronic Models I: The Coma cluster
We use the results from a constrained, cosmological MHD simulation of the
Local Universe to predict the radio halo and the gamma-ray flux from the Coma
cluster and compare it to current observations. The simulated magnetic field
within the Coma cluster is the result of turbulent amplification of the
magnetic field during build-up of the cluster. The magnetic seed field
originates from star-burst driven, galactic outflows. The synchrotron emission
is calculated assuming a hadronic model. We follow four approaches with
different distributions for the cosmic-ray proton (CRp) population within
galaxy clusters. The radial profile the radio halo can only be reproduced with
a radially increasing energy fraction within the cosmic ray proton population,
reaching 100% of the thermal energy content at 1Mpc, e.g. the edge
of the radio emitting region. Additionally the spectral steepening of the
observed radio halo in Coma cannot be reproduced, even when accounting for the
negative flux from the thermal SZ effect at high frequencies. Therefore the
hadronic models are disfavored from present analysis. The emission of
-rays expected from our simulated coma is still below the current
observational limits (by a factor of 6) but would be detectable in the
near future.Comment: Submitted to MNRAS, 5pages, 3 figures, 1 tabl
Determining Supersymmetric Parameters With Dark Matter Experiments
In this article, we explore the ability of direct and indirect dark matter
experiments to not only detect neutralino dark matter, but to constrain and
measure the parameters of supersymmetry. In particular, we explore the
relationship between the phenomenological quantities relevant to dark matter
experiments, such as the neutralino annihilation and elastic scattering cross
sections, and the underlying characteristics of the supersymmetric model, such
as the values of mu (and the composition of the lightest neutralino), m_A and
tan beta. We explore a broad range of supersymmetric models and then focus on a
smaller set of benchmark models. We find that by combining astrophysical
observations with collider measurements, mu can often be constrained far more
tightly than it can be from LHC data alone. In models in the A-funnel region of
parameter space, we find that dark matter experiments can potentially determine
m_A to roughly +/-100 GeV, even when heavy neutral MSSM Higgs bosons (A, H_1)
cannot be observed at the LHC. The information provided by astrophysical
experiments is often highly complementary to the information most easily
ascertained at colliders.Comment: 46 pages, 76 figure
Diffuse Neutrino and Gamma-ray Emissions of the Galaxy above the TeV
We simulate the neutrino and -ray emissions of the Galaxy which are
originated from the hadronic scattering of cosmic rays (CR) with the
interstellar medium (ISM).
Rather than assuming a uniform CR density, we estimate the spatial
distribution of CR nuclei by means of numerical simulations. We consider
several models of the galactic magnetic field and of the ISM distribution
finding only a weak dependence of our results on their choice. We found that by
extrapolating the predicted -ray spectra down to few GeV we get a good
agreement with EGRET measurements. Then, we can reliably compare our
predictions with available observations above the TeV both for the
-rays and the neutrinos. We confirm that the excesses observed by
MILAGRO in the Cygnus region and by HESS in the Galactic Centre Ridge cannot be
explained without invoking significant CR over-densities in those regions.
Finally, we discuss the perspectives that a km neutrino telescope based in
the North hemisphere has to measure the diffuse emission from the inner Galaxy.Comment: 27 pages, 13 figures. Several figures have been added or replaced. A
new model for the ISM distribution has been considered. Accepted for
publication in JCA
Neutralino Dark Matter in Mirage Mediation
We study the phenomenology of neutralino dark matter (DM) in mirage mediation
scenario of supersymmetry breaking which results from the moduli stabilization
in some string/brane models. Depending upon the model parameters, especially
the anomaly to modulus mediation ratio determined by the moduli stabilization
mechanism, the nature of the lightest supersymmetric particle (LSP) changes
from Bino-like neutralino to Higgsino-like one via Bino-Higgsino mixing region.
For the Bino-like LSP, the standard thermal production mechanism can give a
right amount of relic DM density through the stop/stau-neutralino
coannihilation or the pseudo-scalar Higgs resonance process. We also examine
the prospect of direct and indirect DM detection in various parameter regions
of mirage mediation. Neutralino DM in galactic halo might be detected by near
future direct detection experiments in the case of Bino-Higgsino mixed LSP. The
gamma ray flux from Galactic Center might be detectable also if the DM density
profile takes a cuspy shape.Comment: One reference adde
Study on Cosmic Ray Background Rejection with a 30 m Stand-Alone IACT using Non-parametric Multivariate Methods in a sub-100 GeV Energy Range
During the last decade ground-based very high-energy gamma-ray astronomy
achieved a remarkable advancement in the development of the observational
technique for the registration and study of gamma-ray emission above 100 GeV.
It is widely believed that the next step in its future development will be the
construction of telescopes of substantially larger size than the currently used
10 m class telescopes. This can drastically improve the sensitivity of the
ground-based detectors for gamma rays of energy from 10 to 100 GeV. Based on
Monte Carlo simulations of the response of a single stand-alone 30 m imaging
atmospheric Cherenkov telescope (IACT) the maximal rejection power against
background cosmic ray showers for low energy gamma-rays was investigated in
great detail. An advanced Bayesian multivariate analysis has been applied to
the simulated Cherenkov light images of the gamma-ray- and proton-induced air
showers. The results obtained here quantitatively testify that the separation
between the signal and background images degrades substantially at low
energies, and consequently the maximum overall quality factor can only be about
3.1 for gamma rays in the 10-30 GeV energy range. Various selection criteria as
well as optimal combinations of the standard image parameters utilized for
effective image separation have been also evaluated.Comment: Accepted for publication in the Journal of Physics
Gamma rays from Dark Matter Annihilation in the Central Region of the Galaxy
In this article, we review the prospects for the Fermi satellite (formerly
known as GLAST) to detect gamma rays from dark matter annihilations in the
Central Region of the Milky Way, in particular on the light of the recent
astrophysical observations and discoveries of Imaging Atmospheric Cherenkov
Telescopes. While the existence of significant backgrounds in this part of the
sky limits Fermi's discovery potential to some degree, this can be mitigated by
exploiting the peculiar energy spectrum and angular distribution of the dark
matter annihilation signal relative to those of astrophysical backgrounds.Comment: v3: corrected typos, content unchange
Multi-messenger observations of a binary neutron star merger
On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta
Discovery of the VHE gamma-ray source HESS J1832-093 in the vicinity of SNR G22.7-0.2
The region around the supernova remnant (SNR) W41 contains several TeV sources and has prompted the HESS Collaboration to perform deep observations of this field of view. This resulted in the discovery of the new very high energy (VHE) source HESS J1832−093, at the position RA=18h32m50s±3sstat±2ssyst,Dec=−9∘22′36′′±32′′stat±20′′syst(J2000), spatially coincident with a part of the radio shell of the neighbouring remnant G22.7−0.2. The photon spectrum is well described by a power law of index Γ = 2.6 ± 0.3stat ± 0.1syst and a normalization at 1 TeV of Φ0=(4.8±0.8stat±1.0syst)×10−13cm−2s−1TeV−1. The location of the gamma-ray emission on the edge of the SNR rim first suggested a signature of escaping cosmic rays illuminating a nearby molecular cloud. Then a dedicated XMM–Newton observation led to the discovery of a new X-ray point source spatially coincident with the TeV excess. Two other scenarios were hence proposed to identify the nature of HESS J1832−093. Gamma-rays from inverse Compton radiation in the framework of a pulsar wind nebula scenario or the possibility of gamma-ray production within a binary system are therefore also considered. Deeper multiwavelength observations will help to shed new light on this intriguing VHE source.A. Abramowski ... G. Rowell ... et al. [the HESS Collaboration