25 research outputs found
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
The detection of sub-solar mass dark matter halos
Dark matter halos of sub-solar mass are the first bound objects to form in
cold dark matter theories. In this article, I discuss the present understanding
of "microhalos'', their role in structure formation, and the implications of
their potential presence, in the interpretation of dark matter experiments.Comment: 18 pages, 7 figures. Invited contribution to NJP Focus Issue on "Dark
Matter and Particle Physics
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 transientâs 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
Search for Lorentz Invariance breaking with a likelihood fit of the PKS 2155-304 flare data taken on MJD 53944
Several models of Quantum Gravity predict Lorentz Symmetry breaking at energy
scales approaching the Planck scale (10^{19} GeV). With present photon data
from the observations of distant astrophysical sources, it is possible to
constrain the Lorentz Symmetry breaking linear term in the standard photon
dispersion relations. Gamma-ray Bursts (GRB) and flaring Active Galactic Nuclei
(AGN) are complementary to each other for this purpose, since they are observed
at different distances in different energy ranges and with different levels of
variability. Following a previous publication of the High Energy Stereoscopic
System (H.E.S.S.) collaboration, a more sensitive event-by-event method
consisting of a likelihood fit is applied to PKS 2155-304 flare data of MJD
53944 (July 28, 2006) as used in the previous publication. The previous limit
on the linear term is improved by a factor of ~3 up to M^{l}_{QG} > 2.1x10^{18}
GeV and is currently the best result obtained with blazars. The sensitivity to
the quadratic term is lower and provides a limit of M^{q}_{QG} > 6.4x10^10 GeV,
which is the best value obtained so far with an AGN and similar to the best
limits obtained with GRB.Comment: 24 pages, 9 figures. Accepted for publication in Astropart. Phys.
Rev1 is the final accepted version (typo corrections
Discovery and follow-up studies of the extended, off-plane, VHE gamma-ray source HESS J1507-622
Context. The detection of gamma-rays in the very-high-energy (VHE) range (100 GeV?100 TeV) offers the possibility of studying the parent population of ultrarelativistic particles found in astrophysical sources, so it is useful for understanding the underlying astrophysical processes in nonthermal sources.Aims. The discovery of the VHE gamma-ray source HESS J1507-622 is reported and possibilities regarding its nature are investigated.Methods. The H.E.S.S. array of imaging atmospheric Cherenkov telescopes (IACTs) has a high sensitivity compared with previous instruments (~1% of the Crab flux in 25 h observation time for a 5? point-source detection) and has a large field of view (~5° in diameter). HESS J1507-622 was discovered within the ongoing H.E.S.S. survey of the inner Galaxy, and the source was also studied by means of dedicated multiwavelength observations.Results. A Galactic gamma-ray source, HESS J1507-622, located ~3.5° from the Galactic plane was detected with a statistical significance >9?. Its energy spectrum is well fitted by a power law with spectral index ? = 2.24 ± 0.16stat ± 0.20sys and a flux above 1 TeV of (1.5 ± 0.4stat ± 0.3sys) à 10-12 cm-2 s-1. Possible interpretations (considering both hadronic and leptonic models) of the VHE gamma-ray emission are discussed in the absence of an obvious counterpart
Raubenheimer 9 , M. Raue 1,30 , S. M. Rayner 8 , M. Renaud 12,1 , F. Rieger 1,30
ABSTRACT Aims. Our aim is to study the very high energy (VHE; E > 100 GeV) Îł-ray emission from BL Lac objects and the evolution in time of their broad-band spectral energy distribution (SED). Methods. VHE observations of the high-frequency peaked BL Lac object PKS 2005â489 were made with the High Energy Stereoscopic System (HESS) from 2004 through 2007. Three simultaneous multi-wavelength campaigns at lower energies were performed during the HESS data taking, consisting of several individual pointings with the XMM-Newton and RXTE satellites. Results. A strong VHE signal, âŒ17Ï total, from PKS 2005â489 was detected during the four years of HESS observations (90.3 h live time). The integral flux above the average analysis threshold of 400 GeV is âŒ3% of the flux observed from the Crab Nebula and varies weakly on time scales from days to years. The average VHE spectrum measured from âŒ300 GeV to âŒ5 TeV is characterized by a power law with a photon index, Î = 3.20 ± 0.16 stat ± 0.10 syst . At X-ray energies the flux is observed to vary by more than an order of magnitude between 2004 and 2005. Strong changes in the X-ray spectrum (ÎÎ X â 0.7) are also observed, which appear to be mirrored in the VHE band. Conclusions. The SED of PKS 2005â489, constructed for the first time with contemporaneous data on both humps, shows significant evolution. The large flux variations in the X-ray band, coupled with weak or no variations in the VHE band and a similar spectral behavior, suggest the emergence of a new, separate, harder emission component in September 2005
Astronomy & Astrophysics First detection of VHE Îł-rays from SN 1006 by HESS
ABSTRACT Aims. Recent theoretical predictions of the lowest very high energy (VHE) luminosity of SN 1006 are only a factor 5 below the previously published HESS upper limit, thus motivating further in-depth observations of this source. Methods. Deep observations at VHE energies (above 100 GeV) were carried out with the high energy stereoscopic system (HESS) of Cherenkov Telescopes from 2003 to 2008. More than 100 h of data have been collected and subjected to an improved analysis procedure. Results. Observations resulted in the detection of VHE Îł-rays from SN 1006. The measured Îł-ray spectrum is compatible with a power-law, the flux is of the order of 1% of that detected from the Crab Nebula, and is thus consistent with the previously established HESS upper limit. The source exhibits a bipolar morphology, which is strongly correlated with non-thermal X-rays. Conclusions. Because the thickness of the VHE-shell is compatible with emission from a thin rim, particle acceleration in shock waves is likely to be the origin of the Îł-ray signal. The measured flux level can be accounted for by inverse Compton emission, but a mixed scenario that includes leptonic and hadronic components and takes into account the ambient matter density inferred from observations also leads to a satisfactory description of the multi-wavelength spectrum