5,461 research outputs found
Hadronic processes within collective stellar winds
Recently, we have proposed that the interaction between relativistic protons
resulting from Fermi first order acceleration in the superbubble of a stellar
OB association or in other nearby accelerator and ions residing in single
stellar winds of massive stars could lead to TeV sources without strong
counterparts at lower energies. Here we refine this analysis in several
directions. We study collective wind configurations produced by a number of
massive stars, and obtain densities and expansion velocities of the stellar
wind gas that is to be target of hadronic interactions. We study the expected
-ray emission from these regions, considering in an approximate way the
effect of cosmic ray modulation. We compute secondary particle production
(electrons from knock-on interactions and electrons and positrons from charged
pion decay), and solve the loss equation with ionization, synchrotron,
bremsstrahlung, inverse Compton, and expansion losses. We provide examples
where configurations can produce sources for GLAST satellite, and the
MAGIC/HESS/VERITAS telescopes in non-uniform ways, i.e., with or without the
corresponding counterparts. We show that in all cases we studied no EGRET
source is expected. Finally, we comment on HESS J1303-631 and on Cygnus OB 2
and Westerlund 1 as two associations where this scenario could be tested.Comment: Accepted for publication in A&
High energy gamma-ray emission from the starburst nucleus of NGC 253
The high density medium that characterizes the central regions of starburst
galaxies and its power to accelerate particles up to relativistic energies make
these objects good candidates as -rays sources. In this paper, a
self-consistent model of the multifrequency emission of the starburst galaxy
NGC 253, from radio to gamma-rays, is presented. The model is in agreement with
all current measurements and provides predictions for the high energy behavior
of the NGC 253 central region. Prospects for observations with the HESS array
and GLAST satellite are especially discussed.Comment: 17 pages, 13 figures. To appear in A&A. Modelling parameters and
results are unchanged from the previous version but we enhance here the
detail with which they are described. 3 new figures and 1 new section have
been added, including a figure showing the consistency of the model with the
recently reported HESS observations (astro-ph/0507370) of NGC 25
The NMSSM lives: with the 750 GeV diphoton excess
We propose an NMSSM scenario that can explain the excess in the diphoton
spectrum at 750 GeV recently observed by ATLAS and CMS. We show that in a
certain limit with a very light pseudoscalar one can reproduce the experimental
results without invoking exotic matter. The 750 GeV excess is produced by two
resonant heavy Higgs bosons with masses ~750 GeV, that subsequently decay to
two light pseudoscalars. Each of these decays to collimated photon pairs that
appear as a single photon in the electromagnetic calorimeter. A mass gap
between heavy Higgses mimics a large width of the 750 GeV peak. The production
mechanism, containing a strong component via initial b quarks, ameliorates a
possible tension with 8 TeV data compared to other production modes. We also
discuss other constraints, in particular from low energy experiments. Finally,
we discuss possible methods that could distinguish our proposal from other
physics models describing the diphoton excess in the Run-II of the LHC.Comment: 24 pages, 4 figures; minor text improvements; to appear in EPJ
High-energy gamma-rays from stellar associations
It is proposed that TeV gamma-rays and neutrinos can be produced by cosmic
rays (CRs) through hadronic interactions in the innermost parts of the winds of
massive O and B stars. Convection prevents low-energy particles from
penetrating into the wind, leading to an absence of MeV-GeV counterparts. It is
argued that groups of stars located close to the CR acceleration sites in OB
stellar associations may be detectable by ground-based Cherenkov telescopes.Comment: 10 pages, 1 figure. Accepted for publication in Astrophysical Journal
Letter
New Stellar Cross Sections and The "Karlsruhe Astrophysical Database of Nucleosynthesis in Stars"
Since April 2005 a regularly updated stellar neutron cross section
compilation is available online at http://nuclear-astrophysics.fzk.de/kadonis.
This online-database is called the "Karlsruhe Astrophysical Database of
Nucleosynthesis in Stars" project and is based on the previous Bao et al.
compilation from the year 2000. The present version \textsc{KADoNiS} v0.2
(January 2007) includes recommended cross sections for 280 isotopes between
H and Po and 75 semi-empirical estimates for isotopes without
experimental information. Concerning stellar cross sections of the
32 stable, proton-rich isotopes produced by the process experimental
information is only available for 20 isotopes, but 9 of them have rather large
uncertainties of 9%. The first part of a systematic study of stellar
cross sections of the -process isotopes Se, Sr,
Pd, Te, Ba, Ba, Dy, and Hf is
presented. In another application \textsc{KADoNiS} v0.2 was used for an
modification of a reaction library of Basel university. With this modified
library -process network calculations were carried out and compared to
previous results.Comment: Proceedings "International Conference on Nuclear Data for Science and
Technology 2007", Nice/ Franc
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