Fig 2 - uploaded by P. Caraveo
Content may be subject to copyright.
Sky map in celestial J2000 coordinates, R.A. and Dec., of the significance (σ) of the TeV emission detected by the HESS telescope (Aharonian et al., 2008). The blue circle indicates the location of the supernova remnant W28. As in Figure 1 the black contours show the CO intensity emission.
Source publication
Similar publications
A survey of 108 agile practitioners revealed that user stories are the most widely used method for capturing requirements. However, user stories can be interpreted differently by different stakeholders, leading to potential misunderstandings within the development team. Additionally, the interconnectedness of user stories poses challenges during th...
Citations
This chapter presents the elaborated lecture notes on Gamma Rays at Very High Energies given by Felix Aharonian at the 40th Saas-Fee Advanced Course on "Astrophysics at Very High Energies". Any coherent description and interpretation of phenomena related to gammarays requires deep knowledge of many disciplines of physics like nuclear and particle physics, quantum and classical electrodynamics, special and general relativity, plasma physics, magnetohydrodynamics, etc. After giving an introduction to gamma-ray astronomy the author discusses the astrophysical potential of ground-based detectors, radiation mechanisms, supernova remnants and origin of the galactic cosmic rays, TeV emission of young supernova remnants, gamma-emission from the Galactic center, pulsars, pulsar winds, pulsar wind nebulae, and gamma-ray loud binaries.
We present 12 mm Mopra observations of dense molecular gas towards the W28 supernova remnant (SNR) field. The focus is on the dense molecular gas towards the TeV gamma-ray sources detected by the HESS telescopes, which likely trace the cosmic rays from W28 and possibly other sources in the region. Using the NH3 inversion transitions we reveal several dense cores inside the molecular clouds, the majority of which coincide with high-mass star formation and H II regions, including the energetic ultracompact H II region G5.89-0.39. A key exception to this is the cloud north-east of W28, which is well known to be disrupted as evidenced by clusters of 1720 MHz OH masers and broad CO line emission. Here we detect broad NH3, up to the (9,9) transition, with linewidths up to 16 km s-1. This broad NH3 emission spatially matches well with the TeV source HESS J1801-233 and CO emission, and its velocity dispersion distribution suggests external disruption from the W28 SNR direction. Other lines are detected, such as HC3N and HC5N, H2O masers, and many radio recombination lines, all of which are primarily found towards the southern high-mass star formation regions. These observations provide a new view on to the internal structures and dynamics of the dense molecular gas towards the W28 SNR field and, in tandem with future higher-resolution TeV gamma-ray observations, will offer the chance to probe the transport of cosmic rays into molecular clouds.
We investigate escape of cosmic ray (CR) electrons from a supernova remnant
(SNR) to interstellar space. We show that CR electrons escape in order from
high energies to low energies like CR nuclei, while the escape starts later
than the beginning of the Sedov phase at an SNR age of 10^3 - 7*10^3 yrs and
the maximum energy of runaway CR electrons is below the knee about 0.3 - 50 TeV
because unlike CR nuclei, CR electrons lose their energy due to synchrotron
radiation. Highest energy CR electrons will be directly probed by AMS-02,
CALET, CTA and LHAASO experiments, or have been already detected by H.E.S.S.
and MAGIC as a cutoff in the CR electron spectrum. Furthermore, we also
calculate the spatial distribution of runaway CR electrons and their radiation
spectra around SNRs. Contrary to common belief, maximum-energy photons of
synchrotron radiation around 1 keV are emitted by runaway CR electrons which
have been caught up by the shock. Inverse Compton scattering by runaway CR
electrons can dominate the gamma-ray emission from runaway CR nuclei via pion
decay, and both are detectable by CTA and LHAASO as clues to the CR origin and
the amplification of magnetic fluctuations around the SNR. We also discuss
middle-aged and/or old SNRs as unidentified very-high-energy gamma-ray sources.
We study the escape of cosmic-ray (CR) protons accelerated at a supernova
remnant (SNR) by numerically solving a diffusion-convection equation from the
vicinity of the shock front to the region far away from the front. We consider
the amplifications of Alfven waves generated by the escaping CR particles and
their effects on CR escape into interstellar medium (ISM). We find that the
amplification of the waves significantly delays the escape of the particles
even far away from the shock front (on a scale of the SNR). This means that the
energy spectrum of CR particles measured through gamma-ray observations at
molecular clouds around SNRs is seriously affected by the particle scattering
by the waves.
Recently, the gamma‐ray telescopes AGILE and Fermi observed several middle‐aged supernova remnants (SNRs) interacting with molecular clouds. A plausible emission mechanism
of the gamma‐rays is the decay of neutral pions produced by cosmic ray (CR) nuclei (hadronic processes). However, observations
do not rule out contributions from bremsstrahlung emission due to CR electrons. TeV gamma‐ray telescopes also observed many
SNRs and discovered many unidentified sources. It is still unclear whether the TeV gamma‐ray emission is produced via leptonic
processes or hadronic processes. In this Letter, we propose that annihilation emission of secondary positrons produced by
CR nuclei is a diagnostic tool of the hadronic processes. We investigate MeV emissions from secondary positrons and electrons
produced by CR protons in molecular clouds. The annihilation emission of the secondary positrons from SNRs can be robustly
estimated from the observed gamma‐ray flux. The expected flux of the annihilation line from SNRs observed by AGILE and Fermi is sufficient for the future Advanced Compton Telescope to detect. Moreover, synchrotron emission from secondary positrons and electrons and bremsstrahlung emission from CR protons
can be also observed by the future X‐ray telescope NuSTAR and Astro‐H.
We aim to test the plausibility of a theoretical framework in which the
gamma-ray emission detected from supernova remnants may be of hadronic origin,
i.e., due to the decay of neutral pions produced in nuclear collisions
involving relativistic nuclei. In particular, we investigate the effects
induced by magnetic field amplification on the expected particle spectra,
outlining a phenomenological scenario consistent with both the underlying
Physics and the larger and larger amount of observational data provided by the
present generation of gamma experiments, which seem to indicate rather steep
spectra for the accelerated particles. In addition, in order to study to study
how pre-supernova winds might affect the expected emission in this class of
sources, the time-dependent gamma-ray luminosity of a remnant with a massive
progenitor is worked out. Solid points and limitations of the proposed scenario
are finally discussed in a critical way.
Observations of molecular clouds in the gamma ray domain provide us with a tool to study the distribution of cosmic rays in the Galaxy. This is because cosmic rays can penetrate molecular clouds, undergo hadronic interactions in the dense gas, and produce neutral pions that in turn decay into gamma rays. The detection of this radiation allows us to estimate the spectrum and intensity of cosmic rays at the cloud's position. Remarkably, this fact can be used to constrain the cosmic ray diffusion coefficient at specific locations in the Galaxy. Comment: Invited talk, to appear on the proceedings of ICATPP Conference on Cosmic Rays for Particle and Astroparticle Physics, Villa Olmo, Como 7-8 October 2010
GeV and TeV gamma rays have been detected from the supernova remnant W28 and its surroundings. Such emission correlates quite well with the position of dense and massive molecular clouds and thus it is often interpreted as the result of hadronic cosmic ray interactions in the dense gas. Constraints on the cosmic ray diffusion coefficient in the region can be obtained, under the assumption that the cosmic rays responsible for the gamma ray emission have been accelerated in the past at the supernova remnant shock, and subsequently escaped in the surrounding medium. In this scenario, gamma ray observations can be explained only if the diffusion coefficient in the region surrounding the supernova remnant is significantly suppressed with respect to the average galactic one. Comment: To appear in the proceedings of "Journ\'ees de la SF2A 2010" Marseille 21-24 June 2010, 4 pages, 4 figures
One of the most essential but uncertain processes for producing cosmic-rays
(CRs) and their spectra is how accelerated particles escape into the
interstellar space. We propose that the CR electron spectra at >~TeV energy can
provide a direct probe of the CR escape complementary to the CR nuclei and
gamma-rays. We calculate the electron spectra from a young pulsar embedded in
the supernova remnant (SNR), like Vela, taking into account the
energy-dependent CR escape. SNRs would accelerate and hence confine particles
with energy up to 10^{15.5}eV. Only energetic particles can escape first, while
the lower energy particles are confined and released later. Then the observed
electron spectrum should have a low energy cutoff whose position marks the age
of the pulsar/SNR. The low energy cutoff is observable in the $\gtrsim {\rm
TeV}$ energy window, where other contaminating sources are expected to be few
due to the fast cooling of electrons. The spectrum looks similar to a dark
matter annihilation line if the low energy cutoff is close to the high energy
intrinsic or cooling break. The future experiments such as CALET and CTA are
capable of directly detecting the CR escape features toward revealing the
origin of CRs.
It is shown that the radio and gamma-ray emission observed from newly-found
"GeV-bright" supernova remnants (SNRs) can be explained by a model, in which a
shocked cloud and shock-accelerated cosmic rays (CRs) frozen in it are
simultaneously compressed by the supernova blastwave as a result of formation
of a radiative cloud shock. Simple reacceleration of pre-existing CRs is
generally sufficient to power the observed gamma-ray emission through the
decays of neutral pions produced in hadronic interactions between high-energy
protons (nuclei) and gas in the compressed-cloud layer. This model provides a
natural account of the observed synchrotron radiation in SNRs W51C, W44 and IC
443 with flat radio spectral index, which can be ascribed to a combination of
secondary and reaccelerated electrons and positrons.
