403 research outputs found
Cosmic ray penetration in diffuse clouds
Cosmic rays are a fundamental source of ionization for molecular and diffuse
clouds, influencing their chemical, thermal, and dynamical evolution. The
amount of cosmic rays inside a cloud also determines the -ray flux
produced by hadronic collisions between cosmic rays and cloud material. We
study the spectrum of cosmic rays inside and outside of a diffuse cloud, by
solving the stationary transport equation for cosmic rays including diffusion,
advection and energy losses due to ionization of neutral hydrogen atoms. We
found that the cosmic ray spectrum inside a diffuse cloud differs from the one
in the interstellar medium for energies smaller than MeV,
irrespective of the model details. Below , the spectrum is harder
(softer) than that in the interstellar medium if the latter is a power law
with larger (smaller) than .Comment: 5 pages, 4 figures. Published in MNRAS Letters. Minor changes to
match the published versio
On the radial distribution of Galactic cosmic rays
The spectrum and morphology of the diffuse Galactic gamma-ray emission
carries valuable information on cosmic ray (CR) propagation. Recent results
obtained by analyzing Fermi-LAT data accumulated over seven years of
observation show a substantial variation of the CR spectrum as a function of
the distance from the Galactic Center. The spatial distribution of the CR
density in the outer Galaxy appears to be weakly dependent upon the
galactocentric distance, as found in previous studies as well, while the
density in the central region of the Galaxy was found to exceed the value
measured in the outer Galaxy. At the same time, Fermi-LAT data suggest a
gradual spectral softening while moving outward from the center of the Galaxy
to its outskirts. These findings represent a challenge for standard
calculations of CR propagation based on assuming a uniform diffusion
coefficient within the Galactic volume. Here we present a model of non-linear
CR propagation in which transport is due to particle scattering and advection
off self-generated turbulence. We find that for a realistic distribution of CR
sources following the spatial distribution of supernova remnants and the space
dependence of the magnetic field on galactocentric distance, both the spatial
profile of CR density and the spectral softening can easily be accounted for.Comment: 6 pages, 3 figures. Accepted for publivation to MNRAS letter
Cosmic ray driven Galactic winds
The escape of cosmic rays from the Galaxy leads to a gradient in the cosmic
ray pressure that acts as a force on the background plasma, in the direction
opposite to the gravitational pull. If this force is large enough to win
against gravity, a wind can be launched that removes gas from the Galaxy,
thereby regulating several physical processes, including star formation. The
dynamics of these cosmic ray driven winds is intrinsically non-linear in that
the spectrum of cosmic rays determines the characteristics of the wind
(velocity, pressure, magnetic field) and in turn the wind dynamics affects the
cosmic ray spectrum. Moreover, the gradient of the cosmic ray distribution
function causes excitation of Alfven waves, that in turn determine the
scattering properties of cosmic rays, namely their diffusive transport. These
effects all feed into each other so that what we see at the Earth is the result
of these non-linear effects. Here we investigate the launch and evolution of
such winds, and we determine the implications for the spectrum of cosmic rays
by solving together the hydrodynamical equations for the wind and the transport
equation for cosmic rays under the action of self-generated diffusion and
advection with the wind and the self-excited Alfven waves.Comment: 14 pages, 15 figures. Accepted for publication to MNRAS main journa
Acceleration of cosmic rays and gamma-ray emission from supernova remnant/molecular cloud associations
The gamma-ray observations of molecular clouds associated with supernova
remnants are considered one of the most promising ways to search for a solution
of the problem of cosmic ray origin. Here we briefly review the status of the
field, with particular emphasis on the theoretical and phenomenological aspects
of the problem.Comment: Invited talk at SUGAR201
Non-linear diffusion of cosmic rays escaping from supernova remnants - I. The effect of neutrals
Supernova remnants are believed to be the main sources of galactic Cosmic
Rays (CR). Within this framework, particles are accelerated at supernova
remnant shocks and then released in the interstellar medium. The mechanism
through which CRs are released and the way in which they propagate still remain
open issues. The main difficulty is the high non-linearity of the problem: CRs
themselves excite the magnetic turbulence that confines them close to their
sources. We solve numerically the coupled differential equations describing the
evolution in space and time of the escaping particles and of the waves
generated through the CR streaming instability. The warm ionized and warm
neutral phases of the interstellar medium are considered. These phases occupy
the largest fraction of the disc volume, where most supernovae explode, and are
characterised by the significant presence of neutral particles. The friction
between those neutrals and ions results in a very effective wave damping
mechanism. It is found that streaming instability affects the propagation of
CRs even in the presence of ion-neutral friction. The diffusion coefficient can
be suppressed by more than a factor of over a region of few tens of pc
around the remnant. The suppression increases for smaller distances. The
propagation of GeV particles is affected for several tens of
kiloyears after escape, while TeV particles are affected for few
kiloyears. This might have a great impact on the interpretation of gamma-ray
observations of molecular clouds located in the vicinity of supernova remnants.Comment: Revised to match the version published in MNRA
Contribution to Galactic cosmic rays from young stellar clusters
The origin of Galactic cosmic rays (CR) is still a matter of debate.
Diffusive shock acceleration (DSA) applied to supernova remnant (SNR) shocks
provides the most reliable explanation. However, within the current
understanding of DSA several issues remain unsolved, like the CR maximum
energy, the chemical composition and the transition region between Galactic and
extra-Galactic CRs. These issues motivate the search for other possible
Galactic sources. Recently, several young stellar clusters (YSC) have been
detected in gamma rays, suggesting that such objects could be powerful sources
of Galactic CRs. The energy input could come from winds of massive stars hosted
in the clusters which is a function of the cluster total mass and initial mass
function of stars. In this work we evaluate the total CR flux produced by a
synthetic population of YSCs assuming that the CR acceleration occurs at the
termination shock of the collective wind resulting from the sum of cluster's
stellar winds. We show that the spectrum produced by YSC can significantly
contribute to energies TeV if the diffusion inside the wind-blown
bubble is Bohm-like and the spectral slope is harder than the one produced by
SNRs.Comment: Proceeding to the International Cosmic Ray Conference, ICRC 2023,
Nagoya, Japa
A 22-Week-Old Fetus with Nager Syndrome and Congenital Diaphragmatic Hernia due to a Novel SF3B4 Mutation.
Nager syndrome, or acrofacial dysostosis type 1 (AFD1), is a rare multiple malformation syndrome characterized by hypoplasia of first and second branchial arches derivatives and appendicular anomalies with variable involvement of the radial/axial ray. In 2012, AFD1 has been associated with dominant mutations in SF3B4. We report a 22-week-old fetus with AFD1 associated with diaphragmatic hernia due to a previously unreported SF3B4 mutation (c.35-2A>G). Defective diaphragmatic development is a rare manifestation in AFD1 as it is described in only 2 previous cases, with molecular confirmation in 1 of them. Our molecular finding adds a novel pathogenic splicing variant to the SF3B4 mutational spectrum and contributes to defining its prenatal/fetal phenotype
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Improving plan quality and consistency by standardization of dose constraints in prostate cancer patients treated with CyberKnife.
Treatment plans for prostate cancer patients undergoing stereotactic body radiation therapy (SBRT) are often challenging due to the proximity of organs at risk. Today, there are no objective criteria to determine whether an optimal treatment plan has been achieved, and physicians rely on their personal experience to evaluate the plan's quality. In this study, we propose a method for determining rectal and bladder dose constraints achievable for a given patient's anatomy. We expect that this method will improve the overall plan quality and consistency, and facilitate comparison of clinical outcomes across different institutions. The 3D proximity of the organs at risk to the target is quantified by means of the expansion-intersection volume (EIV), which is defined as the intersection volume between the target and the organ at risk expanded by 5 mm. We determine a relationship between EIV and relevant dosimetric parameters, such as the volume of bladder and rectum receiving 75% of the prescription dose (V75%). This relationship can be used to establish institution-specific criteria to guide the treatment planning and evaluation process. A database of 25 prostate patients treated with CyberKnife SBRT is used to validate this approach. There is a linear correlation between EIV and V75% of bladder and rectum, confirming that the dose delivered to rectum and bladder increases with increasing extension and proximity of these organs to the target. This information can be used during the planning stage to facilitate the plan optimization process, and to standardize plan quality and consistency. We have developed a method for determining customized dose constraints for prostate patients treated with robotic SBRT. Although the results are technology specific and based on the experience of a single institution, we expect that the application of this method by other institutions will result in improved standardization of clinical practice
Cosmic ray-driven winds in the Galactic environment and the cosmic ray spectrum
Cosmic rays escaping the Galaxy exert a force on the interstellar medium directed away from the Galactic disc. If this force is larger than the gravitational pull due to the mass embedded in the Galaxy, then galactic winds may be launched. Such outflows may have important implications for the history of star formation of the host galaxy, and in turn affect in a crucial way the transport of cosmic rays, both due to advection with the wind and to the excitation of waves by the same cosmic rays, through streaming instability. The possibility to launch cosmic ray-induced winds and the properties of such winds depend on environmental conditions, such as the density and temperature of the plasma at the base of the wind and the gravitational potential, especially the one contributed by the dark matter halo. In this paper, we make a critical assessment of the possibility to launch cosmic ray-induced winds for a Milky Way-like galaxy and how the properties of the wind depend upon the conditions at the base of the wind. Special attention is devoted to the implications of different conditions for wind launching on the spectrum of cosmic rays observed at different locations in the disc of the galaxy. We also comment on how cosmic ray-induced winds compare with recent observations of Oxygen absorption lines in quasar spectra and emission lines from blank sky, as measured by XMM-Newton/EPIC-MOS
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