96 research outputs found
The e-ASTROGAM space mission: a major step forward for supernova physics
e-ASTROGAM is a gamma-ray observatory operating in a broad energy range, 0.15
MeV - 3 GeV, recently proposed as the M5 Medium-size mission of the European
Space Agency. It has the potential to revolutionize the astronomy of
medium-energy gamma-rays by increasing the number of known sources in this
domain by more than an order of magnitude and providing gamma-ray polarization
information for many of these sources. In these proceedings, we discuss the
expected capacity of the mission to study the physics of supernovae, both
thermonuclear and core-collapse, as well as the origin of cosmic rays in
supernova shocks.Comment: 6 pages, 3 figures. To appear in the proceedings of the IAU Symposium
331 "SN 1987A, 30 years later", eds. Alexandre Marcowith, Gloria Dubner, Alak
Ray, Andre\"i Bykov and Matthieu Renau
Light Element Nucleosynthesis in a Molecular Cloud Interacting with a Supernova Remnant and the Origin of Beryllium-10 in the Protosolar Nebula
The presence of short-lived radionuclides in the early solar system provides
important information about the astrophysical environment in which the solar
system formed. The discovery of now extinct Be in calcium-aluminum-rich
inclusions (CAIs) with Fractionation and Unidentified Nuclear isotope anomalies
(FUN-CAIs) suggests that a baseline concentration of Be in the early
solar system was inherited from the protosolar molecular cloud. In this paper,
we first show that the Be recorded in FUN-CAIs cannot have been produced
in situ by cosmic-ray (CR) irradiation of the FUN-CAIs themselves. We then show
that trapping of Galactic CRs (GCRs) in the collapsing presolar cloud core
induced a negligible Be contamination of the protosolar nebula.
Irradiation of the presolar molecular cloud by background GCRs produced a
steady-state Be/Be ratio ~2.3 times lower than the ratio recorded in
FUN-CAIs, which suggests that the presolar cloud was irradiated by an
additional source of CRs. Considering a detailed model for CR acceleration in a
supernova remnant (SNR), we find that the Be abundance recorded in
FUN-CAIs can be explained within two alternative scenarios: (i) the irradiation
of a giant molecular cloud by CRs produced by >50 supernovae exploding in a
superbubble of hot gas generated by a large star cluster of at least 20,000
members and (ii) the irradiation of the presolar molecular cloud by freshly
accelerated CRs escaped from an isolated SNR at the end of the Sedov-Taylor
phase. The second model naturally provides an explanation for the injection of
other short-lived radionuclides of stellar origin into the cold presolar
molecular cloud (Al, Ca and Cl) and is in agreement with
the solar system originating from the collapse of a molecular cloud shocked by
a supernova blast wave.Comment: 21 pages (ApJ emulator style), 13 figures. Accepted to ApJ (in press
Diffuse 0.5-1 keV X-Rays and Nuclear Gamma-Rays from Fast Particles in the Local Hot Bubble
We show that interactions of fast particles with the boundary shell of the
local hot bubble could make an important contribution to the 0.5-1 keV diffuse
X-ray background observed with ROSAT. The bulk of these nonthermal X-rays are
due to line emission from fast O ions of energies around 1 MeV/nucleon. This is
the typical energy per particle in the ejecta of the supernova which is thought
to have energized the bubble. We find that there is sufficient total energy in
the ejecta to produce X-rays of the required intensity, subject to the details
of the evolution of the fast particle population since the supernova explosion
(about 3 10 years ago based on the age of the Geminga pulsar). The
unequivocal signature of lines from deexcitations in fast ions is their large
width (~0.1 for O lines), which will clearly distinguishes them
from X-ray lines produced in a hot plasma. If a small fraction of the total
ejecta energy is converted into accelerated particle kinetic energy (>~30
MeV/nucleon), the gamma-ray line emission produced in the boundary shell of the
local hot bubble could account for the recently reported COMPTEL observations
of nuclear gamma-ray lines from a broad region towards the Galactic center.Comment: 13 pages, 4 figures, submitted to Ap
Discovery of K-Shell Emission Lines of Neutral Atoms in the Galactic Center Region
The K-shell emission line of neutral irons from the Galactic center (GC)
region is one of the key for the structure and activity of the GC. The origin
is still open question, but possibly due either to X-ray radiation or to
electron bombarding to neutral atoms. To address this issue, we analyzed the
Suzaku X-ray spectrum from the GC region of intense neutral iron line emission,
and report on the discovery of Kalpha lines of neutral argon, calcium, chrome,
and manganese atoms. The equivalent widths of these Kalpha lines indicate that
the metal abundances in the GC region should be ~1.6 and ~4 of solar value,
depending on the X-ray and the electron origins, respectively. On the other
hand, the metal abundances in the hot plasma in the GC region are found to be
~1-2 solar. These results favor that the origin of the neutral Kalpha lines are
due to X-ray irradiation.Comment: 7 pages, 5 figures, accepted for publication in PASJ (Vol.62, No.2,
pp.423--429
Exploring the capabilities of the Anti-Coincidence Shield of the INTEGRAL spectrometer to study solar flares
INTEGRAL is a hard X-ray/gamma-ray observatory for astrophysics (ESA)
covering photon energies from 15 keV to 10 MeV. It was launched in 2002 and
since then the BGO detectors of the Anti-Coincidence shield (ACS) of the SPI
spectrometer have detected many hard X-ray (HXR) bursts from the Sun, producing
lightcurves at photon energies above ~ 100 keV. The spacecraft has a highly
elliptical orbit, providing a long uninterrupted observing time (about 90% of
the orbital period) with nearly constant background due to the reduction of the
crossing time of the Earth's radiation belts. However, due to technical
constraints, INTEGRAL cannot point to the Sun and high-energy solar photons are
always detected in non-standard observation conditions. To make the data useful
for solar studies, we have undertaken a major effort to specify the observing
conditions through Monte-Carlo simulations of the response of ACS for several
selected flares. We check the performance of the model employed for the
Monte-Carlo simulations using RHESSI observations for the same sample of solar
flares. We conclude that, despite the fact that INTEGRAL was not designed to
perform solar observations, ACS is a useful instrument in solar flare research.
In particular, its relatively large effective area allows the determination of
good-quality HXR/gamma-ray lightcurves for X- and M-class solar flares and, in
some cases, probably also for C-class flares.Comment: 18 pages, 6 figures; Solar Physics 201
Lithium-6 from Solar Flares
By introducing a hitherto ignored Li-6 producing process, due to accelerated
He-3 reactions with He-4, we show that accelerated particle interactions in
solar flares produce much more Li-6 than Li-7. By normalizing our calculations
to gamma-ray data we demonstrate that the Li-6 produced in solar flares,
combined with photospheric Li-7, can account for the recently determined solar
wind lithium isotopic ratio, obtained from measurements in lunar soil, provided
that the bulk of the flare produced lithium is evacuated by the solar wind.
Further research in this area could provide unique information on a variety of
problems, including solar atmospheric transport and mixing, solar convection
and the lithium depletion issue, and solar wind and solar particle
acceleration.Comment: latex 9 pages, 2 figures, ApJ Letters in pres
Study of 12C(α,γ)16O reaction via the transfer reaction 12C(7Li,t)16O
International audienceThe 12C(a,g )16O reaction plays an important role in helium burning in massive stars and their evolution. However, despite many experimental studies, the low-energy cross section of 12C(a,g )16O remains highly uncertain. The extrapolation of the measured cross sections to stellar energies (E=300 keV) is made difficult by the presence of the two sub-threshold states at 6.92 (2+) and 7.12 (1−) MeV of 16O. In order to further investigate the contribution of these twosubthreshold resonances to the 12C(a,g )16O cross section, we performed a new determination of the a-reduced widths of the 6.92 and 7.12 MeV of 16O via a measurement of the transfer reaction 12C(7Li,t)16O at two incident energies, 34 and 28 MeV. The measured and calculated differential cross sections are presented as well as the obtained spectroscopic factors and the a-reduced widths for the 2+ and 1− sub-threshold states and their effect on the R-matrix calculations of 12C(a,g )16O
Synthesis and photophysical studies of a pyrenylindole and a phenalenoindole obtained from dehydroamino acid derivatives : application as fluorescent probes for biological systems
Two pyrenyl-dehydroamino acid derivatives were cyclized by a metal-assisted C–N intramolecular cyclization developed in our research group, to give a pyrenylindole and a phenalenoindole. The pyrenylindole was inserted into a peptide by solid-phase coupling, with use of a 2-chlorotrityl chloride resin and a Fmoc strategy. The photophysical properties of the pyrenylindole and phenalenoindole in several solvents were studied and showed that these compounds can be used as fluorescence probes. The results obtained with the peptide labelled with the pyrenylindole moiety show potential for use of this compound as a fluorescence label avoiding the aggregation propensity of pyrene compounds. Photophysical studies of the pyrenylindole and of the phenalenoindole in lipid membranes were also carried out. Steady-state fluorescence anisotropy measurements revealed that both compounds adopt locations inside the lipid bilayers and are able to report the transition between the gel and liquid-crystalline phases. The results point to potential use of these compounds as fluorescent
probes for biological systems.Fundação para a Ciência e a Tecnologia (FCT) - (SFRH/BPD/24548/2005), (SFRH/BD/38766/2007)Fundo Europeu de Desenvolvimento Regional
(FEDER) - Project PTDC/QUI/81238/200
X-Rays from Accelerated Ion Interactions
We have developed in detail the theory of X-ray line and continuum production
due to atomic interactions of accelerated ions, incorporating in our
calculations information from a broad range of laboratory measurements. We
applied our calculations to the Orion region from which nuclear gamma-ray lines
were observed with the COMPTEL instrument on CGRO. The accelerated particles
which produce this gamma-ray emission via nuclear reactions also produce X-ray
lines via atomic interactions. We predict strong line emission in the range
from 0.5 to 1 keV, mainly due to de-excitations in fast O ions. While much of
the diffuse X-ray emission observed with ROSAT from Orion could be due to
accelerated ions, the current X-ray data do not provide unambiguous signatures
for such an origin. If future observations with high spectral resolution would
confirm the predicted X-rays, the combined analysis of the X-ray and gamma-ray
data will set important constraints on the origin of the accelerated particles
and their interaction model.Comment: 26 pages, 14 figure
All-sky Medium Energy Gamma-ray Observatory: Exploring the Extreme Multimessenger Universe
The All-sky Medium Energy Gamma-ray Observatory (AMEGO) is a probe class
mission concept that will provide essential contributions to multimessenger
astrophysics in the late 2020s and beyond. AMEGO combines high sensitivity in
the 200 keV to 10 GeV energy range with a wide field of view, good spectral
resolution, and polarization sensitivity. Therefore, AMEGO is key in the study
of multimessenger astrophysical objects that have unique signatures in the
gamma-ray regime, such as neutron star mergers, supernovae, and flaring active
galactic nuclei. The order-of-magnitude improvement compared to previous MeV
missions also enables discoveries of a wide range of phenomena whose energy
output peaks in the relatively unexplored medium-energy gamma-ray band
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