1,258 research outputs found
Discovery of very high energy gamma-ray emission in the W 28 (G6.4-0.1) region, and multiwavelength comparisons
H.E.S.S. observations of the old-age (>10^4yr; ~0.5deg diameter) composite
supernova remnant (SNR) W 28 reveal very high energy (VHE) gamma-ray emission
situated at its northeastern and southern boundaries. The northeastern VHE
source (HESS J1801-233) is in an area where W 28 is interacting with a dense
molecular cloud, containing OH masers, local radio and X-ray peaks. The
southern VHE sources (HESS J1800-240 with components labelled A, B and C) are
found in a region occupied by several HII regions, including the ultracompact
HII region W 28A2. Our analysis of NANTEN CO data reveals a dense molecular
cloud enveloping this southern region, and our reanalysis of EGRET data reveals
MeV/GeV emission centred on HESS J1801-233 and the northeastern interaction
region.Comment: 4 pages, 3 figures, proceedings of the 30th ICRC, Merida, Mexico,
200
Nonthermal X-radiation of SNR RX J1713.7-3946: The Relations to a Nearby Molecular Cloud
The recent X-ray and CO observations of RX J1713.7-3946 show that a
significant fraction of the nonthermal X-ray emission of this unique supernova
remnant associates, in one way or another, with a molecular cloud interacting
with the west part of the shell. This adds a new puzzle in the origin of X-ray
emission which cannot be easily explained within the standard model in
accordance of which X-rays are result of synchrotron radiation of multi-TeV
electrons accelerated by supernova shock waves. We explore an alternative
origin of the X-ray emission assuming that it is produced by secondary
electrons resulting from high energy hadronic interactions in the molecular
gas. Such a scenario could explain in a quite natural way the apparent
correlation between the X-ray and CO morphologies. However, the TeV gamma-ray
emission recently reported by H.E.S.S. significantly constrains the parameter
space of this model. Namely, this mechanism cannot reproduce the bulk of the
observed X-ray flux unless one postulates existence of a PeV cosmic-ray
component penetrating with an unusually hard spectrum into the dense cloud.Comment: 6 pages, 3 figures, to appear in Proc. of Int. Symp. on High Energy
Gamma-ray Astronomy, Heidelberg (July 2004
Chandra Observations of A Galactic Supernova Remnant Vela Jr.: A New Sample of Thin Filaments Emitting Synchrotron X-Rays
A galactic supernova remnant (SNR) Vela Jr. (RX J0852.04622, G266.61.2)
shows sharp filamentary structure on the north-western edge of the remnant in
the hard X-ray band. The filaments are so smooth and located on the most outer
side of the remnant. We measured the averaged scale width of the filaments
( and ) with excellent spatial resolution of {\it Chandra}, which are
in the order of the size of the point spread function of {\it Chandra} on the
upstream side and 49.5 (36.0--88.8) arcsec on the downstream side,
respectively. The spectra of the filaments are very hard and have no line-like
structure, and were well reproduced with an absorbed power-law model with
2.67 (2.55--2.77), or a {\tt SRCUT} model with = 4.3
(3.4--5.3) Hz under the assumption of . These results
imply that the hard X-rays are synchrotron radiation emitted by accelerated
electrons, as mentioned previously. Using a correlation between a function
and the SNR age, we estimated the
distance and the age of Vela Jr.: the estimated distance and age are 0.33
(0.26--0.50) kpc and 660 (420--1400) years, respectively. These results are
consistent with previous reports, implying that --age relation may be
a useful tool to estimate the distance and the age of synchrotron X-ray
emitting SNRs.Comment: 19 pages, 8 figures, ApJ, in pres
XMM-Newton observations of HESS J1813-178 reveal a composite Supernova remnant
We present X-ray and 12CO(J=1-0) observations of the very-high-energy (VHE)
gamma-ray source HESS J1813-178 with the aim of understanding the origin of the
gamma-ray emission. Using this dataset we are able to undertake spectral and
morphological studies of the X-ray emission from this object with greater
precision than previous studies. NANTEN 12CO(J=1-0) data are used to search for
correlations of the gamma-ray emission with molecular clouds which could act as
target material for gamma-ray production in a hadronic scenario. The NANTEN
12CO(J=1-0) observations show a giant molecular cloud of mass 2.5 10^5
M_{\sun} at a distance of 4 kpc in the vicinity of HESS J1813-178. Even
though there is no direct positional coincidence, this giant cloud might have
influenced the evolution of the gamma-ray source and its surroundings. The
X-ray data show a highly absorbed non-thermal X-ray emitting object coincident
with the previously known ASCA source AX J1813-178 showing a compact core and
an extended tail towards the north-east, located in the centre of the radio
shell-type Supernova remnant (SNR) G12.82-0.2. This central object shows
morphological and spectral resemblance to a Pulsar Wind Nebula (PWN) and we
therefore consider that the object is very likely to be a composite SNR. We
discuss the scenario in which the gamma-rays originate in the shell of the SNR
and the one in which they originate in the central object. We demonstrate, that
in order to connect the core X-ray emission to the VHE gamma-ray emission
electrons have to be accelerated to energies of at least 1 PeV.Comment: Submitted to A&
The multi-band nonthermal emission from the supernova remnant RX J1713.7-3946
Nonthermal X-rays and very high-energy (VHE) -rays have been detected
from the supernova remnant (SNR) RX J1713.7-3946, and especially the recent
observations with the \textit{Suzaku} satellite clearly reveal a spectral
cutoff in the X-ray spectrum, which directly relates to the cutoff of the
energy spectrum of the parent electrons. However, whether the origin of the VHE
-rays from the SNR is hadronic or leptonic is still in debate. We
studied the multi-band nonthermal emission from RX J1713.7-3946 based on a
semi-analytical approach to the nonlinear shock acceleration process by
including the contribution of the accelerated electrons to the nonthermal
radiation. The results show that the multi-band observations on RX J1713.7-3946
can be well explained in the model with appropriate parameters and the TeV
-rays have hadronic origin, i.e., they are produced via proton-proton
(p-p) interactions as the relativistic protons accelerated at the shock collide
with the ambient matter.Comment: 6 pages, 5 figures, accepted by MNRA
Different mechanism of two-proton emission from proton-rich nuclei Al and Mg
Two-proton relative momentum () and opening angle ()
distributions from the three-body decay of two excited proton-rich nuclei,
namely Al p + p + Na and Mg p
+ p + Ne, have been measured with the projectile fragment separator
(RIPS) at the RIKEN RI Beam Factory. An evident peak at MeV/c as
well as a peak in around 30 are seen in the two-proton
break-up channel from a highly-excited Mg. In contrast, such peaks are
absent for the Al case. It is concluded that the two-proton emission
mechanism of excited Mg is quite different from the Al case, with
the former having a favorable diproton emission component at a highly excited
state and the latter dominated by the sequential decay process
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