383 research outputs found
A multi-frequency study of the spectral index distribution in the SNR CTB 80
We have conducted a study at radio wavelengths of the spectral behaviour of
the supernova remnant (SNR) CTB 80. Based on an homogenised data set of
integrated flux densities, we calculated for the whole SNR a radio index -0.36
+/- 0.02. The shape of the global spectrum suggests absorption by ionized gas
in the interstellar medium (ISM) along the line of sight. Spatial spectral
variations across the SNR are investigated based on high-angular resolution
data at 240, 324, 610, and 1380 MHz using different techniques. The three
extended arms associated with this SNR, show a clear indication of spectral
steepening when moving outwards from the central nebula, with variations of up
to - 0.9. However, while the spectral steepening is smooth along the eastern
arm, the northern and soutwestern arms include locally flatter structures,
which in all cases coincide with radio, IR, and optical emission enhancements.
We interpret this spectral property as the result of the combination of two
different particle populations: aging relativistic electrons injected by PSR
B1951+32 and particles accelerated at the sites where the SNR shock front
encounters interstellar gas inhomogeneities. Concerning the central nebula, the
angular resolution of the available database does not permit a detailed
spectral study of the core region, i.e. the 45'' region around PSR B1951+32,
where we can only confirm an average spectral index alpha=0.0. The surrounding
8' plateau nebula has an ~ -0.25, with a peak of alpha ~ -0.29
coincident with a secondary maximun located at the termination of a twisted
filament that trails to the east, behind the pulsar.Comment: 7 pages, 6 figure
A hadronic scenario for HESS J1818-154
Aims: G15.4+0.1 is a faint supernova remnant (SNR) that has recently been
associated with the gamma-ray source HESS J1818-154. We investigate a hadronic
scenario for the production of the gamma-ray emission. Methods: Molecular 13CO
(J=1-0) taken from the Galactic Ring Survey (GRS) and neutral hydrogen (HI)
data from the Southern Galactic Plane Survey (SGPS) have been used in
combination with new 1420 MHz radio continuum observations carried out with the
Giant Metrewave Radio Telescope (GMRT). Results: From the new observations and
analysis of archival data we provided for the first time a reliable estimate
for the distance to the SNR G15.4+0.1 and discovered molecular clouds located
at the same distance. On the basis of HI absorption features, we estimate the
distance to G15.4+0.1 in 4.8+/-1.0 kpc. The 13CO observations clearly show a
molecular cloud about 5 arcmin in size with two bright clumps, labeled A and B,
clump A positionally associated with the location of HESS J1818-154 and clump B
in coincidence with the brightest northern border of the radio SNR shell. The
HI absorption and the 13CO emission study indicates a possible interaction
between the molecular material and the remnant. We estimate the masses and
densities of the molecular gas as (1.2+/-0.5)X10^3 M_sun and (1.5+/-0.4)X10^3
cm^-3 for clump A and (3.0+/-0.7)X10^3 M_sun and (1.1+/-0.3)X10^3 cm^-3 for
clump B. Calculations show that the average density of the molecular clump A is
sufficient to produce the detected gamma-ray flux, thus favoring a hadronic
origin for the high-energy emission.Comment: Accepted to be published in Astronomy and Astrophysics Letter
Feature-tailored spectroscopic analysis of the SNR Puppis A in X-rays
We introduce a distinct method to perform spatially-resolved spectral
analysis of astronomical sources with highly structured X-ray emission. The
method measures the surface brightness of neighbouring pixels to adaptively
size and shape each region, thus the spectra from the bright and faint
filamentary structures evident in the broadband images can be extracted. As a
test case, we present the spectral analysis of the complete X-ray emitting
plasma in the supernova remnant Puppis A observed with XMM-Newton and Chandra.
Given the angular size of Puppis A, many pointings with different observational
configurations have to be combined, presenting a challenge to any method of
spatially-resolved spectroscopy. From the fit of a plane-parallel shocked
plasma model we find that temperature, absorption column, ionization time
scale, emission measure and elemental abundances of O, Ne, Mg, Si, S and Fe,
are smoothly distributed in the remnant. Some regions with overabundances of
O-Ne-Mg, previously characterized as ejecta material, were automatically
selected by our method, proving the excellent response of the technique. This
method is an advantageous tool for the exploitation of archival X-ray data.Comment: Accepted in Astronomy & Astrophysic
Radio and X-ray study of two multi-shell Supernova Remnants: Kes79 and G352.7-0.1
We investigate two multi-shell galactic supernova remnants (SNRs), Kes79 and
G352.7-0.1, to understand the causes of such morphology. The research was
carried out based on new and reprocessed archival VLA observations and
XMM-Newton archival data. The surrounding was investigated based on data
extracted from the HI Canadian Galactic Plane Survey, the 13^CO Galactic Ring
Survey and the HI Southern Galactic Plane Survey. The present study revealed
that the overall morphology of both SNRs is the result of the mass-loss history
of their respective progenitor stars. Kes79 would be the product of the
gravitational collapse of a massive O9 star evolving near a molecular cloud and
within the precursor's wind-driven bubble, while G352.7-0.1 would be the result
of interactions of the SNR with an asymmetric wind from the progenitor together
with projection effects. No radio point source or pulsar wind nebula was found
associated with the X-ray pulsar CXOU J185238.6+004020 in Kes79. The X-ray
study of G352.7-0.1, on its hand, revealed that most of the thermal X-ray
radiation completely fills in the interior of the remnant and originates in
heated ejecta. Characteristic parameters, like radio flux, radio spectral
index, age, distance, shock velocity, initial energy and luminosity, were
estimated for both SNRs.Comment: 14 pages, 13 figures. Accepted to be published in Astronomy and
Astrophysic
The most complete and detailed X-ray view of the SNR Puppis A
With the purpose of producing the first detailed full view of Puppis A in
X-rays, we carried out new XMM-Newton observations covering the missing regions
in the southern half of the supernova remnant (SNR) and combined them with
existing XMM-Newton and Chandra data. The new images were produced in the
0.3-0.7, 0.7-1.0 and 1.0-8.0 energy bands. We investigated the SNR morphology
in detail, carried out a multi-wavelength analysis and estimated the flux
density and luminosity of the whole SNR. The complex structure observed across
the remnant confirms that Puppis A evolves in an inhomogeneous, probably knotty
interstellar medium. The southwestern corner includes filaments that perfectly
correlate with radio features suggested to be associated with shock/cloud
interaction. In the northern half of Puppis A the comparison with Spitzer
infrared images shows an excellent correspondence between X-rays and 24 and 70
microns emission features, while to the south there are some matched and other
unmatched features. X-ray flux densities of 12.6 X 10^-9, 6.2 X 10^-9, and 2.8
X 10^-9 erg cm^-2 s^-1 were derived for the 0.3-0.7, 0.7-1.0 and 1.0-8.0 keV
bands, respectively. At the assumed distance of 2.2 kpc, the total X-ray
luminosity between 0.3 and 8.0 keV is 1.2 X 10^37 erg s^-1. We also collected
and updated the broad-band data of Puppis A between radio and GeV gamma-ray
range, producing its spectral energy distribution. To provide constraints to
the high-energy emission models, we re-analyzed radio data, estimating the
energy content in accelerated particles to be Umin=4.8 X 10^49 erg and the
magnetic field strength B=26 muG.Comment: Article accepted to be published in the Astronomy and Astrophysics
Main Journa
A complete radio study of SNR G15.4+0.1 from new GMRT observations
The supernova remnant G15.4+0.1 is considered to be the possible counterpart
of the gamma-ray source HESSJ1818-154. With the goal of getting a complete view
of this remnant and understanding the nature of the gamma-ray flux, we
conducted a detailed radio study that includes the search for pulsations and a
model of the broadband emission for the G15.4+0.1/HESSJ1818-154 system.
Low-frequency imaging at 624 MHz and pulsar observations at 624 and 1404 MHz
towards G15.4+0.1 were carried out with the Giant Metrewave Radio Telescope
(GMRT). We correlated the new radio data with observations of the source at
X-ray and infrared wavelengths from XMM-Newton and Herschel observatories,
respectively. To characterize the neutral hydrogen medium (HI) towards
G15.4+0.1, we used data from the Southern Galactic Plane Survey. We modelled
the spectral energy distribution using both hadronic and leptonic scenarios.
From the combination of the new GMRT observations with existing data, we
derived a continuum spectral index alpha=-0.62+-0.03 for the whole remnant. The
local synchrotron spectra of G15.4+0.1, calculated from the combination of the
GMRT data with 330 MHz observations from the VLA, tends to be flatter in the
central part of the remnant, accompanying the region where the blast wave is
impinging molecular gas. No spectral index trace was found indicating the radio
counterpart to the pulsar wind nebula proposed from X-ray observations. In
addition, the search for radio pulsations yielded negative results. Emission at
far-infrared wavelengths is observed in the region where the SNR shock is
interacting with dense molecular clumps. We also identified HI features forming
a shell that wraps most of the outer border of G15.4+0.1. Characteristic
parameters were estimated for the shocked HI gas. We found that either a purely
hadronic or leptonic model is compatible with the broadband emission known so
far.Comment: 11 pages, 9 figures, accepted for publication in Astronomy &
Astrophysic
The Supernova Remnant W44: confirmations and challenges for cosmic-ray acceleration
The middle-aged supernova remnant (SNR) W44 has recently attracted attention
because of its relevance regarding the origin of Galactic cosmic-rays. The
gamma-ray missions AGILE and Fermi have established, for the first time for a
SNR, the spectral continuum below 200 MeV which can be attributed to neutral
pion emission. Confirming the hadronic origin of the gamma-ray emission near
100 MeV is then of the greatest importance. Our paper is focused on a global
re-assessment of all available data and models of particle acceleration in W44,
with the goal of determining on a firm ground the hadronic and leptonic
contributions to the overall spectrum. We also present new gamma-ray and CO
NANTEN2 data on W44, and compare them with recently published AGILE and Fermi
data. Our analysis strengthens previous studies and observations of the W44
complex environment and provides new information for a more detailed modeling.
In particular, we determine that the average gas density of the regions
emitting 100 MeV - 10 GeV gamma-rays is relatively high (n= 250 - 300 cm^-3).
The hadronic interpretation of the gamma-ray spectrum of W44 is viable, and
supported by strong evidence. It implies a relatively large value for the
average magnetic field (B > 10^2 microG) in the SNR surroundings, sign of field
amplification by shock-driven turbulence. Our new analysis establishes that the
spectral index of the proton energy distribution function is p1 = 2.2 +/- 0.1
at low energies and p2 = 3.2 +/- 0.1 at high energies. We critically discuss
hadronic versus leptonic-only models of emission taking into account
simultaneously radio and gamma-ray data. We find that the leptonic models are
disfavored by the combination of radio and gamma-ray data. Having determined
the hadronic nature of the gamma-ray emission on firm ground, a number of
theoretical challenges remains to be addressed.Comment: 13 pages, 11 figures, accepted by A&
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