86 research outputs found
Nonthermal emission properties of the northwestern rim of supernova remnant RX J0852-4622
The supernova remnant (SNR) RX J0852-4622 (Vela Jr., G266.6-1.2) is one of
the most important SNRs for investigating the acceleration of multi-TeV
particles and the origin of Galactic cosmic rays because of its strong
synchrotron X-ray and TeV gamma-ray emission, which show a shell-like
morphology similar to each other. Using the XMM-Newton archival data consisting
of multiple pointing observations of the northwestern rim of the remnant, we
investigate the spatial properties of the nonthermal X-ray emission as a
function of distance from an outer shock wave. All X-ray spectra are well
reproduced by an absorbed power-law model above 2 keV. It is found that the
spectra show gradual softening from a photon index 2.56 in the rim region to
2.96 in the interior region. We show that this radial profile can be
interpreted as a gradual decrease of the cutoff energy of the electron spectrum
due to synchrotron cooling. By using a simple spectral evolution model that
includes continuous synchrotron losses, the spectral softening can be
reproduced with the magnetic field strength in the post-shock flow to less than
several tens of uG. If this is a typical magnetic field in the SNR shell,
gamma-ray emission would be accounted for by inverse Compton scattering of
high-energy electrons that also produce the synchrotron X-ray emission. Future
hard X-ray imaging observations with Nustar and ASTRO-H and TeV gamma-ray
observations with the Cherenkov Telescope Array (CTA) will allow to us to
explore other possible explanations of the systematic softening of the X-ray
spectra.Comment: accepted by A&
Overabundance of Calcium in the young SNR RX J08524622: evidence of over-production of Ti
Recently, COMPTEL has detected -rays of 1157 keV from Ti in
the direction of the SNR RX J08524622 (Iyudin et al. 1998). Since Ti
is a product of explosive nucleosynthesis and its half lifetime \tau\sb{1/2}
is about 60 yrs, RX J08524622 must be a young supernova remnant and
radiation is dominated by the ejecta rather than by interstellar matter. We
have detected an X-ray emission line at keV which is thought to
come from highly ionized Ca. The emission line is so far only seen in the
north-west shell region of RX J08524622. The X-ray spectrum can be well
fitted with that of thin hot plasma of cosmic abundances except that of Ca,
which is overabundant by a factor of . Assuming that most of Ca is
Ca, which originates from Ti by radioactive decay, we estimate a
total Ca mass of about . Combining the amount of
Ca and the observed flux of the Ti -ray line, the age of
RX J08524622 is around 1000 yrs.Comment: 14 pages, 5figures, accepted for publication of PAS
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
The Performance Test of pnCCD with FPGA-Based Operating System for a CubeSat Mission
On 17 August 2017, the LIGO/Virgo collaboration detected a signal of gravitational waves, named GW170817, associated with the merger of two neutron stars. This event was the first detection of the electromagnetic counterpart of gravitational wave events. In general, the error image region of the gravitational wave detectors ranges from a few square degrees to several hundred square degrees. To search for the origin of the gravitational waves or the energetic explosions such as the gamma-ray burst, X-ray observation covering a wide field of view with a good sensitivity is essential to achieve the goal. One of the good candidate instruments to achieve our goal is the combination of an X-ray optics called Lobster-eye optics (LEO) and a large area Si pixel imaging sensor. Furthermore, thanks to the light weight of LEO, it is possible to install on a small platform such as a CubeSat. Here, we introduce a future 3U CubeSat mission for searching the electromagnetic counterpart of gravitational waves in the soft X-ray band (0.4 ~ 10 keV) with ~arcmin localization accuracy. The pnCCD detector fabricated by PNSensor Inc. can achieve our mission requirements as an X-ray detector. To operate the pnCCD detector, we developed an FPGA-based fast readout system which is a very compact design to install on the CubeSat mission.Also, we investigate the readout noise of CAMEX, which is the readout ASIC of pnCCD. As a result, the readout noise was ~ 7.4 e-. In this paper, we report the performance of pnCCD applying our compact FPGA-based data processing system
Discriminating the Progenitor Type of Supernova Remnants with Iron K-Shell Emission
Supernova remnants (SNRs) retain crucial information about both their parent
explosion and circumstellar material left behind by their progenitor. However,
the complexity of the interaction between supernova ejecta and ambient medium
often blurs this information, and it is not uncommon for the basic progenitor
type (Ia or core-collapse) of well-studied remnants to remain uncertain. Here
we present a powerful new observational diagnostic to discriminate between
progenitor types and constrain the ambient medium density of SNRs solely using
Fe K-shell X-ray emission. We analyze all extant Suzaku observations of SNRs
and detect Fe K alpha emission from 23 young or middle-aged remnants, including
five first detections (IC 443, G292.0+1.8, G337.2-0.7, N49, and N63A). The Fe K
alpha centroids clearly separate progenitor types, with the Fe-rich ejecta in
Type Ia remnants being significantly less ionized than in core-collapse SNRs.
Within each progenitor group, the Fe K alpha luminosity and centroid are well
correlated, with more luminous objects having more highly ionized Fe. Our
results indicate that there is a strong connection between explosion type and
ambient medium density, and suggest that Type Ia supernova progenitors do not
substantially modify their surroundings at radii of up to several parsecs. We
also detect a K-shell radiative recombination continuum of Fe in W49B and IC
443, implying a strong circumstellar interaction in the early evolutionary
phases of these core-collapse remnants.Comment: Accepted by ApJL; 5 pages with just 1 table and 1 figur
Search for Sc-K line emission from RX J0852.0--4622 Supernova remnant with Suzaku
We searched for evidence of line emission around 4keV from the northwestern
rim of the supernova remnant RX J0852.0-4622 using Suzaku XIS data. Several
papers have reported the detection of an emission line around 4.1keV from this
region of the sky. This line would arise from K-band fluorescence by Sc, the
immediate decay product of 44Ti. We performed spectral analysis for the entire
portion of the NW rim of the remnant within the XIS field of view, as well as
various regions corresponding to regions of published claims of line emission.
We found no line emission around 4.1keV anywhere, and are able to set a
restrictive upper limit to the X-ray flux: 1.1x10^-6 s^-1 cm^-2 for the entire
field. For every region, our flux upper limit falls below that of the
previously claimed detection. Therefore, we conclude that, to date, no definite
X-ray line feature from Sc-K emission has been detected in the NW rim of RX
J0852.0-4622. Our negative-detection supports the recent claim that RX
J0852-4622 is neither young (1700--4000 yr) nor nearby(~750 pc).Comment: Published in PAS
Measuring the Broad-band X-Ray Spectrum from 400 eV to 40 keV in the Southwest Part of the Supernova Remnant RX J1713.7-3946
We report on results from Suzaku broadband X-ray observations of the
southwest part of the Galactic supernova remnant (SNR) RX J1713.7-3946 with an
energy coverage of 0.4-40 keV. The X-ray spectrum, presumably of synchrotron
origin, is known to be completely lineless, making this SNR ideally suited for
a detailed study of the X-ray spectral shape formed through efficient particle
acceleration at high speed shocks. With a sensitive hard X-ray measurement from
the HXD PIN on board Suzaku, we determine the hard X-ray spectrum in the 12--40
keV range to be described by a power law with photon index Gamma = 3.2+/- 0.2,
significantly steeper than the soft X-ray index of Gamma = 2.4+/- 0.05 measured
previously with ASCA and other missions. We find that a simple power law fails
to describe the full spectral range of 0.4-40 keV and instead a power-law with
an exponential cutoff with hard index Gamma = 1.50+/- 0.09 and high-energy
cutoff epsilon_c = 1.2+/- 0.3 keV formally provides an excellent fit over the
full bandpass. If we use the so-called SRCUT model, as an alternative model, it
gives the best-fit rolloff energy of epsilon_{roll} = 0.95+/- 0.04 keV.
Together with the TeV gamma-ray spectrum ranging from 0.3 to 100 TeV obtained
recently by HESS observations, our Suzaku observations of RX J1713.7-3946
provide stringent constraints on the highest energy particles accelerated in a
supernova shock.Comment: 11 pages, 11 figures, accepted for publication in Publications of the
Astronomical Society of Japan (PASJ
A Suzaku Observation of the Low-Ionization Fe-Line Emission from RCW 86
The newly operational X-ray satellite Suzaku observed the southwestern
quadrant of the supernova remnant (SNR) RCW 86 in February 2006 to study the
nature of the 6.4 keV emission line first detected with the Advanced Satellite
for Cosmology and Astronomy (ASCA). The new data confirm the existence of the
line, localizing it for the first time; most of the line emission is adjacent
and interior to the forward shock and not at the locus of the continuum hard
emission. We also report the first detection of a 7.1 keV line that we
interpret as the K-beta emission from low-ionization iron. The Fe-K line
features are consistent with a non-equilibrium plasma of Fe-rich ejecta with
n_{e}t <~ 10^9 cm^-3 s and kT_{e} ~ 5 keV. This combination of low n_{e}t and
high kT_{e} suggests collisionless electron heating in an SNR shock. The Fe
K-alpha line shows evidence for intrinsic broadening, with a width of 47
(34--59) eV (99% error region). The difference of the spatial distributions of
the hard continuum above 3 keV and the Fe-K line emission support a synchrotron
origin for the hard continuum.Comment: 6 pages with 6 figures. Accepted for PASJ Suzaku Special Issue (vo.
58, sp.1
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