56 research outputs found
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
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
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
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
Discovery of a possible X-ray counterpart to HESS J1804-216
Suzaku deep observations have discovered two highly significant nonthermal
X-ray sources, Suzaku J18042142 (Src 1) and Suzaku J18042140 (Src 2),
positionally coincident with the unidentified TeV -ray source, HESS
J1804216. The X-ray sources are not time variable and show no counterpart in
other wavebands, except for the TeV source. Src 1 is unresolved at Suzaku
spatial resolution, whereas Src 2 is extended or composed of multiple sources.
The X-ray spectra are highly absorbed, hard, and featureless, and are well
fitted by absorbed power-law models with best-fit photon indices and absorption
columns of and cm
for Src 1, and and
cm for Src 2. The measured X-ray absorption to the latter source is
significantly larger than the total Galactic neutral hydrogen column in that
direction. The unabsorbed 2--10 keV band luminosities are ergs s (Src 1) and ergs s (Src 2), where is the source distance. Among the
handful of TeV sources with known X-ray counterparts, HESS J1804216 has the
largest ratio of TeV -ray to hard X-ray fluxes. We discuss the nature
of the emission and propose the Suzaku sources as plausible counterparts to the
TeV source, although further observations are necessary to confirm this.Comment: 12 pages, 5 figures, Publications of the Astronomical Society of
Japan, in pres
X-Ray Spectroscopy of SN 1006 with Suzaku
We report on observations of SN 1006 with the X-ray Imaging Spectrometers
(XIS) on board Suzaku. We firmly detected K-shell emission from Fe, for the
first time, and find that the Fe ionization state is quite low. The broad band
spectrum extracted from the southeast of the remnant is well fitted with a
model consisting of three optically thin thermal non-equilibrium ionization
plasmas and a power-law component. Two of the thermal models are highly
overabundant in heavy elements and, hence, are likely due to ejecta. These
components have different ionization parameters:
cm s and cm s and it is the later one
that produces the Fe-K emission. This suggests that Fe has been heated by the
reverse shock more recently than the other elements, consistent with a picture
where the ejecta are stratified by composition with Fe in the interior. On the
other hand, the third thermal component is assumed to be solar abundance, and
we associate it with emission from the interstellar medium (ISM). The electron
temperature and ionization parameter are 0.5 keV and cm s. The electron temperature is lower than that
expected from the shock velocity which suggests a lack of collisionless
electron heating at the forward shock. The extremely low ionization parameter
and extreme non-equilibrium state are due to the low density of the ambient
medium.Comment: 12 pages, 9 figures (14 figure files), accepted for publication in
PAS
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