481 research outputs found
Observations of flux rope ? associated particle bursts with GEOTAIL in the distant tail
International audienceGeotail energetic particle, magnetic field data and plasma observations (EPIC, MGF and CPI experiments) have been examined for a number of energetic particle bursts in the distant tail (120ReGSM|By and/or Bz components, is consistent with the existence of closed field lines extending from Earth and wrapping around the core of the flux rope structure
Suzaku Observation of Two Ultraluminous X-Ray Sources in NGC 1313
Two ultraluminous X-ray sources (ULXs) in the nearby Sb galaxy NGC 1313,
named X-1 and X-2, were observed with Suzaku on 2005 September 15. During the
observation for a net exposure of 28~ks (but over a gross time span of 90~ks),
both objects varied in intensity by about 50~%. The 0.4--10 keV X-ray
luminosity of X-1 and X-2 was measured as
and , respectively, with the former the
highest ever reported for this ULX. The spectrum of X-1 can be explained by a
sum of a strong and variable power-law component with a high energy cutoff, and
a stable multicolor blackbody with an innermost disk temperature of
keV. These results suggest that X-1 was in a ``very high'' state, where the
disk emission is strongly Comptonized. The absorber within NGC 1313 toward X-1
is suggested to have a subsolar oxygen abundance. The spectrum of X-2 is best
represented, in its fainter phase, by a multicolor blackbody model with the
innermost disk temperature of 1.2--1.3 keV, and becomes flatter as the source
becomes brighter. Hence X-2 is interpreted to be in a slim-disk state. These
results suggest that the two ULXs have black hole masses of a few tens to a few
hundreds solar masses.Comment: accepted for publication in PAS
Suzaku Observations of Active Galactic Nuclei Detected in the Swift/BAT Survey: Discovery of "New Type" of Buried Supermassive Black Holes
We present the Suzaku broad band observations of two AGNs detected by the
Swift/BAT hard X-ray (>15 keV) survey that did not have previous X-ray data,
Swift J0601.9-8636 and Swift J0138.6-4001. The Suzaku spectra reveals in both
objects a heavily absorbed power law component with a column density of NH =~
10^{23.5-24} cm^{-2} that dominates above 10 keV, and an intense reflection
component with a solid angle >~ from a cold, optically thick medium. We
find that these AGNs have an extremely small fraction of scattered light from
the nucleus, <~ 0.5% with respect to the intrinsic power law component. This
indicates that they are buried in a very geometrically-thick torus with a small
opening angle and/or have unusually small amount of gas responsible for
scattering. In the former case, the geometry of Swift J0601.9-8636 should be
nearly face-on as inferred from the small absorption for the reflection
component. The discovery of two such objects in this small sample implies that
there must be a significant number of yet unrecognized, very Compton thick AGNs
viewed at larger inclination angles in the local universe, which are difficult
to detect even in the currently most sensitive optical or hard X-ray surveys.Comment: 4 pages, 3 figures, accepted for publication in ApJ Lette
XMM-Newton and Suzaku detection of an X-ray emitting shell around the pulsar wind nebula G54.1+0.3
Recent X-ray observations have proved to be very effective in detecting
previously unknown supernova remnant shells around pulsar wind nebulae (PWNe),
and in these cases the characteristics of the shell provide further clues on
the evolutionary stage of the embedded PWN. However, it is not clear why some
PWNe are still "naked". We carried out an X-ray observational campaign targeted
at the PWN G54.1+0.3, the "close cousin" of the Crab, with the aim to detect
the associated SNR shell. We analyzed an XMM-Newton and Suzaku observations of
G54.1+0.3 and we model out the contribution of dust scattering halo. We
detected an intrinsic faint diffuse X-ray emission surrounding a hard spectrum,
which can be modeled either with a power-law (gamma= 2.9) or with a thermal
plasma model (kT=2.0 keV.). If the shell is thermal, we derive an explosion
energy E=0.5-1.6x10^51 erg, a pre-shock ISM density of 0.2 cm^-3 and an age of
about 2000 yr. Using these results in the MHD model of PWN-SNR evolution, we
obtain an excellent agreement between the predicted and observed location of
the shell and PWN shock.Comment: Accepted for publication in A&A, 8 pages, 5 figures, full-res version
at http://www.astropa.inaf.it/Library/OAPA_preprints/h14298.pd
A strong excess in the 20-100 keV emission of NGC 1365
We present a new Suzaku observation of the obscured AGN in NGC 1365,
revealing an unexpected excess of X-rays above 20 keV of at least a factor ~2
with respect to the extrapolation of the best-fitting 3-10 keV model.
Additional Swift-BAT and Integral-IBIS observations show that the 20-100 keV is
concentrated within ~1.5 arcmin from the center of the galaxy, and is not
significantly variable on time scales from days to years. A comparison of this
component with the 3-10 keV emission, which is characterized by a rapidly
variable absorption, suggests a complex structure of the circumnuclear medium,
consisting of at least two distinct components with rather different physical
properties, one of which covering >80% of the source with a column density
NH~3-4x10^24 cm^(-2). An alternative explanation is the presence of a double
active nucleus in the center of NGC 1365.Comment: 13 pages, 3 figures. Accepted for publication in ApJ Letter
X-Ray Spectral Variability of the Seyfert Galaxy NGC 4051 Observed with Suzaku
We report results from a Suzaku observation of the narrow-line Seyfert 1 NGC
4051. During our observation, large amplitude rapid variability is seen and the
averaged 2--10 keV flux is 8.1x10^-12 erg s^-1 cm^-2, which is several times
lower than the historical average. The X-ray spectrum hardens when the source
flux becomes lower, confirming the trend of spectral variability known for many
Seyfert 1 galaxies. The broad-band averaged spectrum and spectra in high and
low flux intervals are analyzed. The spectra are first fitted with a model
consisting of a power-law component, a reflection continuum originating in cold
matter, a blackbody component, two zones of ionized absorber, and several
Gaussian emission lines. The amount of reflection is rather large (R ~ 7, where
R=1 corresponds to reflection by an infinite slab), while the equivalent width
of the Fe-K line at 6.4 keV is modest (140 eV) for the averaged spectrum. We
then model the overall spectra by introducing partial covering for the
power-law component and reflection continuum independently. The column density
for the former is 1x10^23 cm^-2, while it is fixed at 1x10^24 cm-2 for the
latter. By comparing the spectra in different flux states, we identify the
causes of spectral variability. (abridged)Comment: 19 pages, 18 figures, accepted for publication in PASJ (Suzaku 3rd
special issue
Prospect of Studying Hard X- and Gamma-Rays from Type Ia Supernovae
We perform multi-dimensional, time-dependent radiation transfer simulations
for hard X-ray and gamma-ray emissions, following radioactive decays of 56Ni
and 56Co, for two-dimensional delayed detonation models of Type Ia supernovae
(SNe Ia). The synthetic spectra and light curves are compared with the
sensitivities of current and future observatories for an exposure time of 10^6
seconds. The non-detection of the gamma-ray signal from SN 2011fe at 6.4 Mpc by
SPI on board INTEGRAL places an upper limit for the mass of 56Ni of \lesssim
1.0 Msun, independently from observations in any other wavelengths. Signals
from the newly formed radioactive species have not been convincingly measured
yet from any SN Ia, but the future X-ray and gamma-ray missions are expected to
deepen the observable horizon to provide the high energy emission data for a
significant SN Ia sample. We predict that the hard X-ray detectors on board
NuStar (launched in 2012) or ASTRO-H (scheduled for launch in 2014) will reach
to SNe Ia at \sim15 Mpc, i.e., one SN every few years. Furthermore, according
to the present results, the soft gamma-ray detector on board ASTRO-H will be
able to detect the 158 keV line emission up to \sim25 Mpc, i.e., a few SNe Ia
per year. Proposed next generation gamma-ray missions, e.g., GRIPS, could reach
to SNe Ia at \sim20 - 35 Mpc by MeV observations. Those would provide new
diagnostics and strong constraints on explosion models, detecting rather
directly the main energy source of supernova light.Comment: 14 pages, 7 figures, 1 table, accepted for publication in Ap
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