84 research outputs found
Suzaku Discovery of a Hard X-Ray Tail in the Persistent Spectra from the Magnetar 1E 1547.0-5408 during its 2009 Activity
The fastest-rotating magnetar 1E 1547.0-5408 was observed in broad-band
X-rays with Suzaku for 33 ks on 2009 January 28-29, 7 days after the onset of
its latest bursting activity. After removing burst events, the
absorption-uncorrected 2-10 keV flux of the persistent emission was measured
with the XIS as 5.7e-11 ergs cm-2 s-1, which is 1-2 orders of magnitude higher
than was measured in 2006 and 2007 when the source was less active. The
persistent emission was also detected significantly with the HXD in >10 keV up
to at least ~110 keV, with an even higher flux of 1.3e-10 ergs cm-2 s-1 in
20-100 keV. The pulsation was detected at least up to 70 keV at a period of
2.072135+/-0.00005 s, with a deeper modulation than was measured in a fainter
state. The phase-averaged 0.7-114 keV spectrum was reproduced by an absorbed
blackbody emission with a temperature of 0.65+/-0.02 keV, plus a hard power-law
with a photon index of ~1.5. At a distance of 9 kpc, the bolometric luminosity
of the blackbody and the 2-100 keV luminosity of the hard power-law are
estimated as (6.2+/-1.2)e+35 ergs s-1 and 1.9e+36 ergs s-1, respectively, while
the blackbody radius becomes ~5 km. Although the source had not been detected
significantly in hard X-rays during the past fainter states, a comparison of
the present and past spectra in energies below 10 keV suggests that the hard
component is more enhanced than the soft X-ray component during the persistent
activity.Comment: 12 pages, 7 figures, PASJ Vol.62 No.2 accepte
Suppression of Interferon-induced Oligo-2\u27, 5\u27-adenylate Synthetase Induction in Human Hepatoma Cell Line, Li-7
Induction of oligo-2\u27, 5\u27-adenylate synthetase (2-5AS) activity by interferon (IFN) was investigated in a human hepatoma cell line, Li-7 cells. Little induction of 2-5AS activity by IFN was demonstrated in Li-7 cells in comparison with other types of cell lines including Ramos, NC-37, FL, Co-3. Furthermore, failure to induce 2-5AS was much clearer in old-cultured cells. Cell growth inhibition by IFN was demonstrated in only high titers of IFN (>10? IU/ml), in which the enzyme had one hundred fold higher activity than that of untreated cells. Poor induction of 2-5AS was in part the result of some inhibitor presented in cellular extracts of Li-7 cells and the decreased level of 2-5AS mRNA transcription
Iron and Nickel Line Diagnostics for the Galactic Center Diffuse Emission
We have observed the diffuse X-ray emission from the Galactic center (GC)
using the X-ray Imaging Spectrometer (XIS) on Suzaku. The high-energy
resolution and the low-background orbit provide excellent spectra of the GC
diffuse X-rays (GCDX). The XIS found many emission lines in the GCDX near the
energy of K-shell transitions of iron and nickel. The most pronounced features
are FeI K alpha at 6.4 keV and K-shell absorption edge at 7.1 keV, which are
from neutral and/or low ionization states of iron, and the K-shell lines at 6.7
keV and 6.9 keV from He-like (FeXXV K alpha) and hydrogenic (FeXXVI Ly alpha)
ions of iron. In addition, K alpha lines from neutral or low ionization nickel
(NiI K alpha) and He-like nickel (NiXXVII K alpha), and FeI K beta, FeXXV K
beta, FeXXVI Ly beta, FeXXV K gamma and FeXXVI Ly gamma are detected for the
first time. The line center energies and widths of FeXXV K alpha and FeXXVI Ly
alpha favor a collisional excitation (CE) plasma for the origin of the GCDX.
The electron temperature determined from the line flux ratio of FeXXV K alpha /
FeXXV K beta is similar to the ionization temperature determined from that of
FeXXV K alpha /FeXXVI Ly alpha. Thus it would appear that the GCDX plasma is
close to ionization equilibrium. The 6.7 keV flux and temperature distribution
to the galactic longitude is smooth and monotonic,in contrast to the integrated
point source flux distribution. These facts support the hypothesis that the
GCDX is truly diffuse emission rather than the integration of the outputs of a
large number of unresolved point sources. In addition, our results demonstrate
that the chemical composition of Fe in the interstellar gas near the GC is
constrained to be about 3.5 times solar.Comment: 11 pages, 19 figures. Accepted for publication in PASJ Suzaku Special
Issue (vol. 59 sp. 1
Effect of Interferon on Cells Persistently Infected with Human T Cell Leukemia Virus (HTLV-I)
Spontaneous production of interferon-gamma (IFN- γ) was shown in four (MT-1, MT-2, SMT-1 and HUT 102) of five human T-lymphoblastoid cell lines persistently infected with human T cell leukemea virus type I (MT-1, MT-2, SMT-1, HUT 102 and OKM-2). These four cell lines were not susceptible to the antivirus effect of IFN. In contrast, the multiplication of vesicular stomatitis virus (VSV) was restricted in the nonproducer cell line of IFN, OKM-2 cells by treatment of IFN- α or IFN- γ. Anti-proliferation effect of IFN w as investigated in producer cell line of IFN (MT-2 and SMT-1) and non-producer cell line of IFN (OKM-2). The growth of MT-2 cells was not affected by IFN- α or by IFN- γ. However, SMT-1 and OKM-2 cells were affected by treatment with externally added IFN-α
Spectral evolution of GRB 060904A observed with Swift and Suzaku -- Possibility of Inefficient Electron Acceleration
We observed an X-ray afterglow of GRB 060904A with the Swift and Suzaku
satellites. We found rapid spectral softening during both the prompt tail phase
and the decline phase of an X-ray flare in the BAT and XRT data. The observed
spectra were fit by power-law photon indices which rapidly changed from to within a few hundred
seconds in the prompt tail. This is one of the steepest X-ray spectra ever
observed, making it quite difficult to explain by simple electron acceleration
and synchrotron radiation. Then, we applied an alternative spectral fitting
using a broken power-law with exponential cutoff (BPEC) model. It is valid to
consider the situation that the cutoff energy is equivalent to the synchrotron
frequency of the maximum energy electrons in their energy distribution. Since
the spectral cutoff appears in the soft X-ray band, we conclude the electron
acceleration has been inefficient in the internal shocks of GRB 060904A. These
cutoff spectra suddenly disappeared at the transition time from the prompt tail
phase to the shallow decay one. After that, typical afterglow spectra with the
photon indices of 2.0 are continuously and preciously monitored by both XRT and
Suzaku/XIS up to 1 day since the burst trigger time. We could successfully
trace the temporal history of two characteristic break energies (peak energy
and cutoff energy) and they show the time dependence of while the following afterglow spectra are quite stable. This fact
indicates that the emitting material of prompt tail is due to completely
different dynamics from the shallow decay component. Therefore we conclude the
emission sites of two distinct phenomena obviously differ from each other.Comment: 19 pages, 9 figures, accepted for publication in PASJ (Suzaku 2nd
Special Issue
Mapping dusty star formation in and around a cluster at z=0.81 by wide-field imaging with AKARI
We present environmental dependence of dusty star forming activity in and
around the cluster RXJ1716.4+6708 at z=0.81 based on wide-field and
multi-wavelength observations with Suprime-Cam on the Subaru telescope and IRC
onboard the AKARI satellite. Our optical data shows that the optical colour
distribution of galaxies starts to dramatically change from blue to red at the
medium-density environment such as cluster outskirts, groups and filaments. By
combining with infrared data, we find that 15 micron galaxies tend to have
optical colours between the red sequence and the blue cloud with a tail into
the red sequence.
The spatial distribution of the 15 micron galaxies over ~200 arcmin^2 around
the cluster reveals that few 15 micron galaxies are detected in the cluster
central region. This is probably due to the low star forming activity in the
cluster core. However, interestingly, the fraction of 15 micron galaxies in the
medium-density environments is as high as in the low-density field, despite the
fact that the optical colours start to change in the medium-density
environments. Furthermore, we find that 15 micron galaxies which have optically
red colours (candidates for dusty red galaxies) and galaxies with high specific
star formation rates are also concentrated in the medium-density environment.
These results imply that the star forming activity in galaxies in groups and
filaments is enhanced due to some environmental effects specific to the
medium-density environment, and such a phenomenon is probably directly
connected to the truncation of star forming activity in galaxies seen as the
dramatic change in optical colours in such environments.Comment: 15 pages, 14 figures, accepted for publication in MNRA
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