arXiv subjects

Rie Sato

Publications and source records attributed to Rie Sato.

22 records · Page 2Linked to original sources

arXiv2006

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.

astro-ph↗

arXiv2006

An Optically Dark GRB Observed by HETE-2: GRB 051022

GRB 051022 was detected at 13:07:58 on 22 October 2005 by HETE-2. The location of GRB 051022 was determined immediately by the flight localization system. This burst contains multiple pulses and has a rather long duration of about 190 seconds. The detections of candidate X-ray and radio afterglows were reported, whereas no optical afterglow was found. The optical spectroscopic observations of the host galaxy revealed the redshift z = 0.8. Using the data derived by HETE-2 observation of the prompt emission, we found the absorption N_H = 8.8 -2.9/+3.1 x 10^22 cm^-2 and the visual extinction A_V = 49 -16/+17 mag in the host galaxy. If this is the case, no detection of any optical transient would be quite reasonable. The absorption derived by the Swift XRT observations of the afterglow is fully consistent with those obtained from the early HETE-2 observation of the prompt emission. Our analysis implies an interpretation that the absorbing medium could be outside external shock at R ~ 10^16 cm, which may be a dusty molecular cloud.

astro-ph↗

arXiv2005

Synchronized Magnetization Oscillations in F/N/F Nanopillars

Current-induced magnetization dynamics in a trilayer structure composed of two ferromagnetic free layers and a nonmagnetic spacer is examined. Both free layers are treated as a monodomain magnetic body with an uniform agnetization. The dynamics of the two magnetizations is modeled by modified Landau-Lifshitz-Gilbert equations with spin-transfer torque terms. By solving the equations simultaneously, we discuss their various solutions in detail. We show that there exists the synchronous motion of two magnetizations among the various solutions; the magnetizations are resonantly coupled via spin-transfer torques and perform precessional motions with the same period. The condition to excite the synchronous motion depends on the difference between the intrinsic frequencies of the two ferromagnetic free layers as well as the magnitude of current.

cond-mat.mtrl-sci↗

arXiv2003

Chandra Observation of the Anomalous X-ray Pulsar 1E 1841-045

We present the results from the {\it Chandra} ACIS CC mode observation of an anomalous X-ray pulsar (AXP) 1E 1841-045. This is the first observation in which the pulsar spectrum in wide energy range is spatially discriminated from the surrounding SNR, Kes 73. Like other AXPs, the phase-integrated spectrum is fitted well with power-law plus blackbody model. The spectral parameters are $Γ= 2.0 \pm 0.3$, $kT_{\rm BB} = 0.44 \pm 0.02$ keV, and $N_H = 2.54^{+0.15}_{-0.13} \times 10^{22} {\rm cm}^{-2}$. This photon index is significantly flatter than the other AXPs, and resemble to soft gamma-ray repeaters (SGRs) in the quiescent state. The pulse profile is double-peaked, and we found that the second peak has significantly hard spectrum. The spectra of all phases are consistent with power-law plus blackbody model with constant temperature and photon index. When fitted with two blackbody model, we obtained similarly good fit. These results can be interpreted that there are two emission regions with different energy spectra.

astro-ph↗