530 research outputs found
Neutron-star radii based on realistic nuclear interactions
The existence of neutron stars with requires the strong stiffness
of the equation of state (EoS) of neutron-star matter. We introduce a
multi-pomeron exchange potential (MPP) working universally among 3- and
4-baryons to stiffen the EoS. Its strength is restricted by analyzing the
nucleus-nucleus scattering with the G-matrix folding model. The EoSs are
derived using the Brueckner-Hartree-Fock (BHF) and the cluster variational
method (CVM) with the nuclear interactions ESC and AV18. The mass-radius
relations are derived by solving the Tolmann-Oppenheimer-Volkoff (TOV)
equation, where the maximum masses over are obtained on the basis of
the terrestrial data. Neutron-star radii at a typical mass are
predicted to be km. The uncertainty of calculated radii is
mainly from the ratio of 3- and 4-pomeron coupling constants, which cannot be
fixed by any terrestrial experiment. Though values of are not
influenced by hyperon-mixing effects, finely-observed values for them indicate
degrees of EoS softening by hyperon mixing in the region of
. If is less than about 12.4 km, the
softening of EoS by hyperon mixing has to be weak. Useful information can be
expected by the space mission NICER offering precise measurements for
neutron-star radii within .Comment: 8 pages, 7 figure
Kiso observations for 20 GRBs in HETE-2 era
We have established a GRB follow-up observation system at Kiso observatory
(Japan) in 2001. Since the east Asian area had been blank for the GRB follow-up
observational network, this observational system is very important in studying
the temporal and spectral evolution of early afterglows. Using this system, we
have performed quick observations for optical afterglows from early phase based
on HETE-2 and INTEGRAL alerts. Thanks to the quick follow-up observation
system, we have been able to use the Kiso observatory in 20 events, and conduct
their follow-up observations in optical and near infrared wavelengths.Comment: 5 pages, 4 figure. Accepted for publication into "il nuovo cimento".
Proceeding of the 4th Rome GRB conference, eds. L. Piro, L. Amati, S. Covino,
B. Gendr
GRBs Optical follow-up observation at Lulin observatory, Taiwan
The Lulin GRB program, using the Lulin One-meter Telescope (LOT) in Taiwan
started in July 2003. Its scientific aims are to discover optical counterparts
of XRFs and short and long GRBs, then to quickly observe them in multiple
bands. Thirteen follow-up observations were provided by LOT between July 2003
and Feb. 2005. One host galaxy was found at GRB 031203. Two optical afterglows
were detected for GRB 040924 and GRB 041006. In addition, the optical
observations of GRB 031203 and a discussion of the non-detection of the optical
afterglow of GRB 031203 are also reported in this article.Comment: 5 pages, 2 figure. Accepted for publication into "il nuovo cimento".
Proceeding of the 4th Rome GRB conference, eds. L. Piro, L. Amati, S. Covino,
B. Gendr
Termination of Electron Acceleration in Thundercloud by Intra/Inter-cloud Discharge
An on-ground observation program for high energy atmospheric phenomena in
winter thunderstorms along Japan Sea has been performed via measurements of
gamma-ray radiation, atmospheric electric field and low-frequency radio band.
On February 11, 2017, the radiation detectors recorded gamma-ray emission
lasting for 75 sec. The gamma-ray spectrum extended up to 20 MeV and was
reproduced by a cutoff power-law model with a photon index of
, being consistent with a Bremsstrahlung radiation from a
thundercloud (as known as a gamma-ray glow and a thunderstorm ground
enhancement). Then the gamma-ray glow was abruptly terminated with a nearby
lightning discharge. The low-frequency radio monitors, installed 50 km
away from the gamma-ray observation site recorded leader development of an
intra/inter-cloud discharge spreading over 60 km area with a 300 ms
duration. The timing of the gamma-ray termination coincided with the moment
when the leader development of the intra/inter-cloud discharge passed 0.7 km
horizontally away from the radiation monitors. The intra/inter-cloud discharge
started 15 km away from the gamma-ray observation site. Therefore, the
glow was terminated by the leader development, while it did not trigger the
lightning discharge in the present case.Comment: 12 pages, 4 figures, accepted for publication in Geophysical Research
Letter
Early (0.3 day) R-band light curve of the optical afterglow of GRB030329
We observed the optical afterglow of the bright gamma-ray burst GRB030329 on
the nights of 2003 March 29, using the Kiso observatory (the University of
Tokyo) 1.05 m Schmidt telescope. Data were taken from March 29 13:21:26 UT to
17:43:16 (0.072 to 0.253 days after the burst), using an -band filter. The
obtained -band light curve has been fitted successfully by a single power
law function with decay index of . These results remain
unchanged when incorporating two early photometric data points at 0.065 and
0.073 days, reported by Price et al.(2003) using the SSO 40 inch telescope, and
further including RTT150 data (Burenin et al. 2003) covering at about 0.3 days.
Over the period of 0.065-0.285 days after the burst, any deviation from the
power-law decay is smaller than 0.007 mag. The temporal structure reported
by Uemura et al. (2003) does not show up in our -band light curve.Comment: 9 pages, 2 figures, 1 table, accepted for publication in ApJ
Design and Performance of the Wide-Field X-Ray Monitor on Board the High-Energy Transient Explorer 2
The Wide-field X-ray Monitor (WXM) is one of the scientific instruments
carried on the High Energy Transient Explorer 2 (HETE-2) satellite launched on
2000 October 9. HETE-2 is an international mission consisting of a small
satellite dedicated to provide broad-band observations and accurate
localizations of gamma-ray bursts (GRBs). A unique feature of this mission is
its capability to determine and transmit GRB coordinates in almost real-time
through the burst alert network. The WXM consists of three elements: four
identical Xe-filled one-dimensional position-sensitive proportional counters,
two sets of one-dimensional coded apertures, and the main electronics. The WXM
counters are sensitive to X-rays between 2 keV and 25 keV within a
field-of-view of about 1.5 sr, with a total detector area of about 350 cm.
The in-flight triggering and localization capability can produce a real-time
GRB location of several to 30 arcmin accuracy, with a limiting sensitivity of
erg cm. In this report, the details of the mechanical
structure, electronics, on-board software, ground and in-flight calibration,
and in-flight performance of the WXM are discussed.Comment: 28 pages, 24 figure
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
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
Suzaku X-Ray Imaging and Spectroscopy of Cassiopeia A
Suzaku X-ray observations of a young supernova remnant, Cassiopeia A, were
carried out. K-shell transition lines from highly ionized ions of various
elements were detected, including Chromium (Cr-Kalpha at 5.61 keV). The X-ray
continuum spectra were modeled in the 3.4--40 keV band, summed over the entire
remnant, and were fitted with a simplest combination of the thermal
bremsstrahlung and the non-thermal cut-off power-law models. The spectral fits
with this assumption indicate that the continuum emission is likely to be
dominated by the non-thermal emission with a cut-off energy at > 1 keV. The
thermal-to-nonthermal fraction of the continuum flux in the 4-10 keV band is
best estimated as ~0.1. Non-thermal-dominated continuum images in the 4--14 keV
band were made. The peak of the non-thermal X-rays appears at the western part.
The peak position of the TeV gamma-rays measured with HEGRA and MAGIC is also
shifted at the western part with the 1-sigma confidence. Since the location of
the X-ray continuum emission was known to be presumably identified with the
reverse shock region, the possible keV-TeV correlations give a hint that the
accelerated multi-TeV hadrons in Cassiopeia A are dominated by heavy elements
in the reverse shock region.Comment: Publ. Astron. Soc. Japan 61, pp.1217-1228 (2009
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