Publications (2)0 Total impact
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ABSTRACT: We present analysis of 4U 1626-67, a 7.7 s pulsar in a low-mass X-ray binary
system, observed with the hard X-ray detector of the Japanese X-ray satellite
Suzaku in March 2006 for a net exposure of \sim88 ks. The source was detected
at an average 10-60 keV flux of \sim4 x10^-10 erg cm^-2 s^-1. The
phase-averaged spectrum is reproduced well by combining a negative and positive
power-law times exponential cutoff (NPEX) model modified at \sim 37 keV by a
cyclotron resonance scattering feature (CRSF). The phase-resolved analysis
shows that the spectra at the bright phases are well fit by the NPEX with CRSF
model. On the other hand, the spectrum in the dim phase lacks the NPEX
high-energy cutoff component, and the CRSF can be reproduced by either an
emission or an absorption profile. When fitting the dim phase spectrum with the
NPEX plus Gaussian model, we find that the feature is better described in terms
of an emission rather than an absorption profile. The statistical significance
of this result, evaluated by means of an F-test, is between 2.91 x 10^-3 and
1.53 x 10^-5, taking into account the systematic errors in the background
evaluation of HXD-PIN. We find that, the emission profile is more feasible than
the absorption one for comparing the physical parameters in other phases.
Therefore, we have possibly detected an emission line at the cyclotron
resonance energy in the dim phase.
05/2012;
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H Tsuchiya,
H Miyasaka,
E Takahashi,
S. Shimoda,
Y Yamada,
I Kondo, K. Makishima,
F Zhu,
Y Tan,
H Hu,
Y Tang,
J Zhang,
H Lu,
X Meng
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ABSTRACT: The purpose of this work is to search the Yangbajing neutron monitor data obtained between 1998 October and 2000 June for solar neutrons associated with solar flares. Using the onset times of 166 BATSE-detected flares with the GOES peak flux (1 -- 8 \AA) higher than $1.0 \times 10^{-5}$ $\mathrm{Wm^{-2}}$, we prepare for each flare a light curve of the Yangbajing neutron monitor, spanning $\pm$ 1.5 hours from the BATSE onset time. Based on the light curves, a systematic search for solar neutrons in energies above 100 MeV from the 166 flares was performed. No statistically significant signals due to solar neutrons were found in the present work. Therefore, we put upper limits on the $>$ 100 MeV solar-neutron flux for 18 events consisting of 2 X and 16 M class flares. The calculation assumed a power-law shaped neutron energy spectrum and three types of neutron emission profiles at the Sun. Compared with the other positive neutron detections associated with X-class flares, typical 95% confidence level upper limits for the two X-class flares are found to be comparable to the lowest and second lowest neutron fluxes at the top of the atmosphere.In addition, the upper limits for M-class flares scatter in the range of $10^{-2}$ to 1 neutrons $\mathrm{cm^{-2}s^{-1}}$. This provides the first upper limits on the solar-neutron flux from M-class solar flares, using space observatories as well as ground-based neutron monitors.
04/2007;
