著者

水谷 興平

出版者

IOP PUBLISHING LTD

雑誌

ASTROPHYSICAL JOURNAL (ISSN:0004637X)

巻号頁・発行日

vol.692, no.1, pp.61-72, 2009-02

被引用文献数

49

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The Tibet-III air shower array, consisting of 533 scintillation detectors, has been operating successfully at Yangbajing in Tibet, China since 1999. Using the data set collected by this array from 1999 November through 2005 November, we obtained the energy spectrum of gamma-rays from the Crab Nebula, expressed by a power law as (dJ/dE) = (2.09 +/- 0.32) x 10(-12)(E/3 TeV)(-2.96 +/- 0.14) cm(-2) s(-1) TeV-1 in the energy range of 1.7-40 TeV. This result is consistent with other independent gamma-ray observations by imaging air Cherenkov telescopes. In this paper, we carefully checked and tuned the performance of the Tibet-III array using data on the Moon's shadow in comparison with a detailed Monte Carlo (MC) simulation. The shadow is shifted to the west of the Moon's apparent position as an effect of the geomagnetic field, although the extent of this displacement depends on the primary energy of positively charged cosmic rays. This finding enables us to estimate the systematic error in determining the primary energy from its shower size. This error is estimated to be less than +/- 12% in our experiment. This energy scale estimation is the first attempt among cosmic ray experiments at ground level. The systematic pointing error is also estimated to be smaller than 0 degrees.011. The deficit rate and the position of the Moon's shadow are shown to be very stable within a statistical error of +/- 6% year by year. This guarantees the long-term stability of pointlike source observation with the Tibet-III array. These systematic errors are adequately taken into account in our study of the Crab Nebula.

著者

Bamba Aya Yamazaki Ryo Yoshida Tatsuo Terasawa Toshio Koyama Katsuji

出版者

University of Chicago Press

雑誌

Astrophysical Journal (ISSN:0004637X)

巻号頁・発行日

vol.621, no.2, pp.793-802, 2005-03

被引用文献数

13 218

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The outer shells of young supernova remnants (SNRs) are the most plausible acceleration sites of high-energy electrons with the diffusive shock acceleration (DSA) mechanism. We studied spatial and spectral properties close to the shock fronts in four historical SNRs (Cas A, Kepler's remnant, Tycho's remnant, and RCW86) with excellent spatial resolution of Chandra. In all of the SNRs, hard X-ray emissions were found on the rims of the SNRs, which concentrate in very narrow regions ( so-called filaments); apparent scale widths on the upstreamside are below or on the order of the point-spread function of Chandra, while they are 0.'' 5 - 40 '' (0.01 - 0.4 pc) on the downstream side with most reliable distances. The spectra of these filaments can be fitted with both thermal and nonthermal ( power law and SRCUT) models. The former requires unrealistic high temperature (greater than or similar to 2 keV) and low abundances (less than or similar to 1 solar) for emission from young SNRs and may be thus unlikely. The latter reproduces the spectra with best-fit photon indices of 2.1 - 3.8, or roll-off frequencies of (0.1 28) x 10(17) Hz, which reminds us of the synchrotron emission from electrons accelerated via DSA. We consider various physical parameters as functions of the SNR age, including the previous results on SN 1006; the filament width on the downstream side increases with the SNR age, and the spectrum becomes softer, keeping a nonthermal feature. It was also found that a function, that is, the roll-off frequency divided by the square of the scale width on the downstream side, shows negative correlation with the age, which might provide us some information on the DSA theory.

著者

Doi Akihiro Nagira Hiroshi Kawakatu Nozomu Kino Motoki Nagai Hiroshi Asada Keiichi

出版者

IOP Publishing

雑誌

Astrophysical journal (ISSN:0004637X)

巻号頁・発行日

vol.760, no.1, pp.41, 2012-11

被引用文献数

76

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We report the finding of kiloparsec (kpc)-scale radio structures in three radio-loud narrow-line Seyfert 1 (NLS1) galaxies from the Faint Images of the Radio Sky at Twenty-centimeters of the Very Large Array, which increases the number of known radio-loud NLS1s with kpc-scale structures to six, including two γ-ray-emitting NLS1s (PMN J0948+0022 and 1H 0323+342) detected by the Fermi Gamma-ray Space Telescope. The detection rate of extended radio emissions in NLS1s is lower than that in broad-line active galactic nuclei (AGNs) with a statistical significance. We found both core-dominated (blazar-like) and lobe-dominated (radio-galaxy-like) radio structures in these six NLS1s, which can be understood in the framework of the unified scheme of radio-loud AGNs that considers radio galaxies as non-beamed parent populations of blazars. Five of the six NLS1s have (1) extended radio luminosities suggesting jet kinetic powers of gsim 1044 erg s–1, which is sufficient to make jets escape from hosts' dense environments; (2) black holes of gsim 107 M ☉, which can generate the necessary jet powers from near-Eddington mass accretion; and (3) two-sided radio structures at kpc scales, requiring expansion rates of ~0.01c-0.3c and kinematic ages of gsim 107 years. On the other hand, most typical NLS1s would be driven by black holes of lsim 107 M ☉ in a limited lifetime of ~107 years. Hence, the kpc-scale radio structures may originate in a small window of opportunity during the final stage of the NLS1 phase just before growing into broad-line AGNs.