Ichiro Kondo

Observation of thundercloud-related gamma rays and neutrons in Tibet

During the 2010 rainy season in Yangbajing (4300 m above sea level) in Tibet, China, a long-duration count enhancement associated with thunderclouds was detected by a solar-neutron telescope and neutron monitors installed at the Yangbajing Comic Ray Observatory. The event, lasting for similar to 40 min, was observed on July 22, 2010. The solar-neutron telescope detected significant gamma-ray signals with energies >40 MeV in the event. Such a prolonged high-energy event has never been observed in association with thunderclouds, clearly suggesting that electron acceleration lasts for 40 min in thunderclouds. In addition, Monte Carlo simulations showed that >10 MeV gamma rays largely contribute to the neutron monitor signals, while >1 keV neutrons produced via a photonuclear reaction contribute relatively less to the signals. This result suggests that enhancements of neutron monitors during thunderstorms are not necessarily clear evidence for neutron production, as previously thought.

Gamma-ray observations from Hinotori

Some interesting results on gamma-ray line emission and its time profiles observed by Hinotori are presented. Possible explanations of gamma-ray line and hard X-ray emissions for the impulsive and gradual flares are discussed. Relationship between the gamma-ray line emission and acceleration and escape of the solar particles is also studied.

Gamma-ray spectrometer aboard solar flare observation satellite HINOTORI

Abstract A gamma-ray spectrometer aboard the solar flare obsevation satellite HINOTORI launched on 21 Feb. 1981 is described. The gamma-ray spectrometer consists of a phoswich type scintillator of CsI(Tl) crystal surrounded by a plastic scintillator, which can discriminate between gamma-rays and charged particles. The CsI(Tl) scintillator, whose size is 62 cm2 in area and 5.1 cm in height. covers the energy range 0.21–6.67 MeV. The energy resolution is 0.1E 1 2 (MeV) fwhm and the full energy peak efficiency is 0.40 at 0.662 MeV. The primary data output is a full resolution 128 channel pulse height spectrum every 2 s. Since the launch HINOTORI recorded about forty solar gamma-ray flares and four cosmic gamma-ray bursts, and several interesting results were reported. The typical results of the large solar flare on 27 April 1981 and the cosmic gamma-ray burst on 21 July 1981 are presented in this paper. These observed data could provide important clues for advancing our understanding of high enegry phenomena in solar flares and cosmic gamma-ray bursts.

Discovery of an X-ray burst source XB 1715-321

A new X-ray burst source, XB 1715-321, was discovered with the Hakucho satellite. Three type I X-ray bursts were observed from this source in 1979. The error region for XB 1715-321, about 0.3 square degrees in area, includes a persistent X-ray source MX/2S 1715-321 which has been suspected to be the source of several fast transient events. Those bursts detected by Hakucho are characterized by a slow rise time (5--10 s) and a relatively long burst interval.

The wide band spectrometer for the solar flare satellite SOLAR-A

Abstract The Wide Band Spectrometer (WBS) for the solar flare satellite SOLAR-A scheduled for launch in 1991 consists of three kinds of detectors to observe the wide band spectrum from soft X-rays to gamma-rays. The soft X-ray spectrometer (gas proportional counter), hard X-ray spectrometer (NaI scintillation counter and gamma-ray spectrometer (two BGO scintillation counters) cover the 2–30 keV, 20–400 keV and 0.2–100 MeV bands, respectively. Further, the WBS contains a radiation belt monitor consisting of a NaI scintillation counter which is capable of detecting cosmic gamma-ray bursts. The details of these detectors, electronics systems and data collection are described.

Possible solar neutron events recorded by the ground-based neutron monitor

Possible solar neutron emission associated with five SMM gamma-ray events on 7 June 1980, 21 June 1980, 6 November 1980, 26 November 1982 and 25 April 1984 was found from analysis of 10-minute records of the ground-based neutron monitor at Tokyo. Of these the two events on 21 June 1980 and 25 April 1984 have been already known as neutron events. The time histories of the neutron monitor count rate are compared with those of the gamma-ray count rate and the possibility of energetic neutron emission at the flare site is discussed.

Gamma-ray bursts observed from the Hinotori satellite

During February, 1981 and June, 1982 the gamma-ray and the hard X-ray spectrometers on the Hinotori satellite observed four gamma-ray bursts on 28 February, 21 July, 1981, 26 February and 13 March, 1982. These gamma-ray bursts were simultaneously observed by other satellites. The time histories and energy spectra are shown for these gamma-ray bursts, and the burst sizes (erg cm−2) are estimated. Two possible source locations for the burst of 21 July, 1981 are roughly determined from arrival time delays between two pairs of satellites, PVO-Hinotori and ISEE-3-Hinotori. The weak gamma-ray line peak structure around 1.8 MeV was observed for the burst of 13 March, 1982. The line could be interpreted in terms of gravitationally redshifted neutron capture line at 2.22 MeV.

A large area multitube proportional counter

Abstract A large area and light weight multitube proportional counter (MTPC) has been constructed for a position detector of cosmic ray telescopes. The MTPC composed of aluminium tubes of 10 mm×10 mm cross section and 0.4 mm in thickness. The weight of an x − y pair of the MTPC is 25 kg for an effective area of 1 m×1 m and 50 kg for 1.8 m×1.8 m area, respectively. Position resolutions obtained from data of an engineering balloon experiment are better than ±0.6 cm for Z = 6 and ±0.85 cm for Z = 26.