M. Nakagawa

Observation of a New X-ray Source

THE purpose of this article is to present a preliminary report on a new cosmic X-ray source. The source was observed near Sco X-1 during recent rocket flights to observe Sco X-1 simultaneously with ground-based optical telescopes. It is very likely that we observed the source reported to have appeared between July 6 and July 9 by Conner et al. in an IAU telegram issued on July 30, 1969.

γ-Ray burst observed at balloon altitude

SINCE the γ-ray burst was discovered in 1973, approximately 50 events have been observed using artificial satellites1,2. In addition, several bursts of smaller size have been found using balloon-borne detectors3–6 with large sensitive areas. No burst has yet been located on the celestial sphere, with an adequate precision to associate it with an astronomical object. To determine the precise position of a γ-ray burst which had not been predicted to occur, the detector must have a wide field of view and the capability of precise location of the source. A rotating cross-modulation-collimator (RCMC) proposed7 as a device to fulfill these apparently conflicting requirements was used in the series of balloon observations reported here. A small γ-ray burst was found during ∼ 150 h of observations and its celestial position was determined with a precision of ∼ 0.3°.

A high background rejection method in a proportional counter using field-adjusting electrodes as guard cathodes

Abstract A single anode single large cell counter, with veto-counters around it, is described. To get uniform response of the pulse height and the energy resolution, the counter has field-adjusting electrodes at the end walls of the anode wire, and these electrodes are also used to reject the background events which are caused by cosmic rays passing through near the end walls of the anode. A rocket flight experiment showed that the combination of rise time discrimination and anti-coincidence method reduced the cosmic ray induced background events to a level of 1.2×10 −4 counts s −1 cm −2 keV −1 in the energy range of 2–40 keV, which represented an overall background reduction of 98% in this energy range.

Detector to study low-flux hard X-ray/gamma-ray sources

Abstract We have developed a new kind of phoswich counters that will be capable of detecting low flux hard X-rays/gamma-rays from astronomical objects. The new phoswich counter consists of a small inorganic scintillator with a fast decay time (the detection part) glued to the interior bottom surface of a rectangular well-shaped block of another inorganic scintillator with a slow decay time (the shielding part). Here, the well-shaped shielding part acts as an active collimator as well as an active shield. We have built a detector system consisting of 64 such phoswich counters: newly developed scintillator (GSO) is used for the detection part and CsI( Tl ) is used for the shielding part. The total geometrical area of the 64 detection parts is about 740cm 2 and its 3σ sensitivity is expected to reach below 10 −5 cm −2 s −1 keV −1 up to 700keV. With several improvements such detectors will be able to detect hard X-rays/gamma-rays at a flux level around 10 −6 cm −2 s −1 keV −1 upto 2 MeV.

BALLOON X-RAY ASTRONOMICAL OBSERVATIONS - A CHINA-JAPAN COLLABORATIVE TRANSOCEANIC FLIGHT

A China-Japan X-ray balloon flight took place in 1988 August. Preliminary results are presented for the energy spectrum of Cyg X-1.