Masaya Kuniyoshi

THE CLOSELY POSITIONED THREE RADIO TRANSIENTS IN THE NASU 1.4 GHz WIDE-FIELD SURVEY

In 2004, we started the Nasu 1.4 GHz wide-field survey to study the dynamic universe by simultaneously performing the surveillance of the wide-field sky. We have detected six radio transients with flux densities larger than 1 Jy. In this paper, we report the detection of three new radio transients in the drift-scanning observations at δ ~ +417. Based on their positions in the sky and flux densities, we considered the candidate types of astronomical objects for transients. As a result, it is suggested that the three radio transients could be massive radio flares associated with known extragalactic sources, such as active galactic nuclei, which are usually very faint in X-ray and radio wavelengths. The three transients were found in the sky of 2° × 1°, while nine transients, including the three transients reported in this paper, are distributed at both high and low Galactic latitude. According to the observational results, we suggest that the wide-field survey simultaneously performed would be useful in searching for radio transients to study the dynamic radio sky.

Pulsar huge array with Nyquist-rate digital lens and prism

An 8 X 8 equals 64 element digital interferometer was developed at Waseda University (1989 - 1995). It was an equally spaced two dimensional array of 2.4 m dishes at 10.6 GHz, and a 2D FFT processor was used for Nyquist rate imaging. Recently a spatial-temporal (2 + 1)D FFT processor has been developed for pulsar survey (1996 - 2000), in which a first 2D spatial FFT transforms the electric fields of coordinate represented to those of momentum represented. We obtain the electric fields in each 64 direction at Nyquist rate by the 2D spatial Fourier transform. The following temporal 1D FFT gives the spectrum of 64ch or 256ch to 64 directions respectively also at Nyquist rate. The total bandwidths of each direction are 20 MHz and the resulting frequency resolutions are 20/64 MHz or 20/256 MHz. For sensitive pulsar survey, we also have developed an interferometric array of 20 m spherical dishes in Nasu flat, 160 km north of Tokyo. Five dishes are completed at present. Normal temperature receivers of high electron mobility transistors (HEMT) are used at 1.4 GHz observation and the receiver noise temperatures are below 40 K. Expected rms detection limit (Delta) T is about 10-2K under the condition of 20 MHz band widths and 1s integration time. Preliminary results of zenith survey at (delta) equals 40 deg using a single dish show (Delta) T equals 0.03 K without switching. Sub-reflectors and feed horns were designed so as to observe 5 deg off directions from zenith and they rotate around Az axis. It enable us to survey the declination zone of 32

High and Low Galactic Latitude Radio Transients in the Nasu 1.4 GHz Wide-Field Survey

We report the detection of two radio transients in the Nasu 1.4 GHz wide-field survey. In the survey, we use four pairs of the two-element interferometer aligned east-west to monitor the wide-field sky and simultaneously survey the region at +32° < δ < +42° in drift scanning. In 27 days of continuous observation at a declination between +41° and +42°, we have detected two radio transients of 1 Jy intensity. Since they appeared on only a single day during the 27 days, we consider these detections to be 1 Jy class bursts that brightened and faded within 2 days and have constant emission smaller than 200 mJy, the detection limit of the 27 days of integrated data. While one transient was in low Galactic latitudes, the other transient was detected in high Galactic latitudes and has counterparts only in γ-ray databases. Therefore, the high Galactic latitude transient might be one of the active galactic nuclei that are normally very faint in X-ray and quiet in radio wavelengths.

Quick-Look Data Analysis in the Nasu Radio Transient Search Project

We have developed a new technique, called quick-look data analysis, for radio transient searches at the Nasu Interferometer. Quick-look data, a color map according to the radio source signal-to-noise ratio (S/N), were generated spatially and temporally from drift-scanning data. A steady source appears at the same right ascension with the same color every day. In contrast, transient objects such as radio bursts appear irregularly in the sky, and the resulting map will have sporadic patches. Radio transient WJN J1443+3439 has already been detected using this technique. The quick-look data were created using processes that we call the fringe-detecting method and color image creation, which we describe here, and we show actual color images of Cyg A, 3C 48, Mrk 501, and the transient radio source WJN J1443+3439 found in 2005.

Receiver gain calibration for radio observations at the waseda nasu pulsar observatory

ABSTRACT We have started programs at the Waseda Nasu Pulsar Observatory to identify EGRET γ‐ray sources and to search for radio transients. The observed frequency was \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape

Nasu 1.4 GHz Interferometer Transient Radio Source Survey and Improvement in Detection of Radio Sources

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EGRET Unidentified Source Radio Observations and Performance of Receiver Gain Calibration

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Detection of Transient Sources with 20-m Spherical Antennas at Waseda Nasu Observatory

We have surveyed 1.4GHz transient radio sources in Nasu Pulsar Observatory. To investigate such sources, both immediacy and accuracy are severely maintained. We have developed Data Transfer System and improved antenna control system. Now we have received the fringe data from transient radio source candidates. To get reliable information, we carefully analyze with Fringe Band Pass Filter software and Fringe Fitting method.

Two strong radio bursts at high and medium Galactic latitude

Last year, we have developed the receiver gain calibration system by using Johnson-Nyquist noise, for accuracy flux measurement, because we have been starting radio identification program of transient radio sources, blazars and radio counterpart of The Energetic Gamma Ray Experiment Telescope (EGRET) unidentified γ-ray sources in Waseda Nasu Pulsar Observatory. It is shown that there are a few low correlation data between receiver gain and ambient temperature around receiver for anything troubles of receiver, because we can detect gain and ambient temperature through a day by developed system. Estimated fluctuations of daily data of steady sources decrease by removing low correlation data before analysing. As the result of our analysis by using above system, radio counterpart of EGRET identified source showed fading light-curve for a week.

A 3 Jy Radio Burst at a High Galactic Latitude

As it is impossible to predict when and where transient sources will appear, it is necessary to monitor as large an area as possible, and also as often as possible to survey these sources. Recently, full time wide-field survey radio interferometer at 1.4GHz, which consists of eight 20-m diameter spherical dish array, has been constructed in Nasushiobara, Tochigi prefecture, 160km north of Tokyo. Observations are ongoing and a great amount of data is constantly being obtained. However, analyzing this data was a very slow and time-consuming process, which sometimes took several weeks or more for the one-week data. To address this problem, we developed software to facilitate the analysis of the data, which was created in C++ language. All of the preparations for surveying transient sources are completed at the present time. Here we report the automatic analysis software for searching transient sources.