Astronomy Experiment Research Articles

Rocket altitude atmospheric X-rays from magnetospheric electrons at low and middle latitudes

Like auroral electrons, quasitrapped magnetospheric electrons mirroring in the upper atmosphere at low and middle latitudes will generate X-rays by the bremsstrahlung and K α line excitation processes. These atmospheric X-rays may contribute a diffuse background to rocket-borne astronomy experiments launched from White Sands, New Mexico and Kauai, Hawaii. Calculations of the atmospheric X-ray spectrum at these launch sites based on observations of quasitrapped electrons indicate that this locally generated flux is comparable to the reported soft X-ray flux below a few keV.

Spectral types for early-type stars observed by SKYLAB

MK spectral types are presented for 246 early-type stars observed with the S-019 ultraviolet stellar astronomy experiment on Skylab. K-line types are also given where applicable, and various peculiar stars are identified. The peculiar stars include five silicon stars, a shell star, a helium-rich star, a silicon-strontium star, a chromium-europium star, and two marginal metallic-line stars.

Planetary radio astronomy experiment for Voyager missions

The planetary radio astronomy experiment will measure radio spectra of planetary emissions in the range 1.2 kHz to 40.5 MHz. These emissions result from wave-particle-plasma interactions in the magnetospheres and ionospheres of the planets. At Jupiter, they are strongly modulated by the Galilean satellite Io.

Relationship between auroral substorms and the occurrence of terrestrial kilometric radiation

We have examined the correlation between magnetospheric substorms as inferred from the AE(11) index and the occurrence of terrestrial kilometric radiation (TKR) as observed by the Goddard radio astronomy experiment on board the Imp 6 spacecraft. In general, we find that AE and TKR are well correlated when observations are made from above the 1500–0300 hour local time zone and are rather poorly correlated over the 0300–1500 hour zone. High-resolution dynamic spectra obtained during periods of isolated substorms indicate that low-intensity high-frequency TKR commences at about the same time as the substorm growth phase. The substorm expansion phase corresponds to a rapid intensification and bandwidth increase of TKR. When these new observations are combined with our previous results, they imply that many TKR events begin at low altitudes and high frequencies (∼400–500 kHz) and spread to higher altitudes and lower frequencies as the substorm expands.

Terrestrial kilometric radiation, 3. Average spectral properties

A study is presented of the average spectral properties of terrestrial kilometric radiation (TKR) derived from observations made by radio astronomy experiments onboard the IMP-6 and RAE-2 spacecraft. As viewed from near the equatorial plane, TKR is most intense and most often observed in the 21-24 hr local time zone and is rarely seen in the 09-12 hr zone. The peak flux density usually occurs near 240 kHz, but there is evidence that the peak occurs at a somewhat lower frequency on the dayside. The frequency of the peak in the average flux spectrum varies inversely with increasing substorm activity as inferred from the auroral electrojet index (AE) from a maximum near 300 kHz during very quiet times to a minimum below 200 kHz during very disturbed times. The absolute flux levels in the 100-600 kHz TKR band increase significantly with increasing AE. The average power associated with a particular source region seems to decrease rapidly with increasing source altitude.

Possible radio emission from Uranus at 0.5 MHz

Radio emission from the direction of Uranus has been detected in data from the Goddard radio astronomy experiment on the IMP-6 spacecraft. Previously, emission from the direction of Jupiter and Saturn had been observed by IMP-6 at a number of frequencies near 1 MHz and were identified through an analysis of the phase of the observed modulated signal detected from the spinning dipole antenna. This technique was applied to the direction of Uranus with possible positive results. Over the approximately 500 days of data, three to six bursts with unique spectral characteristics have been found. The events persisted less than 3 minutes and are strongest in intensity near 0.5 MHz. Identification with Uranus is confused by the likely presence of low-level terrestrial and solar emission. Because of the unfavorable angular separation of earth and Uranus, there is a possibility that the bursts are atypical terrestrial magnetospheric phenomena, although the uniqueness of the set of events indicates the probable detection of radiation from Uranus.

X-ray emission from γ Cas

THE Copernicus orbiting observatory contains two astronomical experiments, the Princeton ultraviolet spectrometer and the MSSL X-ray package. They are coaligned, and during ultraviolet observations the 3–8 keV collimated proportional counter routinely collects background data1. When the observatory was pointed at the ultraviolet target γ Cas on December 21, 1975 and again on January 20, 1976, a clear excess of counts was seen in the 3–8 keV channel compared to preceding and following targets. This count rate corresponds to a flux at the Earth of ∼ 1.2×10−10 erg cm−2S−1, and lies 5σ above the mean background level determined from several weeks of observations (Table 1).

Use of a direct non-parametric pattern recognition method for the automatic selection of high energy gamma-ray events in spark chamber pictures

The problem of the automatic selection from background events of electron pairs due to gamma-ray conversion in a multiplate spark chamber is dealt with by means of a direct non-parametric pattern recognition method. The method is applied to the data obtained in a gamma-ray astronomy experiment using a balloon-borne optical spark chamber. A filter operation is initially introduced to exclude clearly evident spurious events; the remaining spark chamber images are then reduced to their most significant zone in order to lower time and cost of subsequent analysis. The feature selection is performed by using a “training set” of labeled events and the classification made introducing a pre-established linear threshold decision function. Results are presented giving the percent of correct classification as a function of the threshold value chosen.

A scintillation counter for use in a telescope for gamma-ray astronomy

Abstract A plastic scintillation counter has been developed for use in the gamma-ray astronomy experiment to be carried by the ESRO satellite COS-B. The mission requires the ability to measure the number of particles simultaneously traversing the counter over its whole area and within the solid angle defined by the telescope of which it forms a part. To achieve this, a high uniformity of response and good pulse-height resolution are required. Theoretical predictions of these characteristics are presented and compared with measurements carried out with a beam of positrons, which demonstrate that the counter meets the requirements. The resulting response to gamma-rays of the counter as part of the complete experiment is briefly discussed.

Type II Bursts at Hectometric and Kilometric Wavelengths from Interplanetary Shocks

The first type II radio burst to be observed at frequencies below the ionospheric cutoff was recorded by the Goddard radio astronomy experiment on the Interplanetary Monitoring Platform, IMP-6. It occurred on June 30, 1971; a tracing made from the intensity contour plot of the radio data is shown in Figure 1. On the original, intensity contours were plotted in dB above background as a function of frequency and time. The figure shows 32 discrete frequencies from 4.9 MHz to 30 kHz received by the IMP-6 experiment. The time scale covers a period of almost five hours. During this time, five individual type III bursts and one group of type III's occurred; they are shown by their outlines to be drifting rapidly from high to low frequencies. The relatively narrow-band, slowly-drifting radiation with clearly defined fundamental and second harmonic is the type II. The average drift rate, represented by the straight lines drawn through the burst, is approximately 2.5 kHz min−1 in this frequency range, and is roughly 100 times slower than that of the type III bursts. The ovals defining the type II emission were traced from the record and show modulation of the signal caused by the spin of the satellite and the resultant sweeping of the antenna pattern of the dipole across the source direction. On the original record, the outlines of the type III's are also filled with a pattern of modulation ovals that were omitted from the figure for clarity. The shaded portion of the record at the lower frequencies represents magnetospheric noise.

Correction [to “Observations of noise bands associated with the upper hybrid resonance by the Imp 6 Radio Astronomy Experiment”

The intense noise bands occurring near the upper hybrid resonanace frequency have been observed with the Imp 6 GSFC radio astronomy experiment in the plasmasphere. The identification of the upper hybrid resonance provides an accurate measure of the local electron density and allows the observed noise data to be fit to the scale of characteristic frequencies in the plasma. The data are consistent with earlier theoretical interpretations in which noise is generated between the upper hybrid and plasma frequencies and propagates to region 4 of the CMA diagram, where it is reflected at the L=0 plasma cutoff.

The Luminosity Function of Galactic X-Ray Sources - a Cutoff and a "standard Candle"?

We analyze the 2-10 keV luminosity distribution of 36 X-ray sources in the Local Group having known or estimated distances and find that there exists a luminosity cutoff of approximately 10 ergs 1 in agreement with the theoretical (Eddington) limit for the luminosity of an approximately 1 M0 star. Furthermore, among the complete sample of high-luminosity sources, there appears to be a statistically significant group of X-ray "standard candles" at (within < 0.8 mag) the critical luminosity. This finding (which is in agreement with the self-consistent mass flow accretion models) presents the possibility that X-ray sources may be used as extragalactic distance indicators in the next generation of X-ray astronomy experiments. Subject headings: luminosities - X-ray sources

LF radio noise from the Earth's magnetosphere

Gyro‐synchrotron radio noise emitted by electrons trapped in the Earth's magnetosphere has been a subject of extensive research. Previous efforts, which considered frequencies greater than 1 MHz, have shown that this noise should not be detectable in the MF to HF range because its intensity is below the cosmic background noise level. This author, however, has investigated the LF range and has found that appreciable noise is generated at these frequencies. In fact, the theoretical results for this LF noise agree very well with experimental data obtained by the Goddard Space Flight Center radio astronomy experiment aboard the IMP 6 spacecraft. A comparison showed that the model predicted both variation in the observed noise intensity with Kp and the noise spectral characteristics. Consequently, it is concluded that detectable LF radio noise is emitted, by means of the cyclotron‐synchrotron mechanism, by electrons trapped in the Earth's magnetosphere, and that this noise is observable only for frequencies below about 300 kHz. For higher frequencies, the theoretical model and the experimental data reconfirm that this noise is below that of cosmic origin.

Spectra of radioactivity induced in caesium iodide scintillator crystals by 155 MeV protons

Previous work has shown the importance of induced radioactivity as a source of background counts in X- and γ-ray astronomy experiments which use scintillation detectors. Comprehensive data on the decay spectra observed in Caesium Iodide crystals following irradiation by 155 MeV protons has been obtained by the Imperial College group and is presented here. The spectra cover the energy loss range from 20 keV to 3.4 MeV and were collected at times after irradiation ranging from 1 min until 200 d. A sufficient selection of spectra is given to enable calculations to be made of the time variations in radioactivity which would be observed in similar space-borne detectors subjected to irradiation by inner belt and cosmic ray protons. Examples of such calculations are given.

Electron Microscopy and X-Ray Microanalysis of Metal Spheres Formed in a Low Gravity Environment: A Prelude to Skylab

Skylab is America's first manned space station. It offers a unique opportunity to conduct experiments in astronomy, geoscience, the life sciences and engineering. Included in the latter category is the M512 facility for materials processing in space. In addition to other experiments this unit is equipped with a chamber which can be vented to space vacuum and an electron beam heating source capable of melting small metal pendants attached to a rotating pin wheel which may be successively placed at the electron gun focal point. Mechanical fixtures are provided to release the molten body from its support post, if desired, allowing it to solidify under high-vacuum zerogravity conditions.

A Density Scale for the Interplanetary Medium from Observations of a Type II Solar Radio Burst Out to 1 Astronomical Unit

A type II (slow-drift) solar radio burst occurring during the 3B flare of 1972 August 7 has been observed down to 30 kHz by the GSFC radio astronomy experiment on the IMP-6 satellite. For this event, the associated shock front has been tracked from the Sun out to nearly 1 a.u., the last observation being made just before the occurrence of a sudden-commencement geomagnetic storm. In addition to the importance of the data to the study of the properties and propagation of interplanetary shock waves, these new observations lead to an interplanetary electron density scale consistent with that derived from measurements of type III (fast-drift) bursts, provided the type III emission is observed at the second harmonic of the plasma frequency. (auth)

Decay time of type III solar bursts observed at kilometric wavelengths

Type III bursts were observed between 3.5 MHz and 50 kHz by the University of Michigan radio astronomy experiment aboard the OGO-5 satellite.

Observations of noise bands associated with the upper hybrid resonance by the Imp 6 Radio Astronomy Experiment

The intense noise bands occurring near the upper hybrid resonance frequency have been observed with the Imp 6 GSFC radio astronomy experiment in the plasmasphere. The identification of the upper hybrid resonance provides an accurate measure of the local electron density and allows the observed noise data to be fit to the scale of characteristic frequencies in the plasma. The data are consistent with earlier theoretical interpretations in which noise is generated between the upper hybrid and plasma frequencies and propagates to region 4 of the CMA diagram, where it is reflected at the L = 0 plasma cutoff.

The Galactic Radio Spectrum Between 130 and 26OOkHz

view Abstract Citations (108) References (6) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Galactic Radio Spectrum Between 130 and 26OOkHz Brown, Larry W. Abstract The IMP-6 radio astronomy experiment has provided new measurements of the galactic background spectrum at 22 frequencies between 130 and 2600 kHz. A highly accurate spectrum is presented which corresponds to the minimum galactic radiation observed with a short dipole antenna. The estimated maximum spectrum is presented also. The data demonstrate the need to include the effect of the ambient plasma on synchrotron emission in low-frequency galactic models. Subject headings: cosmic background radiation radio radiation synchrotron radiation Publication: The Astrophysical Journal Pub Date: March 1973 DOI: 10.1086/151968 Bibcode: 1973ApJ...180..359B full text sources ADS |

An X-Ray Observation of the Large Magellanic Cloud

A Skylark rocket (SL727) carrying an X-ray astronomy experiment prepared by the University of Adelaide and Tasmania (UAT) was launched from Woomera at 0030 UT on July 10, 1970. The Large Magellanic Cloud (LMC) was detected during the flight, and the recent observation of structure within the Cloud is confirmed. In particular, the data support the suggestion of X-ray emission from the 30 Doradus (Tarantula) Nebula.