HEASARC Staff Scientist Position - Applications are now being accepted for a Staff Scientist with significant experience and interest in the technical aspects of astrophysics research, to work in the High Energy Astrophysics Science Archive Research Center (HEASARC) at NASA Goddard Space Flight Center (GSFC) in Greenbelt, MD. Refer to the AAS Job register for full details.
The proportional counters and hard X-ray telescope on board OSO-7 scanned
the entire sky and obtained good exposure of point sources through repeated
scans.
Data from the proportional counters yielded a "multi-color"
catalog of 184 sources (Markert et al., 1979) and the detection from
Centaurus A of rapid intensity variability (Winkler & White,
1975). The X-ray telescope studied the high energy temporal and
spectral behavior of a number of sources including Her X-1 (Ulmer er
al., 1973) and Vela X-1 (Ulmer et al., 1972).
Just under three years of data on celestial X-ray sources were obtained
using the MIT instrumentation aboard the OSO-7 satellite. The detection
system consisted of two banks of proportional counters which viewed the
sky through 1- and 3-deg tubular collimators (FWHM) and covered a 1 to
60-keV energy range in five broad energy intervals (1-1.5 keV; 1-6 keV;
3-10 keV; 15-40 keV; 30-60 keV). The data were recorded in 256 azimuthal
bins as the detector scanned across a small circle on the sky with each
spin. The time resolution was 3.2 minutes.
The UCSD OSO-7 X-ray telescope was designed to detect X-rays in the
range from about 7 to 550 keV. It consisted of a 1 cm thick NaI(Tl)
crystal inside a massive CsI(Na) anticoincidence shield. There were 128
energy loss channels. Each event signature also contained a clock time
good to 0.625 ms. The field of view was 6.5 degrees FWHM and the sensitive
area was ~ 64 sq-cm. The total detector weight was 85 lbs.
The UNH gamma-ray monitor consisted of a 7.6 cm x 7.6 cm NaI(Tl)
scintillator which operated in the range 300 keV - 10 MeV. The detector was
surrounded on all sides by a ~ 4 cm thick CsI(Na) scintillator cup. The
exception was a forward aperture which was covered by a 0.5 cm thick
CsI(Na) slab. The instrument was calibrated regularly each orbit with a 60Co
source. The resolution was 7.8% at 662 keV. The instrument was in the wheel
section of OSO-7. Data were accumulated in 0.5 s bins when the detector was
looking at the Sun/anti-Sun during each 2-s spin. The monitor operated until
25 December 1972, but was usually turned off during the periodic penetration
of the satellite into the radiation belts.
A sky map of the X-ray intensity was derived directly from several hundred
days of data from the MIT experiment. The same experiment also produced
results for three important compact galactic sources: Sco X-1,
Her X-1 and Cyg X-1, as well as results of observations of the supernova
remnant IC 443, supernova 1972e, and a unique flare source, GX 354+3.
The UCSD experiment produced results on Cyg X-3 which showed the 4.8-hr
period present in the 6-21 keV range, but not in the 21-98 keV range.
HEASARC Staff Scientist Position - Applications are now being accepted for a Staff Scientist with significant experience and interest in the technical aspects of astrophysics research, to work in the High Energy Astrophysics Science Archive Research Center (HEASARC) at NASA Goddard Space Flight Center (GSFC) in Greenbelt, MD. Refer to the AAS Job register for full details.
