First Results from XTE
XTE is now in orbit with all instruments providing data. Presented here
are some very preliminary first-cut results. A number of the plots were
obtained using real-time software and any conclusions drawn from these
results are at your own risk! As more thorough analyses of calibration
data are completed we will provide more definitive updates on
The first object to be observed with the PCA was the 3 mCrab source PSR
1509-58. This is a pulsar which is embedded in a nebula which has a
similar brightness in the PCA. The
begins with the PCA looking at
the Earth. As the source emerges from behind the Earth, the count rate
is seen to increase as we detect the pulsar. The background level is
estimated to be similar to the Earth eclipse level and the short
drop-out occurs when the EDS resets. EDS reset times have been
modified and GO observations should not be affected by EDS resets to
the same extent as in this light curve. The X-axis is in seconds and
the Y-axis shows counts/second.
Analysis of the light curve with a
shows the presence of the fundamental and several harmonics of the pulses
from this source. The X-axis of the diagram is labeled in Hz.
HEXTE was able to obtain a
of this source and, in 4200s, the pulsar was detected up to about 60
keV. Instead of a model fit, the solid line shows the model spectrum
derived by Kawai et al. from Ginga data. The response matrix used was
that from the first NASA Research Announcement which has an incorrect
gain around 30 keV. The deficit in observed counts below about 30 keV
may be due to the settings of the pulse shape and lower-level
spectrum of the Crab
could be fitted with a power-law, again using the NRA response matrix.
In both cases the normalizations of the fits are very close to the expected
A PCA observation of the Crab that was obtained using four
single bit modes enables
pulse profiles in four energy bands
to be obtained. The curves shown here are based on just 30 seconds of data.
For a subsequent observation of Cygnus X-2, an 800 second section of data
clearly shows the presence of strong
QPO at approximately 20 Hz.
As an example of ASM performance on a bright source, we show data from an
SSC 1 observation of Sco X-1 .
The source is nearly on-axis with respect to the coded masks but is about
27 degrees off in the "long" axis. Each panel in the figure shows the
position histogram obtained from one of the eight anode wires. The patterns
that are seen are caused by the coded mask that creates the shadows on the
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Responsible NASA Official: