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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 instrument performance.

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 light curve 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 power spectrum 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 spectrum 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 discriminators. A 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 values.

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 anodes.


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This page is maintained by the RXTE SOF and was last modified on Tuesday, 13-Jul-2004 11:39:50 EDT.

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Last Revised: Tuesday, 13-Jul-2004 11:39:50 EDT