11. What do the Einstein@Home S3 search results look like?

Shown in the figures below is part of the output of the final post-processing step. It shows, in a band from 300 to 325 Hz, and for each grid point in the sky, the maximum number of ten-hour data segments for which the value of 2F exceeded 25. Because there were sixty different ten-hour data segments, this number could range from 0 to 60.

The first figure (a) shows the declination - right ascension color map of the maximum number counts at each grid point on the sky. The second figure (b) shows the declination - frequency color map of the maximum number counts at each grid point on the sky. These two figures show that over the entire sky we have no prominent events in the 300-325 Hz frequency band. This band is one of the typical clean band in our S3 LIGO Hanford detector data. The majority of the frequency bands are as clean as this example.

Figure 11.1: Color map of the number of coincidences among sixty 10-hour data segments for the frequency range 300 to 325 Hz. (a) All-Sky map. (b) Frequency declination plane.

(a) All-Sky map	(b) Declination - Frequency map

The most benign type of instrument noise (Gaussian noise) would produce a number count of around 6 by random chance. For this type of noise, any events having number counts larger than, say, 20 would be potential candidates for further follow-up studies.

Notice that the largest number of segments that contained the consistent signature of a pulsar was 6. In contrast to this, a very strong pulsar signal would have appeared in all or nearly all of the 60 segments, A source near our threshold for detection would have appeared in many (say, more than half) of the segments. This was illustrated in the section on hardware/software injection for some "fake" sources added to the data set.

Based on this plot, we conclude that Einstein@Home did not find any credible sources in the frequency band from 300 to 325 Hz. This is not surprising. The LIGO instruments are still undergoing commissioning to reach their design sensitivity. And even at design sensitivity, the level of noise in the instruments will be high enough that they may obscure all astrophysical sources of gravitational waves. So whether or not we can detect something depends upon Nature and our luck. It depends upon Nature because we do not yet confidently know how frequently pulsars form, how many of them spin at the right rate, and how many there are in our Galaxy. And it depends upon luck because we don't know if one of them happens to be so close to the Earth and emitting strongly enough that its gravitational wave signal can overcome the noise in our instruments.

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Einstein@Home S3 Analysis Summary	Last Revised: 2005.09.11 16:22:17 UTC
Copyright © 2005 Bruce Allen for the LIGO Scientific Collaboration	Document version: 1.97