¶ Scratchy
Description:
Scratchy glitches are a somewhat wide band of mid-frequency glitches that look something like a ripply path through time-frequency space. The glitch path can last for several seconds and be filled with a number of repeating glitches. They occurred primarily at LIGO Hanford, and were one of the key limitations in searches for binary black hole mergers. Search experts referred to them as "that annoying scratchy noise."
Cause:
Scattered light back-reflected into the beam by the so-called Swiss Cheese Baffles, which were removed at both LHO and LLO after the second observing run (O2).
Status:
Extinct in their original form, although other vibrating reflecting items have occasionally been producing somewhat similar-looking glitches, with rows of narrow arches at medium frequencies.
Examples:
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Audio Example:
Make sure to wear good headphones!
More Information:
- Prior to May 2017, most of the LIGO Hanford scratchy glitches seemed to have 12-15 nodes (bright dots) per second, though some of them had more. After work on the Hanford detector in May 2017, in which the "swiss cheese baffle" was damped with rubber corks so that it moves less, most of the scratchy glitches appear with about 25 nodes per second.
- Further investigations have been performed to see what effect the damping of the Swiss Cheese Baffle had on scratchy glitches; see the LIGO-Hanford electronic log from 21 September 2017 and the LIGO-Livingston electronic log from 22 September 2017.