QScan for SciMons

Overview

QScan is a tool to investigate multiple detector channels around times of interest (such as glitches, hardware injections, or candidate events). For statistically significant channels, QScan produces Q spectrograms that are similar to conventional spectrograms, but are based on the Q transform instead of the Fourier transform. The corresponding basis functions are sinusoidal Gaussians of varying central time, central frequency, and Q. The following images are taken from an example QScan of an inspiral hardware injection and are typical of time series and spectrograms produced by QScan.

QScan is a computationally intensive tool. As a result, it takes ~1 hour to run on general computing Solaris machines such as fortress (LHO) and decatur (LLO), and running multiple simultaneous scans should be avoided. For this reason, the general computing Linux machines defiance (LHO) and chestnut (LLO) are now available for running QScans at the LIGO sites. In addition, users with grid certificates are encouraged to run on LIGO laboratory computer clusters.

Quick Start

The following commands will run an example default QScan on the machine chestnut at LLO.

ssh user@chestnut.ligo-la.caltech.edu
~qscan/qscan/bin/qscan.sh 843214981.5

A QScan for the same time can also be run on the machine defiance at LHO.

ssh user@defiance.ligo-wa.caltech.edu
~qscan/qscan/bin/qscan.sh 843214981.5

The results of these two QScans will be visible at the URLs

http://www.ligo-la.caltech.edu/~user/qscans/843214981.5/
http://www.ligo-wa.caltech.edu/~user/qscans/843214981.5/

where user is the name of the user who ran the scan.

Note that QScans for events more than 5 days old may take significantly longer due to the need to recover the data from tape. This can be avoided by running on the cluster since the data is also available on the cluster nodes.

Syntax

QScan is called using the syntax:

${QSCAN}/bin/qscan.sh eventTime [configurationFile frameCacheFile outputDirectory]

were ${QSCAN} is the site specific installation directory listed in the table below.

Only the GPS time of the event is required. By default, QScan selects site dependent configuration and frame cache files and writes its output to the directory ~/public_html/qscans/eventTime.

More detailed information can be found on the QScan web page and in a presentation (PowerPoint, PDF) given at the August 2006 LLO SciMon camp.

QPipeline

To generate meaningful output, QScan requires knowledge of the time of an event to within less than a second. In order to provide this information, The QPipeline has also been installed with QScan. The QPipeline uses the same approach as QScan, but it is applied only to the gravitational-wave channel and produces multiple triggers over longer periods of time.

The syntax of QPipeline is similar to QScan, except that both a start and stop time must be specified instead of a single event time.

${QSCAN}/bin/qpipeline.sh startTime stopTime [parameterFile frameCacheFile outputDirectory]

Only the GPS start and stop time of the segment are required. By default, QPipeline selects site dependent parameter and frame cache files and writes its output to the subdirectories log and results in the current working directory.

For example, the following commands will run the QPipeline on 100 seconds of L1 data.

ssh user@chestnut.ligo-la.caltech.edu
mkdir -p ~/qpipeline_example
cd ~/qpipeline_example
~qscan/qscan/bin/qpipeline.sh 843214931 843215031

The results of this search will be available in the files

~user/qpipeline_example/results/L1:LSC-DARM_ERR_843214931-843215031.txt
~user/qpipeline_example/results/livetime_843214931-843215031.txt
~user/qpipeline_example/log/status/status_843214931-843215031.txt

where user is the again the name of the user who ran the analyses.

The resulting livetime file records the block number, effective start time, and effective stop time of each analyzed data block as a three column ASCII text.

0001 843214933.829101562 843214992.170898438
0002 843214969.829101562 843215028.170898438

The resulting triggers file records the central time, central frequency, duration, bandwidth, and log significance of statistically significant tiles as 5 column ASCII text.

...
843214963.000000000 1012.438 0.012609324 0079.306 9.587e+00
843214959.382812500 0069.797 0.022863045 0043.739 9.579e+00
843214934.058593750 0657.406 0.019418971 0051.496 9.574e+00
843214981.609375000 0168.125 0.075932508 0013.170 6.470e+01
843214981.500000000 0157.047 0.081288806 0012.302 5.168e+01
843214981.078125000 0130.938 0.097498066 0010.257 5.111e+01
843214981.406250000 0150.078 0.085063383 0011.756 4.267e+01
...

The time of the most significant tile can then be found by sorting on signficance.

Note that, in the case of hardware injections or candidate astrophysical events, the most significant tile may be due to a nearby glitch and is not necessarily the signal of interest.

Note also that, due to the overlap of analyses blocks, the resulting trigger files will likely contain redundant triggers.

Installations

QScan and QPipeline are installed on most LSC computing clusters and LIGO Laboratory general computing machines. The installation location varies some between sites, and is summarized in the following tables.