Tutorial: Getting Data

In this tutorial, we'll fetch LIGO data associated with specific times, and present the relevant data arrays to be searched.

Data discovery

Let us assume there was an astrophysical event at some precise past time, a gamma or X-ray burst perhaps, and we have a new precise theory of the resulting ravitational waveform, and we want to run a search in the minutes around the event. Suppose the event occurred at 2007-09-19T00:00:00 UTC, then we can use the GPS-UTC time converter to find that this is GPS time 874195214.

Let us go to the Archive Section of the LOSC web site, where you will find a list of all released Events and Runs. An Event is a short data release of about an hour, surrounding a confirmed detection, and a Run is a months-long release suitable for searching.

Data from a Run

A more specific time-based query can find precisely which of the LOSC datasets covers the given time. This query asks for data covering a ten-minute interval:

https://losc.ligo.org//archive/874195200/874195360/

and we see that the S5 Run covers this time. To drill deeper and get the data files, use the bulk data form for S5, putting in the GPS times above, and you will be redirected to this URL:

https://losc.ligo.org/archive/links/S5/H1/874195214/874195214/simple/

where you can see a single file listed for H1. Download this (108 Mbyte), then substitute L1 in the URL to get the other file (117 MByte).

Data from an Event

Fetching data release associated with Events is different. Suppose it is known that LIGO detected an Event in September 2015; we can search for the data with the same kind of link as above, using the GPS times for Sept 1 and Oct 1 as the range:

https://losc.ligo.org//archive/1125100817/1127692817/

then we find that the event is named GW150914, and a further click takes us to the web page for GW150914 with not only strain data but a lot of other content.

There is a tutorial about automating the above process to search the LIGO data against a long list of candidate events. There is another tutorial about automatically downloading all the data from a Run, or all the open data from all Events.