Features for EM Collaboration

On logging in

A successful login is required in to access GraceDB events and upload followup information. The login process is the same as for the LV-EM wiki: namely, click “LOGIN” at the upper right and then choose the login method according to the identity you used for registering for LV-EM membership at gw-astronomy.org.

Note

Some users may have multiple identities available from the identity providers listed on the login page. However, only the identity used to register for LV-EM will work for GraceDB access. For example, even though I have identities from LIGO, UW-Milwaukee, and Google, only my LIGO login will work for GraceDB since that is the one I used to register for LV-EM membership. The reason is that there is no way (at present) to map these different identities to the same underlying user.

Scripted access for LV-EM members

Some processes need to access GraceDB in a scripted manner. For example, an observational group might set up an automated process to listen for LIGO/Virgo GCN notices and then download the skymaps for further processing (see the tutorial). As these alerts could come at any time of the day or night, it is not generally possible for the user to go through the usual login sequence. Traditionally, GraceDB has handled scripted access with X509 robot certificates or robot Kerberos keytabs, but these may not be easily accessible to all LV-EM group members.

Thus, there is an alternative using basic auth (a simple username-and-password scheme). First, obtain a robotic access password by navigating to this page and clicking “Get me a password!” (or by clicking “OPTIONS” on the navigation menu and then “Password Manager.” Each time you click the button, you will get a new basic auth password, and the old one will be lost. (Note that these passwords only last for 1 year.) The password is a 20 character random sequence.

Note

This robotic password does not affect the way in which you login to the GraceDB web interface. It is only for use with the REST interface as described in the examples below. You will need to continue logging into the web interface using the identity with which you registered for LV-EM membership.

Once you’ve obtained a robotic password, the best way to use it is to create a .netrc file containing your username and password (with permissions 0600 to make sure that only you can read it). The .netrc file could look like this:

machine   gracedb.ligo.org
login     myself@institution.edu
password  abc123.....

Place the resulting .netrc file in your home directory. Once that’s done, you should be able to access the GraceDB REST API using any tool that supports basic auth. For example, you can use the GraceDB Python client in much the same way as described in Basic usage of the REST client, except that the client class is specially formulated for basic auth:

from ligo.gracedb.rest import GraceDbBasic, HTTPError

service_url = 'https://gracedb.ligo.org/api/'
client = GraceDbBasic(service_url)

try:
    r = client.ping()
except HTTPError, e:
    print e.message

print "Response code: %d" % r.status
print "Response content: %s" % r.json()

The only real difference is that the GraceDbBasic client class is used instead of the GraceDb class (which assumes that X509 credentials are available). If you’re not comfortable using Python for scripted access to GraceDB, it is also possible to use curl to directly make requests to the server with the same basic auth credentials. Some examples of using curl are available here.

Downloading a skymap

The GraceDB Python client can be used to download files from Gracedb or add comments, plots, or observation records (see the next section). Here, we’ll show an example of downloading a skymap. Suppose we know that a particular GraceDB event (T125738) has a skymap file called bayestar.fits.gz. This file can be retrieved in the following way:

from ligo.gracedb.rest import GraceDbBasic

grace_id = 'T125738'            # identifier for the event
filename = 'bayestar.fits.gz'  # filename of desired skymap

# Prepend with grace_id for output filename
out_filename = grace_id + '_' + filename

# Instantiate the GraceDB client
service_url = 'https://gracedb.ligo.org/api/'
client = GraceDbBasic(service_url)

# Grab the file from the server and write it
out_file = open(out_filename, "w")
r = client.files(grace_id, filename)
out_file.write(r.read())
out_file.close()

Reporting coordinates of followup observations

In the following example, the GraceDB Python client is used to create an observation record consisting of three separate footprints:

# Define the parameters of the observation to be reported
grace_id      = 'M158044'           # the event's UID
group         = 'CRTS'              # the MOU group
comment       = 'hello my friend'   # free text comment
raList        = [123.0,124.0,125.0] # RAs of centers (degrees)
decList       = [10.0,11.0,13.0]    # Dec of centers (degrees)
startTimeList = [                   # beginnings of exposures (UTC)
    '2015-05-31T12:45:00',
    '2015-05-31T12:49:00',
    '2015-05-31T12:53:00']
raWidthList   = 10.0       # list (or one for all) of widths in RA (degrees)
decWidthList  = 10.0       # list (or one for all) of widths in Dec (degrees)
durationList  = 20.0       # list (or one for all) of exposure times in sec

# Instantiate the GraceDB client
client = GraceDbBasic()

# Write the EMObservation record to GraceDB
r = client.writeEMObservation(grace_id, group, raList, raWidthList,
    decList, decWidthList, startTimeList, durationList, comment)

if r.status == 201:       # 201 means 'Created'
    print 'Success!'

Note that the start times are always assumed to be in UTC. For users not familiar with Python, there are several other options available for uploading observation records:

  • by using the webform on each event page (scroll down to the ‘EM Observations’ section and click on ‘add observation record’). However, this method requires by-hand data entry.
  • by curl-ing directly against the EM observation resource in the API (example)
  • by email (not yet available, but in the works)

If you discover a mistake in your observation record, the best way to correct it is to submit a new observation record with corrected values and request that the old one be deleted. Please send an email to uwm-help@cgca.uwm.edu with something like “delete GraceDB EMObservation” in the subject line. Tell us which entry you’d like deleted, and we’ll take care of it. In the future, we are hoping to make these observation records editable by the submitter.

For more on the GraceDB event page and creating EM observation records, see this helpful video by Roy Williams. There is a companion video on the SkymapViewer here.