Hotwiring the Transient Universe

Understanding and Annotating LIGO-Virgo Probability Maps

Roy WilliamsLIGO Lab - Caltech

Hotwiring the Transient Universe

How to get your Nobel Prize for the GW-EM counterpart

• Apply to join the MOU group here– When approved register here

• Ask GCN to allow your IP-address to connect– send email to Scott and Teresa (section 1 here)

• Login to event database (Gracedb) here– and get a password (section 2 here)

• When VOEvent / GCN-Notice arrives, get the skymap– using your password– View it with Skymap Viewer – or process it with healpy– or with pygcn

• If you observe, share footprints at Gracedb

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Hotwiring the Transient Universe

How is LIGO followup different?

The Skymap

• Not a position. A probability distribution• represented with FITS/Healpix

• healpix.jpl.nasa.gov• sudo pip install healpy• EA in HEALPIX means all pixels on the sphere have

equal area• sample code and tech info here

• Should I observe?• If so, where?

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Hotwiring the Transient Universe

Next ....• Skymap Viewer

• Here is the open version with 1600 mock skymaps• Here for MOU partners• direct link from Gracedb

• And sharing footprints• like the minor planet center• don't observe what is already covered• we want to ask for the image itself if we need to

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Hotwiring the Transient Universe

Skymap Viewer

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N

S

EW

moon

view from Tasmania

Observations so far

Hotwiring the Transient Universe

Image and Catalog

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Click on the Layers icon

WHAT OTHER

CATALOGS HERE?

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size of square is ~galaxy mass *

skymap

click the center to get Simbad and NED

70 Mpc

Hotwiring the Transient Universe

Zoom and drilldown

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• set image = DSS colored• keep zooming in ESO336-016• click the marker then NED link• much more data (eg 2MASS image)

zoom control

Hotwiring the Transient Universe

Gracedb: the LIGO event database• Communication: Click, Curl, or Code?

• clicking allows reading, experiment, understanding• a curl command is automatable and transparent• a code library integrates well with other code

– try pygcn

• Curl example

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curl --insecure --netrc https://gracedb.ligo.org/gracedb/apibasic/events/M137112/files/bayestar.fits.gz > M137112_bayestar.fits.gz

Hotwiring the Transient Universe

Reading a Skymap• Reading a skymap file

• Healpix/FITS– Process with healpy– View with Skymap Viewer (convert to json and load)

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map,header = healpy.read_map(filename, h=True)# map is a long vector of floats# header is dictionary of FITS header

# interpolate# th is codeclination (radians), ph is RA (radians)probability = healpy.pixelfunc.get_interp_val(map, th, ph)

# handle every pixelnside = healpy.get_nside(map)(th, ph) = healpy.pix2ang(nside, i)probability = map[i]

Hotwiring the Transient Universe

Using Gracedb for Sharing• EM followup

• Shared messages from LV-EM partners• GCN Circulars

• EM Observations • Footprints (required by MOU)• Candidates• Visualizing shared effort

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From the MOU

Hotwiring the Transient Universe

Using Gracedb for Sharing

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gracedb.ligo.orgcollapse the Event Log Messagesopen the "EM followup" and "EM Observations"

Like GCN Circulars (includes them)

observation footprints

Hotwiring the Transient Universe

Sharing observation footprints

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comma-separatedRA, Dec lists RAwidth, Decwidth can be list

You don't need to click a web form you can• build a curl command• use pygcn

click,

curl,

or code

Hotwiring the Transient Universe

Footprints in Skymap Viewer

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Open the "Sky Localization" tab

Click the gray button

Hotwiring the Transient Universe

Footprints in Skymap Viewer

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Hotwiring the Transient Universe

Helping the follow-uppers• Nearby galaxy catalogs

• To ~200 Mpc• Got any more?

• Galaxy cluster catalogs• Suggestions welcome• But most galaxies not in clusters

• Light curves• has this object been variable before• forced photometry services from surveys?

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Hotwiring the Transient Universe

Helping the follow-uppers• Most likely galaxies

• Catalog with rate prior (eg galaxy luminosity)• Multiply by skymap probability

• Ordered list of your fields• Sky tesselated into YOUR rectangular fields

– which have most dark sky + probability?

• Personal alarm for GW events• When YOUR telescope has a chance

– dark sky + probability > X steradians

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