Understanding and Annotating LIGO

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Understanding and Annotating LIGO
Understanding and Annota.ng LIGO-­‐Virgo Probability Maps Roy Williams LIGO 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 ScoL and Teresa (sec.on 1 here) •  Login to event database (Gracedb) here –  and get a password (sec.on 2 here) •  When VOEvent / GCN-­‐No.ce arrives, get the skymap – 
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using your password View it with Skymap Viewer or process it with healpy or with pygcn •  If you observe, share footprints at Gracedb May 15, 2015
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How is LIGO followup different? The Skymap •  Not a posi.on. A probability distribu.on •  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? May 15, 2015
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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 May 15, 2015
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Skymap Viewer N
moon
E
W
view from Tasmania
Observations so far
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S
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Image and Catalog 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
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Zoom and drilldown zoom control
• 
• 
• 
• 
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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)
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Gracedb: the LIGO event database •  Communica.on: 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 curl --insecure --netrc https://gracedb.ligo.org/gracedb/apibasic/events/M137112/files/bayestar.fits.gz
> M137112_bayestar.fits.gz"
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Reading a Skymap •  Reading a skymap file •  Healpix/FITS –  Process with healpy –  View with Skymap Viewer (convert to json and load) 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 pixel"
nside = healpy.get_nside(map)"
(th, ph) = healpy.pix2ang(nside, i)"
probability = map[i]"
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Using Gracedb for Sharing •  EM followup •  Shared messages from LV-­‐EM partners •  GCN Circulars •  EM Observa.ons From the MOU
•  Footprints (required by MOU) •  Candidates •  Visualizing shared effort May 15, 2015
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Using Gracedb for Sharing gracedb.ligo.org
collapse the Event Log Messages
open the "EM followup" and "EM Observations"
Like GCN Circulars (includes them)
observation footprints
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Sharing observa.on footprints click,
comma-­‐separated RA, Dec lists RAwidth, Decwidth can be list You don't need to click a web form you can •  build a curl command •  use pygcn May 15, 2015
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curl,
or code
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Footprints in Skymap Viewer Open the "Sky Localization" tab
Click the gray button
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Footprints in Skymap Viewer May 15, 2015
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Helping the follow-­‐uppers •  Nearby galaxy catalogs •  To ~200 Mpc •  Got any more? •  Galaxy cluster catalogs •  Sugges.ons welcome •  But most galaxies not in clusters •  Light curves •  has this object been variable before •  forced photometry services from surveys? May 15, 2015
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Helping the follow-­‐uppers •  Most likely galaxies •  Catalog with rate prior (eg galaxy luminosity) •  Mul.ply 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 May 15, 2015
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