TITLE:   GCN CIRCULAR
NUMBER:  21506
SUBJECT: LIGO/Virgo G298048: Fermi GBM trigger 170817.529 and LIGO single IFO trigger
DATE:    17/08/17 13:47:37 GMT
FROM:    Valerie Connaughton at USRA  <valerie@nasa.gov>

V. Connaughton (USRA) reports on behalf of the GBM-LIGO Group:

L. Blackburn (CfA), M. S. Briggs (UAH), J. Broida (Carleton College), E.
Burns (NASA/GSFC), J. Camp (NASA/GSFC), T. Dal Canton (NASA/GSFC), N.
Christensen (Carleton College), A. Goldstein (USRA), R. Hamburg (UAH), C.
M. Hui (NASA/MSFC), P. Jenke (UAH), D. Kocevski (NASA/MSFC), N. Leroy
(LAL), T. Littenberg (NASA/MSFC), J. McEnery (NASA/GSFC), R. Preece (UAH),
J. Racusin (NASA/GSFC), P. Shawhan (UMD), K. Siellez (GA Tech), L. Singer
(NASA/GSFC), J. Veitch (Birmingham), P. Veres (UAH), and C. Wilson-Hodge 
(NASA/MSFC)

The on-board trigger time of Fermi GBM trigger 170817.529 524666471 
at 12:41:06.47 UT is approximately 2 seconds after the single interferometer
LIGO trigger reported in GCN 21505.

Inspection of the real-time data suggests the trigger is consistent with a
weak short GRB, location RA, Dec = 176.8, -39.8 deg (J2000).  The
statistical uncertainty on this location is 11.6 deg 
(radius, 1-sigma containment,
statistical only; there is additionally a systematic
error which we have characterized as a core-plus-tail model, with 90% of
GRBs having a 3.7 deg error and a small tail suffering a larger than 10 deg
systematic error. [Connaughton et al. 2015, ApJS, 216, 32] )

The GBM localization sky map for this event is available at the Fermi Science Support Center 
and shows the uncertainty region including the systematic component:

https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2017/bn170817529/quicklook/glg_locplot_all_bn170817529.png <https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2017/bn170817529/quicklook/glg_locplot_all_bn170817529.png>

and as a FITS file:

https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2017/bn170817529/quicklook/glg_locprob_all_bn170817529.fit <https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2017/bn170817529/quicklook/glg_locprob_all_bn170817529.fit> 

We are producing a HEALPIX map for dissemination to the lv-em observers which should be available very shortly
and will report further analysis of this event when the science data are downlinked from the spacecraft, on a time-scale
of hours.

[GCN OPS NOTE(17aug17): Per author's request, the LIGO/VIRGO ID
was added to the beginning of the Subject-line.]