As soon as the GW trigger came in, we prepared OBs for FORS2 imaging, Xshooter and HAWK-I assuming a somewhat fainter source. The NS-BH suggested fainter, redder and more slowly evolving counterpart and the larger distance compared to GW170817 meant that it should be a few magnitudes fainter than GW170817.
While the OBs were being prepped, we were trying to see if any obvious candidates could be targeted with MUSE, however the number of potential candidate galaxies made that we did not manage to go forward with this.
We agreed, that the long GRB was very likely related to the GW source, however we did not put weight to this going forward.
fcmaker did initially not work, due to the GAIA web-service being down and we had to manually prepare finding charts, however it was found that the GAIA website should be back up shortly.
Then the list of targets came out. I feel now, that the 6 candidates came out simultanously, but there was a small delay between GWT1-5 and GWT6.
The PanSTARRS source, although at 2-sigma to the GW position seemed like an obvious goto source to take a classification spectrum of, so we immediately submitted a 2x300 s X-shooter OBs to obtain a short classification spectrum.
In the mean time, we could go through the rest of the sources. GWT1 was too bright, GWT2 was just next to a CV, GWT5 had a host too far away, so we were left with GWT3 and GWT4.
Because GWT4 was the fainter source, we decided to submit a FORS2 spec trigger for GWT4 and an X-shooter one for GWT3.
We were preparing the OBs to follow up GWT3 when the GCN 005 came in, which made us think that we had made a mistake. When the EC sent new data, we could see it was an unrelated supernova, however the GCN 005 made us stop the preparation of OBs for GWT3.
We then triggered HAWK-I, and X-shooter for further follow-up of GWT3.
In total, we triggered 2 x (2x300s) X-shooter, 2x (2 x 1 hr) HAWK-I and 1 x (4x600s) Xshooter. Jonatan Selsing, on behalf of team A
Selsing, Bruun, Benetti, Callis, Fynbo, Galbany, Jonker, Kostrzewa-Rutkowska, Mandel, Onori