TITLE: GCN CIRCULAR NUMBER: 21160 SUBJECT: LIGO/Virgo G268556: optical observations and classification of Pan-STARRS1 transients DATE: 17/05/28 21:05:39 GMT FROM: Alexei Pozanenko at IKI,Moscow A. Pozanenko (IKI), A. Volnova (IKI), E. Mazaeva (IKI), E. Klunko (ISTP), A. Kusakin (AFIF), I. Reva (AFIF) on behalf of IKI-GW follow-up collaboration: We report results of photometric observations and possible classifications of Pan-STARRS1 transients PS17dp, PS17fl, PS17fn, PS17gl (Smartt et al, GCN 20410) detected in the LIGO G268556 localizations (LIGO Scientific Collaboration, GCN 20364). Observations were conducted using telescopes/observatories AZT-33IK/Mondy and Zeiss-1000/TSHAO. =============== PS17dp RA 09:00:51.09 Dec +45:26:44.3 We observed the source PS17dp taking 5 observational sets in different epochs between Jan. 19 and 24. All observations were performed with filter R. The photometry is based on nearby SDSS stars. Date UT start Filter MJD mag err 2017-01-19 18:24:02 R 57770.77716 16.93 0.04 2017-01-21 17:56:26 R 57774.75795 16.91 0.05 2017-01-22 17:40:22 R 57775.74680 16.90 0.05 2017-01-23 17:04:07 R 57776.72092 16.93 0.05 2017-01-24 21:17:52 R 57777.89783 17.02 0.04 The source is fading during our observations. There is an SDSS galaxy J090050.96+452642.7 at the position of the source with r = 17.280 +/- 0.006 and R = 17.050 +/- 0.015 (Lupton 2005 transformation equations) which might be a host galaxy of the transient. At the last observational epoch the source faded to the host galaxy level within 1 sigma. =============== PS17fl RA 08:02:09.73 Dec +28:49:44.7 We observed the source PS17fl taking 9 observational sets in different epochs between January 17 and March 28. All observations were performed with filter R. The photometry is based on nearby SDSS stars. Date UT start Filter MJD mag err 2017-01-17 16:24:04 R 57770.69727 18.15 0.10 2017-01-19 16:52:12 R 57772.71590 18.16 0.02 2017-01-21 15:21:07 R 57774.65356 18.20 0.02 2017-01-22 15:47:17 R 57775.66825 18.18 0.02 2017-01-23 15:39:48 R 57776.66306 18.17 0.02 2017-01-24 19:43:15 R 57777.82865 18.21 0.03 2017-01-25 16:24:35 R 57778.69277 18.18 0.03 2017-01-28 18:32:47 R 57781.78667 18.12 0.02 2017-03-28 17:18:32 R 57840.73404 18.22 0.03 The brightness of the source slowly decreases and in our last observational set has a magnitude consistent within 2 sigma with that of its host galaxy SDSS J080209.69+284945.3 (Chambers et al. GCN 20437) with r = 18.47 +/- 0.01 and R = 18.29 +/- 0.02 (Lupton 2005 transformation equations). If SN Ib/Ic (suggested by Chambers et al. GCN 20437) then maximum can be between MJD 57761.4876 and 57770.69727 and therefore could be related to G268556 event. =============== PS17fn RA 08:05:51.40 Dec +28:42:51.9 We observed the source PS17fn taking 8 observational sets in different epochs between Jan. 17 and 28. All observations were performed with filter R. The photometry is based on nearby SDSS stars. Date UT start Filter MJD mag err 2017-01-17 17:52:24 R 57770.75515 19.51 0.16 2017-01-19 17:34:47 R 57772.74354 19.18 0.04 2017-01-21 16:15:49 R 57774.68807 19.11 0.04 2017-01-22 16:19:52 R 57775.69088 19.15 0.04 2017-01-23 16:32:34 R 57776.69970 19.15 0.40 2017-01-24 20:05:57 R 57777.84441 19.31 0.05 2017-01-25 16:53:02 R 57778.71114 19.33 0.04 2017-01-28 19:15:36 R 57781.80806 19.31 0.07 There is an SDSS galaxy J080209.69+284945.3 at the position of the source with r = 19.801 +/- 0.032 and R = 19.612 +/- 0.063 (Lupton 2005 transformation equations) which might be a host galaxy of the transient. The source is rising above the host level for more then 3 sigma, than fading.The photometry of the source might be contaminated by a nearby galaxy J080551.85+284253.6 in 6 arcseconds to the East of the source. The temporal behavior of the transient allows to confirm it to be a supernova (Chambers et al. 20437) with the maximum around of MJD = 57774.68807 and therefore the source is inconsistent with the G268556 trigger. =============== PS17gl RA 08:34:50.85 Dec +61:13:02.2 We observed the source PS17fl taking 5 observational sets in different epochs between Jan. 19 and 25. All observations were performed with filter R. The photometry is based on nearby SDSS stars. Date UT start Filter MJD mag err 2017-01-19 18:59:34 R 57772.80185 17.38 0.03 2017-01-21 16:48:39 R 57774.71087 17.39 0.03 2017-01-22 16:57:34 R 57775.71707 17.40 0.03 2017-01-24 20:36:10 R 57777.87095 17.56 0.02 2017-01-25 18:51:56 R 57778.79509 17.57 0.02 There is an SDSS galaxy J083450.96+611258.7 at the position of the source with r = 17.704 +/- 0.009 and R = 17.502 +/- 0.020 (Lupton 2005 transformation equations) which might be a host galaxy of the transient. The source is fading during our observations down to the level of the host galaxy within 2 sigma. This may be a supernova or a GRB afterglow.