TITLE: GCN CIRCULAR NUMBER: 20459 SUBJECT: LIGO/Virgo G268556: spectra of two nuclear transients PS17fr and PS17er DATE: 17/01/14 23:19:15 GMT FROM: S. J. Smartt at Queens U Belfast M. E. Huber (IfA), K. C. Chambers (IfA), T.-W. Chen (MPE), S. J. Smartt, (QUB), K. W. Smith (QUB), D. R. Young, D. E. Wright, E. Kankare, R. Kotak, C. Inserra (QUB), M. Coughlin (Harvard), L. Denneau, H. Flewelling, A. Heinze, E. A. Magnier (IfA), A. Rest (STScI), B. Stalder (IfA), A. S. B. Schultz, C. W. Stubbs (Harvard) J. Tonry, C. Waters, R. J. Wainscoat, H. Weiland (IfA) Further to our Pan-STARRS campaign (Smartt et al, GCN 20410) and classification of transients (Chambers et al. GCN 20437) we report spectra of two further objects at the cores of galaxies. -------------------------------------------------------------- PS17fr - possible luminous nuclear SN or TDE --------------------------------------------------------------- PS17fr was discovered coincident with the nucleus of an r=18.36 galaxy (SDSS J081152.10+252521.3), with a photometric redshift z=0.199. The magnitude on the first epoch MJD=57758.433 (from the difference image) was i=19.2, rising 0.6 mag in 3 days. A spectrum with the UH2.2m + SNIFS (R~1300, 3200-10000A) was taken on MJD=57997 and shows broad H-alpha, H-beta and He I 5876. The line profiles are asymmetric. The strong H-alpha has a width at half maximum of 5200 km/s, but is either multicomponent or significantly asymmetric with a red excess. Assuming the centroid of the peak velocity is representative of the host and transient, then z = 0.1862 +/- 0.0003. This implies an absolute magnitude of M_r = -21.1. The object may be a a superluminous supernova of type II or IIn. We note that it is within the volume defined by the LALInference 3D map, at a luminosity distance of 918 Mpc (Ho=69, Omega_M=0.3, Omega_Lam=0.7). As this is a nuclear transient, AGN activity is possible. But we see no strong [N II], [OIII] or [O II]. A weak feature close to, but not exactly at the expected position of [O III] 5007 is visible in the SNIFS data. Another spectrum is required to confirm. A tidal disruption event is also a possible explanation. In summary this is an unusually luminous transient within the LIGO skymap and at a distance consistent with the central 80% of the probability distribution. Further multi-wavelength follow-up is encouraged to determine its nature. Coords : 08:11:52.11 +25:25:21.4 (J2000) ------------------------------------------------------------- PS17er - probable AGN/Seyfert 2 variability ------------------------------------------------------------- PS17er is also a rising transient (now at i=20) at the core of the r=19.2 galaxy SDSS J084157.26+405507.6. A spectrum with Gemini-N+GMOS (R400 grating, 4491-8778 A) on 57764.4223666319 shows it to be at a redshift of z=0.4064 from the [O III] 4959/5007 Angs, implying M_g = -21.3. These lines have a resolved width of 700 km/s, and there is a broader (4000 km/s) H-beta line in emission. The ratio Log([OIII]/Hb) ~ 0.8, is normal for an AGN. In Pan-STARRS regular survey mode, we have seen various detections of i ~ 20 variability. Hence we consider this as likely ongoing Seyfert 2 activity, similar to episodes previously detected in PSST (Huber et al. 2015, ATel 7153).