TITLE: GCN CIRCULAR NUMBER: 20627 SUBJECT: LIGO/Virgo G270580: Gemini-South Spectroscopic Classification of Optical Transients DATE: 17/02/08 10:38:35 GMT FROM: Zach Cano at U of Iceland ​S. Schulze (Weizmann Institute) & Z. Cano (IAA-CSIC) report on behalf of a larger collaboration: Using the 8.2-m Gemini-South telescope mounted with GMOS-S we initiated follow-up spectral classifications of the brightest transients identified by the Transient Name Server (TNS; https://wis-tns.weizmann.ac.il) within the LIGO/Virgo G270580 error region. Originally hindered by bad weather, we successfully observed two transients on 2017-01-28 (PS17rz) and 2017-01-31 (AT2017ux). Both spectroscopic classifications were performed using SNID (Blondin & Tonry, 2007, ApJ, 666, 1024). Survey Name | IAU Name | RA (J2000) | Dec (J2000) | Date | Time (UT) | Grism | Exposure | Type | Phase | Redshift | Note ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- PS17rz | - | 09:36:57.18 | 29:40:06.10 | 2017-01-28 | 06:37:56 | R400 | 3 x 600s | SN Ia | pre-max | 0.151(4) | (1) AT2017ux | SN2017ux | 09:22:53.20 | -03:12:52.30 | 2017-01-31 | 07:07:14 | R400 | 2 x 600s | SN Ia | max | 0.065(6) | (2,3) Notes: (1) The best-fitting templates were all SNe Ia at an average phase of -4 days before peak light. (2) The best-fitting templates were all SNe Ia at an average phase of -1 day before peak light. (3) Our measured SN classification (Ia) and redshift matches well with that already reported to the TNS (z=0.07). ​