An unusually fast brightness decline in optical of young type II supernova SN 2016gkg from ASAS-SN follow-up observations
ATel #9529; Ping Chen, Subo Dong, S. Bose (KIAA-PKU), J. L. Prieto (Diego Portales; MAS), K. Z. Stanek, C. S. Kochanek, J. S. Brown, T. W.-S. Holoien, J. Shields (Ohio State), B. J. Shappee (Hubble Fellow, Carnegie Observatories), D. Bersier (LJMU), J. Brimacombe (Coral Towers Observatory), B. Nicholls (Mt. Vernon Obs., New Zealand)
on 22 Sep 2016; 14:24 UT
Credential Certification: Subo Dong (dongsubo@pku.edu.cn)
Subjects: Optical, Ultra-Violet, Supernovae
The All Sky Automated Survey for SuperNovae (ASAS-SN or "Assassin") collaboration reports an unusually fast brightness decline in optical for SN 2016gkg at an averaged rate of ~1 mag/d in V-band between UT 2016-09-21.7 (JD 2457653.2) and UT 2016-09-22.4 (JD 2457653.9). The light curve is shown at SN2016gkg.pdf">this URL.
SN 2016gkg was first reported by Victor Buso and Sebastian Otero, confirmed by ASAS-SN (Atel #9521) and ATLAS (Atel #9526), and spectroscopically classified as a young type II supernova (Atel #9528). Optical photometry by Buso & Otero, ASAS-SN and ATLAS suggest that SN 2016gkg rises rapidly by ~2+ mag between UT 2016-09-20 and UT 2016-09-21.
Using ASAS-SN data obtained from the quadruple 14-cm "Cassius" telescope in Cerro Tololo, Chile taken on UT 2016-09-22.3, we measure the supernova at V = 15.73 +/- 0.05, which is about 0.7 magnitude dimmer than the previous ASAS-SN epoch at about a day ago on 2016-09-21.3 (V~15.0). Such a fast brightness decline in optical is corroborated by observations from LCOGT 1m telescope in Cerro Tololo taken on UT 2016-09-22.1 (V = 15.54 +/- 0.03) and UT 2016-09-22.4 (V = 15.84 +/- 0.06). We also obtain Swift UVOT data on UT 2016-09-21.7 with V = 15.09 +/- 0.05. The ASAS-SN, LCOGT and Swift observations taken between UT 2016-09-21.7 and UT 2016-09-22.4 are all consistent with a brightness decline at a high rate of about 1 mag/d in V-band, and such a fast brightness decline in optical is very unusual for a type II supernova.
The LCOGT observations are performed with BVgri filters, and the Swift UVOT data are taken with all its optical and UV filters. Swift data show that the supernova is UV bright (UVW1-V ~ -1.3), consistent with a young type II supernova. All derived photometry are given in the table below. We also include the photometry previously reported by Buso & Otero, ASAS-SN (Atel #9521) and ATLAS (Atel #9526) in the table.
Obs. JD Mag Site Filter
2457651.7484 17.6 +/- 0.5 Buso & Otero Clear
2457652.6398 14.5 +/-0.2 Buso & Otero Clear
2457651.6653 >17.36 ASAS-SN V
2457652.7987 15.01 +/- 0.04 ASAS-SN V
2457653.7884 15.73 +/- 0.05 ASAS-SN V
2457652.04 15.94 +/- 0.13 ATLAS o
2457652.05 15.78 +/- 0.08 ATLAS o
2457653.6276 15.70 +/- 0.04 LCOGT B
2457653.8946 16.01 +/- 0.08 LCOGT B
2457653.6289 15.54 +/- 0.03 LCOGT V
2457653.8959 15.84 +/- 0.06 LCOGT V
2457653.6302 15.61 +/- 0.03 LCOGT g
2457653.8972 15.91 +/- 0.07 LCOGT g
2457653.6328 15.59 +/- 0.04 LCOGT r
2457653.8998 15.85 +/- 0.08 LCOGT r
2457653.6315 15.65 +/- 0.04 LCOGT i
2457653.1608 13.92 +/- 0.04 Swift UVW2
2457653.2318 15.28 +/- 0.25 Swift UVM2
2457653.1569 13.75 +/- 0.04 Swift UVW1
2457653.1588 13.97 +/- 0.04 Swift U
2457653.1598 15.21 +/- 0.04 Swift B
2457653.1645 15.09 +/- 0.05 Swift V
Follow-up observations are encouraged.
We thank the Swift Team for rapid approval and scheduling of ToO observations. We thank LCOGT and its staff for their continued support of ASAS-SN. ASAS-SN is supported by NSF grant AST-1515927, the Center for Cosmology and AstroParticle Physics (CCAPP) at OSU, and the Mt. Cuba Astronomical Foundation. For more information about the ASAS-SN project, see the ASAS-SN Homepage and the list of all ASAS-SN transients.
SN 2016gkg light curve