Massive stars exploding in a He-rich circumstellar medium - VII. The metamorphosis of ASASSN-15ed from a narrow line Type Ibn to a normal Type Ib Supernova

Pastorello, A.; Prieto, J. L.; Elias-Rosa, N.; Bersier, D.; Hosseinzadeh, G.; Morales-Garoffolo, A.; Noebauer, U. M.; Taubenberger, S.; Tomasella, L.; Kochanek, C. S.; Falco, E.; Basu, U.; Beacom, J. F.; Benetti, S.; Brimacombe, J.; Cappellaro, E.; Danilet, A. B.; Dong, Subo; Fernandez, J. M.; Goss, N.; Granata, V.; Harutyunyan, A.; Holoien, T. W. -S.; Ishida, E. E. O.; Kiyota, S.; Krannich, G.; Nicholls, B.; Ochner, P.; Pojmanski, G.; Shappee, B. J.; Simonian, G. V.; Stanek, K. Z.; Starrfield, S.; Szczygiel, D.; Tartaglia, L.; Terreran, G.; Thompson, T. A.; Turatto, M.; Wagner, R. M.; Wiethoff, W. S.; Wilber, A.; Wozniak, P. R.
2015
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
DOI
10.1093/mnras/stv1812
We present the results of the spectroscopic and photometric monitoring campaign of ASASSN-15ed. The transient was discovered quite young by the All Sky Automated Survey for Super-Novae (ASAS-SN) survey. Amateur astronomers allowed us to sample the photometric SN evolution around maximum light, which we estimate to have occurred on JD=2457087.4 +/- 0.6 in the r band. Its apparent r-band magnitude at maximum was r = 16.91 +/- 0.10, providing an absolute magnitude M-r approximate to -20.04 +/- 0.20, which is slightly more luminous than the typical magnitudes estimated for Type Ibn SNe. The post-peak evolution was well monitored, and the decline rate (being in most bands around 0.1 mag d(-1) during the first 25 d after maximum) is marginally slower than the average decline rates of SNe Ibn during the same time interval. The object was initially classified as a Type Ibn SN because early-time spectra were characterized by a blue continuum with superimposed narrow P-Cygni lines of He I, suggesting the presence of a slowly moving (1200-1500 km s(-1)), He-rich circumstellar medium. Later on, broad P-Cygni He I lines became prominent. The inferred velocities, as measured from the minimum of the broad absorption components, were between 6000 and 7000 km s(-1). As we attribute these broad features to the SN ejecta, this is the first time we have observed the transition of a Type Ibn SN to a Type Ib SN.