• Filippenko, A. V.
• Foley, R. J.
• Ayani, K.
• Masi, G.
• Buczynski, D.
• Yusa, T.
• Kiyota, S.
• Nakano, S.
• Zheng, W.
• Noguchi, T.

Abstract

T. Yusa, Osaki, Japan, reports the discovery by Kunihiro Shima (Fuchu, Tokyo) of an apparent supernova (mag 15.5) on an unfiltered CCD frame (limiting magnitude 18.6) taken on Mar. 23.788 UT with a 0.45-m f/12 reflector (+ FLI ML-8300 camera) at Fujimi-machi, Nagano, Japan.The new object is located at R.A. = 20h37m25s.58, Decl. = +66d07'11".5 (equinox 2000.0), which is 68".7 east and 51".4 north of the center of NGC 6951. Shima notes that nothing is visible at this position on red and blue images from the Digitized Sky Survey.His discovery image was posted at the following website URL: http://space.geocities.jp/yusastar77/supernova/PSNinN6951_150324.htm. The variable was designated PSN J20372558+6607115 when it was posted at the Central Bureau's TOCP webpage and is here designated SN 2015G based on the spectroscopic confirmation reported below.Additional CCD magnitudes for 2015G:Jan. 12.447, [18.0 (Shima); Mar. 24.125, 15.9 (D. Buczynski, Portmahomack, U.K.; 35.6-cm reflector + SBIG ST9XE camera; position end figures 25s.58, 11".6); 24.534, 16.4 (T. Noguchi, Katori, Chiba-ken, Japan; 0.23-m f/6.3 reflector + FLI ML0261E camera; limiting mag 18.5; position end figures 25s.57, 11".6; offset 69" east, 52" north; UCAC4 reference stars; image posted at URL http://park8.wakwak.com/~ngc/images/PSNinNGC6951.jpg; communicated via S. Nakano); 24.540, V = 16.26, I_c = 15.89 (S. Kiyota, Kamagaya, Japan; remotely with an iTelescope 0.61-m f/6.5 CDK astrograph + FLI PL09000 camera at the Sierra Remote Observatory near Auberry, CA, USA; image posted at http://meineko.sakura.ne.jp/ccd/PSN_J20372558+6607115.jpg); 26.481, B = 16.8, V = 16.4, R = 16.3 (T. Yusa, Osaki, Japan; 0.43-m f/6.8 astrograph at Mayhill, NM; position end figures 25s.57, 11".6; image posted at http://space.geocities.jp/yusastar77/supernova/PSNinN6951_150324.htm); 31.056, 16.7 (G. Masi, remotely using a 43-cm telescope near Ceccano, Italy; position end figures 25s.58, 11".6).K. Ayani, Bisei Astronomical Observatory (BAO), Ibara, Okayama, Japan, obtained a low-resolution spectrogram (range 400-800 nm; resolution 0.8 nm at H-alpha) of PSN J20372558+6607115 = SN 2015G with the BAO 1.01-m telescope on Mar. 25.8 UT.The spectrum is likely that of a type-Ib supernova.Cross- correlation with a library of supernova spectra using the "SuperNova Identification" code (SNID; Blondin and Tonry 2007, Ap.J. 666, 1024) shows that the spectrum of 2015G best matches (although rather poorly) with spectra of type-Ib supernovae about a month past maximum, though the emission and absorption features of the BAO spectrum are weaker than the SNID templates. The spectrum can be viewed via website URL http://tinyurl.com/loq5zbd.R. J. Foley, University of Illinois; W. Zheng and A. V. Filippenko, University of California, Berkeley; and S. D. Van Dyk, Infrared Processing and Analysis Center, California Institute of Technology, report that they obtained a spectrogram (range 345-1050 nm) of PSN J20372558+6607115 = SN 2015G on Mar. 26.51 UT with the Lick 3-m Shane telescope (+ Kast).The supernova has a blue continuum and relatively narrow He I emission lines, and it lacks any discernible H emission.They therefore classify 2015G as a type- Ibn supernova.SN 2015G is spectrally similar to SN 2006jc (Foley et al. 2007, Ap.J. Let. 657, 105; Pastorello et al. 2007, Nature 447, 829), although there are some differences.In particular, the emission features of SN 2015G have smaller equivalent widths than those of SN 2006jc, and SN 2015G lacks a strong pseudo-continuum at wavelengths below 500 nm. Nonetheless, the continuum is blue and consistent with a 8500-K blackbody spectrum.Additionally, SN 2015G has relatively strong, narrow P-Cyg absorption features embedded in each He I emission line.For He I 706.5-nm, which has a FWHM of 5500 km/s, the P-Cyg absorption is blue-shifted by 1300 km/s.The host galaxy, NGC 6951, is at a distance of roughly 25 Mpc; correcting for the large Milky Way absorption (A_V = 1.0 mag), 2015G peaked (or will peak) at absolute magnitude M 〈 -17.4, similar to that of SN 2006jc.

Topics

• impedance spectroscopy