------------------------------------------------------------------- THE ASTRONOMER Electronic Circular No 3098 2015 Aug 12 19.44UT Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise, Basingstoke, Hants, RG22 4PP,England.Telephone/FAX(01256)471074Int:+441256471074 INTERNET: GUY@TAHQ.DEMON.CO.UK Backup: gmh@wdcc1.bnsc.rl.ac.uk WORLD WIDE WEB http://www.theastronomer.org ------------------------------------------------------------------- SUPERNOVA 2015 IN NGC 5837 (=PSN J15044078+1237436) Further to TA E-Circular 3085 announcing Ron Arbour's discovery of a probable supernova in NGC 5837, the nature of the object has now been confirmed. The relevant ATEL 7690 did not initially reach me:. D C. Leonard (San Diego State University), et. al. report on optical spectroscopic observations of PSN J15044078+1237436 in NGC 5837 (z = 0.028723; Fisher et al. 1995, ApJ Suppl 100, 69, via NED) taken on 2015 June 20.3 and 2015 June 21.3 UT with the 2.3-m Bok telescope (+ Boller & Chivens spectrograph) at Kitt Peak. The spectra cover the range 370 - 680 nm, with a resolution of 0.8 nm. Of particular note to their report is that the transient had a reported discovery magnitude (unfiltered) of 17.53 mag; subsequent observations showed it at mag 17.7 (unfiltered, but calibrated to R; 2015 June 16.932) and mag 17.4 (unfiltered; 2015 June 16.965); no pre-discovery non-detections are listed. Taking the approximate magnitude of the transient to be ~17.5 (in R-band), an estimated distance modulus to the host galaxy of m-M = 35.25 +/- 0.41 (via NED; the mean of 5 Tully-Fisher distances), and an R-band Galactic extinction of 0.08 mag (Schlafly & Finkbeiner, 2011, ApJ, 737, 103) yields an absolute R-band magnitude of approximately -17.8 for PSN J15044078+1237436. The spectra are characterised by a blue continuum with Balmer emission lines (at the approximate redshift of NGC 5837) that are well-fit with Lorentzian profiles (FWHM ~ 1100 km/s; HWZI ~3500 km/s); sharp absorption dips at v ~ 800 km/s are apparent in the blue wings of the Balmer emission lines. He I 587.6 and 501.6 emission is also seen. There does not appear to be significant evolution of the spectra over the one day time interval between them, although the signal-to-noise ratio does not allow a detailed comparison. Cross-correlation with a library of spectra GELATO finds best matches with spectra of the peculiar Type IIn event SN 2009ip taken during the broad peak of its second optical brightening in 2012 (i.e., the "2012-B event", which peaked at M_r ~ -18.3 mag between 2012 October 6 and 2012 October 15; see Graham et al. 2014, ApJ, 787, 163), during which the ejecta were believed to be strongly interacting with a dense CSM. The true nature of SN 2009ip remains a subject of considerable debate, with some contending the 2012 events to have been associated with a true supernova and others proposing a non-terminal event. We note that a reasonable spectral match is also found with the "classical" Type IIn SN 1995G two days after its discovery; in particular the Balmer line profiles -- including especially the low-velocity, blue-shifted absorption dip (not seen in the spectra of SN 2009ip) -- are extremely similar, although PSN J15044078+1237436 does not show any evidence of the multiple Fe II lines seen in the spectrum of SN 1995G. Editor: The above report means that all four supernovae found by Ron Arbour and listed in the UK Nova/Supernova Report being submitted to the BAA Journal and TA magazine have been spectroscopically confirmed although as yet the Central Bureau has not assigned a formal designation. Guy M Hurst