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Optical Spectroscopy of PSN J15044078+1237436

ATel #7690; D. C. Leonard (San Diego State University), P. Sheehan, D. McCarthy (University of Arizona), K. Follette (Stanford University), J. Moustakas (Siena College), D. Cantillo, A. Cazares-Kelly, S. Cazares-Kelly, Y. Cendes, N. Damm, A. Donati, E. Douglas, L. Ferrell, H. Fosbiner-Elkins, C. Fox, M. Greenberg, K. Hart, H. Hensley, A. Holt, E. Hooper, C. Juran, J. Keane, K. Key, L. Korus, T. Lee, K. Leidig, E. Merchak, K. Nessmann, S. Pendyala, S. Pirkl, J. Reeder, A. Roos, S. Rounseville, E. Ruddy, A. Schlingman, W. Schlingman, W. Schlingman, E. Schwartzman, V. Shanmugam, E. Silver, A. Stein, N. Stock, B. Svoboda, B. Thomas, N. Thomas, K. Thompson-Taylor, H. Walton (2015 Advanced Teen Astronomy Camp)
on 22 Jun 2015; 21:45 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: D. C. Leonard (leonard@astro.caltech.edu)

Subjects: Optical, Supernovae, Transient, Variables

We 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. Information on PSN J15044078+1237436, discovered by R. Arbour on 2015 June 16.028 UT, was announced through the CBAT Transient Object Followup Reports (http://www.cbat.eps.harvard.edu/index.html) and is also available from the "Bright Supernova" website (http://www.rochesterastronomy.org/snimages/). Of particular note to our 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 characterized 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 using the comparison tool GELATO (Harutyunyan et al. 2008, A&A, 488, 383) 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 (e.g., Smith et al. 2014, MNRAS, 438, 1191) and others proposing a non-terminal event (e.g., Moriya et al. 2015, ApJL 803, 26, and references therein). We note that a reasonable spectral match is also found with the "classical" Type IIn SN 1995G two days after its discovery (Pastorello et al. 2002, MNRAS, 333, 27); 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.

Given the similarities of PSN J15044078+1237436 to Type IIn events and, especially, to spectra of SN 2009ip during a particularly interesting phase, further observations at all wavelengths are encouraged, as are examinations of pre-discovery images to potentially constrain prior outbursts.