Displaying the heterogeneity of the SN 2002CX-like subclass of type IA supernovae with observations of the pan-starrs-1 discovered sn 2009ku The Harvard community has made this article openly available. Please share how this access benefits you. Your story matters Citation Narayan, G., R. J. Foley, E. Berger, M. T. Botticella, R. Chornock, M. E. Huber, A. Rest, et al. 2011. Displaying the heterogeneity of the SN 2002CX-like subclass of type IA supernovae with observations of the pan-starrs-1 discovered sn 2009ku. The Astrophysical Journal 731, no. 1: L11. doi:10.1088/2041-8205/731/1/l11. Published Version doi:10.1088/2041-8205/731/1/l11 Citable link http://nrs.harvard.edu/urn-3:HUL.InstRepos:30410832 Terms of Use This article was downloaded from Harvard University’s DASH repository, and is made available under the terms and conditions applicable to Open Access Policy Articles, as set forth at http:// nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of- use#OAP Draft version August 27, 2010 A Preprint typeset using LTEX style emulateapj v. 11/10/09 DISPLAYING THE HETEROGENEITY OF THE SN 2002CX-LIKE SUBCLASS OF TYPE IA SUPERNOVAE WITH OBSERVATIONS OF THE PAN-STARRS-1 DISCOVERED SN 2009ku* G. Narayan1, R. J. Foley2,3, E. Berger2, M. T. Botticella6, R. Chornock2, M. E. Huber5, A. Rest2,4, D. Scolnic5, S. Smartt6, S. Valenti6, A. M. Soderberg2, W. S. Burgett7, K. C. Chambers7, G. Gates7, T. Grav5, N. Kaiser7, R. P. Kirshner2, E. A. Magnier7, J .S.Morgan7, P. A. Price7,8, A. G. Riess5,4 C. W. Stubbs1, W. E. Sweeney7, J. L. Tonry7, R. J. Wainscoat7 W. M. Wood-Vasey10 Draft version August 27, 2010 ABSTRACT SN 2009ku, discovered by Pan-STARRS-1, is a Type Ia supernova (SN Ia), and a member of the distinct SN 2002cx-like class of SNe Ia. Its light curves are similar to the prototypical SN 2002cx, but are slightly broader and have a later rise to maximum in g. SN 2009ku is brighter (∼0.6 mag) than other SN 2002cx-like objects, peaking at MV = −18.4 mag — which is still significantly fainter than typical SNe Ia. SN 2009ku, which had an ejecta velocity of ∼2000 kms−1 at 18 days after maximum brightness is spectroscopically most similar to SN 2008ha, which also had extremely low- velocity ejecta. However, SN 2008ha had an exceedingly low luminosity, peaking at MV = −14.2 mag, ∼4 mag fainter than SN 2009ku. The contrast of high luminosity and low ejecta velocity for SN 2009ku is contrary to an emerging trend seen for the SN 2002cx class. SN 2009ku is a counter-example of a previously held belief that the class was more homogeneous than typical SNe Ia, indicating that the class has a diverse progenitor population and/or complicated explosion physics. As the first example of a member of this class of objects from the new generation of transient surveys, SN 2009ku is an indication of the potential for these surveys to find rare and interesting objects. Subject headings: supernovae: general — supernovae: individual(SN 2009ku) 1. INTRODUCTION bers) dominating the outliers. Members of this sub- Most Type Ia supernovae (SNe Ia) can be described class, labeled “SN 2002cx-like” after the prototypical ∼ by a single parameter that relates peak luminosity object (Li et al. 2003), have peak magnitudes 2 mag with light-curve shape (Phillips 1993), intrinsic color below that of normal SNe Ia and spectra that resemble the high-luminosity SN Ia 1991T (Filippenko et al. 1992; (Riess et al. 1996), and 56Ni mass (Mazzali et al. 2007). Phillips et al. 1992) at early and intermediate phases, There are examples of particular SNe Ia not following except with significantly lower expansion velocities and this parameterization (e.g., Li et al. 2001; Foley et al. having late-time (∼1 yr after maximum) spectra which 2010b), with a single, relatively large subclass of ob- show low-velocity Fe II lines, few lines from intermediate- jects (see Foley et al. 2009 for a recent list of mem- mass elements, and no strong forbidden lines (Jha et al. 2006; Sahu et al. 2008). The extreme characteristics of [email protected] * this class can be explained if the objects are full de- This paper includes data gathered with the 6.5 m Magellan flagrations of a white dwarf (WD) (Branch et al. 2004; Telescopes located at the Las Campanas Observatory, Chile; the Subaru Telescope, which is operated by the National Astronom- Phillips et al. 2007). Because of their low velocities, ical Observatory of Japan; the Nordic Optical Telescope, oper- which eases line identification, and probing of the de- ated by Denmark, Finland, Iceland, Norway, and Sweden and flagration process, which is essential to all SN Ia explo- the Liverpool Telescope operated by the Liverpool John Moores sions, this subclass is particularly useful for understand- University with financial support from the UK Science and Tech- nology Facilities Council on the island of La Palma in the Span- ing typical SN Ia explosions. For a review of this class, arXiv:1008.4353v1 [astro-ph.SR] 25 Aug 2010 ish Observatorio del Roque de los Muchachos of the Instituto de see Jha et al. (2006). Astrofisica de Canarias; and the Gemini Observatory, which is A recent addition to this class, SN 2008ha (Foley et al. operated by the Association of Universities for Research in As- tronomy, Inc., under a cooperative agreement with the NSF 2009; Valenti et al. 2009; Foley et al. 2010a), was much 1 Department of Physics, Harvard University, 17 Oxford fainter (peaking at MV = −14.2 mag) and had a sig- Street, Cambridge, MA 02138 ≈ −1 2 nificantly lower velocity (v 2000 kms ) than the Harvard-Smithsonian Center for Astrophysics, 60 Garden typical member. Although its maximum-light spec- Street, Cambridge, MA 02138 3 Clay Fellow. Electronic address [email protected] . trum indicates that the object underwent C/O burn- 4 Space Telescope Science Institute, 3700 San Martin Drive, ing (Foley et al. 2010a), certain observations are consis- Baltimore, MD 21218 5 tent with a massive-star progenitor (Foley et al. 2009; Department of Physics and Astronomy, Johns Hopkins Uni- Valenti et al. 2009; Moriya et al. 2010). SN 2008ha gen- versity, 3400 N. Charles Street, Baltimore, MD 21218 −3 56 6 Astrophysics Research Centre, School of Mathematics and erated ∼10 M⊙ of Ni and ejected ∼0.3M⊙ of material Physics, Queen’s University Belfast, Belfast, BT7 1NN, UK 7 (Foley et al. 2010a), suggesting that the most plausible Institute for Astronomy, University of Hawaii at Manoa, explanation was a failed deflagration of a WD that did Honolulu, HI 96822 8 Department of Astrophysical Sciences, Princeton University, not destroy the progenitor star (Foley et al. 2009, 2010a). Princeton, NJ 08544 Furthermore, another member of this class, SN 2008ge, 10 Department of Physics and Astronomy, University of Pitts- was hosted in an S0 galaxy with no signs of star for- burgh, 3941 O’Hara Street, Pittsburgh PA 15260 2 Narayan et al. mation or massive stars, including at the SN position in pre-explosion HST imaging (Foley et al. 2010c). Using a small sample of SN 2002cx-like objects, 17 z − 2.5 McClelland et al. (2010) suggested that their peak lumi- i − 1.5 nosities correlated with light-curve shapes and ejecta ve- locity (with more luminous SNe having faster ejecta and r slower declining light curves). These correlations are sim- 18 g + 0.5 ilar to that of the relationship between light-curve shape and peak luminosity in “normal” SNe Ia (Phillips 1993) 19 and suggest that SN 2002cx-like objects can possibly be described by a single parameter. As part of the Medium Deep Survey (MDS) SN 2009ku 20 was discovered by Pan-STARRS-1 (PS1) on 2009 Oct. 4.83 (UT dates are used throughout this paper) at mag 19.9 (Rest et al. 2009) in APMUKS(BJ) B032747.73- 21 281526.1, an Sc galaxy with a redshift of 0.0792 in the MD02 field (coincident with the CDF-S field). Spec- troscopy showed that it was a SN Ia similar to SN 2002cx Apparent Brightness (mag) 22 (Rest et al. 2009). From the discovery magnitude and redshift alone, SN 2009ku had a peak magnitude of Mr . −18 mag, similar to that of SN 2002cx, but much 23 brighter than SN 2008ha. With our full light curves, we SSS S measure its peak brightness below. We also show that the spectra of SN 2009ku are similar to SN 2002cx and −20 0 20 40 60 80 most similar to those of SN 2008ha, with both objects Rest Days Relative to r Max having small expansion velocities. We present and discuss our observations in Section 2. Fig. 1.— griz light curves of SN 2009ku. The uncertainties In Section 3, we place SN 2009ku in the context of other for most data points are smaller than the plotted symbols. Also objects in the SN 2002cx-like subclass and typical SNe Ia. plotted are comparison light curves of SNe 2002cx (VRI ; dashed We discuss our results and summarize our conclusions in lines), 2005hk (griz; solid lines), and 2008ha (VRI ; dotted lines) after applying a magnitude offset to match the peak in each band. Section 4. Throughout this work, we use the concordance The epoch of each spectrum is marked with an ‘S.’ cosmology of (H0, Ωm, ΩΛ) = (70, 0.3, 0.7). 2. OBSERVATIONS AND DATA REDUCTION 07 to images obtained by the Sloan Digital Sky Survey SN 2009ku was discovered before maximum bright- (SDSS) and then extrapolating the zero points to obser- ness by the 1.8 m PS1 telescope on Haleakala as part vations of the MD02 on the same night.