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SN 2011Fe: a Laboratory for Testing Models of Type Ia Supernovae

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SN 2011Fe: a Laboratory for Testing Models of Type Ia Supernovae SN 2011fe: A Laboratory for Testing Models of Type Ia Supernovae Laura ChomiukA;B;C A Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824 B National Radio Astronomy Observatory, P.O. Box O, Socorro, NM 87801 C Email: [email protected] Abstract: SN 2011fe is the nearest supernova of Type Ia (SN Ia) discovered in the modern multi- wavelength telescope era, and it also represents the earliest discovery of a SN Ia to date. As a normal SN Ia, SN 2011fe provides an excellent opportunity to decipher long-standing puzzles about the nature of SNe Ia. In this review, we summarize the extensive suite of panchromatic data on SN 2011fe, and gather interpretations of these data to answer four key questions: 1) What explodes in a SN Ia? 2) How does it explode? 3) What is the progenitor of SN 2011fe? and 4) How accurate are SNe Ia as standardizeable candles? Most aspects of SN 2011fe are consistent with the canonical picture of a massive CO white dwarf undergoing a deflagration-to-detonation transition. However, there is minimal evidence for a non-degenerate companion star, so SN 2011fe may have marked the merger of two white dwarfs. Keywords: supernovae: general | supernovae: individual (SN 2011fe) | white dwarfs | novae, cataclysmic variables 1 Introduction 2 SN 2011fe: A normal SN Ia The multi-band light curve of SN 2011fe, measured in Discovered on 2011 August 24 by the Palomar Tran- exquisite detail at UV through IR wavelengths, is typ- sient Factory, SN 2011fe1 was announced as a Type ical of SNe Ia (Figure 2; Vink´oet al. 2012; Brown Ia supernova (SN Ia) remarkably soon after explosion et al. 2012; Richmond & Smith 2012; Munari et al. (just 31 hours; Nugent et al. 2011a,b). SN 2011fe is 2013; Pereira et al. 2013). In the B-band, the light nearby, located in the well-studied galaxy M101 at a curve declines by ∆m15 = 1:1 mag in 15 days (Rich- distance of ∼7 Mpc (Figure 1; Shappee & Stanek 2011; mond & Smith 2012; Pereira et al. 2013). To power the 56 Lee & Jang 2012). As the earliest and nearest SN Ia light curve of SN 2011fe, ∼0.5 M of Ni is required discovered in the modern multi-wavelength telescope (Nugent et al. 2011b; Bloom et al. 2012; Pereira et al. era, SN 2011fe presents a unique opportunity to test 2013). This 56Ni mass is quite typical for SNe Ia (How- models and seek answers to long-standing questions ell et al. 2009). about SNe Ia. In addition, time-resolved optical spectroscopy shows SN 2011fe to be a spectroscopically-normal Such a testbed has been sorely needed. SNe Ia SN Ia (Parrent et al. 2012; Pereira et al. 2013; Maz- are widely used by cosmologists to measure the ex- zali et al. 2013). SN 2011fe can be classified as \core pansion parameters of the Universe, and led to the normal" in the schemes of Benetti et al. (2005) and Nobel Prize-winning discovery of dark energy (Riess Branch et al. (2006). et al. 1998; Perlmutter et al. 1999). However, impor- In all relevant details, SN 2011fe appears to be a tant unknowns remain that stymie the use of SNe Ia normal SN Ia. It has, therefore, been taken to be as precise cosmological tools. The progenitor systems representative of its class. Conclusions reached for of SNe Ia are poorly understood, and the explosion SN 2011fe may be extrapolated to SNe Ia generally, mechanism itself is elusive (reviews by Hillebrandt & but we must be careful in this extrapolation, remem- Niemeyer 2000; Livio 2001; Howell 2011; Wang & Han bering that SN 2011fe is only one object. A number of arXiv:1307.2721v1 [astro-ph.HE] 10 Jul 2013 2012 contain more details). recent studies have shown that SNe Ia are diverse, and This paper reviews the significant body of work that differences in their observational properties may already published on SN 2011fe as of mid-2013. I focus imply real variety in progenitor systems and explosion on five questions: (i) Is SN 2011fe a normal SN Ia? (ii) mechanisms (e.g., Foley et al. 2012; Wang et al. 2013) What exploded in SN 2011fe? (iii) How did it explode? . (iv) What is the progenitor of SN 2011fe? and (v) How accurately can we use SNe Ia as standard candles? A concise summary follows in Section 6. 3 What exploded in SN 2011fe? While it has long been thought that a SN Ia marks 1The source was originally dubbed PTF 11kly. the complete disruption of a white dwarf (e.g., Hoyle & 1 2 Publications of the Astronomical Society of Australia Figure 1: Images of M101 obtained on three successive nights, from left to right: 2011 Aug 23.2, Aug g 24.2, andFigure Aug 25.2 1: PTF UT. The-band green image arrow sequence points of the to field SN 2011fe, of Messier which 101 was showing not detected the appearance in the of first image but subsequentlySN 2011fe. brightened From left to dramatically. right, images are Figure from August from 23.22,Nugent 24.17, et al. and (2011b), 25.16 UT. reprinted The supernova by permission from Macmillanwas not detected Publishers on the Ltd: first Nature, night to copyright a 3-s limiting 2011. magnitude of 21.5, was discovered at magni- tude 17.35, and increased by a factor of 10 in brightness to mag 14.86 the following night. The supernova peaked at magnitudeVink´oet al.:9.9, Distance making to M101 it the from fifth SN 2011fe brightest supernova in the past century. ⇠ PTF is a wide-field optical experiment designed to systematically explore the variable sky on a 9.5 9.5 Table 5. SALT2 best-fitting parameters 22, 23 10 variety of timeB scales, with 10 one particularV focus theon very knowing early detection the precise of SNe time of. theDiscoveries explosion. This is 10.5 10.5 11 11 estimated to be UT 2011 August 23 16:29±20 minutes 11.5 such as this one have been 11.5 made possible by coupling real-timeParameter computational Value tools to extensive 12 12 24, 25 t (JD) 2,455,815.505 (0.047) 12.5 astronomical follow-up 12.5 observations . by Nugent0 et al. (2011b). They derive this time by 13 13 m$ (mag) 9.959 (0.027) 13.5 13.5 fittingB a power law to the early optical light curve, 14 14 x1 0.296 (0.049) Observed magnitude 14.5 Observed magnitude 14.5 followingc the expectation−0.030 (0.018) that the SN luminosity L will -20 -10 0 10 20 30 40 50 -20 -10 0 10 20 30 40 50 − increaseµ0(G10) as the (mag) area 29.034 of the (0.078) optically-thick photosphere, Days from B-maximum Days from B-maximum 2 producingµ0(K09) the (mag) relation 29.068L (0.062)/ t . This simple model fits 9.5 10 µ (final) (mag) 29.05 (0.08) 10 R 10.5 I the photometry0 very well over the first four days (see 10.5 11 11 11.5 Notes. ErrorsFigures are given 3 and in parentheses. 4). The final distance modulus (last 11.5 12 12 row) is the average of the G10 and K09 estimates. 12.5 12.5 The modeling of the shock breakout is aided by the 13 13 13.5 13.5 serendipitous availability of optical imaging of M101 14 14 Observed magnitude 14.5 Observed magnitude 14.5 Contrarythat hadto MLCS been,the obtainedSALT2 model a mere does four not explicitly hours after in- Nugent -20 -10 0 10 20 30 40 50 -20 -10 0 10 20 30 40 50 Days from B-maximum Days from B-maximum clude theet distance al.'s estimated or the distance time modulus, of explosion, thus, it must but bebefore de- the SN rived fromwas the actually fitting parameters. discovered We followed (Bloom two et slightly al. 2012). dif- These Figure 2: BV RI LightSALT2 curves for SN 2011fe mea- Fig. 7. The fitting of LCs to the observed data of ferent proceduresdata, obtained for this: thewith one The presented Open by University's Guy et al. (2010) 0.4-m tele- suredSN 2011fe. in the Johnson-Cousins system (Vega magni-(G10) and an independent realization given by Kessler et al. scope, yield a robust non-detection at$ this epoch. The tudes). Best-fit SN Ia templates from SALT2 are(2009) (K09). Starting from the fitting parameters mB, x1 and c, first detection of SN 2011fe was made 11 hours after plotted as black lines. Figure from Vink´oet al.the distance modulus µ0 in the G10 calibration can be obtained 3.3.1. MLCS2k2 as Nugent et al.'s estimated explosion time. (2012), reproduced with permission c ESO. $ The faint optical flux at very early times places The fitting of Eq. 2 was performed by using a simple, self- mBB = mB 0.008( 0.005) x1 + 0.013( 0.004) χ2 strong− constraints± · on the shock± breakout signal, imply- developed -minimization code, which scans through the al- CC = 0.997( 0.097) C + 0.002( 0.009) x1 + 0.035( 0.008) lowed parameter space with a given step and finds the lowest ing that± the exploding· ± star was· compact,± with a radius 2 s = 0.107( 0.006) x1 + 0.991( 0.006) 56 χ within this range. The fitted parameters were the moment of R? . ±0:02 R· (Figure± 3). From the measured Ni FowlerB-maximum 1960), (t ), little the V direct-band extinction proof existedA ,theLC-parameter until SN 2011fe.∆ µ0 = mBB MB + a (s 1) b CC, (5) 0 V mass,− we know· − the− star· was &0.5 M .
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