Optical observations of SN 2011fe
D.Yu.Tsvetkov, S.Yu. Shugarov, I.M. Volkov, V.P. Goranskij, N.N. Pavlyuk, N.A. Katysheva, E.A. Barsukova, A.F. Valeev
aa r X i v : . [ a s t r o - ph . S R ] N ov Contrib. Astron. Obs. Skalnat´e Pleso , 94 – 109, (2013) Optical observations of SN 2011fe
D.Yu. Tsvetkov , S.Yu. Shugarov , , I.M. Volkov , , V.P. Goranskij ,N.N. Pavlyuk , N.A. Katysheva , E.A. Barsukova and A.F. Valeev Sternberg Astronomical Institute, M.V. Lomonosov Moscow StateUniversity, Universitetskii pr. 13, 119992 Moscow, Russia(E-mail: [email protected]) Astronomical Institute of the Slovak Academy of Sciences059 60 Tatransk´a Lomnica, The Slovak Republic Special Astrophysical Observatory of the Russian Academy of Sciences,Nizhniy Arkhyz, Karachai-Cherkesia, 369167 Russia
Received: June 19, 2013; Accepted: October 16, 2013
Abstract.
We present
UBVRI photometry of the supernova 2011fe in M101,obtained in the interval of 1 – 652 days after its discovery, as well as onespectrum, taken 105 days after the brightness maximum in the B band. Wederived parameters of the light curves, constructed the colour curves and a”quasi–bolometric” light curve. The light curves, colour evolution and spectrumof the object indicate that SN 2011fe belongs to the ”normal” subset of type Iasupernovae. It is practically identical to a well-studied ”normal” SN Ia 2003du. Key words: supernovae: individual (SN 2011fe)
1. Introduction
Supernova (SN) 2011fe, located at α = 14 h m s . , δ = +54 ◦ ′ ′′ . et al. , 2011). It is the closest and brightest type Ia SN since SN 1972E, so itprovides an unprecedented opportunity for numerous follow-up studies.Li et al . (2011) checked the archival HST images of the site and found outthat a luminous red giant cannot be the companion to the SN progenitor. Thisconclusion was confirmed by early X-ray and radio observations (Horesh etal. , 2012; Chomiuk et al. , 2012). The results of photometric monitoring werepresented by Vinko et al. (2012, hereafter V12), Richmond and Smith (2012,hereafter RS12) and Munari et al. (2013, hereafter M13). Pereira et al. (2013,hereafter P13) reported spectrophotomeric observations and derived synthetic UBVRI magnitudes based on these data. Infrared photometry was presented byMatheson et al. (2012). Optical spectral evolution was investigated by Parrent et al. (2012), Smith et al. (2011), Patat et al. (2013) and Shappee et al. (2013).This bright nearby event should provide a wealth of information on the natureof thermonuclear supernovae. ptical observations of SN 2011fe
2. Observations
We present here photometry of SN 2011fe in the
UBVRI passbands obtainedat five sites, starting one day after the discovery and continuing for a period of652 days. Most of the data were obtained at the Star´a Lesn´a Observatory of theAstronomical Institute of the Slovak Academy of Sciences. The other observ-ing sites were the Crimean Laboratory of the Sternberg Astronomical Institute(SAI)(Nauchniy, Crimea, Ukraine); the Simeiz Observatory of the Crimean As-trophysical Observatory (Simeiz, Crimea, Ukraine); the Moscow Observatory ofSAI (Moscow, Russia); the Special Astrophysical Observatory of RAS (NizhniyArkhyz, Russia). A list of the observing facilities is given in Table 1.
Table 1.
Telescopes and detectors employed for the observations.
Tele- Location Aperture CCD Filters Scale FoVscope [m] camera [arcsec [arcmin]code pixel − ]T50 Star´a 0.5 SBIG U BV R C I C BV R C I C U BV R C I J U BV R C I J U BV R C I J U BV R C I J U BV R C I C V .The magnitudes of the SN were derived by an aperture photometry or a PSF- IRAF is distributed by the National Optical Astronomy Observatory, which is operated byAURA under cooperative agreement with the National Science Foundation. D.Yu. Tsvetkov et al. fitting relatively to a sequence of local standard stars. The CCD image of SN2011fe and local standard stars is presented in Fig. 1.
Figure 1.
The image of SN2011fe and local standard stars, obtained by the T50telescope in the R band. The
BVRI magnitudes of stars No.2-5 were taken from Henden et al. (2012).Star No.1 (HD 122601) was calibrated on 5 photometric nights using the tele-scopes C60 and M70. The resulting magnitudes are U = 9 . ± . B =9 . ± . V = 9 . ± . R = 8 . ± .
01; and I = 8 . ± .
02. The U -band magnitudes of the stars No 2, 3 and 4, measured relatively to the starNo.1, are 13.44 ± ± ± et al. (2011),Tsvetkov et al. (2008), and Tsvetkov et al. (2006). The type of R - and I -filtersis indicated in Table 1. We transformed the photometry in the R, I -bands toCousins system, so R and I are equivalent to R C , I C . The reported errorswere computed by adding in quadratures the fitting errors returned by IRAFtasks and the uncertainties of local standards calibration. The brightness ofthe SN near the maximum presented a significant difficulty for photometry, asno sufficiently bright comparison stars could be found close to the object. Theimages at the telescopes with large FoV (T50, T15) were obtained with the SN ptical observations of SN 2011fe Table 2.
UBV RI magnitudes of SN2011fe from the 50-cm reflector at Star´a Lesn´a. JD − U σ U B σ B V σ V R σ R I σ I D.Yu. Tsvetkov et al.
Table 3.
Photometry of SN2011fe from the 60-cm reflector at Crimea. JD − U σ U B σ B V σ V R σ R I σ I B -maximum, we applied image subtraction using SDSS images of the fieldaround the SN position. ptical observations of SN 2011fe Table 4.
Photometry of SN2011fe at 6 telescopes. JD − U σ U B σ B V σ V R σ R I σ I Tel.24500005808.30 10.50 0.01 10.38 0.02 10.42 0.02 T155817.25 9.80 0.04 10.05 0.01 10.04 0.01 10.04 0.01 S1005818.24 9.92 0.04 10.09 0.01 10.05 0.01 S1005819.24 9.92 0.04 10.15 0.01 10.07 0.01 10.06 0.01 S1005820.24 10.10 0.04 10.20 0.01 10.10 0.01 S1005821.23 10.15 0.04 10.24 0.01 10.12 0.01 S1005822.20 10.31 0.04 10.32 0.01 10.18 0.01 10.23 0.01 S1005823.25 10.33 0.04 10.40 0.01 10.20 0.01 10.30 0.01 S1005825.22 10.56 0.04 10.55 0.01 10.32 0.01 10.43 0.01 S1005825.22 10.42 0.05 10.65 0.01 10.30 0.03 10.44 0.03 10.89 0.01 N1005830.22 11.27 0.04 11.11 0.01 10.63 0.01 10.73 0.01 S1005831.22 11.39 0.08 11.22 0.01 10.72 0.01 10.75 0.01 S1005832.21 11.70 0.05 11.36 0.01 10.76 0.02 10.75 0.02 S1005835.22 11.61 0.03 10.86 0.02 10.75 0.04 10.77 0.03 T155852.25 11.91 0.02 11.59 0.02 11.27 0.02 T155852.26 13.20 0.08 13.07 0.01 11.90 0.02 11.63 0.02 11.18 0.03 T605853.22 13.06 0.05 T605853.22 11.94 0.02 11.66 0.02 11.33 0.02 T155856.23 12.06 0.02 11.79 0.03 11.51 0.03 T155856.23 13.16 0.02 T605919.61 13.64 0.04 N6005953.49 14.61 0.03 14.48 0.02 14.65 0.02 14.54 0.03 M705954.69 14.63 0.05 14.59 0.03 14.81 0.02 14.63 0.04 T605955.60 15.71 0.08 14.58 0.02 14.58 0.02 14.80 0.02 14.56 0.03 T605987.61 15.17 0.04 15.19 0.02 15.61 0.03 15.59 0.04 T156014.35 15.50 0.03 15.46 0.03 15.97 0.04 15.60 0.05 M706022.45 17.17 0.11 15.65 0.02 15.77 0.03 16.21 0.02 15.73 0.03 S1006025.40 15.69 0.03 15.84 0.06 16.31 0.06 S1006194.23 18.16 0.05 18.39 0.04 18.86 0.05 S1006196.20 18.45 0.06 18.81 0.09 S1006199.20 18.30 0.08 18.46 0.07 18.88 0.08 S1006387.48 21.20 0.14 S1006441.31 21.23 0.07 22.00 0.12 S1006442.34 22.07 0.11 S1006446.28 21.15 0.17 S1006450.36 21.36 0.08 S10000
D.Yu. Tsvetkov et al.
The spectroscopic observations were carried out at the 6-m BTA telescopeof SAO RAS (N600) on UT 2011 December 24.13. The focal reducer SCORPIOwith the grism VPHG1200G provided the wavelength range of 4044–5858 ˚Awith a dispersion of 0.88 ˚Apixel − . The spectra were bias and flat-field corrected,extracted and wavelength calibrated in ESO/MIDAS. The spectrophotometricstandard AGK+81 ◦
266 was used for flux calibrated spectra, but the night wasnot photometric and the absolute flux values may have significant errors.
3. Light and colour curves
The light curves of SN 2011fe are presented in Fig. 2. The results for all thetelescopes are in a fairly good agreement, the largest differences are found inthe U -band. The shape of the light curves is typical for SNe Ia.We fitted the light curves with cubic splines and determined the dates andmagnitudes of maximum light in different bands and the decline rate parameters∆ m . These are reported in Table 5. The errors of magnitudes at maximum and∆ m are about 0.02–0.05 mag, the errors of their times are 0.1–0.2 days. Theresults are consistent with the data reported by other authors (V12, RS12, M13).At late phases we used linear fits for the light curves. The resulting parametersare listed in Table 6. The rates of decline in the interval JD 2456000–6250 (whichcorresponds to phases 180–430 days after the B -maximum) in the BVR- bandsare significantly greater than the mean values for SNe Ia (Lair et al. , 2006). Thecomparison with the data for SN 2003du, which has similar ∆ m (Stanishev etal. , 2007), reveals that the rate of decline for SN 2011fe is larger in the B - and V -band and lower in the R -band. After JD 2456250 (phase 430 days) the declinein the VR - bands slows down. Similar behaviour of the V -band light curve canbe noticed for SN 2000E (Lair et al. , 2006) and SN 1992A (Cappellaro et al. ,1997). Table 5.
Dates and magnitudes of maximum light and the decline rate parameters indifferent passbands.
Band JD − m Primary maximum U B V R I I ptical observations of SN 2011fe Figure 2.
The light curves of SN 2011fe in the
UBVRI bands. Circles show the datafrom T50, squares – from C60, triangles – from other telescopes. For clarity of presen-tation, the data in BR bands are plotted with open symbols and the curves are shiftedin magnitude. The shifts for every band are reported. The error bars are plotted onlywhen they exceed the size of a symbol. Dashed lines present the linear fits to the latephases. Fig. 3 presents the comparison of photometry by different authors near themaximum brightness. The superposed light curves are in a good agreement.We may only note some outlying points by RS12 in the R -band and for ourdata in the I -band. We computed mean differences between our data and otherfour main sets (RS12, M13, V12, P13) in different bands. We found the bestconsistency with the RS12 and M13 data, where the mean difference does notexceed 0.04 mag. The agreement with the V12 and P13 data is worse. Themaximum mean difference is 0.13 mag.As seen from colour curves, presented in Fig. 4, the data from different tele-02 D.Yu. Tsvetkov et al.
Table 6.
Rates of brightness decline (in mag/100 d ) at different late stages of SN 2011feevolution. Band JD 2455900-6000 JD 2456000-6250 JD 2456250-6450 U ± B ± ± V ± ± ± R ± ± ± I ± Figure 3.
The photometric data for SN 2011fe from different authors. ptical observations of SN 2011fe
Figure 4.
The colour curves of SN 2011fe. The meaning of the symbols is the same asin Fig. 2. The colour curves of SN 2003du (dashed line) and SN 2005cf (solid line) areplotted for comparison. The curves for SN 2005cf were corrected for E ( B − V ) = 0 . B − V diagram is the Lira-Phillips relation. scopes are in a fairly good agreement. Some inconsistencies and large errorsare evident for the U − B colour and for the late-time R − I data. The colourevolution is typical for SN Ia, this is confirmed by comparison with the colourcurves for ”normal”, unreddened SNe Ia with nearly the same value of ∆ m :SN 2003du (Stanishev et al. , 2007) and SN 2005cf (Pastorello et al. , 2007). The B − V colour curve is also compared with the ”Lira-Phillips relation” (Phillips et al. , 1999), showing the time dependence of B − V in the phase interval 30-90 days for most of SNe Ia that suffered no extinction. It is obvions, that theinterstellar extinction towards SN 2011fe is very low.The ”quasi-bolometric” light curve for SN 2011fe, constructed by integratingthe flux from U - to I -bands, assuming distance modulus µ = 29 .
04 (Shappee04
D.Yu. Tsvetkov et al.
Figure 5.
The ”quasi-bolometric” light curve of SN 2011fe, compared to the lightcurves of SNe 2003du and 2005c. and Stanek, 2011) and extinction E ( B − V ) = 0 .
009 (Schlegel et al. , 1998)is shown in Fig. 5. On the dates when observations in some bands were miss-ing, we interpolated or extrapolated the colour curves to estimate the colourof SN and then calculated the missing magnitudes. We compare SN 2011fe toSNe 2003du and 2005cf, for which the ”quasi-bolometric” light curves were con-structed analogously. The adopted distance modulus and extinction for theseobjects are: µ = 32 . E ( B − V ) = 0 .
01 for SN 2003du (Tsvetkov et al. , 2011)and µ = 32 . E ( B − V ) = 0 .
097 for SN 2005cf (Pastorello et al. , 2007). The”quasi-bolometric” light curves for SN 2011fe and 2003du are nearly identical,while SN 2005cf is slightly brighter. The rate of decline for bolometric lumi-nosity is 1.72 ± d in the interval JD 2455900-2456100, 1.55 ± ± ptical observations of SN 2011fe . × ergs.
4. Spectrum
The spectrum of SN 2011fe obtained by N600 telescope on December 24.13 UT(JD 2455919.63, 105 days after the B -band maximum) is shown in Fig. 6. Thespectrum of SN 2003du obtained 109 days after its maximum by Stanishev etal. (2007) is displayed for comparison. The observed wavelengths are plotted forthe spectrum of SN 2011fe, while the spectrum of SN 2003du was deredshiftedusing z = 0 . Figure 6.
Spectra of SN 2011fe and 2003du.
The two spectra are nearly identical, confirming the physical resemblance ofboth SNe. This phase in the evolution of type Ia SNe is considered as transi-tional between photospheric and nebular stages. The identification of prominentemission peaks was proposed by Bowers et al. (1997): features labeled 1,2 and 3are blends of forbidden lines of [Fe III] and [Fe II]. We measured the wavelength06
D.Yu. Tsvetkov et al. centroid of the peaks in our spectrum: 1 – 4646˚A, 2 – 4971˚A, 3 – 5309˚A. Theabsorption feature 4 is attributed to Na I by Branch et al. (2008). The wave-length of this line in our spectrum is 5697˚A which corresponds to the expansionvelocity of about 10100 km s − .
5. Conclusions
We present the light and colour curves of SN 2011fe during 652 days after itsdiscovery, as well as one spectrum taken 105 days after its B -band maximum.The photometry was carried out at five sites, with 8 telescopes, equipped withdifferent CCD cameras and filter sets. We used linear colour-terms to transformphotometry to the standard Johnson-Cousins system. It is well known that thesecolour corrections do not work well for SNe, because the SN spectral energy dis-tribution is different from that of normal stars, and the so-called ” S -correction”method is preferrable (see, e.g., Stanishev et al. , 2007). Another sources of errorswere the use of different comparison stars at different telescopes and possiblefield errors. Nevertheless, the results were found to be generally consistent whencomparing data from different telescopes from our set and comparing our datawith that of other authors.The light and colour curves for SN 2011fe show that it belongs to the ”nor-mal” subset of type Ia SNe and is almost unreddened. The decline rate parameter∆ m ( B ) = 1 .
10 is close to the mean value for SNe Ia (see, e.g., Wang et al. ,2008). The comparison of light, colour curves and spectrum show that SN 2011feis nearly identical in all observed parameters to the well-studied ”normal” SNIa2003du during the first ∼
200 days of evolution.We found out that the rate of brightness decline in the
BVR bands is higherthan average for SNe Ia in the interval of phases 180–430 days. Afterwards,the decline for V , R and ”quasi-bolometric” light curves slows down. This maybe caused by the emergence of the light echo, but some models of late-timeluminosity evolution also predict slowing–down of the decline at that phase(see, e.g., Milne et al. , 2001). Acknowledgements.
The work of DT and NP was partly supported by the RFBRgrant 13-02-92119. SSh and NK acknowledge support by the grant of the Presidentof RF No. NSh-2374.2012.2. In 2012 NK was supported by the National ScholarshipProgram (SAIA) of the Slovak Republic. IV was supported by the RFBR grant 11-02-01213a and by the National Scholarship Program (SAIA) of the Slovak Republic.This work has been supported by the Slovak Academy of Sciences VEGA Grant No.2/0002/13 and RFBR grant 11-02-00258a.We are grateful to D. Chochol for constructive suggestions, which helped to improvethe presentation. ptical observations of SN 2011fe
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