Pre-discovery and Follow-up Observations of the Nearby SN 2009nr:
Implications for Prompt Type Ia SNe

Rubab Khan, J. L. Prieto, G. Pojmanski, K. Z. Stanek, J. F. Beacom, D. M. Szczygiel, B. Pilecki, K. Mogren, J. D. Eastman, P. Martini, R. Stoll

We present photometric and spectroscopic observations of the Type Ia supernova SN 2009nr in UGC 8255 (z=0.0122). Following the discovery announcement at what turned out to be ten days after peak, we detected it at V ~15.7 mag in data collected by the All Sky Automated Survey (ASAS) North telescope 2 weeks prior to the peak, and then followed it up with telescopes ranging in aperture from 10-cm to 6.5-m. Using early photometric data available only from ASAS, we find that the SN is similar to the over-luminous Type Ia SN 1991T, with a peak at Mv=-19.6 mag, and a slow decline rate of Dm_15(B)=0.95 mag. The early post-maximum spectra closely resemble those of SN 1991T, while the late time spectra are more similar to those of normal Type Ia SNe. Interestingly, SN 2009nr has a projected distance of 13.0 kpc (~4.3 disk scale lengths) from the nucleus of the small star-forming host galaxy UGC 8255. This indicates that the progenitor of SN 2009nr is not associated with a young stellar population, calling into question the conventional association of luminous SNe Ia with the ``prompt'' component directly correlated with current star formation. The pre-discovery observation of SN 2009nr using ASAS demonstrates the science utility of high cadence all sky surveys conducted using small telescopes for the discovery of nearby (d=<50 Mpc) supernovae.

Fig. 1.— SDSS g-band image of the SN 2009nr host galaxy UGC 8255 (left) and ASAS V-band images of the same field taken prior to (center) and after (right)the explosion. Each image has the same orientation and shows the same region. The location of SN 2009nr is marked with a cross.

Fig. 2.— V- and I-band light curves of SN 2009nr. The horizontal axis is in days from the date of maximum brightness in the B band. The two solid lines are SN Ia light curve template fits to the ASAS data points only. The dotted line shows the epoch of the discovery announcement (∼10 days after Bmax). TheV-band light curve is shifted by +1 mag for clarity.

Fig. 3.— Comparison of V-band light curve of SN 2009nr with those of the overluminous Type Ia SN 1991T (Lira et al. 1998), the normal Type Ia SN 2003du (Stanishev et al. 2007), and the possibly super-Chandrasekhar mass Type Ia SN 2009dc (Silverman et al. 2010). The black solid line is the SN Ia light curve template fit to the ASAS data points only. The light curves of the comparison SNe are shifted so that their peaks approximately match that ofSN 2009nr.

Fig. 4.— Same as Figure 3, but for I band.

Fig. 5.— Color evolution of SN 2009nr (black data points) compared to those of the overluminous Type Ia SN 1991T (red; Lira et al. 1998), the normal Type Ia SN 2003du (blue; Stanishev et al. 2007), and the possibly super-Chandrasekhar Type Ia SN 2009dc (green; Silverman et al. 2010). The horizontal axis is same as in Figure 2. The continuous lines are connected colorevolution data points of the respective SNe.

Fig. 6.— Spectral evolution of SN 2009nr. Epochs are in days since the date of maximum brightness in the B band. The vertical displacements are arbitrary.The telluric lines at 6800 \C5, 7200 \C5, and 7600 \C5 are labeled.

Fig. 7.— Comparison of the earliest SN 2009nr spectrum (black continuous line) and the spectrum of SN 1991T like supernova SN 1997br (red long dashed line, dereddened by E(B − V ) = 0.35 mag; Li et al. 1999), both collected 12 days after the date of maximum brightness in the B band, with a normal SN Ia spectrum template for the same post-maximum epoch (green short-dashed line; Hsiao et al. 2007). All the spectra are corrected to the rest frame and shiftedso that their flux approximately match at 5500 \C5.

Fig. 8.— Spectral evolution of SN 2009nr as compared to spectroscopically similar SNe at the relevant phase as determined by SNID (Blondin & Tonry 2007). Important features are labeled along with the telluric lines (6800 \C5, 7200 \C5, and 7600 \C5). The data for SN 1991T, SN 1998aq, and SN 2003du are from Mazzali et al. (1995), Branch et al. (2003), and Stanishev et al. (2007), respectively. All the spectra are corrected to the rest frame using
the redshifts (zhelio) of the hosts. The SN 1991T spectra is dereddened by E(B − V ) = 0.13 mag (Li et al. 1999; Saha et al. 2001). Host extinction for SN 1998aq (Reindl et al. 2005), SN 2003du (Stanishev et al. 2007), and SN 2009nr (Section 3.1) are consistent with zero.

Fig. 9.— SDSS r-band image of the SN 2009nr host galaxy UGC 8255 (left) and the residuals after subtracting a simple GALFIT (Peng et al. 2002) profile using abulge/disk decomposition (Sersic and exponential disk profiles). The location of SN 2009nr is marked with a circle.

Fig. 10.— Radial oxygen abundance profile of the SN 2009nr host galaxy UGC 8255 along a slit going through the SN and the center of the host (based on six off-center Hii regions). The oxygen abundance is calculated using the [N ii]/ Hα ratio. The dashed line shows a linear fit to the oxygen abundance measurements and has a gradient of∼0.06 dex kpc−1. The solid linemarks the position ofthe SN.

Fig. 11.— History of Type Ia SNe discovery within d~50 Mpc over the past 20 years according to the Sternberg Astronomical Institute SN Catalogue (Bartunov et al. 2007). SN 2009nr is shown with a red starred symbol. The histograms show projections on the respective axes. The dashed line in the histogram to the right indicates the z = 0 extrapolation of the cosmic SN Ia rate density (Horiuchi & Beacom 2010) for this local volume. (The distances were obtained assuming the Hubble flow. Because of the importance of SN Ia at the closest distances, two objects apparently within 10 Mpc were examined separately and found to have distance estimates in the literature beyond 10 Mpc, and were corrected. See Horiuchi & Beacom (2010) for further discussion onnearby SN Ia rates.)