Online material

Appendix A: Basic information on the sample of SN 1987-like transients

• 1.

  SN 1987A is the prototype of this family of H-rich core-collapse SNe, and -since it exploded in the nearby LMC- it is the best studied SN ever. The SN was discovered on 1987 February 24th by Shelton. Strong constraints on the time of the core-collapse came from the detection of a neutrino burst on February 23.316 UT by IMB and Kamiokande II (Bionta et al. 1987; Hirata et al. 1987). Extensive data sets at all wavelengths are provided by a large number of publications (e.g. Menzies et al. 1987; Catchpole et al. 1987, 1988, 1989; Whitelock et al. 1988, 1989; Hamuy et al. 1988; Phillips et al. 1988, 1990; Pun et al. 1995). More recent papers have unveiled the complex structure of the circumstellar environment of SN 1987A and its interaction with the SN ejecta (e.g. Borkowski et al. 1997). SN 1987A is one of the few objects for which we have robust contraints on the nature of the progenitor star. Pre-explosion images of the source at the SN position (Sk −69 202) showed it to be a blue (B3 I) supergiant (Gilmozzi et al. 1987; Sonneborn et al. 1987) whose mass is estimated to be around 20 M_⊙ (see Arnett et al. 1989, for a review). A small initial radius of the progenitor star is also used to explain the unusual, slow rise to maximum of the light curves of SN 1987A. In this paper we adopt as distance modulus of LMC and as total reddening toward SN 1987A the values of μ = 18.50 mag (Sakai et al. 2004) and E(B − V) = 0.19 mag (Arnett et al. 1989).

• 2.

  SN 1909A is a historical SN that exploded in M101. Its photometric evolution shows striking similarity with that of SN 1987A (Young & Branch 1988; Patat et al. 1994, see also Appendix B). A well-sampled light curve from photographic plates rescaled to the B-band system was published by Sandage & Tammann (1974). We assume negligible extinction toward SN 1909A and a distance modulus of μ = 29.34 mag (Rizzi et al. 2007, see Table 4 for details). Although multiband observations are missing for this event, the B-band absolute magnitude at maximum (M_B ≈ −15.9, see Table 5) suggests that SN 1909A is one of the intrinsically brightest SNe in our sample.

• 3.

  SN 1982F in NGC 4490 is a poorly followed under-luminous type II SN. Sparse data around maximum from photographic plates were published by Yamagata & Iye (1982) and Tsvetkov (1984, 1988). The light curves share remarkable similarity with SN 2000cb (see below), more than with SN 1987A. No spectrum exists for this object to our knowledge.

• 4.

  SN 1998A is a well studied 1987A-like event which exploded in a spiral arm of the SBc galaxy IC 2627. The SN was discovered on 1998 January 6 by the Automated Supernova Search Program of the Perth Astronomy Research Group (PARG, Williams et al. 1998). Optical photometry and spectroscopy were published by Woodings et al. (1998) and Pastorello et al. (2005). Adopting the HyperLeda recessional velocity corrected for local infall onto Virgo v_Vir = 1976 km s^-1, we obtain a distance of 27.4 Mpc (μ = 32.19 mag). Since there was no evidence of additional extinction in the host galaxy, we adopt the same total reddening estimate as in Pastorello et al. (2005), i.e. E(B − V) = 0.12 mag.

• 5.

  SN 1998bt was discovered in the Abell cluster 1736 by the Mount Stromlo Abell cluster supernova search team on March 10, 1998 (Germany 1998). Initially, no background galaxy was seen to be associated with the SN. However, subsequent deep imaging of the SN field revealed a very faint parent galaxy of R = 23.4 (Germany et al. 2004). Unfortunately, spectroscopic classification for this SN does not exist. However, the overall behaviour of the light curve (see Fig. B.1) is reminiscent of that of SN 1987A.

• 6.

  SN 2000cb in IC 1158 is one of the best followed 1987A-like events in our sample. Discovered on April 27.4 2000 using the 0.8-m Katzman Automatic Imaging Telescope (KAIT, Papenkova & Li 2000), it was classified as a young type II SN by Jha et al. (2000) and Aldering & Conley (2000). Optical photometric and spectroscopic observations have been presented by Hamuy (2001) and Kleiser et al. (2011). The photometric evolution of SN 2000cb is different from that of SN 1987A. The light curve in the B band shows a maximum at  ≈ 40 days past core-collapse, followed by a slow decline up to 60 days and a short pseudo-plateau. At about 90 days a steep post plateau decline to the radioactive tail is visible, as in normal type IIP SNe. The evolution in the VRI bands is somewhat different, showing broad light curve peaks at 60−80 days (depending on the band) after core-collapse (Hamuy 2001; Kleiser et al. 2011). The light curve peaks are significantly broader than those of SN 1987A. We adopted the observed parameters of SN 2000cb as presented in Hamuy (2001). The explosion epoch, the adopted distance and the total reddening are those of Hamuy (2001). Their values are listed in Tables 4 and 5.

• 7.

  OGLE-2003-NOOS-005 never had a SN designation. It was discovered by the Optical Gravitational Lensing Experiment (OGLE, Udalski 2003) collaboration at and (J2000.0). It exploded in a faint spiral galaxy labelled by the NED database as 2MASX J05553978-6855381, behind LMC, and falls in the OGLE field LMC198.6 9 (Udalski et al. 2008). The well-followed I-band light curve of OGLE-2003-NOOS-005¹² well matches that of SN 1987A. Unfortunately multiband observations for this SN do not exist. The redshift of the host galaxy was spectroscopically determined measuring the positions of a few selected spectral features of a host galaxy spectrum obtained on 2009 August 14 with NTT (equipped with EFOSC2 and grism 11; resolution = 22 Å). Despite the low signal-to-noise, we identified a few absorption features (Ca II H&K, the g-band λ4200, Mg Ib λ5173), and Hα in emission. In addition the emission line of [O II] λ3727 was marginally detected. This allowed to fix the redshift at z = 0.0302   ±   0.0008 (v_rec ≈  9151   ±   236 km s^-1), which corresponds to a distance of about 127 Mpc (μ = 35.52 mag). These values are remarkably similar to those reported by NED (v_rec ≈  9176   ±   45 km s^-1; Jones et al. 2009). and HyperLeda (v_rec ≈  9177   ±   60 km s^-1). The recessional velocity corrected for Local Group infall into the Virgo Cluster is slightly lower (v_Vir ≈  8882 km s^-1). Adopting the Hubble Constant value of H₀ = 72 km s^-1 Mpc^-1, we obtain a distance of 123.4 Mpc, i.e. distance modulus μ = 35.46 mag. We also assume in our analysis a total reddening toward the transient of E(B − V) = 0.16   ±   0.10 mag. This was determined including the contribution of the Galaxy E_MW(B − V) = 0.075 mag (Schlegel et al. 1998) and the reddening at the position of 2MASX J05553978-6855381 due to the intrinsic contribution of LMC that was computed using the maps of Zaritsky et al. (2004) (E_LMC(B − V) = 0.087 mag). The I-band light curve of this SN is shown in Appendix B.

• 8.

  SN 2004em was discovered by Armstrong (2004) on Sept. 14, 2004 when the SN was at mag = 17.5. The transient, later classified as a young type II by Filippenko et al. (2004), was hosted in an Sc galaxy (IC 1303). The object was significantly reddened by Galactic dust (E(B - V) = 0.108, fromSchlegel et al. 1998). Preliminary information on the Caltech Core-Collapse Project light curve has been provided by Gal Yam et al. (2007).

• 9.

  SN 2005ci, a LOSS discovery (Madison & Li. 2005), was classified as a type II SN by Modjaz et al. (2005) on the basis of the presence of P-Cygni Balmer lines. Its peculiar light curve was first noted by Arcavi et al. (2009), and some early-time unfiltered photometry was provided by Kleiser et al. (2011), showing a clear light curve rise by about 2.5 mag in  ~45 days. Unfortunately, with the modest amount of data available so far, we cannot estimate the main SN parameters. The host galaxy, NGC 5682, is an Sb-type; the Galaxy reddening is modest, E(B − V) = 0.033 mag (Schlegel et al. 1998), but the relatively red continuum shown by the spectrum presented by Kleiser et al. (2011, see their Fig. 12) suggests a non negligible host galaxy reddening. The narrow host galaxy Na ID feature is not clearly detected and the amount of internal reddening cannot be constrained.

• 10.

  SN 2006V was discovered in the course of the Taiwan Supernova Survey on Feb. 4, 2006 UT at a magnitude of about 18 (Chen et al. 2006). The object was classified as a type II SN after maximum by Blondin et al. (2006) and extensively followed by the Carnegie Supernova Project collaboration, who noted the slowly rising, 1987A-like light curve (Taddia et al. 2011). The galaxy hosting SN 2006V is UGC 6510, which is classified as a face-on spiral (SABc, HyperLeda source) suffering of small Galactic reddening (E(B - V) = 0.029 mag,Schlegel et al. 1998). The lack of detection of narrow Na ID absorption at the redshift of UGC 6510, suggest no additional host galaxy extinction toward SN 2006V (Taddia et al. 2011). A comparison between the multi-band light curves of SNe 2006V and 1987A can be found in Fig. 3 of Taddia et al. (2011).

• 11.

  SN 2006au was a discovery of the Tenagra Observatory Supernova Search using the 0.35-m Tenagra telescope in Oslo (on Mar. 7.20 UT). At the discovery, the object had mag 17.2 (Trondal et al. 2006). SN 2006au was later classified by the Nearby Supernova Factory as a type II SN (Blanc et al. 2006). Again, a comprehensive study is presented in Taddia et al. (2011) and comparisons with the light curves of SN 1987A are shown in their Fig. 4. The host galaxy, UGC 11057, is a late spiral (possibly an Sc-type, according to HyperLeda) with rather large Galactic reddening, i.e. E(B − V) = 0.172 mag (Schlegel et al. 1998). However, Taddia et al. (2011) found that SN 2006au suffered also of large extinction due to dust in the host galaxy, deriving a total reddening of E(B − V)_tot = 0.312 mag.

Appendix B: Light curves of 1987A-like events

	Fig. B.1 Light curves of 1987A-like events: first group of 4 events. The solid (or dashed) blue lines represent the light curves of SN 1987A, our template. The light curves of SN 1987A have been arbitrarily shifted in magnitude to match the peaks of the other transients.
Open with DEXTER

In this section, the light curves of seven 1987A-like type II SNe are compared with those of the prototype SN 1987A (solid or dashed blue lines, see Figs. B.1 and B.2). The light curves of SN 1987A are arbitrarily shifted in magnitude to match the peak magnitudes of the other objects. In the comparison, we assumed the JDs listed in Table 4 as explosion epochs. For a few individual events (e.g. SNe 1982F or 2000cb) the 1987A-likeness is more evident in the red bands than in the blue ones. As mentioned in Sect. 4, data for SN 2004em have not been published yet.

	Fig. B.2 Light curves of 1987A-like events: second group of 3 events. The solid (and dashed) blue lines represent the light curves of SN 1987A, our template. The light curves of SN 1987A have been arbitrarily shifted in magnitude to match the peaks of the other transients.
Open with DEXTER

© ESO, 2012