Peculiar Type Ia Supernova Research Articles

The Subluminous Type Ia Supernova 1998de in NGC 252

ABSTRACTWe present spectroscopic and extensive photometric observations of supernova (SN) 1998de in the S0 galaxy NGC 252, discovered during the course of the Lick Observatory Supernova Search. These data, which span a time period of 8 days before to 76 days after B‐band maximum, unambiguously establish SN 1998de as a peculiar and subluminous Type Ia supernova (SN Ia) with strong similarities to SN 1991bg, the prototype of these intrinsically dim SNe Ia. We find that SN 1998de, which has Δm15(B) = 1.95 ± 0.09 mag, rises and declines much faster than normal SNe Ia and does not exhibit the usual plateau in the R band. In the I band it shows a short plateau phase or possibly a secondary maximum, soon after the first maximum. We find that subluminous SNe Ia with the same value of Δm15(B) can have slightly different light curves at longer wavelengths. The notable spectroscopic similarities between SN 1998de and SN 1991bg are the wide Ti ii trough at 4100–4500 Å, the strong Ca ii features, and the early onset of the nebular phase. We observe that spectroscopic deviations of SN 1998de from SN 1991bg increase toward redder wavelengths. These deviations include the absence of the conspicuous Na i D absorption found in SN 1991bg at 5700 Å and the evolution of a region (6800–7600 Å) from featureless to feature‐rich. Several lines of evidence suggest that SN 1998de was a slightly more powerful explosion than SN 1991bg. We discuss the implications of our observations for progenitor models and the explosion mechanism of peculiar, subluminous SNe Ia. The extensive photometric data make SN 1998de a better template than SN 1991bg for calibrating the low‐luminosity end of the luminosity versus decline rate relationship.

Spectroscopically Peculiar Type Ia Supernovae and Implications for Progenitors

ABSTRACTIn a recent paper Li et al. reported that 36% of 45 Type Ia supernovae (SNe Ia) discovered since 1997 in two volume‐limited supernova searches were spectroscopically peculiar, and they suggested that because this peculiarity rate is higher than that reported for an earlier observational sample by Branch et al., it is now more likely that SNe Ia are produced by more than one kind of progenitor. In this paper I discuss and clarify the differences between the results of Li et al. and Branch et al., and I suggest that multiple‐progenitor systems are now less likely than they were before.

Supernova 1991T and the Value of the Hubble Constant

Based upon multi-epoch Hubble Space Telescope observations, we present the discovery of sixteen high-quality Cepheid candidates in NGC 4527. Corrected for metallicity effects in the Cepheid period-luminosity relation, we derive a distance, including both random (r) and systematic (s) uncertainties, of 13.0+/-0.5(r)+/-1.2(s) Mpc. Our result is then used to provide a calibration of the peak B-, V-, and I-band luminosities of the peculiar Type Ia supernova SN 1991T, a resident of NGC 4527. Despite its documented spectroscopic peculiarities, after correction for the decline rate-luminosity correlation the corrected peak luminosity is indistinguishable from those of so-called ``normal'' Type Ia SNe. With now nine local calibrators at our disposal, we determine a robust value for the Hubble Constant of H_0=73+/-2(r)+/-7(s) km/s/Mpc.

The Type I[CLC]a[/CLC] Supernova 1997[CLC]br[/CLC] in ESO 576-G40

The peculiar type Ia supernova SN 1997br in ESO 576-G40 was extensively observed at Beijing Astronomical Observatory and Lick Observatory. In this paper, we present and discuss the BVRI photometry and the spectra collected over 3 months, beginning 9 days before maximum brightness. The light curves of SN 1997br are similar to those of SN 1991T, with slow decline rates after the B maximum. Well-sampled data before the B maximum show unambiguously that SN 1997br rises more slowly and has a wider peak than normal type Ia supernovae. The optical color evolution of SN 1997br is also similar to that of SN 1991T. We estimate the extinction of SN 1997br to be E(B-V) = 0.35 ± 0.10 mag by comparing its BVRI light curves with those of SN 1991T and by measuring the equivalent width of interstellar Na I D absorption lines. We have conducted a thorough comparison of the spectroscopic evolution of SN 1997br, SN 1991T, and SN 1994D. Although SN 1997br is generally very similar to SN 1991T, it shows some interesting differences at various epochs. Spectra of SN 1997br seem to indicate an earlier transition to the dominant phase of Fe-peak elements after the B maximum. Si II lines in SN 1997br show a very short duration after the B maximum. We discuss the implications of our observations of SN 1997br for models of type Ia supernovae. Specifically, we suggest that some SNe Ia may result from decelerated detonations of white dwarfs.

The Canarias Type I[CLC]a[/CLC] Supernova Archive. II. A Standard Spectral Evolution Sequence

In a previous paper, we presented an atlas containing 59 low-resolution spectra that correspond to 27 Type Ia supernovae, covering about 1 year of Type Ia supernova evolution. This paper is a continuation, with the aim of performing a standard spectral evolution for normal Type Ia supernovae from the homogeneous set of data compiled in the Canarias Type Ia Supernova Archive. This standard sequence could be useful in yielding clues leading to the detection of the peculiar Type Ia supernova events. Furthermore, it could help in assigning a more accurate phase to a given Type Ia supernova from its spectrum when no photometric evolution of the supernova is available.

The properties of the peculiar type Ia supernova 1991bg -- II. The amount of 56Ni and the total ejecta mass determined from spectrum synthesis and energetics considerations

The properties of the peculiar type Ia supernova 1991bg -- II. The amount of 56Ni and the total ejecta mass determined from spectrum synthesis and energetics considerations

The properties of the peculiar type Ia supernova 1991bg -- I. Analysis and discussion of two years of observations

Observations of the peculiar type Ia SN~1991bg in NGC~4374 collected at ESO--La Silla and Asiago are presented and discussed. The broad--band light curves in the early months have a narrower peak and a luminosity decline faster than other SNIa while the R and I light curves do not show the secondary peak. The SN is intrinsically very red (\bv$_{max}=0.74$) and faint ($B_{max}=-16.54$). The $uvoir$ bolometric light curve of SN~1991bg is fainter with a steeper decline than that of the normal SNIa (e.g. 1992A). This object enhances the correlation which exists between the peak luminosity of SNIa, the decline rate and the kinetic energy. Although a number of spectral peculiarities are present the spectral evolution retains a general resemblance to that of other SNIa until the latest available observation (day 203). This work suggests that the explosion energy was probably a factor 3 to 5 lower than in normal SNIa.

Radio Observations of the Type Ia Supernova 1986G as a Test of a Symbiotic-Star Progenitor

Searches for prompt radio emission from Type Ia supernovae (SNe Ia) have been proposed as a test of the symbiotic-star progenitor scenario, in which a white dwarf accretes mass from the wind of a companion red giant (Boffi & Branch 1995a). We report the results of a VLA search for radio emission from the Type Ia supernova 1986G in NGC 5128 (Centaurus A), 1 week before its optical maximum. These observations allow us to establish earlier and lower limits on SN Ia radio emission than previously available. Our 3 σ upper limits of 1.0 mJy at 6 cm and 0.7 mJy at 2 cm indicate that the progenitor of SN 1986G probably was not a symbiotic star. SN 1986G was a peculiar Type Ia supernova, and further searches for prompt radio emission from other SNe Ia are needed to more thoroughly test the symbiotic-star progenitor scenario.

SN 1991F in NGC 3458: A peculiar type IA supernova?

view Abstract Citations (9) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS SN 1991F in NGC 3458: A Peculiar Type 1a Supernova Gomez, G. ; Lopez, R. Abstract Supernova 1991F appeared in lenticular galaxy NGC 3458 (UGC 6037). On discovery, it was classified as type I, although no subtype (i.e., Ia or Ib/c) was assigned to it. In this paper, we present several low resolution spectra of this supernova. One of them was recorded ten days after the discovery. No others show the supernova spectral evolution over three months. Our SN 1991F spectra show very close similarities with the spectra of the well studied peculiar supernova 1991bg, which correspond to phases 80-200 days after maximum brightness. We propose that SN 1991F was a peculiar type Ia supernova with similar characteristics to those of the subluminous SN 1991bg. Publication: The Astronomical Journal Pub Date: February 1995 DOI: 10.1086/117316 Bibcode: 1995AJ....109..737G Keywords: Brightness Distribution; Emission Spectra; Evolution (Development); Lenticular Bodies; Supernovae; Astronomical Spectroscopy; Elliptical Galaxies; Magnitude; Astronomy; SUPERNOVAE: INDIVIDUAL: SN 1991F full text sources ADS | data products SIMBAD (10) NED (2)

On the relative frequencies of spectroscopically normal and peculiar type IA supernovae

After defining what we mean by spectroscopically 'normal' and 'peculiar' Type Ia supernove, we report the results of an attempt to subclassify 84 SNe Ia either as normal or as like one of the recent, peculiar SNe Ia: 1991T, 1991bg, or 1986G. Only SNe 1957A and 1960H are found to have been certifiably abnormal, with SN 1957A; appearing to have been like SN 1991bg, and SN 1960H having been like SN 1991bg or SN 1988G; SNe 1971I and 1980I are under suspicion of having been like SN 1986G, and SN 1988G of having been like SN 1991T. Of the SNe Ia we have been able to classify either as normal or as peculiar, 89% (or 83%, counting those under suspicion as peculiar) are normal. Our main conclusion is that the observational sample of SNe Ia is strongly peaked at 'spectroscopically normal.' We further conclude that when arranged in the photometric sequence of Phillips (1993) SNe Ia also form a spectroscopic sequence, and that peculiar SNe Ia are over-represented in the Phillips sample.

The subluminous, spectroscopically peculiar type IA supernova 1991bg in the elliptical galaxy NGC 4374

We present photometric and spectroscopic observations of SN 1991bg, a very peculiar Type Ia supernova located in the outskirts of the E1 galaxy NGC 4374 (M84) in the Virgo cluster. At maximum brightness SN 1991bg was 1.6 mag subluminous in V and 2.5 mag subluminous in B, compared with normal SNe Ia. The colors were unusually red, but the object was not significantly reddened by dust. The decline from maximum was certainly quite steep; we measure an initial linear V fading of 0.10 mag d^-1^ rather than the typical value of 0.06 mag d^-1^ for SNe Ia, and a late- time decline of 0.034 mag d^-1^ rather than 0.026 mag d^-1^. Furthermore, the knee in the Flight curve of SN 1991bg occurs only ~17 d past B maximum, in contrast to the usual value of 30-40 d. Unlike normal SNe Ia, the I light curve does not exhibit a secondary maximum, and the R light curve shows no sign of a plateau. Despite having prominent Si II absorption near 6150 A, characteristic of SNe Ia, SN 1991bg was spectroscopically peculiar at maximum brightness; e.g. a deep trough was present around 4200 A. Spectral synthesis suggests that much of this feature was produced by Ti II. Indeed, Ti II was present elsewhere in the spectrum whereas Fe II was weak or absent. Lines due to other intermediate-mass elements were also strong near maximum brightness, but the expansion velocity (~10 000 km s^-1^) was slightly lower than average (11 000-13 000 km s^-1^) for SNe Ia. A spectrum obtained 3 weeks past maximum has a rather narrow absorption line attributed to Na I D; the strength of this feature grew with time. In certain other respects the spectrum 3 weeks past maximum more closely resembles spectra of SNe Ib/Ic than of SNe Ia. We identify emission lines of [Ca II] λλ7291, 7324, O I λ7773, the Ca II infrared triplet, and (tentatively) [O I] λ5577, all superimposed on a complex blend of P Cygni scattering lines; apparently the nebular phase began very early in SN 1991bg. Three months past maximum the [Ca II] blend started to dominate the spectrum. The properties of SN 1991bg suggest that this object was produced by the slow deflagration of a white dwarf. The observed expansion velocity, however, is too large unless a sub-Chandrasekhar mass of material was ejected. An unusually low mass for the ejecta expanding at a nearly normal velocity, is consistent with the early transition to the nebular phase as well as with the rapid decline and the early knee in the V light curve. Thus, SN 1991bg may have resulted from the deflagration of only the outer layer of material on top of a C-O core, thereby leaving a compact remnant; alternatively, perhaps the complete explosion of a low-mass (~1.0 M_sun_) white dwarf was responsible. We show that some properties of the peculiar SN 1986G in Cen A were similar to those of SN 1991bg, and it may have been intrinsically dim by several magnitudes. Moreover, SN 1971I in NGC 5055 is known to have resembled SN 1986G; thus, SN 1991bg was probably a close cousin of these two objects. SN 1991bg clearly demonstrates that at least some SNe 1a are mavericks, both photometrically and spectroscopically. These objects must be carefully eliminated from samples of SNe 1a used in determinations of cosmological parameters.