SN 2002cx
- REDIRECT Template:Infobox astronomical event
SN 2002cx is a peculiar Type Ia supernova.[1][2][3] It was discovered in May 2002 by a team of researchers from LBL.[4] It behaved differently from normal Type Ia supernovae, and differently from several other previously observed peculiar Type Ia supernovae including SN 1991T and SN 1991bg.[5][6]
SN 2002cx is now classified as Type Iax supernova, which are subluminal and do not result in complete destruction of the progenitor white dwarf.[7]
Discovery
SN 2002cx was discovered on 2002 May 12.21 UT by W. M. Wood-Vasey, G. Aldering, and P. Nugent of LBL with the Oschin 1.2-m telescope at Palomar.[8][4] On 2002 May 17.2 a spectrum taken by T. Matheson, S. Jha, P. Challis, and R. Kirshner of the CfA with the 1.5-m telescope at FLWO suggested it was a peculiar SN 1991T like Type Ia.[8][9] SN 2002cx had photometric follow up taken at Lick using KAIT and the Nickel telescope, and further spectra were taken at FLWO and Keck.[8]
Features
Light curve
SN 2002cx hit maximum light in the B-band at 2452415.2 JD (2002 May 20.7) at 17.68, and in the V-band on 2452417.5 JD (2002 May 23) at 17.57.[10] The B-band light curve of SN 2002cx before 15 days after maximum evolves in a similar manner to SN 1999ac, brightening faster than SN 1991T but slower than SN 1994D or SN 2000cx.[6] SN 2002cx declines in brightness faster than SN 1991T and SN 2000cx in the B-band.[6] In the V-band SN 2002cx is similar to SN 1999ac until 30 days after max.[6] Again SN 2002cx declines faster in the V-band than SN 1991T, but slower than is typical for a Type Ia.[6]
SN 2002cx is peculiar in the R-band, as it brightens very fast in a manner wholly different from SN 1999ac.[11] It has no secondary maximum in R-band as expected if it were similar to SN 1991T, but instead has a plateau after max.[11] The R-band also declines more slowly than normal.[11] The I-band behaves similarly to the R-band, with a quick brightening, a plateau and slow decline.[11] While a plateau in the I-band is expected for sub-luminous supernovae, the following slow decline is not.[11]
Spectra
The first spectrum of SN 2002cx was obtained with FLWO on 2002 May 17, 4 days before B-band max.[12] At this point SN 2002cx is similar to SN 1997br as both have a blue continuum, with absorption lines from Fe III λ4404 and Fe III λ5129.[12] Si II λ6355 though is not apparent in SN 2002cx at this point, and it has very weak Ca II H & K lines suggesting that SN 2002cx is similar to SN 1991T which also lacked such lines.[12] This spectrum for SN 2002cx has a low expansion velocity measuring only ~6400 km s−1.[12] This marked one way in which it was different from SN 1997br, as SN 1997br's expansion velocity was ~10,400 km s−1 at the same point relative to its own B-band maximum.[12] At the time of measurement SN 2002cx's expansion velocity was the lowest measured for an early time Type Ia,[12] Another spectrum taken on 2002 May 20, 1 day before B-band maximum light, showed little evolution from the one taken on 2002 May 17.[13]
Four later spectra were taken on June 2, June 6, June 12, and June 16 at FLWO.[14] The spectrum of SN 2002cx has evolved by this point to have a redder continuum.[14] It has also lost the Fe III absorption lines and its Fe II lines have gained prominence at λ4555 and λ5129.[14] The Ca II H & K lines continue to remain weak, a further departure from SN 1997br.[14] Unlike another type of sub-luminous Type Ia, SN 1991bg, SN 2002cx does not show Ti II lines around 4100–4400 Å.[14]
Spectra were taken at Keck corresponding to 20, 25, and 26 days after maximum light in the B-band.[15] So little evolution was observed between these spectra that they were all combined in order to increase the signal-to-noise ratio and study less pronounced features.[15] Fe II still dominates the spectrum.[15] The Ca II infrared triplet is weak in SN 2002cx as compared to other Type Ia supernovae, as expected since the Ca II H & K line is also weak in SN 2002cx.[15] Unlike other Type Ia supernova, SN 2002cx has double-peaked emission lines which may be due to jet-like emissions or rotating ejecta, or may simply only be seen in SN 2002cx because its low expansion velocity does not wash them out.[15] The emission or ejecta hypothesis is considered less likely because if it were the case all the peaks should share equal separation, which they do not.[15][16] SN 2002cx has absorption and emission lines between 6400 Å and 7000 Å that are unique among previously discovered Type Ia supernovae.[16]
A final spectrum of SN 2002cx was taken on July 16, 56 days after B-band maximum.[17] SN 2002cx was by then in the nebular phase, with emission lines dominating over absorption lines.[17] The lines were far narrower than previously observed Type Ia supernovae and are less pronounced as well.[17] SN 2002cx most clearly differs from other Type Ia supernovae in the region between 6500 Å and 8500 Å where it has a primarily flat continuum and weak Ca II infrared triplet absorption.[17] Because this is the region covered by the R and I-bands, it may explain the odd color evolution of SN 2002cx in these bands.[17]
SN 2002cx did not evolve much between 4 days and 1 day before max, nor did it evolve much from 12 days after max to 27 days after max,[14] However, it underwent dramatic evolution during the two weeks after maximum light in the B-band.[14]
Based on the odd behavior of SN 2002cx's spectrum there are some questions as to whether it is a Type Ia supernova or not.[18] Although it does not show Si II lines near 6150 Å as is required of a Type Ia, SN 2002cx's evolution is explainable using the paradigm of other Type Ia observations and so Li et al. consider their classification as a Type Ia as secure.[18]
Color
SN 2002cx does not suffer from much host related reddening, as evidenced by its very blue spectra.[5] It is extinct in B−V color by 0.034 magnitudes from dust in Milky Way.[5]
SN 2002cx is similar to SN 1999ac in B−V at max, but also at times as late as 50 days after max which is unexpected as the two supernovae evolve differently at late times.[5] SN 2002cx has a B−V color of Script error: No such module "val". at 4 days before max, and 0.04±0.05 at the time of max in the B-band which is bluer than SN 1991bg at the same time.[5] The color of SN 2002cx is consistent with Lira-Phillips law at late times.[19]
The V−R color of SN 2002cx evolves similar to other Type Ia supernovae before 5 days after max, although it is somewhat redder.[19] After 5 days after max SN 2002cx gets progressively redder, although still slightly bluer than SN 1991bg.[5] At 25 days after max SN 2002cx continues to redden, while SN 1991bg starts to get bluer.[5]
SN 2002cx's V−I color is red for all times, only slightly bluer than SN 1991bg before 25 days after max, and redder after 25 days after max.[5]
References
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- ↑ Li et al., 2003 p. 1
- ↑ Branch et al., 2004
- ↑ Jha et al., 2006
- ↑ a b Cite error: Script error: No such module "Namespace detect".Script error: No such module "Namespace detect".
- ↑ a b c d e f g h Li et al., 2003 p. 12
- ↑ a b c d e Li et al., 2003 p. 10
- ↑ Script error: No such module "citation/CS1".
- ↑ a b c Cite error: Script error: No such module "Namespace detect".Script error: No such module "Namespace detect".
- ↑ Matheson et al., 2002
- ↑ Li et al., 2003 p. 9
- ↑ a b c d e Li et al., 2003 p. 11
- ↑ a b c d e f Li et al., 2003 p. 15
- ↑ Li et al., 2003 p. 16
- ↑ a b c d e f g Li et al., 2003 p. 17
- ↑ a b c d e f Li et al., 2003 p. 18
- ↑ a b Li et al., 2003 p. 19
- ↑ a b c d e Li et al., 2003 p. 20
- ↑ a b Li et al., 2003 p. 24
- ↑ a b Li et al., 2003 p. 13
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Bibliography
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External links
- Light curves and spectra Script error: No such module "webarchive". on the Open Supernova Catalog Script error: No such module "webarchive".