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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 than normal type Ia supernovae, and different from several other previously observed peculiar type Ia supernovae including SN 1991T and SN 1991bg.[5][6]

Discovery

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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.[7][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.[7][8] SN 2002cx had photometric follow up taken at Lick using KAIT and the Nickel telescope, and further spectra were taken at FLWO and Keck.[7]

Features

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Light curve

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The light curve of SN 2002cx.

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.[9] The B-band light curve of SN 2002cx before 15 days after max 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.[10] It has not secondary maximum in R-band as expected if it were similar to SN 1991T, but instead has a plateau after max.[10] The R-band also declines more slowly than normal.[10] The I-band behaves similarly to the R-band, with a quick brightening, a plateau and slow decline.[10] While a plateau in I-band is expect for sub-luminous supernovae, the following slow decline is not.[10]

Spectra

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Four spectra of SN 2002cx.

The first spectrum of SN 2002cx was obtained with FLWO on 2002 May 17, 4 days before B-band max.[11] 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.[11] 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.[11] This spectrum for SN 2002cx has a low expansion velocity measuring only ~6400 km s-1.[11] 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.[11] At the time of measurement SN 2002cx's expansion velocity was the lowest measured for an early time type Ia,[11] 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.[12]

Four later spectra were taken on June 2, June 6, June 12, and June 16 at FLWO.[13] The spectrum of SN 2002cx has evolved by this point to have a redder continuum.[13] It has also lost the Fe III absorption lines and its Fe II lines have gained prominence at λ4555 and λ5129.[13] The Ca II H & K lines continue to remain weak, a further departure from SN 1997br.[13] Unlike another type of sub-luminous type Ia, SN 1991bg, SN 2002cx does not show Ti II lines around 4100-4400 Å.[13]

Spectra were taken at Keck corresponding to 20, 25, and 26 days after maximum light in the B-band.[14] 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.[14] Fe II still dominates the spectrum.[14] 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.[14] 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.[14] 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.[14][15] SN 2002cx has absorption and emission lines between 6400 Å and 7000 Å that are unique among previously discovered type Ia supernovae.[15]

A final spectrum of SN 2002cx was taken on July 16, 56 days after B-band maximum.[16] SN 2002cx was by then in the nebular phase, with emission lines dominating over absorption lines.[16] The lines were far narrower than previously observed type Ia supernovae and are less pronounced as well.[16] 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.[16] 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.[16]

SN 2002cx did not evolve much between 4 days and 1 day before max, not did it evolve much from 12 days after max to 27 days after max,[13] However, it underwent dramatic evolution during the two weeks after maximum light in the B-band.[13]

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.[17] Although it does not show Si II lines neat 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.[17]

Color

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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 -0.04±0.04 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.[18]

The V-R color of SN 2002cx evolves similar to other type Ia supernovae before 5 days after max, although it is somewhat redder.[18] 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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  1. ^ Li et al., 2003 p. 1
  2. ^ Branch et al., 2004
  3. ^ Jha et al., 2006
  4. ^ a b Cite error: The named reference Wood-Vasey02 was invoked but never defined (see the help page).
  5. ^ a b c d e f g h Li et al., 2003 p. 12
  6. ^ a b c d e Li et al., 2003 p. 10
  7. ^ a b c Cite error: The named reference Li03p5 was invoked but never defined (see the help page).
  8. ^ Matheson et al., 2002
  9. ^ Li et al., 2003 p. 9
  10. ^ a b c d e Li et al., 2003 p. 11
  11. ^ a b c d e f Li et al., 2003 p. 15
  12. ^ Li et al., 2003 p. 16
  13. ^ a b c d e f g Li et al., 2003 p. 17
  14. ^ a b c d e f Li et al., 2003 p. 18
  15. ^ a b Li et al., 2003 p. 19
  16. ^ a b c d e Li et al., 2003 p. 20
  17. ^ a b Li et al., 2003 p. 24
  18. ^ a b Li et al., 2003 p. 13

Bibliography

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  • Branch, David; Baron, E.; Thomas, R. C.; Kasen, D.; Li, Weidong; Filippenko, Alexei V. (10/2004). "Reading the Spectra of the Most Peculiar Type Ia Supernova 2002cx". Publications of the Astronomical Society of the Pacific. 116 (824). Chicago, Illinois: University of Chicago Press: 903–908. arXiv:astro-ph/0408130. doi:10.1086/425081. {{cite journal}}: Check date values in: |date= (help)
  • Jha, Saurabh; Branch, David; Chornock, Ryan; Foley, Ryan J.; Li, Weidong; Swift, Brandon J.; Casebeer, Darrin; Filippenko, Alexei V. (07/2006). "Late-Time Spectroscopy of SN 2002cx: The Prototype of a New Subclass of Type Ia Supernovae". Astronomical Journal. 132 (1). Chicago, Illinois: American Astronomical Society: 189–196. arXiv:astro-ph/0602250. doi:10.1086/504599. {{cite journal}}: Check date values in: |date= (help)
  • Li, Weidong; Filippenko, Alexei V.; Chornock, Ryan; Berger, Edo; Berlind, Perry; Calkins, Michael L.; Challis, Peter; Fassnacht, Chris; Jha, Saurabh; Kirshner, Robert P.; Matheson, Thomas; Sargent, Wallace L. W.; Simcoe, Robert A.; Smith, Graeme H.; Squires, Gordon (04/2003). "SN 2002cx: The Most Peculiar Known Type Ia Supernova". Publications of the Astronomical Society of the Pacific. 115 (806). Chicago, Illinois: University of Chicago Press: 453–473. arXiv:astro-ph/0301428. doi:10.1086/374200. {{cite journal}}: Check date values in: |date= (help)
  • Matheson, T. (2002 May 17). "Circular No. 7903". Central Bureau for Astronomical Telegrams. Smithsonian Astrophysical Observatory, Cambridge, Massachusetts: International Astronomical Union. Retrieved 2009-06-20. {{cite journal}}: Check date values in: |date= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
  • Wood-Vasey, W. M. (2002 May 17). "Circular No. 7902". Central Bureau for Astronomical Telegrams. Smithsonian Astrophysical Observatory, Cambridge, Massachusetts: International Astronomical Union. Retrieved 2009-06-19. {{cite journal}}: Check date values in: |date= (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
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