SN 2002cx

Key takeaways

SN 2002cx belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect SN 2002cx to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of SN 2002cx from memory before moving on to harder problems.

Reference excerpt

SN 2002cx is a peculiar Type Ia supernova. It was discovered in May 2002 by a team of researchers from LBL. 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. SN 2002cx is now classified as Type Iax supernova, which are subluminal and do not result in complete destruction of the progenitor white dwarf.

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

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. 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. SN 2002cx declines in brightness faster than SN 1991T and SN 2000cx in the B-band. In the V-band SN 2002cx is similar to SN 1999ac until 30 days after max. Again SN 2002cx declines faster in the V-band than SN 1991T, but slower than is typical for a Type Ia. SN 2002cx is peculiar in the R-band, as it brightens very fast in a manner wholly different from SN 1999ac. It has no secondary maximum in R-band as expected if it were similar to SN 1991T, but instead has a plateau after max. The R-band also declines more slowly than normal. The I-band behaves similarly to the R-band, with a quick brightening, a plateau and slow decline. While a plateau in the I-band is expected for sub-luminous supernovae, the following slow decline is not.

Spectra

The first spectrum of SN 2002cx was obtained with FLWO on 2002 May 17, 4 days before B-band max. 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. 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. This spectrum for SN 2002cx has a low expansion velocity measuring only ~6400 km s−1. 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. At the time of measurement SN 2002cx's expansion velocity was the lowest measured for an early time Type Ia, 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. Four later spectra were taken on June 2, June 6, June 12, and June 16 at FLWO. The spectrum of SN 2002cx has evolved by this point to have a redder continuum. It has also lost the Fe III absorption lines and its Fe II lines have gained prominence at λ4555 and λ5129. The Ca II H & K lines continue to remain weak, a further departure from SN 1997br. Unlike another type of sub-luminous Type Ia, SN 1991bg, SN 2002cx does not show Ti II lines around 4100–4400 Å. Spectra were taken at Keck corresponding to 20, 25, and 26 days after maximum light in the B-band. 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. Fe II still dominates the spectrum. 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. 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. 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. SN 2002cx has absorption and emission lines between 6400 Å and 7000 Å that are unique among previously discovered Type Ia supernovae. A final spectrum of SN 2002cx was taken on July 16, 56 days after B-band maximum. SN 2002cx was by then in the nebular phase, with emission lines dominating over absorption lines. The lines were far narrower than previously observed Type Ia supernovae and are less pronounced as well. 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. 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. 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, However, it underwent dramatic evolution during the two weeks after maximum light in the B-band. 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. 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.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with SN 2002cx

Start with the simplest possible case. Write down what SN 2002cx claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to SN 2002cx before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about SN 2002cx ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of SN 2002cx

In research: SN 2002cx appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses SN 2002cx in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: SN 2002cx is common in secondary-school and first-year university syllabi. It links to neighbouring topics Astronomical objects discovered in 2002, Type Ia supernovae, Virgo (constellation), so understanding it makes those chapters shorter.
In everyday life: Look for SN 2002cx outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study SN 2002cx in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what SN 2002cx means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain SN 2002cx out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is SN 2002cx in simple terms?

SN 2002cx is a peculiar Type Ia supernova. It was discovered in May 2002 by a team of researchers from LBL.

Why does SN 2002cx matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study SN 2002cx?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on SN 2002cx.