Article

The Cow: Discovery of a Luminous, Hot, and Rapidly Evolving Transient

S. PrenticeAstrophysics Research Centre, School of Mathematics and Physics, Queen's University Belfast, BT7 1NN, UKK. MaguireAstrophysics Research Centre, School of Mathematics and Physics, Queen's University Belfast, BT7 1NN, UKStephen SmarttAstrophysics Research Centre, School of Mathematics and Physics, Queen's University Belfast, BT7 1NN, UKM. MageeAstrophysics Research Centre, School of Mathematics and Physics, Queen's University Belfast, BT7 1NN, UKP. SchadyMax-Planck-Institut für Extraterrestrische Physik, Giessenbachstraße, D-85748, Garching, GermanyStuart SimAstrophysics Research Centre, School of Mathematics and Physics, Queen's University Belfast, BT7 1NN, UKT.-W. ChenMax-Planck-Institut für Extraterrestrische Physik, Giessenbachstraße, D-85748, Garching, GermanyP. ClarkAstrophysics Research Centre, School of Mathematics and Physics, Queen's University Belfast, BT7 1NN, UKCarole ColinUniversite de Pierre et Marie Curie (Paris IV), 4 Place Jussieu, F-75252, Paris Cedex 5, FranceM. FultonAstrophysics Research Centre, School of Mathematics and Physics, Queen's University Belfast, BT7 1NN, UKO. McbrienAstrophysics Research Centre, School of Mathematics and Physics, Queen's University Belfast, BT7 1NN, UKD. O’NeillAstrophysics Research Centre, School of Mathematics and Physics, Queen's University Belfast, BT7 1NN, UKK. W. SmithAstrophysics Research Centre, School of Mathematics and Physics, Queen's University Belfast, BT7 1NN, UKC. AshallDepartment of Physics, Florida State University 77 Chefitan Way, Tallahasee 32304, USAK. C. ChambersInstitute for Astronomy, University of Hawai'i, 2680 Woodlawn Drive, Honolulu, HI 96822, USAL. DenneauInstitute for Astronomy, University of Hawai'i, 2680 Woodlawn Drive, Honolulu, HI 96822, USAH. FlewellingInstitute for Astronomy, University of Hawai'i, 2680 Woodlawn Drive, Honolulu, HI 96822, USAA. N. HeinzeInstitute for Astronomy, University of Hawai'i, 2680 Woodlawn Drive, Honolulu, HI 96822, USAT. W. S. HoloienThe Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101, USAM. E. HuberInstitute for Astronomy, University of Hawai'i, 2680 Woodlawn Drive, Honolulu, HI 96822, USAC. S. KochanekDepartment of Astronomy, The Ohio State University, 140 W. 18th Avenue, Columbus, OH 43210, USAP. A. MazzaliAstrophysics Research Institute, Liverpool John Moores University, IC2, Liverpool Science Park, 146 Brownlow Hill, Liverpool, L3 5RF, UKJose L. PrietoMillennium Institute of Astrophysics, Santiago, ChileA. RestDepartment of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218, USAB. J. ShappeeInstitute for Astronomy, University of Hawai'i, 2680 Woodlawn Drive, Honolulu, HI 96822, USAB. StalderLSST, 950 N. Cherry Avenue, Tucson, AZ 95719, USAK. Z. StanekDepartment of Astronomy, The Ohio State University, 140 W. 18th Avenue, Columbus, OH 43210, USAM. StritzingerDepartment of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, DenmarkTodd A. ThompsonCenter for Cosmology and AstroParticle Physics, The Ohio State University, 191 W. Woodruff Avenue, Columbus, OH 43210, USAJ. TonryInstitute for Astronomy, University of Hawai'i, 2680 Woodlawn Drive, Honolulu, HI 96822, USA

2018en

ABI

Abstract

Abstract We present the ATLAS discovery and initial analysis of the first 18 days of the unusual transient event, ATLAS18qqn/AT2018cow. It is characterized by a high peak luminosity (∼1.7 × 10 44 erg s −1 ), rapidly evolving light curves (>5 mag rise to peak in ∼3.5 days), and hot blackbody spectra, peaking at ∼27,000 K that are relatively featureless and unchanging over the first two weeks. The bolometric light curve cannot be powered by radioactive decay under realistic assumptions. The detection of high-energy emission may suggest a central engine as the powering source. Using a magnetar model, we estimated an ejected mass of 0.1–0.4 M , which lies between that of low-energy core-collapse events and the kilonova, AT2017gfo. The spectra cooled rapidly from 27,000 to 15,000 K in just over two weeks but remained smooth and featureless. Broad and shallow emission lines appear after about 20 days, and we tentatively identify them as He i although they would be redshifted from their rest wavelengths. We rule out that there are any features in the spectra due to intermediate mass elements up to and including the Fe group. The presence of r -process elements cannot be ruled out. If these lines are due to He, then we suggest a low-mass star with residual He as a potential progenitor. Alternatively, models of magnetars formed in neutron star mergers, or accretion onto a central compact object, give plausible matches to the data.

Identifiers

DOI: 10.3847/2041-8213/aadd90

Citations and references

Cited by 20 references

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