Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Fast, Luminous Ultraviolet Transient AT2018cow: Extreme Supernova,
  or Disruption of a Star by an Intermediate-Mass Black Hole?   Wide-field optical surveys have begun to uncover large samples of fast
(t_rise < 5d), luminous (M_peak < -18), blue transients. While commonly
attributed to the breakout of a supernova shock into a dense wind, the great
distances to the transients of this class found so far have hampered detailed
investigation of their properties. We present photometry and spectroscopy from
a comprehensive worldwide campaign to observe AT2018cow (ATLAS18qqn), the first
fast-luminous optical transient to be found in real time at low redshift. Our
first spectra (<2 days after discovery) are entirely featureless. A very broad
absorption feature suggestive of near-relativistic velocities develops between
3-8 days, then disappears. Broad emission features of H and He develop after
>10 days. The spectrum remains extremely hot throughout its evolution, and the
photospheric radius contracts with time (receding below R<10^14 cm after 1
month). This behaviour does not match that of any known supernova, although a
relativistic jet within a fallback supernova could explain some of the observed
features. Alternatively, the transient could originate from the disruption of a
star by an intermediate-mass black hole, although this would require
long-lasting emission of highly super-Eddington thermal radiation. In either
case, AT2018cow suggests that the population of fast luminous transients
represents a new class of astrophysical event. Intensive follow-up of this
event in its late phases, and of any future events found at comparable
distance, will be essential to better constrain their origins.

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The categories of this paper are: supr-con
5
The categories of this paper are: gr-qc
11
The categories of this paper are: hep-lat
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The categories of this paper are: atom-ph
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The categories of this paper are: q-alg
9
The categories of this paper are: nlin
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The categories of this paper are: q-fin
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The categories of this paper are: dg-ga
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The categories of this paper are: adap-org
3
The categories of this paper are: physics
10
The categories of this paper are: q-bio
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The categories of this paper are: cmp-lg
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The categories of this paper are: acc-phys
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The categories of this paper are: nucl-th
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The categories of this paper are: math
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The categories of this paper are: hep-ex