Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Deep optical observations of unusual neutron star Calvera with the GTC   Calvera is an unusual isolated neutron star with pure thermal X-ray spectrum
typical for central compact objects in supernova remnants. On the other hand,
its rotation period and spin-down rate are typical for ordinary
rotation-powered pulsars. It was discovered and studied in X-rays and not yet
detected in other spectral domains. We present deep optical imaging of the
Calvera field obtained with the Gran Telescopio Canarias in $g'$ and $i'$
bands. Within $\approx 1^{\prime\prime}$ vicinity of Calvera, we detected two
point-like objects invisible at previous shallow observations. However,
accurate astrometry showed that none of them can be identified with the pulsar.
We put new upper limits on its optical brightness of $g' > 27.87$ and $i' >
26.84$. We also reanalyzed all available archival X-ray data on Calvera.
Comparison of the Calvera thermal emission parameters and upper limits on
optical and non-thermal X-ray emission with respective data on rotation-powered
pulsars shows that Calvera might belong to the class of ordinary middle-aged
pulsars, if we assume that its distance is in the range of $1.5-5$ kpc.

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The categories of this paper are: q-alg
11
The categories of this paper are: hep-lat
17
The categories of this paper are: q-fin
35
The categories of this paper are: mtrl-th
37
The categories of this paper are: supr-con
3
The categories of this paper are: physics
27
The categories of this paper are: comp-gas
18
The categories of this paper are: econ
16
The categories of this paper are: stat
36
The categories of this paper are: cmp-lg
5
The categories of this paper are: gr-qc
20
The categories of this paper are: acc-phys
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The categories of this paper are: funct-an
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The categories of this paper are: atom-ph
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The categories of this paper are: nlin
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The categories of this paper are: solv-int