Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Violent intra-night optical variability of the blazar S4 0954+65 during
  its unprecedented 2015 February outburst   In this letter we present results from intra-night monitoring in three colors
(BRI) of the blazar S4 0954+65 during its recent (2015 February) unprecedented
high state. We find violent variations on very short time scales, reaching
magnitude change levels of 0.1-0.2 mag/h. On some occasions, changes of ~0.1
mag are observed even within ~10 min. During the night of 14.02.2015 an
exponential drop of ~0.7 magnitudes is detected for about 5 hours.
Cross-correlation between the light curves does not reveal any detectable
wavelength-dependent time delays, larger than ~5 min. Color changes
"bluer-when-brighter" are observed on longer time scales. Possible variability
mechanisms to explain the observations are discussed and a preference to the
geometrical one is given.

19
The categories of this paper are: eess
24
The categories of this paper are: dg-ga
33
The categories of this paper are: plasm-ph
15
The categories of this paper are: nucl-ex
5
The categories of this paper are: gr-qc
4
The categories of this paper are: cond-mat
23
The categories of this paper are: solv-int
21
The categories of this paper are: adap-org
28
The categories of this paper are: alg-geom
16
The categories of this paper are: stat
8
The categories of this paper are: hep-ex
12
The categories of this paper are: nucl-th
2
The categories of this paper are: math
20
The categories of this paper are: acc-phys
9
The categories of this paper are: nlin
11
The categories of this paper are: hep-lat