Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Observations of a Correlated Gamma-Ray and Optical Flare for BL Lacertae   The latest observations of BL Lacertae with the EGRET instrument on CGRO show
that the gamma-ray flux was four times higher than the previous detection.
Within the 1997 July 15-22 observation there was a dramatic factor of 2.5
increase in the gamma-ray flux, with a sharp peak of about 8 hours, and
apparently preceding a brief optical flare by several hours. The gamma-ray
photon spectral index was significantly harder than that for the previous
detection.

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The categories of this paper are: hep-th
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The categories of this paper are: quant-ph
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The categories of this paper are: nlin
21
The categories of this paper are: adap-org
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The categories of this paper are: chem-ph
32
The categories of this paper are: atom-ph
37
The categories of this paper are: supr-con
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The categories of this paper are: acc-phys
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The categories of this paper are: alg-geom
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The categories of this paper are: math-ph
25
The categories of this paper are: patt-sol
22
The categories of this paper are: chao-dyn
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The categories of this paper are: mtrl-th
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The categories of this paper are: nucl-th
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The categories of this paper are: math
29
The categories of this paper are: funct-an