Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: VERITAS Long-Term Observations of Hard Spectrum Blazars   The VERITAS collaboration has approved long-term observations on several
distant, hard-spectrum blazars. We present first results from VERITAS long-term
observations of 1ES1218+304, 1ES0229+200, and 1ES0414+009. Gamma-ray
observations of distant, hard-spectrum blazars has emerged as an effective,
indirect probe of the universe's diffuse extragalactic background light (EBL),
due to the extinction of gamma-rays via the pair production interaction
$\gamma_{TeV}\gamma_{EBL}\rightarrow e^{+}e^{-}$, which is expected to produce
absorption features in distant gamma-ray sources. The sources presented here
emit spectra that are well fit by power laws.

14
The categories of this paper are: math-ph
20
The categories of this paper are: acc-phys
22
The categories of this paper are: chao-dyn
23
The categories of this paper are: solv-int
33
The categories of this paper are: plasm-ph
35
The categories of this paper are: mtrl-th
3
The categories of this paper are: physics
15
The categories of this paper are: nucl-ex
34
The categories of this paper are: chem-ph
5
The categories of this paper are: gr-qc
8
The categories of this paper are: hep-ex
0
The categories of this paper are: hep-ph
4
The categories of this paper are: cond-mat
11
The categories of this paper are: hep-lat
25
The categories of this paper are: patt-sol
10
The categories of this paper are: q-bio