Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Pulsar Timing at Urumqi Astronomical Observatory: Observing System and
  Results   A pulsar timing system has been operating in the 18-cm band at the Urumqi
Astronomical Observatory 25-m telescope since mid-1999. Frequency resolution
allowing dedispersion of the pulsar signals is provided by a 2X128X2.5 MHz
filterbank/digitiser system. Observations of 74 pulsars over more than 12
months have resulted in updated pulsar periods and period derivatives, as well
as improved positions. Comparison with previous measurements showed that the
changes in period and period derivative tend to have the same sign and to be
correlated in amplitude. A model based on unseen glitches gives a good
explanation of the observed changes, suggesting that long-term fluctuations in
period and period derivatives are dominated by glitches. In 2000 July, we
detected a glitch of relative amplitude Delta_nu/nu~24X1e-9 in the Crab pulsar.
The post-glitch decay appears similar to other large Crab glitches.

14
The categories of this paper are: math-ph
22
The categories of this paper are: chao-dyn
2
The categories of this paper are: math
12
The categories of this paper are: nucl-th
29
The categories of this paper are: funct-an
27
The categories of this paper are: comp-gas
20
The categories of this paper are: acc-phys
24
The categories of this paper are: dg-ga
8
The categories of this paper are: hep-ex
3
The categories of this paper are: physics
26
The categories of this paper are: bayes-an
31
The categories of this paper are: ao-sci
19
The categories of this paper are: eess
35
The categories of this paper are: mtrl-th
23
The categories of this paper are: solv-int
28
The categories of this paper are: alg-geom