Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A transient I band excess in the optical spectrum of the accreting
  millisecond pulsar SAX J1808.4-3658   The optical counterpart of the transient, millisecond X-ray pulsar SAX
J1808.4-3658 was observed in four colours (BVRI) for five weeks during the 2005
June-July outburst. The optical fluxes declined by ~2 magnitudes during the
first 16 days and then commenced quasi-periodic secondary outbursts, with
time-scales of several days, similar to those seen in 2000 and 2002. The
broadband spectra derived from these measurements were generally consistent
with emission from an X-ray heated accretion disc. During the first 16 days
decline in intensity the spectrum became redder. We suggest that the primary
outburst was initiated by a viscosity change driven instability in the inner
disc and note the contrast with another accreting millisecond pulsar, XTE
J0929--314, for which the spectrum becomes bluer during the decline. On the
night of 2005 June 5 (HJD 2453527) the I band flux was ~0.45 magnitudes
brighter than on the preceding or following nights whereas the BVR bands showed
no obvious enhancement. A Type I X-ray burst was detected by the RXTE
spacecraft during this I band integration. It seems unlikely that reprocessed
radiation from the burst was sufficient to explain the observed increase. We
suggest that a major part of the I band excess was due to synchrotron emission
triggered by the X-ray burst. Several other significant short duration changes
in V-I were detected. One occurred at about HJD 2453546 in the early phase of
the first secondary outburst and may be due to a mass transfer instability or
to another synchrotron emission event.

31
The categories of this paper are: ao-sci
19
The categories of this paper are: eess
17
The categories of this paper are: q-fin
22
The categories of this paper are: chao-dyn
20
The categories of this paper are: acc-phys
7
The categories of this paper are: hep-th
37
The categories of this paper are: supr-con
2
The categories of this paper are: math
1
The categories of this paper are: cs
27
The categories of this paper are: comp-gas
23
The categories of this paper are: solv-int
28
The categories of this paper are: alg-geom
12
The categories of this paper are: nucl-th
16
The categories of this paper are: stat
8
The categories of this paper are: hep-ex
15
The categories of this paper are: nucl-ex