Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A four-year baseline Swift study of enigmatic X-ray transients located
  near the Galactic center   We report on continued monitoring observations of the Galactic center carried
out by the X-ray telescope aboard the Swift satellite in 2008 and 2009. This
campaign revealed activity of the five known X-ray transients AX J1745.6-2901,
CXOGC J174535.5-290124, GRS 1741-2853, XMM J174457-2850.3 and CXOGC
J174538.0-290022. All these sources are known to undergo very faint X-ray
outbursts with 2-10 keV peak luminosities of Lx,peak~1E34-1E36 erg/s, although
the two confirmed neutron star low-mass X-ray binaries AX J1745.6-2901 and GRS
1741-2853 can also become brighter (Lx,peak~1E36-1E37 erg/s). We discuss the
observed long-term lightcurves and X-ray spectra of these five enigmatic
transients. In 2008, AX J1745.6-2901 returned to quiescence following an
unusually long accretion outburst of more than 1.5 years. GRS 1741-2853 was
active in 2009 and displayed the brightest outburst ever recorded for this
source, reaching up to a 2-10 keV luminosity of Lx~1E37 (D/7.2 kpc)^2 erg/s.
This system appears to undergo recurrent accretion outbursts approximately
every 2 years. Furthermore, we find that the unclassified transient XMM
J174457-2850.3 becomes bright only during short episodes (days) and is often
found active in between quiescence (Lx~1E32 erg/s) and its maximum outburst
luminosity of Lx~1E36 erg/s. CXOGC J174535.5-290124 and CXOGC J174538.0-290022,
as well as three other very-faint X-ray transients that were detected by Swift
monitoring observations in 2006, have very low time-averaged mass-accretion
rates of ~< 2E-12 Msun/yr. Despite having obtained two years of new data in
2008 and 2009, no new X-ray transients were detected.

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The categories of this paper are: adap-org
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The categories of this paper are: comp-gas
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The categories of this paper are: alg-geom
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The categories of this paper are: q-alg
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The categories of this paper are: supr-con
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The categories of this paper are: physics
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The categories of this paper are: cs
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The categories of this paper are: math-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: plasm-ph
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The categories of this paper are: gr-qc
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The categories of this paper are: q-bio
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The categories of this paper are: hep-ex
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The categories of this paper are: hep-lat
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The categories of this paper are: q-fin
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The categories of this paper are: dg-ga