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 L _ { \mathrm { X,peak } } \sim 10 ^ { 34 - 36 } ~ { } \mathrm { erg~ { } s } ^ { -1 } , although the two confirmed neutron star low-mass X-ray binaries AX J1745.6–2901 and GRS 1741–2853 can also become brighter ( L _ { \mathrm { X,peak } } \sim 10 ^ { 36 - 37 } ~ { } \mathrm { erg~ { } s } ^ { -1 } ) .
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 L _ { \mathrm { X } } \sim 1 \times 10 ^ { 37 } ~ { } ( D / 7.2 ~ { } \mathrm { kpc } ) ^ { 2 } ~ { } \mathrm { erg~% { } s } ^ { -1 } .
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 ( L _ { \mathrm { X } } \sim 10 ^ { 32 } ~ { } \mathrm { erg~ { } s } ^ { -1 } ) and its maximum outburst luminosity of L _ { \mathrm { X } } \sim 10 ^ { 36 } ~ { } \mathrm { erg~ { } s } ^ { -1 } .
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 \langle \dot { M } \rangle _ { \mathrm { long } } \lesssim 2 \times 10 ^ { -12 } ~ { } \mathrm { M } _ { % \odot } ~ { } \mathrm { yr } ^ { -1 } .
Despite having obtained two years of new data in 2008 and 2009 , no new X-ray transients were detected .