X-ray softening in the new X-ray transient XTE J1719-291 during its 2008
  outburst decay
  The X-ray transient XTE J1719-291 was discovered with RXTE/PCA during its
outburst in 2008 March, which lasted at least 46 days. Its 2-10 keV peak
luminosity is 7E35 erg/s assuming a distance of 8 kpc, which classifies the
system as a very faint X-ray transient. The outburst was monitored with Swift,
RXTE, Chandra and XMM-Newton. We analysed the X-ray spectral evolution during
the outburst. We fitted the overall data with a simple power-law model
corrected for absorption and found that the spectrum softened with decreasing
luminosity. However, the XMM-Newton spectrum can not be fitted with a simple
one-component model, but it can be fitted with a thermal component (black body
or disc black body) plus power-law model affected by absorption. Therefore, the
softening of the X-ray spectrum with decreasing X-ray luminosity might be due
to a change in photon index or alternatively it might be due to a change in the
properties of the soft component. Assuming that the system is an X-ray binary,
we estimated a long-term time-averaged mass accretion rate of ~ 7.7E-13
M_sun/yr for a neutron star as compact object and ~ 3.7E10-13 M_sun/yr in the
case of a black hole. Although no conclusive evidence is available about the
nature of the accretor, based on the X-ray/optical luminosity ratio we
tentatively suggest that a neutron star is present in this system.
