We report the X-ray data analysis of two transient ultraluminous X-ray sources ( ULXs , hereafter X1 and X2 ) located in the nearby galaxy NGC 7090 .
While they were not detected in the 2004 XMM-Newton and 2005 Chandra observations , their 0.3–10 keV X-ray luminosities reached > 3 \times 10 ^ { 39 } erg s ^ { -1 } in later XMM-Newton or Swift observations , showing increases in flux by a factor of > 80 and > 300 for X1 and X2 , respectively .
X1 showed indications of spectral variability : at the highest luminosity , its X-ray spectra can be fitted with a powerlaw ( \Gamma = 1.55 \pm 0.15 ) , or a multicolour disc model with T _ { \mathrm { in } } = 2.07 ^ { +0.30 } _ { -0.23 } keV ; the X-ray spectrum became softer ( \Gamma = 2.67 ^ { +0.69 } _ { -0.64 } ) , or cooler ( T _ { \mathrm { in } } = 0.64 ^ { +0.28 } _ { -0.17 } keV ) at lower luminosity .
No strong evidence for spectral variability was found for X2 .
Its X-ray spectra can be fitted with a simple powerlaw model ( \Gamma = 1.61 ^ { +0.55 } _ { -0.50 } ) , or a multicolour disc model ( 1.69 ^ { +1.17 } _ { -0.48 } keV ) .
A possible optical counterpart for X1 is revealed in HST imaging .
No optical variability is found , indicating that the optical radiation may be dominated by the companion star .
Future X-ray and optical observations are necessary to determine the true nature of the compact object .