XSS J12270–4859 ( J12270 ) is an enigmatic source of unknown nature .
Previous studies revealed that the source has unusual X-ray temporal characteristics , including repetitive short-term flares followed by spectral hardening , non-periodic dips , and dichotomy in activity ; i.e .
intervals filled with flares and those without .
Together with a power-law X-ray spectrum , it is suggested to be a low-mass X-ray binary ( LMXB ) .
In order to better understand the object , we present the results of our near-infrared ( NIR ) photometry and linear polarimetry observations as well as X-ray spectroscopy observations , which overlap with each other partially in time , taken respectively with the InfraRed Survey Facility ( IRSF ) and the Rossi X-ray Timing Explorer ( RXTE ) .
We detected several simultaneous NIR and X-ray flares for the first time .
No significant NIR polarization was obtained .
We assembled data taken with IRSF , RXTE , Suzaku , Swift , and other missions in the literature and compared the flare profile and the spectral energy distribution ( SED ) with some representative high-energy sources .
Based on some similarities of the repetitive NIR and X-ray flaring characteristics and the broad SED , we argue that J12270 is reminiscent of microquasars with a synchrotron jet , which is at a very low luminosity state of \approx 10 ^ { -4 } Eddington luminosity for a stellar mass black hole or neutron star at a reference distance of 1 kpc .