Quasi-periodic whispers from a transient ULX in M 101: signatures of a fast-spinning neutron star?
Quasi-periodic whispers from a transient ULX in M 101: signatures of a fast-spinning neutron star?
We have studied the unusual time variability of an ultraluminous X-ray source in M 101, 4XMM J140314.2$+$541806 (henceforth, J1403), using Chandra and XMM-Newton data. Over the last two decades, J1403 has shown short-duration outbursts with an X-ray luminosity $\sim1-3 \times 10^{39}$ erg s$^{-1}$, and longer intervals at luminosities $\sim0.5-1 \times …