Speaker
Description
Ultraluminous X-ray sources (ULXs) are extragalactic X-ray emitters located off-center of their host galaxy and with a luminosity in excess of a few $10^{39}$ erg/s, if emitted isotropically. The discovery of periodic modulation revealed that in some ULXs the accreting compact object is a neutron star (NS), indicating luminosities substantially above their Eddington limit. The most extreme object in this respect is NGC 5907 ULX-1 (ULX1), with a peak luminosity that exceeds by 500 times its Eddington limit. During a Chandra observation to probe a low state of ULX1, we detected diffuse X-ray emission at the position of ULX1. We interpret this extended structure as an expanding nebula powered by the wind of ULX1. Its diameter of $\sim$200 pc, characteristic energy of $\sim$2 keV, and luminosity of $\sim$$5\times10^{38}$ erg/s imply a mechanical power of $\sim2\times10^{41}$ erg/s and an age $\sim6\times10^{4}$ yr. This proves that a genuinely super-Eddington regime can be sustained for time scales much longer than the spin-up time of the NS powering the system. Since the mechanical power from a single ULX nebula can rival the injection rate of cosmic rays of an entire galaxy, ULX nebulae could be important cosmic ray accelerators.
| Affiliation | INAF IASF-MI |
|---|---|
| Topic | Compact and diffuse sources in galaxies and in the Galactic Center |
