A Deep Campaign to Characterize the Synchronous Radio/X-Ray Mode Switching of PSR B0943+10

Observations of PSR B0943+10 with XMM-Newton and the LOFAR, LWA, and Arecibo radio telescopes in 2014 November confirm the synchronous X-ray/radio switching between a radio-bright (B) mode and a radio-quiet (Q) mode, in which the X-ray flux is a factor ∼2.4 higher than in the B-mode. We discovered X-ray pulsations during the B-mode (0.5-2 keV pulsed fraction of (38 ± 5)%) and confirm their presence in the Q-mode, where the pulsed fraction increases with energy from ∼20% to ∼65% at 2 keV. We found marginal evidence for an increase in the X-ray pulsed fraction during the B-mode on a timescale of hours. The X-ray spectrum during the Q-mode requires a fit with either a power law plus blackbody or the sum of two blackbodies, while in the B-mode it is well fit by a single blackbody (a single power law is rejected). In the Q-mode, the pulsed emission has a blackbody spectrum with temperature ∼ 3.4× {10}⁶ K and the unpulsed emission is a power law with photon index ∼2.5, while during the B-mode both the pulsed and unpulsed emission can be fit by either a blackbody or a power law with similar values of temperature and index. A Chandra image does not show diffuse X-ray emission. These results support a scenario in which unpulsed non-thermal emission, likely magnetospheric, and pulsed thermal emission from a small polar cap (∼1500 m²) with a non-dipolar field (∼10¹⁴ G) are present during both modes and vary in a correlated way. This is broadly consistent with the partially screened gap model and does not necessarily imply global magnetospheric rearrangements to explain the mode switching.