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“It’s not fully understood why there are variations between different pulsars,” said Posselt. “One of the main ideas here is that pulse differences have a lot to do with geometry — and it also depends on how the pulsar’s spin and magnetic axes are oriented with respect to line of sight whether you see certain pulsars or not, as well as how you see them.”
“This is one of the nicest results of our larger study of pulsar wind nebulae,” said Roger W. Romani, professor of physics at Stanford University and principal investigator of the Chandra PWN project. “By making the 3-D structure of these winds visible, we have shown how one can trace back to the plasma injected by the pulsar at the center. Chandra’s fantastic X-ray acuity was essential for this study, so we are happy that it was possible to get the deep exposures that made these faint structures visible.”
“The tails seem to tell us why that is,” said Posselt, adding that the pulsars’ spin axis and magnetic axis orientations influence what emissions are seen on Earth.
“For Geminga, we view the bright gamma ray pulses and the edge of the pulsar wind nebula torus, but the radio beams near the jets point off to the sides and remain unseen,” Posselt said.
“For B0355+54, a jet points nearly at us so we detect the bright radio pulses while most of the gamma-ray emission is directed in the plane of the sky and misses the Earth,” said Kargaltsev. “This implies that the pulsar’s spin axis direction is close to our line-of-sight direction and that the pulsar is moving nearly perpendicularly to its spin axis.”
“In particular, it may be tricky to detect a PWN from a pulsar moving close to the line-of-sight and having a small angle between the spin axis and our line-of-sight,” said Klingler.
“In both scenarios, Geminga provides exciting new constraints on the acceleration physics in pulsar wind nebulae and their interaction with the surrounding interstellar matter,” she said.