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takyon writes:

The NuSTAR space telescope, launched in 2012, has been used to find some of the universe's brightest known pulsars:

The brightest pulsar, as reported in the journal Science [DOI: 10.1126/science.aai8635] [DX], is called NGC 5907 ULX. In one second, it emits the same amount of energy as our sun does in three-and-a-half years. The European Space Agency's XMM-Newton satellite found the pulsar and, independently, NASA's NuSTAR (Nuclear Spectroscopic Telescope Array) mission also detected the signal. This pulsar is 50 million light years away, which means its light dates back to a time before humans roamed Earth. It is also the farthest known neutron star.

"This object is really challenging our current understanding of the accretion process for high-luminosity pulsars," said Gian Luca Israel, from INAF-Osservatorio Astronomica di Roma, Italy, lead author of the Science paper. "It is 1,000 times more luminous than the maximum thought possible for an accreting neutron star, so something else is needed in our models in order to account for the enormous amount of energy released by the object."

The previous record holder for brightest pulsar was reported in October 2014. NuSTAR had identified M82 X-2, located about 12 million light-years away in the "Cigar Galaxy" galaxy Messier 82 (M82), as a pulsar rather than a black hole. The pulsar reported in Science, NGC 5907 ULX, is 10 times brighter.

Another extremely bright pulsar, the third brightest known, is called NGC 7793 P13. Using a combination of XMM-Newton and NuSTAR, one group of scientists reported the discovery in the Astrophysical Journal Letters [DOI: 10.3847/2041-8205/831/2/L14] [DX], while another used XMM-Newton to report it in the Monthly Notices of the Royal Astronomical Society [DOI: 10.1093/mnrasl/slw218] [DX]. Both studies were published in October 2016. Scientists call three extremely bright pulsars "ultraluminous X-ray sources" (ULXs). Before the 2014 discovery, many scientists thought that the brightest ULXs were black holes.

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