Discovery of Pulsed Gamma Rays and a New Spin-Down State of the LMC Pulsar B0540-69
Abstract
The young pulsar B0540-69 in the nearby Large Magellanic Cloud has the third largest spin-down luminosity of the ~2500 known pulsars. Multi-year observations with Fermi/LAT using the ephemerides from RXTE reveal that B0540-69 is the most luminous gamma-ray pulsar ever detected. Its pulsed luminosity above 100 MeV is 5.7x1036 erg/s, about 20 times brighter than the Crab Pulsar, the next brightest. The pulse profile in gamma rays is similar to that seen in X-rays and optical light; the giant radio pulses align with the shoulders of the high-energy profiles. The detection of B0540-69 in gamma rays offers a new look at particle acceleration and emission in the magnetospheres of very young pulsars. Unpulsed gamma-ray emission has also been detected from PSR J0537-6910, another young pulsar in the LMC. The two pulsars contribute most of the gamma-ray emission from the 30 Doradus nebula, indicating that cosmic rays contribute only a small part. Recent monitoring of B0540-69 with the Swift/XRT shows a large, sudden, and persistent increase in the spin-down rate of B0540-69. The relative increase in the spin-down rate of 36% is unprecedented for B0540-69. No accompanying change in the spin rate was seen, and no change was seen in the pulsed X-ray emission from B0540-69 following the change in the spin-down rate. Such large relative changes in the spin-down rate are seen in the recently discovered class of ``intermittent pulsars'', and we compare the properties of B0540-69 to such pulsars. We consider possible changes in the magnetosphere of the pulsar that could cause such a large change in the spin-down rate. These changes are likely to result in a new braking index for the pulsar. We report on continued monitoring with Swift/XRT to determine the new braking index and to detect a new state change, should it occur.
- Publication:
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American Astronomical Society Meeting Abstracts #227
- Pub Date:
- January 2016
- Bibcode:
- 2016AAS...22742304M