A new , low braking index for the LMC PULSAR B0540-69

F E Marshall (1) , Lucas Guillemot (2, 3) , A A Harding (1) , Pierre Martin (4) , D A Smith (5)

1 GSFC Astrophysics Science Division
2 USN - Unité Scientifique de la Station de Nançay
3 LPC2E - Laboratoire de Physique et Chimie de l'Environnement et de l'Espace
4 Département SHS
5 CENBG - Centre d'Etudes Nucléaires de Bordeaux Gradignan

We report the results of a 16-month monitoring campaign using the Swift satellite of PSR 0 ¯ 540, a young pulsar in the Large Magellanic Cloud. Phase connection was maintained throughout the campaign so that a reliable ephemeris could be determined, and the length of the campaign is adequate to accurately determine the spin frequency ν and its first and second derivatives. The braking index n is 0.031 ± 0.013 (90% confidence), a value much lower than previously reported for 0 ¯ 540 and almost all other young pulsars. We use data from the extensive monitoring campaign with RXTE to show that timing noise is unlikely to significantly affect the measurement. This is the first measurement of the braking index in the pulsar's recently discovered high spin-down state. We discuss possible mechanisms for producing the low braking index.

Keywords: pulsars: individual (PSR B0540–69)

Domains: Cosmology and Extra-Galactic Astrophysics [astro-ph.CO]; Solar and Stellar Astrophysics [astro-ph.SR]

F E Marshall, Lucas Guillemot, A A Harding, Pierre Martin, D A Smith. A new , low braking index for the LMC PULSAR B0540-69. The Astrophysical journal letters, 2016, 827 (2), pp.39-39. ⟨10.3847/2041-8205/827/2/L39⟩. ⟨insu-01400560⟩