The optical light curve of the LMC pulsar B0540-69 in 2009

TL;DR

This study presents a detailed optical light curve analysis of the pulsar PSR B0540-69 in 2009, revealing a double-peaked structure and refining its spin-down parameters, with implications for its age and braking index.

Contribution

The paper provides the first detailed optical light curve of PSR B0540-69 in 2009 and extends the timing analysis to refine the pulsar's braking index and age estimates.

Findings

Double-peaked optical light curve with Gaussian fits

Refined spin frequency derivatives over 3.5 years

Braking index of 2.087 ± 0.007 and age around 1700 years

Abstract

This paper reports a detailed analysis of the optical light curve of PSR B0540-69, the second brightest pulsar in the visible band, obtained in 2009 (Jan. 18 and 20, and Dec. 14, 15, 16, 18) with the very high speed photon counting photometer Iqueye mounted at the ESO 3.6-m NTT in La Silla (Chile). The optical light curve derived by Iqueye shows a double structure in the main peak, with a raising edge steeper than the trailing edge. The double peak can be fitted by two Gaussians with the same height and FWHM of 13.3 and 15.5 ms respectively. Our new values of spin frequencies allow to extend by 3.5 years the time interval over which a reliable estimate of frequency first and second derivatives can be performed. A discussion of implications on the braking index and age of the pulsar is carried out. A value of n = 2.087 +/- 0.007 for the overall braking index from 1987 to 2009 is derived. The braking index corrected age is confirmed around 1700 years.