Journal of The Korean Astronomical Society (천문학회지)

The Korean Astronomical Society (한국천문학회)
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MEASURING TIMING PROPERTIES OF PSR B0540-69

  • Kim, Minjun (Department of Astronomy and Space Science, Chungbuk National University) ;
  • An, Hongjun (Department of Astronomy and Space Science, Chungbuk National University)
  • Received : 2019.07.10
  • Accepted : 2019.02.20
  • Published : 2019.04.30
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Abstract

We report on the timing properties of the 'Crab twin' pulsar PSR B0540-69 measured with X-ray data taken with the Swift telescope over a period of 1100 days. The braking index of the pulsar was estimated to be $n=0.03{\pm}0.013$ in a previous study performed in 2015 with 500-day Swift data. This small value of n is unusual for pulsars, and a comparison with an old estimate of $n{\approx}2.1$ for the same target determined ~10 years earlier suggests a dramatic change in the braking index. To confirm the small value and therefore the large change of n, we used 1100-day Swift observations including the data used in the earlier determination of n = 0.03. In this study we find that the braking index of PSR B0540-69 is $n=0.163{\pm}0.001$, somewhat larger than 0.03. Since the measured value of n is still much smaller than 2.1, we can confirm the dramatic change in the braking index for this pulsar.

Keywords

CMHHBA_2019_v52n2_41_f0001.tif 이미지

Figure 1. Results of the direct frequency measurement using the $Z_{1}^{2}$-test. Top: Frequencies measured for each continuous data segment (black data points) and a linear fit (red solid line) to measure the frequency derivative. Bottom: Residuals left after subtracting the best-fit linear function.

CMHHBA_2019_v52n2_41_f0002.tif 이미지

Figure 2. 0.5-7-keV pulse profiles of PSR B0540-69. Top: The pulse profiles in the first 500 days of data produced with the known timing solution of Marshall et al. (2016). Bottom: The pulse profile made with the 1100-day data and the refined solution. Blue and black points are pulse profiles of the source before and after background subtraction, respectively. Best-fit sine functions are shown as smooth lines, the background profile is shown in red. We used 128 bins for the profiles and show two cycles for clarity. The profiles for the 500-day and 1100-day data appear similar, with pulsed fractions of 0.295(6) and 0.280(4).

CMHHBA_2019_v52n2_41_f0003.tif 이미지

Figure 3. Timing residuals after fitting out the cubic trend (timing solution) from the phase-shift measurements of the 1100-day data.

CMHHBA_2019_v52n2_41_f0004.tif 이미지

Figure 4. Timing residuals obtained in TEMPO2 after whitening the timing noise.

Table 1 List of pulsars with a measured braking index

CMHHBA_2019_v52n2_41_t0001.tif 이미지

Table 2 Several timing solutions for PSR B0540−69 obtained in previous works as well as this work

CMHHBA_2019_v52n2_41_t0002.tif 이미지

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