Abstract
Abstract We report on a Nuclear Spectroscopic Telescope Array (NuSTAR) observation of the young, energetic pulsar PSR J1617–5055. Parkes Observatory 3 GHz radio observations of the pulsar (taken about 7 yr before the NuSTAR observations) are also reported here. NuSTAR detected pulsations at a frequency of f ≈ 14.4 Hz (P ≈ 69.44 ms) and, in addition, the observation was long enough to measure the source’s frequency derivative, f ̇ ≈ − 2.8 × 10 − 11 Hz s−1. We find that the pulsar shows one peak per period at both hard X-ray and radio wavelengths, but that the hard X-ray pulse is broader (having a duty cycle of ∼0.7), than the radio pulse (having a duty cycle of ∼0.08). Additionally, the radio pulse is strongly linearly polarized. J1617's phase-integrated hard X-ray spectrum is well fit by an absorbed power-law model, with a photon index Γ = 1.59 ± 0.02. The hard X-ray pulsations are well described by three Fourier harmonics, and have a pulsed fraction that increases with energy. We also fit the phase-resolved NuSTAR spectra with an absorbed power-law model in five phase bins and find that the photon index varies with phase from Γ = 1.52 ± 0.03 at phases around the flux maximum to Γ = 1.79 ± 0.06 around the flux minimum. Last, we compare our results with other pulsars whose magnetospheric emission is detected at hard X-ray energies and find that, similar to previous studies, J1617's hard X-ray properties are more similar to the MeV pulsars than the GeV pulsars.
Highlights
Broadband X-ray observations of young, energetic pulsars provide a means to probe particle acceleration in pulsar magnetospheres
The improved angular resolution and sensitivity afforded by the Nuclear Spectroscopic Telescope Array (NuSTAR), has made it possible to study these
The NuSTAR pulse profile is similar to what has been observed at slightly lower X-ray energies by XMM-Newton and RXTE PCA (Becker & Aschenbach 2002; Kuiper & Hermsen 2015), showing an asymmetric pulse profile with a rise that is faster than the decay
Summary
Broadband X-ray observations of young, energetic pulsars provide a means to probe particle acceleration in pulsar magnetospheres. Studies of these sources at hard X-ray energies have been hampered by the high background of non-imaging instruments, making it difficult to measure the spectrum of their off-pulsed emission, especially when there is contamination from a bright pulsar wind nebula (see, e.g., Kuiper & Hermsen 2015). Pulsations from PSR J1617–5055 (J1617 hereafter) with a period P ≈ 69 ms were first discovered in X-rays with Ginga and ASCA (Aoki et al 1992; Torii et al 1998), and in the radio with the Parkes Observatory (Kaspi et al 1998) It is a young (τ = 8.3 kyr), energetic (E = 1.6 ́ 1037 erg s−1) pulsar with a magnetic field B = 3.1 × 1012 G. A description of our approach to the X-ray timing is provided in the Appendix
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