NuSTAR observations of the young, energetic radio pulsar PSR B1509-58

Abstract

We report on Nuclear Spectroscopic Telescope Array (NuSTAR) hard X-ray observations of the young rotation-powered radio pulsar PSR B1509$-$58 in the supernova remnant MSH 15$-$52. We confirm the previously reported curvature in the hard X-ray spectrum, showing that a log parabolic model provides a statistically superior fit to the spectrum compared with the standard power law. The log parabolic model describes the NuSTAR data, as well as previously published gamma-ray data obtained with COMPTEL and AGILE, all together spanning 3 keV through 500 MeV. Our spectral modelling allows us to constrain the peak of the broadband high energy spectrum to be at 2.6$\pm$0.8 MeV, an improvement of nearly an order of magnitude in precision over previous measurements. In addition, we calculate NuSTAR spectra in 26 pulse phase bins and confirm previously reported variations of photon indices with phase. Finally, we measure the pulsed fraction of PSR B1509$-$58 in the hard X-ray energy band for the first time. Using the energy resolved pulsed fraction results, we estimate that the pulsar's off-pulse emission has a photon index value between 1.26 and 1.96. Our results support a model in which the pulsar's lack of GeV emission is due to viewing geometry, with the X-rays originating from synchrotron emission from secondary pairs in the magnetosphere.

10 pages, 8 figures, 6 tables, ApJ accepted

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• Calibration of the NuSTAR High Energy Focusing X-ray Telescope
• When A Standard Candle Flickers
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• {\it NuSTAR} hard X-ray studies of the pulsar wind nebula 3C~58
• A NuSTAR and Chandra Investigation of the Misaligned Outflow of PSR J1101-6101 and the Lighthouse Pulsar Wind Nebula
• An observational argument against accretion in magnetars
• Precise timing and phase-resolved spectroscopy of the young pulsar J1617-5055 with NuSTAR
• A Method for Pulsar Searching: Combining a Two-dimensional Autocorrelation Profile Map and a Deep Convolutional Neural Network