NuSTAR Hard X-Ray Observations of the Energetic Millisecond Pulsars PSR B1821-24, PSR B1937+21, and PSR J0218+4232
Abstract
We present Nuclear Spectroscopic Telescope Array (NuSTAR) hard X-ray timing and spectroscopy of the three exceptionally energetic rotation-powered millisecond pulsars PSRs B1821-24, B1937+21, and J0218+4232. By correcting for the frequency and phase drifts of the NuSTAR onboard clock, we are able to recover the intrinsic hard X-ray pulse profiles of all three pulsars with a resolution down to ≤slant 15 μ {{s}}. The substantial reduction of background emission relative to previous broadband X-ray observations allows us to detect for the first time pulsed emission up to ∼50 keV, ∼20 keV, and ∼25 keV for the three pulsars, respectively. We conduct phase-resolved spectroscopy in the 0.5-79 keV range for all three objects, obtaining the best measurements yet of the broadband spectral shape and high-energy pulsed emission to date. We find extensions of the same power-law continua seen at lower energies, with no conclusive evidence for a spectral turnover or break. Extrapolation of the X-ray power-law spectrum to higher energies reveals that a turnover in the 100 keV to 100 MeV range is required to accommodate the high-energy γ-ray emission observed with Fermi-LAT, similar to the spectral energy distribution observed for the Crab pulsar.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- August 2017
- DOI:
- 10.3847/1538-4357/aa813c
- arXiv:
- arXiv:1704.02964
- Bibcode:
- 2017ApJ...845..159G
- Keywords:
-
- pulsars: general;
- pulsars: individual: PSR B1821-24;
- PSR B1937+21;
- PSR J0218+4232;
- stars: neutron;
- X-rays: stars;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 12 pages, 10 figures, 2 tables