NuSTAR Observations of the State Transition of Millisecond Pulsar Binary PSR J1023+0038
Abstract
We report 3-79 keV NuSTAR observations of the remarkable millisecond pulsar-low mass X-ray binary (LMXB) transition system PSR J1023+0038 from June and October 2013, before and after the formation of an accretion disk around the neutron star. Between June 10-12, shortly before the radio disappearance of the pulsar, the 3-79 keV X-ray spectrum was well fit by a simple power law with a photon index of Γ = 1.17±0.08 with a 3-79 keV luminosity of 7.4±0.4×1032 erg/s. Significant orbital modulation was observed with a modulation fraction of 36±10%. During the October 19-21 observation, the spectrum is described by a softer power law (Γ = 1.66±0.06) with an average luminosity of 5.8±0.2×1033 erg/s and a peak luminosity of ≈ 1.2×1034 erg/s observed during a flare. No significant orbital modulation was detected. The spectral observations are consistent with previous and current multi-wavelength observations and show the hard X-ray power law extending to 79 keV without a spectral break. Unusual, sharp edged, flat bottomed ‘dips’ are observed with widths between 30-1000 s and ingress and egress time-scales of 30-60 s. These dips are distinct from dipping activity observed in LMXBs. We compare and contrast these dips to observations of dips and state changes in the similar transition systems PSR J1824-2452I and XSS J1227.0-4859 and discuss possible interpretations based on the transitions in the inner disk.
- Publication:
-
AAS/High Energy Astrophysics Division #14
- Pub Date:
- August 2014
- Bibcode:
- 2014HEAD...1412223T