A NICER Thermonuclear Burst from the Millisecond X-Ray Pulsar SAX J1808.4–3658
Abstract
The Neutron Star Interior Composition Explorer (NICER) has extensively monitored the 2019 August outburst of the 401 Hz millisecond X-ray pulsar SAX J1808.4–3658. In this Letter, we report on the detection of a bright helium-fueled Type I X-ray burst. With a bolometric peak flux of (2.3 ± 0.1) × 10⁻⁷ erg s⁻¹ cm⁻², this was the brightest X-ray burst among all bursting sources observed with NICER to date. The burst shows a remarkable two-stage evolution in flux, emission lines at 1.0 and 6.7 keV, and burst oscillations at the known pulsar spin frequency, with ≈4% fractional sinusoidal amplitude. We interpret the burst flux evolution as the detection of the local Eddington limits associated with the hydrogen and helium layers of the neutron star envelope. The emission lines are likely associated with Fe, due to reprocessing of the burst emission in the accretion disk.
Additional Information
© 2019 The American Astronomical Society. Received 2019 September 8; revised 2019 September 29; accepted 2019 October 4; published 2019 October 23. This work was supported by NASA through the NICER mission and the Astrophysics Explorers Program, and made use of data and software provided by the High Energy Astrophysics Science Archive Research Center (HEASARC). P.B. was supported by an NPP fellowship at NASA Goddard Space Flight Center. G.K.J. was supported by the Marie Skłodowska-Curie Actions grant No. 713683 (H2020). D.A. acknowledges support from the Royal Society. R.M.L. acknowledges the support of NASA through Hubble Fellowship Program grant HST-HF2-51440.001. Facilities: ADS - , HEASARC - , NICER. - Software: heasoft (v6.26), nicerdas (v6a), xspec (v12.10).Attached Files
Published - Bult_2019_ApJL_885_L1.pdf
Submitted - 1909.03595.pdf
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Additional details
- Eprint ID
- 99426
- Resolver ID
- CaltechAUTHORS:20191023-155157476
- HST-HF2-51440.001
- NASA Hubble Fellowship
- NASA Postdoctoral Program
- 713683
- Marie Curie Fellowship
- Royal Society
- NASA Einstein Fellowship
- Created
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2019-10-23Created from EPrint's datestamp field
- Updated
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2021-11-16Created from EPrint's last_modified field