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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,045 records · Page 58
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NASA NTRS2020

Modeling the Precession of the Warped Inner Accretion Disk in the Pulsars LMC X-4 and SMC X-1 with NuSTAR and XMM-Newton

We present a broad-band X-ray study of the effect of superorbital periods on X-ray spectra and pulse profiles in the neutron star X-ray binaries LMC X-4 and SMC X-1. These two sources display periodic or quasi-periodic variations in luminosity on the order of tens of days which are known to be superorbital, and are attributed to warped, precessing accretion disks. Using joint NuSTAR and XMM-Newton observations that span a complete superorbital cycle, we examine the broad-band spectra of these sources and find the shape to be well described by an absorbed power law with a soft blackbody component. Changes in spectral shape and pulse profile shape are periodic with superorbital period, as expected from a precessing disk. We perform X-ray tomography using the changes in pulse profiles to model the geometry and kinematics of the inner accretion disk. Our simple beam and inner disk geometric model indicates that the long term changes in soft pulse shape and phase are consistent with reprocessed emission from a precessing inner disk.

Brumback, McKinley C.↗
NASA NTRS2021

A Broadband X-Ray View of the Precessing Accretion Disk and Pre-eclipse Dip in the Pulsar Her X-1 with NuSTAR and XMM-Newton

We present a broad-band X-ray study of the variation with the super orbital cycle of the pulse profiles and spectral shape in the low-mass X-ray binary Her X-1. This source shows a 35-day superorbital modulation in X-ray flux that is most likely caused by occultation by a warped, precessing accretion disk. Our data set consists of four joint XMM-Newton and NuSTAR observations of Her X-1 which span a complete super orbital cycle. However, We focus our analysis on the first and fourth observa-tion, which occur during the bright “main-on” phase, that have sufficient signal to noise to resolve pulsations. In order to broaden our coverage of the superorbital cycle, we supplemented our weakly pulsed observations with an archival XMM-Newton observation during the “short-on” phase of the superorbital cycle. We find that the energy-resolved pulse profiles show variations with superorbital phase and that pulse profiles from observations at similar superorbital phases show the same shape and relative phase, which we expect from a precessing disk. We determine that the broad-band spectrum is well fit by an absorbed power law with a soft black body component. We demonstrate that a simple precessing accretion disk model is sufficient to reproduce the observed pulse profiles. The results of this model support the idea that the similarities in the observed pulse profiles are due to reprocessing by a precessing disk that has returned to its original precession phase. We also present a brief analysis of the energy resolved light curves of a pre-eclipse dip, which shows soft X-ray absorption and hard X-ray variability during the dip.

McKinley C Brumback↗
NASA NTRS2022

MAXI J1957+032: A New Accreting Millisecond X-ray Pulsar in an Ultra-Compact Binary

The detection of coherent X-ray pulsations at ∼314 Hz (3.2 ms) classifies MAXI J1957+032 as a fast-rotating, accreting neutron star. We present the temporal and spectral analysis performed using NICER observations collected during the latest outburst of the source. Doppler modulation of the X-ray pulsation revealed the ultra-compact nature of the binary system characterized by an orbital period of ∼1 h and a projected semimajor axis of 14 lt-ms. The neutron star binary mass function suggests a minimum donor mass of 1.7 × 10 −2 M ⊙ , assuming a neutron star mass of 1.4 M ⊙ and a binary inclination angle lower than 60 deg. This assumption is supported by the lack of eclipses or dips in the X-ray light curve of the source. We characterized the 0.5–10 keV energy spectrum of the source in outburst as the superposition of a relatively cold black-body-like thermal emission compatible with the emission from the neutron star surface and a Comptonization component with photon index consistent with a typical hard state. We did not find evidence for iron K α lines or reflection components.

X-rays:binaries↗