Engineering topics

King, Ashley L.

Publications and source records attributed to King, Ashley L..

3 records

NASA NTRS2016

A NuSTAR Observation of the Reflection Spectrum of the Low-Mass X-Ray Binary 4U 1728-34

We report on a simultaneous NuSTAR and Swift observation of the neutron star low-mass X-ray binary 4U 1728-34. We identified and removed four Type I X-ray bursts during the observation in order to study the persistent emission. The continuum spectrum is hard and described well by a blackbody with kT=1.5 keV and a cutoff power law with Lambda = 1.5, and a cutoff temperature of 25 keV. Residuals between 6 and 8 keV provide strong evidence of a broad Fe K(alpha) line. By modeling the spectrum with a relativistically blurred reflection model, we find an upper limit for the inner disk radius of R(sub in) < or = 2R(sub ISCO). Consequently, we find that R(sub NS) < or = 23 km, assuming M = 1.4 Stellar Mass and a = 0.15. We also find an upper limit on the magnetic field of B < or =2 x 10(exp 8) G.

accretion disks↗

NASA NTRS2016

Measuring a Truncated Disk in Aquila X-1

We present NuSTAR and Swift observations of the neutron star Aquila X-1 during the peak of its 2014 July outburst. The spectrum is soft with strong evidence for a broad Fe K(alpha) line. Modeled with a relativistically broadened reflection model, we find that the inner disk is truncated with an inner radius of 15 +/- 3RG. The disk is likely truncated by either the boundary layer and/or a magnetic field. Associating the truncated inner disk with pressure from a magnetic field gives an upper limit of B < 5+/- 2x10(exp 8) G. Although the radius is truncated far from the stellar surface, material is still reaching the neutron star surface as evidenced by the X-ray burst present in the NuSTAR observation.

accretion disks aEuro" magnetic fields aEuro" star↗

NASA NTRS2014

The Disk Wind in the Rapidly Spinning Stellar-mass Black Hole 4U 1630-472 Observed with NuSTAR

We present an analysis of a short NuSTAR observation of the stellar-mass black hole and low-mass X-ray binary 4U 1630−472. Reflection from the inner accretion disk is clearly detected for the first time in this source, owing to the sensitivity of NuSTAR. With fits to the reflection spectrum, we find evidence for a rapidly spinning black hole, a∗ = 0.985(+0.005/−0.014) (1 sigma statistical errors). However, archival data show that the source has relatively low radio luminosity. Recently claimed relationships between jet power and black hole spin would predict either a lower spin or a higher peak radio luminosity. We also report the clear detection of an absorption feature at 7.03 +/- 0.03 keV, likely signaling a disk wind. If this line arises in dense, moderately ionized gas (log xi = 3.6(+0.2/−0.3) and is dominated by He-like Fe xxv, the wind has a velocity of v/c = 0.043(+0.002/−0.007) (12900(+600/−2100) km s(exp −1)). If the line is instead associated with a more highly ionized gas (log xi = 6.1(+0.7/−0.6)), and is dominated by Fe xxvi, evidence of a blueshift is only marginal, after taking systematic errors into account. Our analysis suggests the ionized wind may be launched within 200-1100 Rg, and may be magnetically driven.

accretion disks↗