arXiv subjects

Andrew C. Liebmann

Publications and source records attributed to Andrew C. Liebmann.

4 recordsLinked to original sources

arXiv2026

Spectral Analysis of the 2019 and 2022 Outbursts of SAX J1808.4-3658

The accreting millisecond pulsar SAX J1808.4-3658 went into outburst from July to November in 2019 and August to October in 2022, which were observed by \textit{NICER} and \textit{NuSTAR}. In this paper, we first present the light curve for both outbursts using \textit{NICER} data. Several thermonuclear bursts occurred during these outbursts. We analyze the evolution of the spectra of two thermonuclear bursts that took place during the 2019 \textit{NuSTAR} observation. We proceed by analyzing the combined broad-band spectrum using \textit{NICER} and \textit{NuSTAR} for the first time for this source. We jointly modeled the combined quiescent spectra of both outbursts with a self-consistent reflection component. In our best-fit model, we find evidence of reflection, consistently constrain the inclination to 72°$^{+1°}_{-4°}$\, considering this reflection, and identify a 1 keV feature during persistent emission.

astro-ph.HE↗

arXiv2023

Ambipolar Heating of Magnetars

Magnetars, neutron stars thought to be with ultra-strong magnetic fields of $10^{14 - 15}$ G, are observed to be much hotter than ordinary pulsars with $\sim 10^{12}$ G, and additional heating sources are required. One possibility is heating by the ambipolar diffusion in the stellar core. This scenario is examined by calculating the models using the relativistic thermal evolutionary code without making the isothermal approximation. The results show that this scenario can be consistent with most of the observed magnetar temperature data.

astro-ph.HE↗

arXiv2020

MXB1659-298: The Fastest Spinning Millisecond Pulsar

We do not present the discovery of strong nearly coherent oscillations (NCOs) at 890.44 Hz for the low mass X-ray binary MXB 1659-298. We find that what we are detecting is dead time in the NuSTAR detectors. Instead consider this paper as further evidence for why standard timing methods should not be used with NuSTAR data.

astro-ph.HE↗

arXiv2014

X-ray Properties of Hard X-ray Selected AGN

Using the latest 70 month Swift-BAT catalog we examined hard X-ray selected Seyfert I galaxies which are relatively little known and little studied, and yet potentially promising to test the ionized relativistic reflection model. From this list we chose 13 sources which have been observed by XMM-Newton for less than 20 ks, in order to explore the broad band soft to hard X-ray properties with the analysis of combined XMM-Newton and Swift data. Out of these we found seven sources which exhibit potentially promising features of the relativistic disc reflection, such as a strong soft excess, a large Compton hump and/or a broadened Fe line. Longer observations of four of these sources with the currently operating satellite missions, such as Suzaku, XMM-Newton and NuStar and two others by such future missions as ASTRO-H, will be invaluable, in order to better understand the relativistic disc reflection closest to the central black hole and constrain such important effects of strong gravity as the black hole spin.

astro-ph.GA↗