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28 papers
Observatory Science with eXTP
Ping Zhou, Jirong Mao, Liang Zhang +97
Scheduled for launch in 2030, the enhanced X-ray Timing and Polarization (eXTP) telescope is a Chinese space-based mission aimed at studying extreme conditions and phenomena in ast…
Constraining the Neutron Star Mass--Radius Relation and Dense Matter Equation of State with NICER. III. Model Description and Verification of Parameter Estimation Codes
Slavko Bogdanov, Alexander J. Dittmann, Wynn C. G. Ho +16
We describe the X-ray pulse profile models we use, and how we use them, to analyze Neutron Star Interior Composition Explorer (NICER) observations of rotation-powered millisecond p…
Constraining the Neutron Star Mass-Radius Relation and Dense Matter Equation of State with NICER. II. Emission from Hot Spots on a Rapidly Rotating Neutron Star
Slavko Bogdanov, Frederick K. Lamb, Simin Mahmoodifar +10
We describe the model of surface emission from a rapidly rotating neutron star that is applied to Neutron Star Interior Composition Explorer X-ray data of millisecond pulsars in or…
PSR J0030+0451 Mass and Radius from NICER Data and Implications for the Properties of Neutron Star Matter
M. C. Miller, F. K. Lamb, A. J. Dittmann +18
Neutron stars are not only of astrophysical interest, but are also of great interest to nuclear physicists, because their attributes can be used to determine the properties of the…
NICER Observation of Unusual Burst Oscillations in 4U 1728-34
Simin Mahmoodifar, Tod E. Strohmayer, Peter Bult +9
The Neutron Star Interior Composition Explorer (NICER) has observed seven thermonuclear X-ray bursts from the Low Mass X-ray Binary (LMXB) neutron star 4U 1728-34 from the start of…
NICER Discovers Spectral Lines During Photospheric Radius Expansion Bursts from 4U 1820-30: Evidence for Burst-driven Winds
T. E. Strohmayer, D. Altamirano, Z. Arzoumanian +14
We report the discovery with the Neutron Star Interior Composition Explorer (NICER) of narrow emission and absorption lines during photospheric radius expansion (PRE) X-ray bursts…
NICER Detection of Strong Photospheric Expansion during a Thermonuclear X-Ray Burst from 4U 1820-30
L. Keek, Z. Arzoumanian, D. Chakrabarty +13
The Neutron Star Interior Composition Explorer (NICER) on the International Space Station (ISS) observed strong photospheric expansion of the neutron star in 4U 1820-30 during a Ty…
NICER Observes the Effects of an X-Ray Burst on the Accretion Environment in Aql X-1
L. Keek, Z. Arzoumanian, P. Bult +18
Accretion disks around neutron stars regularly undergo sudden strong irradiation by Type I X-ray bursts powered by unstable thermonuclear burning on the stellar surface. We investi…
NICER Discovers the Ultracompact Orbit of the Accreting Millisecond Pulsar IGR J17062-6143
Tod E. Strohmayer, Zaven Arzoumanian, Slavko Bogdanov +17
We present results of recent Neutron Star Interior Composition Explorer observations of the accreting millisecond X-ray pulsar IGR J17062-6143 that show that it resides in a circul…
NICER Discovers mHz Oscillations in the "Clocked" Burster GS 1826-238
Tod E. Strohmayer, Keith C. Gendreau, Diego Altamirano +12
We report the discovery with the Neutron Star Interior Composition Explorer (NICER) of mHz X-ray brightness oscillations from the "clocked burster." NICER observed the source in th…
A NICER look at the Aql X-1 hard state
Peter Bult, Zaven Arzoumanian, Edward M. Cackett +16
We report on a spectral-timing analysis of the neutron star low-mass X-ray binary Aql~X-1 with the Neutron Star Interior Composition Explorer (NICER) on the International Space Sta…
NICER Detects a Soft X-ray Kilohertz Quasi-periodic Oscillation in 4U 0614+09
Peter Bult, Diego Altamirano, Zaven Arzoumanian +16
We report on the detection of a kilohertz quasi-periodic oscillation (QPO) with the Neutron Star Interior Composition Explorer (NICER). Analyzing approximately 165 ks of NICER expo…
Where Are the r-modes? Chandra Observations of Millisecond Pulsars
Simin Mahmoodifar, Tod Strohmayer
We present the results of {\it Chandra} observations of two non-accreting millisecond pulsars, PSRs J16402224 (J1640) and J17092313 (J1709), with low inferred magnetic fields…
eXTP -- enhanced X-ray Timing and Polarimetry Mission
S. N. Zhang, M. Feroci, A. Santangelo +181
eXTP is a science mission designed to study the state of matter under extreme conditions of density, gravity and magnetism. Primary targets include isolated and binary neutron star…
X-ray Burst Oscillations: From Flame Spreading to the Cooling Wake
Simin Mahmoodifar, Tod Strohmayer
Type I X-ray bursts are thermonuclear flashes observed from the surfaces of accreting neutron stars (NSs) in Low Mass X-ray Binaries. Oscillations have been observed during the ris…
The LOFT perspective on neutron star thermonuclear bursts
J. J. M. in 't Zand, D. Altamirano, D. R. Ballantyne +31
This is a White Paper in support of the mission concept of the Large Observatory for X-ray Timing (LOFT), proposed as a medium-sized ESA mission. We discuss the potential of LOFT f…
Discovery of a Neutron Star Oscillation Mode During a Superburst
Tod Strohmayer, Simin Mahmoodifar
Neutron stars are among the most compact objects in the universe and provide a unique laboratory for the study of cold ultra-dense matter. While asteroseismology can provide a powe…
A new crystalline phase in magnetar crusts
Paulo F. Bedaque, Simin Mahmoodifar, Nathan Ng +1
We show that ions at the low densities and high magnetic fields relevant to the outer crust of magnetars form a novel crystalline phase where ions are strongly coupled along the ma…
A Non-radial Oscillation Mode in an Accreting Millisecond Pulsar?
Tod Strohmayer, Simin Mahmoodifar
We present results of targeted searches for signatures of non-radial oscillation modes (such as r- and g-modes) in neutron stars using {\it RXTE} data from several accreting millis…
Friedel crystals and the outer crust of magnetars
Paulo F. Bedaque, Simin Mahmoodifar, Srimoyee Sen
The strong magnetic fields found on the surface of magnetars are known to have profound effects in the physics of atoms in magnetar envelopes. We argue that the Friedel oscillation…
Upper bounds on r-mode amplitudes from observations of low-mass X-ray binary neutron stars
Simin Mahmoodifar, Tod Strohmayer
We present upper limits on the amplitude of r-mode oscillations, and gravitational-radiation-induced spin-down rates, in low mass X-ray binary neutron stars, under the assumption t…
Impact of r-modes on the cooling of neutron stars
Mark G. Alford, Simin Mahmoodifar, Kai Schwenzer
Studying the frequency and temperature evolution of a compact star can give us valuable information about the microscopic properties of the matter inside the star. In this paper we…
Viscous damping of r-modes: Large amplitude saturation
Mark G. Alford, Simin Mahmoodifar, Kai Schwenzer
We analyze the viscous damping of r-mode oscillations of compact stars, taking into account non-linear viscous effects in the large-amplitude regime. The qualitatively different ca…
Non-linear viscous saturation of r-modes
Mark Alford, Simin Mahmoodifar, Kai Schwenzer
Pulsar spin frequencies and their time evolution are an important source of information on compact stars and their internal composition. Oscillations of the star can reduce the rot…