12 research outputs found
Neutron Star Radius-to-mass Ratio from Partial Accretion Disc Occultation as Measured through Fe K Line Profiles
We present a new method to measure the radius-to-mass ratio (R/M) of weakly
magnetic, disc-accreting neutron stars by exploiting the occultation of parts
of the inner disc by the star itself. This occultation imprints characteristic
features on the X-ray line profile that are unique and are expected to be
present in low mass X-ray binary systems seen under inclinations higher than
~65 degrees. We analyse a NuSTAR observation of a good candidate system, 4U
1636-53, and find that X-ray spectra from current instrumentation are unlikely
to single out the occultation features owing to insufficient signal-to-noise.
Based on an extensive set of simulations we show that large-area X-ray
detectors of the future generation could measure R/M to ~2{\div}3% precision
over a range of inclinations. Such is the precision in radius determination
required to derive tight constraints on the equation of state of ultradense
matter and it represents the goal that other methods too aim to achieve in the
future.Comment: 17 pages, 8 figures; this is a pre-print edition of an article that
has been accepted for publication in the Astrophysical Journa
Science case study and scientific simulations for the enhanced X-ray Timing Polarimetry mission, eXTP
The X-ray astronomy mission eXTP (enhanced X-ray Timing Polarimetry) is designed to study matter under extreme conditions of density, gravity and magnetism. Primary
goals are the determination of the equation of state (EoS) of matter at supranuclear density,
the physics in extremely strong magnetic fields, the study of accretion in strong-field gravity
(SFG) regime. Primary targets include isolated and binary neutron stars, strong magneticfield systems like magnetars, and stellar-mass and supermassive black holes. In this paper
we report about key observations and simulations with eXTP on the primary objectives
involving accretion under SFG regimes and determination of NS-Eo
Scalp Psoriasiform Contact Dermatitis with Acute Telogen Effluvium due to Topical Minoxidil Treatment
Topical minoxidil, the only approved treatment for female pattern hair loss (FPHL), has been associated with scalp allergic contact dermatitis (ACD). We report the case of 2 female patients who developed ACD from minoxidil solution with severe telogen effluvium and psoriasiform scalp dermatitis. Scalp dermoscopy was useful to identify the psoriasiform vascular pattern, whereas patch testing made it possible to differentiate the cause of sensitization. In one case, minoxidil was the sole cause of scalp dermatitis, while in the other patient it was only the vehicle, thus permitting the patient to continue the treatment for FPHL
Extreme amplification regimes of the Schwarzschild gravitational lens
We investigated a complete set of relativistic images of a small source located at an arbitrary distance from a Schwarzschild black hole gravitational lens. This paper offers a description of a simple and efficient fully relativistic method for calculating the bolometric intensity amplification. We focused our analysis primarily on sources located at small radii and close angular distance from the caustic line, both behind and in front of the compact lens. We term the corresponding large deflection regime ‘extreme lensing’. We approximated the regime of fully-relativistic, extreme amplification of point sources by simple analytical formulae valid over a wide range of source distances. Using such approximations, we also derived formulae for the maximum amplification of extended sources close to or intercepted by the caustic line. Simple analytical approximations of the time delay between the brightest consecutive images in extreme amplification regimes are also presented
Disfiguring papular sarcoidosis of the face: dramatic improvement with pimecrolimus
Letter to the Edito