49 research outputs found
Deep Chandra Survey of the Small Magellanic Cloud. II. Timing Analysis of X-ray Pulsars
We report the timing analysis results of X-ray pulsars from a recent deep
Chandra survey of the Small Magellanic Cloud (SMC). We have analyzed a total
exposure of 1.4 Ms from 31 observations over a 1.2 deg region in the SMC
under a Chandra X-ray Visionary Program. Using the Lomb-Scargle and epoch
folding techniques, we have detected periodic modulations from 20 pulsars and a
new candidate pulsar. The survey also covers 11 other pulsars with no clear
sign of periodic modulation. The 0.5-8 keV X-ray luminosity () of the
pulsars ranges from to erg s at 60 kpc. All the
Chandra sources with erg s exhibit
X-ray pulsations. The X-ray spectra of the SMC pulsars (and high mass X-ray
binaries) are in general harder than those of the SMC field population. All but
SXP~8.02 can be fitted by an absorbed power-law model with a photon index of
1.5. The X-ray spectrum of the known magnetar SXP~8.02 is
better fitted with a two-temperature blackbody model. Newly measured pulsation
periods of SXP~51.0, SXP~214 and SXP~701 are significantly different from the
previous XMM-Newton and RXTE measurements. This survey provides a rich data set
for energy-dependent pulse profile modeling. Six pulsars show an almost
eclipse-like dip in the pulse profile. Phase-resolved spectral analysis reveals
diverse spectral variation during pulsation cycle: e.g., for an absorbed
power-law model, some exhibit an (anti)-correlation between absorption and
X-ray flux, while others show more intrinsic spectral variation.Comment: 24 pages, 19 figures, 11 tables, submitted to Ap
The First TESS Self-Lensing Pulses: Revisiting KIC 12254688
We report the observations of two self-lensing pulses from KIC 12254688 in
Transiting Exoplanet Survey Satellite (TESS) light curves. This system,
containing a F2V star and white-dwarf companion, was amongst the first
self-lensing binary systems discovered by the Kepler Space Telescope over the
past decade. Each observed pulse occurs when the white dwarf transits in front
of its companion star, gravitationally lensing the star's surface, thus making
it appear brighter to a distant observer. These two pulses are the very first
self-lensing events discovered in TESS observations. We describe the methods by
which the data were acquired and detrended, as well as the best-fit binary
parameters deduced from our self-lensing+radial velocity model. We highlight
the difficulties of finding new self-lensing systems with TESS, and we discuss
the types of self-lensing systems that TESS may be more likely to discover in
the future.Comment: Accepted for publication in ApJ Letters, 12 Pages, 6 Figures, and 1
Tabl
Flaring Activity from Quiescent States in Neutron-Star X-Ray Binaries
We examine systematically the observed X-ray luminosity jumps (or flares) from quiescent states in millisecond binary pulsars (MSBPs) and high-mass X-ray binary pulsars (HMXBPs). We rely on the published X-ray light curves of seven pulsars: four HMXBPs, two MSBPs and the ultraluminous X-ray pulsar M82 X-2. We discuss the physics of their flaring activities or lack thereof, paying special attention to their emission properties when they are found on the propeller line, inside the Corbet gap or near the light-cylinder barrier.We provide guiding principles for future interpretations of faint X-ray observations, as well as a method of constraining the propeller lines and the dipolar surfacemagnetic fields of pulsars using a variety of quiescent states. In the process, we clarify some disturbing inaccuracies that have made their way into the published literature
Radial Distribution of X-ray Point Sources near the Galactic Center
(Abridged) We present the LogN-LogS and spatial distributions of X-ray point
sources in seven Galactic Bulge (GB) fields within 4 deg from the Galactic
Center (GC). We compare the properties of 1159 X-ray point sources discovered
in our deep (100 ks) Chandra observations of three low extinction Window fields
near the GC with the X-ray sources in the other GB fields centered around Sgr
B2, Sgr C, the Arches Cluster and Sgr A* using Chandra archival data. To reduce
the systematic errors induced by the uncertain X-ray spectra of the sources
coupled with field-and-distance dependent extinction, we classify the X-ray
sources using quantile analysis and estimate their fluxes accordingly. The
result indicates the GB X-ray population is highly concentrated at the center,
more heavily than the stellar distribution models. We also compare the total
X-ray and infrared surface brightness using the Chandra and Spitzer
observations of the regions. The radial distribution of the total infrared
surface brightness from the 3.6 band m images appears to resemble the
radial distribution of the X-ray point sources better than predicted by the
stellar distribution models. Assuming a simple power law model for the X-ray
spectra, the closer to the GC the intrinsically harder the X-ray spectra
appear, but adding an iron emission line at 6.7 keV in the model allows the
spectra of the GB X-ray sources to be largely consistent across the region.
This implies that the majority of these GB X-ray sources can be of the same or
similar type. Their X-ray luminosity and spectral properties support the idea
that the most likely candidate is magnetic cataclysmic variables (CVs),
primarily intermediate polars (IPs). Their observed number density is also
consistent with the majority being IPs.Comment: 17 pages, 7 figures, 6 tables, accepted for publication in
Astrophysical Journa