29 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
Addressing Outstanding Problems in the Physics of Massive Stars with the Line Emission Mapper X-ray Probe
We present some of the salient aspects of the scientific motivation for high
resolution soft X-ray spectroscopy of early-type stars with the Line Emission
Mapper X-ray Probe. The major strength of {\it LEM} for hot star physics is its
large effective area, aided by the inherent energy resolution of its
microcalorimeter that readily achieves resolving powers of 1000 and obviates
the need for relatively inefficient dispersive optical elements. This increased
sensitivity enables much fainter and more distant high mass stars to be
observed than are accessible with present-day facilities, greatly increasing
the pool of potential targets. For brighter sources, the sensitivity opens up
time domain studies, wherein sufficient signal can be garnered in short order
and exposure times, probing source variations on ks timescales. We argue that
these capabilities of {\it LEM} will yield breakthroughs in all types of hot
star systems, from understanding single OB and WR star winds and how they vary
with metallicity, to probing the shocks of colliding wind systems and the
magnetically channeled winds of magnetic OB stars. {\it LEM} will also study
the energetics of WR star bubbles and feedback from their powerful pre-SN
stellar winds.Comment: A Line Emission Mapper White Pape
On the Nature of the X-ray Emission from the Ultraluminous X-ray Source, M33 X-8: New Constraints from NuSTAR and XMM-Newton
We present nearly simultaneous NuSTAR and XMM-Newton observations of the
nearby (832 kpc) ultraluminous X-ray source (ULX) M33 X-8. M33 X-8 has a 0.3-10
keV luminosity of LX ~ 1.4 x 10^39 erg/s, near the boundary of the
"ultraluminous" classification, making it an important source for understanding
the link between typical Galactic X-ray binaries and ULXs. Past studies have
shown that the 0.3-10 keV spectrum of X-8 can be characterized using an
advection-dominated accretion disk model. We find that when fitting to our
NuSTAR and XMM-Newton observations, an additional high-energy (>10 keV)
Comptonization component is required, which allows us to rule out single
advection-dominated disk and classical sub-Eddington models. With our new
constraints, we analyze XMM-Newton data taken over the last 17 years to show
that small (~30%) variations in the 0.3-10 keV flux of M33 X-8 result in
spectral changes similar to those observed for other ULXs. The two most likely
phenomenological scenarios suggested by the data are degenerate in terms of
constraining the nature of the accreting compact object (i.e., black hole
versus neutron star). We further present a search for pulsations using our
suite of data; however, no clear pulsations are detected. Future observations
designed to observe M33 X-8 at different flux levels across the full 0.3-30 keV
range would significantly improve our constraints on the nature of this
important source.Comment: Accepted for publication in ApJ (15 pages, 4 tables, 6 figures
SXP214, an X-ray Pulsar in the Small Magellanic Cloud, Crossing the Circumstellar Disk of the Companion
Located in the Small Magellanic Cloud (SMC), SXP214 is an X-ray pulsar in a
high mass X-ray binary system with a Be-star companion. A recent survey of the
SMC under a Chandra X-ray Visionary program found the source in a transition
when the X-ray flux was on a steady rise. The Lomb-Scargle periodogram revealed
a pulse period of 211.49 +/- 0.42 s, which is significantly (>5sigma) shorter
than the previous measurements with XMM-Newton and RXTE. This implies that the
system has gone through sudden spin-up episodes recently. The pulse profile
shows a sharp eclipse-like feature with a modulation amplitude of >95%. The
linear rise of the observed X-ray luminosity from <~2x to 7x10^35 erg s^-1 is
correlated with steady softening of the X-ray spectrum, which can be described
by the changes in the local absorption from N_H ~ 10^24 to <~10^20 cm^-2 for an
absorbed power-law model. The soft X-ray emission below 2 keV was absent in the
early part of the observation when only the pulsating hard X-ray component was
observed, whereas at later times both soft and hard X-ray components were
observed pulsating. A likely explanation is that the neutron star was initially
hidden in the circumstellar disk of the companion, and later came out of the
disk with the accreted material that continued fueling the observed pulsation.Comment: 8 pages, 4 figures, 1 table, accepted for publication in Ap