50 research outputs found
Two XTE A01 Projects: A Multifrequency Study of Circinus X-1 and a Search for Microsecond Variability From Bright Galactic X-Ray Source
This final report describes the research of a single common portion of the above-named two projects, conducted by G. Jernigan, i.e., the theory for a new method, a variation of a Kolmogorov-Smirnov test, for determining the fastest variability present in an X-ray source. The current phase involves testing the newly developed code on real example sources (CYG X1). Unfortunately, there are no calibration sources for testing the code, which therefore required the development of an X-ray source simulation code. The goal is to evaluate the sensitivity of the code for the detection of a range of different types of variability (bursts, pulsations, etc.)
Discovery of kHz Fluctuations in Centaurus X-3: Evidence for Photon Bubble Oscillations (PBO) and Turbulence in a High Mass X-ray Binary Pulsar
We report the discovery of kHz fluctuations, including quasi-periodic
oscillations (QPO) at ~330 Hz and ~760 Hz and a broadband kHz continuum in the
power density spectrum of the high mass X-ray binary pulsar Centaurus X-3.
These observations of Cen X-3 were carried out with the Rossi X-ray Timing
Explorer (RXTE). The fluctuation spectrum is flat from mHz to a few Hz, then
steepens to behavior between a few Hz and ~100 Hz. Above a hundred Hz,
the spectrum shows the QPO features, plus a flat continuum extending to ~1200
Hz and then falling out to ~1800 Hz. These results, which required the
co-adding three days of observations of Cen X-3, are at least as fast as the
fastest known variations in X-ray emission from an accreting compact object
(kHz QPO in LMXB sources) and probably faster since extension to ~1800 Hz is
indicated by the most likely parameterization of the data.
Multi-dimensional radiation hydrodynamics simulations of optically thick
plasma flow onto the magnetic poles of an accreting neutron star show that the
fluctuations at frequencies above 100 Hz are consistent with photon bubble
turbulence and oscillations (PBO) previously predicted to be observable in this
source. For a polar cap opening angle of 0.25 radians, we show that the
spectral form above 100 Hz is reproduced by the simulations, including the
frequencies of the QPO and the relative power in the QPO and the kHz continuum.
This has resulted in the first model-dependent measurement of the polar cap
size of an X-ray pulsar.Comment: received ApJ: April 1, 1999 accepted ApJ: September 1, 199
The X-ray Afterglows of GRB 020813 and GRB 021004 with Chandra HETGS: Possible Evidence for a Supernova Prior to GRB 020813
We report on the detection of an emission line near 1.3 keV, which we
associate with blue-shifted hydrogen-like sulfur (S XVI), in a 76.8 ksec
Chandra HETGS spectrum of the afterglow of GRB 020813. The line is detected at
3.3 sigma significance. We also find marginal evidence for a line possibly due
to hydrogen-like silicon (Si XIV) with the same blue-shift. A line from Fe is
not detected, though a very low significance Ni feature may be present. A
thermal model fits the data adequately, but a reflection model may provide a
better fit. There is marginal evidence that the equivalent width of the S XVI
line decrease as the burst fades. We infer from these results that a supernova
likely occurred >~ 2 months prior to the GRB. We find no discrete or variable
spectral features in the Chandra HETGS spectrum of the GRB 021004 afterglow.Comment: 26 pages, 11 figures, submitted to Ap
The Dynamic X-ray Sky of the Local Universe
Over the next decade, we can expect time domain astronomy to flourish at
optical and radio wavelengths. In parallel with these efforts, a dedicated
transient "machine" operating at higher energies (X-ray band through soft
gamma-rays) is required to reveal the unique subset of events with variable
emission predominantly visible above 100 eV. Here we focus on the transient
phase space never yet sampled due to the lack of a sensitive, wide-field and
triggering facility dedicated exclusively to catching high energy transients
and enabling rapid coordinated multi-wavelength follow-up. We first describe
the advancements in our understanding of known X-ray transients that can only
be enabled through such a facility and then focus on the classes of transients
theoretically predicted to be out of reach of current detection capabilities.
Finally there is the exciting opportunity of revealing new classes of X-ray
transients and unveiling their nature through coordinated follow-up
observations at longer wavelengths.Comment: 8 pages, 2 figures; White Paper submitted to the Astro2010 SSE pane
LSST Science Book, Version 2.0
A survey that can cover the sky in optical bands over wide fields to faint
magnitudes with a fast cadence will enable many of the exciting science
opportunities of the next decade. The Large Synoptic Survey Telescope (LSST)
will have an effective aperture of 6.7 meters and an imaging camera with field
of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over
20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with
fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a
total point-source depth of r~27.5. The LSST Science Book describes the basic
parameters of the LSST hardware, software, and observing plans. The book
discusses educational and outreach opportunities, then goes on to describe a
broad range of science that LSST will revolutionize: mapping the inner and
outer Solar System, stellar populations in the Milky Way and nearby galaxies,
the structure of the Milky Way disk and halo and other objects in the Local
Volume, transient and variable objects both at low and high redshift, and the
properties of normal and active galaxies at low and high redshift. It then
turns to far-field cosmological topics, exploring properties of supernovae to
z~1, strong and weak lensing, the large-scale distribution of galaxies and
baryon oscillations, and how these different probes may be combined to
constrain cosmological models and the physics of dark energy.Comment: 596 pages. Also available at full resolution at
http://www.lsst.org/lsst/sciboo
LSST: from Science Drivers to Reference Design and Anticipated Data Products
(Abridged) We describe here the most ambitious survey currently planned in
the optical, the Large Synoptic Survey Telescope (LSST). A vast array of
science will be enabled by a single wide-deep-fast sky survey, and LSST will
have unique survey capability in the faint time domain. The LSST design is
driven by four main science themes: probing dark energy and dark matter, taking
an inventory of the Solar System, exploring the transient optical sky, and
mapping the Milky Way. LSST will be a wide-field ground-based system sited at
Cerro Pach\'{o}n in northern Chile. The telescope will have an 8.4 m (6.5 m
effective) primary mirror, a 9.6 deg field of view, and a 3.2 Gigapixel
camera. The standard observing sequence will consist of pairs of 15-second
exposures in a given field, with two such visits in each pointing in a given
night. With these repeats, the LSST system is capable of imaging about 10,000
square degrees of sky in a single filter in three nights. The typical 5
point-source depth in a single visit in will be (AB). The
project is in the construction phase and will begin regular survey operations
by 2022. The survey area will be contained within 30,000 deg with
, and will be imaged multiple times in six bands, ,
covering the wavelength range 320--1050 nm. About 90\% of the observing time
will be devoted to a deep-wide-fast survey mode which will uniformly observe a
18,000 deg region about 800 times (summed over all six bands) during the
anticipated 10 years of operations, and yield a coadded map to . The
remaining 10\% of the observing time will be allocated to projects such as a
Very Deep and Fast time domain survey. The goal is to make LSST data products,
including a relational database of about 32 trillion observations of 40 billion
objects, available to the public and scientists around the world.Comment: 57 pages, 32 color figures, version with high-resolution figures
available from https://www.lsst.org/overvie
HETE-2 Observations of the X-Ray Flash XRF 040916
A long X-ray flash was detected and localized by the instruments aboard the
High Energy Transient Explorer II (HETE-2) at 00:03:30 UT on 2004 September 16.
The position was reported to the GRB Coordinates Network (GCN) approximately 2
hours after the burst. This burst consists of two peaks separated by 200 s,
with durations of 110 s and 60 s. We have analyzed the energy spectra of the
1st and 2nd peaks observed with the Wide Field X-Ray Monitor (WXM) and the
French Gamma Telescope (FREGATE). We discuss the origin of the 2nd peak in
terms of flux variabilities and timescales. We find that it is most likely part
of the prompt emission, and is explained by the long-acting engine model. This
feature is similar to some bright X-ray flares detected in the early afterglow
phase of bursts observed by the Swift satellite.Comment: 9 pages, 4 figures, Accepted for publication in PAS