321 research outputs found
Swift/BAT and RXTE Observations of the Peculiar X-ray Binary 4U 2206+54 - Disappearance of the 9.6 Day Modulation
Observations of the high-mass X-ray binary 4U 2206+54 with the Swift Burst
Alert Telescope (BAT) do not show modulation at the previously reported period
of 9.6 days found from observations made with the Rossi X-ray Timing Explorer
(RXTE) All-Sky Monitor (ASM). Instead, the strongest peak in the power spectrum
of the BAT light curve occurs at a period of 19.25 +/- 0.08 days, twice the
period found with the RXTE ASM. The maximum of the folded BAT light curve is
also delayed compared to the maximum of the folded ASM light curve. The most
recent ASM data folded on twice the 9.6 day period show similar morphology to
the folded BAT light curve. This suggests that the apparent period doubling is
a recent secular change rather than an energy-dependent effect. The 9.6 day
period is thus not a permanent strong feature of the light curve. We suggest
that the orbital period of 4U 2206+54 may be twice the previously proposed
value.Comment: Accepted for publication in The Astrophysical Journa
Swift Observations of Hard X-ray Emitting White Dwarfs in Symbiotic Stars
The X-ray emission from most accreting white dwarfs (WDs) in symbiotic binary
stars is quite soft. Several symbiotic WDs, however, produce strong X-ray
emission at energies greater than ~20 keV. The Swift BAT instrument has
detected hard X-ray emission from 4 such accreting WDs in symbiotic stars: RT
Cru, T CrB, CD -57 3057, and CH Cyg. In one case (RT Cru), Swift detected
X-rays out to greater than 50 keV at a > 5 sigma confidence level. Combining
data from the XRT and BAT detectors, we find that the 0.3-150 keV spectra of RT
Cru, T CrB, and CD -57 3057 are well described by emission from a
single-temperature, optically thin thermal plasma, plus an unresolved 6.4-6.9
keV Fe line complex. The X-ray spectrum of CH Cyg contains an additional bright
soft component. For all 4 systems, the spectra suffer high levels of absorption
from material that both fully and partially covers the source of hard X-rays.
The XRT data did not show any of the rapid, periodic variations that one would
expect if the X-ray emission were due to accretion onto a rotating, highly
magnetized WD. The X-rays were thus more likely from the accretion-disk
boundary layer around a massive, non-magnetic WD in each binary. The X-ray
emission from RT Cru varied on timescales of a few days. This variability is
consistent with being due to changes in the absorber that partially covers the
source, suggesting localized absorption from a clumpy medium moving into the
line of sight. The X-ray emission from CD -57 3057 and T CrB also varied during
the 9 months of Swift observations, in a manner that was also consistent with
variable absorption.Comment: Accepted for publication in ApJ. 9 pages, 6 figure
Correlations of the IR Luminosity and Eddington Ratio with a Hard X-ray Selected Sample of AGN
We use the SWIFT Burst Alert Telescope (BAT) sample of hard x-ray selected
active galactic nuclei (AGN) with a median redshift of 0.03 and the 2MASS J and
K band photometry to examine the correlation of hard x-ray emission to
Eddington ratio as well as the relationship of the J and K band nuclear
luminosity to the hard x-ray luminosity. The BAT sample is almost unbiased by
the effects of obscuration and thus offers the first large unbiased sample for
the examination of correlations between different wavelength bands. We find
that the near-IR nuclear J and K band luminosity is related to the BAT (14 -
195 keV) luminosity over a factor of in luminosity ()and thus is unlikely to be due to dust. We also find that the
Eddington ratio is proportional to the x-ray luminosity. This new result should
be a strong constraint on models of the formation of the broad band continuum.Comment: accepted to ApJ
Maternal Anxiety Associated with Newborn Hearing Screening
The purpose of this study was to determine if newborn hearing screening increases maternal anxiety. Mothers whose infants were screened for hearing were asked how worried they were prior to hospital discharge and again six weeks later. They were also asked if they were more concerned about their baby’s hearing than they were about other aspects of the infant’s health and behavior.
Results showed that mothers worried as much or more about many other aspects of their infants’ health and behavior as about hearing. Mothers whose infants had a false positive screening result were initially more worried about hearing than other aspects of their infant’s health, but this effect disappeared within six weeks. There were no significant differences at Time 1 or Time 2 for maternal anxiety as measured by the State Trait Anxiety Inventory between mothers whose infants had a false positive hearing screen compared to mothers of infants who passed their initial hearing screen.
Participation in newborn hearing screening is not associated with undue worry among mothers of newborns
The 1 keV to 200 keV X-ray Spectrum of NGC 2992 and NGC 3081
The Seyfert 2 galaxies NGC 2992 and NGC 3081 have been observed by INTEGRAL
and Swift. We report about the results and the comparison of the spectrum above
10 keV based on INTEGRAL IBIS/ISGRI, Swift/BAT, and BeppoSAX/PDS. A spectrum
can be extracted in the X-ray energy band ranging from 1 keV up to 200 keV.
Although NGC 2992 shows a complex spectrum below 10 keV, the hard tail observed
by various missions exhibits a slope with photon index = 2, independent on the
flux level during the observation. No cut-off is detectable up to the detection
limit around 200 keV. In addition, NGC 3081 is detected in the INTEGRAL and
Swift observation and also shows an unbroken Gamma = 1.8 spectrum up to 150
keV. These two Seyfert galaxies give further evidence that a high-energy
cut-off in the hard X-ray spectra is often located at energies E_C >> 100 keV.
In NGC 2992 a constant spectral shape is observed over a hard X-ray luminosity
variation by a factor of 11. This might indicate that the physical conditions
of the emitting hot plasma are constant, while the amount of plasma varies, due
to long-term flaring activity.Comment: 8 pages, 4 figures, accepted for publication in Ap
BAT X-ray Survey - III: X-ray Spectra and Statistical Properties
In this concluding part of the series of three papers dedicated to the
Swift/BAT hard X-ray survey (BXS), we focus on the X-ray spectral analysis and
statistical properties of the source sample. Using a dedicated method to
extract time-averaged spectra of BAT sources we show that Galactic sources
have, generally, softer spectra than extragalactic objects and that Seyfert 2
galaxies are harder than Seyfert 1s. The averaged spectrum of all Seyfert
galaxies is consistent with a power-law with photon index of 2.00 (+/-0.07).
The cumulative flux-number relation for the extragalactic sources in the 14-170
keV band is best described by a power-law with a slope alpha=1.55 (+/-0.20) and
a normalization of 9.6 AGN deg (or 396(+/-80) AGN
all-sky) above a flux level of 2erg cm s (~0.85
mCrab). The integration of the cumulative flux per unit area indicates that BAT
resolves 1-2% of the X-ray background emission in the 14-170 keV band. A
sub-sample of 24 extragalactic sources above the 4.5 sigma detection limit is
used to study the statistical properties of AGN. This sample comprises local
Seyfert galaxies (z=0.026, median value) and ~10% blazars. We find that 55% of
the Seyfert galaxies are absorbed by column densities of Log(N_H)>22, but that
none is a bona fide Compton-thick. This study shows the capabilities of BAT to
probe the hard X-ray sky to the mCrab level.Comment: Accepted for publication in The Astrophysical Journal; 42 pages, 4
tables, 51 figure
The Gamma-Ray Imaging Spectrometer (GRIS): A new balloon-borne experiment for gamma-ray line astronomy
High resolution gamma-ray spectroscopy is a relatively new field that holds great promise for further understanding of high energy astrophysical processes. When the high resolution gamma-ray spectrometer (GRSE) was removed from the GRO payload, a balloon program was initiated to permit continued development and improvement of instrumentation in this field, as well as continued scientific observations. The Gamma-Ray Imaging Spectrometer (GRIS) is one of the experiments selected as part of this program. The instrument contains a number of new and innovative features that are expected to produce a significant improvement in source location accuracy and sensitivity over previous balloon and satellite experiments
Suzaku Observations of Four Heavily Absorbed HMXBs
We report on Suzaku observations of four unidentified sources from the
INTEGRAL and Swift BAT Galactic plane surveys. All the sources have a large
neutral hydrogen column density and are likely members of an emerging class of
heavily absorbed high mass X-ray binary (HMXB) first identified in INTEGRAL
observations. Two of the sources in our sample are approximately constant flux
sources, one source shows periodic variation and one source exhibited a short,
bright X-ray outburst. The periodicity is transient, suggesting it is produced
by a neutron star in an elliptical orbit around a stellar wind source. We
analyze the flaring source in several segments to look for spectral variation
and discuss the implications of the findings for the nature of the source. We
conclude that all four sources in our sample can be identified with the
emerging class of highly absorbed HMXBs, that one is a newly identified
transient X-ray pulsar and that at least one is a newly identified supergiant
fast X-ray transient (SFXT).Comment: 22 pages, 5 figures, submitted to Ap
- …