1,115 research outputs found
Development of a graphite radiant heater
Design and tests of graphite radiant heater for high heat flux source in spacecraft thermostructural test
Long-term X-ray changes in the emission from the anomalous X-ray pulsar 4U 0142+61
We present results obtained from X-ray observations of the anomalous X-ray
pulsar (AXP) 4U 0142+61 taken between 2000-2007 using XMM-Newton, Chandra and
Swift. In observations taken before 2006, the pulse profile is observed to
become more sinusoidal and the pulsed fraction increased with time. These
results confirm those derived using the Rossi X-ray Timing Explorer and expand
the observed evolution to energies below 2 keV. The XMM-Newton total flux in
the 0.5-10 keV band is observed to be nearly constant in observations taken
before 2006, while an increase of ~10% is seen afterwards and coincides with
the burst activity detected from the source in 2006-2007. After these bursts,
the evolution towards more sinusoidal pulse profiles ceased while the pulsed
fraction showed a further increase. No evidence for large-scale, long-term
changes in the emission as a result of the bursts is seen. The data also
suggest a correlation between the flux and hardness of the spectrum, with
brighter observations on average having a harder spectrum. As pointed out by
other authors, we find that the standard blackbody plus power-law model does
not provide the best spectral fit to the emission from 4U 0142+61. We also
report on observations taken with the Gemini telescope after two bursts. These
observations show source magnitudes consistent with previous measurements. Our
results demonstrate the wide range of X-ray variability characteristics seen in
AXPs and we discuss them in light of current emission models for these sources.Comment: 10 pages, 9 figures, in emulateapj style. Submitted to Ap
The first multi-wavelength campaign of AXP 4U 0142+61 from radio to hard X-rays
For the first time a quasi-simultaneous multi-wavelength campaign has been
performed on an Anomalous X-ray Pulsar from the radio to the hard X-ray band.
4U 0142+61 was an INTEGRAL target for 1 Ms in July 2005. During these
observations it was also observed in the X-ray band with Swift and RXTE, in the
optical and NIR with Gemini North and in the radio with the WSRT. In this paper
we present the source-energy distribution. The spectral results obtained in the
individual wave bands do not connect smoothly; apparently components of
different origin contribute to the total spectrum. Remarkable is that the
INTEGRAL hard X-ray spectrum (power-law index 0.79 +/- 0.10) is now measured up
to an energy of ~230 keV with no indication of a spectral break. Extrapolation
of the INTEGRAL power-law spectrum to lower energies passes orders of magnitude
underneath the NIR and optical fluxes, as well as the low ~30 microJy (2 sigma)
upper limit in the radio band.Comment: 6 pages, 1 figure. To be published in the proceedings of the
conference "Isolated Neutron Stars: from the Interior to the Surface" (April
24-28, 2006, London, UK), eds. S. Zane, R. Turolla and D. Pag
Echo-Mapping of Swift J1753.5-0127
We present two epochs of coordinated X-ray-optical timing observations of the
black hole candidate Swift J1753.5-0127 during its 2005 outburst. The first
epoch in July occurred at outburst peak. Two consecutive nights of observations
using the McDonald Observatory Argos camera with the Rossi X-ray Timing
Explorer show a consistent correlation with an immediate response and an
extended tail lasting ~5s. The properties of the variability and the
correlation are consistent with thermal reprocessing in an accretion disk. The
shortness of the lag suggests a short orbital period consistent with that
recently claimed. The second epoch in August used the VLT FORS2 HIT mode again
in conjunction with RXTE. Again a repeatable correlation is seen between two
independent subsets of the data. In this case, though, the cross-correlation
function has an unusual structure comprising a dip followed by a double-peak.
We suggest that this may be equivalent to the dip plus single peak structure
seen by Kanbach et al. (2001) in XTE J1118+480 and attributed there to
synchrotron emission; a similar structure was seen during later activity of
Swift J1753.5-0127 by Durant et al. (2008).Comment: 7 pages, accepted for publication in Monthly Notices of the Royal
Astronomical Societ
A Strong, Broad Absorption Feature in the X-ray Spectrum of the Nearby Neutron Star RX J1605.3+3249
We present X-ray spectra taken with XMM-Newton of RX J1605.3+3249, the third
brightest in the class of nearby, thermally emitting neutron stars. In contrast
to what is the case for the brightest object, RX J1856.5-3754, we find that the
spectrum of RX J1605.3+3249 cannot be described well by a pure black body, but
shows a broad absorption feature at 27\AA (0.45 keV). With this, it joins the
handful of isolated neutron stars for which spectral features arising from the
surface have been detected. We discuss possible mechanisms that might lead to
the features, as well as the overall optical to X-ray spectral energy
distribution, and compare the spectrum with what is observed for the other
nearby, thermally emitting neutron stars. We conclude that we may be observing
absorption due to the proton cyclotron line, as was suggested for the other
sources, but weakened due to the strong-field quantum electrodynamics effect of
vacuum resonance mode conversion.Comment: 30 pages, 7 figures, accepted for publication in Ap
Correlated Infrared and X-ray Flux Changes Following the 2002 June Outburst of the Anomalous X-ray Pulsar 1E 2259+586
We present the results of a near-infrared monitoring program of the Anomalous
X-ray Pulsar 1E 2259+586, performed at the Gemini Observatory. This program
began three days after the pulsar's 2002 June outburst, and spans ~1.5 years.
We find that after an initial increase associated with the outburst, the
near-infrared flux decreased continually and reached the pre-burst quiescent
level after about one year. We compare both the near-infrared flux enhancement
and its decay to those of the X-ray afterglow, and find them to be remarkably
consistent. Fitting simple power laws to the RXTE pulsed flux and near-infrared
data for t>1 day post-burst, we find the following decay indices:
alpha=-0.21+/-0.01 (X-ray), alpha=-0.21+/-0.02 (near-infrared), where flux is a
function of time such that F is proportional to t^alpha. This suggests that the
enhanced infrared and X-ray fluxes have a physical link post-outburst, most
likely from the neutron-star magnetosphere.Comment: 11 pages, 1 figure, accepted for publication in ApJL; minor wording
changes, added observation program IDs, improved figure resolutio
The variable radio-to-X-ray spectrum of the magnetar XTE J1810-197
We have observed the 5.54s anomalous X-ray pulsar XTE J1810-197 at radio,
millimeter, and infrared (IR) wavelengths, with the aim of learning about its
broad-band spectrum. At the IRAM 30m telescope, we have detected the magnetar
at 88 and 144GHz, the highest radio-frequency emission ever seen from a pulsar.
At 88GHz we detected numerous individual pulses, with typical widths ~2ms and
peak flux densities up to 45Jy. Together with nearly contemporaneous
observations with the Parkes, Nancay, and Green Bank telescopes, we find that
in late 2006 July the spectral index of the pulsar was -0.5<alpha<0 over the
range 1.4-144GHz. Nine dual-frequency Very Large Array and Australia Telescope
Compact Array observations in 2006 May-September are consistent with this
finding, while showing variability of alpha with time. We infer from the IRAM
observations that XTE J1810-197 remains highly linearly polarized at millimeter
wavelengths. Also, toward this pulsar, the transition frequency between strong
and weak scattering in the interstellar medium may be near 50GHz. At Gemini, we
detected the pulsar at 2.2um in 2006 September, at the faintest level yet
observed, K_s=21.89+-0.15. We have also analyzed four archival IR Very Large
Telescope observations (two unpublished), finding that the brightness
fluctuated within a factor of 2-3 over a span of 3 years, unlike the monotonic
decay of the X-ray flux. Thus, there is no correlation between IR and X-ray
flux, and it remains uncertain whether there is any correlation between IR and
radio flux.Comment: Accepted for publication in ApJ; contains improved discussion of
infrared uncertaintie
Recent Progress on Anomalous X-ray Pulsars
I review recent observational progress on Anomalous X-ray Pulsars, with an
emphasis on timing, variability, and spectra. Highlighted results include the
recent timing and flux stabilization of the notoriously unstable AXP 1E
1048.1-5937, the remarkable glitches seen in two AXPs, the newly recognized
variety of AXP variability types, including outbursts, bursts, flares, and
pulse profile changes, as well as recent discoveries regarding AXP spectra,
including their surprising hard X-ray and far-infrared emission, as well as the
pulsed radio emission seen in one source. Much has been learned about these
enigmatic objects over the past few years, with the pace of discoveries
remaining steady. However additional work on both observational and theoretical
fronts is needed before we have a comprehensive understanding of AXPs and their
place in the zoo of manifestations of young neutron stars.Comment: 10 pages, 6 figures; to appear in proceedings of the conference
"Isolated Neutron Stars: From the Interior to the Surface" eds. S. Zane, R.
Turolla, D. Page; Astrophysics & Space Science in pres
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Evaluating the structure and magnitude of the ash plume during the initial phase of the 2010 Eyjafjallajökull eruption using lidar observations and NAME simulations
The Eyjafjallajökull volcano in Iceland erupted explosively on 14 April 2010, emitting a plume of ash into the atmosphere. The ash was transported from Iceland toward Europe where mostly cloud-free skies allowed ground-based lidars at Chilbolton in England and Leipzig in Germany to estimate the mass concentration in the ash cloud as it passed overhead. The UK Met Office's Numerical Atmospheric-dispersion Modeling Environment (NAME) has been used to simulate the evolution of the ash cloud from the Eyjafjallajökull volcano during the initial phase of the ash emissions, 14–16 April 2010. NAME captures the timing and sloped structure of the ash layer observed over Leipzig, close to the central axis of the ash cloud. Relatively small errors in the ash cloud position, probably caused by the cumulative effect of errors in the driving meteorology en route, result in a timing error at distances far from the central axis of the ash cloud. Taking the timing error into account, NAME is able to capture the sloped ash layer over the UK. Comparison of the lidar observations and NAME simulations has allowed an estimation of the plume height time series to be made. It is necessary to include in the model input the large variations in plume height in order to accurately predict the ash cloud structure at long range. Quantitative comparison with the mass concentrations at Leipzig and Chilbolton suggest that around 3% of the total emitted mass is transported as far as these sites by small (<100 μm diameter) ash particles
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