1,045 research outputs found
X-ray and UV observations of nova V598 Puppis between 147 and 255 days after outburst
Aims: The launch of Swift has allowed many more novae to be observed
regularly over the X-ray band. Such X-ray observations of novae can reveal
ejecta shocks and the nuclear burning white dwarf, allowing estimates to be
made of the ejecta velocity. Methods: We analyse XMM-Newton and Swift X-ray and
UV observations of the nova V598 Pup, which was initially discovered in the
XMM-Newton slew survey. These data were obtained between 147 and 255 days after
the nova outburst, and are compared with the earlier, brighter slew detection.
Results: The X-ray spectrum consists of a super-soft source, with the soft
emission becoming hotter and much fainter between days ~147 and ~172 after the
outburst, and a more slowly declining optically thin component, formed by
shocks with kT ~ 200-800 eV (corresponding to velocities of 400-800 km s^-1).
The main super-soft phase had a duration of less than 130 days. The Reflection
Grating Spectrometer data show evidence of emission lines consistent with
optically thin emission of kT ~100 eV and place a limit on the density of the
surrounding medium of log(n_e/cm^-3) < 10.4 at the 90 % level. The UV emission
is variable over short timescales and fades by at least one magnitude (at
lambda ~ 2246-2600 angstrom) between days 169 and 255.Comment: 6 pages, 5 figures, accepted for publication in A&
The SSS phase of RS Ophiuchi observed with Chandra and XMM-Newton I.: Data and preliminary Modeling
The phase of Super-Soft-Source (SSS) emission of the sixth recorded outburst
of the recurrent nova RS Oph was observed twice with Chandra and once with
XMM-Newton. The observations were taken on days 39.7, 54.0, and 66.9 after
outburst. We confirm a 35-sec period on day 54.0 and found that it originates
from the SSS emission and not from the shock. We discus the bound-free
absorption by neutral elements in the line of sight, resonance absorption lines
plus self-absorbed emission line components, collisionally excited emission
lines from the shock, He-like intersystem lines, and spectral changes during an
episode of high-amplitude variability. We find a decrease of the oxygen K-shell
absorption edge that can be explained by photoionization of oxygen. The
absorption component has average velocities of -1286+-267 km/s on day 39.7 and
of -771+-65 km/s on day 66.9. The wavelengths of the emission line components
are consistent with their rest wavelengths as confirmed by measurements of
non-self absorbed He-like intersystem lines. We have evidence that these lines
originate from the shock rather than the outer layers of the outflow and may be
photoexcited in addition to collisional excitations. We found collisionally
excited emission lines that are fading at wavelengths shorter than 15A that
originate from the radiatively cooling shock. On day 39.5 we find a systematic
blue shift of -526+-114 km/s from these lines. We found anomalous He-like f/i
ratios which indicates either high densities or significant UV radiation near
the plasma where the emission lines are formed. During the phase of strong
variability the spectral hardness light curve overlies the total light curve
when shifted by 1000sec. This can be explained by photoionization of neutral
oxygen in the line of sight if the densities of order 10^{10}-10^{11} cm^{-3}.Comment: 16 pages, 10 figures, 4 tables. Accepted by ApJ; v2: Co-author
Woodward adde
Swift X-ray Observations of Classical Novae
The new gamma-ray burst mission Swift has obtained pointed observations of
several classical novae in outburst. We analyzed all the observations of
classical novae from the Swift archive up to 30 June, 2006. We analyzed usable
observations of 12 classical novae and found 4 non-detections, 3 weak sources
and 5 strong sources. This includes detections of 2 novae exhibiting spectra
resembling those of Super Soft X-ray binary Source spectra (SSS) implying
ongoing nuclear burning on the white dwarf surface. With these new Swift data,
we add to the growing statistics of the X-ray duration and characteristics of
classical novae.Comment: Accepted for ApJ; this version contains additional material: 18
pages, 16 figure
Short-period X-ray oscillations in super-soft novae and persistent SSS
Transient short-period <100s oscillations have been found in the X-ray light
curves of three novae during their SSS phase and in one persistent SSS. We
pursue an observational approach to determine possible driving mechanisms and
relations to fundamental system parameters such as the white dwarf mass.
We performed a systematic search for short-period oscillations in all
available XMM-Newton and Chandra X-ray light curves of persistent SSS and novae
during their SSS phase. To study time evolution, we divided each light curve
into short time segments and computed power spectra. We then constructed
dynamic power spectra from which we identified transient periodic signals even
when only present for a short time. From all time segments of each system, we
computed fractions of time when periodic signals were detected.
In addition to the previously known systems with short-period oscillations,
RS Oph (35s), KT Eri (35s), V339 Del (54s), and Cal 83 (67s), we found one
additional system, LMC 2009a (33s), and also confirm the 35s period from
Chandra data of KT Eri. The amplitudes of oscillations are of order <15% of the
respective count rates and vary without any clear dependence on the X-ray count
rate. The fractions of the time when the respective periods were detected at
2-sigma significance (duty cycle) are 11.3%, 38.8%, 16.9%, 49.2%, and 18.7% for
LMC 2009a, RS Oph, KT Eri, V339 Del, and Cal 83, respectively. The respective
highest duty cycles found in a single observation are 38.1%, 74.5%, 61.4%,
67.8%, and 61.8%.Comment: accepted for publication in A&
Coronal density diagnostics with Helium-like triplets: CHANDRA--LETGS observations of Algol, Capella, Procyon, Eps Eri, Alpha Cen A&B, UX Ari, AD Leo, YY Gem, and HR1099
We present an analysis of ten cool stars (Algol, Capella, Procyon, Eps Eri,
Alpha Cen A&B, UX Ari, AD Leo, YY Gem, and HR1099) observed with the Low Energy
Transmission Grating Spectrometer (LETGS) on board the Chandra X-ray
Observatory. This sample contains all cools stars observed with the LETGS
presently available to us with integration times sufficiently long to warrant a
meaningful spectral analysis. Our sample comprises inactive, moderately active,
and hyperactive stars and samples the bulk part of activity levels encountered
in coronal X-ray sources. We use the LETGS spectra to carry out density and
temperature diagnostics with an emphasis on the H-like and the He-like ions. We
find a correlation between line flux ratios of the Lyman-Alpha and He-like
resonance lines with the mean X-ray surface flux. We determine densities using
the He-like triplets. For active stars we find no significant deviations from
the low-density limit for the ions of Ne, Mg, and Si, while the measured line
ratios for the ions of C, N, and O do show evidence for departures from the
low-density limit in the active stars, but not in the inactive stars. Best
measurements can be made for the OVII triplet where we find significant
deviations from the low-density limit for the stars Algol, Procyon, YY Gem, Eps
Eri, and HR1099. We discuss the influence of radiation fields on the
interpretation of the He-like triplet line ratios in the low-Z ions, which is
relevant for Algol, and the influence of dielectronic satellite lines, which is
relevant for Procyon. For the active stars YY Gem, Eps Eri, and HR1099 the low
f/i ratios can unambiguously be attributed to high densties in the range 1--3
10^10 cm^-3 at OVII temperatures. We find our LETGS spectra to be an extremely
useful tool for plasma diagnostics of stellar coronae.Comment: 17 pages, Latex2e, 12 figures. accepted for A&A under MS262
Chandra LETGS Observation of the Active Binary Algol
A high-resolution spectrum obtained with the low-energy transmission grating
onboard the Chandra observatory is presented and analyzed. Our analysis
indicates very hot plasma with temperatures up to T=15-20MK from the continuum
and from ratios of hydrogen-like and helium-like ions of Si, Mg, and Ne. In
addition lower temperature material is present since OVII and NVI are detected.
Two methods for density diagnostics are applied. The He-like triplets from NVII
to SiXIII are used and densities around 10^11 cm^-3 are found for the low
temperature ions. Taking the UV radiation field from the B star companion into
account, we find that the low-Z ions can be affected by the radiation field
quite strongly, such that densities of 3 10^10 cm^-3 are also possible, but
only assuming that the emitting plasma is immersed in the radiation field. For
the high temperature He-like ions only low density limits are found. Using
ratios of FeXXI lines produced at similar temperatures are sensitive to lower
densities but again yield only low density limits. We thus conclude that the
hot plasma has densities below 10^12 cm^-3. Assuming a constant pressure corona
we show that the characteristic loop sizes must be small compared to the
stellar radius and that filling factors below 0.1 are unlikely.Comment: 16 pages, Latex2e, 23 figure
Swift Observations of Shock Evolution in RS Ophiuchi
Our \textit{Swift} observations of RS Oph form an unprecedented X-ray dataset
to undertake investigations of both the central source and the interaction of
the outburst ejecta with the circumstellar environment. Over the first month,
the XRT data are dominated by emission from rapidly evolving shocks. We discuss
the differences in derived parameters from those found for \textit{RXTE} at
early times and the evolution of the X-ray emission to much later times. It is
apparent that at late times several emission components are present. We find no
strong evidence of the proposed shock break-out in our data.Comment: 5 pages, 3 figures, to appear in ASP conference proceedings Volume
401 "RS Ophiuchi (2006) and the recurrent nova phenomenon
Modeling CHANDRA Low Energy Transmission Grating Spectrometer Observations of Classical Novae with PHOENIX. I. V4743 Sagittarii
We use the PHOENIX code package to model the X-ray spectrum of Nova V4743
Sagittarii observed with the LETGS onboard the Chandra satellite on March 2003.
Our atmosphere models are 1D spherical, expanding, line blanketed, and in full
NLTE. To analyze nova atmospheres and related systems with an underlying
nuclear burning envelope at X-ray wavelengths, it was necessary to update the
code with new microphysics, as discussed in this paper. We demonstrate that the
X-ray emission is dominated by thermal bremsstrahlung and that the hard X-rays
are dominated by Fe and N absorption. The best fit to the observation is
provided at a temperature of T_eff = 5.8 x 10^5 K, with L_bol = 50 000 L_sun.
The models are calculated for solar abundances. It is shown that the models can
be used to determine abundances in the nova ejecta.Comment: 8 pages, 6 figures, accepted for publication in Astronomy &
Astrophysic
X-ray Eclipse Diagnosis of the Evolving Mass Loss in the Recurrent Nova U Scorpii 2010
We report the Suzaku detection of the earliest X-ray eclipse seen in the
recurrent nova U Scorpii 2010. A target-of-opportunity observation 15 days
after the outburst found a 27+/-5% dimming in the 0.2-1.0 keV energy band at
the predicted center of an eclipse. In comparison with the X-ray eclipse depths
seen at two later epochs by XMM-Newton, the source region shrank by about
10-20% between days 15 and 35 after the outburst. The X-ray eclipses appear to
be deeper than or similar to contemporaneous optical eclipses, suggesting the
X-ray and optical source region extents are comparable on day 15. We raise the
possibility of the energy dependency in the photon escape regions, and that
this would be a result of the supersoft X-ray opacity being higher than the
Thomson scattering optical opacity at the photosphere due to bound-free
transitions in abundant metals that are not fully ionized. Assuming a
spherically symmetric explosion model, we constrain the mass-loss rate as a
function of time. For a ratio of actual to Thomson opacity of 10-100 in
supersoft X-rays, we find a total ejecta mass of about 10^{-7}-10^{-6}
M_{\odot}.Comment: To appear in the Astrophysical Journal Letters; 5 pages, 3 figure
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