49 research outputs found
Early Super Soft Source spectra in RS Oph
Recent Swift X-ray monitoring campaigns of novae have revealed extreme levels
of variability during the early super-soft-source (SSS) phase. The first time
this was observed was during the 2006 outburst of the recurrent nova RS Oph
which was also extensively covered by grating observations with XMM-Newton and
Chandra. I focus here on an XMM-Newton observation taken on day 26.1, just
before Swift confirmed the start of the SSS phase, and a Chandra observation
taken on day 39.7. The first observation probes the evolution of the shock
emission produced by the collision of the nova ejecta with the stellar wind of
the companion. The second observation contains bright SSS emission longwards of
15A while at short wavelengths, the shock component can be seen to have hardly
changed. On top of the SSS continuum, additional emission lines are clearly
seen, and I show that they are much stronger than those seen on day 26.1,
indicating line pumping caused by the SSS emission. The lightcurve on day 39.7
is highly variable on short time scales while the long-term Swift light curve
was still variable. In 2007, we have shown that brightness variations are
followed by hardness variations, lagging behind 1000 seconds. I show now that
the hardness variations are owed to variations in the depth of the neutral
hydrogen column density of order 25%, particularly affecting the oxygen K-shell
ionization edge at 0.5 keV.Comment: Accepted for Acta Polytechnica. 4 pages, 4 figures, conference
proceedings PALERMO WORKSHOP 201
The value of density measurements in stellar coronae
The grating instruments on board Chandra and XMM-Newton now allow
measurements of electron densities. These rely on the ratios of fluxes in
emission lines, where one line depends on both collisional and radiative decay
rates. The electron density is required to constrain the physical extent of the
emitting region, and large samples of measurements are of interest in the
context of trends in coronal activity. Here we discuss the important He {\sc
i}-like ions and the differences in densities that result when different
current data bases are used.Comment: 3 pages, 3 figures, proceedings ITAMP Workshop: X-ray Diagnostics for
Astrophysical Plasmas: Theory, Experiment and Observation. 2004 November
15-17 Cambridge, US
What we learn from the X-Ray grating spectra of Nova SMC 2016
Peer ReviewedPostprint (published version
The supersoft X-ray source in V5116 Sagittarii: I. the high resolution spectra
Context. Classical nova explosions occur on the surface of an accreting white dwarf in a binary system. After ejection of a fraction of the envelope and when the expanding shell becomes optically thin to X-rays, a bright source of supersoft X-rays arises, powered by residual H burning on the surface of the white dwarf. While the general picture of the nova event is well established, the details and balance of accretion and ejection processes in classical novae are still full of unknowns. The long-term balance of accreted matter is of special interest for massive accreting white dwarfs, which may be promising supernova Ia progenitor candidates. Nova V5116 Sgr 2005b was observed as a bright and variable supersoft X-ray source by XMM-Newton in March 2007, 610 days after outburst. The light curve showed a periodicity consistent with the orbital period. During one third of the orbit the luminosity was a factor of seven brighter than during the other two thirds of the orbital period.
Aims. In the present work we aim to disentangle the X-ray spectral components of V5116 Sgr and their variability.
Methods. We present the high resolution spectra obtained with XMM-Newton RGS and Chandra LETGS/HRC-S in March and August 2007.
Results. The grating spectrum during the periods of high-flux shows a typical hot white dwarf atmosphere dominated by absorption lines of N VI and N VII. During the low-flux periods, the spectrum is dominated by an atmosphere with the same temperature as during the high-flux period, but with several emission features superimposed. Some of the emission lines are well modeled with an optically thin plasma in collisional equilibrium, rich in C and N, which also explains some excess in the spectra of the high-flux period. No velocity shifts are observed in the absorption lines, with an upper limit set by the spectral resolution of 500 km s-1, consistent with the expectation of a non-expanding atmosphere so late in the evolution of the post-nova.Postprint (published version
X-Ray Spectroscopy of the Classical Nova V458 Vulpeculae with Suzaku
We conducted a target of opportunity X-ray observation of the classical nova
V458 Vulpeculae 88 days after the explosion using the Suzaku satellite. With a
20 ks exposure, the X-ray Imaging Spectrometer detected X-ray emission
significantly harder than typical super-soft source emission. The X-ray
spectrum shows K lines from N, Ne, Mg, Si, and S, and L-series emission from Fe
in highly ionized states. The spectrum can be described by a single temperature
(0.64 keV) thin thermal plasma model in collisional equilibrium with a
hydrogen-equivalent extinction column density of ~3e21/cm2, a flux of ~1e-12
erg/s/cm2, and a luminosity of ~6e34 erg/s in the 0.3-3.0 keV band at an
assumed distance of 13 kpc. We found a hint of an enhancement of N and
deficiencies of O and Fe relative to other metals. The observed X-ray
properties can be interpreted as the emission arising from shocks of ejecta
from an ONe-type nova.Comment: Accepted for publication in PASJ (9 pages, 4 Postscript figures