14,546 research outputs found
Resolving the large scale spectral variability of the luminous Seyfert 1 galaxy 1H 0419-577: Evidence for a new emission component and absorption by cold dense matter
An XMM-Newton observation of the luminous Seyfert 1 galaxy 1H 0419-577 in
September 2002, when the source was in an extreme low-flux state, found a very
hard X-ray spectrum at 1-10 keV with a strong soft excess below ~1 keV.
Comparison with an earlier XMM-Newton observation when 1H 0419-577 was `X-ray
bright' indicated the dominant spectral variability was due to a steep power
law or cool Comptonised thermal emission. Four further XMM-Newton observations,
with 1H 0419-577 in intermediate flux states, now support that conclusion,
while we also find the variable emission component in intermediate state
difference spectra to be strongly modified by absorption in low ionisation
matter. The variable `soft excess' then appears to be an artefact of absorption
of the underlying continuum while the `core' soft emission can be attributed to
recombination in an extended region of more highly ionised gas. We note the
wider implications of finding substantial cold dense matter overlying (or
embedded in) the X-ray continuum source in a luminous Seyfert 1 galaxy.Comment: 34 pages, 15 figures, submitted to Ap
A NuSTAR observation of the fast symbiotic nova V745 Sco in outburst
The fast recurrent nova V745 Sco was observed in the 3-79 keV X-rays band
with NuSTAR 10 days after the optical discovery. The measured X-ray emission is
consistent with a collisionally ionized optically thin plasma at temperature of
about 2.7 keV. A prominent iron line observed at 6.7 keV does not require
enhanced iron in the ejecta. We attribute the X-ray flux to shocked
circumstellar material. No X-ray emission was observed at energies above 20
keV, and the flux in the 3-20 keV range was about 1.6 10 erg
cm s. The emission measure indicates an average electron density
of order of 10 cm.
The X-ray flux in the 0.3-10 keV band almost simultaneously measured with
Swift was about 40 times larger, mainly due to the luminous central supersoft
source emitting at energy below 1 keV. The fact that the NuSTAR spectrum cannot
be fitted with a power law, and the lack of hard X-ray emission, allow us to
rule out Comptonized gamma rays, and to place an upper limit of the order of
10 erg cm s on the gamma-ray flux of the nova on the
tenth day of the outburst.Comment: in press in Monthly Notices of the Royal Astronomical Society, 201
An XMM-Newton observation of Mrk 3 - a Seyfert galaxy just over the edge
A 100ks XMM-Newton observation of the nearby Seyfert 2 galaxy Mrk 3 offers a
unique opportunity to explore the complexity of its X-ray spectrum. We find the
\~3-8 keV continuum to be dominated by reflection from cold matter, with
fluorescent K-shell lines detected from Ni, Fe, Ca, Ar, S, Si and Mg. At higher
energies an intrinsic power law continuum, with canonical Seyfert 1 photon
index, is seen through a near-Compton-thick cold absorber. A soft excess below
\~3 keV is found to be dominated by line emission from an outflow of `warm'
gas, photo-ionised and photo-excited by the intrinsically strong X-ray
continuum. Measured blue-shifts in the strong Fe K-alpha and OVII and VIII
emission lines are discussed in terms of the properties of the putative
molecular torus and ionised outflow.Comment: 16 figures; accepted for publication in MNRA
An XMM-Newton observation of the Narrow Line Seyfert 1 Galaxy, Markarian 896
XMM-Newton observations of the NLS1 Markarian 896 are presented. Over the
2-10 keV band, an iron emission line, close to 6.4 keV, is seen. The line is
just resolved and has an equivalent width of ~170 eV. The broad-band spectrum
is well modelled by a power law slope of gamma ~ 2.03, together with two
blackbody components to fit the soft X-ray excess. Using a more physical
two-temperature Comptonisation model, a good fit is obtained for an input
photon distribution of kT ~ 60eV and Comptonising electron temperatures of ~0.3
and 200 keV. The soft excess cannot be explained purely through the
reprocessing of a hard X-ray continuum by an ionised disc reflector.Comment: 6 pages, 4 figures, accepted by MNRA
Fe K emission and absorption features in XMM-Newton spectra of Mkn 766 - evidence for reprocessing in flare ejecta
We report on the analysis of a long XMM-Newton EPIC observation in 2001 May
of the Narrow Line Seyfert 1 galaxy Mkn 766. The 3-11 keV spectrum exhibits a
moderately steep power law continuum, with a broad emission line at ~6.7 keV,
probably blended with a narrow line at ~6.4 keV, and a broad absorption trough
above ~8.7 keV. We identify both broad spectral features with reprocessing in
He-like Fe. An earlier XMM-Newton observation of Mkn 766 in 2000 May, when the
source was a factor ~2 fainter, shows a similar broad emission line, but with a
slightly flatter power law and absorption at a lower energy. In neither
observation do we find a requirement for the previously reported broad 'red
wing' to the line and hence of reflection from the innermost accretion disc.
More detailed examination of the longer XMM-Newton observation reveals evidence
for rapid spectral variability in the Fe K band, apparently linked with the
occurrence of X-ray 'flares'. A reduction in the emission line strength and
increased high energy absorption during the X-ray flaring suggests that these
transient effects are due to highly ionised ejecta associated with the flares.
Simple scaling from the flare avalanche model proposed for the luminous QSO PDS
456 (Reeves etal. 2002) confirms the feasibility of coherent flaring being the
cause of the strong peaks seen in the X-ray light curve of \mkn.Comment: 9 pages, 11 figures, submitted to MNRA
A search for thermal X-ray signatures in Gamma-Ray Bursts I: Swift bursts with optical supernovae
The X-ray spectra of Gamma-Ray Bursts can generally be described by an
absorbed power law. The landmark discovery of thermal X-ray emission in
addition to the power law in the unusual GRB 060218, followed by a similar
discovery in GRB 100316D, showed that during the first thousand seconds after
trigger the soft X-ray spectra can be complex. Both the origin and prevalence
of such spectral components still evade understanding, particularly after the
discovery of thermal X-ray emission in the classical GRB 090618. Possibly most
importantly, these three objects are all associated with optical supernovae,
begging the question of whether the thermal X-ray components could be a result
of the GRB-SN connection, possibly in the shock breakout. We therefore
performed a search for blackbody components in the early Swift X-ray spectra of
11 GRBs that have or may have associated optical supernovae, accurately
recovering the thermal components reported in the literature for GRBs 060218,
090618 and 100316D. We present the discovery of a cooling blackbody in GRB
101219B/SN2010ma, and in four further GRB-SNe we find an improvement in the fit
with a blackbody which we deem possible blackbody candidates due to
case-specific caveats. All the possible new blackbody components we report lie
at the high end of the luminosity and radius distribution. GRB 101219B appears
to bridge the gap between the low-luminosity and the classical GRB-SNe with
thermal emission, and following the blackbody evolution we derive an expansion
velocity for this source of order 0.4c. We discuss potential origins for the
thermal X-ray emission in our sample, including a cocoon model which we find
can accommodate the more extreme physical parameters implied by many of our
model fits.Comment: 16 pages, 6 figures, accepted for MNRA
A simultaneous XMM-Newton and BeppoSAX observation of the archetypal Broad Line Seyfert 1 galaxy NGC 5548
We report the spectral analysis of a long XMM-Newton observation of the
well-studied, moderate luminosity Broad Line Seyfert 1 galaxy NGC 5548. The
source was at an historically average brightness and we find the hard (3-10
keV) spectrum can be well fitted by a power law of photon index gamma ~ 1.75,
together with reflection. The only feature in the hard X-ray spectrum is a
narrow emission line near 6.4 keV, with an equivalent width of ~ 60 eV. The
energy and strength of this line is consistent with fluorescence from `neutral'
iron distant from the central continuum source. We find no evidence for a broad
Fe K line, with an upper limit well below previous reports, suggesting the
inner accretion disc is now absent or highly ionised. The addition of
simultaneous BeppoSAX data allows the analysis to be extended to 200 keV,
yielding important constraints on the total reflection. Extrapolation of the
hard X-ray power law down to 0.3 keV shows a clear `soft excess' below ~ 0.7
keV. After due allowance for the effects of a complex warm absorber, measured
with the XMM-Newton RGS, we find the soft excess is better described as a
smooth upward curvature in the continuum flux below ~ 2 keV. The soft excess
can be modelled either by Comptonised thermal emission or by enhanced
reflection from the surface of a highly ionised disc.Comment: 9 pages, 11 figures, accepted by MNRAS; minor changes to text and
figure
X-ray emission mechanisms in accreting white dwarfs
In this chapter we consider the processes which can lead to X-ray emission
from different types of cataclysmic variable stars (CVs). CVs are
semi-detached, binary star systems where material is transferred from the donor
star (also known as the companion or secondary star) onto the white dwarf
primary. CVs are divided into several sub-classes based on the observed
phenomenology in the optical and X-ray bands, which, in turn, is largely
defined by the magnetic field strength of the accretor. In non-magnetic
systems, a variety of observed behaviours are identified, depending on the
accretion rate: novae, dwarf novae, nova-like variables, symbiotic binaries and
supersoft sources are all examples of non-magnetic CVs. In magnetic systems
(polars and intermediate polars, or AM Her and DQ Her systems, respectively),
the accretion flow is channelled to polar regions, and the observational
appearance is different. X-rays are typically produced through hot or energetic
processes, and in CVs they are formed via shocks (within a boundary layer or
accretion column, or through interactions either internal to the nova ejecta,
or between the ejecta and a stellar wind) or from hydrogen burning (either
steady fusion, or a thermonuclear runaway). All of these different types of
accreting white dwarfs are discussed here, considering both spectral and
temporal variability in the different populations.Comment: 48 pages (though pages 36 onwards consist entirely of references, due
to a poorly designed style file!), 15 figures. Invited (and accepted) chapter
for the Handbook of X-ray and Gamma-ray Astrophysic
Composite Reflective/Absorptive IR-Blocking Filters Embedded in Metamaterial Antireflection Coated Silicon
Infrared (IR) blocking filters are crucial for controlling the radiative
loading on cryogenic systems and for optimizing the sensitivity of bolometric
detectors in the far-IR. We present a new IR filter approach based on a
combination of patterned frequency selective structures on silicon and a thin
(50 thick) absorptive composite based on powdered reststrahlen
absorbing materials. For a 300 K blackbody, this combination reflects
50\% of the incoming light and blocks \textgreater 99.8\% of the total
power with negligible thermal gradients and excellent low frequency
transmission. This allows for a reduction in the IR thermal loading to
negligible levels in a single cold filter. These composite filters are
fabricated on silicon substrates which provide excellent thermal transport
laterally through the filter and ensure that the entire area of the absorptive
filter stays near the bath temperature. A metamaterial antireflection coating
cut into these substrates reduces in-band reflections to below 1\%, and the
in-band absorption of the powder mix is below 1\% for signal bands below 750
GHz. This type of filter can be directly incorporated into silicon refractive
optical elements
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