19 research outputs found
High Resolution X-ray Imaging Observations of two low luminosity Seyfert Galaxies
An extended component of X-ray emission has been detected in Seyfert galaxies
- NGC 1365 and NGC 4051, using the ROSAT HRI. Its size is about 2 kpc and it
contains 56% +- 8% of the total observed flux in NGC 1365, and 21% +- 6% in NGC
4051. Extended emission in NGC 1365 is aligned with the inner disk structure,
has wings along the east and west direction aligned with the inner spiral arms,
and has an elongated edge-brightened structure (``chimney'') breaking out of
the disk in the north-west direction. In NGC 4051 it is co-spatial with the
disk of the galaxy, and shows an elongation coincident with a ``banana''-like
feature in the north-east seen in the 6 cm radio band. Starburst activity
driving strong winds through the disk of NGC 1365 can account for most of the
extended soft X-ray emission in it. Both nuclear activity and starburst induced
activity maybe needed to explain extended X-ray emission in NGC 4051. The
nuclear component of NGC 4051 shows soft X-ray variability with X-ray intensity
changing by a factor of 2-3 on a time-scale of a few 100s. At low frequencies
the power spectrum of variability is best characterised by a power-law and a
Gaussian. The power-law slope of -1.8 is consistent with the previous EXOSAT
observations, and the presence of a Gaussian feature signifies the persistence
of a quasi-periodic oscillation that was seen earlier with EXOSAT. During its
low intensity and low variability state the extended component of soft X-ray
emission dominates the flux in NGC 4051.Comment: 18 pages of text, 13 jpeg figures. To appear in MNRA
Surface activity of rapidly rotating stars from simultaneous X-ray and UV observations with AstroSat
Our study focuses on analysing the coronal, transition and chromospheric
activity of four rapidly rotating stars located within 50 pc in the solar
neighbourhood. We have used the multi-wavelength capabilities of AstroSat, to
investigate the outer atmospheres of AB Dor, BO Mic, DG CVn and GJ 3331. These
stars, classified as M and K type active stars, are known for their short
rotation periods, leading to increased surface magnetic activity. Our soft
X-ray observations provide the coronal properties such as emission measures,
temperatures and elemental coronal abundances. We report the detection of X-ray
flares from AB Dor, BO Mic, and DG CVn, while UV light curves reveal flares in
both BO Mic and DG CVn.Comment: Accepted for publication in Journal of Astrophysics and Astronom
Dashing through the cluster: An X-ray to radio view of UGC 10420 undergoing ram-pressure stripping
We present multi-wavelength data and analysis, including new FUV
AstroSat/UVIT observations of the spiral galaxy UGC 10420 (z=0.032), a member
of the cluster Abell 2199. UGC 10420 is present on the edge of the X-ray
emitting region of the cluster at a distance of ~ 680 kpc from the centre. The
FUV data shows intense knots of star formation on the leading edge of the
galaxy, accompanied by a tail of the same on the diametrically opposite side.
Our analysis shows that the images of the galaxy disk in the optical and
mid-infrared are much smaller in size than that in the FUV. While the broadband
optical colours of UGC 10420 are typical of a post-starburst galaxy, the SFR
derived from a UV-to-IR spectral energy distribution is at least a factor of
nine higher than that expected for a star-forming field galaxy of similar mass
at its redshift. A careful removal of the contribution of the diffuse
intracluster gas shows that the significant diffuse X-ray emission associated
with the inter-stellar medium of UGC 10420 has a temperature, T_X =
0.24^{+0.09}_{-0.06} keV (0.4-2.0 keV) and luminosity, L_X = 1.8+/-0.9 x
10^{40} erg/s, which are typical of the X-ray emission from late-type spiral
galaxies.
Our analysis favours a scenario where the interaction of a galaxy with the
hot intra-cluster medium of the cluster, perturbs the gas in the galaxy causing
starburst in the leading edge of the disk. On the other hand, the turbulence
thus developed may also push some of the gas out of the disk. Interactions
between the gas ejected from the galaxy and the intracluster medium can then
locally trigger star formation in the wake of the galaxy experiencing
ram-pressure stripping. Our data however does not rule out the possibility of a
flyby encounter with a neighbouring galaxy, although no relevant candidates are
observed in the vicinity of UGC 10420. (abridged)Comment: Accepted for publication in the Publication of the Astronomical
Society of Australia (PASA). 16 pages, 11 figure
A ROSAT PSPC study of NGC 55
The Position Sensitive Proportional Counter onboard ROSAT imaged the spiral galaxy NGC 55 in X-rays for 18.9 ksec. Twenty-two point-like X-ray sources are detected covering the PSPC field-of-view, of which 7 sources are candidate members of NGC 55. The spectra of the brightest sources that are nearest to NGC 55 are consistent either with a heavily absorbed source or a foreground star. The absorbed sources are very likely members of NGC 55. None of the brightest sources appear to be variable in a periodic fashion. Weak diffuse emission is detected in the plane of the galaxy, but only in the energy bands above ~0.5 keV. This emission is either the tail of a hot component of the ISM or the emission of unresolved point sources. We argue that the emission is a hot ISM component. A hot plume, visible in the 0.75 keV band, appears to align with an H I plume detected in a VLA total H I map. The cool H I gas appears to surround the hot gas, so the structure represents a chimney
X-ray Activity on the Star-Planet Interaction Candidate HD 179949
We carry out detailed spectral and timing analyses of the X-ray
data of HD 179949, a prototypical example of a star with a close-in giant
planet with possible star-planet interaction (SPI) effects. We find a low
coronal abundance Fe/H0.2 relative to the solar photosphere, as well
as lower abundances of high FIP elements O/Fe 1, Ne/Fe
0.1, but with indications of higher abundances of N and Al. This star also has
an anomalous FIP bias of , larger than expected for
stars of this type. We detect significant intensity variability over time
scales ranging from 100~s - 10~ks, and also evidence for spectral variability
over time scales of 1-10~ks. We combine the flux measurements with
and measurements to detect periodicities, and determine
that the dominant signal is tied to the stellar polar rotational period,
consistent with expectations that the corona is rotational-pole dominated. We
also find evidence for periodicity at both the planetary orbital frequency and
at its beat frequency with the stellar polar rotational period, suggesting the
presence of a magnetic connection between the planet and the stellar pole. If
these periodicities represent an SPI signal, the lack of phase dependence in
coronal temperature or flaring suggests that the SPI in this system is driven
by a quasi-continuous form of heating (e.g., magnetic field stretching) rather
than a highly sporadic, hot, impulsive form (e.g., flare-like reconnection).Comment: 23 pages, 12 figures, 9 tables. Submitted to the Astrophysical
Journal. Comments welcome
Multi-wavelength observations of multiple eruptions of the recurrent nova M31N 2008-12a
We report the optical, UV, and soft X-ray observations of the
eruptions of the recurrent nova M31N 2008-12a. We infer a steady decrease in
the accretion rate over the years based on the inter-eruption recurrence
period. We find a ``cusp'' feature in the and band light curves close
to the peak, which could be associated to jets. Spectral modelling indicates a
mass ejection of 10 to 10 M during each eruption, and
an enhanced Helium abundance of He/He 3. The super-soft
source (SSS) phase shows significant variability, which is anti-correlated to
the UV emission, indicating a common origin. The variability could be due to
the reformation of the accretion disk. A comparison of the accretion rate with
different models on the plane yields the mass of a CO
WD, powering the ``H-shell flashes'' every 1 year to be
M and growing with time, making M31N 2008-12a a strong candidate for
the single degenerate scenario of Type Ia supernovae progenitor.Comment: Submitted to AJ, 22 pages, 14 figures, 5 table
Timescale-dependent X-ray to UV time lags of NGC 4593 using high-intensity XMM-Newton observations with Swift and AstroSat
We present a 140ks observation of NGC 4593 with XMM-Newton providing
simultaneous and continuous PN X-ray and OM UV (UVW1 2910\AA) lightcurves which
sample short-timescale variations better than previous observations. These
observations were simultaneous with 22d of Swift X-ray and UV/optical
monitoring, reported previously, and 4d of AstroSat X-ray (SXT), far (FUV
1541\AA), and near (NUV 2632\AA) UV allowing lag measurements between them and
the highly-sampled XMM. From the XMM we find that UVW1 lags behind the X-rays
by 29.51.3ks, half the lag previously determined from the Swift
monitoring. Re-examination of the \textit{Swift} data reveals a bimodal lag
distribution, with evidence for both the long and short lags. However if we
detrend the Swift lightcurves by LOWESS filtering with a 5d width, only the
shorter lag (23.821.2ks) remains. The NUV observations, compared to PN and
SXT, confirm the 30ks lag found by XMM and, after 4d filtering is applied
to remove the long-timescale component, the FUV shows a lag of 23ks. The
resultant new UVW1, FUV, and NUV lag spectrum extends to the X-ray band without
requiring additional X-ray to UV lag offset, which if the UV arises from
reprocessing of X-rays, implies direct illumination of the reprocessor. By
referencing previous Swift and HST lag measurements, we obtain an X-ray to
optical lag spectrum which agrees with a model using the KYNreverb
disc-reprocessing code, assuming the accepted mass of
and a spin approaching maximum. Previously noted
lag contribution from the BLR in the Balmer and Paschen continua are still
prominent.Comment: 13 pages, 23 figure