203 research outputs found
The soft X-ray excess AGN RE J2248-511
We model the spectral energy distribution of the ultrasoft broad-line AGN RE
J2248-511 with Comptonised accretion disc models. These are able to reproduce
the steep optical and ultrasoft X-ray slopes, and the derived black hole mass
is consistent with independent mass estimates. This AGN displays properties of
both broad and narrow line Seyfert 1 galaxies, but we conclude that it is
intrinsically a `normal' Seyfert 1 viewed at high inclination angle.Comment: 4 pages, 1 figure. MG10 Proceeding
On the spin modulated circular polarization from the intermediate polars NY Lup and IGRJ1509-6649
We report on high time resolution, high signal/noise, photo-polarimetry of
the intermediate polars NY Lup and IGRJ1509-6649. Our observations confirm the
detection and colour dependence of circular polarization from NY Lup and
additionally show a clear white dwarf, spin modulated signal. From our new high
signal/noise photometry we have unambiguously detected wavelength dependent
spin and beat periods and harmonics thereof. IGRJ1509-6649 is discovered to
also have a particularly strong spin modulated circularly polarized signal. It
appears double peaked through the I filter and single peaked through the B
filter, consistent with cyclotron emission from a white dwarf with a relatively
strong magnetic field.
We discuss the implied accretion geometries in these two systems and any
bearing this may have on the possible relationship with the connection between
polars and soft X-ray-emitting IPs. The relatively strong magnetic fields is
also suggestive of them being polar progenitors.Comment: 8 pages, 6 figures and 1 table. Accepted for publication in MNRA
Supersoft X-ray sources identified with Be binaries in the Magellanic Clouds
We investigated four luminous supersoft X-ray sources (SSS) in the Magellanic
Clouds suspected to have optical counterparts of Be spectral type. If the
origin of the X-rays is in a very hot atmosphere heated by hydrogen burning in
accreted envelopes of white dwarfs (WDs), like in the majority of SSS, these
objects are close binaries, with very massive WD primaries. Using the South
African Large Telescope (SALT), we obtained the first optical spectra of the
proposed optical counterparts of two candidate Be stars associated with SUZAKU
J0105-72 and XMMU J010147.5-715550, respectively a transient and a recurrent
SSS, and confirmed the proposed Be classification and Small Magellanic Clouds
membership. We also obtained new optical spectra of two other Be stars proposed
as optical counterparts of the transient SSS XMMU J052016.0-692505 and
MAXI-J0158-744. The optical spectra with double peaked emission line profiles,
are typical of Be stars and present characteristics similar to many high mass
X-ray binaries with excretion disks, truncated by the tidal interaction with a
compact object. The presence of a massive WD that sporadically ignites nuclear
burning, accreting only at certain orbital or evolutionary phases, explains the
supersoft X-ray flares. We measured equivalent widths and distances between
lines' peaks, and investigated the variability of the prominent emission lines'
profiles. The excretion disks seem to be small in size, and are likely to be
differentially rotating. We discuss possible future observations and the
relevance of these objects as a new class of type Ia supernovae progenitors.Comment: Accepted for publication in teh Astrophysical Journa
X-ray Spectra of the RIXOS source sample
We present results of an extensive study of the X-ray spectral properties of
sources detected in the RIXOS survey, that is nearly complete down to a flux
limit of 3e-14 cgs (0.5-2 keV). We show that for X-ray surveys containing
sources with low count rate spectral slopes estimated using simple hardness
ratios in the ROSAT band can be biased. Instead we analyse three-colour X-ray
data using statistical techniques appropriate to the Poisson regime which
removes the effects of this bias. We have then applied this technique to the
RIXOS survey to study the spectral properties of the sample. For the AGN we
find an average energy index of 1.05+-0.05 with no evidence for spectral
evolution with redshift. Individual AGN are shown to have a range of properties
including soft X-ray excesses and intrinsic absorption. Narrow Emission Line
Galaxies also seem to fit to a power-law spectrum, which may indicate a
non-thermal origin for their X-ray emission. We infer that most of the clusters
in the sample have a bremsstrahlung temperature >3 keV, although some show
evidence for a cooling flow. The stars deviate strongly from a power-law model
but fit to a thermal model. Finally, we have analysed the whole RIXOS sample
containing 1762 sources. We find that the mean spectral slope of the sources
hardens at lower fluxes in agreement with results from other samples. However,
a study of the individual sources demonstrates that the hardening of the mean
is caused by the appearance of a population of very hard sources at the lowest
fluxes. This has implications for the nature of the soft X-ray background.Comment: 31,LaTeX file, 2 PS files with Table 2 and 22 PS figures. MNRAS in
pres
Polarized QPOs from the INTEGRAL polar IGRJ14536-5522 (=Swift J1453.4-5524)
We report optical spectroscopy and high speed photometry and polarimetry of
the INTEGRAL source IGRJ14536-5522 (=Swift J1453.4-5524). The photometry,
polarimetry and spectroscopy are modulated on an orbital period of 3.1564(1)
hours. Orbital circularly polarized modulations are seen from 0 to -18 per
cent, unambiguously identifying IGRJ14536-5522 as a polar.
Some of the high speed photometric data show modulations that are consistent
with quasi-periodic oscillations (QPOs) on the order of 5-6 minutes.
Furthermore, for the first time, we detect the (5-6) minute QPOs in the
circular polarimetry. We discuss the possible origins of these QPOs. We also
include details of HIPPO, a new high-speed photo-polarimeter used for some of
our observations.Comment: Accepted for publication by MNRAS. The paper contains 7 figures and 1
tabl
Chandra Multiwavelength Project: Normal Galaxies at Intermediate Redshift
(abridged) We have investigated 136 Chandra extragalactic sources without
broad optical emission lines, including 93 galaxies with narrow emission lines
(NELG) and 43 with only absorption lines (ALG). Based on fx/fo, Lx, X-ray
spectral hardness and optical emission line diagnostics, we have conservatively
classified 36 normal galaxies (20 spirals and 16 ellipticals) and 71 AGNs. We
found no statistically significant evolution in Lx/LB, within the limited z
range. We have built log(N)-log(S), after correcting for completeness based on
a series of simulations. The best-fit slope is -1.5 for both S and B energy
bands, which is considerably steeper than that of the AGN-dominated cosmic
background sources, but slightly flatter than the previous estimate, indicating
normal galaxies will not exceed the AGN population until fx ~ 2 x 10-18 erg s-1
cm-2 (a factor of ~5 lower than the previous estimate). A group of NELGs appear
to be heavily obscured in X-rays, i.e., a typical type 2 AGN. After correcting
for intrinsic absorption, their X-ray luminosities could be Lx > 10^44 erg s-1,
making them type 2 quasar candidates. While most X-ray luminous ALGs (XBONG -
X-ray bright, optically normal galaxy candidates) do not appear to be
significantly absorbed, we found two heavily obscured objects, which could be
as luminous as an unobscured broad-line quasar. Among 43 ALGs, we found two E+A
galaxy candidates with strong Balmer absorption lines, but no [OII] line. The
X-ray spectra of both galaxies are soft and one of them has a nearby close
companion galaxy, supporting the merger/interaction scenario rather than the
dusty starburst hypothesis.Comment: 31 pages, 9 figures, accepted for publication in ApJ (20 June 2006,
v644), replaced with minor correction
The unusual pulsation spectrum of the cool ZZ Ceti star HS 0507+0434B
We present the analysis of one week of single-site high-speed CCD photometric
observations of the cool ZZ Ceti star HS 0507+0434B. Ten independent
frequencies are detected in the star's light variations: one singlet and three
nearly-equally spaced triplets. We argue that these triplets are due to
rotationally split modes of spherical degree l=1. This is the first detection
of consistent multiplet structure in the amplitude spectrum of a cool ZZ Ceti
star and it allows us to determine the star's rotation period: 1.70 +/- 0.11 d.
We report exactly equal frequency, not period, spacings between the detected
mode groups. In addition, certain pairs of modes from the four principal groups
have frequency ratios which are very close to 3:4 or 4:5; while these ratios
are nearly exact (within one part in 10^4), they still lie outside the computed
error bars. We speculate that these relationships between different frequencies
could be caused by resonances. One of the three triplets may not be constant in
amplitude and/or frequency.
We compare our frequency solution for the combination frequencies (of which
we detected 38) to Wu's (1998, 2001) model thereof. We obtain consistent
results when trying to infer the star's convective thermal time and the
inclination angle of its rotational axis. Theoretical combination-frequency
amplitude spectra also resemble those of the observations well, and direct
theoretical predictions of the observed second-order light-curve distortions
were also reasonably successful assuming the three triplets are due to l=1
modes. Attempts to reproduce the observed combination frequencies adopting all
possible l=2 identifications for the triplets did not provide similarly
consistent results, supporting their identification with l=1.Comment: Accepted for publication in MNRAS; 12 pages, 8 figure
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