24,181 research outputs found
Multiwavelength spectral evolution during the 2011 outburst of the very faint X-ray transient Swift J1357.2-0933
We report our multiwavelength study of the 2011 outburst evolution of the
newly discovered black hole candidate X-ray binary Swift J1357.2-0933. We
analysed the Swift X-ray telescope and Ultraviolet/Optical telescope (UVOT)
data taken during the ~7 months duration of the outburst. It displayed a 2-10
keV X-ray peak luminosity of ~1E35(D/1.5 kpc)^2 erg s-1 which classifies the
source as a very faint X-ray transient. We found that the X-ray spectrum at the
peak was consistent with the source being in the hard state, but it softened
with decreasing luminosity, a common behaviour of black holes at low
luminosities or returning to quiescence from the hard state. The correlations
between the simultaneous X-ray and ultraviolet/optical data suggest a system
with a black hole accreting from a viscous disc that is not irradiated. The
UVOT filters provide the opportunity to study these correlations up to
ultraviolet wavelengths a regime so far unexplored. If the black hole nature is
confirmed, Swift J1357.2-0933 would be one of the very few established black
hole very-faint X-ray transients.Comment: 6 pages, 2 tables, 5 figures. Accepted by MNRA
Serendipitous Kepler observations of a background dwarf nova of SU UMa type
We have discovered a dwarf nova (DN) of type SU UMa in Kepler data which is
7.0 arcsec from the G-type exoplanet survey target KIC 4378554. The DN appears
as a background source in the pixel aperture of the foreground G star. We
extracted only the pixels where the DN is present and observed the source to
undergo five outbursts -- one a superoutburst -- over a timespan of 22 months.
The superoutburst was triggered by a normal outburst, a feature that has been
seen in all DNe superoutburst observed by Kepler. Superhumps during the super
outburst had a period of 1.842+/-0.004 h and we see a transition from
disc-dominated superhump signal to a mix of disc and accretion stream impact.
Predictions of the number of DNe present in Kepler data based on previously
published space densities vary from 0.3 to 258. An investigation of the
background pixels targets would lead to firmer constraints on the space density
of DN.Comment: Accepted for publication in MNRA
The Parkes Pulsar Timing Array
Detection and study of gravitational waves from astrophysical sources is a
major goal of current astrophysics. Ground-based laser-interferometer systems
such as LIGO and VIRGO are sensitive to gravitational waves with frequencies of
order 100 Hz, whereas space-based systems such as LISA are sensitive in the
millihertz regime. Precise timing observations of a sample of millisecond
pulsars widely distributed on the sky have the potential to detect
gravitational waves at nanohertz frequencies. Potential sources of such waves
include binary super-massive black holes in the cores of galaxies, relic
radiation from the inflationary era and oscillations of cosmic strings. The
Parkes Pulsar Timing Array (PPTA) is an implementation of such a system in
which 20 millisecond pulsars have been observed using the Parkes radio
telescope at three frequencies at intervals of two -- three weeks for more than
two years. Analysis of these data has been used to limit the gravitational wave
background in our Galaxy and to constrain some models for its generation. The
data have also been used to investigate fluctuations in the interstellar and
Solar-wind electron density and have the potential to investigate the stability
of terrestrial time standards and the accuracy of solar-system ephemerides.Comment: 9 pages, 6 figures, Proceedings of "40 Years of Pulsars: Millisecond
Pulsars, Magnetars and More", Montreal, August 2007. Corrected SKA detection
limi
RRS James Clark Ross Cruises JR265 and JR254D, 27 Nov-24 Dec 2011. Part 1: The Drake Passage hydrographic repeat section SR1b
This report describes the 17th complete occupation of the Drake Passage CTD section, established during the World Ocean Circulation Experiment as repeat section SR1b. It wasfirst occupied by National Oceanography Centre (previously IOSDL and then SOC) in collaboration with the British Antarctic Survey in 1993, and has been re-occupied most years since then. Thirty two full depth stations were performed during JR265: two test stations, and all 30 of the nominal stations for the SR1b Drake Passage section. An initial result is that the estimated total transport measured across the section was 133 Sv which compares well to an average transport measured from the 16 previous UK cruises of 135 Sv (standard deviation of 7 Sv). In conjunction with the hydrographic cruise, a "Waves Aerosol and Gas Exchange Study" (WAGES) intensive observation cruise JR245D was also carried out. WAGES involves continuous measurement of the air-sea turbulent fluxes of CO2, sea spray aerosol, momentum and sensible and latent heat fluxes, plus directional sea-state and whitecap parameters using systems installed on the ship in May 2010. In addition to the continuous measurements, a number of intensive observation periods (IOPs) have been carried out by WAGES staff on board the ship. These involve deployments of a spar buoy to measure wave breaking and an aerial camera system to measure whitecap fraction. The activities of JR254D are summarised here, but are described in detail in a separate cruise report. Cruise JR264 was carried out by NOC-L staff at the same time as JR265 and JR254D. JR264 is also the subject of a separate cruise report. The CTD was an underwater SBE 9 plus unit equipped with the following sensors: dual temperature and conductivity sensors, a pressure sensor encased in the SBE underwater unit, a SBE-43 oxygen probe, an Aquatracka MKIII fluorometer, a transmissometer, an upwardlooking downwelling PAR sensor, and an altimeter. A downward-looking LADCP (RDI Workhorse Monitor 300 kHz) was deployed on all stations. Various underway measurements were obtained, including navigation, VM-ADCP, sea surface temperature and salinity, water depth and various meteorological parameters. A practical aim during this cruise was to update the detailed guides for each of the hydrographic data streams which were first written duringJR195 in 2009. The hydrographic data analysis was performed using "MSTAR", a suite of Matlab programs developed at NOCS by Brian King and used on the JCR for the first time during JR195
A vigorous activity cycle mimicking a planetary system in HD200466
Stellar activity can be a source of radial velocity (RV) noise and can
reproduce periodic RV variations similar to those produced by an exoplanet. We
present the vigorous activity cycle in the primary of the visual binary
HD200466, a system made of two almost identical solar-type stars with an
apparent separation of 4.6 arcsec at a distance of 44+/-2 pc. High precision RV
over more than a decade, adaptive optics (AO) images, and abundances have been
obtained for both components. A linear trend in the RV is found for the
secondary. We assumed that it is due to the binary orbit and once coupled with
the astrometric data, it strongly constrains the orbital solution of the binary
at high eccentricities (e~0.85) and quite small periastron of ~21 AU. If this
orbital motion is subtracted from the primary radial velocity curve, a highly
significant (false alarm probability <0.1%) period of about 1300 d is obtained,
suggesting in a first analysis the presence of a giant planet, but it turned
out to be due to the stellar activity cycle. Since our spectra do not include
the Ca~II resonance lines, we measured a chromospheric activity indicator based
on the Halpha line to study the correlation between activity cycles and
long-term activity variations. While the bisector analysis of the line profile
does not show a clear indication of activity, the correlation between the
Halpha line indicator and the RV measurements identify the presence of a strong
activity cycle.Comment: Accepted on Astronomy and Astrophysics Main Journal 2014, 16 pages,
18 figure
XMM-Newton observation of PSR B2224+65 and its jet
We have investigated the pulsar PSR B2224+65 and its X-ray jet with
XMM-Newton. Apart from the long X-ray jet which is almost perpendicular to the
direction of proper motion, a putative extended feature at the pulsar position,
which oriented in the opposite direction of the proper motion, is also
suggested by this deep X-ray imaging. Non-detection of any coherent X-ray
pulsation disfavors the magnetospheric origin of the X-rays observed from the
position of PSR B2224+65 and hence suggest that the interpretation of pulsar
wind nebula is more viable. We have also probed the origin of PSR B2224+65 and
identified a runaway star, which possibly originated from the Cygnus OB9
association, as a candidate for the former binary companion of the neutron
star's progenitor.Comment: 24 pages, 8 figures, 3 tables, accepted for publication in Ap
ESO 243-49 HLX-1: scaling of X-ray spectral properties and black hole mass determination
We report the results of Swift/XRT observations (2008-2015) of a
hyper-luminous X-ray source, ESO 243-49 HLX-1. We found a strong observational
evidence that ESO 243-49 HLX-1 underwent spectral transitions from the low/hard
state to the high/soft state during these observations. The spectra of ESO
243-49 HLX-1 are well fitted by the so-{called} bulk motion Comptonization
model for all spectral states. We have established the photon index Gamma
saturation level, Gamma_{sat}$=3.0+/-0.1, in the correlation of Gamma versus
mass accretion rate dot M. This Gamma-dot M correlation allows us to estimate
the black hole (BH) mass in ESO 243-49 HLX-1 to be M_{BH}~ 7x 10^4 solar
masses, assuming the distance to ESO 243-49 of 95 Mpc. For the BH mass estimate
we used the scaling method, taking Galactic BHs XTE~J1550-564, H~1743-322 and
4U~1630-472, and an extragalactic BH source, M101 ULX-1 as reference sources.
The Gamma-dot M correlation revealed in ESO 243-49 HLX-1 is similar to those in
a number of Galactic and extragalactic BHs and it clearly shows the correlation
along with the strong Gamma saturation at ~ 3. This is a reliable observational
evidence of a BH in ESO 243-49 HLX-1. We also found that the seed (disk) photon
temperatures are quite low, of order of 50-140 eV which are consistent with a
high BH mass in ESO 243-49 HLX-1.Comment: 21 pages, 8 figures, accepted by Astronomy and Astrophysics on August
29, 201
Structure in the Disk of epsilon Aurigae: Analysis of the ARCES and TripleSpec data obtained during the 2010 eclipse
Context: Worldwide interest in the recent eclipse of epsilon Aurigae resulted
in the generation of several extensive data sets, including those related to
high resolution spectroscopic monitoring. This lead to the discovery, among
other things, of the existence of a mass transfer stream, seen notably during
third contact. Aims: We explored spectroscopic facets of the mass transfer
stream during third contact, using high resolution spectra obtained with the
ARCES and TripleSpec instruments at Apache Point Observatory. Methods: One
hundred and sixteen epochs of data between 2009 and 2012 were obtained, and
equivalent widths and line velocities measured, selected according to reports
of these being high versus low eccentricity disk lines. These datasets also
enable greater detail to be measured of the mid-eclipse enhancement of the He I
10830A line, and the discovery of the P Cygni shape of the Pa beta line at
third contact. Analysis: We found evidence of higher speed material, associated
with the mass transfer stream, persisting between third and fourth eclipse
contacts. We visualize the disk and stream interaction using SHAPE software,
and use CLOUDY software to estimate that the source of the enhanced He I 10830A
absorption arises from a region with log n = 10 (/cm3) and temperature of
20,000 K consistent with a mid B type central star. Results and Next Steps: Van
Rensbergen binary star evolutionary models are somewhat consistent with the
current binary parameters for the case of a 9 plus 8 solar mass initial binary,
evolving into a 2.3 and 14.11 solar mass end product after 35 Myr. Prior to the
next eclipse, it is possible to make predictions which suggest that continued
monitoring will help resolve standing questions about this binary
The supermassive black hole and double nucleus of the core elliptical NGC5419
We obtained adaptive-optics assisted SINFONI observations of the central
regions of the giant elliptical galaxy NGC5419 with a spatial resolution of 0.2
arcsec ( pc). NGC5419 has a large depleted stellar core with a
radius of 1.58 arcsec (430 pc). HST and SINFONI images show a point source
located at the galaxy's photocentre, which is likely associated with the
low-luminosity AGN previously detected in NGC5419. Both the HST and SINFONI
images also show a second nucleus, off-centred by 0.25 arcsec (
pc). Outside of the central double nucleus, we measure an almost constant
velocity dispersion of km/s. In the region where the double
nucleus is located, the dispersion rises steeply to a peak value of
km/s. In addition to the SINFONI data, we also obtained stellar kinematics at
larger radii from the South African Large Telescope. While NGC5419 shows low
rotation ( km/s), the central regions (inside ) clearly
rotate in the opposite direction to the galaxy's outer parts. We use
orbit-based dynamical models to measure the black hole mass of NGC5419 from the
kinematical data outside of the double nuclear structure. The models imply
M M. The enhanced velocity
dispersion in the region of the double nucleus suggests that NGC5419 possibly
hosts two supermassive black holes at its centre, separated by only pc. Yet our measured M is consistent with the black hole mass
expected from the size of the galaxy's depleted stellar core. This suggests,
that systematic uncertainties in M related to the secondary nucleus
are small.Comment: Accepted for publication in MNRA
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