135 research outputs found
Photometric Observations of Three High Mass X-Ray Binaries and a Search for Variations Induced by Orbital Motion
We searched for long period variation in V-band, Ic-band and RXTE X-ray light
curves of the High Mass X-ray Binaries (HMXBs) LS 1698 / RX J1037.5-5647, HD
110432 / 1H 1249-637 and HD 161103 / RX J1744.7-2713 in an attempt to discover
orbitally induced variation. Data were obtained primarily from the ASAS
database and were supplemented by shorter term observations made with the 24-
and 40-inch ANU telescopes and one of the robotic PROMPT telescopes. Fourier
periodograms suggested the existence of long period variation in the V-band
light curves of all three HMXBs, however folding the data at those periods did
not reveal convincing periodic variation. At this point we cannot rule out the
existence of long term V-band variation for these three sources and hints of
longer term variation may be seen in the higher precision PROMPT data. Long
term V-band observations, on the order of several years, taken at a frequency
of at least once per week and with a precision of 0.01 mag, therefore still
have a chance of revealing long term variation in these three HMXBs.Comment: Accepted, RAA, May, 201
The progenitor and early evolution of the Type IIb SN 2016gkg
We report initial observations and analysis on the Type IIb SN~2016gkg in the
nearby galaxy NGC~613. SN~2016gkg exhibited a clear double-peaked light curve
during its early evolution, as evidenced by our intensive photometric follow-up
campaign. SN~2016gkg shows strong similarities with other Type IIb SNe, in
particular with respect to the \he~emission features observed in both the
optical and near infrared. SN~2016gkg evolved faster than the prototypical
Type~IIb SN~1993J, with a decline similar to that of SN~2011dh after the first
peak. The analysis of archival {\it Hubble Space Telescope} images indicate a
pre-explosion source at SN~2016gkg's position, suggesting a progenitor star
with a mid F spectral type and initial mass \msun, depending on
the distance modulus adopted for NGC~613. Modeling the temperature evolution
within of explosion, we obtain a progenitor radius of
\rsun, smaller than that obtained from the analysis of the
pre-explosion images (\rsun).Comment: 7 pages, 5 figures. Submitted to ApJ Letter
Observing the clustering properties of galaxy clusters in dynamical dark-energy cosmologies
We study the clustering properties of galaxy clusters expected to be observed
by various forthcoming surveys both in the X-ray and sub-mm regimes by the
thermal Sunyaev-Zel'dovich effect. Several different background cosmological
models are assumed, including the concordance CDM and various
cosmologies with dynamical evolution of the dark energy. Particular attention
is paid to models with a significant contribution of dark energy at early times
which affects the process of structure formation. Past light cone and selection
effects in cluster catalogs are carefully modeled by realistic scaling
relations between cluster mass and observables and by properly taking into
account the selection functions of the different instruments. The results show
that early dark-energy models are expected to produce significantly lower
values of effective bias and both spatial and angular correlation amplitudes
with respect to the standard CDM model. Among the cluster catalogues
studied in this work, it turns out that those based on \emph{eRosita},
\emph{Planck}, and South Pole Telescope observations are the most promising for
distinguishing between various dark-energy models.Comment: 16 pages, 10 figures. A&A in pres
Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Planets and Celestial Calibration Sources
(Abridged) We present WMAP seven-year observations of bright sources which
are often used as calibrators at microwave frequencies. Ten objects are studied
in five frequency bands (23 - 94 GHz): the outer planets (Mars, Jupiter,
Saturn, Uranus and Neptune) and five fixed celestial sources (Cas A, Tau A, Cyg
A, 3C274 and 3C58). The seven-year analysis of Jupiter provides temperatures
which are within 1-sigma of the previously published WMAP five-year values,
with slightly tighter constraints on variability with orbital phase, and limits
(but no detections) on linear polarization. Scaling factors are provided which,
when multiplied by the Wright Mars thermal model predictions at 350 micron,
reproduce WMAP seasonally averaged observations of Mars within ~2%. An
empirical model is described which fits brightness variations of Saturn due to
geometrical effects and can be used to predict the WMAP observations to within
3%. Seven-year mean temperatures for Uranus and Neptune are also tabulated.
Uncertainties in Uranus temperatures are 3%-4% in the 41, 61 and 94 GHz bands;
the smallest uncertainty for Neptune is ~8% for the 94 GHz band. Intriguingly,
the spectrum of Uranus appears to show a dip at ~30 GHz of unidentified origin,
although the feature is not of high statistical significance. Flux densities
for the five selected fixed celestial sources are derived from the seven-year
WMAP sky maps, and are tabulated for Stokes I, Q and U, along with polarization
fraction and position angle. Fractional uncertainties for the Stokes I fluxes
are typically 1% to 3%. Source variability over the seven-year baseline is also
estimated. Significant secular decrease is seen for Cas A and Tau A: our
results are consistent with a frequency independent decrease of about 0.53% per
year for Cas A and 0.22% per year for Tau A.Comment: 72 pages, 21 figures; accepted to ApJS; (v2) corrected Mars model
scaling factors, added figure 21, added text to Mars, Saturn and celestial
sources section
NoSOCS in SDSS. I. Sample Definition and Comparison of Mass Estimates
We use Sloan Digital Sky Survey (SDSS) data to investigate galaxy cluster
properties of systems first detected within DPOSS. With the high quality
photometry of SDSS we derived new photometric redshifts and estimated richness
and optical luminosity. For a subset of low redshift () clusters, we
have used SDSS spectroscopic data to identify groups in redshift space in the
region of each cluster, complemented with massive systems from the literature
to assure the continuous mass sampling. A method to remove interlopers is
applied, and a virial analysis is performed resulting in estimates of velocity
dispersion, mass, and a physical radius for each low- system. We discuss the
choice of maximum radius and luminosity range in the dynamical analysis,
showing that a spectroscopic survey must be complete to at least M if one
wishes to obtain accurate and unbiased estimates of velocity dispersion and
mass. We have measured X-ray luminosity for all clusters using archival data
from RASS. For a smaller subset (twenty-one clusters) we selected temperature
measures from the literature and estimated mass from the M-T relation,
finding that they show good agreement with the virial estimate. However, these
two mass estimates tend to disagree with the caustic results. We measured the
presence of substructure in all clusters of the sample and found that clusters
with substructure have virial masses higher than those derived from T. This
trend is not seen when comparing the caustic and X-ray masses. That happens
because the caustic mass is estimated directly from the mass profile, so it is
less affected by substructure.Comment: 21 pages, 17 figures, 5 tables, Accepted to MNRA
Late-epoch optical and near-infrared observations of the GRB000911 afterglow and its host galaxy
We present the results of an optical and near-infrared (NIR) monitoring
campaign of the counterpart of Gamma-Ray Burst (GRB) 000911, located at
redshift z=1.06, from 5 days to more than 13 months after explosion. Our
extensive dataset is a factor of 2 larger and spans a time interval about 4
times longer than the ones considered previously for this GRB afterglow; this
allows a more thorough analysis of its light curve and of the GRB host galaxy
properties. The afterglow light curves show a single power-law temporal
decline, modified at late times by light from a host galaxy with moderate
intrinsic extinction, and possibly by an emerging supernova (SN). The afterglow
evolution is interpreted within the classical "fireball" scenario as a weakly
collimated adiabatic shock propagating in the interstellar medium. The presence
of a SN light curve superimposed on the non-thermal afterglow emission is
investigated: while in the optical bands no significant contribution to the
total light is found from a SN, the NIR J-band data show an excess which is
consistent with a SN as bright as the known hypernova SN1998bw. If the SN
interpretation is true, this would be the farthest GRB-associated SN, as well
as the farthest core-collapse SN, discovered to date. However, other possible
explanations of this NIR excess are also investigated. Finally, we studied the
photometric properties of the host, and found that it is likely to be a
slightly reddened, subluminous, extreme starburst compact galaxy, with
luminosity about 0.1 L*, an age of about 0.5 Gyr and a specific Star Formation
Rate (SFR) of approximately 30 Msol yr-1 (L/L*)-1. This is the highest specific
SFR value for a GRB host inferred from optical/NIR data.Comment: 13 pages, 6 figures, 3 tables. Accepted for publication in A&A, main
journa
High Quality Early Time Light Curves of GRB 060206: Implications for Gamma Ray Burst Environments and Energetics
The 2-m robotic Liverpool Telescope (LT) reacted promptly to the
high-redshift (z=4.048) gamma-ray burst GRB 060206. The afterglow was
identified automatically and multicolor r'i'z' imaging was triggered without
human intervention. Combining our data with those obtained from later
follow-ups provides a well-sampled optical light-curve from 5 minutes to >2d
after the gamma event. The light-curve is highly structured with at least three
bumps evident in the first 75 minutes, including a major rebrightening
(Delta_r'=-1.6 at t=3000s), interpreted as late energy injection. At early time
(t=440s), we find evidence for fast (Delta t_(rest)<4s<<t) variability,
indicating on-going internal-engine activity. We emphasise that a low redshift
GRB (z<1) with similar intrinsic properties would have been interpreted
completely differently due to undersampling of the light curve in the rest
frame at early times; the light-curve behaviour of GRB 060206 should therefore
not be considered peculiar. Finally, although the observed late-time steepening
of the optical light curve resembles a jet break if taken in isolation, the
lack of a corresponding change in the X-ray slope rules out a jet-break
interpretation. Traditionally, GRB jet breaks have been inferred from optical
data in the absence of simultaneous X-ray data. We suggest therefore that
current estimates of the jet opening angle distribution might be biased by
events like GRB060206. Consequently, the GRB explosion energy distribution and
event rates may have to be revised.Comment: 9 pages, 5 figures, Submitted to Ap
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