8 research outputs found
BRITE-Constellation: Data processing and photometry
The BRITE mission is a pioneering space project aimed at the long-term
photometric monitoring of the brightest stars in the sky by means of a
constellation of nano-satellites. Its main advantage is high photometric
accuracy and time coverage inaccessible from the ground. The main aim of this
paper is the presentation of procedures used to obtain high-precision
photometry from a series of images acquired by the BRITE satellites in two
modes of observing, stare and chopping. We developed two pipelines
corresponding to the two modes of observing. The assessment of the performance
of both pipelines is presented. It is based on two comparisons, which use data
from six runs of the UniBRITE satellite: (i) comparison of photometry obtained
by both pipelines on the same data, which were partly affected by charge
transfer inefficiency (CTI), (ii) comparison of real scatter with theoretical
expectations. It is shown that for CTI-affected observations, the chopping
pipeline provides much better photometry than the other pipeline. For other
observations, the results are comparable only for data obtained shortly after
switching to chopping mode. Starting from about 2.5 years in orbit, the
chopping mode of observing provides significantly better photometry for
UniBRITE data than the stare mode. This paper shows that high-precision space
photometry with low-cost nano-satellites is achievable. The proposed meth- ods,
used to obtain photometry from images affected by high impulsive noise, can be
applied to data from other space missions or even to data acquired from
ground-based observations
Detection of spectral evolution in the bursts emitted during the 2008-2009 active episode of SGR J1550 - 5418
In early October 2008, the Soft Gamma Repeater SGRJ1550 - 5418 (1E 1547.0 -
5408, AXJ155052 - 5418, PSR J1550 - 5418) became active, emitting a series of
bursts which triggered the Fermi Gamma-ray Burst Monitor (GBM) after which a
second especially intense activity period commenced in 2009 January and a
third, less active period was detected in 2009 March-April. Here we analyze the
GBM data all the bursts from the first and last active episodes. We performed
temporal and spectral analysis for all events and found that their temporal
characteristics are very similar to the ones of other SGR bursts, as well the
ones reported for the bursts of the main episode (average burst durations \sim
170 ms). In addition, we used our sample of bursts to quantify the systematic
uncertainties of the GBM location algorithm for soft gamma-ray transients to <
8 deg. Our spectral analysis indicates significant spectral evolution between
the first and last set of events. Although the 2008 October events are best fit
with a single blackbody function, for the 2009 bursts an Optically Thin Thermal
Bremsstrahlung (OTTB) is clearly preferred. We attribute this evolution to
changes in the magnetic field topology of the source, possibly due to effects
following the very energetic main bursting episode.Comment: 17 pages, 7 figures, 2 table
The contribution of microlensing surveys to the distance scale
In the early nineties several teams started large scale systematic surveys of
the Magellanic Clouds and the Galactic Bulge to search for microlensing
effects. As a by product, these groups have created enormous time-series
databases of photometric measurements of stars with a temporal sampling
duration and accuracy which are unprecedented. They provide the opportunity to
test the accuracy of primary distance indicators, such as Cepheids, RRLyrae
stars, the detached eclipsing binaries, or the luminosity of the red clump. We
will review the contribution of the microlensing surveys to the understanding
of the physics of the primary distance indicators, recent differential studies
and direct distance determinations to the Magellanic Clouds and the Galactic
Bulge.Comment: Invited review article to appear in: `Post-Hipparcos Cosmic Candles',
A. Heck & F. Caputo (Eds), Kluwer Academic Publ., Dordrecht, in press. 21
pages; uses Kluwer's crckapb.sty LaTeX style file, enclose