24,432 research outputs found
Stellar Polarimetry: Where Are We and Where Are We Going?
On the final day of the Stellar Polarimetry conference, participants split up
into three "breakout sessions" to discuss the future of the field in the areas
of instrumentation, upcoming opportunities, and community priorities. This
contribution compiles the major recommendations arising from each breakout
session. We hope that the polarimetric community will find these ideas useful
as we consider how to maintain the vitality of polarimetry in the coming years.Comment: 7 pages, published in proceedings of "Stellar Polarimetry: From Birth
to Death" (Madison, WI, June 2011
Detailed optical and near-infrared polarimetry, spectroscopy and broadband photometry of the afterglow of GRB 091018: Polarisation evolution
[Abridged] A number of phenomena have been observed in GRB afterglows that
defy explanation by simple versions of the standard fireball model, leading to
a variety of new models. Polarimetry can be a major independent diagnostic of
afterglow physics, probing the magnetic field properties and internal structure
of the GRB jets. In this paper we present the first high quality multi-night
polarimetric light curve of a Swift GRB afterglow, aimed at providing a well
calibrated dataset of a typical afterglow to serve as a benchmark system for
modelling afterglow polarisation behaviour. In particular, our dataset of the
afterglow of GRB 091018 (at redshift z=0.971) comprises optical linear
polarimetry (R band, 0.13 - 2.3 days after burst); circular polarimetry (R
band) and near-infrared linear polarimetry (Ks band). We add to that high
quality optical and near-infrared broadband light curves and spectral energy
distributions as well as afterglow spectroscopy. The linear polarisation varies
between 0 and 3%, with both long and short time scale variability visible. We
find an achromatic break in the afterglow light curve, which corresponds to
features in the polarimetric curve. We find that the data can be reproduced by
jet break models only if an additional polarised component of unknown nature is
present in the polarimetric curve. We probe the ordered magnetic field
component in the afterglow through our deep circular polarimetry, finding
P_circ < 0.15% (2 sigma), the deepest limit yet for a GRB afterglow, suggesting
ordered fields are weak, if at all present. Our simultaneous R and Ks band
polarimetry shows that dust induced polarisation in the host galaxy is likely
negligible.Comment: 20 pages, 14 figures, 3 tables. Accepted for publication in MNRAS.
Some figures are reduced in quality to comply with arXiv size requirement
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
Data Reduction Techniques for High Contrast Imaging Polarimetry. Applications to ExPo
Imaging polarimetry is a powerful tool for detecting and characterizing
exoplanets and circumstellar environments. Polarimetry allows a separation of
the light coming from an unpolarized source such as a star and the polarized
source such as a planet or a protoplanetary disk. Future facilities like SPHERE
at the VLT or EPICS at the E-ELT will incorporate imaging polarimetry to detect
exoplanets. The Extreme Polarimeter (ExPo) is a dual-beam imaging polarimeter
that currently can reach contrast ratios of 10^5, enough to characterize
circumstellar environments. We present the data reduction steps for a dual-beam
imaging polarimeter that can reach contrast ratios of 10^5. The data obtained
with ExPo at the William Herschel Telescope (WHT) are analyzed. Instrumental
artifacts and noise sources are discussed for an unpolarized star and for a
protoplanetary disk (AB Aurigae). The combination of fast modulation and
dual-beam techniques allow us to minimize instrumental artifacts. A proper data
processing and alignment of the images is fundamental when dealing with large
contrasts. Imaging polarimetry proves to be a powerful method to resolve
circumstellar environments even without a coronagraph mask or an Adaptive
Optics system.Comment: 9 pages, 12 Figures, Accepted for publication in A&
X-Ray Polarimetry: Historical Remarks and Other Considerations
We briefly discuss the history of X-ray polarimetry for astronomical
applications including a guide to the appropriate statistics. We also provide
an introduction to some of the new techniques discussed in more detail
elsewhere in these proceedings. We conclude our discussion with our concerns
over adequate ground calibration, especially with respect to unpolarized beams,
and at the system level.Comment: 8 pages, 1 figure presented at "The Coming of Age if X-ray
Polarimetry", Rome, Italy April 27, 200
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