17,795 research outputs found
Estimating the magnetic field strength from magnetograms
A properly calibrated longitudinal magnetograph is an instrument that
measures circular polarization and gives an estimation of the magnetic flux
density in each observed resolution element. This usually constitutes a lower
bound of the field strength in the resolution element, given that it can be
made arbitrarily large as long as it occupies a proportionally smaller area of
the resolution element and/or becomes more transversal to the observer and
still produce the same magnetic signal. Yet, we know that arbitrarily stronger
fields are less likely --hG fields are more probable than kG fields, with
fields above several kG virtually absent-- and we may even have partial
information about its angular distribution. Based on a set of sensible
considerations, we derive simple formulae based on a Bayesian analysis to give
an improved estimation of the magnetic field strength for magnetographs.Comment: 8 pages, 7 figures, accepted for publication in A&
Constraining our Universe with X-ray & Optical Cluster Data
We have used recent X-ray and optical data in order to impose some
constraints on the cosmology and cluster scaling relations. Generically two
kind of hypotheses define our model. First we consider that the cluster
population is well described by the standard Press-Schechter (PS) formalism,
and second, these clusters are supposed to follow scaling relations with mass:
Temperature-Mass (T-M) and X-ray Luminosity-Mass (L_x - M). As a difference
with many other authors we do not assume specific scaling relations to model
cluster properties such as the usual virial relation or one observational
determination of the relation. Instead we consider general free
parameter scaling relations. With the previous model (PS plus scalings) we fit
our free parameters to several X-ray and optical data with the advantage over
many other works that we consider all the data sets at the same time. This
prevents us from being inconsistent with some of the available observations.
Among other interesting conclusions, we find that only low-density universes
are compatible with all the data considered and that the degeneracy between
and is broken. Also we obtain interesting limits on the
parameters characterizing the scaling relations.Comment: 11 pages, 7 figures. MNRAS accepted versio
- …