6 research outputs found
The magnetic field topology associated to two M flares
On 27 October, 2003, two GOES M-class flares occurred in the lapse of three
hours in active region NOAA 10486. The two flares were confined and their
associated brightenings appeared at the same location, displaying a very
similar shape both at the chromospheric and coronal levels. We focus on the
analysis of magnetic field (SOHO/MDI), chromospheric (HASTA, Kanzelhoehe Solar
Observatory, TRACE) and coronal (TRACE) observations. By combining our data
analysis with a model of the coronal magnetic field, we compute the magnetic
field topology associated to the two M flares. We find that both events can be
explained in terms of a localized magnetic reconnection process occurring at a
coronal magnetic null point. This null point is also present at the same
location one day later, on 28 October, 2003. Magnetic energy release at this
null point was proposed as the origin of a localized event that occurred
independently with a large X17 flare on 28 October, 2003, at 11:01 UT. The
three events, those on 27 October and the one on 28 October, are homologous.
Our results show that coronal null points can be stable topological structures
where energy release via magnetic reconnection can happen, as proposed by
classical magnetic reconnection models.Comment: 14 pages, 7 figure
A burst with double radio spectrum observed up to 212 GHz
We study a solar flare that occurred on September 10, 2002, in active region
NOAA 10105 starting around 14:52 UT and lasting approximately 5 minutes in the
radio range. The event was classified as M2.9 in X-rays and 1N in H\alpha.
Solar Submillimeter Telescope observations, in addition to microwave data give
us a good spectral coverage between 1.415 and 212 GHz. We combine these data
with ultraviolet images, hard and soft X-rays observations and full-disk
magnetograms. Images obtained from Ramaty High Energy Solar Spectroscopic
Imaging data are used to identify the locations of X-ray sources at different
energies and to determine the X-ray spectrum, while ultra violet images allow
us to characterize the coronal flaring region. The magnetic field evolution of
the active region is analyzed using Michelson Doppler Imager magnetograms. The
burst is detected at all available radio-frequencies. X-ray images (between 12
keV and 300 keV) reveal two compact sources and 212 GHz data, used to estimate
the radio source position, show a single compact source displaced by 25" from
one of the hard X-ray footpoints. We model the radio spectra using two
homogeneous sources, and combine this analysis with that of hard X-rays to
understand the dynamics of the particles. Relativistic particles, observed at
radio wavelengths above 50 GHz, have an electron index evolving with the
typical soft-hard-soft behaviour.Comment: Submitted to Solar Physics, 20 pages, 8 fugure
Hydrogen reionization ends by z = 5.3: Lyman-α optical depth measured by the XQR-30 sample
The presence of excess scatter in the Ly-α forest at z ∼5.5, together with the existence of sporadic extended opaque Gunn-Peterson troughs, has started to provide robust evidence for a late end of hydrogen reionization. However, low data quality and systematic uncertainties complicate the use of Ly-α transmission as a precision probe of reionization's end stages. In this paper, we assemble a sample of 67 quasar sightlines at z > 5.5 with high signal-to-noise ratios of >10 per ≤15 km s-1 spectral pixel, relying largely on the new XQR-30 quasar sample. XQR-30 is a large program on VLT/X-Shooter which obtained deep (SNR > 20 per pixel) spectra of 30 quasars at z > 5.7. We carefully account for systematics in continuum reconstruction, instrumentation, and contamination by damped Ly-α systems. We present improved measurements of the mean Ly-α transmission over 4.9 3.5σ). Our results indicate that reionization-related fluctuations, whether in the UVB, residual neutral hydrogen fraction, and/or IGM temperature, persist in the intergalactic medium until at least z = 5.3 (t = 1.1 Gyr after the big bang). This is further evidence for a late end to reionization. © 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.Open access articleThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
Euclid. I. Overview of the Euclid mission
International audienceThe current standard model of cosmology successfully describes a variety of measurements, but the nature of its main ingredients, dark matter and dark energy, remains unknown. Euclid is a medium-class mission in the Cosmic Vision 2015-2025 programme of the European Space Agency (ESA) that will provide high-resolution optical imaging, as well as near-infrared imaging and spectroscopy, over about 14,000 deg^2 of extragalactic sky. In addition to accurate weak lensing and clustering measurements that probe structure formation over half of the age of the Universe, its primary probes for cosmology, these exquisite data will enable a wide range of science. This paper provides a high-level overview of the mission, summarising the survey characteristics, the various data-processing steps, and data products. We also highlight the main science objectives and expected performance