101 research outputs found
The BL Lac objects OQ 530 and S5 0716+714. Simultaneous observations in the X-rays, radio, optical and TeV bands
We present the results of the BeppoSAX observations of two BL Lacs, OQ 530
and S5 0716+714, as part of a ToO program for the simultaneous observation at
radio, optical, X-ray and TeV energies. Both sources are detected in the LECS
and MECS, with S5 0716+714 visible also in the PDS band, up to about 60 keV.
The X-ray spectra of both sources are better fitted by a double power-law
model, with a steep soft X-ray component flattening at harder energies, with
breaks at 0.3 and 1.5 keV, respectively. The concave shape of the spectra in
both objects is consistent with soft X-rays being produced by the synchrotron
and harder X-rays by the inverse Compton processes. Also the X-ray variability
properties confirm this scenario, in particular for S5 0716+714 our observation
shows variations by about a factor 3 over one hour below 3 keV and no
variability above. Their simultaneous broad band energy spectral distributions
can be successfully interpreted within the frame of a homogeneous synchrotron
and inverse Compton model, including a possible contribution from an external
source of seed photons with the different spectral states of S5 0716+714 being
reproduced by changing the injected power. The resulting parameters are fully
consistent with the two sources being intermediate objects within the
"sequence" scenario proposed for blazars.Comment: 10 pages, 8 figures, accepted by A&
First results from the Solar Orbiter Heavy Ion Sensor
Context.
Aims. Solar Orbiter launched in February 2020 with the goal of revealing the connections between the Sunâs interior, atmosphere, and
the heliosphere. The Solar Orbiter Heavy Ion Sensor (HIS) is a time-of-flight ion mass spectrometer dedicated to measuring heavy
ions in the solar wind.
Methods. We present an overview of the first measurements of heavy ion composition from HIS, reviewing the methods used to
transform the spectra obtained on board into scientific data products and examining two solar wind case studies as well as the
statistical properties of the heavy ion composition observed by HIS. We also carried out a comparison with prior measurements of
heavy ions at L1.
Results. The HIS data set provides the first mass- and charge-resolved heavy ion measurements in the inner heliosphere.
Conclusions. These high temporal resolution data have the potential to transform our understanding of the connections between the
solar wind and its origin at the Sun, as well as the interaction between the solar wind and the environment around planets, comets,
and in the interstellar medium
Multi-colour optical monitoring of eight red blazars
We present the observational results of multi-colour optical monitoring of
eight red blazars from 2003 September to 2004 February. The aim of our
monitoring is to investigate the spectral variability as well as the flux
variations at short and long time scales. The observations were carried out
using the 1.0 m robotic telescope of Mt. Lemmon Optical Astronomy Observatory,
in Arizona, USA, the 0.6 m telescope of Sobaeksan Optical Astronomy Observatory
and the 1.8 m telescope of Bohyunsan Optical Astronomy Observatory, in the
Republic of Korea. During the observations, all sources show strong flux
variations with amplitudes of larger than 0.5 mag. Variations with amplitudes
of over 1 mag are found in four sources. Intraday variations with amplitudes
larger than 0.15 mag, and a rapid brightness increase with a rate of ~0.2 mag
per day in four days, are detected in S5 0716+71. We investigate the
relationship between the colour index and source brightness for each source. We
find that two out of three FSRQs tend to be redder when they are brighter, and,
conversely, all BL Lac objects tend to be bluer. In particular, we find a
significant anti-correlation between the V-I colour index and R magnitude for
3C 454.3. This implies that the spectrum became steeper when the source was
brighter, which is opposite to the common trend for blazars. In contrast,
significant positive correlations are found in 3C 66A, S5 0716+71, and BL Lac.
However, there are only very weak correlations for PKS 0735+17 and OJ 287. We
propose that the different relative contributions of the thermal versus
non-thermal radiation to the optical emission may be responsible for the
different trends of the colour index with brightness in FSRQs and BL Lac
objects.Comment: 15 pages, 12 figures. Accepted for publication in A&
First Solar Orbiter observation of the Alfvénic slow wind and identification of its solar source
Context: Turbulence dominated by large amplitude nonlinear Alfvén-like fluctuations mainly propagating away from the Sun is
ubiquitous in high speed solar wind streams. Recent studies have shown that also slow wind streams may show strong Alfvénic
signatures, especially in the inner heliosphere.
Aims: The present study focuses on the characterisation of an Alfvénic slow solar wind interval observed by Solar Orbiter on July
14-18, 2020 at a heliocentric distance of 0.64 AU.
Methods: Our analysis is based on plasma moments and magnetic field measurements from the Solar Wind Analyser (SWA) and
Magnetometer (MAG) instruments, respectively. We compare the behaviour of different parameters to characterise the stream in
terms of the Alfvénic content and magnetic properties. We perform also a spectral analysis to highlight spectral features and waves
signature using power spectral density and magnetic helicity spectrograms, respectively. Moreover, we reconstruct the Solar Orbiter
magnetic connectivity to the solar sources via both a ballistic and a Potential Field Source Surface (PFSS) model.
Results: The Alfvénic slow wind stream described in this paper resembles in many respects a fast wind stream. Indeed, at large scales,
the time series of the speed profile shows a compression region, a main portion of the stream and a rarefaction region, characterised by
different features. Moreover, before the rarefaction region, we pinpoint several structures at different scales recalling the spaghetti-like
flux-tube texture of the interplanetary magnetic field. Finally, we identify the connections between Solar Orbiter in situ measurements,
tracing them down to coronal streamer and pseudostreamer configurations.
Conclusions. The characterisation of the Alfvénic slow wind stream observed by Solar Orbiter and the identification of its solar
source are extremely important aspects to understand possible future observations of the same solar wind regime, especially as solar
activity is increasing toward a maximum, where a higher incidence of this solar wind regime is expected
Magnetic reconnection as a mechanism to produce multiple protonpopulations and beams locally in the solar wind
Context. Spacecraft observations early revealed frequent multiple proton populations in the solar wind. Decades of research on their origin have focused on processes such as magnetic reconnection in the low corona and wave-particle interactions in the corona and locally in the solar wind.Aims.This study aims to highlight that multiple proton populations and beams are also produced by magnetic reconnection occurring locally in the solar wind. Methods. We use high resolution Solar Orbiter proton velocity distribution function measurements, complemented by electron and magnetic field data, to analyze the association of multiple proton populations and beams with magnetic reconnection during a period of slow Alfv\'enic solar wind on 16 July 2020. Results. At least 6 reconnecting current sheets with associated multiple proton populations and beams, including a case of magnetic reconnection at a switchback boundary, are found during this day. This represents 2% of the measured distribution functions. We discuss how this proportion may be underestimated, and how it may depend on solar wind type and distance from the Sun. Conclusions. Although suggesting a likely small contribution, but which remains to be quantitatively assessed, Solar Orbiter observations show that magnetic reconnection must be considered as one of the mechanisms that produce multiple proton populations and beams locally in the solar wind
Parker solar probe: four years of discoveries at solar cycle minimum
Launched on 12 Aug. 2018, NASAâs Parker Solar Probe had completed 13 of its scheduled 24 orbits around the Sun by Nov. 2022. The missionâs primary science goal is to determine the structure and dynamics of the Sunâs coronal magnetic field, understand how the solar corona and wind are heated and accelerated, and determine what processes accelerate energetic particles. Parker Solar Probe returned a treasure trove of science data that far exceeded quality, significance, and quantity expectations, leading to a significant number of discoveries reported in nearly 700 peer-reviewed publications. The first four years of the 7-year primary mission duration have been mostly during solar minimum conditions with few major solar events. Starting with orbit 8 (i.e., 28 Apr. 2021), Parker flew through the magnetically dominated corona, i.e., sub-AlfvĂ©nic solar wind, which is one of the missionâs primary objectives. In this paper, we present an overview of the scientific advances made mainly during the first four years of the Parker Solar Probe mission, which go well beyond the three science objectives that are: (1) Trace the flow of energy that heats and accelerates the solar corona and solar wind; (2) Determine the structure and dynamics of the plasma and magnetic fields at the sources of the solar wind; and (3) Explore mechanisms that accelerate and transport energetic particles
First light observations of the solar wind in the outer corona with the Metis coronagraph
In this work, we present an investigation of the wind in the solar corona that has been initiated by observations of the resonantly scattered ultraviolet emission of the coronal plasma obtained with UVCS-SOHO, designed to measure the wind outflow speed by applying Doppler dimming diagnostics. Metis on Solar Orbiter complements the UVCS spectroscopic observations that were performed during solar activity cycle 23 by simultaneously imaging the polarized visible light and the H?» I Lyman-α corona in order to obtain high spatial and temporal resolution maps of the outward velocity of the continuously expanding solar atmosphere. The Metis observations, taken on May 15, 2020, provide the first HI Lyman-α images of the extended corona and the first instantaneous map of the speed of the coronal plasma outflows during the minimum of solar activity and allow us to identify the layer where the slow wind flow is observed. The polarized visible light (580-640 nm) and the ultraviolet HI Lyα (121.6 nm) coronal emissions, obtained with the two Metis channels, were combined in order to measure the dimming of the UV emission relative to a static corona. This effect is caused by the outward motion of the coronal plasma along the direction of incidence of the chromospheric photons on the coronal neutral hydrogen. The plasma outflow velocity was then derived as a function of the measured Doppler dimming. The static corona UV emission was simulated on the basis of the plasma electron density inferred from the polarized visible light. This study leads to the identification, in the velocity maps of the solar corona, of the high-density layer about ±10° wide, centered on the extension of a quiet equatorial streamer present at the east limb - the coronal origin of the heliospheric current sheet - where the slowest wind flows at about 160 ± 18 km s-1 from 4 Râ to 6 Râ. Beyond the boundaries of the high-density layer, the wind velocity rapidly increases, marking the transition between slow and fast wind in the corona
Coronal Heating Rate in the Slow Solar Wind
This Letter reports the first observational estimate of the heating rate in the slowly expanding solar corona. The analysis exploits the simultaneous remote and local observations of the same coronal plasma volume, with the Solar Orbiter/Metis and the Parker Solar Probe instruments, respectively, and relies on the basic solar wind magnetohydrodynamic equations. As expected, energy losses are a minor fraction of the solar wind energy flux, since most of the energy dissipation that feeds the heating and acceleration of the coronal flow occurs much closer to the Sun than the heights probed in the present study, which range from 6.3 to 13.3 R & ODOT;. The energy deposited to the supersonic wind is then used to explain the observed slight residual wind acceleration and to maintain the plasma in a nonadiabatic state. As derived in the Wentzel-Kramers-Brillouin limit, the present energy transfer rate estimates provide a lower limit, which can be very useful in refining the turbulence-based modeling of coronal heating and subsequent solar wind acceleration
EFSA Panel on Dietetic Products, Nutrition, and Allergies (NDA); Scientific Opinion on Dietary Reference Values for fats, including saturated fatty acids, polyunsaturated fatty acids, monounsaturated fatty acids, trans fatty acids, and cholesterol
This Opinion of the EFSA Panel on Dietetic Products, Nutrition, and Allergies (NDA) deals with the setting of Dietary Reference Values (DRVs) for fats. A lower bound of the reference intake range for total fat of 20 energy % (E%) and an upper bound of 35 E% are proposed. Fat intake in infants can gradually be reduced from 40 E% in the 6-12 month period to 35-40 E% in the 2nd and 3rd year of life. For specific fatty acids the following is proposed: saturated fatty acid (SFA) and trans fatty acid intake should be as low as possible; not to set any DRV for cis-monounsaturated fatty acids; not to formulate a DRV for the intake of total cis-polyunsaturated fatty acids (PUFA); not to set specific values for the n-3/n-6 ratio; to set an Adequate Intake (AI) of 4 E% for linolenic acid; not to set any DRV for arachidonic acid; not to set an UL for total or any of the n-6 PUFA; to set an AI for alpha-linilenic acid (ALA) of 0.5 E%; not to set an UL for ALA; to set an AI of 250 mg for eicosapentaenoic acid (EPA) plus docosahexaenoic acid (DHA) for adults; to set an AI of 100 mg DHA for infants (>6 months) and young children <24 months; to increase by 100-200 mg preformed DHA in addition to the AI for adults as an adequate supply of n-3 long chain PUFA during pregnancy and lactation; not to set any DRV for conjugated linoleic acid. For cholesterol it was decided not to propose a reference value beside the limitation on the intake of SF
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