870 research outputs found
Three-dimensional Magnetic Reconnection Triggering an X-class Confined Flare in Active Region 12192
We present an extensive analysis of the X2.0-class confined flare on 2014
October 27 in the great active region AR 12192, observed by the \emph{Interface
Region Imaging Spectrograph} and the \emph{Solar Dynamics Observatory}. The
slipping motion of the substructures within the negative-polarity flare ribbon
(R1) and continual reconnection-induced flows during the confined flare are
first presented. The substructures within ribbon R1 were observed to slip in
opposite directions at apparent speeds of 10-70 km s. The slipping
motion exhibited the quasi-periodic pattern with a period of 80-110 s, which
can be observed since the flare start and throughout the impulsive phase of the
flare. Simultaneously quasi-periodic flows moved along a reverse-S shaped
filament, with an average period of about 90 s. The period of
reconnection-induced flows is similar to that of the slippage of ribbon
substructures, implying the occurrence of quasi-periodic slipping magnetic
reconnection. The spectral observations showed that the Si {\sc iv} line was
blueshifted by 50-240 km s at the location of the flows. During the
process of the flare, the filament did not show the rise phase and was not
associated with any failed eruption. The flare mainly consisted of two sets of
magnetic systems, with both of their east ends anchoring in ribbon R1. We
suggest that the slipping magnetic reconnection between two magnetic systems
triggers the confined flare.Comment: 21 pages, 7 figures; accepted for publication in Ap
Two Episodes of Magnetic Reconnections During a Confined Circular-ribbon Flare
We analyze a unique event with an M1.8 confined circular-ribbon flare on 2016
February 13, with successive formations of two circular ribbons at the same
location. The flare had two distinct phases of UV and EUV emissions with an
interval of about 270 s, of which the second peak was energetically more
important. The first episode was accompanied by the eruption of a mini-filament
and the fast elongation motion of a thin circular ribbon (CR1) along the
counterclockwise direction at a speed of about 220 km/s. Two elongated
spine-related ribbons were also observed, with the inner ribbon co-temporal
with CR1 and the remote brightenings forming ~20 s later. In the second
episode, another mini-filament erupted and formed a blowout jet. The second
circular ribbon and two spine-related ribbons showed similar elongation motions
with that during the first episode. The extrapolated 3D coronal magnetic fields
reveal the existence of a fan-spine topology, together with a quasi-separatrix
layer (QSL) halo surrounding the fan plane and another QSL structure outlining
the inner spine. We suggest that continuous null-point reconnection between the
filament and ambient open field occurs in each episode, leading to the
sequential opening of the filament and significant shifts of the fan plane
footprint. For the first time, we propose a compound eruption model of
circular-ribbon flares consisting of two sets of successively formed ribbons
and eruptions of multiple filaments in a fan-spine-type magnetic configuration.Comment: Accepted for publication in the Astrophysical Journal, 20 pages, 6
figure
A secondary fan-spine magnetic structure in active region 11897
Fan-spine is a special topology in solar atmosphere and is closely related to
magnetic null point as well as circular-ribbon flares, which can provide
important information for understanding the intrinsic three-dimensional (3D)
nature of solar flares. However, the fine structure within the fan has rarely
been investigated. In present paper, we investigate a secondary fan-spine (SFS)
structure within the fan of a larger fan-spine topology. On 2013 November 18,
this large fan-spine structure was traced out due to the partial eruption of a
filament, which caused a circular-ribbon flare in active region 11897. The
extrapolated 3D magnetic fields and squashing factor Q maps depict distinctly
this fan-spine topology, its surrounding quasi-separatrix layer (QSL) halo, and
a smaller quasi-circular ribbon with high Q located in the center, which
implies the existence of fine structure within the fan. The imaging
observations, extrapolated 3D fields, and Q maps on November 17 show that there
indeed exists an SFS surrounded by a QSL, which is enveloped by another
QSL-halo corresponding to the overlying larger domeshaped fan. Moreover, the
material flows caused by the null-point reconnection are also detected along
this SFS. After checking the evolution of the underneath magnetic fields, we
suggest that the continuous emergence of magnetic flux within the central
parasitic region encompassed by the opposite-polarity fields results in the
formation of the SFS under the large fan.Comment: 22 pages, 7 figures, accepted for publication in Ap
Two Types of Solar Confined Flares
With the aim of understanding the physical mechanisms of confined flares, we
selected 18 confined flares during 2011-2017, and classified the confined
flares into two types based on their different dynamic properties and magnetic
configurations. "Type I" of confined flares are characterized by slipping
reconnection, strong shear, and stable filament. "Type II" flares have nearly
no slipping reconnection, and have a configuration in potential state after the
flare. Filament erupts but is confined by strong strapping field. "Type II"
flares could be explained by 2D MHD models while "type I" flares need 3D MHD
models. 7 flares of 18 (39 \%) belong to "type I" and 11 (61 \%)
are "type II" confined flares. The post-flare loops (PFLs) of "type I" flares
have a stronger non-potentiality, however, the PFLs in "type II" flares are
weakly sheared. All the "type I" flares exhibit the ribbon elongations parallel
to the polarity inversion line (PIL) at speeds of several tens of km s.
For "type II" flares, only a small proportion shows the ribbon elongations
along the PIL. We suggest that different magnetic topologies and reconnection
scenarios dictate the distinct properties for the two types of flares. Slipping
agnetic reconnections between multiple magnetic systems result in "type I"
flares. For "type II" flares, magnetic reconnections occur in anti-parallel
magnetic fields underlying the erupting filament. Our study shows that "type I"
flares account for more than one third of the overall large confined flares,
which should not be neglected in further studies.Comment: 42 pages, 17 figures. Accepted for publication in ApJ
Emergence of fermionic finite-temperature critical point in a Kondo lattice
The underlying Dirac point is central to the profound physics manifested in a
wide class of materials. However, it is often difficult to drive a system with
Dirac points across the massless fermionic critical point. Here by exploiting
screening of local moments under spin-orbit interactions in a Kondo lattice, we
show that below the Kondo temperature, the Kondo lattice undergoes a
topological transition from a strong topological insulator to a weak
topological insulator at a finite temperature . At , massless Dirac
points emerge and the Kondo lattice becomes a Dirac semimetal. Our analysis
indicates that the emergent relativistic symmetry dictates non-trivial thermal
responses over large parameter and temperature regimes. In particular, it
yields critical scaling behaviors both in magnetic and transport responses near
.Comment: 5 pages, 3 figures, to appear in Phys. Rev. Let
Mapping the sensitivity of hadronic experiments to nucleon structure
Determinations of the proton's collinear parton distribution functions (PDFs)
are emerging with growing precision due to increased experimental activity at
facilities like the Large Hadron Collider. While this copious information is
valuable, the speed at which it is released makes it difficult to quickly
assess its impact on the PDFs, short of performing computationally expensive
global fits. As an alternative, we explore new methods for quantifying the
potential impact of experimental data on the extraction of proton PDFs. Our
approach relies crucially on the Hessian correlation between theory-data
residuals and the PDFs themselves, as well as on a newly defined quantity ---
the sensitivity --- which represents an extension of the correlation and
reflects both PDF-driven and experimental uncertainties. This approach is
realized in a new, publicly available analysis package PDFSense, which operates
with these statistical measures to identify particularly sensitive experiments,
weigh their relative or potential impact on PDFs, and visualize their detailed
distributions in a space of the parton momentum fraction and factorization
scale . This tool offers a new means of understanding the influence of
individual measurements in existing fits, as well as a predictive device for
directing future fits toward the highest impact data and assumptions. Along the
way, many new physics insights can be gained or reinforced. As one of many
examples, PDFSense is employed to rank the projected impact of new LHC
measurements in jet, vector boson, and production and leads us to
the conclusion that inclusive jet production at the LHC has a potential for
playing an indispensable role in future PDF fits. These conclusions are
independently verified by preliminarily fitting this experimental information
and investigating the constraints they supply using the Lagrange multiplier
technique.Comment: 43 pages, 10 figures, 17 tables --- published in Phys. Rev. D and
validated against Lagrange Multiplier scans in Sect.IV.D. Minor clarification
added to Table XIV of the Supplemental Materia
PDFSense: Mapping the sensitivity of hadronic experiments to nucleon structure
Recent high precision experimental data from a variety of hadronic processes
opens new opportunities for determination of the collinear parton distribution
functions (PDFs) of the proton. In fact, the wealth of information from
experiments such as the Large Hadron Collider (LHC) and others, makes it
difficult to quickly assess the impact on the PDFs, short of performing
computationally expensive global fits. As an alternative, we explore new
methods for quantifying the potential impact of experimental data on the
extraction of proton PDFs. Our approach relies crucially on the correlation
between theory-data residuals and the PDFs themselves, as well as on a newly
defined quantity --- the sensitivity --- which represents an extension of the
correlation and reflects both PDF-driven and experimental uncertainties. This
approach is realized in a new, publicly available analysis package PDFSense,
which operates with these statistical measures to identify particularly
sensitive experiments, weigh their relative or potential impact on PDFs, and
visualize their detailed distributions in a space of the parton momentum
fraction x and factorization scale \mu. This tool offers a new means of
understanding the influence of individual measurements in existing fits, as
well as a predictive device for directing future fits toward the highest impact
data and assumptions.Comment: 6 pages, 3 figures. arXiv admin note: substantial text overlap with
arXiv:1803.0277
Magnetic Flux of Active Regions Determining the Eruptive Character of Large Solar Flares
We establish the largest eruptive/confined flare database to date and analyze
322 flares of \emph{GOES} class M1.0 and larger that occurred during
20102019, i.e., almost spanning the entire solar cycle 24. We find that the
total unsigned magnetic flux () of active regions (ARs) is a key
parameter in governing the eruptive character of large flares, with the
proportion of eruptive flares exhibiting a strong anti-correlation with
. This means that an AR containing a large magnetic flux has a
lower probability for the large flares it produces to be associated with a
coronal mass ejection (CME). This finding is supported by the high positive
correlation we obtained between the critical decay index height and
, implying that ARs with a larger have a stronger
magnetic confinement. Moreover, the confined flares originating from ARs larger
than 1.0 Mx have several characteristics in common: stable
filament, slipping magnetic reconnection and strongly sheared post-flare loops.
Our findings reveal new relations between the magnetic flux of ARs and the
occurrence of CMEs in association with large flares. These relations obtained
here provide quantitative criteria for forecasting CMEs and adverse space
weather, and have also important implications for "superflares" on solar-type
stars and stellar CMEs. The link of database is
https://doi.org/10.12149/101030.Comment: 31 pages, 13 figures, accepted for publication in Ap
Reconstruction of Monte Carlo replicas from Hessian parton distributions
We explore connections between two common methods for quantifying the
uncertainty in parton distribution functions (PDFs), based on the Hessian error
matrix and Monte-Carlo sampling. CT14 parton distributions in the Hessian
representation are converted into Monte-Carlo replicas by a numerical method
that reproduces important properties of CT14 Hessian PDFs: the asymmetry of
CT14 uncertainties and positivity of individual parton distributions. The
ensembles of CT14 Monte-Carlo replicas constructed this way at NNLO and NLO are
suitable for various collider applications, such as cross section reweighting.
Master formulas for computation of asymmetric standard deviations in the
Monte-Carlo representation are derived. A correction is proposed to address a
bias in asymmetric uncertainties introduced by the Taylor series approximation.
A numerical program is made available for conversion of Hessian PDFs into
Monte-Carlo replicas according to normal, log-normal, and Watt-Thorne sampling
procedures.Comment: 21 pages, 10 figures; final JHEP version, extended Sec. 2 to discuss
sampling of asymmetric PDF replica distributions with imposed positivity
constraint
Multi-Wavelength Observations of GRB 111228A and Implications for the Fireball and its environment
Observations of very early multi-wavelength afterglows are critical to reveal
the properties of the radiating fireball and its environment as well as the
central engine of gamma-ray bursts (GRBs). We report our optical observations
of GRB 111228A from 95 sec to about 50 hours after the burst trigger and
investigate its properties of the prompt gamma-rays and the ambient medium
using our data and the data observed with {\em Swift} and {\em Fermi} missions.
Our joint optical and X-ray spectral fits to the afterglow data show that the
ambient medium features as low dust-to-gas ratio. Incorporating the energy
injection effect, our best fit to the afterglow lightcurves with the standard
afterglow model via the Markov Chain Monte Carlo (MCMC) technique shows that
, , ,
cm. The low medium density likely implies that the afterglow jet may be
in a halo or in a hot ISM. Achromatic shallow decay segment observed in the
optical and X-ray bands is well explained with the long-lasting energy
injection from the central engine, which would be a magnetar with a period of
about 1.92 ms inferred from the data. The of its time-integrated prompt
gamma-ray spectrum is KeV. Using the initial Lorentz factor
() derived from our afterglow model fit, it is
found that GRB 111228A satisfies the
relation and bridges the typical GRBs and low luminosity GRBs in this relation.Comment: 33 pages, 18 figures, 2 tables. Accepted by Ap
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