SN 2018agk: A Prototypical Type Ia Supernova with a Smooth Power-law Rise in Kepler (K2)

We present the 30 minutes cadence Kepler/K2 light curve of the Type Ia supernova (SN Ia) SN 2018agk, covering approximately one week before explosion, the full rise phase, and the decline until 40 days after peak. We additionally present ground-based observations in multiple bands within the same time range, including the 1 day cadence DECam observations within the first ∼5 days after the first light. The Kepler early light curve is fully consistent with a single power-law rise, without evidence of any bump feature. We compare SN 2018agk with a sample of other SNe Ia without early excess flux from the literature. We find that SNe Ia without excess flux have slowly evolving early colors in a narrow range (g − i ≈ −0.20 ± 0.20 mag) within the first ∼10 days. On the other hand, among SNe Ia detected with excess, SN 2017cbv and SN 2018oh tend to be bluer, while iPTF16abc’s evolution is similar to normal SNe Ia without excess in g − i. We further compare the Kepler light curve of SN 2018agk with companion-interaction models, and rule out the existence of a typical nondegenerate companion undergoing Roche lobe overflow at viewing angles smaller than 45°.

Spectral Evolution of an Eruptive Polar Crown Prominence With IRIS Observations

Prominence eruption is closely related to coronal mass ejections and is an important topic in solar physics. Spectroscopic observation is an effective way to explore the plasma properties, but the spectral observations of eruptive prominences are rare. In this paper we will introduce an eruptive polar crown prominence with spectral observations from the Interface Region Imaging Spectrograph (IRIS), and try to explain some phenomena that are rarely reported in previous works. The eruptive prominence experiences a slow-rise and fast-rise phase, while the line-of-sight motions of the prominence plasma could be divided into three periods: 2 hours before the fast-rise phase, opposite Doppler shifts are found at the two sides of the prominence axis; then, red shifts dominate the prominence gradually; in the fast-rise phase, the prominence gets to be blue-shifted. During the second period, a faint component appears in Mg ii k window with a narrow line width and a large red shift. A faint region is also found in AIA 304Å images along the prominence spine, and the faint region gets darker during the expansion of the spine. We propose that the opposite Doppler shifts in the first period is a feature of the polar crown prominence that we studied. The red shifts in the second period are possibly due to mass drainage during the elevation of the prominence spine, which could accelerate the eruption in return. The blue shifts in the third period are due to that the prominence erupts toward the observer. We suggest that the faint component appears due to the decreasing of the plasma density, and the latter results from the expansion of the prominence spine.

A Summary Report on Excavation at Marnel Park (Phase 2), Popley, Basingstoke, 2018

An archaeological excavation was undertaken by Cotswold Archaeology in February 2018, at Marnel Park (Phase 2 area), Popley, Basingstoke. The excavation was targeted on a group of later prehistoric pits identified by evaluation. Excavation confirmed a single phase of Late Bronze Age /Early Iron Age activity, represented by a group of eight pits, some of which were intercutting. Three pit fills were notably rich in charcoal and charred plant remains, while others may represent backfill deposits. One pit contained quantities of fired clay, together with quern fragments and remains of pottery vessels which appeared to have been broken in situ. These finds appear to represent a structured deposit. A small assemblage of worked flint is largely redeposited. The Marnel Park (Phase 2) site has produced evidence of peripheral Late Bronze Age and Early Iron Age activity around the excavated Marnel Park/Merton Rise Phase 1 site, to the south and west.

Source-region characteristics of anemone active regions in the ascending phase of solar cycle 24

Context. Active regions in close proximity to coronal holes, also known as anemone regions, are the best candidates for studying the interaction between closed and open magnetic field topologies at the Sun. Statistical investigation of their source-region characteristics can provide vital clues regarding their possible association with energetic events, relevant from space weather perspectives. Aims. The main goal of our study is to understand the distinct properties of flaring and non-flaring anemone active regions and their host coronal holes, by examining spatial and magnetic field distributions during the rise phase of the solar cycle, in the years 2011–2014. Methods. Anemone regions were identified from the minimum-distance threshold, estimated using the data available in the online catalogs for on-disk active regions and coronal holes. Along with the source-region area and magnetic field characteristics, associated filament and flare cases were also located. Regions with and without flare events were further selected for a detailed statistical examination to understand the major properties of the energetic events, both eruptive and confined, at the anemone-type active regions. Results. Identified anemone regions showed weak asymmetry in their spatial distribution over the solar disk, with yearly average independent from mean sunspot number trend, during the rise phase of solar cycle 24. With the progression in solar cycle, the area and minimum-distance parameters indicated a decreasing trend in their magnitudes, while the magnetic field characteristics indicated an increase in their estimated magnitudes. More than half of the regions in our database had an association with a filament structure, and nearly a third were linked with a magnetic reconnection (flare) event. Anemone regions with and without flares had clear distinctions in their source-region characteristics evident from the distribution of their properties and density analysis. The key differences included larger area and magnetic field magnitudes for flaring anemone regions, along with smaller distances between the centers of the active region and its host coronal hole.

Dynamic processes in an active region in the initial and impulsive phases of the eruptive flare event on June 7, 2011

We present the results of an analysis of Hα monochromatic and spectral observations obtained at the Crimean Astrophysical Observatory for an impressive filament eruption during a flare occurred on June 7, 2011. Our ground-based observations are combined with data acquired by multiple instruments onboard the Solar Dynamics Observatory (SDO/AIA, SDO/HMI). The evolution and dynamics of the eruptive process, the cause of eruption, the structure of the line-of-sight velocity field and fine internal structure of the eruptive filament are studied and a number of physical parameters of the eruptive filament are determined. The results of the analysis have shown that: 1) The evolution of the filament eruption consists of two phases: the slow-rise phase, which began about two hours before the flare onset, and the fast-rise phase, which began almost simultaneously with the flare onset. 2) The eruptive filament had a very complex internal structure and complicated line-of-sight velocity field. The filament does not erupt as a single structure. Several discrete massive absorption fragments are seen with a large number of fine-structure elements inside fragments with different velocities, as well as many plasma blobs that detach from the fragments. 3) The motion of the filament fragments is a combination of rotational motion around the axis of the fragment and a movement as a whole towards the observer. The velocities of such plasma motions are determined. 4) Hα line profiles show a large variety of contrast values, Doppler half-widths and Doppler shifts in eruptive filament elements.

Evolution of the hard X-ray photon index in black-hole X-ray binaries: hints for accretion physics

ABSTRACT Negative and positive correlations between the X-ray photon index and the Eddington-scaled X-ray luminosity were found in the decay phase of X-ray binary outbursts and a sample of active galactic nuclei in former works. We systematically investigate the evolution of the X-ray spectral index, along with the X-ray flux and Eddington ratio, in eight outbursts of four black-hole X-ray binaries, where all selected outbursts have observational data from the Rossi X-ray Timing Explorer in both rise and decay phases. In the initial rise phase, the X-ray spectral index is anticorrelated with the flux and the X-ray spectrum quickly softens when the X-ray flux is approaching the peak value. In the decay phase, the X-ray photon index and the flux follow two different positive correlations and they become anticorrelated again when the X-ray flux is below a critical value, where the anticorrelation part follows the same trend as found in the initial rise phase. Compared with other X-ray binaries, GRO J1655−40 has an evident lower critical Eddington ratio for the anticorrelation and positive transition, which suggests that its black-hole mass and distance are not well constrained, or its intrinsic physics is different.

Mechanical Properties, Failure Mode, and Microstructure of Soil-Cement Modified with Fly Ash and Polypropylene Fiber

In order to investigate the effects of fly ash and polypropylene fiber on mechanical properties, failure mode, and microstructure of soil-cement, the unconfined compression test, splitting tension test, and scanning electron microscopy (SEM) test of soil-cement with different polypropylene fiber contents (0%, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% by weight of dry soil) and fly ash contents (0%, 4%, 8%, and 12% by weight of dry soil) were carried out. The compressive and tensile strengths, deformation characteristics, failure mode, and microstructure of soil-cement modified with fly ash and polypropylene fiber were analyzed. The results show that the unconfined compressive strength and splitting tensile strength of soil-cement show a trend of increasing first and then decreasing with the increase of polypropylene fiber and fly ash content. Under the condition of 0.4% polypropylene fiber and 8% fly ash, the unconfined compressive strength and the splitting tensile strength are 4.90 MPa and 0.91 MPa, respectively, which increased by 32.79% and 51.67% as compared with the plain soil-cement, respectively. When 8% fly ash was used in the experiment, the unconfined compressive peak strain and the splitting tensile peak strain of the inclusion of 0.4% polypropylene fiber were 0.0410 and 0.0196, respectively. The corresponding peak strains were increased by 20.94% and 68.97% as compared with non-fiber-stabilized soil-cement, respectively. The stress-strain curve of fly ash soil-cement modified with polypropylene fiber can be divided into compaction phase, linear rise phase, nonlinear rise phase, and failure phase. Polypropylene fiber constrains the lateral deformation of fly ash soil-cement, which improves the peak strain and the failure mode of soil-cement.