A Center-Median Filtering Method for Detection of Temporal Variation in Coronal Images

Events in the solar corona are often widely separated in their timescales, which can allow them to be identified when they would otherwise be confused with emission from other sources in the corona. Methods for cleanly separating such events based on their timescales are thus desirable for research in the field. This paper develops a technique for identifying time-varying signals in solar coronal image sequences which is based on a per-pixel running median filter and an understanding of photon-counting statistics. Example applications to 'EIT Waves' and small-scale dynamics are shown, both using data from the 193 Angstrom channel on AIA. The technique is found to discriminate EIT Waves more cleanly than the running and base difference techniques most commonly used. It is also demonstrated that there is more signal in the data than is commonly appreciated, finding that the waves can be traced to the edge of the AIA field of view when the data are rebinned to increase the signal-to-noise ratio.Comment: 15 pages, 7 Figures, Accepted to Journal of Space Weather and Space Climate; version 2 has slight text changes and updated movie URL

Fast Differential Emission Measure Inversion of Solar Coronal Data

We present a fast method for reconstructing Differential Emission Measures (DEMs) using solar coronal data. On average, the method computes over 1000 DEMs per second for a sample active region observed by the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO), and achieves reduced chi-squared of order unity with no negative emission in all but a few test cases. The high performance of this method is especially relevant in the context of AIA, which images of order one million solar pixels per second. This paper describes the method, analyzes its fidelity, compares its performance and results with other DEM methods, and applies it to an active region and loop observed by AIA and by the Extreme-ultraviolet Imaging Spectrometer (EIS) on Hinode.Comment: 22 Pages, 11 Figures; submitted to The Astrophysical Journal. This version (2) includes clarifications in the text and reflects improvements to the DEM cod

Coronal Loop Expansion Properties Explained Using Separators

One puzzling observed property of coronal loops is that they are of roughly constant thickness along their length. Various studies have found no consistent pattern of width variation along the length of loops observed by TRACE and SOHO. This is at odds with expectations of magnetic flux tube expansion properties, which suggests that loops are widest at their tops, and significantly narrower at their footpoints. Coronal loops correspond to areas of the solar corona which have been preferentially heated by some process, so this observed property might be connected to the mechanisms that heat the corona. One means of energy deposition is magnetic reconnection, which occurs along field lines called separators. These field lines begin and end on magnetic null points, and loops forming near them can therefore be relatively wide at their bases. Thus, coronal energization by magnetic reconnection may replicate the puzzling expansion properties observed in coronal loops. We present results of a Monte Carlo survey of separator field line expansion properties, comparing them to the observed properties of coronal loops.Comment: 16 pages, 9 figures, to be submitted to Ap

LATOR Covariance Analysis

We present results from a covariance study for the proposed Laser Astrometric Test of Relativity (LATOR) mission. This mission would send two laser-transmitter spacecraft behind the Sun and measure the relative gravitational light bending of their signals using a hundred-meter-baseline optical interferometer to be constructed on the International Space Station. We assume that each spacecraft is equipped with a $< 1.9 \times 10^{-13} \mathrm{m} \mathrm{s}^2 \mathrm{Hz}^{-1/2}$ drag-free system and assume approximately one year of data. We conclude that the observations allow a simultaneous determination of the orbit parameters of the spacecraft and of the Parametrized Post-Newtonian (PPN) parameter $\gamma$ with an uncertainty of $2.4 \times 10^{-9}$. We also find a $6 \times 10^{-9}$ determination of the solar quadrupole moment, $J_2$, as well as the first measurement of the second-order post-PPN parameter $\delta$ to an accuracy of about $10^{-3}$.Comment: 9 pages, 3 figures. first revision: minor changes to results. Second revision: additional discussion of orbit modelling and LATOR drag-free system requirement feasibility. Added references to tables I and V (which list PPN parameter uncertainties), removed word from sentence in Section III. 3rd revision: removed 2 incorrect text fragments (referring to impact parameter as distance of closest approach) and reference to upcoming publication of ref. 2, removed spurious gamma from eq. 1 - Last error is still in cqg published versio

Constraining the Black Hole Mass Spectrum with LISA Observations II: Direct comparison of detailed models

A number of scenarios have been proposed for the origin of the supermassive black holes (SMBHs) that are found in the centres of most galaxies. Many such scenarios predict a high-redshift population of massive black holes (MBHs), with masses in the range 100 to 100000 times that of the Sun. When the Laser Interferometer Space Antenna (LISA) is finally operational, it is likely that it will detect on the order of 100 of these MBH binaries as they merge. The differences between proposed population models produce appreciable effects in the portion of the population which is detectable by LISA, so it is likely that the LISA observations will allow us to place constraints on them. However, gravitational wave detectors such as LISA will not be able to detect all such mergers nor assign precise black hole parameters to the merger, due to weak gravitational wave signal strengths. This paper explores LISA's ability to distinguish between several MBH population models. In this way, we go beyond predicting a LISA observed population and consider the extent to which LISA observations could inform astrophysical modellers. The errors in LISA parameter estimation are applied with a direct method which generates random sample parameters for each source in a population realisation. We consider how the distinguishability varies depending on the choice of source parameters (1 or 2 parameters chosen from masses, redshift or spins) used to characterise the model distributions, with confidence levels determined by 1 and 2-dimensional tests based on the Kolmogorov-Smirnov test.Comment: 32 pages, 21 Figures, 6 Tables; Submitted to MNRA

Three-Dimensional Reconstructions of Coronal Wave Surfaces Using a New Mask-Fitting Method

Coronal waves are large-scale disturbances often driven by coronal mass ejections (CMEs). We investigate a spectacular wave event on 7 March 2012, which is associated with an X5.4 flare (SOL2012-03-07). By using a running center-median (RCM) filtering method for the detection of temporal variations in extreme ultraviolet (EUV) images, we enhance the EUV disturbance observed by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) and the Sun Watcher using Active Pixel System detector and Image Processing (SWAP) onboard the PRoject for Onboard Autonomy 2 (PROBA2). In coronagraph images, a halo front is observed to be the upper counterpart of the EUV disturbance. Based on the EUV and coronagraph images observed from three different perspectives, we have made three-dimensional (3D) reconstructions of the wave surfaces using a new mask-fitting method. The reconstructions are compared with those obtained from forward-fitting methods. We show that the mask fitting method can reflect the inhomogeneous coronal medium by capturing the concave shape of the shock wave front. Subsequently, we trace the developing concave structure and derive the deprojected wave kinematics. The speed of the 3D-wave nose increases from a low value below a few hundred $\mathrm{km\,s^{-1}}$ to a maximum value of about 3800 $\mathrm{km\,s^{-1}}$, and then slowly decreases afterwards. The concave structure starts to decelerate earlier and has significantly lower speeds than those of the wave nose. We also find that the 3D-wave in the extended corona has a much higher speed than the speed of EUV disturbances across the solar disk.Comment: Solar Physics: Topical Collection "Ten Years of Solar Observations with PROBA2", accepte