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T A Howard - One of the best experts on this subject based on the ideXlab platform.
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interplanetary coronal Mass ejections that are undetected by Solar coronagraphs
Journal of Geophysical Research, 2008Co-Authors: T A Howard, G M SimnettAbstract:[1] From February 2003 to September 2005 the Solar Mass Ejection Imager on the Coriolis spacecraft detected 207 interplanetary coronal Mass ejections (ICME) in the inner heliosphere. We have examined the data from the Large Angle Spectroscopic Coronagraph (LASCO) on the SOHO spacecraft for evidence of coronal transient activity that might have been the Solar progenitor of the Solar Mass Ejection Imager (SMEI) events, taking into account the projected speed of the SMEI event and its position angle in the plane of the sky. We found a significant number of SMEI events where there is either only a weak or unlikely coronal Mass ejection (CME) detected by LASCO or no event at all. A discussion of the effects of projection across large distances on the ICME measurements is made, along with a new technique called the Cube-Fit procedure that was designed to model the ICME trajectory more accurately than simple linear fits to elongation-time plots. Of the 207 SMEI events, 189 occurred during periods of full LASCO data coverage. Of these, 32 or 17% were found to have a weak or unlikely LASCO counterpart, and 14 or 7% had no apparent LASCO transient association. Using Solar X-ray, EUV and Hα data we investigated three main physical possibilities for ICME occurrence with no LASCO counterpart: (1) Corotating interaction regions (CIRs), (2) erupting magnetic structures (EMS), and (3) flare blast waves. We find that only one event may possibly be a CIR and that flare blast waves can be ruled out. The most likely phenomenon is investigated and discussed, that of EMS. Here, the transient erupts in the same manner as a typical CME, except that they do not have sufficient Mass to be detected by LASCO. As the structure moves outward, it accumulates and concentrates Solar wind material until it is bright enough to be detected by SMEI.
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tracking halo coronal Mass ejections from 0 1 au and space weather forecasting using the Solar Mass ejection imager smei
Journal of Geophysical Research, 2006Co-Authors: T A Howard, D F Webb, S J Tappin, Donald R Mizuno, J C JohnstonAbstract:[1] The Solar Mass Ejection Imager (SMEI) has been tracking coronal Mass ejections (CMEs) from the Sun to the Earth and beyond since it came online in February 2003. This paper presents some results from the first 19 months of data from SMEI, when over 140 transients of many kinds were observed in SMEI's all-sky cameras. We focus specifically on 20 earthward directed transients, and compare distance-time plots obtained from the SMEI transients with those observed in halo CMEs by Large-Angle Spectrometric Coronograph (LASCO) aboard Solar and Heliospheric Observatory (SOHO), and the arrival time of the shock observed by ACE at 0.99 AU. The geometry of one particular transient is compared using both LASCO and SMEI images in a first attempt to investigate geometry evolution as the transient propagates through the interplanetary medium. For some events, the halo CME, SMEI transient, and shock at 0.99 AU do not match, suggesting that some transients may not correspond to a halo CME. Finally, an evaluation of the potential of SMEI to be used as a predictor of space weather is presented, by comparing the transients observed in SMEI with the 22 geomagnetic storms which occurred during this timeframe. A transient was observed in 14 cases, and distance-time profiles would have allowed a prediction of the arrival time at ACE within 2 hours of its actual arrival for three events, and within 10 hours for eight events. Of these eight events, seven were detected by SMEI more than 1 day before the transient's arrival at the Earth.
C Affeldt - One of the best experts on this subject based on the ideXlab platform.
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gw190412 observation of a binary black hole coalescence with asymmetric Masses
Physical Review D, 2020Co-Authors: R Abbott, T D Abbott, S Abraham, F Acernese, K Ackley, C Adams, R X Adhikari, V B Adya, C Affeldt, M AgathosAbstract:We report the observation of gravitational waves from a binary-black-hole coalescence during the first two weeks of LIGO's and Virgo's third observing run. The signal was recorded on April 12, 2019 at 05:30:44 UTC with a network signal-to-noise ratio of 19. The binary is different from observations during the first two observing runs most notably due to its asymmetric Masses: a ~30 Solar Mass black hole merged with a ~8 Solar Mass black hole companion. The more Massive black hole rotated with a dimensionless spin magnitude between 0.17 and 0.59 (90% probability). Asymmetric systems are predicted to emit gravitational waves with stronger contributions from higher multipoles, and indeed we find strong evidence for gravitational radiation beyond the leading quadrupolar order in the observed signal. A suite of tests performed on GW190412 indicates consistency with Einstein's general theory of relativity. While the Mass ratio of this system differs from all previous detections, we show that it is consistent with the population model of stellar binary black holes inferred from the first two observing runs.
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gw190814 gravitational waves from the coalescence of a 23 Solar Mass black hole with a 2 6 Solar Mass compact object
The Astrophysical Journal, 2020Co-Authors: R Abbott, T D Abbott, S Abraham, F Acernese, K Ackley, C Adams, R X Adhikari, V B Adya, C AffeldtAbstract:We report the observation of a compact binary coalescence involving a 22.2–24.3 M ⊙ black hole and a compact object with a Mass of 2.50–2.67 M ⊙ (all measurements quoted at the 90% credible level). The gravitational-wave signal, GW190814, was observed during LIGO's and Virgo's third observing run on 2019 August 14 at 21:10:39 UTC and has a signal-to-noise ratio of 25 in the three-detector network. The source was localized to 18.5 deg2 at a distance of ${241}_{-45}^{+41}$ Mpc; no electromagnetic counterpart has been confirmed to date. The source has the most unequal Mass ratio yet measured with gravitational waves, ${0.112}_{-0.009}^{+0.008}$, and its secondary component is either the lightest black hole or the heaviest neutron star ever discovered in a double compact-object system. The dimensionless spin of the primary black hole is tightly constrained to ≤0.07. Tests of general relativity reveal no measurable deviations from the theory, and its prediction of higher-multipole emission is confirmed at high confidence. We estimate a merger rate density of 1–23 Gpc−3 yr−1 for the new class of binary coalescence sources that GW190814 represents. Astrophysical models predict that binaries with Mass ratios similar to this event can form through several channels, but are unlikely to have formed in globular clusters. However, the combination of Mass ratio, component Masses, and the inferred merger rate for this event challenges all current models of the formation and Mass distribution of compact-object binaries.
G M Simnett - One of the best experts on this subject based on the ideXlab platform.
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interplanetary coronal Mass ejections that are undetected by Solar coronagraphs
Journal of Geophysical Research, 2008Co-Authors: T A Howard, G M SimnettAbstract:[1] From February 2003 to September 2005 the Solar Mass Ejection Imager on the Coriolis spacecraft detected 207 interplanetary coronal Mass ejections (ICME) in the inner heliosphere. We have examined the data from the Large Angle Spectroscopic Coronagraph (LASCO) on the SOHO spacecraft for evidence of coronal transient activity that might have been the Solar progenitor of the Solar Mass Ejection Imager (SMEI) events, taking into account the projected speed of the SMEI event and its position angle in the plane of the sky. We found a significant number of SMEI events where there is either only a weak or unlikely coronal Mass ejection (CME) detected by LASCO or no event at all. A discussion of the effects of projection across large distances on the ICME measurements is made, along with a new technique called the Cube-Fit procedure that was designed to model the ICME trajectory more accurately than simple linear fits to elongation-time plots. Of the 207 SMEI events, 189 occurred during periods of full LASCO data coverage. Of these, 32 or 17% were found to have a weak or unlikely LASCO counterpart, and 14 or 7% had no apparent LASCO transient association. Using Solar X-ray, EUV and Hα data we investigated three main physical possibilities for ICME occurrence with no LASCO counterpart: (1) Corotating interaction regions (CIRs), (2) erupting magnetic structures (EMS), and (3) flare blast waves. We find that only one event may possibly be a CIR and that flare blast waves can be ruled out. The most likely phenomenon is investigated and discussed, that of EMS. Here, the transient erupts in the same manner as a typical CME, except that they do not have sufficient Mass to be detected by LASCO. As the structure moves outward, it accumulates and concentrates Solar wind material until it is bright enough to be detected by SMEI.
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the Solar Mass ejection imager smei
Solar Physics, 2003Co-Authors: C J Eyles, A Buffington, M P Cooke, P P Hick, B V Jackson, G M Simnett, Nicholas R Waltham, J M King, Phillip A Anderson, P E HolladayAbstract:We describe an instrument (SMEI) which has been specifically designed to detect and forecast the arrival of Solar Mass ejections and other heliospheric structures which are moving towards the Earth. Such events may cause geomagnetic storms, with resulting radiation hazards and disruption to military and commercial communications; damage to Earth-orbiting spacecraft; and also terrestrial effects such as surges in transcontinental power transmission lines. The detectors are sensitive over the optical wave-band, which is measured using CCD cameras. SMEI was launched on 6 January 2003 on the Coriolis spacecraft into a Sun-synchronous polar orbit as part of the US DoD Space Test Programme. The instrument contains three cameras, each with a field of view of 60°×3°, which are mounted onto the spacecraft such that they scan most of the sky every 102-min orbit. The sensitivity is such that changes in sky brightness equivalent to a tenth magnitude star in one square degree of sky may be detected. Each camera takes an image every 4 s. The normal telemetry rate is 128 kbits s−1. In order to extract the emission from a typical large coronal Mass ejection, stellar images and the signal from the zodiacal dust cloud must be subtracted. This requires accurate relative photometry to 0.1%. One consequence is that images of stars and the zodiacal cloud will be measured to this photometric accuracy once per orbit. This will enable studies of transient zodiacal cloud phenomena, flare stars, supernovae, comets, and other varying point-like objects.
D F Webb - One of the best experts on this subject based on the ideXlab platform.
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v arc interplanetary coronal Mass ejections observed with the Solar Mass ejection imager
Journal of Geophysical Research, 2007Co-Authors: S W Kahler, D F WebbAbstract:[1] Since February 2003, the Solar Mass Ejection Imager (SMEI) has been observing interplanetary coronal Mass ejections (ICMEs) at Solar elongation angles e > 20°. The ICMEs generally appear as loops or arcs in the sky, but five show distinct outward concave shapes that we call V arcs. We expect to observe some V arcs, formed by trailing edges of ICME flux ropes or by leading ICME edges sheared by Solar wind (SW) speed gradients at the heliospheric current sheet. We characterize the properties of these V arcs and compare them with average properties of all SMEI ICMEs. The typical V arc speeds argue against a slow MHD shock interpretation for their structures. We estimate the V arc Solar source locations and their opening angle dynamics as tests for SW shearing. The first test contradicts but the second supports the SW shearing explanation. The implications of the small number of V arcs observed with SMEI is considered. The point P approximation used to determine the V arc locations and inferred Solar source regions is critically examined in Appendix A.
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tracking halo coronal Mass ejections from 0 1 au and space weather forecasting using the Solar Mass ejection imager smei
Journal of Geophysical Research, 2006Co-Authors: T A Howard, D F Webb, S J Tappin, Donald R Mizuno, J C JohnstonAbstract:[1] The Solar Mass Ejection Imager (SMEI) has been tracking coronal Mass ejections (CMEs) from the Sun to the Earth and beyond since it came online in February 2003. This paper presents some results from the first 19 months of data from SMEI, when over 140 transients of many kinds were observed in SMEI's all-sky cameras. We focus specifically on 20 earthward directed transients, and compare distance-time plots obtained from the SMEI transients with those observed in halo CMEs by Large-Angle Spectrometric Coronograph (LASCO) aboard Solar and Heliospheric Observatory (SOHO), and the arrival time of the shock observed by ACE at 0.99 AU. The geometry of one particular transient is compared using both LASCO and SMEI images in a first attempt to investigate geometry evolution as the transient propagates through the interplanetary medium. For some events, the halo CME, SMEI transient, and shock at 0.99 AU do not match, suggesting that some transients may not correspond to a halo CME. Finally, an evaluation of the potential of SMEI to be used as a predictor of space weather is presented, by comparing the transients observed in SMEI with the 22 geomagnetic storms which occurred during this timeframe. A transient was observed in 14 cases, and distance-time profiles would have allowed a prediction of the arrival time at ACE within 2 hours of its actual arrival for three events, and within 10 hours for eight events. Of these eight events, seven were detected by SMEI more than 1 day before the transient's arrival at the Earth.
P E Holladay - One of the best experts on this subject based on the ideXlab platform.
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very high altitude aurora observations with the Solar Mass ejection imager
Journal of Geophysical Research, 2005Co-Authors: D R Mizuno, A Buffington, M P Cooke, C J Eyles, P P Hick, P E Holladay, B V Jackson, J C Johnston, T A Kuchar, J B MozerAbstract:[1] The Solar Mass Ejection Imager (SMEI) is a sensitive scanning instrument mounted on the Coriolis satellite that assembles an approximately all-sky image of the heliosphere in red-biased visible light once per orbit. Its lines of sight pass obliquely through the topside ionosphere and magnetosphere. We present serendipitous observations of a visual phenomenon detected at high altitudes (≥840 km) over the auroral zones and polar caps. The phenomenon is observed in two basic forms. The first, and more common, are periods of brief (1–3 min), nearly uniform illumination of the imager's field of view, which we interpret as transits of the satellite through a luminous medium. The second appear as localized filamentary structures, which we interpret as columns of luminous material, viewed from a distance, possibly extending to visible altitudes of 2000 km or higher. More than 1000 occurrences of these phenomena were recorded during the first full year of operations. These observations are well correlated in brightness and frequency with periods of enhanced geomagnetic activity.
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the Solar Mass ejection imager smei
Solar Physics, 2003Co-Authors: C J Eyles, A Buffington, M P Cooke, P P Hick, B V Jackson, G M Simnett, Nicholas R Waltham, J M King, Phillip A Anderson, P E HolladayAbstract:We describe an instrument (SMEI) which has been specifically designed to detect and forecast the arrival of Solar Mass ejections and other heliospheric structures which are moving towards the Earth. Such events may cause geomagnetic storms, with resulting radiation hazards and disruption to military and commercial communications; damage to Earth-orbiting spacecraft; and also terrestrial effects such as surges in transcontinental power transmission lines. The detectors are sensitive over the optical wave-band, which is measured using CCD cameras. SMEI was launched on 6 January 2003 on the Coriolis spacecraft into a Sun-synchronous polar orbit as part of the US DoD Space Test Programme. The instrument contains three cameras, each with a field of view of 60°×3°, which are mounted onto the spacecraft such that they scan most of the sky every 102-min orbit. The sensitivity is such that changes in sky brightness equivalent to a tenth magnitude star in one square degree of sky may be detected. Each camera takes an image every 4 s. The normal telemetry rate is 128 kbits s−1. In order to extract the emission from a typical large coronal Mass ejection, stellar images and the signal from the zodiacal dust cloud must be subtracted. This requires accurate relative photometry to 0.1%. One consequence is that images of stars and the zodiacal cloud will be measured to this photometric accuracy once per orbit. This will enable studies of transient zodiacal cloud phenomena, flare stars, supernovae, comets, and other varying point-like objects.
