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Carl R. Gwinn - One of the best experts on this subject based on the ideXlab platform.
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Interstellar scintillation of PSR J0437-4715 on two scales
Astronomy & Astrophysics, 2006Co-Authors: Carl R. Gwinn, C. Hirano, Stanislav BoldyrevAbstract:Aims. We sought to determine the scale of scintillation in the Interstellar Plasma of PSR J0437-4715. Methods. We used the Very Long Baseline Array to obtain scintillation amplitude and phase data, from dynamic spectra at 327 MHz. Results. We observe two scales of scintillation of pulsar PSR J0437-4715, differing by more than an order of magnitude in scintillation bandwidth. The wider-bandwidth scale of scintillation that we observe indicates less scattering for this pulsar than for other nearby pulsars, other than PSR B0950+08.
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Interstellar Scintillation of PSR J0437-4715 on Two Scales
Astronomy & Astrophysics, 2006Co-Authors: Carl R. Gwinn, C. Hirano, Stanislav BoldyrevAbstract:We sought to determine the scale of scintillation in the Interstellar Plasma of PSR J0437-4715. We used the Very Long Baseline Array to obtain scintillation amplitude and phase data, from dynamic spectra at 327 MHz. We observe two scales of scintillation of pulsar PSR J0437-4715, differing by more than an order of magnitude in scintillation bandwidth. The wider-bandwidth scale of scintillation that we observe indicates less scattering for this pulsar than for other nearby pulsars, except for PSR B0950+08.
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Small-Scale Variations of H I Spectra from Interstellar Scintillation
The Astrophysical Journal, 2001Co-Authors: Carl R. GwinnAbstract:I suggest that radio-wave scattering by the Interstellar Plasma, in combination with subsonic gradients in the Doppler velocity of Interstellar H I, is responsible for the observed small-scale variation in H I absorption spectra of pulsars. Velocity gradients on the order of 0.05-0.3 km s-1 across 1 AU can produce the observed variations. I suggest observational tests to determine the relative importance of such gradients and AU-scale absorbing cloudlets in producing the spectral variations.
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Studying Pulsar Emission Regions Using Interstellar Scattering
Astrophysics and Space Science, 2001Co-Authors: Carl R. GwinnAbstract:Radio-wave scattering in the Interstellar Plasma provides the means to circumvent the diffraction limit for earth-based instruments, and to image the emission regions of pulsars. For the past 25 years, observers have sought to exploit this fact to learn how pulsars shine. I review the techniques developed, and summarize measurements of size of emission regions of pulsars to date.
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A speckle hologram of the Interstellar Plasma
The Astrophysical Journal, 1992Co-Authors: K. M. Desai, Carl R. Gwinn, John E. Reynolds, E. A. King, D. L. Jauncey, C. S. Flanagan, George D. Nicolson, Robert A. Preston, Dayton L. JonesAbstract:Observations of a speckle hologram of scattering material along the line of sight to the Vela pulsar indicate that this material is concentrated in the Vela supernova remnant, deep within the Gum Nebula. The speckle hologram is observed through the amplitude and phase variations of the interferometric cross-power spectrum with time and frequency. These variations describe the density fluctuations of the Interstellar Plasma, in a holographic fashion. The decorrelation due to the phase variations of the speckles yields the angular size of the scattering disk; comparison with the bandwidth of their amplitude variations yields a characteristic distance from earth to the scattering material of 0.81 +/- 0.03 of the distance from earth to the pulsar. This result is consistent with theories of irregularities associated with particle acceleration in shocks in supernova remnants.
V I Shishov - One of the best experts on this subject based on the ideXlab platform.
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Revealing compact structures of Interstellar Plasma in the Galaxy with RadioAstron
Monthly Notices of the Royal Astronomical Society, 2018Co-Authors: E. N. Fadeev, T V Smirnova, V I Shishov, A S Andrianov, M V Popov, M. S. Burgin, Alexey Rudnitskiy, V. A. ZugaAbstract:The aim of our work was to study the spatial structure of inhomogeneities of Interstellar Plasma in the directions of five pulsars: B0823+26, B0834+06, B1237+25, B1929+10, and B2016+28. Observations of these pulsars were made with RadioAstron space-ground radio interferometer at 324 MHz. We measured the angular size of the scattering disks to be in range between 0.63 and 3.2 mas. We determined the position of scattering screens on the line of sight. Independent estimates of the distances to the screens were made from the curvature of parabolic arcs revealed in the secondary spectra of four pulsars. The model of uniform distribution of inhomogeneities on the line of sight is not suitable. According to the results, we came to the conclusion that scattering is mainly produced by compact Plasma layers and the uniform model of inhomogeneties distribution on the line of sight in not applicable.
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distribution of Interstellar Plasma in the direction of psr b0525 21 from data obtained on a ground space interferometer
Astronomy Reports, 2017Co-Authors: A S Andrianov, T V Smirnova, V I Shishov, C. R. Gwinn, M V PopovAbstract:Observations on the RadioAstron ground–space interferometer with the participation of the Green Bank and Arecibo ground telescopes at 1668 MHz have enabled studies of the characteristics of the Interstellar Plasma in the direction of the pulsar PSR B0525+21. The maximum projected baseline for the ground–space interferometer was 233 600 km. The scintillations in these observations were strong, and the spectrum of inhomogeneties in the Interstellar Plasma was a power law with index n = 3.74, corresponding to a Kolmogorov spectrum. A new method for estimating the size of the scattering disk was applied to estimate the scattering angle (scattering disk radius) in the direction toward PSR B0525+21, θ scat = 0.028 ± 0.002 milliarcsecond. The scattering in this direction occurs in a Plasma layer located at a distance of 0.1Z from the pulsar, where Z is the distance from the pulsar to the observer. For the adopted distance Z = 1.6 kpc, the screen is located at a distance of 1.44 kpc from the observer.
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Distribution of Interstellar Plasma in the direction of PSR B0525+21 from data obtained on a ground–space interferometer
Astronomy Reports, 2017Co-Authors: A S Andrianov, T V Smirnova, V I Shishov, C. R. Gwinn, M V PopovAbstract:Observations on the RadioAstron ground–space interferometer with the participation of the Green Bank and Arecibo ground telescopes at 1668 MHz have enabled studies of the characteristics of the Interstellar Plasma in the direction of the pulsar PSR B0525+21. The maximum projected baseline for the ground–space interferometer was 233 600 km. The scintillations in these observations were strong, and the spectrum of inhomogeneties in the Interstellar Plasma was a power law with index n = 3.74, corresponding to a Kolmogorov spectrum. A new method for estimating the size of the scattering disk was applied to estimate the scattering angle (scattering disk radius) in the direction toward PSR B0525+21, θ _scat = 0.028 ± 0.002 milliarcsecond. The scattering in this direction occurs in a Plasma layer located at a distance of 0.1 Z from the pulsar, where Z is the distance from the pulsar to the observer. For the adopted distance Z = 1.6 kpc, the screen is located at a distance of 1.44 kpc from the observer.
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measurement of the inner turbulence scale of the Interstellar Plasma toward the pulsar psr b2111 46
Astronomy Reports, 2010Co-Authors: T V Smirnova, V I ShishovAbstract:The pulsar PSR B2111+46 has been observed at 112 MHz, and a new approach to analyzing pulsar pulses scattered in turbulent Interstellar Plasma applied. This method is based on the dependence of the normalized energy in the trailing part of a pulse on the intrapulse time. Since the trailing edge of a pulse follow exponential law to high accuracy, the inner turbulence scale of the Interstellar Plasma exceeds the field coherence scale. The measured scattering parameter is τ sc = 147 ± 1 ms. Analysis of the parameters of diffractive and refractive scintillations of the pulsar at 610 MHz together with the 112 MHz data shows that the spectrum of the Interstellar Plasma toward PSR B2111+46 is a piecewise power law: on scales of 1013–1014 cm, the exponent of the turbulence spectrum is n ≃ 4, whereas n = 3.5 on scales of 2 × 108−1013 cm. The spectrum flattens with approach to the inner turbulence scale l: n = 3–3.2. The obtained inner turbulence scale is l = (3.5 ± 1.5) × 107 cm. The distribution of the Interstellar Plasma toward the pulsar is close to statistically homogeneous. The local density (N e = 0.4 cm−3) and filling factor (F = 0.04) of the Interstellar Plasma have been estimated. The similarity of N e estimates obtained from the inner scale of the inhomogeneities and the ratio of the emission measure to the dispersion measure provides evidence that the inner turbulence scale corresponds to the ion inertial length.
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Measurement of the inner turbulence scale of the Interstellar Plasma toward the pulsar PSR B2111+46
Astronomy Reports, 2010Co-Authors: T V Smirnova, V I ShishovAbstract:The pulsar PSR B2111+46 has been observed at 112 MHz, and a new approach to analyzing pulsar pulses scattered in turbulent Interstellar Plasma applied. This method is based on the dependence of the normalized energy in the trailing part of a pulse on the intrapulse time. Since the trailing edge of a pulse follow exponential law to high accuracy, the inner turbulence scale of the Interstellar Plasma exceeds the field coherence scale. The measured scattering parameter is τ _ sc = 147 ± 1 ms. Analysis of the parameters of diffractive and refractive scintillations of the pulsar at 610 MHz together with the 112 MHz data shows that the spectrum of the Interstellar Plasma toward PSR B2111+46 is a piecewise power law: on scales of 10^13–10^14 cm, the exponent of the turbulence spectrum is n ≃ 4, whereas n = 3.5 on scales of 2 × 10^8−10^13 cm. The spectrum flattens with approach to the inner turbulence scale l : n = 3–3.2. The obtained inner turbulence scale is l = (3.5 ± 1.5) × 10^7 cm. The distribution of the Interstellar Plasma toward the pulsar is close to statistically homogeneous. The local density ( N _ e = 0.4 cm^−3) and filling factor ( F = 0.04) of the Interstellar Plasma have been estimated. The similarity of N _ e estimates obtained from the inner scale of the inhomogeneities and the ratio of the emission measure to the dispersion measure provides evidence that the inner turbulence scale corresponds to the ion inertial length.
T V Smirnova - One of the best experts on this subject based on the ideXlab platform.
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Revealing compact structures of Interstellar Plasma in the Galaxy with RadioAstron
Monthly Notices of the Royal Astronomical Society, 2018Co-Authors: E. N. Fadeev, T V Smirnova, V I Shishov, A S Andrianov, M V Popov, M. S. Burgin, Alexey Rudnitskiy, V. A. ZugaAbstract:The aim of our work was to study the spatial structure of inhomogeneities of Interstellar Plasma in the directions of five pulsars: B0823+26, B0834+06, B1237+25, B1929+10, and B2016+28. Observations of these pulsars were made with RadioAstron space-ground radio interferometer at 324 MHz. We measured the angular size of the scattering disks to be in range between 0.63 and 3.2 mas. We determined the position of scattering screens on the line of sight. Independent estimates of the distances to the screens were made from the curvature of parabolic arcs revealed in the secondary spectra of four pulsars. The model of uniform distribution of inhomogeneities on the line of sight is not suitable. According to the results, we came to the conclusion that scattering is mainly produced by compact Plasma layers and the uniform model of inhomogeneties distribution on the line of sight in not applicable.
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distribution of Interstellar Plasma in the direction of psr b0525 21 from data obtained on a ground space interferometer
Astronomy Reports, 2017Co-Authors: A S Andrianov, T V Smirnova, V I Shishov, C. R. Gwinn, M V PopovAbstract:Observations on the RadioAstron ground–space interferometer with the participation of the Green Bank and Arecibo ground telescopes at 1668 MHz have enabled studies of the characteristics of the Interstellar Plasma in the direction of the pulsar PSR B0525+21. The maximum projected baseline for the ground–space interferometer was 233 600 km. The scintillations in these observations were strong, and the spectrum of inhomogeneties in the Interstellar Plasma was a power law with index n = 3.74, corresponding to a Kolmogorov spectrum. A new method for estimating the size of the scattering disk was applied to estimate the scattering angle (scattering disk radius) in the direction toward PSR B0525+21, θ scat = 0.028 ± 0.002 milliarcsecond. The scattering in this direction occurs in a Plasma layer located at a distance of 0.1Z from the pulsar, where Z is the distance from the pulsar to the observer. For the adopted distance Z = 1.6 kpc, the screen is located at a distance of 1.44 kpc from the observer.
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Distribution of Interstellar Plasma in the direction of PSR B0525+21 from data obtained on a ground–space interferometer
Astronomy Reports, 2017Co-Authors: A S Andrianov, T V Smirnova, V I Shishov, C. R. Gwinn, M V PopovAbstract:Observations on the RadioAstron ground–space interferometer with the participation of the Green Bank and Arecibo ground telescopes at 1668 MHz have enabled studies of the characteristics of the Interstellar Plasma in the direction of the pulsar PSR B0525+21. The maximum projected baseline for the ground–space interferometer was 233 600 km. The scintillations in these observations were strong, and the spectrum of inhomogeneties in the Interstellar Plasma was a power law with index n = 3.74, corresponding to a Kolmogorov spectrum. A new method for estimating the size of the scattering disk was applied to estimate the scattering angle (scattering disk radius) in the direction toward PSR B0525+21, θ _scat = 0.028 ± 0.002 milliarcsecond. The scattering in this direction occurs in a Plasma layer located at a distance of 0.1 Z from the pulsar, where Z is the distance from the pulsar to the observer. For the adopted distance Z = 1.6 kpc, the screen is located at a distance of 1.44 kpc from the observer.
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distribution of inhomogeneities in the Interstellar Plasma in the directions of three distant pulsars from observations with the radioastron ground space interferometer
Astronomy Reports, 2016Co-Authors: M V Popov, T V Smirnova, D. L. Jauncey, C. R. Gwinn, A S Andrianov, N Bartel, B C Joshi, N S Kardashev, A G Rudnitskii, V A SoglasnovAbstract:The RadioAstron ground–space interferometer has been used to measure the angular sizes of the scattering disks of the three distant pulsars B1641–45, B1749–28, and B1933+16. The observations were carried out with the participation of the Westerbork Synthesis Radio Telescope; two 32-m telescopes at Torun, Poland and Svetloe, Russia (the latter being one antenna of the KVAZAR network); the Saint Croix VLBA antenna; the Arecibo radio telescope; the Parkes, Narrabri (ATCA), Mopra, Hobart, and Ceduna Australian radio telescopes; and the Hartebeesthoek radio telescope in South Africa. The full widths at half maximum of the scattering disks were 27 mas at 1668 MHz for B1641–45, 0.5 mas at 1668 MHz for B1749–28, and 12.3 at 316 MHz and 0.84 mas at 1668 MHz for B1933+16. The characteristic time scales for scatter-broadening of the pulses on inhomogeneities in the Interstellar Plasma τsc were also measured for these pulsars using various methods. Joint knowledge of the size of the scattering disk and the scatter-broadening time scale enables estimation of the distance to the effective scattering screen d. For B1641–45, d = 3.0 kpc for a distance to the pulsar D = 4.9 kpc, and for B1749–28, d = 0.95 kpc for D = 1.3 kpc. Observations of B1933+16 were carried out simultaneously at 316 and 1668 MHz. The positions of the screen derived using the measurements at the two frequencies agree: d1 = 2.6 and d2 = 2.7 kpc, for a distance to the pulsar of 3.7 kpc. Two screens were detected for this pulsar from an analysis of parabolic arcs in the secondary dynamic spectrum at 1668 MHz, at 1.3 and 3.1 kpc. The scattering screens for two of the pulsars are identified with real physical objects located along the lines of sight toward the pulsars: G339.1–04 (B1641–45) and G0.55–0.85 (B1749–28).
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measurement of the inner turbulence scale of the Interstellar Plasma toward the pulsar psr b2111 46
Astronomy Reports, 2010Co-Authors: T V Smirnova, V I ShishovAbstract:The pulsar PSR B2111+46 has been observed at 112 MHz, and a new approach to analyzing pulsar pulses scattered in turbulent Interstellar Plasma applied. This method is based on the dependence of the normalized energy in the trailing part of a pulse on the intrapulse time. Since the trailing edge of a pulse follow exponential law to high accuracy, the inner turbulence scale of the Interstellar Plasma exceeds the field coherence scale. The measured scattering parameter is τ sc = 147 ± 1 ms. Analysis of the parameters of diffractive and refractive scintillations of the pulsar at 610 MHz together with the 112 MHz data shows that the spectrum of the Interstellar Plasma toward PSR B2111+46 is a piecewise power law: on scales of 1013–1014 cm, the exponent of the turbulence spectrum is n ≃ 4, whereas n = 3.5 on scales of 2 × 108−1013 cm. The spectrum flattens with approach to the inner turbulence scale l: n = 3–3.2. The obtained inner turbulence scale is l = (3.5 ± 1.5) × 107 cm. The distribution of the Interstellar Plasma toward the pulsar is close to statistically homogeneous. The local density (N e = 0.4 cm−3) and filling factor (F = 0.04) of the Interstellar Plasma have been estimated. The similarity of N e estimates obtained from the inner scale of the inhomogeneities and the ratio of the emission measure to the dispersion measure provides evidence that the inner turbulence scale corresponds to the ion inertial length.
Barney J. Rickett - One of the best experts on this subject based on the ideXlab platform.
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Pulsar Scintillation Arcs reveal filaments in the Interstellar Plasma
2011Co-Authors: Barney J. Rickett, Dan Stinebring, Bill Coles, Gao Jian‐jianAbstract:Both forward and reverse Scintillation Arcs are seen in observations of several pulsars. We study the arcs, which are seen in the 2‐D Fourier transform of the dynamic spectrum, from PSRs B0834+06 and B1737+13. In both cases we conclude that the underlying scattered image is highly extended along an axis and also highly modulated along that axis. The corresponding spatial structure in the ionized Interstellar medium must be bundles of spaghetti‐like filaments—highly anisotropic turbulence (on scales of 1000–10000 km) which is also very intermittent on scales of an AU. We speculate on their possible origin as remnant turbulence from long past supernovae.
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Scattering of Pulsar Radio Emission by the Interstellar Plasma
The Astrophysical Journal, 2010Co-Authors: W. A. Coles, Barney J. Rickett, J. J. Gao, George Hobbs, Joris P. W. VerbiestAbstract:We present simulations of scattering phenomena which are important in pulsar observations, but which are analytically intractable. The simulation code, which has also been used for solar wind and atmospheric scattering problems, is available from the authors. These simulations reveal an unexpectedly important role of dispersion in combination with refraction. We demonstrate the effect of analyzing observations which are shorter than the refractive scale. We examine time-of-arrival fluctuations in detail: showing their correlation with intensity and dispersion measure, providing a heuristic model from which one can estimate their contribution to pulsar timing observations, and showing that much of the effect can be corrected making use of measured intensity and dispersion. Finally, we analyze observations of the millisecond pulsar J0437–4715, made with the Parkes radio telescope, that show timing fluctuations which are correlated with intensity. We demonstrate that these timing fluctuations can be corrected, but we find that they are much larger than would be expected from scattering in a homogeneous turbulent Plasma with isotropic density fluctuations. We do not have an explanation for these timing fluctuations.
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International Colloquium "Scattering and Scintillation in Radio Astronomy" was held on June 19-23, 2006 in Pushchino, Moscow region, Russia
arXiv: Astrophysics, 2006Co-Authors: V I Shishov, William A. Coles, Barney J. Rickett, M. K. Bird, A. I. Efimov, L. N. Samoznaev, V. K. Rudash, I. V. Chashei, D. Plettemeier, S. R. SpanglerAbstract:Topics of the Colloquium: a) Interplanetary scintillation b) Interstellar scintillation c) Modeling and physical origin of the interplanetary and the Interstellar Plasma turbulence d) Scintillation as a tool for investigation of radio sources e) Seeing through interplanetary and Interstellar turbulent media Ppt-presentations are available on the Web-site: this http URL
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Radio Scintillation due to Discontinuities in the Interstellar Plasma Density
The Astrophysical Journal, 2000Co-Authors: H. C. Lambert, Barney J. RickettAbstract:We develop the theory of Interstellar scintillation as caused by an irregular Plasma having a power-law spatial-density spectrum with a spectral exponent of β = 4 corresponding to a medium with abrupt changes in its density. An "outer scale" is included in the model that represents the typical scale over which the density of the medium remains uniform. Such a spectrum could be used to model Plasma shock fronts in supernova remnants or other Plasma discontinuities. We investigate and develop equations for the decorrelation bandwidth of diffractive scintillations and the refractive scintillation index and compare our results with pulsar measurements. We consider both a medium concentrated in a thin layer and an extended irregular medium. We conclude that the β = 4 model gives satisfactory agreement for many diffractive measurements, in particular the VLBI measurements of the structure function exponent between 5/3 and 2. However, it gives less satisfactory agreement for the refractive scintillation index than does the Kolmogorov turbulence spectrum. The comparison suggests that the medium consists of a pervasive background distribution of turbulence embedded with randomly placed discrete Plasma structures such as shocks or H II regions. This can be modeled by a composite spectrum following the Kolmogorov form at high wavenumbers and steepening at lower wavenumbers corresponding to the typical (inverse) size of the discrete structures. Such a model can also explain the extreme scattering events. However, lines of sight through the enhanced scattering prevalent at low Galactic latitudes are accurately described by the Kolmogorov spectrum in an extended medium and do not appear to have a similar low-wavenumber steepening.
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Interstellar Scattering: Observations and Interpretations
International Astronomical Union Colloquium, 1996Co-Authors: Barney J. RickettAbstract:The successful theory for radio propagation through the Interstellar Plasma is reviewed, where the density spectrum follows the Kolmogorov model. However, there are also several observations indicating more refraction than expected. A particular model of enhanced refraction is proposed in which isolated regions of the warm ionized medium support filaments of enhanced density on a scale of 1 AU, which do not couple to a turbulent cascade.
Martin M. Sirk - One of the best experts on this subject based on the ideXlab platform.
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EUV Spectra of the Full Solar Disk: Analysis and Results of the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS)
Solar Physics, 2010Co-Authors: Martin M. Sirk, M Hurwitz, Wiliam MarchantAbstract:We analyze EUV spectra of the full solar disk from the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS) spanning a period of two years. The observations were obtained via a fortuitous off-axis light path in the 140 – 275 Å passband. The general appearance of the spectra remained relatively stable over the two-year time period, but did show significant variations of up to 25% between two sets of Fe lines that show peak emission at 1 MK and 2 MK. The variations occur at a measured period of 27.2 days and are caused by regions of hotter and cooler Plasma rotating into, and out of, the field of view. The CHIANTI spectral code is employed to determine Plasma temperatures, densities, and emission measures. A set of five isothermal Plasmas fit the full-disk spectra well. A 1 – 2 MK Plasma of Fe contributes 85% of the total emission in the CHIPS passband. The standard Differential Emission Measures (DEMs) supplied with the CHIANTI package do not fit the CHIPS spectra well as they over-predict emission at temperatures below log _10 T =6.0 and above log _10 T =6.3. The results are important for cross-calibrating TIMED, SORCE, SOHO/EIT, and CDS/GIS, as well as the recently launched Solar Dynamics Observatory .
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Iron emission lines in solar and laboratory Plasmas
Journal of Physics: Conference Series, 2008Co-Authors: J K Lepson, Martin M. Sirk, M Hurwitz, Peter Beiersdorfer, Takako Kato, N. YamamotoAbstract:We present a spectrum of the Sun taken by the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS) covering 150 to 275 A. This spectrum is dominated in the 200 A region by emission lines from intermediate charge states of iron (Fe VIII - FeXVI). We also made laboratory measurements of iron emission at temperatures relevent to solar emission on the EBIT-II electron beam ion trap and the Large Helical Device stellerator. We used our laboratory measurements to identify lines and check the CHIANTI database and then used CHIANTI to validate line identifications in the CHIPS spectrum.
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A search for extreme-ultraviolet emission from comets with the cosmic hot Interstellar Plasma spectrometer (chips)
The Astrophysical Journal, 2006Co-Authors: T. P. Sasseen, Martin M. Sirk, Mark Hurwitz, Carey M. Lisse, V. Kharchenko, Damian J. Christian, Scott J. Wolk, A. DalgarnoAbstract:We have obtained EUV spectra between 90 and 255 8 of the comets C/2002 T7 (LINEAR), C/2001 Q4 (NEAT), and C/2004 Q2 (Machholz) near their perihelion passages in 2004 with the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS). We obtained contemporaneous data on NEAT with the Chandra ACIS instrument, marking the firstsimultaneousEUVandX-rayspectralobservationsofacomet.ThetotalCHIPS/EUVobservingtimeswere337ks for NEAT, 234 ks for LINEAR, and 483 ks for Machholz, and for both CHIPS and Chandra we calculate we have capturedall the comet flux in the instrumentfield of view. We set upper limits on solar wind charge-exchange emission lines of O, C, N, Ne, and Fe occurring in the spectral bandpass of CHIPS. The spectrum of NEAT obtained with ChandracanbereproducedbymodelingemissionlinesofC,N,O,Mg,Fe,Si,S,andNesolarwindions.Themeasured X-rayemission-lineintensitiesareconsistentwithourpredictionsfromasolarwindcharge-exchangemodel.Themodel predictions for the EUVemission-line intensities are determined from the intensity ratios of the cascading X-ray and EUVphotonsarisinginthecharge-exchangeprocesses.Theyarecompatiblewiththemeasuredlimitsontheintensities of the EUV lines. For NEAT, we measured a total X-ray flux of 3:7 ; 10 � 12 ergs cm � 2 s � 1 and derive from model predictions a total EUV flux of 1:5 ; 10 � 12 ergs cm � 2 s� 1. The CHIPS observations occurred predominantly while the satellite was on the dayside of Earth. For much of the observing time, CHIPS performed observations at smaller solar angles than it was designed for, and EUVemission from the Sun scattered into the instrument limited the sensitivity of the EUV measurements. Subject headingg comets: general — comets: individual (C/2002 T7 (LINEAR), C/2001 Q4 (NEAT), C/2004 Q2 (Machholz)) — ultraviolet: solar system
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A Search for EUV Emission from Comets with the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS)
The Astrophysical Journal, 2006Co-Authors: T. P. Sasseen, Martin M. Sirk, Mark Hurwitz, Carey M. Lisse, V. Kharchenko, Damian J. Christian, Scott J. Wolk, A. DalgarnoAbstract:We have obtained EUV spectra between 90 and 255 \AA of the cometsC/2002 T7 (LINEAR), C/2001 Q4 (NEAT), and C/2004 Q2 (Machholz) near their perihelion passages in 2004 with the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS). We obtained contemporaneous data on Comet NEAT Q4 with the $Chandra$ X-ray Observatory ACIS instrument, marking the first simultaneous EUV and X-ray spectral observations of a comet. The total CHIPS/EUV observing times were 337 ks for Q4, 234 ks for T7, and 483 ks for Machholz and for both CHIPS and $Chandra$ we calculate we have captured all the comet flux in the instrument field of view. We set upper limits on solar wind charge exchange emission lines of O, C, N, Ne and Fe occurring in the spectral bandpass of CHIPS. The spectrum of Q4 obtained with $Chandra$ can be reproduced by modeling emission lines of C, N O, Mg, Fe, Si, S, and Ne solar wind ions. The measured X-ray emission line intensities are consistent with our predictions from a solar wind charge exchange model. The model predictions for the EUV emission line intensities are determined from the intensity ratios of the cascading X-ray and EUV photons arising in the charge exchange processes. They are compatible with the measured limits on the intensities of the EUV lines. For comet Q4, we measured a total X-ray flux of 3.7$\times 10^{-12}$ ergs cm$^{-2}$ s$^{-1}$, and derive from model predictions a total EUV flux of 1.5$\times 10^{-12}$ erg cm$^{-2}$ s$^{-1}$. The CHIPS observations occurred predominantly while the satellite was on the dayside of Earth. For much of the observing time, CHIPS performed observations at smaller solar angles than it was designed for and EUV emission from the Sun scattered into the instrument limited the sensitivity of the EUV measurements.
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Observations of Diffuse Extreme-Ultraviolet Emission with the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS)
The Astrophysical Journal, 2005Co-Authors: Mark Hurwitz, T. P. Sasseen, Martin M. SirkAbstract:The Cosmic Hot Interstellar Plasma Spectrometer (CHIPS) was designed to study diffuse emission from hot gas in the local Interstellar cavity in the wavelength range 90-265 A. Between launch in 2003 January and early 2004, the instrument was operated in narrow-slit mode, achieving a peak spectral resolution of about 1.4 A FWHM. Observations were carried out preferentially at high Galactic latitudes; weighted by observing time, the mean absolute value of the Galactic latitude for all narrow-slit observations combined is about 45°. The total integration time is about 13.2 Ms (74% day, 26% night). In the context of a standard collisional ionization equilibrium Plasma model, the CHIPS data set tight constraints on the emission measure at temperatures between 105.55 and 106.4 K. At 106.0 K, the 95% upper limit on the emission measure is about 0.0004 cm-6 pc for solar-abundance Plasma with a foreground neutral hydrogen column of 2 × 1018 cm-2. This constraint, derived primarily from limits on the extreme ultraviolet emission lines of highly ionized iron, is well below the range for the local hot bubble estimated previously from soft X-ray studies. If the pattern of elemental depletion in the hot gas follows that observed in much denser Interstellar clouds, the gas-phase abundance of iron, relative to other heavy elements that contribute more to the soft X-ray emission, might be much lower than solar. However, to support the emission measures inferred previously from X-ray data would require depletions much higher than the moderate values reported previously for hot gas. Excluding the He II Lyman lines, which are known to be primarily terrestrial in origin, the brightest feature we find in the integrated spectrum is an Fe IX line at 171.1 A. The sky-averaged flux of the feature is about 6 photons cm-2 s-1 sr-1, a flux that exceeds the 1 σ shot noise significantly but is comparable to the systematic uncertainty. We find bright 171.1 A emission (flux greater than 10 photons cm-2 s-1 sr-1 and S/N >2) in about 10% of the observing time. However, these bright observations overwhelmingly select for daytime (96% of 1.3 Ms). Thus, a local rather than Interstellar origin for much of the 171.1 A emission seems likely.
