. Aschwanden, M. J., Brown, J. C., & Kontar, E. P. Lin, R. P., Dennis, B. R., & Benz, A. O., editors. Chromospheric Height and Density Measurements in a Solar Flare Observed with RHESSI, pages 383–405. Springer Netherlands, Dordrecht, 2003. ![Chromospheric Height and Density Measurements in a Solar Flare Observed with RHESSI [link]](https://bibbase.org/img/filetypes/link.svg "link")
Paper doi abstract bibtex We present an analysis of hard X-ray imaging observations from one of the first solar flares observed with the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) spacecraft, launched on 5 February 2002. The data were obtained from the 22 February 2002, 11:06 UT flare, which occurred close to the northwest limb. Thanks to the high energy resolution of the germanium-cooled hard X-ray detectors on RHESSI we can measure the flare source positions with a high accuracy as a function of energy. Using a forward-fitting algorithm for image reconstruction, we find a systematic decrease in the altitudes of the source centroids z($ε$) as a function of increasing hard X-ray energy $ε$, as expected in the thick-target bremsstrahlung model of Brown. The altitude of hard X-ray emission as a function of photon energy $ε$ can be characterized by a power-law function in the $ε$ = 15–50 keV energy range, viz., z($ε$) ≈ 2.3($ε$/20 keV)−1.3 Mm. Based on a purely collisional 1-D thick-target model, this height dependence can be inverted into a chromospheric density model n(z), as derived in Paper I, which follows the power-law function ne(z) = 1.25 × 1013(z/1 Mm)−2.5 cm−3. This density is comparable with models based on optical/UV spectrometry in the chromospheric height range of h ≲ 1000 km, suggesting that the collisional thick-target model is a reasonable first approximation to hard X-ray footpoint sources. At h ≈ 1000–2500 km, the hard X-ray based density model, however, is more consistent with the `spicular extended-chromosphere model' inferred from radio sub-mm observations, than with standard models based on hydrostatic equilibrium. At coronal heights, h ≈ 2.5–12.4 Mm, the average flare loop density inferred from RHESSI is comparable with values from hydrodynamic simulations of flare chromospheric evaporation, soft X-ray, and radio-based measurements, but below the upper limits set by filling-factor insensitive iron line pairs.
@Inbook{Aschwanden2003,
author="Aschwanden, Markus J.
and Brown, John C.
and Kontar, Eduard P.",
editor="Lin, Robert P.
and Dennis, Brian R.
and Benz, Arnold O.",
title="Chromospheric Height and Density Measurements in a Solar Flare Observed with RHESSI",
bookTitle="The Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI): Mission Description and Early Results",
year="2003",
publisher="Springer Netherlands",
address="Dordrecht",
pages="383--405",
abstract="We present an analysis of hard X-ray imaging observations from one of the first solar flares observed with the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) spacecraft, launched on 5 February 2002. The data were obtained from the 22 February 2002, 11:06 UT flare, which occurred close to the northwest limb. Thanks to the high energy resolution of the germanium-cooled hard X-ray detectors on RHESSI we can measure the flare source positions with a high accuracy as a function of energy. Using a forward-fitting algorithm for image reconstruction, we find a systematic decrease in the altitudes of the source centroids z($\epsilon$) as a function of increasing hard X-ray energy $\epsilon$, as expected in the thick-target bremsstrahlung model of Brown. The altitude of hard X-ray emission as a function of photon energy $\epsilon$ can be characterized by a power-law function in the $\epsilon$ = 15--50 keV energy range, viz., z($\epsilon$) ≈ 2.3($\epsilon$/20 keV)−1.3 Mm. Based on a purely collisional 1-D thick-target model, this height dependence can be inverted into a chromospheric density model n(z), as derived in Paper I, which follows the power-law function ne(z) = 1.25 {\texttimes} 1013(z/1 Mm)−2.5 cm−3. This density is comparable with models based on optical/UV spectrometry in the chromospheric height range of h ≲ 1000 km, suggesting that the collisional thick-target model is a reasonable first approximation to hard X-ray footpoint sources. At h ≈ 1000--2500 km, the hard X-ray based density model, however, is more consistent with the `spicular extended-chromosphere model' inferred from radio sub-mm observations, than with standard models based on hydrostatic equilibrium. At coronal heights, h ≈ 2.5--12.4 Mm, the average flare loop density inferred from RHESSI is comparable with values from hydrodynamic simulations of flare chromospheric evaporation, soft X-ray, and radio-based measurements, but below the upper limits set by filling-factor insensitive iron line pairs.",
isbn="978-94-017-3452-3",
doi="10.1007/978-94-017-3452-3_22",
url="https://doi.org/10.1007/978-94-017-3452-3_22"
}
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P."],"bibdata":{"bibtype":"inbook","type":"inbook","author":[{"propositions":[],"lastnames":["Aschwanden"],"firstnames":["Markus","J."],"suffixes":[]},{"propositions":[],"lastnames":["Brown"],"firstnames":["John","C."],"suffixes":[]},{"propositions":[],"lastnames":["Kontar"],"firstnames":["Eduard","P."],"suffixes":[]}],"editor":[{"propositions":[],"lastnames":["Lin"],"firstnames":["Robert","P."],"suffixes":[]},{"propositions":[],"lastnames":["Dennis"],"firstnames":["Brian","R."],"suffixes":[]},{"propositions":[],"lastnames":["Benz"],"firstnames":["Arnold","O."],"suffixes":[]}],"title":"Chromospheric Height and Density Measurements in a Solar Flare Observed with RHESSI","booktitle":"The Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI): Mission Description and Early Results","year":"2003","publisher":"Springer Netherlands","address":"Dordrecht","pages":"383–405","abstract":"We present an analysis of hard X-ray imaging observations from one of the first solar flares observed with the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) spacecraft, launched on 5 February 2002. The data were obtained from the 22 February 2002, 11:06 UT flare, which occurred close to the northwest limb. Thanks to the high energy resolution of the germanium-cooled hard X-ray detectors on RHESSI we can measure the flare source positions with a high accuracy as a function of energy. Using a forward-fitting algorithm for image reconstruction, we find a systematic decrease in the altitudes of the source centroids z($ε$) as a function of increasing hard X-ray energy $ε$, as expected in the thick-target bremsstrahlung model of Brown. The altitude of hard X-ray emission as a function of photon energy $ε$ can be characterized by a power-law function in the $ε$ = 15–50 keV energy range, viz., z($ε$) ≈ 2.3($ε$/20 keV)−1.3 Mm. Based on a purely collisional 1-D thick-target model, this height dependence can be inverted into a chromospheric density model n(z), as derived in Paper I, which follows the power-law function ne(z) = 1.25 × 1013(z/1 Mm)−2.5 cm−3. This density is comparable with models based on optical/UV spectrometry in the chromospheric height range of h ≲ 1000 km, suggesting that the collisional thick-target model is a reasonable first approximation to hard X-ray footpoint sources. At h ≈ 1000–2500 km, the hard X-ray based density model, however, is more consistent with the `spicular extended-chromosphere model' inferred from radio sub-mm observations, than with standard models based on hydrostatic equilibrium. At coronal heights, h ≈ 2.5–12.4 Mm, the average flare loop density inferred from RHESSI is comparable with values from hydrodynamic simulations of flare chromospheric evaporation, soft X-ray, and radio-based measurements, but below the upper limits set by filling-factor insensitive iron line pairs.","isbn":"978-94-017-3452-3","doi":"10.1007/978-94-017-3452-3_22","url":"https://doi.org/10.1007/978-94-017-3452-3_22","bibtex":"@Inbook{Aschwanden2003,\r\nauthor=\"Aschwanden, Markus J.\r\nand Brown, John C.\r\nand Kontar, Eduard P.\",\r\neditor=\"Lin, Robert P.\r\nand Dennis, Brian R.\r\nand Benz, Arnold O.\",\r\ntitle=\"Chromospheric Height and Density Measurements in a Solar Flare Observed with RHESSI\",\r\nbookTitle=\"The Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI): Mission Description and Early Results\",\r\nyear=\"2003\",\r\npublisher=\"Springer Netherlands\",\r\naddress=\"Dordrecht\",\r\npages=\"383--405\",\r\nabstract=\"We present an analysis of hard X-ray imaging observations from one of the first solar flares observed with the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) spacecraft, launched on 5 February 2002. The data were obtained from the 22 February 2002, 11:06 UT flare, which occurred close to the northwest limb. Thanks to the high energy resolution of the germanium-cooled hard X-ray detectors on RHESSI we can measure the flare source positions with a high accuracy as a function of energy. Using a forward-fitting algorithm for image reconstruction, we find a systematic decrease in the altitudes of the source centroids z($\\epsilon$) as a function of increasing hard X-ray energy $\\epsilon$, as expected in the thick-target bremsstrahlung model of Brown. The altitude of hard X-ray emission as a function of photon energy $\\epsilon$ can be characterized by a power-law function in the $\\epsilon$ = 15--50 keV energy range, viz., z($\\epsilon$) ≈ 2.3($\\epsilon$/20 keV)−1.3 Mm. Based on a purely collisional 1-D thick-target model, this height dependence can be inverted into a chromospheric density model n(z), as derived in Paper I, which follows the power-law function ne(z) = 1.25 {\\texttimes} 1013(z/1 Mm)−2.5 cm−3. This density is comparable with models based on optical/UV spectrometry in the chromospheric height range of h ≲ 1000 km, suggesting that the collisional thick-target model is a reasonable first approximation to hard X-ray footpoint sources. At h ≈ 1000--2500 km, the hard X-ray based density model, however, is more consistent with the `spicular extended-chromosphere model' inferred from radio sub-mm observations, than with standard models based on hydrostatic equilibrium. At coronal heights, h ≈ 2.5--12.4 Mm, the average flare loop density inferred from RHESSI is comparable with values from hydrodynamic simulations of flare chromospheric evaporation, soft X-ray, and radio-based measurements, but below the upper limits set by filling-factor insensitive iron line pairs.\",\r\nisbn=\"978-94-017-3452-3\",\r\ndoi=\"10.1007/978-94-017-3452-3_22\",\r\nurl=\"https://doi.org/10.1007/978-94-017-3452-3_22\"\r\n}\r\n\r\n","author_short":["Aschwanden, M. J.","Brown, J. C.","Kontar, E. P."],"editor_short":["Lin, R. P.","Dennis, B. R.","Benz, A. 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