Steven Christe [1], S. White [2], S. Krucker [1]
1 Space Sciences Lab, U.C. Berkeley
2 Astronomy Department, University of Maryland.
Presented at AAS/SPD 2009 (link)
Abstract
We present a statistical survey of RHESSI microflares observed in hard X-rays (HXR) with simultaneous observations by the Nobeyama Radio Heliograph at 17 GHz and 34 GHz. These microflares were found using a new flare-finding algorithm designed to search the 6-12 keV count-rate when RHESSI’s full sensitivity was available, in order to find the smallest events. Between March 2002 and March 2007, a total of ~25000 events are identified, of which ~8500 are also observed by Nobeyama at 17 and 34 GHz. We compare HXR and radio fluxes and analyze the relationship statistically. When the events are detected at both wavelengths, the relationship between the lightcurves falls into several classes. Radio and HXR images of a small selection of events are used to investigate the relative locations of the two emissions, and we discuss the physical conditions that affect the relationship between the HXR and radio emission.
Steven Christe [1], K. Watanabe [2], S. Krucker [1]
1 Space Sciences Lab, U.C. Berkeley,
2 ISAS/JAXA, Japan.
Presented at AAS/SPD 2009 (link)
Abstract:
In this study we investigate the relationship between RHESSI flares and white light emission as observed by Hinode/SOT at 3968.6 angstroms (Ca II H line), 4306.4 angstroms (G band), and 4505.1 angstroms(blue continuum) images. The emission mechanism for white light emission in flares is not yet understood though it is believed that emission at these wavelengths originates from the chromosphere, photosphere, and deep photosphere respectively. Using a combination of the official RHESSI flare list and a microflare-finding algorithm, we investigate all RHESSI flares with simultaneous observations by RHESSI and Hinode/SOT (a total of ~200 events). Single event studies suggest that microflares are frequently observed in Ca II H line. Photospheric emission is searched for using the location of the Ca II H line chromospheric emission. We discuss the physical conditions necessary that may affect the relationship between HXR and white light emission.
S. Christe [1], Sam Krucker [1], H. Hudson [1], R. Lin [1]
1 Space Sciences Lab, U.C. Berkeley
Presented at AAS/SPD 2009 (link)
Abstract
We present the first in-depth statistical survey of flare source heights observed by RHESSI between March 2002 and March 2007, a total of 25,705 events. These flares were found using a new flare-finding algorithm designed to search the 6-12 keV count-rate when RHESSI’s full sensitivity was available in order to find the smallest events. Thermal (4-10 keV) and nonthermal (15-25 keV) images were made for all microflares and source centroid locations were found for each event. In order to extract the height information from source positions, a Monte-Carlo model was developed with an assumed source height distribution where height is measured from the photosphere. We find that the best source height model is given by an exponential distribution with a scale height of 2.1 (0.3) Mm and a minimum height of 3.1 (0.3) Mm. Comparing with previously published loop length measurements, we find that the average loop tilt is ~44 degrees as measured from the vertical.
Steven Christe, S. Krucker
Space Sciences Lab, U.C. Berkeley
Presented at Fall AGU Meeting 2008 (presentation link)
Abstract:
We present an in-depth statistical survey of flare heights of all X-ray microflares as observed by RHESSI between March 2002 and March 2007, a total of >25,000 events, an order of magnitude larger then previous studies. The microflares were found using a new flare-finding algorithm designed to search the 6– 12~keV count-rate when RHESSI’s full sensitivity was available in order to find the smallest events. The flare centroid position are found at the peak time and as a function of energy (3-6, 6-12, 12-25 keV). Flares are found to occur only in active regions, not in the “quiet” Sun. Flare heights are found using two independent methods including that of Matsushita (1992). The distribution of flares at the limb are fitted with a Monte Carlo simulations and the flare height deduced. We find that the 6-12 keV flare heights are consistent with a flare height of ~3 arcseconds above the photosphere with small separation between the thermal and nonthermal sources. The Matsushita method confirm these values.
Abstract Reference Number: 2516
Abstract Title: The Microflare Height Distribution
Paper Number: SH13A-1510
Presentation Type – POSTER
Cite abstracts as S. Christe and S. Krucker (2008), “The Microflare Height Distribution”, Eos Trans. AGU, 89(53), Fall Meet. Suppl., Abstract SH13A-1510
Iain Hannah[1], S. Christe[1,2], S. Krucker[1], H. Hudson[1], R.P. Lin[1,2], E. DeLuca[3]
1 Space Sciences Lab, U.C. Berkeley
2 Physics Department, U.C. Berkeley
3 Harvard-Smithsonian Center for Astrophysics
Presented at Fall AGU Meeting 2007 (presentation link).
Abstract:
We present analysis of microflares (small active region associated flares below GOES C class) using RHESSI and Hinode/XRT. RHESSI has observed well over 1,000 microflares since Hinode launched late in 2006 and of these over 150 have good Hinode/XRT coverage. We use RHESSI to obtain the temperature, emission measure and non-thermal power-law parameters from spectral fitting. We compare RHESSI and Hinode/XRT images to locate the thermal and non-thermal emissions. Taking advantage of the sensitive high-resolution capability of XRT for the softer X-rays, we investigate the resulting heating and evaporation from the accelerated electrons observed via the non-thermal emission by RHESSI.
Steven Christe[1,2], I. Hannah[1], S. Krucker[1], G. Hurford[1], J. McTiernan[1], R.P. Lin[1,2]
1 Space Sciences Lab, U.C. Berkeley
2 Physics Department, U.C. Berkeley
Presented at Fall AGU Meeting 2007 (presentation link)
Abstract:
We present the first in-depth statistical survey of all X-ray microflares observed by RHESSI between March 2002 and March 2007, a total of 25,705 events. These microflares were found using a new flare-finding algorithm designed to search the 6–12~keV count rate when RHESSIs full sensitivity was available in order to find the smallest events. These microflares are small flares, from low GOES C Class to below A Class (background subtracted) and associated with active regions. Each microflare is automatically analyzed at the peak time of the 6–12~keV emission. Spectral parameters are determined both by considering ratios between energy channels and by forward fitting a thermal plus non-thermal model. Flare images are created using back-projection and centroids and by forward fitting the complex visibilities. The combination of imaging and spectral parameters allow for the first time analysis of the thermal and non-thermal energy at the peak time of these microflares.
