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This paper presents an algorithm to decompose the modulated RHESSI light curves into periodic functions and a smooth function,
representing the true (demodulated) time profile of an impulsive source. The decomposition is achieved by optimizing a trade-off
between the Poisson likelihood, a smoothness constraint, and conditions on the average grid transmission and the (modulating
or non-modulating) background. The algorithm, which operates on the level of count rates and does not require imaging information,
is verified by numerical simulations and applied to some early RHESSI data, where – as a preliminary result – several impulsive
features on time scales < 4 s may have been identified. 相似文献
2.
E. Suarez-Garcia W. Hajdas C. Wigger K. Arzner M. Güdel A. Zehnder P. Grigis 《Solar physics》2006,239(1-2):149-172
The degree of linear polarization in solar flares has not yet been precisely determined despite multiple attempts to measure
it with different missions. The high energy range, in particular, has very rarely been explored, due to its greater instrumental
difficulties. We approached the subject using the Reuven Ramaty High Energy Spectroscopic Imager (RHESSI) satellite to study
six X-class and 1 M-class flares in the energy range between 100 and 350 keV. Using RHESSI as a polarimeter requires the application
of strict cuts to the event list in order to extract those photons that are Compton scattered between two detectors. Our measurements
show polarization values between 2 and 54%, with errors ranging from 10 to 26% in 1σ level. In view of the large uncertainties
in both the magnitude and direction of the polarization vector, the results can only reject source models with extreme properties. 相似文献
3.
Dryer M. Andrews M. D. Aurass H. DeForest C. Galvin A. B. Garcia H. Ipavich F. M. Karlický M. Kiplinger A. Klassen A. Meisner R. Paswaters S. E. Smith Z. Tappin S. J. Thompson B. J. Watari S. I. Michels D. J. Brueckner G. E. Howard R. A. Koomen M. J. Lamy P. Mann G. Arzner K. Schwenn R. 《Solar physics》1998,181(1):159-183
The first X-class flare in four years occurred on 9 July 1996. This X2.6/1B flare reached its maximum at 09:11 UT and was located in active region 7978 (S10° W30°) which was an old-cycle sunspot polarity group. We report the SOHO LASCO/EIT/MDI and SOONSPOT observations before and after this event together with Yohkoh SXT images of the flare, radio observations of the type II shock, and GOES disk-integrated soft X-ray flux during an extended period that included energy build-up in this active region.The LASCO coronagraphs measured a significant coronal mass ejection (CME) on the solar west limb beginning on 8 July at about 09:53 UT. The GOES 8 soft X-ray flux (0.1–0.8 nm) had started to increase on the previous day from below the A-level background (10-8 W m-2). At the start time of the CME, it was at the mid-B level and continued to climb. This CME is similar to many events which have been seen by LASCO and which are being interpreted as disruption of existing streamers by emerging flux ropes.LASCO and EIT were not collecting data at the time of the X-flare due to a temporary software outage. A larger CME was in progress when the first LASCO images were taken after the flare. Since the first image of the 'big' CME was obtained after the flare's start time, we cannot clearly demonstrate the physical connection of the CME to the flare. However, the LASCO CME data are consistent with an association of the flare and the CME. No eruptive filaments were observed during this event.We used the flare evidence noted above to employ in real time a simplified Shock-Time-of-Arrival (STOA) algorithm to estimate the arrival of a weak shock at the WIND spacecraft. We compare this prediction with the plasma and IMF data from WIND and plasma data from the SOHO/CELIAS instrument and suggest that the flare - and possibly the interplanetary consequences of the 'big' CME - was the progenitor of the mild, high-latitude, geomagnetic storm (daily sum of Kp=16+, Ap=8) on 12 July 1996. We speculate that the shock was attenuated enroute to Earth as a result of interaction with the heliospheric current/plasma sheet.presently at High Altitude Observatory, Boulder, CO80309, U.S.A.presently at Naval Research Laboratory, Washington DC, 20375, U.S.A. 相似文献
4.
Makhmutov V. S. Costa J. E. R. Raulin J.-P. Kaufmann P. Lagrotta P.R. Giménez de Castro C.G. Magun A. Arzner K. 《Solar physics》1998,178(2):393-403
The onset phase of the 22 October 1989 great solar burst was observed at 48 GHz using the multiple beam technique, which allows unambiguous flux determination irrespective of spatial angular position changes in time. We found strong quasi-periodic pulsating structures as the flux started to rise. Two significantly different time scales of 2.5–4.5 s and 0.2–0.5 s have been observed. These pulsations might be related to magnetohydrodynamic perturbations in the active region. However the fast component also might be a signature of the acceleration and/or injection of energetic electrons. 相似文献
5.
We investigate the relative timing between hard X-ray (HXR) peaks and structures in metric and decimetric radio emissions
of solar flares using data from the RHESSI and Phoenix-2 instruments. The radio events under consideration are predominantly
classified as type III bursts, decimetric pulsations and patches. The RHESSI data are demodulated using special techniques
appropriate for a Phoenix-2 temporal resolution of 0.1 s. The absolute timing accuracy of the two instruments is found to
be about 170 ms, and much better on the average. It is found that type III radio groups often coincide with enhanced HXR emission,
but only a relatively small fraction (∼20%) of the groups show close correlation on time scales < 1 s. If structures correlate,
the HXRs precede the type III emissions in a majority of cases, and by 0.69 ± 0.19 s on the average. Reversed drift type III
bursts are also delayed, but high-frequency and harmonic emission is retarded less. The decimetric pulsations and patches
(DCIM) have a larger scatter of delays, but do not have a statistically significant sign or an average different from zero.
The time delay does not show a center-to-limb variation excluding simple propagation effects. The delay by scattering near
the source region is suggested to be the most efficient process on the average for delaying type III radio emission. 相似文献
6.
Kaspar Arzner 《Astrophysics and Space Science》2003,284(3):1113-1113
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