Search Publications
Short-term Solar Flare Level Prediction Using a Bayesian Network Approach
Huang, Xin; Yu, Daren; Wang, Huaning +3 more
A Bayesian network approach for short-term solar flare level prediction has been proposed based on three sequences of photospheric magnetic field parameters extracted from Solar and Heliospheric Observatory/Michelson Doppler Imager longitudinal magnetograms. The magnetic measures, the maximum horizontal gradient, the length of neutral line, and th…
Fast Contraction of Coronal Loops at the Flare Peak
Wang, Haimin; Liu, Rui
On 2005 September 8, a coronal loop overlying the active region NOAA 10808 was observed in TRACE 171 Å to contract at ~100 km s-1 at the peak of an X5.4-2B flare at 21:05 UT. Prior to the fast contraction, the loop underwent a much slower contraction at ~6 km s-1 for about 8 minutes, initiating during the flare preheating pha…
Unusual Trends in Solar P-Mode Frequencies During the Current Extended Minimum
Hill, F.; Jain, K.; Tripathy, S. C. +1 more
We investigate the behavior of the intermediate-degree mode frequencies of the Sun during the current extended minimum phase to explore the time-varying conditions in the solar interior. Using contemporaneous helioseismic data from the Global Oscillation Network Group (GONG) and the Michelson Doppler Imager (MDI), we find that the changes in reson…
On the Solar Chromosphere Observed at the LIMB with Hinode
Judge, Philip G.; Carlsson, Mats
Broadband images in the Ca II H line, from the Broadband Filter Imager (BFI) instrument on the Hinode spacecraft, show emission from spicules emerging from and visible right down to the observed limb. Surprisingly, little absorption of spicule light is seen along their lengths. We present formal solutions to the transfer equation for given (ad hoc…
Direct Evidence for Gravitational Instability and Moonlet Formation in Saturn's Rings
Cooper, N. J.; Murray, C. D.; Evans, M. W. +3 more
New images from the Cassini spacecraft reveal optically thick clumps, capable of casting shadows, and associated structures in regions of Saturn's F ring that have recently experienced close passage by the adjacent moon Prometheus. Using these images and modeling, we show that Prometheus' perturbations create regions of enhanced density and low re…
Galaxy Clusters in the Swift/BAT Era. II. 10 More Clusters Detected Above 15 keV
Böhringer, H.; Cusumano, G.; Cappelluti, N. +4 more
We report on the discovery of 10 additional galaxy clusters detected in the ongoing Swift/Burst Alert Telescope (BAT) all-sky survey. Among the newly BAT-discovered clusters there are Bullet, A85, Norma, and PKS 0745-19. Norma is the only cluster, among those presented here, which is resolved by BAT. For all the clusters, we perform a detailed spe…
The Axis Ratio Distribution of X-ray Clusters Observed by XMM-Newton
Kawahara, Hajime
We derive the axis ratio distribution of X-ray clusters using the XMM-Newton catalog. By fitting the contour lines of the X-ray image by ellipses, we confirm that the X-ray distribution is well approximated by the elliptic distribution with a constant axis ratio and direction. We construct a simple model describing the axis ratio of the X-ray gas …
Deep HST/ACS Photometry of the M81 Halo
Chandar, Rupali; Sarajedini, Ata; Durrell, Patrick R.
We present a deep color-magnitude diagram (CMD) for individual stars in the halo of the nearby spiral galaxy M81, at a projected distance of 19 kpc, based on data taken with the Advanced Camera for Surveys on the Hubble Space Telescope (HST). The CMD reveals a red giant branch (RGB) that is narrow and fairly blue, and a horizontal branch that has …
Detection of Strong Short-term Variability in NGC 6946 X-1
Feng, Hua; Kaaret, Philip; Rao, Fengyun
Using two archival XMM-Newton observations, we identify strong X-ray flux variations in NGC 6946 X-1 indicating that it is the most variable ultraluminous X-ray source (ULX) on mHz timescales known so far. The 1-10 keV light curve exhibits variability with a fractional rms amplitude of 60% integrated in the frequency range of 1-100 mHz. The power …
First Very Low Frequency Detection of Short Repeated Bursts from Magnetar SGR J1550-5418
Takahashi, T.; Hayakawa, M.; Tanaka, Y. T. +7 more
We report on the first detection of ionospheric disturbances caused by short repeated gamma-ray bursts from the magnetar SGR J1550-5418. Very low frequency (VLF) radio wave data obtained in South America clearly show sudden amplitude and phase changes at the corresponding times of eight soft gamma-ray repeater bursts. Maximum amplitude and phase c…