Search Publications
On the Origin of TeV Gamma-Ray Emission from HESS J1834-087
Gotthelf, E. V.; Mukherjee, R.; Halpern, J. P.
We present an X-ray study of the field containing the extended TeV source HESS J1834-087 using data obtained with the XMM-Newton telescope. Previously, the coincidence of this source with both the shell-type supernova remnant (SNR) W41 and a giant molecular cloud (GMC) was interpreted as favoring π0-decay γ-rays from interaction of the …
On the Accretion Rates of SW Sextantis Nova-like Variables
Sion, Edward M.; Ballouz, Ronald-Louis
We present accretion rates for selected samples of nova-like variables having IUE archival spectra and distances uniformly determined using an infrared method by Knigge. A comparison with accretion rates derived independently with a multiparametric optimization modeling approach by Puebla et al. is carried out. The accretion rates of SW Sextantis …
Imaging the Solar Tachocline by Time-Distance Helioseismology
Kosovichev, A. G.; Zhao, Junwei; Hartlep, Thomas +1 more
The solar tachocline at the bottom of the convection zone is an important region for the dynamics of the Sun and the solar dynamo. In this region, the sound speed inferred by global helioseismology exhibits a bump of approximately 0.4% relative to the standard solar model. Global helioseismology does not provide any information on possible latitud…
Energy-dependent Time Lags in the Seyfert 1 Galaxy NGC 4593
Rao, A. R.; Sriram, K.; Agrawal, V. K.
We investigate the energy-time lag dependence of the source NGC 4593 using XMM-Newton/EPIC pn data. We found that the time lag dependency is linear in nature with respect to the logarithm of different energy bands. We also investigate the frequency-dependent time lags and identify that at some frequency range (5 × 10-5 Hz to 2 × 10…
Supersonic Continuation of the Evershed Flow Outside a Sunspot as Observed with Hinode
Martínez Pillet, V.; Katsukawa, Y.; Ruiz Cobo, B. +1 more
We report on the discovery of mostly horizontal field channels just outside sunspot penumbrae (in the so-called "moat" region) that are seen to sustain supersonic flows (line-of-sight component of 6 km s-1). The spectral signature of these supersonic flows corresponds to circular polarization profiles with an additional, satellite, thir…
Multiwavelength Observation of Electron Acceleration in the 2006 December 13 Flare
Krucker, S.; Kubo, M.; Isobe, H. +8 more
We present a multiwavelength observation of a solar flare occurring on 2006 December 13 with Hinode, RHESSI, and the Nobeyama Radio Observatory to study the electron acceleration site and mechanism. The Solar Optical Telescope (SOT) on board Hinode observed elongated flare ribbons, and RHESSI observed double-footpoint hard X-ray (HXR) sources appe…
X-rays from the Power Sources of the Cepheus A Star-Forming Region
Ezoe, Yuichiro; Tsuboi, Yohko; Pravdo, Steven H. +1 more
We report an observation of X-ray emission from the exciting region of Cepheus A with the Chandra/ACIS instrument. What had been an unresolved X-ray source comprising the putative power sources is now resolved into at least three point-like sources, each with similar X-ray properties and differing radio and submillimeter properties. The sources ar…
Solar Flows and Their Effect on Frequencies of Acoustic Modes
Antia, H. M.; Chatterjee, Piyali
We have calculated the effects of large-scale solar flows, such as the meridional circulation, giant convection cells, and solar rotation on the helioseismic splitting coefficients using quasi-degenerate perturbation theory (QDPT). Our investigation reveals that the effect of poloidal flows like the large-scale meridional circulation are difficult…
Magnetic Helicity Exchange Between Neighboring Active Regions
Zhang, H.; Yang, S.; Büchner, J.
Addressing the long-lasting problem of the magnetic helicity distribution in the solar corona, a proof for magnetic helicity exchange between two neighboring emerging active regions (ARs) was found: when AR 9188 emerged, it first started to accumulate positive helicity, while the later neighboring emerging AR 9192 accumulated negative helicity. At…
A New Way to Infer Variations of the Seismic Solar Radius
Hill, F.; González Hernández, I.; Scherrer, P.
We show that the mean phase of waves propagating all the way from the far side of the Sun to the front side, as measured by seismic holography, varies with time. The change is highly anticorrelated with solar cycle activity and is consistent with other recent results on the variation of the seismic radius of the Sun. The phase change that we obser…