Search Publications
The Quiet-Sun Differential Emission Measure from Radio and UV Measurements
Landi, E.; Chiuderi Drago, F.
In the present work we combine UV and radio observations of the quiet Sun to determine the differential emission measure (DEM) of the average quiet solar atmosphere from the photosphere (5600 K) to the corona. UV line intensities have been used to constrain the DEM above 30,000 K, and the radio spectrum from 1.5 to 345 GHz has been used to extend …
XMM-Newton and Chandra Observations of Abell 2626: Interacting Radio Jets and Cooling Core with Jet Precession?
Sarazin, Craig L.; Reiprich, Thomas H.; Wong, Ka-Wah +1 more
We present a detailed analysis of the XMM-Newton and Chandra observations of Abell 2626 focused on the X-ray and radio interactions. Within the region of the radio minihalo (~70 kpc), there are substructures that are probably produced by the central radio source and the cooling core. We find that there is no obvious correlation between the radio b…
Prevalence of Tidal Interactions among Local Seyfert Galaxies
Tang, Ya-Wen; Ho, Paul T. P.; Lim, Jeremy +1 more
No mechanisms have hitherto been conclusively demonstrated to be responsible for initiating optically luminous nuclear (Seyfert) activity in local disk galaxies. Only a small minority of such galaxies are visibly disturbed in optical starlight, with the observed disturbances being at best marginally stronger than those found in matched samples of …
Correlation between the Sharp Variation of the Transport Rate of Magnetic Helicity and Solar Eruptive Events
Tan, Baolin; Zhang, Yin; Yan, Yihua
In this Letter we report a close relationship between the variations of the transport rate of magnetic helicity (dH/dt) and a microwave burst. The latter may be regarded as a prompt signal of nonthermal energetic particles originating from the magnetic reconnection during solar flaring events. We analyze the observations of magnetograms of MDI/SOH…
The Thermal Structure of an Active Region Observed Outside the Solar Disk
Landi, E.; Feldman, U.
In the present work we analyze an extensive active region spectrum observed by the SUMER instrument on board SOHO with the aim of determining the thermal structure of the emitting plasma. We found that the plasma is made of three distinct, isothermal components, whose physical properties are similar to coronal hole, quiet-Sun, and active region pl…
Comparative Analysis of Nonthermal Emissions and Electron Transport in a Solar Flare
Yokoyama, T.; Minoshima, T.; Mitani, N.
We study nonthermal emission in a solar flare occurring on 2003 May 29 using RHESSI hard X-ray (HXR) and Nobeyama microwave observations. This flare shows several typical behaviors of HXR and microwave emission: time delay of microwave peaks relative to HXR peaks, loop-top microwave and footpoint HXR sources, and a harder electron energy distribut…
XMM-Newton Observations of the TeV BL Lacertae Object PKS 2155-304 in 2006: Signature of Inverse Compton X-Ray Emission?
Zhang, Y. H.
This paper reports the first discovery of possible inverse Compton (IC) X-ray emission below 10 keV in the typical high-energy peaked BL Lac object (HBL) PKS 2155-304. Two XMM-Newton observations performed in 2006 reveal that the 0.6-10 keV X-ray spectra of the source harden (Δ Γ ~ 0.1-0.3) at break energies of ~4 keV. The concave X-ray spectra of…
On the Origin of Magnetic Helicity in the Solar Corona
Alexander, David; Tian, Lirong
Twenty-three active regions associated with pronounced sigmoidal structure in Yohkoh soft X-ray observations are selected to investigate the origin of magnetic helicity in the solar corona. We calculate the radial magnetic flux of each polarity, the rate of magnetic helicity injection, and total flux of the helicity injection (Δ HLCT) o…
A Jet Associated with the Classical T Tauri Star RY Tauri
Bastien, Pierre; St-Onge, Gilbert
High spatial resolution images have been taken on the Gemini North telescope of the classical T Tauri star RY Tauri. The Hα image, with the continuum properly subtracted, shows a jet extending out to at least 31'' at a position angle of about 295° from the star. A counterjet extending to at least 3.5' in the opposite direction is also visible. The…
Hinode Observations of Chromospheric Brightenings in the Ca II H Line during Small-Scale Flux Emergence Events
Guglielmino, S. L.; Romano, P.; Bellot Rubio, L. R. +1 more
Ca II H emission is a well-known indicator of magnetic activity in the Sun and other stars. It is also viewed as an important signature of chromospheric heating. However, the Ca II H line has not been used as a diagnostic of magnetic flux emergence from the solar interior. Here we report on Hinode observations of chromospheric Ca II H brightenings…