Search Publications
Sizes of transition-region structures in coronal holes and in the quiet Sun
Tu, C. -Y.; Marsch, E.; Tian, H. +2 more
Aims: We study the height variations of the sizes of chromospheric and transition-region features in a small coronal hole and the adjacent quiet Sun, considering images of the intensity, Doppler shift, and non-thermal motion of ultraviolet emission lines as measured by SUMER (Solar Ultraviolet Measurements by Emitted Radiation), together with the …
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…
IGRJ16479-4514: the first eclipsing supergiant fast X-ray transient?
Campana, S.; Israel, G.; Stella, L. +2 more
Supergiant fast X-ray transients (SFXTs) are a new class of high-mass X-ray binaries recently discovered with INTEGRAL. Hours-long outbursts from these sources have been observed on numerous occasions at luminosities of ~1036-1037ergs-1, whereas their low-level activity at ~1032-1034ergs-…
Evidence of a type 1/type 2 dichotomy in the correlation between quasar optical polarization and host-galaxy/extended emission position angles
Magain, P.; Hutsemékers, D.; Borguet, B. +2 more
Aims:For Seyfert galaxies, the AGN unification model provides a simple and well-established explanation of the type 1/type 2 dichotomy through orientation-based effects. The generalization of this unification model to the higher luminosity AGNs that quasars are remains a key question. The recent detection of type 2 radio-quiet quasars seems to sup…
Spitzer Space Telescope observations of the nucleus of comet 67P/Churyumov-Gerasimenko
Jorda, L.; Lamy, P. L.; Groussin, O. +3 more
Context: Comet 67P/Churyumov-Gerasimenko is the target of the Rosetta mission, and an early characterization of its nucleus is required to assist in preparing the orbital strategy of the spacecraft, the delivery of the Philae surface module and the science operations. We detected the nucleus using the Hubble Space Telescope in March 2003, but had …
The Suzaku Observation of NGC3516: Complex Absorption and the Broad and Narrow FeK Lines
Fabian, Andrew C.; Kunieda, Hideyo; Okajima, Takashi +10 more
We present results from a 150ks Suzaku observation of the Seyfert 1.5 NGC3516 in 2005 October. The source was in a relatively highly absorbed state. Our best-fit model is consistent with the presence of a low-ionization absorber having a column density near 5×1022 cm-2 and covering most of the X-ray continuum source (covering…
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…