Search Publications
Resolving the Large-Scale Spectral Variability of the Luminous Seyfert 1 Galaxy 1H 0419-577: Evidence for a New Emission Component and Absorption by Cold Dense Matter
O'Brien, P. T.; Reeves, J. N.; Page, K. L. +1 more
An XMM-Newton observation of the luminous Seyfert 1 galaxy 1H 0419-577 in 2002 September, when the source was in an extreme low-flux state, found a very hard X-ray spectrum at 1-10 keV with a strong soft excess below ~1 keV. Comparison with an earlier XMM-Newton observation when 1H 0419-577 was ``X-ray bright'' indicated that the dominant spectral…
On the Formation of the Resonance Lines of Helium in the Sun
Judge, Philip G.; Pietarila, Anna
To investigate the cause of anomalously bright resonance lines of helium in the Sun, we have studied the magnitude of the enhancements and some proposals made to explain them. Calculations in new semiempirical solar models indicate that the resonance lines of helium are enhanced by factors of 2-5 for He I and between 2 and 9 for He II, depending o…
Simultaneous Production of Disk and Lobes: A Single-Wind MHD Model for the η Carinae Nebula
Balick, Bruce; Matt, Sean
The luminous blue variable η Carinae is surrounded by a complex and highly structured nebula of ejected material. The best-studied and axisymmetric components of this outflow consist of bipolar lobes (the ``homunculus'') and an equatorial ``skirt.'' Recent proper-motion measurements suggest that the skirt was ejected at the same time as the lobes,…
Abundance of Substructure in Clusters of Galaxies
Springel, Volker; Natarajan, Priyamvada
It is widely recognized that cold dark matter (CDM) models predict abundant dark matter substructure in halos of all sizes. Galaxy-galaxy lensing provides a unique opportunity to directly measure the presence and the mass of such substructures in clusters of galaxies. Here we present the mass function of substructures obtained from lensing in mass…
Variations in the Spin Period of the Radio-quiet Pulsar 1E 1207.4-5209
Pavlov, George G.; Zavlin, Vyacheslav E.; Sanwal, Divas
The X-ray source 1E 1207.4-5209 is a compact central object in the G296.5+10.0 supernova remnant. Its spin period of 424 ms, discovered with Chandra, suggests that it is a neutron star. The X-ray spectrum of this radio-quiet pulsar shows at least two absorption lines, the first spectral features discovered in radiation from an isolated neutron sta…
XMM-Newton Observation of the Merging Galaxy Cluster A1644
Sarazin, Craig L.; Reiprich, Thomas H.; Tittley, Eric +1 more
We present an XMM-Newton imaging spectroscopy analysis of the galaxy cluster A1644. A1644 is a complex merging system consisting of a main cluster and a subcluster. A trail of cool, metal-rich gas has been discovered close to the subcluster. The combination of results from X-ray, optical, and radio data and a comparison to a hydrodynamic simulatio…
Physical Structure of the Protoplanetary Nebula CRL 618. II. Interferometric Mapping of Millimeter-Wavelength HCN J = 1-0, HCO+ J = 1-0, and Continuum Emission
Sahai, R.; Sánchez Contreras, C.
We present interferometric maps with high angular resolution, 1.1" to 1.9", of the HCO + J=1-0 and HCN J=1-0 emission lines in the protoplanetary nebula CRL 618. These molecules are present in both the slowly (~10-20 km s-1) and rapidly (~200 km s-1) outflowing components of the molecular envelope of CRL 618. The …
Waiting in the Wings: Reflected X-Ray Emission from the Homunculus Nebula
Weis, K.; Davidson, K.; Smith, N. +14 more
We report the first detection of X-ray emission associated with the Homunculus nebula that surrounds the supermassive star η Car. The emission is characterized by a temperature in excess of 100 MK and is consistent with scattering of the time-delayed X-ray flux associated with the star. The nebular emission is bright in the northwestern lobe and n…
Pronounced Long-Term Flux Variability of the Anomalous X-Ray Pulsar 1E 1048.1-5937
Tiengo, A.; Mereghetti, S.; Stella, L. +4 more
We present XMM-Newton and Chandra observations of 1E 1048.1-5937, being the first to show evidence for a significant variation in the X-ray luminosity of this anomalous X-ray pulsar (AXP). While during the first XMM-Newton (2000 December) and Chandra (2001 July) observations the source had a flux consistent with that measured on previous occasions…
Magnetic Field-Minimum Intensity Correlation in Sunspots: A Tool for Solar Dynamo Diagnostics
Norton, Aimee A.; Gilman, Peter A.
Within a sunspot umbra, the continuum intensity is known to be inversely proportional to the magnetic field strength. Studied less is the relationship between the minimum continuum intensity and the maximum field strength of different sunspots. We conduct a test of this global relationship, using brightness ratios and magnetic field data from the …