Search Publications
A Study of Quasar Evolution in the X-Ray Band with the Aid of Gravitational Lensing
Eracleous, Michael; Garmire, Gordon P.; Dai, Xinyu +1 more
We present results from a minisurvey of relatively high redshift (1.7<z<4), gravitationally lensed, radio-quiet quasars observed with the Chandra X-Ray Observatory and with XMM-Newton. The lensing magnification effect allows us to search for changes with redshift in quasar spectroscopic and flux variability properties, ranging over 3 orders …
The 1998 May 2-3 Magnetic Cloud: An Interplanetary ``Highway'' for Solar Energetic Particles Observed with SOHO/ERNE
Riihonen, Esa; Kocharov, Leon; Torsti, Jarmo
Using the Energetic and Relativistic Nuclei and Electron (ERNE) instrument on the Solar and Heliospheric Observatory (SOHO), we have measured the 17-22 MeV proton flux anisotropy during the 1998 May 2-3 solar energetic particle (SEP) event, when SOHO was inside a magnetic cloud associated with a previous coronal mass ejection (CME). The ability of…
The Small Blue Straggler Star Population in the Dense Galactic Globular Cluster NGC 6752
Sabbi, E.; Ferraro, F. R.; Rood, R. T. +1 more
We used high-resolution Hubble Space Telescope (HST)-WFPC2 and wide-field ground-based observations to construct a catalog of blue straggler stars (BSSs) that spans the entire radial extent of the globular cluster NGC 6752. The BSS sample is the most extensive ever obtained for this cluster. Although NGC 6752 is a high-density cluster with a large…
X-Ray Observations of Stellar Clusters Near the Galactic Center
Yusef-Zadeh, F.; Law, C.
We report the first detection of X-ray emission from the Quintuplet star cluster and compare its X-ray emission to that of the Arches star cluster. Four point sources are significantly detected near the core of the Quintuplet cluster with a total absorption-corrected luminosity of ~1×1033 ergs s-1. Diffuse, thermal emission i…
Evidence of Magnetic Reconnection along Coronal Hole Boundaries
Doyle, J. G.; Madjarska, M. S.; van Driel-Gesztelyi, L.
The present study reveals for the first time the existence of bidirectional jets, which are a signature of magnetic reconnection, occurring along coronal hole boundaries. The Solar Ultraviolet Measurement of Emitted Radiation spectrometer observations obtained in the N IV 765.15 Å (1.3×105 K) and Ne VIII 770.42 Å (6×105 K) em…
Chandra Observations of the Three Most Metal Deficient Blue Compact Dwarf Galaxies Known in the Local Universe, SBS 0335-052, SBS 0335-052W, and I Zw 18
Bauer, Franz E.; Thuan, Trinh X.; Izotov, Yuri I. +1 more
We present an X-ray study of the three most metal deficient blue compact dwarf (BCD) galaxies known in the local universe, based on deep Chandra observations of SBS 0335-052 (0.025 Zsolar), SBS 0335-052W (0.02 Zsolar), and I Zw 18 (0.02 Zsolar). All three are detected, with more than 90% of their X-ray emission ari…
The Iron Unresolved Transition Array in Active Galactic Nuclei
Netzer, Hagai
The unresolved transition array (UTA) of iron M-shell ions is a prominent absorption feature in the X-ray spectrum of many active galactic nuclei (AGNs). Modeling photoionized plasmas in an attempt to match the observed silicon and oxygen lines fails to predict the level of ionization of iron as inferred by this feature. It is suggested that the d…
Revisiting the Origin of Impulsive Electron Events: Coronal Magnetic Restructuring
Maia, Dalmiro Jorge Filipe; Pick, Monique
We revisit the impulsive beamlike particle events detected in situ from 1997 to 2000 by the Electron, Proton, and Alpha Monitor (EPAM) experiment on the Advanced Composition Explorer spacecraft. We study in detail a subset of events for which there are radio coronal observations from the Nançay Radioheliograph. EPAM measures electrons in the energ…
Chandra and Hubble Space Telescope Confirmation of the Luminous and Variable X-Ray Source IC 10 X-1 as a Possible Wolf-Rayet, Black Hole Binary
Brandt, W. N.; Bauer, Franz E.
We present a Chandra and Hubble Space Telescope study of IC 10 X-1, the most luminous X-ray binary in the starburst galaxy closest to the Milky Way. Our new hard X-ray observation of X-1 confirms that it has an average 0.5-10 keV luminosity of 1.5×1038 ergs s-1, is strongly variable (a factor of ~2 in <~3 ks), and is spati…
X-Raying A2125: A Large-Scale Hierarchical Complex of Galaxies and Hot Gas
Wang, Q. Daniel; Owen, Frazer; Ledlow, Michael
We present an 82 ks Chandra ACIS-I observation of a large-scale hierarchical complex, which consists of various clusters/groups of galaxies and low surface brightness X-ray emission at z=0.247. This high-resolution Chandra observation allows us for the first time to separate unambiguously the X-ray contributions from discrete sources and large-sca…