| High-Resolution, Wide-Field Imaging of the Galactic Center Region at 330 MHz |
OCT 2004 |
26 pages |
| Authors:
Michael E. Nord; T. J. Lazio; Namir E. Kassim; S. D. Hyman; T. N. LaRosa; C. L. Brogan; N. Duric; NAVAL RESEARCH LAB WASHINGTON DC REMOTE SENSING DIV
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 | We present a wide-field, subarcminute-resolution VLA image of the Galactic center region at 330 MHz. With a resolution of -7" x 12" and an rms noise of 1.6 mJy beam (exp -1), this image represents a significant increase in resolution and sensitivity over the previously published VLA image at this frequency. The improved sensitivity has more than tripled the census of small-diameter sources in the region, has resulted in the ... |
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| New Nonthermal Filaments at the Galactic Center: Are They Tracing a Globally Ordered Magnetic Field |
20 MAY 2004 |
8 pages |
| Authors:
T. N. LaRosa; Michael E. Nord; T. J. Lazio; Namir E. Kassim; KENNESAW STATE UNIV GEORGIA DEPARTMENT OF BIOLOGICAL AND PHYSICAL SCIENCES
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| New high-resolution, wide-field 90 cm Very Large Array (VLA) observations of the Galactic center (GC) region by Nord and coworkers have revealed 20 nonthermal filament (NTF) candidates. We report 6 cm polarization observations of six of these. All of the candidates have the expected NTF morphology, and two show extended polarization, confirming their identification as NTFs. One of the new NTFs appears to be part of a system of NTFs ... |
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| Detection of Sagittarius A* at 330 MHz With the Very Large Array |
20 JAN 2004 |
5 pages |
| Authors:
Michael E. Nord; T. J. Lazio; Namir E. Kassim; W. M. Goss; N. Duric; NAVAL RESEARCH LAB WASHINGTON DC
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| The central radio-bright region of our Galaxy, known as the Sagittarius Complex, is composed of three major components: the supernova remnant (SNR) Sgr A East, the Sgr A West H II region, and Sgr A*, recently established as our Galaxy's central massive black hole (e.g., Ghez et al. 2000; Eckart et al. 2002). Models attempting to explain the emission from Sgr A* fall into three broad classes. Emission is modeled ... |
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| Near-Infrared K-Band Imaging of a Sample of Ultra-Steep-Spectrum Radio Sources Selected at 74 MHz |
2004 |
12 pages |
| Authors:
Matt J. Jarvis; Maria J. Cruz; Aaron S. Cohen; Huub J. Roettgering; Namir E. Kassim; NAVAL RESEARCH LAB WASHINGTON DC
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| In this paper we present near-infrared K-band imaging of a sample of ultra-steep-spectrum (USS) radio sources selected at 74 MHz. The dual selection criteria of low frequency and USS mean that we should be sensitive to the highest-redshift (z > 5) radio galaxies. We have obtained K-band magnitudes for all of the objects in our sample of 26 and discuss the properties of each. There is a pronounced bias in ... |
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| Spatially Resolved Thermal Continuum Absorption Against Supernova Remnant W49B |
01 OCT 2001 |
10 pages |
| Authors:
C. K. Lacey; T. J. Lazio; Namir E. Kassim; N. Duric; D. S. Briggs; K. K. Dyer; NAVAL RESEARCH LAB WASHINGTON DC REMOTE SENSING DIV
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| We present subarcminute resolution imaging of the Galactic supernova remnant W49B at 74 MHz (25") and 327 MHz (6"), the former being the lowest frequency at which the source has been resolved. While the 327 MHz image shows a shell-like morphology similar to that seen at higher frequencies, the 74 MHz image is considerably different, with the southwest region of the remnant almost completely attenuated. The implied 74 MHz optical ... |
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| A New System of Parallel Isolated Nonthermal Filaments Near the Galactic Center: Evidence for a Local Magnetic Field Gradient |
14 AUG 2001 |
10 pages |
| Authors:
T. N. LaRosa; T. J. Lazio; Namir E. Kassim; KENNESAW STATE UNIV GEORGIA DEPARTMENT OF BIOLOGICAL AND PHYSICAL SCIENCES
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| We report the discovery of a system of isolated nonthermal filaments approximately northwest 0 degrees.5 (75 pc in projection) of Sgr A. Unlike other isolated nonthermal filaments which show subfilamentation, braiding of subfilaments, and flaring at their ends, these filaments are simple linear structures and more closely resemble the parallel bundled filaments in the Galactic center radio arc. However, the most unusual feature of these filaments is that the 20/90 ... |
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| M87 at 90 Centimeters: A Different Picture |
15 JUN 2000 |
10 pages |
| Authors:
Frazer N. Owen; Jean A. Eilek; Namir E. Kassim; NATIONAL RADIO ASTRONOMY OBSERVATORY SOCORRO NM
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| We report new radio imaging of the large-scale radio structure of M87 with the VLA at 90 cm. These new images show the complex structure of the radio emission more clearly than previous attempts, some of which date back to the 1940s. The images suggest that the outward flow from the M87 nucleus extends well beyond the 2 kpc jet. Two "bubbles" of synchrotron emission appear to be inflated by ... |
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| Spatial Variations of the Synchrotron Spectrum Within Tycho's Supernova Remnant (3C 10): A Spectral Tomography Analysis of Radio Observations at 20 and 90 Centimeter Wavelengths |
20 JAN 2000 |
11 pages |
| Authors:
D. M. Katz-Stone; Namir E. Kassim; T. J. Lazio; R. O'Donnell; NAVAL ACADEMY ANNAPOLIS MD DEPT OF PHYSICS
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| We present subarcminute-resolution (approx. 10"), high-dynamic range radio observations of Tycho's supernova remnant (3C 10) at lambda = 20 cm and lambda = 90 cm with the Very Large Array (VLA). The thermal-noise-limited 90 cm image has been compensated properly for the noncoplanar characteristics of the VLA and is the most sensitive low-frequency image of this source presently available. We use these images to search for spatial variations in the ... |
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| A Wide-Field 90 Centimeter VLA Image of the Galactic Center Region |
JAN 2000 |
36 pages |
| Authors:
T. N. LaRosa; Namir E. Kassim; T. J. Lazio; S. D. Hyman; KENNESAW STATE UNIV GEORGIA DEPARTMENT OF BIOLOGICAL AND PHYSICAL SCIENCES
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| We present a wide-field, high dynamic range, high-resolution, long-wavelength (lambda = 90 cm) Very Large Array (VLA) image of the Galactic center region. The image is centered on Sgr A, covers an area of 4 deg. x 5 deg. with an angular resolution of 43", and has a rms sensitivity of approx. 5 mJy beam(expo. -1). The image was constructed from archival (1989 and 1991) VLA data of Pedlar et ... |
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| Upper Limits on the Continuum Emission from Geminga at 74 and 326 MHz |
20 DEC 1999 |
5 pages |
| Authors:
Namir E. Kassim; T. J. Lazio; NAVAL RESEARCH LAB WASHINGTON DC REMOTE SENSING DIV
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| We report a search for radio continuum emission from the gamma-ray pulsar Geminga. We have used the VLA to image the location of the optical counterpart of Geminga at 74 and 326 MHz. We detect no radio counterpart. We derive upper limits to the pulse-averaged flux density of Geminga, taking diffractive scintillation into account. We find that diffractive scintillation is probably quenched at 74 MHz and does not influence our ... |
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| G359.87+0.18, An FR II Radio Galaxy 15' from Sagittarius A*: Implications for the Scattering Region in the Galactic Center |
10 APR 1999 |
11 pages |
| Authors:
T. J. Lazio; K. R. Anantharmaiah; W. M. Goss; Namir E. Kassim; James M. Cordes; NAVAL RESEARCH LAB WASHINGTON DC REMOTE SENSING DIV
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| G359.87 + 0.18 is an enigmatic object located 15' from Sgr A*. It has been variously classified as an extragalactic source, a Galactic jet source, and a young supernova remnant. We present new observations of G359.87 + 0.18 between 0.33 and 15 GHz and an H I absorption spectrum and use these to argue that this source is an FR II radio galaxy. We are able to place a crude ... |
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| 1051 Ergs: The Evolution of Shell Supernova Remnants |
15 NOV 1997 |
28 pages |
| Authors:
T. W. Jones; Lawrence Rudnick; Byung-Il Jun; Kazimierz J. Borkowski; Gloria Dubner; Dale A. Frail; Hyesung Kang; Namir E. Kassim; Richard McCray; MINNESOTA UNIV MINNEAPOLIS DEPT OF ASTRONOMY
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| Although the title points only to classical, shell SNR structures, the workshop also considered dynamical issues involving X-ray filled composite remnants and pulsar-driven shells, such as that in the Crab Nebula. Approximately 75 observers, theorists, and numerical simulators with wide-ranging interests attended the workshop. An even larger community helped through extensive on-line debates prior to the meeting to focus issues and galvanize discussion. In order to deflect thinking away from ... |
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| X-Ray Observations of Supernova Remnants as Distance Indicators |
01 JUN 1994 |
4 pages |
| Authors:
Namir E. Kassim; Paul Hertz; Schuyler D. Van Dyk; Kurt W. Weiler; NAVAL RESEARCH LAB WASHINGTON DC
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| SNRs are important in Galactic astrophysics because they are the major source of energy input to the interstellar medium, serve as the site of cosmic-ray acceleration and play a role in triggering star formation. Unlike H-II regions, whose distances can be constrained kinematically, Galactic SNRs have poorly determined distances. Of the currently known 180 Galactic remnants, only 15% have distance determinations and only a limited subset of these are likely ... |
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| ROSAT Observations of the Composite Supernova Remnant G326.3-1.8 |
20 DEC 1993 |
7 pages |
| Authors:
Namir E. Kassim; Paul Hertz; Kurt W. Weiler; NAVAL RESEARCH LAB WASHINGTON DC
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| We have observed X-ray emission from the radio-defined composite (shell plus filled-center plerion) Galactic supernova remnant (SNR) 0326.3 - 1.8 with the ROSAT position sensitive proportional counter (PSPC). The derived distance falls within the range of a variety of previous but poor and uncertain distance estimates and is consistent with the only reliable lower limit of D > 1.5 kpc. Evidence exists in the literature from both optical and radio ... |
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| The Galaxy Activity-Interaction Connection. 2. Radio Observations |
JAN 1993 |
8 pages |
| Authors:
Eric P. Smith; Namir E. Kassim; NATIONAL AERONAUTICS AND SPACE ADMINISTRATION GREENBELT MD GODDARD SPACE FLIGHT CENTER
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| As the second part of an ongoing investigation into the triggering of nuclear radio emission in inter acting galaxies, we present the results of a Very Large Array snapshot survey of southern interacting galaxies at 6 and 20 cm. The purpose of the survey was to search for and classify the nature of radio emission in a set of advanced-interaction disk galaxies which we had previously imaged optically. There were ... |
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| 330 MHz VLA Observations of 20 Galactic Supernova Remnants |
MAR 1992 |
12 pages |
| Authors:
Namir E. Kassim; NAVAL RESEARCH LAB WASHINGTON DC
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| We present 330 MHz images and integrated flux densities for 20 previously identified 1st quadrant Galactic Supernova Remnants (SNRs). The observations were made in the D configuration of the VLA giving an angular resolution of -3' and providing good sensitivity to extended structure. Such emission, particularly if it is nonthermal, might be missed on higher frequency surveys due to confusion with the Galactic background and confusion with thermal sources in ... |
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| A New Look at the "Jet" in the CTB 37A/B Supernova Remnant Complex |
10 JUN 1991 |
7 pages |
| Authors:
Namir E. Kassim; Stefi A. Baum; Kurt W. Weiler; NAVAL RESEARCH LAB WASHINGTON DC
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| Very Large Array observations of the unusual southern Galactic supernova remnant (SNR) complex near l = 348 degrees, b = 0 degrees at wavelengths of 6, 20, and 90 cm are presented. Derived continuum spectra and observed morphologies indicate that G348.5+0.1 (CTB 37A) does not have a "jet" as reported by previous observers but is instead superposed on a second, previously unidentified SNR lying along the line of sight. This ... |
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| W30 Revealed: Separation and Analysis of Thermal and Nonthermal Emission in a Galactic Complex |
01 SEP 1990 |
14 pages |
| Authors:
Namir E. Kassim; Kurt W. Weiler; NAVAL RESEARCH LAB WASHINGTON DC
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| We present new VLA observations of the W30 Galactic complex at 90 and 20 cm. By combining these data with existing radio continuum and recombination line observations extending from wavelengths of 10 m to 3 cm, we are able to do the following: (1) We can improve estimates of the spectra and physical properties of H II regions in the complex. For thermal sources which are optically thick at 90 ... |
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| Structure in Small Molecular Clouds: Pedestals and Clumping |
AUG 1990 |
23 pages |
| Authors:
Loris Magnani; John M. Carpenter; Leo Blitz; Namir E. Kassim; Biman B. Nath; NAVAL RESEARCH LAB WASHINGTON DC
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| Observations of wings or pedestals from three regions in high-latitude molecular clouds are presented in order to determine the morphology and physical conditions of the gas responsible for this phenomenon. High-sensitivity spectra along 10-25 lines of sight in each region show extended emission in addition to the typical narrow Gaussian emission from cold clumps. The pedestal profiles resemble the wings seen in CO and other molecules in low-luminosity molecular outflow ... |
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| Low-Frequency Observations of Galactic Supernova Remnants and the Distribution of Low-Density Ionized Gas in the Interstellar Medium |
15 DEC 1989 |
11 pages |
| Authors:
Namir E. Kassim; NAVAL RESEARCH LAB WASHINGTON DC E O HULBURT CENTER FOR SPACE RESEARCH
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| New long-wavelength observations of Galactic supernova remnants (SNRs) at 30.9 and 57.5 MHz are used to derive detailed low-frequency radio spectra for 32 SNRs. Of these, approximately two-thirds show turnovers at low frequencies, implying the presence of a widespread, but inhomogeneous, ionized absorbing medium along the lines of sight. These observations are combined with other low-frequency data to derive free-free optical depths toward 47 SNRs and to constrain the physical ... |
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| Radio Spectrum Studies of 32 First-Quadrant Galactic Supernova Remnants |
DEC 1989 |
18 pages |
| Authors:
Namir E. Kassim; NAVAL RESEARCH LAB WASHINGTON DC
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| We present a comprehensive list of integrated radio continuum flux density measurements for 32 first- quadrant Galactic supernova remnants (SNRs). The list includes all available measurements from the literature, as well as some previously unpublished low-frequency measurements from the Clark Lake Galactic plane survey. All measurements have been placed on the same absolute flux density scale, and those which are deemed poor or otherwise inappropriate for the purposes of constructing ... |
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| Improved Estimates of Galactic H II Region Emission Measures and Filling Factors: Low-Frequency VLA Observations Near Sharpless 53 |
01 MAR 1989 |
11 pages |
| Authors:
Namir E. Kassim; Kurt W. Weiler; William C. Erickson; T. L. Wilson; NAVAL RESEARCH LAB WASHINGTON DC E O HULBURT CENTER FOR SPACE RESEARCH
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| VLA observations at 20 and 90 cm of five distant Galactic H II regions in an area including the Sharpless S53 complex have been used to measure their effective sizes and optically thick continuum flux densities. These data have been combined with shorter wavelength, optically thin flux density measurements and electron temperature estimates to determine accurate emission measures where previous results gave only lower limits. Our analysis indicates that existing ... |
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