High-Resolution, Wide-Field Imaging of the Galactic Center Region at 330 MHz

Nord, Michael E.; Lazio, T. Joseph W.; Kassim, N. E.; Hyman, S. D.; Larosa, T. N.; Brogan, C. L.; Duric, Nebojsa

doi:10.1086/424001

Cited by 99 publications

(156 citation statements)

References 41 publications

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“…These filaments are observed only in the GC region, but are found there in abundance, with about 15 known and several dozen candidates in the central 2 of the Galaxy ( Nord et al 2004;Paper I). The nonthermal spectra and linearly polarized radio emission from the NRFs indicate that they emit synchrotron radiation.…”

Section: Introductionmentioning

confidence: 99%

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A Wide‐Area VLA Continuum Survey near the Galactic Center at 6 and 20 cm Wavelengths

Law

Yusef‐Zadeh

Cotton

2008

ASTROPHYS J SUPPL S

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We describe the results of a millijansky sensitivity VLA survey of roughly 1 deg 2 near the Galactic center at 6 and 20 cm. Catalogs of compact and filamentary structures are given and compared to previous surveys of the region. Eight of the unusual nonthermal radio filaments are detected in 6 cm polarized emission; three of these are the first such detections, confirming their nonthermal nature. This survey found emission from a filament at (l; b) ¼ (359:1; 0:75), or a projected distance from Sgr A Ã of 200 pc, greatly extending the latitude range observed with such features. There is also new evidence for spatial gradients in the 6/20 cm spectral indices of some filaments, and we discuss models for these gradients. In studying compact sources, the combination of spectral index and polarization information allows us to identify pulsar candidates and compact H ii regions in the survey. There is also some evidence that the flux measurements of compact sources may be affected by electron scattering from the interstellar medium in the central few hundred parsecs of the Galaxy.

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Section: Introductionmentioning

confidence: 99%

“…Recent technological changes, such as new imaging algorithms and receivers, have enabled more sensitive, systematic study over a wider range of wavelengths (Gray 1994;Brogan et al 2003;Nord et al 2004). In Yusef-Zadeh et al (2004, hereafter Paper I), we presented a comprehensive 20 cm imaging survey of the GC region.…”

Section: Introductionmentioning

confidence: 99%

A Wide‐Area VLA Continuum Survey near the Galactic Center at 6 and 20 cm Wavelengths

Law

Yusef‐Zadeh

Cotton

2008

ASTROPHYS J SUPPL S

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“…1, the peak flux density we derived from the 2002 discovery observation is 91 ± 14 mJy beam −1 . A large fraction of the difference with the integrated flux measurement by Nord et al (2004) is probably caused by extended emission. Indeed, when we exclude the shortest spacings, uv min = 1.0 kλ, we find a much lower peak flux density of 73 ± 5 mJy beam −1 .…”

Section: The Source On the Opposite Side Of The Supernova Remnantmentioning

confidence: 91%

“…1 is resolved in VLA A configuration. From a combination of three VLA datasets, two in A configuration and one in B configuration, this source was detected with a peak flux density of 17.1 ± 2 mJy beam −1 and an integrated flux of 47.6 mJy (see Nord et al 2004, Table 2, source 72). Apparently the synthesized beam of the combination of these datasets (12 × 7 ) resolves this source.…”

Section: The Source On the Opposite Side Of The Supernova Remnantmentioning

confidence: 99%

“…We found a peak flux density of 900 ± 23 mJy beam −1 and this J2000 position: α = 17h45m05.015s ± 0.045s, δ = −30 • 09 52.19 ±0.52 . This position of GCRT J1745-3009 has not yet been corrected for ionospheric-induced refraction (see Nord et al 2004, for some background). That correction, which is basically, but not exactly, a global position shift of all sources in the field, will significantly increase the uncertainty in the position of GCRT J1745-3009.…”

Section: Position and Flux Measurements; Spectral Index Determinationmentioning

confidence: 99%

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A new perspective on GCRT J1745-3009

Spreeuw

Scheers

Braun

et al. 2009

A&A

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Context. Reports on a transient source about 1.25 • south of the Galactic Centre motivated these follow-up observations with the WSRT and the reinvestigation of archival VLA data. The source GCRT J1745-3009 was detected during a 2002 Galactic Centre monitoring programme with the VLA at 92 cm by five powerful 10-min bursts with a 77-min recurrence while apparently lacking any interburst emission. Aims. The WSRT observations were performed and archival VLA data reduced to detect GCRT J1745-3009 again at different epochs and frequencies, to constrain its distance, and to determine its nature. We attempted to extract a more accurate lightcurve from the discovery dataset of GCRT J1745-3009 to rule out some of the models that have been suggested. We also investigated the transient behaviour of a nearby source. Methods. The WSRT data were taken in the "maxi-short" configuration, using 10 s integrations, on 2005 March 24 at 92 cm and on 2005 May 14/15 at 21 cm. Five of the six VLA observations we reduced are the oldest of this field in this band. Results. GCRT J1745-3009 was not redetected. With the WSRT we reached an rms sensitivity of 0.21 mJy beam −1 at 21 cm and 3.7 mJy beam −1 at 92 cm. Reanalysis of the discovery observation data resulted in a more accurate and more complete lightcurve. The five bursts appear to have the same shape: a steep rise, a more gradual brightening, and a steep decay. We found variations in burst duration of order 3%. We improved the accuracy of the recurrence period of the bursts by an order of magnitude: 77.012 ± 0.021 min. We found no evidence of aperiodicity. We derived a very steep spectral index: α = −6.5 ± 3.4. We improved the 5σ upper limits for interburst emission and fractional circular polarisation to 31 mJy beam −1 and 8%, respectively. Any transient behaviour of a nearby source could not be established. Conclusions. Models that predict symmetric bursts can be ruled out, but rotating systems are favoured, because their periodicity is precise. Scattering constraints imply that GCRT J1745-3009 cannot be located far beyond the GC. If this source is an incoherent emitter and not moving at a relativistic velocity, it must be closer than 14 pc.

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Magnetic Fields in the Milky Way and Other Spiral Galaxies

Beck

2004

How Does the Galaxy Work?

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The average strength of the total magnetic field in the Milky Way, derived from radio synchrotron data under the energy equipartition assumption, is 6µG locally and 10µG at 3 kpc Galactic radius. Optical and synchrotron polarization data yield a strength of the local regular field of 4µG (an upper limit if anisotropic fields are present), while pulsar rotation measures give 1.5µG (a lower limit if small-scale fluctuations in regular field strength and in thermal electron density are anticorrelated). In spiral arms of external galaxies, the total [regular] field strength is up to 35µG [ 15µG]. In nuclear starburst regions the total field reaches 50µG. --Little is known about the global field structure in the Milky Way. The local regular field may be part of a "magnetic arm" between the optical arms, a feature that is known from other spiral galaxies. Unlike external galaxies, rotation measure data indicate several global field reversals in the Milky Way, but some of these could be due to field distortions. The Galaxy is surrounded by a thick radio disk of similar extent as around many edge-on spiral galaxies. While the regular field of the local disk is of even symmetry with respect to the plane (quadrupole), the regular field in the inner Galaxy or in the halo may be of dipole type. The Galactic center region hosts highly regular fields of up to milligauss strength which are oriented perpendicular to the plane.

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High-Resolution, Wide-Field Imaging of the Galactic Center Region at 330 MHz

Cited by 99 publications

References 41 publications

A Wide‐Area VLA Continuum Survey near the Galactic Center at 6 and 20 cm Wavelengths

A Wide‐Area VLA Continuum Survey near the Galactic Center at 6 and 20 cm Wavelengths

A new perspective on GCRT J1745-3009

Magnetic Fields in the Milky Way and Other Spiral Galaxies

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