A Wide-Field 90 Centimeter VLA Image of the Galactic Center Region

Abstract

We present a wide-Ðeld, high dynamic range, high-resolution, long-wavelength (j \ 90 cm) VLA image of the Galactic center region. The image is centered on Sgr A, covers an area of 4¡ ] 5¡ with an angular resolution of 43A, and has a rms sensitivity of B5 mJy beam~1. The image was constructed from archival (1989 and 1991) VLA data of Pedlar et al. and Anantharamaiah et al. using new threedimensional image restoration techniques. These three-dimensional imaging techniques resolve the problem of non-coplanar baselines encountered at long wavelengths and yield distortion-free imaging of far-Ðeld sources with improved sensitivity. At j \ 90 cm the VLA is sensitive to both thermal and nonthermal emission and the resulting image gives an unprecedented contextual perspective of the largescale radio structure in this unique and complicated region. We have catalogued over a hundred sources from this image and present for each source its 90 cm Ñux density, position, and size. For many of the small-diameter sources, we also derive the 20/90 cm spectral index. The spectral index as a function of length along several of the isolated nonthermal Ðlaments has been estimated and found to be constant. We have found six new small-diameter sources, as well as several extended regions of emission, which are clearly distinct sources that have not been previously identiÐed at higher frequencies. These data are presented as a Ðrst epoch of VLA observations that can be used to search for source variability in conjunction with a second epoch of observations that were recently initiated.

A peek behind the dusty curtain:KS-band polarization photometry and bow shock models of the Galactic center source IRS 8

“…The magnetic field at the position of IRS 8 is considered to be parallel to the north-south axis (Aitken et al 1998;Morris 1998;LaRosa et al 2000;Glasse et al 2003). The presented polarization maps show polarization vectors parallel to the magnetic field of the NA as they would be produced by absorptive scattering on dust grains, aligned by Davis-Greenstein alignment (Davis & Greenstein 1951).…”

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

“…However, the manner in which the magnetic field in NRFs is amplified and how their electrons are accelerated is still debated (e.g., Heyvaerts et al 1988;Benford 1988;Serabyn & Morris 1994;Yusef-Zadeh 2003. Several observations have measured the radio and X-ray spectral indices of NRFs (e.g., Lang et al 1999b;LaRosa et al 2000;Lu et al 2003), but there has not been much systematic study. Thus, a goal of this survey work is to find new examples of NRFs and make more robust measurements of their spectral indices, to help better constrain theoretical models.…”

Low-Frequency Radio Transients in the Galactic Center

“…We have used recent advances in low-frequency and three-dimensional imaging to produce a wide-field image (%2=5) of the GC, with uniform and high resolution across the field, from 0.33 GHz VLA observations made between 1986and 1989(LaRosa et al 2000. A second image, designed to exploit the increase in number and quality of the 0.33 GHz receivers on the VLA since the acquisition of the data used by LaRosa et al (2000), is in progress and will be reported elsewhere (Nord et al 2002).…”

“…The observations that form our new GC imaging program were obtained in 1998. The data were calibrated in the standard fashion (similar to that of LaRosa et al 2000), with 3C 48 and 3C 286 used to calibrate the visibility amplitudes and frequent observations of the VLA calibrators B1822À096 and B1830À360 used to calibrate the visibility phases. The observations were made in spectral line mode in order to permit efficient excision of radio-frequency interference and to reduce bandwidth smearing effects during imaging, with Cygnus A used to calibrate the bandpass.…”

“…We identified one source on a 1998 image (GCRT J1746À2757, x 3.1) that did not appear in the image of LaRosa et al (2000). Additional 1.42 and 4.86 GHz continuum observations of this source were acquired in 2000 July and December.…”