The VLBA Imaging and Polarimetry Survey

The VLBA Imaging and Polarimetry Survey, VIPS for short, is a combined 5 GHz and 15 GHz survey with the Very Long Baseline Array of ~1100 active galactic nuclei (AGN) with full polarization and high dynamic range. The parent sample is the CLASS survey in the region covered by the Sloan Digital Sky Survey in order to facilitate multi-wavelength science.

The VIPS team is: Greg Taylor (UNM/NRAO), Joe Helmboldt (UNM), Steve Tremblay (UNM), Chris Fassnacht (UCD), Craig Walker (NRAO), Steve Myers (NRAO), Lorant Sjouwerman (NRAO), Tim Pearson (Caltech), Tony Readhead (Caltech), Larry Weintraub (Caltech), Neil Gehrels (NASA GSFC), Roger Romani (Stanford), Steve Healey (Stanford), Peter Michelson (Stanford), Roger Blandford (KIPAC), and Garret Cotter (Oxford)

A paper describing the properties of VIPS sources associated with EGRET blazers by Taylor et al. has just been submitted to ApJ.

The first stage of 5 GHz observations for the VIPS survey was completed on September 6, 2006, on budget and on time. These results are described in the VIPS 5 GHz Survey paper by Helmboldt et al. (2007, ApJ, 658, 203, astro-ph/0611459). VIPS was allocated 195 hours at 256 Mbps in order to obtain first epoch images of all 1127 sources at 5 GHz. One out of the 18 observing runs had to be re-observed due to a combination of scheduled maintenance and a recording problem that resulted in the combined loss of 2 antennas. This last run was performed on August 12, 2006. To see all the images check out the VIPS data collection index page. If you should make use of VIPS data, please reference the paper by Helmboldt et al. above.

The reduction of the pilot project, that began when Chris Fassnacht visited NRAO in August 2004, is finished. Here is the paper as accepted for publication in the Astrophysical Journal Supplement describing the pilot project. This version has the figures at full resolution unlike the astro-ph/0503234 posting. Notes on the data reduction procedure used can be found for BF072A, BF072B, BF072C, BF072D. The VLBA pilot images and links to other catalogs can be found in the VIPS pilot data page. The VIPS sample is explained in detail on the VIPS catalog page.

Polarization is detected in roughly a third of sources. Here is our combined UV coverage compared to a one frequency coverage.

The VIPS pipeline consists of:

Step 1: VIPSUTIL and VIPSPIPE.HLP to calibrate, average and SPLIT the data.
Step 2: Automatic Imaging in Difmap of our calibrators using these scripts for step 2.
Step 3: Polarization calibration in AIPS with these procedures for step 3.
Step 4: Automatic Imaging in Difmap of all sources using these scripts for step 4.
Step 5: EVPA calibration (not fully automatic) and final image generation with these step 5 procedures.

VIPS Optical Identifications and Redshifts:

Five nights in December have been awarded on the 200", and two nights on Keck have been awarded for Jan. 2008. Five nights were awarded on the Palomar 200" telescope for fall/winter 2005. Four nights on the 200" and 2 nights on Keck have been awarded for fall/winter 2006. To obtain the maximum scientific return on the VIPS complete optical identification and redshifts are highly desirable. Nearly all sources will be successfully imaged by SDSS in multiple colors, and the brighter ~25% will have spectroscopic redshifts. In addition to this we have made a good start on the fainter objects with the Hobby-Ebberly Telescope (HET), Palomar, and Keck telescopes. Of the 1127 targets 582 (52%) have spectroscopic IDs with 208 of these being recently contributed by our team members at Stanford. This figure shows the location on the sky of the VIPS sources already identified, and those yet to be observed, as a function of magnitude.

VIPS Talks given so far:

Powerpoint Talk given at GLAST lunch October 21, 2004 by Greg

Powerpoint slides in pdf for GLAST lunch talk

Powerpoint Talk given at Berkeley November 29, 2004 by Greg

Powerpoint Talk given at MIT on January 27 and Haystack on Jan. 28 by Greg

Powerpoint Talk given at UC Davis on Feb. 3, 2005 by Greg

Analysis of robustness and conclusions. Lorant and Greg have studied how the results degrade as we discard antennas and reduce time on source. Take a look at the plots and statistics. We believe that in order to maintain a high dynamic range and sensitivity to weak polarized emission we want to keep the rms noise close to the level in the pilot of 0.25 mJy/beam. This was achieved by observing 1.75 hours/source @128 Mbps. Calibration overhead was 15% within each 12 hour run. By going to 12 sources within a 24 hour period we can reduce the overhead to 7% from 15%. Switching to 256 Mbps at 50% duty cycle (to maintain 128 Mbps average), we can observe 15 sources in each 24 hour run. We can't afford to give up half of the observing time (see plots) or two antennas. We can afford to give up any 1 antenna. If we start with 1 antenna down, then we can survive a loss of another antenna provided we don't incur a combination of SC+MK, PT+LA, or other short baseline pairs. We would do better to observe at 256 Mbps and use 2 bit sampling with the existing frequency setups. We could also combine 4607 + 4677, 4992 + 5097, 14904 + 14970, 15267 + 15366 MHz in the reduction, to knock down to 4 frequencies in total, although this would give up some sensitivity to extreme RMs.

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