Presentation on theme: "Arecibo 40th Anniversary Workshop--R. L. Brown The Arecibo Astrometric/Timing Array Robert L. Brown."— Presentation transcript:
Arecibo 40th Anniversary Workshop--R. L. Brown The Arecibo Astrometric/Timing Array Robert L. Brown
Arecibo 40th Anniversary Workshop--R. L. Brown Continuum sensitivity of the Arecibo telescope at L-band: Radiometer Equation T sys = 25K ALFA RF Bandwidth 300 MHz 1 Second Integration time Telescope 11 K/Jy S (rms) = 0.13 mJy S(rms:NVSS) = 0.45 mJy/beam (45” beam)
Arecibo 40th Anniversary Workshop--R. L. Brown Continuum sensitivity of the Arecibo telescope at L-band: Reality Source confusion limits the L-band continuum to ~few mJy (i.e. less than a second of integration) Solution: Spatially resolve the confusing sources by incorporating the Arecibo telescope in an interferometric array—preserve the sensitivity with the Arecibo telescope, enhance the resolution by correlating the Arecibo telescope with a few remote antennas.
Arecibo 40th Anniversary Workshop--R. L. Brown Continuum sensitivity of the Arecibo telescope at L-band: Single Baseline Interferometer Flux density rms for a single-baseline interferometer This equation is for a single polarization (TMS 9.5). Numerically, if the remote antennas are 30m diameter, the correlated bandwidth is 300 MHz and we observe for 1 second, S(rms) = 0.57 mJy per baseline (1 second of integration) And in one hour of integration S(rms) = 10 microJy per baseline (1 hour of integration)
Arecibo 40th Anniversary Workshop--R. L. Brown Continuum sensitivity of the Arecibo telescope at L-band: Interferometer Array For an array of N remote antennas that are correlated with the Arecibo telescope, the sensitivity of the array is approximately sqrt(N) better than that of the single baseline interferometer (because the additional sensitivity added by pairs of the remote antennas is very little). For four remote 30 m antennas, i.e. N=4 S(rms) = 0.3 mJy in one second of integration S(rms) = 5.0 microJy in one hour of integration Synthesized beam ~ 0.4” x 0.”9 for PR-scale interferometer array
Arecibo 40th Anniversary Workshop--R. L. Brown Arecibo Interferometer: Example, Sky Maps in the Continuum and HI Absorption Technical Description: N=4 remote 30m antennas connected via optical fiber links with the Arecibo telescope—performance and sky coverage of the remote antennas not significantly different from that of the Arecibo telescope (up to the point that this is a cost issue); Single frequency front ends (L-band); 300 MHz analyzed bandwidth (1225-1525 MHz) Bandwidth Synthesis used to enhance the uv-coverage Science Objectives: Deep continuum sky surveys, use with ALFA on the Arecibo telescope, 7 simultaneous maps (not images) covering ~11’ beam area; HI absorption, z=0 to 0.14 see tau(HI) 2 mJy using integration times of less than one hour.
Arecibo Interferometer: Discovery Science, the Transient Radio Sky Science question: Are there physical phenomena in cosmic sources that give rise to transient radio emission? Observational Complication: Single dish, total power telescope, has difficulty distinguishing transient emission from RFI; Search strategy employing geographically separated telescopes and coincidence-sampling has been used successfully on a limited scale (usually) with limited sensitivity.
Arecibo 40th Anniversary Workshop--R. L. Brown Arecibo Interferometer: Discovery Science, the Transient Radio Sky (2) Interferometric Search Techniques: Use the ALFA front end on the Arecibo telescope, 7 spatial beams, 2 polarizations per beam Correlate each of the 7 ALFA beams with (4) remote antennas leading to good signal discrimination –RFI at the site of either ALFA or the remote antennas will not correlate; –The same source of (distant) RFI seen at both telescopes (e.g the SJU radar) will not correlate (time, delay, directionality is incommensurate); –Artificial, sky-based RFI (satellite, airplane) signals will correlate but will move (rapid phase changes, beam-to-beam)
Arecibo 40th Anniversary Workshop--R. L. Brown Arecibo Interferometer: Discovery Science, the Transient Radio Sky (3) Use 28 (x2) sensitive interferometers to identify and locate cosmic sources of transient radio emission. Remote#1-A1Remote#2-A1Remote#3-A1Remote#4-A1 Remote#1-A2Remote#2-A2Remote#3-A2Remote#4-A2 Remote#1-A3Remote#2-A3Remote#3-A3Remote#4-A3 Remote#1-A4Remote#2-A4Remote#3-A4Remote#4-A4 Remote#1-A5Remote#2-A5Remote#3-A5Remote#4-A5 Remote#1-A6Remote#2-A6Remote#3-A6Remote#4-A6 Remote#1-A7Remote#2-A7Remote#3-A7Remote#4-A7 All interferometers dual polarization (RR, LL) [Red color coding shows a ‘real’ detection; green shows no correlation]
Arecibo 40th Anniversary Workshop--R. L. Brown Arecibo Interferometer: Educational Outreach in Partnership with the University of Puerto Rico University Partnerships: Design remote antennas by means of a funded competition among interested university groups (astronomy, engineering)—NAIC seeking innovative solutions leading to inexpensive apertures that have limited sky coverage, total surface rms 1.5 mm or better (equal to or better than the AO telescope) and are suited to a tropical environment. Competitive design/fabricate correlator procurement among university and/or observatory groups. Locate the remote antennas on University of Puerto Rico campuses (Rio Piedras, Arecibo, Mayaguez, Ponce); use as stand-alone instructional array when not being correlated with the Arecibo telescope.
Arecibo 40th Anniversary Workshop--R. L. Brown UPR-Ponce UPR-Rio Piedres UPR-Arecibo UPR-Mayaguez Arecibo Observatory