1. Scalable cm-Wavelength Aperture Arrays
Steve Ellingson, Virginia Tech
Dunc Lorimer, West Virginia Univ.
U.S. Radio/Millimeter/Submillimeter Science Futures II
Baltimore MD
Aug 4, 2016

2. Instrument & Science Fast radio bursts (FRBs) Pulsars
Localization & survey
Monitor for repeating FRBs
Learn how to exploit FRBs as probes of the IGM
Pulsars
Spin-down monitoring
Giant pulses
Other science in which time on sky is more useful than sensitivity
Small L-band aperture arrays (“tiles”)
Lots of wide beams
Long baselines  Localization
Initially small collecting area, but scalable
U.S. Radio/Millimeter/Submillimeter Science Futures II, Baltimore, MD, Aug 4, 2016

3. Fast Radio Bursts (FRBs) – 1-Slide Primer
Brief (~ms), dispersed (probably extragalactic), bright (~Jy) in L-band
17+ detected by 3+ instruments
~4400/sky/day
Could be: Compact object mergers, anomalous NS behaviors, Cosmic strings, …
But one (so far) repeats
U.S. Radio/Millimeter/Submillimeter Science Futures II, Baltimore, MD, Aug 4, 2016

4. Fast Radio Bursts (FRBs) – Science & Requirements
Localization
Need < 2’’ for confidence in an association at z=1
Need more (1000s)
Understand the population(s)
Find the anomalous cases
Find repeating FRBs
Need multiwavelength detections
Co-observe with instruments in other wavebands
To-Do List
Interferometry
GHz
Instrument Requirements
The Science
What are they?
Guaranteed to be interesting
Applications: Probe the IGM
Baryon consensus
Cosmic magnetism
Photon mass constraints
Very high duty cycle (time on sky)
Need to steer
(purely commensal
mode not OK)
Then maximize sensitivity
U.S. Radio/Millimeter/Submillimeter Science Futures II, Baltimore, MD, Aug 4, 2016

5. Taking Stock of Existing Instruments
Suggests:
O(10 m) apertures
Lots of beams
Spread out over 10s of km for localization
Incoherently combined to maintain FOV
Then lots of them, for sensitivity
Given plausible Tsys & BW specs, productive searching is possible with just a few such apertures  scalability 4'
7 beams 7º
1 beam
14'
13 beams
~2-50''
~0.5-16' LAS
Productive
Searching
Typical FRB flux, Typical Tsys & BW, Increasing dish size
U.S. Radio/Millimeter/Submillimeter Science Futures II, Baltimore, MD, Aug 4, 2016

6. Large Array of Small Arrays (LASA) – “Tile”
Conservative Specs:
MHz tuning range
Ae ~ 3 m2
TR ~ 70 K (Tsys < 100 K)
16 dual-pol beams (8, 32)
FWHM 6.3° (1.45 GHz, zenith)
Z < 30° (> 30° with degradation)
100 MHz BW (50, 200 MHz)
US$50K
1700 W
U.S. Radio/Millimeter/Submillimeter Science Futures II, Baltimore, MD, Aug 4, 2016

7. LASA – System Equiv. dish: 3-m 9-m 34-m x 16 (eap=0.5, Tsys=30 K)
# tiles 3 32
512
Ae/Tsys [m2/K]
0.09
0.96
15.36
POP Cost [USD]
200K 2M
30M
Long Baselines
Equiv. dish: m m m x 16 (eap=0.5, Tsys=30 K)
U.S. Radio/Millimeter/Submillimeter Science Futures II, Baltimore, MD, Aug 4, 2016

8. Performance of Relative Performance for FRB Survey CHIME: UTMOST:
LASA-512, 32 beams beams
CHIME:
MHz
14’ (no loco.)
UTMOST:
843 MHz
20’’ (coarse loco.)
VLA (Realfast)
L-Band
< 2” in A config
Low availability
Low time resolution (5 ms)
AO, GBT, Parkes
All: Respect!
LASA-512, 8 beams
LASA-32, 32 beams
LASA-32, 8 beams
LASA-3, 32 beams
Parkes (100% duty cycle)
LASA-3, 8 beams
VLA (Realfast) (100% duty cycle)
actual duty cycle)
U.S. Radio/Millimeter/Submillimeter Science Futures II, Baltimore, MD, Aug 4, 2016

9. 16 Beams that Don’t Have to be Pointed in any Particular Direction … What Else Can Be Done?
Transient science that can’t be done by any other instrument
Monitor coordinates of all known FRBs to check for repeaters
Follow instruments in same and other bands … co-detections
Triggering by other instruments – phased arrays can be repointed quickly
Generally: Projects in which time on sky is more useful than maximizing sensitivity
Giant pulse surveys – productive even with LASA-3
Monitor spin-down of normal bright pulsars: Better understanding of timing noise processes – productive even with LASA-3
SETI
Your project here?
U.S. Radio/Millimeter/Submillimeter Science Futures II, Baltimore, MD, Aug 4, 2016

10. Concluding Remarks
LASA-3, 16 beams, ~US$1M yields a productive FRB instrument + other interesting science
LASA-32, 16 beams, ~US$3M yields a front-line FRB instrument + other interesting science
No “technology development” (only “design”) required - not even the antenna array (tile)
Wait a minute… isn’t this SKA2 AA-MID?
NO. Very modest requirements  Much smaller, simpler instrument
BUT: Definitely potential two-way synergy that would be useful to pursue
Effort underway to get this started; inquiries & collaborators welcome!
U.S. Radio/Millimeter/Submillimeter Science Futures II, Baltimore, MD, Aug 4, 2016