lasa and the wfbt: two concepts for all-sky transient ... · taking full advantage of...
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LASA and the WFBT: Two Concepts for All-Sky Transient Telescopes
Ryan LynchGreen Bank Observatory
On Behalf of Duncan Lorimer, Maura McLaughlin, Kevin Bandura (WVU) and Steve
Ellingson (Virginia Tech)
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CommensalSciencePartners
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▸ Taking full advantage of multi-messenger (MM) astronomy requires 24/7 full-sky coverage
▸ FRBs offer a rich MM discovery space for wide-field telescopes
▸ LASA and the WFBT are cost-effective concepts for all-sky telescopes with commensal science opportunities
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▸ Taking full advantage of multi-messenger (MM) astronomy requires 24/7 full-sky coverage
▸ FRBs offer a rich MM discovery space for wide-field telescopes
▸ LASA and the WFBT are cost-effective concepts for all-sky telescopes with commensal science opportunities
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Abbott et al. 2017, ApJ, 848, 13
Mooley et al., 2018, Nature, 554, 207
Arcavi, 2018, ApJL, 855, 223
Pooley et al,, 2018ApJ, 859, 23
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70 EM + 3 GW observatories> 450 publications
LIGO-Virgo
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LIGO-Virgo
▸ Both GW and EM observatories needed for precise localization
▸ 24/7 all-sky coverage and rapid data sharing and response time were essential
Andersson, 2013, CQG, 30, 193002
LIGO
LIGO-Virgo
Global NetworkAn
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na R
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se P
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▸ Taking full advantage of multi-messenger (MM) astronomy requires 24/7 full-sky coverage
▸ FRBs offer a rich MM discovery space for wide-field telescopes
▸ LASA and the WFBT are cost-effective concepts for all-sky telescopes with commensal science opportunities
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Fast Radio Bursts
▸ Extra-galactic, ms-duration radio flashes
▸ 51 FRBs discovered to-date (http://frbcat.org)
▸ Only one FRB known to repeat▹ Only source with precision localization,
host galaxy identification
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▸ FRB 121102: only repeating FRB to-date
▸ Discovered by Arecibo PALFA survey
▸ Rules out cataclysmic source for (at least some) FRBs
▸ Complex morphology may point to plasma lensing
Spitler et al., 2016, Nature, 531, 202
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▸ Precise VLA/EVN localization▹ Host at z=0.2
▸ Bursts 100% polarized
▸ Highest Faraday RM▹ RM not constant
▸ Parallels with Galactic center magnetar?
Chatterjee et al., 2017, Nature, 541, 58
Michilli et al., 2018, Nature, 553, 182
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▸ Physical source of FRBs remains mysterious▹ Building evidence for a connection to
young, energetic compact objects...but no smoking gun
▸ Cannot rule out multiple populations
▸ Still a relatively small population, but this is changing….
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▸ Discovery rate is increasing rapidly▹ Need T x Ω
▸ Telescopes like ASKAP, CHIME, DSA-2000 are poised to discover and localize 100s-1000s of FRBs
Data from frbcat.orgArrival time (not discovery date)
▸ Prediction: in the next decade we will know population statistics and start using FRBs for cosmology
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▸ CHIME FoV ~ 150 deg2 @ 600 MHz
▸ ASKAP FoV ~ 30 deg2 @ 1.4 GHz
▹ Fly’s-eye mode leads to increases of several
▹ Already found 23 FRBs
▸ But neither offers all-sky coverage
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▸ 24/7 all-sky telescope network needed to maximize MM astronomy with FRBs
▸ Will need to be…▹ Globally distributed▹ Easily to deploy / maintain▹ Cost-effective at scale▹ Ideally homogeneous
▸ Cast a shallow but wide net▹ Catch brightest (closest) sources for
detailed follow-up
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▸ Taking full advantage of multi-messenger (MM) astronomy requires 24/7 full-sky coverage
▸ FRBs offer a rich MM discovery space for wide-field telescopes
▸ LASA and the WFBT are cost-effective concepts for all-sky telescopes with commensal science opportunities
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L-Band Array of Small Arrays
▸ Array of tiles, each with 256 dipoles▹ Each tile can form 16 beams pointable w/in 30
deg of zenith
▹ Each beam covers ~30 deg2 @ 1.45 GHz
▸ 100 MHz band tunable w/in 1.2 – 1.7 GHz
▸ Up to 10 tiles chained to form “supertiles”▹ Supertiles spaced over several km for
localization
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▸ Dipoles grouped into “quads”▹ Output of each
quad summed before beamforming
▹ Significant cost savings
▸ 10 tiles per supertile
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▸ Backend consists of beamformer and search-engine
▸ Down-converted and sampled 12-bit @ 250 Msps
▸ GPS-disciplined chip-scale atomic clock for time an frequency standard
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▸ LASA-30 would consist of 3 supertiles
▸ Spaced over 3-4 km▹ ~0.2 arcmin
localization
▸ Expect several FRBs per month
▸ Additional tiles can be added to increase sensitivity or more stations for sky-coverage
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▸ Backend spectrometer and search-engine based on GBTrans▹ Successfully deployed on GBO 20-m
telescope
▸ Real-time dedispersion and transient search on compute nodes
▸ Would also include pulsar observing modes
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Wide Field Burst Telescope
▸ 64-element quad-ridge horn array▹ Sparser packing, fewer elements than EMBRACE
▹ 64 beams per station covering ~300 deg2 @ 1 GHz
▸ 0.4 – 1.2 GHz
▸ Dual polarization
▸ Arcsecond localization by correlating stations
▸ ~few FRBs/month expected with first phase prototype
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▸ 8-m x 8-m stations
▸ Room-temp LNAs▹ Proto-type based
non Minicircuits SAV-541 transistor has been tested
▸ RFOF to electronics rooms▹ Based on CHIME
technology
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▸ Correlator based on ICE-system design▹ Already tested as part of CHIME
▸ 8-bit @ 1.25 Gsps ADCs
▸ 16 compute nodes for correlation, beamforming, averaging, and real-time searching
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▸ ICE enables large array of interconnected FPGAs for signal processing/networking▹ Built around custom motherboard and backplane
connecting 16 FPGAs per crate▹ Each motherboard connects to 2 FMC daughter boards
for specific applications▹ Custom software for automatic configuration, M&C
▸ Single low-noise clock and absolute time tagging
▸ Easily adaptable for VLBI
▸ Highly scalable and cost effective
▸ Robust, easy to maintain
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▸ Complex voltage for 1024 channels sent through corner-turn to 16 compute nodes▹ 625 Gpbs total data rate
▸ GPU-cluster will act as X-engine and perform real-time transient search using “Bonsai” code-base used in CHIME
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▸ WFBT designed to be scalable▹ More horns → higher sensitivity▹ More baselines → better localization,
cleaner beam▹ More stations → cover more sky
▸ Currently seeking funding for prototype to be deployed at Green Bank Observatory
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▸ FRB pipelines designed for broad-band, dispersed, impulsive signals▹ Repeating FRB demonstrating need for searches
of band-limited signals (see Zhang et al., 2018, arXiv:1809.03043)
▸ Parallel pipelines could be implemented for different signal types / commensal science▹ e.g. SETI, monitoring ISM effects in bright MSPs
(important for GW detection using pulsars)
Commensal Science
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▸ Taking full advantage of multi-messenger (MM) astronomy requires 24/7 full-sky coverage
▸ FRBs offer a rich MM discovery space for wide-field telescopes
▸ LASA and the WFBT are cost-effective concepts for all-sky telescopes with commensal science opportunities
Thanks!