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The  Ecosystem  of  Radio  Observatories

Dale  A.  FrailNRAO

Special  thanks  to…• Tony  Readhead and    Sterl Phinney• Bronagh Glaser• Vikram Ravi• Radio  pioneers  (Clark,  Cohen  &  Wienreb)  

Credit:  D.  Medlin/NRAO/AUI/NSF

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B&E  Speaker  Demographics• PhD  Students   =  3:  – Carbone,  Alexander,  Zackay

• Postdocs   =  6:– Ravi,  Akiyama,  Mooley,  Price,  Duev,  Vedantham

• Early  Career  =  11:– Law,  Vanderlinde,  van  Leeuwen,  Bannister,  Akahori,  Ofek,  Wen,  Corsi,  Hallinan,  Hessles,  Fujisawa  

• Mid  Career  =  7:– Bailes,  Kramer,  Croft,  Sivakoff,  Myers,  Groot,  Frail

• Late  Career  =  5:– Cordes,  Sunyaev,  Kawai,  Werthimer,  Cohen  

Transient  Topics  for  Discussion

• The  Cambrian-­‐like  explosion  in  radio  astronomy• Near  term  opportunities   in  radio  transients• What  is  special  about  radio  transient  studies?

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Pre-­‐Cambrian  and  Cambrian  Eras

HERA

Meters Centimeters Millimeters

MWA

LWA

SKA1-Low

HIRAX

OotyOVRO-LWA

21CM

UTMOST

EDGES

LEDA

MWA

CHIME

ASKAPVLBA

Bonn

Arecibo

VLBA

MeerKAT EVN

eMERLIN

GBT LovellSKA1-mid FAST

ngVLA

ApertifParkes

AMI

HSA

KVN

ATCA Shanghai

NancaySardinia QTT

NOEMA IRAM 30-mLMT APEX

Mopra EHTGLTASTE

Green = future telescope

Historical  Digression• In  addition   to  the  standard  quest  for  increased  sensitivity,   there  has  also  been  a  steady  march  away  from  MHz  to  GHz  to  THz.  Why?– Partially  science  but  also  a  quest  for  increased  positional  accuracy  and  to  escape  confusion

– Difficulties  with  calibrating  and  imaging  these  full  fields  at  low  frequencies

• With  few  exceptions  we  tend  to  run  faculties  and  not  experiments

• It  all  changed  starting  about  a  decade  ago– Proliferation   of  facilities   small  and  large  and  at  all  frequencies– Biodiversity   reigns!  Many  ecological  niches   are  filled

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V-­‐LITELOFAR

LWA1

LWA-­‐OVRO

MWA

V-­‐LITE

MWA

Radio  Joins  the  Synoptic  RevolutionMeerKATASKAP

• Large investments in SKA-prototypes• Focal-plane array technology to give

FoV 8 deg2 for WSRT/Apertif and 30 deg2 for ASKAP.

• LNSD design for MeerKAT• Optimized for 1.4 GHz • Time domain is Key Science programWSRT/Apertif

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OVRO-­‐LWA  Long  Baseline  Project  2015Courtesy  Gregg  Hallinan

Fruit  Picking  for  Graduate  Students

• Fast  Radio  Bursts  (FRBs)• Propagation  phenomena   (ESEs  and  IDVs)• GW  EM  counterparts• The  GHz  radio  sky• The  MHz  radio  sky

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The  Fox  versus  The  Lemmings

Fast  Radio  Bursts• Event  rates  (Lemmings)

– UTMOST,  HIRAX,  CHIME,  P-­‐ALPHA,  Bonn  PAF– DM,  RM  and  SM  continue   to  lead  to  insight  and  puzzles  (ΔRM=0?)– Is  there  a  discrepancy  in  the  rates?– Why  do  the  smaller  telescopes   detect  more  events  than  larger?– What  is  role  of  ISS  on  rates,  detectability   and  spectra?– High  frequency  (>1.4  GHz)  is  new  frontier– If  GRBs  are  a  guide,  we  learn  more  from  one  bright  event  than  10  

weak  events

• Positions  (Foxes)– N-­‐UTMOST  (Deller),   RealFAST (Law),  DSA-­‐10  (Kulkarni)– One  well  localized  event  will  be  a  game-­‐changer– Need  some  faster  imaging  algorithms

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Propagation  Phenomena• Extreme  scattering  events  (ESEs)

– One  over-­‐worked  fox  (Bannister)– New  phenomenology?

• High  space  density  of  lensing  sources• Pressure  is  102 to  104 of  ISM

– No  reddening  in  optical  seen  to  date– More  events  with  RM  measurements  and  high  cadence  VLBI

• Intra-­‐day  variables  (IDVs)– Barely  mentioned  at  this  meeting  at  all– A  30-­‐year  old  mystery  that  gets  little  attention  today– Pushes  our  understanding  of  AGN  physics  to  extremes– Read  about  it,  think  about  it  and  become  a  fox

EM  Counterparts  to  GWs• Optical  (Lemmings)– >50%  chance   to  being  first  detect  detect  EM  counterpart– Clever  fox-­‐like strategies  by  Kasliwal et  al.  to  reduce   the  area  searched  using  catalog  of  nearby  galaxies  (CLU)

• Radio  (Foxes)– Two  fundamental  approaches

• Blind   search  of  entire   error   ellipse  (Mooley)• Follow-­‐up  of  optical   candidates  (Corsi)

– False  positives.  BH-­‐BH  may  be  dominant  GW  channel• A  prompt,   coherent   signal  may  be  present  in  this  case  (Wen)• Beware  of  pixie   dust  models.  Cannot   predict   the  brightness  a  priori• If  you  own  the  telescope  this  is  not  a  problem   (LWA-­‐OVRO,  MWA,  LOFAR  AARTFAC)

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Slow  transients  in  the  GHz  radio  sky

Act  Like  A  Buccaneer:  Own  the  Follow-­‐up

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Follow-­‐up:  A  biased  but  rewarding  approach

Be  a  Cartographer:    Carry  out  a  systematic  exploration  of  the  radio  sky

From  Geoff  Bower

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Slow  transients  in  the  GHz  radio  sky

Opportunities

• All-­‐sky  radio  surveys– VAST,  VLASS,  ThunderKAT,  Apertif– Serendipity.  open  new  phase  space– Variability  (timescale,  frequency  and  galactic)

• Follow-­‐up  of  optical/X-­‐ray  surveys– ZTF.  e.g.  rare  SNe (Corsi,  Horesh)– Spektr-­‐Rentgen-­‐Gamma  e.g.  TDEs  (Alexander)

• Bring  the  optical  to  the  radio  (Groot)

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Where  are  all  the  MHz  transients?  

• Lemmings  over-­‐promised  and  under-­‐delivered• LOFAR  Transients  Key  Science  Project– Pulsars:  classical  radio  pulsars,   AXPs,   RRATs– Jet  sources:  AGN,  GRBs,  accreting  white  dwarfs,  neutron  stars  and  stellar-­‐mass  black  holes

– Flare  stars:  M,  L,  and  T  dwarfs  and  active  binaries– Planets:  solar  system  objects  and  exoplanets

Where  are  all  the  MHz  transients?  

• Mismatch  between  the  survey  cadence  and  the  evolutionary  timescales  of  the  transients– Luminous,   incoherent  events  cannot  evolve  on  arbitrary  timescales

– Results  in  oversampling.  Repeated  visits  do  not  add  any  significant  new  information

• For  fixed  time,  optimal  survey  strategy  is  wide,  and  shallow  and  with  a  cadence  matched  to  the  timescale  of  interest

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Slow  transients  in  the  MHz  radio  sky

Polisenskyet  al.  astro-­‐ph/1604.00667

Unknown  Transients:  Mystery  Flares  

• Six  12-­‐hr  epochs  toward  SWIRE  deep  fields– VLA  at  325  MHz,  6.5  deg2

– Cadence   1  d  to  3  months– One  6-­‐hr   duration  transient  

at  peak  of  2.1  mJy

• 2149  11-­‐min  snapshots  toward  the  NCP– LOFAR  at  60  MHz,  175  deg2

– One  11-­‐min   duration  transient  peaked  at  15-­‐25  Jy

Jaeger  et  al.  (201

2)Stew

art  et  al.  (201

6)

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GCRT  1745-­‐3009  (aka  The  Burper)  • A  10  year  mystery  with   little  

progress• Discovered  in  Galactic  Center  

monitoring  programs• Five  1  Jy bursts,  10  min  

duration,  every  ~70  min– 100%  polarized– Steep   spectra– No  quiescent  X-­‐ray  or  OIR  

• More  events  seen  over  years• What  is  it?

– 1  Jy in  10  min  is  the  key– D<70  pc,  Tb<1012 K  (isotropic)– D>70  pc,  Tb>1012 K  (exotic)– Kulkarni  &  Phinney (2005)  

suggest  that  it  is  a  nulling  pulsar

Hyman  et  al.  (2005)

Where  the  promise  comes  true?• Coherent   transients   appear  to  

have  no  restriction   on  the  maximum  brightness   temperature

• Timescale  is  still   important   but  for  a  different   reason

• Phase  space  is  enormous– range  of  possible  luminosities  and  

timescales  is  very  large– Cannot  predict  a  priori– “What  we  bring,  we  find.”

• Worrying  signs?– No  FRBs– No  flare  stars  (duty  cycle?)

Spangler  and

 Moffett  (1

976)

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Special  considerations?

• What  are  the  opportunities   that   I’ve  missed?• How  do  we  use  boutiques   to  get  the  best  science  returns  from  the  behemoth  surveys?

• How  do  we  better  coordinate  optical  and  X-­‐ray  follow-­‐up  efforts  with  radio?

www.nrao.eduscience.nrao.edu

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