Observing Cosmic Dawn with the LWA-1 PIs: Judd Bowman (ASU), Greg Taylor (UNM) Jake Hartman (JPL) Jayce Dowell, Joe Craig (UNM) Steve Ellingson (Virginia Tech) Jackie Monkiewicz Arizona State University

The “Dark Ages” and Cosmic Dawn 2/20 Dark Ages: z = 1,100 to z~ 40 matter-dominated H & He are neutral 1st structures collapsing Cosmic Dawn: z = st stars & galaxies 1st QSOs? Early heating, reionization of small bubbles

Cosmic Dawn project purpose: 3/20 Detect/constrain signal of 1st generation of stars in 21-cm absorption of hydrogen at z ~ 30 REQUIRES: 1.Low frequency experiment, MHz LWA-1 2.Long Integration time 3.Very accurate bandpass calibration 4. Novel beamforming techniques

Cosmic Dawn in 21 cm: (Furlanetto 2006, Pritchard & Loeb 2010) 4/20  T b = T s – T cmb Seen against CMB: Thermal History of IGM

Cosmic Dawn in 21 cm: 1 st stars create absorption trough Additional heating sources mitigate trough (Furlanetto 2006, Pritchard & Loeb 2010) 5  T b = T s - T cmb

Observing strategy: REQUIREMENTS: Very good bandpass calibration! Looking for broad, shallow absorption trough need > 10 4 S/N in any spectral channel But only need ~10% accuracy in absolute power… 6/20 A E D B C ν (MHz) Δ T 21 (mK) −50 −100 (Pritchard & Loeb 2010)

Observing strategy: STRATEGY: Simultaneously observe bright calibrators & dark (low T sys ) science field 2 x 19.6 MHz beams on bright calibrator 2 x 19.6 MHz beams on science field 520 hours on-sky 6/20

Observing Strategy -- COMPLICATION: Frequency variation of beam shape couples of foreground structure to sidelobes mistake sources drifting through sidelobes for 21-cm spectral features? 8/ −15−10− Offset (degrees) Relative gain 74 MHz 38 MHz

Novel Beamforming Strategies: Mitigate potential foreground-frequency coupling of sidelobes: 9/20 1. Defocusing (e.g. gaussian smoothing) 2. Sidelobe steering 3. Nulling 4. Sidelobe shimmering 5. “Optimized” beam-forming (account for mutual coupling of antennas)

Work to date: 10/20 Learning the LWA Software Library! (and PYTHON in general) Phase-and-Sum Beamforming with TBN Raster Mapping of TBN Beam (pseudo-beams)

Phase-and-Sum Beamforming: 11/20 TBN data: narrow bandwidth ( < 100 kHz) Commissioning scripts for TBN (J.Dowell): (follows “Fun with TBN” memo, S. Ellingson) 1. Fringe all antenna outlier stand #258 (simpleFringe.py ) 2.Fringe stop on bright source --- Cyg A or flaring Sun back out delay coefficients (solveCoeffs.py) 3.Use array geometry to point beam (formBeam.py)

Phase-and-Sum Beamforming: 12/20 Find bursting Sun produces much better coefficients than Cyg A --- not surprising?

Raster Mapping: 13/20 Use bright source in TBN data to map structure of sidelobes --- “Pseudo-beam”

Raster Mapping – Variation with elevation 14/20 Cyg A: Transit EL = 83 deg -1 hour EL = 76 deg -2 hours EL = 65 deg

15/20 Cas Cyg A transit EL = 46 deg -2 hours before Cyg A transit EL = 34 Cyg A transit EL = 34 deg … What is going on in the North/Northeast during the Cyg A transit on Sept 21, 2011??

16 PASI started recording Sept 23, 2011:

Pseudo-beam Maps over full frequency range: 17/20 Acquired TBN observations of 4 frequency groups: 87 MHz 80 MHz 73 MHz 71 MHz 64 MHz 57 MHz …corresponding to 4 DRX tunings for main Cosmic Dawn observations 55 MHz 48 MHz 41 MHz 39 MHz 32 MHz 25 MHz Beam 1 Tuning 1 Beam 1 Tuning 2 Beam 2 Tuning 1 Beam 2 Tuning 2

Test our Beamforming Strategies: 18/17 1. Defocusing (e.g. gaussian smoothing) 2. Sidelobe steering 3. Nulling 4. Sidelobe shimmering 5. “Optimized” beam-forming (account for mutual coupling of antennas) Which is the “quickest and dirtiest”?

Test our Beamforming Strategies: 19/17 1. Defocusing (e.g. gaussian smoothing) 2. Sidelobe steering 3. Nulling 4. Sidelobe shimmering 5. “Optimized” beam-forming (account for mutual coupling of antennas) Which is the “quickest and dirtiest”?

Pseudo-beam Maps over full frequency range: 20/20 Apply some of our novel beam-forming strategies Defocusing is simplest, fastest  apply Gaussian to antenna gains  \ Acquire raster maps of customized DRX beams, compare with TBN predictions, confirm shape

LWA-OCD Project Outputs: 21/20 Beamforming: Detailed measurements of beam Strategies for custom beamforming Deep integrations: Very high S/N spectra of bright calibrators Very high S/N spectra of diffuse Galaxy (including high-level H recombination lines) Serendipitous radio transients Lots of opportunity for RFI mitigation! Detection/contraints on First Light absorption trough. END

RFI environment at LWA: 22

The “Dark Ages” and Cosmic Dawn 23/17 z = redshift (decreases with increasing time) z = ∞ z = 0

The “Dark Ages” and Cosmic Dawn 24/17

Wouthuysen-Field Effect: 25

Phase-and-sum Beamforming: 26/17 Use bright source to back out coefficients Only works for narrow (< 10 KHz bandwidth) insensitive to 2  offsets Delay-and-sum Beamforming: Do phase-and-sum over full LWA frequency range Solve for true delays for each antenna

System noise for LWA: 27 From Pihlstrom, 2012, internal memo

Acronyms: 28