COMMENTARY ON TIANLAI JANUARY 2018 DISH OBSERVATIONS OF THE NORTH - - PowerPoint PPT Presentation

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COMMENTARY ON TIANLAI JANUARY 2018 DISH OBSERVATIONS OF THE NORTH CELESTIAL POLE longest continuous run to date ~10 days using pipeline calibrated data / no RFI removal Tianlai Collaboration Meeting 2018 Albert Stebbins Pingtang County,

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SLIDE 1

COMMENTARY ON TIANLAI JANUARY 2018 DISH OBSERVATIONS OF THE NORTH CELESTIAL POLE

longest continuous run to date ~10 days using pipeline calibrated data / no RFI removal

Albert Stebbins Fermilab Theoretical Astrophysics Tianlai Collaboration Meeting 2018 Pingtang County, Guizhou Province, China 19 September 2018

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SLIDE 2

BY POINTING DISH ARRAY TOWARD POLE WILL INTEGRATE DOWN TO LOW MAP NOISE TEMPERATURE VERY RAPIDLY SINCE ONE IS ALWAYS POINTING AT SAME SPOT ON SKY.

  • 90
  • 60
  • 30

30 60 90 50 100 200 500 pointing declination (°) raw δTvoxel (µk) dish array in week for (100 Mpc)3 voxel Δz = 0.01 Δν = 4 MHz

TIANLAI DISH “POLARSCOPE”

TIANLAI HIGHLY CONFIGURABLE!

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SLIDE 3

January 2018 Dish Data

  • This is the longest run to date ~10 days.
  • Analysis starts with Timestream data calibrated by Cas A observation at the

beginning of run generated by John Marriner.

  • No RFI removal was applied.
  • There were a few iterations of rawTimestream → Timestream as we learned

about how to use the pipeline.

  • Further analysis was done using Mathematica code.
  • There are apparently some bugs still left (possibly in Mathematica code).
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SLIDE 4

example of one “good” visibility V3x31. this is raw correlator data 11 sidereal days top to bottom

2018-01-02 02:44:15 to 2018-01-11 20:44:12

brightness gives |V3x31| color gives complex phase bright swath are fringes of the Sun

fringes vary because Earth rotates bow occurs when Sun passes “above” baseline direction Sun dominant source even 110° off axis

dimmer fringes still visible at night

sidereal time ⇒ frequency ⇒

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SLIDE 5

nighttime only view of V3x31

nighttime mean subtracted for each frequency image intensified to show nighttime fringes

visibilities repeat with sidereal day period

signal from the sky

fringe pattern more complicated than bow

indicating multiple bright sources in 2° beam centered on North Celestial Pole

bright and dark patches

constructive/destructive interference between sources

good S/N in 1min x1MHz pixels rapid frequency fringe rate

N-S baseline: large ν-dependent phase difference

variable temporal fringe rate

caused by Earth rotation - sources at different declinations

sidereal time ⇒ frequency ⇒

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SLIDE 6

John Marriner w/ others worked past few weeks on understanding how to use python pipeline - applying it to this run. Apparently there are still some misunderstandings leading to large mis-calibrations.

Good and Bad Baselines

worst best

1min × 244kHz pixels

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SLIDE 7

sidereal time ⇒ frequency ⇒

WORST

sidereal time ⇒ frequency ⇒

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SLIDE 8

“Good” Median Nightly Averages

have good measure of visibilities from foreground sources

ribbon candy

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SLIDE 9

looking for non-smooth spectrum components

Cone of Silence Foreground Wedge

Due to chromaticity of beams non-smooth angular structure

  • f sources will leak into frequency structure (mode mixing)

filling the foreground wedge. Ideally the cone of silence, the complement of the wedge, is not contaminated by smooth spectrum sources, however there is no well defined boundary so one must determine the leakage of smooth spectrum sources into all parts of k-space. Discover the Hilbert subspace of the “space of beams” with little contamination.

Hi- k|| Analysis

To search for non-smooth spectrum emission one might initially look as far away from the foreground wedge as possible, e.g. large k|| for individual visibilities. This requires no knowledge of the beam,

  • nly that | k|| |≫| k⟂|.

At present 21cm intensity mapping experiments suffer from non-detection of 21cm emission. “Finding it” should be a high priority. We can do so by looking for non-smooth spectrum emission away from the wedge.

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SLIDE 10

Power Law Decomposition

One can expand a visibility covering a given band into Legendre polynomials (or any other polynomial expansion) the larger n is the less smooth the frequency dependence. A carefully designed discrete analog of this works better than a discrete Fourier

  • transform. The integer index n is an

analog of k||. For small bandwidth

V[ν] =

N

∑

n=0

anPn[ 2(ν − νmid) νmax − νmin ]

k|| ≈ 2π ΔRco (n + 1)

  • 80db numerical floor
  • 70db numerical floor
  • 75db numerical floor
  • 70db numerical floor

Numerical Tests on Sinusoids+

much spill-back, rapid fall-off, little spill-forward

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SLIDE 11

Are Good Tianlai Visibilities Smooth Spectrum?

noise floor

60sec × 244kHz pixels 1 5 10 50 100 500 0.1 0.2 0.5 1 0.01 0.1 1 1 + polynomial order mode amplitude (Kelvin [nominal]) pseudo k∥ (Mpc-1)

1 nights 3 nights 11 nights rms = 5.44 K, 4.64 K, 4.34 K

3 12 EAST WEST NORTH SOUTH

60sec × 244kHz pixels 1 5 10 50 100 500 0.1 0.2 0.5 1 0.01 0.1 1 1 + polynomial order mode amplitude (Kelvin [nominal]) pseudo k∥ (Mpc-1)

1 nights 3 nights 11 nights rms = 5.29 K, 4.55 K, 4.1 K

3 31 EAST WEST NORTH SOUTH

60sec × 244kHz pixels 1 5 10 50 100 500 0.1 0.2 0.5 1 2 0.01 0.1 1 1 + polynomial order mode amplitude (Kelvin [nominal]) pseudo k∥ (Mpc-1)

1 nights 3 nights 11 nights rms = 6.55 K, 5.75 K, 5.53 K

5 25 EAST WEST NORTH SOUTH

60sec × 244kHz pixels 1 5 10 50 100 500 0.1 0.5 1 0.01 0.1 1 1 + polynomial order mode amplitude (Kelvin [nominal]) pseudo k∥ (Mpc-1)

1 nights 3 nights 11 nights rms = 5.59 K, 4.93 K, 4.55 K

7 29 EAST WEST NORTH SOUTH

60sec × 244kHz pixels 1 5 10 50 100 500 0.1 0.2 0.5 1 2 0.01 0.1 1 1 + polynomial order mode amplitude (Kelvin [nominal]) pseudo k∥ (Mpc-1)

1 nights 3 nights 11 nights rms = 5.65 K, 4.88 K, 4.54 K

9 17 EAST WEST NORTH SOUTH

60sec × 244kHz pixels 1 5 10 50 100 500 0.1 0.2 0.5 1 2 0.01 0.1 1 1 + polynomial order mode amplitude (Kelvin [nominal]) pseudo k∥ (Mpc-1)

1 nights 3 nights 11 nights rms = 6.34 K, 5.72 K, 5.31 K

9 22 EAST WEST NORTH SOUTH

noise floor noise floor noise floor noise floor noise floor noise floor

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SLIDE 12

Power Distribution 03x31

←pseudo-m→ n→

log of power in 1min × 244kHz pixels pseudo-m because not full sidereal day m=+471 m=-470 m=0 n=0 n=472

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SLIDE 13

Noteworthy Conclusions

  • for n>50 the visibilities do indeed seem to decrease in amplitude like the

inverse of the square root of integration time - and can be thought of as system noise.

  • in the n-m representation of the data space nearly all of the area appears

to be uniform white noise - totally untainted by the foregrounds - this includes a lot of regions where 21cm lives.

  • If n-expansion works as well for removing Sun as for polar foregrounds
  • ne could use both nighttime and daytime data.
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SLIDE 14

Things to do

  • find remaining bugs in implementation of pipeline and reprocess January data
  • this may bring many more baselines into the “good” category
  • estimate effective noise temperature from hi-k|| white noise region (!)
  • check whether hi-k|| analysis effective in removing the Sun
  • if so obtain full day maps of white noise region and proceed with true m-mode analysis.
  • fit to NVSS catalog and see if it make any sense
  • process/calibrate older NCP dish runs and combine all together
  • this could more than double the total integration time
  • predict how much more NCP integration time expected to reach 21cm floor
  • request additional NCP runs as needed
  • see if we find a different floor (systematics? other contamination?) en route to 21cm floor