MKSP sensitivity issues Rainer Beck

MKSP sensitivity issues Rainer Beck

LOFAR sensitivity

and MKSP Project Plan

Rainer Beck

Theoretical LOFAR HBA rms noise

LOFAR webpage: thermal noise ≈ 0.25 mJy

(mean over HBA band 120-180 MHz, 20 subbands,

effective BW 3.57 MHz, 40 Dutch stations, 1h integration time)

BW 38 MHz: thermal noise ≈ 0.08 mJy

10h integration: thermal noise ≈ 0.025 mJy

100h integration: thermal noise ≈ 0.008 mJy

Expected intensities of galaxies

150 MHz, 10" beam:

• Inner disk (Stokes I): ≈ 1 mJy/beam

5σ detection needs 0.2 h (thermal noise)

• Inner disk (Stokes Q+U): ≤ 0.1 mJy/beam (p ≤ 10%)

5σ detection needs ≥ 16 h (thermal noise)

• Outer disk (Stokes I): ≈ 0.1 mJy/beam

5σ detection needs 16 h (thermal noise)

• Outer disk (Stokes Q+U): ≤ 0.03 mJy/beam (p ≤ 30%)

5σ detection needs ≥ 180 h (thermal noise)

• RM grid of polarized background sources:

high S/N and large BW needed, but flux densities unknown

Increased noise due to dipole projection

(using Tobia’s estimate):

Restrict to DEC=+40° - 70° ?

James Anderson, priv. comm.

Polarized source counts at 1.4 GHz (VLA):

lower than expected?

Larry Rudnick, priv. comm.

Faraday depolarization within the sources?

Arshakian & Beck 2011

MKSP "Reserved Access" proposal: Surveys

Survey KSP "Reserved Access" proposal

MKSP "Reserved Access" proposal: Target list

SKSP proposal plan for Semester 1 ("Tier 0")

Realistic rms noise

• Present imaging results: rms 10x higher than thermal

→ 100x higher integration times needed

(IF noise decreases with 1/√t )

→ no chance to reach the goals of the MKSP

• Improved imaging results: rms 3x higher than thermal

→ 10x higher integration times needed

(IF noise decreases with 1/√t )

→ goals of the MKSP can be partly reached

(smoothing to larger beam?)

Revised MKSP Project Plan for galaxies

• Tier 0 survey (Semester 1):

- Are we ready/willing to invest our reserved time

from the national budgets?

- If yes, how many – how many teams are available?

• Tier 1 all-sky shallow survey (Semester 2, 2013?):

- Extract total intensity maps and spectra,

test RM Synthesis on few selected galaxies

- But what if the time estimate or the processing requirements

turn out to be unrealistic?

• Tier 2 deep survey (2014):

- Restrict on less galaxies at high declinations?

- Diffuse polarisation: hard to detect because the sources

are too broad in Faraday space (Faraday-thick)?

- RM Grid: source density smaller than expected?

- High-resolution images (and hence intensive processing) needed

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