Title The populations of relativistic particles and magnetic field structure in the Crab Nebula and other plerions Pi R. Bandiera Time 229 hrs 1. Name of program and authors Name: The populations of relativistic particles and magnetic field structure in the Crab Nebula and other plerions. Authors: R. Bandiera, R. Cesaroni, L. Testi 2. One short paragraph with science goal(s) Map at high angular resolution and sensitivity the polarized continuum emission at 1.3 and 3mm of the Crab nebula and other plerions. Recent single dish 1.3mm observations of the Crab nebula at ~10 arcsec resolution have shown evidence for: 1. a second synchrotron component in the continumm emission whose presence challenges the existing models; 2. smaller-scale spatial variations of the radio-mm spectral index across the nebula that may be an indication of filaments of stronger magnetic field (Bandiera et al. 2002). The single dish observations do not have the spatial resolution and polarimetric capabilities needed to confirm these indications. Equally important would be the possibility of a careful measurement of the variation of the spectral index across the nebula in the mm range (at nu<250GHz in order to measure the synchrotron emission and not the dust). ALMA will offer the required sensitivity, spatial resolution and calibration accuracy needed to perform a detailed study of the Crab and of other plerions, which may show similar features. Beyond the Crab nebula, plerions with a synchrotron spectral break around 100 GHz have been selected, since they are more likely to show morphological differences between the mm and the radio range, which could be used a diagnostic tool for the nebular physical conditions. Need to: Map the SNRs (size ~7' Crab, ~1' the others) at: <=0.5 arcsec resolution and rms~0.03 mJy/beam, for the Crab (scaling Bandiera et al. 2002 numbers); <=0.2 arcsec and 0.01 mJy/beam for the others. Polarization maps. 3. Number of sources 3 Source Name R.A.(1950) Dec.(1950) Crab Neb. 05:31:30.0 +21:59:00 (pure plerion, size 7'x5') G0.9+0.1 17:44:12.0 -28:08:00 (composite. plerionic core of 2' diam.) G21.5-0.9 18:30:47:0 -10:36:30 (pure plerion, of 1.2' diam.) 4. Coordinates: 4.1. Rough RA and DEC Source Name R.A.(1950) Dec.(1950) Crab Neb. 05:31:30.0 +21:59:00 (pure plerion, size 7'x5') G0.9+0.1 17:44:12.0 -28:08:00 (composite. plerionic core of 2' diam.) G21.5-0.9 18:30:47:0 -10:36:30 (pure plerion, of 1.2' diam.) 4.2. Moving target: no 4.3. Time critical: no 4.4. Scheduling constraints: no 5. Spatial scales: 5.1. Angular resolution (arcsec): ~0.5 arcsec Crab, ~0.2 arcsec the others 5.2. Range of spatial scales/FOV (arcsec): up to 7 arcmin (Crab); up to 1.2 arcmin (G21.5-0.9); up to 2 arcmin (G0.9+0.1) 5.3. Required pointing accuracy: 0.05 PrimaryBeam 6. Observational setup 6.1. Single dish total power data: required Observing modes for single dish total power: on-the-fly mapping 6.2. Stand-alone ACA: required 6.3. Cross-correlation of 7m ACA and 12m baseline-ALMA antennas: beneficial (mainly for cross-calibration and accuracy) 6.4. Subarrays of 12m baseline-ALMA antennas: no 7. Frequencies: 7.1. Receiver band: Band 3, 6 7.2. Lines and Frequencies (GHz): N/A (approximate; do _not_ go into detail of correlator set-up but indicate whether multi-line or single line; apply redshift correction yourself; for multi-line observations in a single band requiring different frequency settings, indicate e.g. "3 frequency settings in Band 7" without specifying each frequency (or give dummies: 340., 350., 360. GHz). For projects of high-z sources with a range of redshifts, specify, e.g., "6 frequency settings in Band 3". Apply redshift correction yourself.) 7.3. Spectral resolution (km/s): 7.4. Bandwidth or spectral coverage (km/s or GHz): 8. Continuum flux density: 8.1. Typical value (Jy): Total Flux ~300 Jy (Crab), but low surface brightness (up to 10 mJy/beam at the required resolution) 8.2. Required continuum rms (Jy or K): 0.010-0.015 mJy/beam 0.03 mJy/beam for the Crab (Note the Crab is so large that it is very time consuming to do at 1.3mm, it should attempted only if the results of the 3mm map guarantee a good S/N with 0.03mJy/beam rms). 8.3. Dynamic range within image: <~1000 8.4. Calibration requirements: absolute ( 5% ) repeatability ( n/a ) relative ( 1-3% ) 9. Line intensity: N/A 9.1. Typical value (K or Jy): (take average value of set of objects) (optional: provide range of values for set of objects) 9.2. Required rms per channel (K or Jy): 9.3. Spectral dynamic range: 9.4. Calibration requirements: absolute ( 1-3% / 5% / 10% / n/a ) repeatability ( 1-3% / 5% / 10% / n/a ) relative ( 1-3% / 5% / 10% / n/a ) 10. Polarization: yes 10.1. Required Stokes parameters: I, U, Q, V 10.2. Total polarized flux density (Jy): 10% of unpolarized flux 10.3. Required polarization rms and/or dynamic range: (<~1000) 0.010-0.015 mJy/beam 0.03 mJy/beam for the Crab 10.4. Polarization fidelity: ? 10.5. Required calibration accuracy: 10% 11. Integration time for each observing mode/receiver setting (hr): Crab: 16m/pointing at 3mm for a 200 pointings mosaic at 3mm. 200x16m/sqrt(2)=38hrs (sqrt(2) is for the sampling). The 1.3mm observations depend on the result of the 3mm, if the surface brightness is high enough, one could use the same integration time as for 3mm but on a 800 points grid, with a corresponding total integration time of ~155hrs. G21.5/G0.9, each: 1h/pointing at 1.3mm; 15min/point at 3mm ~16 point mosaic at 1.3mm (16h); ~8 point at 3mm (~2h) 12. Total integration time for program (hr): 38h Crab at 3mm, 36hrs G21/G0.9 = 74hrs (+ 155 hrs for the Crab at 1mm) 13. Comments on observing strategy : (optional) (e.g. line surveys, Target of Opportunity, Sun, ...):-------------------------------------------------- Review v2.0: 3.5.4 rev The populations of relativistic particles and the magnetic field structure in the Crab Nebular and other pleions Bandiera 229 ALMA can provide key reference images of these important objects. This proposal looks good to me.