LOFAR update: long baselines and other random topics

Transcription

1 LOFAR update: long baselines and other random topics AIfA/MPIfR lunch colloquium Olaf Wucknitz Bonn, 6th April 20 LOFAR update: long baselines and other random topics LOFAR previous long-baseline images the Sun with LOFAR long-baseline HBA images long-baseline observations of crab the pulsar using long baselines to calibrate the short ones: crab nebula polarisation of the crab pulsar wide-band RFI from airplanes LOFAR The Effelsberg station at Google maps LOw Frequency ARray low frequencies LBA: 0(0) 80 MHz HBA: MHz 40 stations in Netherlands additional stations in Germany ( 5 +?), France (), England (), Sweden ( ), Italy?, Poland?, Finland?... wide field of view, several beams good survey speed full synthesis imaging at low frequencies with high resolution long baselines: subarcsec resolution, useful for lens surveys 2 The Effelsberg station from the 00m International LOFAR stations [ James Anderson ] 4 5 German LOFAR stations LOFAR core: the superterp 6 7

2 One year ago: C96 with LBA, LOFAR and MERLIN UV coverage with long and short baselines [ Wucknitz + Lonsdale & Morison (980) ] 8 9 Dutch only vs. international LBA long-baseline map: some details NL only, 0 beam NL+DE,. 5 beam C96, LBA, / 60 subbands, / 0 80 MHz (ripple!) bandwidth 6 MHz / 48 MHz D h on 2/ Feb NL + DE stations (Effelsberg, Unterweilenbach, Tautenburg) corrected for µsec and 7 µsec constant delays RR and LL from XX/XY/YX/YY using geometric model (self-)calibrated and imaged LL/RR in difmap MFS with/without spectral index correction 0 First interferometric Solar observations The very first map initiated by Solar KSP (Mann, Vocks, Breitling), Anderson, Polatidis, Wucknitz 8 ten-minute scans on 9th June 200, 9:48 5:50 UT 4 with LBA and HBA each phase/pointing centre near Sun and calibrator sources LBA difficult, other sources dominating: C2, CygA, CasA,... situation unclear HBA much clearer signal, Sun dominating on short baselines self-calibration possible because of compact component only short baselines used! 2 Imaging strategy Dynamic spectra first steps in own software assess data quality dynamic spectra for data inspection fringe-fitting to determine clock offsets; correction flagging convert to circular polarisation (if wanted) averaging in time and frequency write UVFITS file imaging/calibration in difmap / AIPS not used external calibrators yet CLEAN / selfcal loop, compact emission helps! Significant variability as function of time and frequency! 4 5

3 Variability: 0 min in 0 sec steps ( subband) Variability: 0 sec in sec steps (8 subbands) 6 7 Difference imaging attempts: 0 min at 50. MHz in 0 sec steps wavelength As function of time and frequency time 8 First sub-arcsec observations 9 Images of C96: first attempt (6 h, L ) no station calibration in DE60,FR606, snow on DE60: L L L C48 C47 C96 h h 6h Jan 20 Jan 20 /4 Jan 20 station calibration okay, no snow, high freqs weak in DE60: L L C96 C47 2 h 2 h 20/2 Jan 20 2/24 Jan 20 all with HBA (ca MHz) with DE60, FR606, UK608 plus 5 RS plus 2 CS 20 Images of C96: current best (2 h, L ) international resolution: Components of C96 (2 h, L ) Dutch 22 2

4 Preliminary image of C47 (2 h, L ) Long-baseline observations of the crab (TauA/M/C44) 2h on /4 Feb 20 L MHz international stations: DE60, DE60, FR606 NL stations: CS02, RS06,205,208,06,07,406,50 This is with only 20% of the subbands, RR pol. Dynamic range already 000:, still room for improvement. problems DE60 failed 50% of subbands bad in blocks of 0/ significant ionospheric delays, differential Faraday rotation Preliminary image of the pulsar: it is a point-source! Imaging the nebula PLot file version created 22-FEB-20 8:05: BOTH: RR MHZ 240.RCL DECLINATION (J2000) RIGHT ASCENSION (J2000) Grey scale flux range= JY/BEAM Cont peak flux = 9.800E+00 JY/BEAM Levs = 9.80E-02 * (-,, 2, 4, 8, 6, 2, 64) The nebula with the VLA at 5GHz Comparison with 9 mm Effelsberg LOFAR 2.5 m Effelsberg 9 mm [ Bietenholz (2004) ] [ Effelsberg image and filtering by Wolfgang Reich ] Comparison with HST (contours) Polarisation: expectation pulsar is (sometimes) linearly polarised sometimes > 50%, sometimes much less RM= 42rad/m 2 (or 45?) see Ger de Bruyn, LOFAR Status Meeting 29 Oct 2008 periodicity about MHz [ Andrei Lobanov ] leakage terms more constant separate the two without full calibration polarised and unpolarised at same time 0

5 calibrated RR and LL, averaged over 0min POSSM plots: IQUV (set I to 0Jy) Plot file version 6 created 04-MAR-20 7:49: MULTI. Freq = 0.50 GHz, Bw = MH Calibrated with CL # and BP # (BP mode ) IF (I) IF (U) IF 2(I) IF 2(U) I U IF (I) IF (U) IF (Q) IF (V) IF 2(Q) IF 2(V) Lower frame: Real Jy Top frame: Imag Jy Vector averaged cross-power spectrum Baseline: FR606HBA(04) - RS06HBA(08) Timerange: 00/20:0:7 to 00/2:00:7 FR606 RS06 Q V IF (Q) IF (V) imag real imag real Faraday dispersion function from Q and U (0 subbands) 2 After subtraction of leakage peak (one CLEAN iteration) As function of frequency: blocks of 0 subbands each MHz MHz MHz MHz 4 5 Shorter integrations: 0min (highest block) RFI spikes strong spikes (< sec) left after initial flagging had consistent phases and sometimes small delays seen on all Dutch baselines wide: < 5MHz 4MHz beyond airband detectable for about 0min 6 7 phases not calibrated Mapping the signal can measure delays on Dutch baselines constant delay corresponds to hyperboloid baselines sufficient to determine position (in d) add all baselines incoherently scan in 2d or d first attempt: 2d scan of sky positions (at infinity) giant pulses? exotic transient? scan shows no clear peak 2d scan at ground level Terrestrial RFI? no sharp peak but large blob moving with time: aircraft? 2d scan at 0km height find clear moving peak, scans with 8 60 subbands 8 9

6 Altitude and nearby trajectory (d scans) Full trajectory focused at 0200 m (2d scans) 40 4 The d peak: cuts in XY / XZ / YZ Trajectory almost directly overhead 0 subbands accuracy m can be improved with more subbands but: mind the gaps! Aircraft RFI strong spikes (flux not measured yet) can be flagged, but may flag transients! aircraft at altitude of 0km, speed ca. 800 km/h first detection at distance of 50km (horizon) what is it? communication is narrow-band, more restricted reflections from the ground? only one such source over 2 hours! higher-frequency radar? no non-linearity military jamming equipment? more info at de/~wucknitz/wiki/doku.php/lbg:tau_a: airtraffic Identification AFL 2 Moscow to Brussels aircraft VP-BUO Summary good progress with long baselines Sun can be imaged, but difficult sub-arcsec imaging long baselines good for calibration of short baselines (crab nebula) polarisation of crab pulsar LOFAR as passive radar: wide-band aircraft RFI more info at ~wucknitz/wiki/doku.php/lbg:start 46