Localising radio transients with international LOFAR baselines

Transcription

1 Localising radio transients with international LOFAR baselines Olaf Wucknitz Locating Astrophysical Transients, May, Lorentz Center, Leiden

2 Localising radio transients with international LOFAR baselines international array, resolutions LOFAR and transients transient detection with Artemis localising transients other offline correlation experiments airplanes O. Wucknitz

3 International LOFAR Array (without KAIRA) O. Wucknitz

4 Resolution fringe-spacing θ = λ/l resolution λ/m freq/mhz 1 km 30 km 300 km 1000 km 8000 km O. Wucknitz

5 Image of the Crab pulsar (HBA 2011) PLot file version 1 created 26-JUN :14:37 BOTH: IPOL MHZ ICL DECLINATION (J2000) RIGHT ASCENSION (J2000) Grey scale flux range= JY/BEAM Cont peak flux = E+00 JY/BEAM Levs = 8.566E-03 * (-2, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024) 0 O. Wucknitz

6 Crab nebula with LOFAR (HBA) O. Wucknitz

7 Some LOFAR aspects of transients LOFAR Transient KSP! NL array good for slow transients (normal imaging) wide-field imaging with international baselines challenging LB good to confirm new sources (no SN in NGC ) single stations or superterp good for fast transients poor resolution, need long baselines combine single stations with long baselines? trigger locally and combine later? O. Wucknitz

8 Where do these come from? [ Lorimer et al. (2007) ] O. Wucknitz

9 Artemis (1) reduced data 3.2Gbps data 800Mbps data 800Mbps data 800Mbps data 800Mbps data [ Aris Karastergiou ] Thursday, 3 May 2012 O. Wucknitz

10 Chris Williams Artemis (2) Steve Roberts Wes Armour Mike Giles Aris Karastergiou hardware Fred Dulwich Dell Poweredge C6100 Ben Mort [ Aris Karastergiou ] Thursday, 3 May 2012 Dell Poweredge C410x Dalal Ait Allal Alessio Magro Stef Salvini O. Wucknitz

11 originally Local trigger and offline correlation Artemis running at one or several international stations online flagging, de-dispersion, transient detection record Stokes parameters for a few seconds sometimes coincident detections! (from where?) new approach Artemis running locally as before record raw voltages instead! (same data volume) correlate later, use own software not ideal yet difficulty with time stamps written data are channelised O. Wucknitz

12 First three-station experiment (Feb 2013) B recorded locally with Artemis (few sec) FR606, SE607, UK608 correlated offline in Bonn fringe-search for one pulse (7 msec, de-dispersed) with Aris Karastergiou and Maciej Serylak O. Wucknitz

13 Delay spectra O. Wucknitz

14 Does it work? without any calibration measured offset equal to geometric delay within < 1µsec over 1000 km baseline: 1 arcmin position accuracy! (equivalent to large-scale ionospheric refraction) clock residuals: 1 arcsec how to calibrate ionosphere? use TEC models (not very accurate) use dispersion (need SNR and bandwidth) use calibrators (not many available) O. Wucknitz

15 Sky positions and 3-d positions sky position needs 3 stations (two delays) position accuracy: θ c τ/l for 1 µsec and 1000km: 1 arcmin 3-d position needs 4 stations (three delays) distance accuracy: (1/D) 4c τ/l 2 for 1 µsec and 1000km: 1/ km can identify local RFI at distance of Moon! localisation easy, with calibration better than arcsec O. Wucknitz

16 An intercontinental experiment [ vlbi-with-kaira-lofar-and-lwa. html ] O. Wucknitz

17 LOFAR + KAIRA + LWA baseline LOFAR LWA ca km 1 hour on B LBA: DE601, SE607, KAIRA, LWA (2 19.6MHz) recorded raw data; delay compensation, channelisation, correlation offline LWA: Frank Schinzel, DE601 and analysis: Tobia Carozzi, KAIRA: Derek McKay O.W., SE607: Thanks for the observing time and the help! no fringes yet... lwa_2013_mar:start O. Wucknitz

18 LWA pulsar detection O. Wucknitz

19 LOFAR LBA SE607 (Onsala) DE601 (Effelsberg) O. Wucknitz

20 Misalignment LWA LOFAR folded profiles offset by 290 msec intensity correlation reveals 1 sec offset reason unclear O. Wucknitz

21 Localising and identifying RFI 2011: correlated RFI spikes for 30 min on NL baselines wide-band: < 115 MHz 141 MHz use all baselines for 2-d or 3-d imaging 2d scan at 10 km height: moving peak O. Wucknitz

22 Altitude and nearby trajectory (3-d scans) O. Wucknitz

23 Full trajectory focused at m (2-d scans) O. Wucknitz

24 Trajectory O. Wucknitz

25 Identification AFL 231 Moscow to Brussels aircraft VP-BUO O. Wucknitz

26 Summary for fast transients combine local recording and triggering offline correlation on long baselines international stations often idle useful even without calibration potentially 3-d localisation (rule out RFI) combine with TBB? (subbands mode broken!) offline correlations for other special experiments KAIRA LWA, GMRT,... long baselines also important for slow transients O. Wucknitz