How to detect them? LOFAR hardware/software FRATS Tools All Sky LOFAR All the time Parallel Observations (Piggybacking). Triggering ○ Sander’s Talk ○ ARTEMIS ○ Others… Look back in time TBBs (1-5 sec) Offline processing. Bright events Coherent addition: ○ High SNR Accurate position Multi-station Imaging
Summary Future Work Coherent Beams Multi-Station Imaging Use larger number of stations FRATS pipeline RFI mitigation (from CR tasks) Antenna gain Imaging: projected station positions Store complex beams from beamformed LOFAR data
Some more fun physics… DM by measuring the time delay. RM by measuring the bandwidth needed for full polarization shift. We can calculate > just by calculating the RM and DM.
How to detect them? All Sky LOFAR Beamsize: LBA: All-sky (30000 sq. deg) HBA: 500 sq. deg All the time Parallel observations Internal and external triggers. (AARTFAAC, ARTEMIS, Nancay trigger?, Xray telescopes?) Look back in time.
The Stationary, Quasi-Monochromatic Radio-Frequency Interferometer X s s b c g / s b⋅ = τ ) ( cos 2 t E V ω = ] ) ( cos[ 1 g t E V τ ω − = ] ) 2 ( cos ) ( [cos g g t P ωτ ω ωτ − + multiply average The path lengths from sensors to multiplier are assumed equal! Geometric Time Delay Rapidly varying, with zero mean Unchanging ) ( cos g C P R ωτ =
LOFAR and TBBs Transient Buffer Board (TBBs): RAM, used as ring buffer, on each LBA/HBA Data Storage: ring stopped, dump to disk. Can reproduce any LOFAR signal. 1Gb memory ~ 1 sec /antenna element (5 sec in the future)
Dispersion Measure (DM) Dispersive nature of interstellar plasma: radio wave interaction with free electrons makes for slower group velocities for lower frequencies. Time delay is calculated by: DM Total column density of free electrons, or a distance estimate with ne models of the ISM.
Faraday Rotation If the ISM has a B, then it becomes birefringent. LCP and RCP have different refractive index : different group velocities. Rotates linearly polarized waves. λ
Pulsar B A β Aristeidis Noutsos, Astronomische Gesellschaft 2010 PSR B0329+54 d β = λ2 * RM RM = π*/(λ1 –λ2 )2