1. ATUC Science Meeting 24 th Oct 2011 Radio emission from CU Virginis Kitty Lo Collaborators: Justin Bray, George Hobbs, Tara Murphy, Bryan Gaensler, Don Melrose

2. ATUC Science Meeting 24 th Oct 2011 Introducing CU Virginis ›CU Virginis is a magnetic chemically peculiar Ap star ›V magnitude of 5.01 ›Rotation period of 0.52 days ›Polar magnetic field of ~3kG (determined optically) ›Distance of ~80pc Source: DSS2 image from Aladin

3. ATUC Science Meeting 24 th Oct 2011 CU Vir emits two coherent radio pulses every rotation period 2 1.37GHz 1.67GHz 1.87GHz 2.17GHz 2.62GHz Lo et. al, 2011 (submitted)

4. ATUC Science Meeting 24 th Oct 2011 The Pulsar lighthouse model 3

5. ATUC Science Meeting 24 th Oct 2011 Period of CU Vir ›Pyper (1998) found an abrupt increase in period of ~2 seconds around 1984 4 Spectrosopic variation versus phase (Pyper A&A 1998) ›More recently, Mikulášek (2011) shows CU Vir goes through intervals of rotational acceleration and braking Period variation of CU Vir (Mikulasek A&A 2011)

6. ATUC Science Meeting 24 th Oct 2011 Radio observations 5 20cm 13cm Lo et. al, 2011 (submitted)

7. ATUC Science Meeting 24 th Oct 2011 Electron Cyclotron Maser ›Electron cyclotron frequency, eB/2πm >> plasma frequency, e√(n e /m)/2π -Usually in magnetized plasmas with low electron density and/or high magnetic field strength ›Population inversion in the electron distribution -E.g. Loss cone distribution 6 Melrose & Dulk (1982) Electrons with small pitch angle precipitate to the surface Electrons reflected by magnetic mirroring

8. ATUC Science Meeting 24 th Oct 2011 Why ECM? ›High degree of circular polarization ›High brightness temperature (> 10 10 K) ›Highly beamed emission ›Very narrow band ›Emission frequency ~ cyclotron frequency or its second harmonic -Magnetic field of Earth – 0.6G, ECM in kHz -Magnetic field of CU Vir - ~3kG, ECM in GHz 7

9. ATUC Science Meeting 24 th Oct 2011 ECM is related to auroras ›ECM from Earth is known as the Auroral Kilometric Radiation (AKR) ›AKR is generated on auroral magnetic field lines above the auroral zone ›Typical frequency is 50 to 500kHz ›AKR closely correlated with occurrence of auroras (Gurnett 1974) 8 Mutel (2004)

10. ATUC Science Meeting 24 th Oct 2011 ECM has been observed on planets and brown dwarfs 9 Composite of optical and IR image from Cassini of Saturn Radio light curve of TVLM-513 Hallinan et al, ApJ, 2007

11. ATUC Science Meeting 24 th Oct 2011 Model of CU Vir magnetosphere 10

12. ATUC Science Meeting 24 th Oct 2011 Simple ECM model does not produce the correct frequency dependence 11

13. ATUC Science Meeting 24 th Oct 2011 We can get the right frequency dependence if emission is along B field 12

14. ATUC Science Meeting 24 th Oct 2011 To get radio pulses to arrive at the right phase, emission need to be ducted 13

15. ATUC Science Meeting 24 th Oct 2011 Ducting of ECM 14 Ergun, ApJ, 2004

16. ATUC Science Meeting 24 th Oct 2011 Summary ›CU Vir is a unique source which emits pulses of coherent radio emission ›Electron cyclotron maser is believed to be the emission mechanism ›Simple models of ECM does not fit the frequency dependence of the pulse arrival time ›Propagation effect must play a role ›ASKAP, LOFAR, MWA could potentially find a lot more of these objects 15