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The Radio Afterglow produced by the Giant Flare from the Magnetar SGR 1806-20

The Radio Afterglow produced by the Giant Flare from the Magnetar SGR 1806-20. Greg Taylor (NRAO/KIPAC). UCSC/SCIPP - 4/26/2005. with: J. Granot, B. M. Gaensler, C. Kouveliotou, J. D. Gelfand , D. Eichler, E. Ramirez-Ruiz, R. A. M. J. Wijers, Y. E. Lyubarsky, R. W. Hunstead,

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The Radio Afterglow produced by the Giant Flare from the Magnetar SGR 1806-20

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  1. The Radio Afterglow produced by the Giant Flare from the Magnetar SGR 1806-20 Greg Taylor (NRAO/KIPAC) UCSC/SCIPP - 4/26/2005 with: J. Granot, B. M. Gaensler, C. Kouveliotou, J. D. Gelfand,D. Eichler, E. Ramirez-Ruiz, R. A. M. J. Wijers, Y. E. Lyubarsky, R. W. Hunstead, D. Campbell-Wilson, A. J. van der Host, M. A. McLaughlin, R. P. Fender, M. A. Garrett, K. J. Newton-McGee, D. M. Palmer, N. Gehrels,

  2. The Mystery of Gamma Ray Bursts (GRBs) • Short overview of soft gamma repeaters (SGRs) • The 2004 Dec. 27 Giant Flare from SGR 1806-20 • The Radio Afterglow produced by the giant flare (astro-ph/0504363) • A dynamical model for the radio observations • Implications for short gamma-ray bursts Outline

  3. An early gamma ray-burst Vela satellite

  4. A Gamma Ray Burst Sampler

  5. Bursts of all sorts (Woods & Thompson 2004)

  6. Radio Light Curves from long GRBs

  7. GRB 970508 • First VLBI detection of a GRB Afterglow • absolute position to < 1 mas • Size < 10**19 cm • Distance > 3 kpc

  8. Relativistic Expansion v ~ 0.96c E ~ 10**53 ergs (isotropic equivalent) R ~ (E/n)**1/8 astro-ph/0412483

  9. Long GRBs clearly connected to Supernovae Hjorth et al 2003

  10. SGR Light Curves & Durations: t ~ 0.2 s (Woods & Thompson 2004)

  11. From Pulsed quiescent X-ray emission: Woods & Thompson 2004

  12. The Magnetar Model for SGRs • Lquiescent~ a few 1035 erg/s • The energy release in a single giant flare is of the order of the total rotational energy ~1044.5erg • another energy source is required • Main competing model for the energy source: accretion - does not work well (no binary companion or quiescent IR emission) • The measurement of the period and its time derivative was considered a confirmation of the magnetar model: B ~ 1015 G ~ 1048erg

  13. Adapted from Duncan and Thompson 1992

  14. Giant Flares from SGRs • Initial spike: t ~ 0.3 s , Eiso ~ a few1044 erg • hard spectrum • ~ ms rise time • Pulsating tail • Lasts a few min. • Modulated at the NS rotation period • Softer spectrum • Only 2 previous events ever recorded: in 1979 (SGR 0526-66 in LMC) & 1998 (SGR 1900-14) The 1998 August 27 giant flare from SGR 1900+14

  15. SGR 1806-20 on 2004 Dec 27

  16. Rise time: < 1 ms, te-folding ~ 0.3 ms The rise is resolved for the first time Swift (Palmer et al. 2005)

  17. Sudden Ionospheric Disturbance (SID) Cambell et al. 2005 Washington, USA to Alberta, CA

  18. was ~5ofrom the sun • It’s distance ≈ 15 kpc • Eiso ~ (2-9)1046 erg • Eiso,spike/Eiso,tail ~ 300 The 2004 Dec. 27 Giant Flare RHESSI Swift (Hurley et al. 2005) (Palmer et al. 2005)

  19. Aperture Synthesis – Basic Concept If the source emission is unchanging, there is no need to collect all of the incoming rays at one time. One could imagine sequentially combining pairs of signals. If we break the aperture into N sub- apertures, there will be N(N-1)/2 pairs to combine. This approach is the basis of aperture synthesis.

  20. The VLA 27 antennas each 25 m in diameter Synthesised aperature after 45 minutes.

  21. B ~ 0.3 mG Raphaeli 2001

  22. Source Size, Shape & Polarization: From Gaensler et al. 2005 (accepted to Nature)

  23. Radio Afterglow has a Steep Spectrum ~ -0.6 at t+7 days down to 220 MHz Flux > 1 Jy at early times and low frequencies. From Cameron et al. 2005

  24. VLA Y Special Advertising Supplement: The Long Wavelength Array Exploring the Transient Universe from 20 - 80 MHz Full LWA: 50 stations spread across NM 1 “LWA Station” = 256 antennas State of New Mexico 400 km 100 m

  25. Growth of the Radio Afterglow VLA 8.5 GHz Velocity to t + 30 days ~ 0.8 c Size at t+7 days 1016 cm Decrease in vexp

  26. Proper motion of the Flux Centroid: VLA 8.5 GHz

  27. Image Evolution VLA 8.5 GHz

  28. The supersonic motion of the SGR in the ISM creates a bow shock & a thin shell of shocked wind and shocked ISM, surrounding a cavity Theoretical Interpretation: Observations (Gaensler et al. 2003) Simulation (Bucciantini 2002)

  29. The outflowing material that was ejected from the magnetar during the giant flare collides with the bow shock shell and “lights up” • The merged shocked shell continues to coast outward & the shock accelerated electrons cool adiabatically: reproduces the observed fast decay and constant expansion velocity ~ 0.3c • A shock is driven into the ISM that eventually slows down the shell causing a bump in the light curve which naturally peaks at the time tdec when significant deceleration occurs

  30. R  t0.4 Log(R) R  t Log(t) tdec~ 33 days tcol~ 5 days What we missed

  31. The observed Linear Polarization: VLA 8.5 GHz

  32. Image Evolution VLA 8.5 GHz Observed Polarization Angle

  33. linear polarization perpendicular to the projection of B on the plane of the sky Polarization of Synchrotron Emission Projection of the magnetic field on plane of the sky The direction of the polarization B P B e Cone of angle 1/e Plane of the sky

  34. A magnetic field that is produced at a relativistic collisionless shock, due to the two-stream instability, is expected to be tangled within the plane of the shock(Medvedev & Loeb 1999) Shock Produced Magnetic Field: P = 0 Magnetic field tangled within a (shock) plane Photon emitted normal to plane nph =nsh P = Pmaxsin2/(1+cos2)  P (Laing 1980) P P = Pmax Photon emitted along the plane nph nsh

  35. Elongated emission region gives rise to net polarization Net Pol.

  36. Energetics from R(tdec) & tdec: • M~ (4/3)R3 ~ 1026 (nISM / 1 cm-3) gr • E~ Mv2 ~ 1046 (nISM / 1 cm-3) erg

  37. Implications for Short GRBs BATSE detection rate ~ 150 yr-1 Rate of Giant Flares in our galaxy ~ 0.03 yr-1 Giant Flares can be detected to 40 Mpc Assume SGRs proportional to star formation Local (z=0) SFR ~ 0.013 Msun yr-1 Mpc-3 Milky Way SFR ~ 1.3 Msun yr-1 Expected Giant Flares within 40 Mpc ~ 80 yr-1 But where is Virgo concentration?

  38. The radio afterglow of the SGR 1806-20 giant flare is a unique opportunity to study a nearby relativistic outflow. • Giant flares from extragalactic SGRs might explain short duration GRBs. • After 35 years we have a fair start on understanding the origin of GRBs. • Low frequency observations of the transient universe could dramatically improve our understanding and may open up entirely new puzzles. Conclusions:

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