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Recent Results and the Future of Radio Afterglow Observations Alexander van der Horst Astronomical Institute Anton Pannekoek University of Amsterdam Suite of radio follow-up observatories • • • • • • Very Large Array Westerbork Synthesis Radio Telescope Australian Telescope Compact Array Giant Metrewave Radio Telescope Ryle Telescope Combined Array for Millimeter-wave Astronomy New era in radio follow-up observations • • • • • • • • • • • • Very Large Array Jansky Very Large Array Westerbork Synthesis Radio Telescope Apertif Australian Telescope Compact Array Giant Metrewave Radio Telescope Ryle Telescope Arcminute Microkelvin Imager Combined Array for Millimeter-wave Astronomy Atacama Large Millimeter Array Low Frequency Array Square MeerKAT Kilometer Australian SKA Pathfinder Array Murchison Widefield Array Long Wavelength Array Broadband spectrum Piran 2003 Wijers & Galama 1999 Radio observations: • Peak flux & frequency • Self-absorption frequency • Non-relativistic evolution • Scintillation & image size Physical parameters • Electron energy distribution index p • Energy in electrons εe • Fraction of emitting electrons ξ • Energy in magnetic field εB • Blast wave energy E • Density of circumburst medium n • Structure of circumburst medium k • Jet opening angle θ0 • Observing angle θobs GRB 030329 Berger, Kulkarni et al. 2003 Van der Horst, Kamble et al. 2008 Pihlstrom, Taylor et al. 2007 Current radio afterglow sample • 1/3 of observed GRBs detected in radio • Narrow observed flux range • Sensitivity limited • No clear correlations with other wave bands (optical?) • Detected radio afterglows brighter in prompt emission, X rays & optical • Biased because of strategy Chandra & Frail 2012 Average light curves Chandra & Frail 2012 • Forward & reverse shock • Bright future for 8 GHz and above (including ALMA) • How about low radio frequencies? Radio predictions: p & εe Radio predictions: εB & n Radio predictions: E & z Radio calorimetry • Late-time evolution: no relativistic complications • Blast wave spherical? Progenitor constraints • Very low frequencies and/or very late times GRB 970508 & GRB 980703 (Berger et al. 2004) GRB 030329 with LOFAR (Van der Horst, Kamble et al. 2008) LOFAR: afterglows & prompt emission • (Very) late-time afterglows: • Automatic monitoring on various timescales • Complementing the radio afterglow sample • Automated response: • Triggers by high-energy satellites or LOFAR • New beam formed pointing to GRB location LOFAR: afterglows & prompt emission • AARTFAAC: Amsterdam-ASTRON Radio Transients Facility And Analysis Centre • 24/7 all-sky monitor with 6 central stations • Piggy-back mode in all LOFAR observations • LBA: whole sky, HBA: 1000 deg2 • Transient Buffer Boards • 5 second storage • Dispersion delay subband approach • Coming soon: LOFAR UK-Chibolton responding to Swift triggers (1 hour follow-up) Reverse shock – radio flares Kulkarni, Frail et al. 1999 Melandri, Kobayashi et al. 2010 • Optical flash early radio flare • Probe GRB ejecta & jet magnetization AMI fast follow-up • • • • • Large array at 15 GHz ~0.13 mJy rms in 10 minutes 5.5’ primary beam ~30’’ synthesised beam First responses within 4-5 minutes!! AMI fast follow-up • • • • • Large array at 15 GHz ~0.13 mJy rms in 10 minutes 5.5’ primary beam ~30’’ synthesised beam First responses within 4-5 minutes!! AMI observations of GRB 120422A Staley, Titterington et al., in prep. Dark bursts Radio • Host galaxy • High redshift • Intrinsic? X-ray Rol, Van der Horst et al. 2008 GRB 051022 Van der Horst, Kouveliotou et al. 2009 Compact binary mergers Piran, Nakar & Rosswog 2012 • Sub-relativistic dynamically ejected outflow • Detectable up to ~300 Mpc LIGO/VIRGO • Short GRBs(?) relativistic jet Conclusions • Dawn of a new radio era: • Many SKA pathfinders • Upgrades of new facilities • Extensions of the frequency & time domains • Radio observations crucial for pinning down afterglow physics • Current sample sensitivity limited • Probing parameter space of “regular” afterglows • Studies of early reverse shock emission and possible coherent prompt emission