Radio Afterglows. What Good are They? Dale A. Frail. National Radio Astronomy Observatory. Gamma Ray Bursts: The Brightest Explosions in the Universe

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1 Radio Afterglows What Good are They? Dale A. Frail National Radio Astronomy Observatory Gamma Ray Bursts: The Brightest Explosions in the Universe The 2 nd Harvard-Smithsonian Conference on Theoretical Astrophysics May 20-23, 2002

2 Will radio observations be relevant in the SWIFT era?

3 Talk Outline The Radio Afterglow Sample detection statistics Energetics beaming angles and broadband modeling Sedov-Taylor estimates Circumburst Environment density indicators dark bursts Host Galaxies obscured star formation

4 A Coordinated Radio Network Ryle 15 GHz Pooley OVRO 99 & 210 GHz Walter & Shepherd VLBA 0.6 to 43 GHz Taylor & Galama ATCA 1.4 to 8.6 GHz Wieringa et al. VLA 0.3 to 43 GHz Frail, Berger, & Taylor IRAM 30-m 250 GHz Bertoldi, Peck & Menten JCMT 150 to 660 GHz Moriarty-Schieven

5 The First Five Years: Optical O=5 XO=4 X=14 X-ray XOR=12 OR=7 XR=4 R=1 Venn Diagram Radi

6 Histogram of Peak Flux Densities 8.46 GHz Max peak=2 mjy 75 bursts, 5 years Median=0.25 mjy 50% of all SWIFT bursts will be at least as bright as R=17.7 Turnover=0.2 mjy 10x range, severely sensitivity limited

7 Spectral Luminosity at 8.5 GHz M87

8 Spectral Luminosity at 8.5 GHz

9 Energy and Beaming Corrections Frail et al. (2001) Use isotropic gamma-ray energy as a proxy for total energy in outflow E γ = erg Need to correct for the geometry of the outflow Signature of a jet is an achromatic break in the light curve

10 Jet Signatures: Optical/X-ray Piran, Science, 08 Feb 2002

11 Jet Signatures: Give me a break! Flux Density -1 t -2 t t jet -1/3 t X-ray time radio optical The jet signature in radio is different - rise decay - Peak flux cascade ISM, iso : F ISM, Wind, iso : F Radiative jet : F : F m m m m ν ν ν ν 0 m 1/2 m 1/3 m 0.08 m ( ε e = 0.1)

12 Peak Flux Cascade: GRB Yost et al. (2002) 350 GHz: 2.5 mjy 90 GHz: 1.5 mjy 8.46 GHz: 0.35 mjy 4.86 GHz: 0.20 mjy 1.43 GHz: 0.10 mjy F m ν m 0.59± 0.07 Other examples: GRB GRB

13 Jets Breaks and Opening Angles Frail et al. (2001) Determining the true gamma-ray energy requires measuring achromatic breaks over a wide range of timescales The different jet signature in radio bands gives added confidence X-ray: flares Optical: host-dominated, density fluctuations, lensing, refreshed shocks, wide angle jets

14 Jets Breaks and Opening Angles GRB Determining the true gamma-ray energy requires measuring achromatic breaks over a wide range of timescales The different jet signature in radio bands gives added confidence X-ray: flares Optical: host-dominated, density fluctuations, lensing, refreshed shocks, wide angle jets

15 Energy and Circumburst Density Criticism: Geometry-corrected gamma-ray energy depends on circumburst density but E 4 10 no γ 10 6 t jet cm 1 + z -3 Hydrodynamic evolution of the blast-wave depends strongly on: E γ,iso total energy in outflow, geometry of outflow, and density structure of circumburst medium broadband afterglow modeling is the key 3/4 n 1/ 4 o η 1/ 4 γ

16 Broadband Modeling: GRB Radio (4.86 GHz) Optical/NIR (R and H) X-ray Panaitescu & Kumar (2001) modeled with extensive optical, NIR and X-ray data but only two epochs of early radio data n o cm 3

17 Broadband Modeling: GRB Panaitescu & Kumar (2001) model does not predict future radio evolution problem lies with the self-absorption frequency

18 Broadband Modeling: GRB Frail et al. (2002) have carried out recent modeling of all radio, optical, NIR and X-ray data n o 27 cm 3

19 GRB Environments: GRB GRB AG Model n 4 10 o Harrison et al. (2001) vs Piro et al (2001) -3 n o 30 cm vs no 4 4 cm cm -3 Radio AGs rule out extreme densities and yield n o 10 cm Most GRB AGs can be described by a jet-like outflow in a constant density medium In order to conclusively link GRBs and massive stars we must see the wind signature Radio measurements are sensitive to both the absolute value of the gas density and its radial dependence (i.e., ρ (r) r -2 ) -3

20 Fireball Calorimetry Frail, Waxman & Kulkarni (2000) E n o o cm erg Long-lived radio afterglow makes a transition to NR expansion no geometric uncertainties can employ robust Sedov formulation for dynamics compare with equipartition radius and cross check with ISS-derived radius Different methods agree

21 The Population of Dark Bursts Optical O=5 XO=4 X=14 X-ray XOR=12 OR=7 XR=4 Dark Bursts R=1 Radi

22 How Do You Make a Dark Burst? Intrinsically faint afterglow low energy, fast decay, etc. Dust extinction Dust and gas along the line-of-sight or within the circumburst environment High redshift Absorption by Ly-alpha forest for z>5 predictions of up to 50% of all bursts Need a sample of well-localized bursts

23 X-ray/Radio (XR) Dark Bursts Why? use arcsecond position to Optical identify host galaxy (if any) and derive its redshift O=5 use X-ray and radio afterglow to infer gas properties (either line-ofsight or circumburst) OR=7 N H : X - ray n o : X - ray via ν c n o : Radio via ν ab A : AG modeling V Radi XR=4 X-ray Well-localized dark bursts

24 X-ray/Radio Dark Bursts GRB z=0.846 GRB host galaxies are at modest redshifts (no z>5 candidates) X-ray/radio predict bright optical afterglow (not faint) significant extinction required (A_v>4-10) GRB z=1.31 Holland et al Frail et al. (1999) Holland et al GRB z=0.958 Piro et al. (2002) Bloom et al. (2002) Taylor et al. (2000)

25 X-ray/Radio Dark Bursts GRB z=0.846 GRB Chandra/XMM has identified four new dark candidates (D. Fox, in prep) Frail et al. (1999) GRB z=1.31 Holland et al Holland et al XRF , XRF GRB , GRB Piro et al. (2002) GRB z=0.958 Bloom et al. (2002) Taylor et al. (2000)

26 Obscured Star Formation at High z Burning question: What is the fraction of star formation hidden by dust? Optical/NIR FIR/Submm GRBs offer a complementary probe of SF(z): Immune to dust Bright afterglows with measurable z Visible to high z (z>20)

27 Obscured Star Formation at High z A search for cm (synchrotron) and submm (hot dust) emission from GRB host galaxies PhD, E. Berger Optical/NIR FIR/Submm VLA: late time centimeter emission ATCA: search for emission from 4 GRB hosts JCMT: SCUBA survey of 13 host galaxies IRAM PdB: search for redshifted CO

28 Host galaxies: GRB z = R host SFR = M (I - K) = 2.1 D opt = yr = 3.7 kpc A persistent VLA radio source seen from 350 to 1000 days after the burst afterglow emission is expected to be 1-2 orders of magnitude fainter during this time an ULIRG undergoing a nuclear starburst Radio properties SFR L = = 3 10 SFR = 500 M FIR 90 M 12 yr yr L 1 1 (M > 5 M ( IMF) )

29 Obscured Star Formation at High z Spectral energy distribution is strongly peaked in submm SFR 10 L FIR 3 M few 10 yr 12 1 L GRB host galaxies have intermediate colors

30 Will radio observations be relevant in the SWIFT era? Radio observations of afterglows have an important (and sometimes unique) role Samples the part of the afterglow spectrum which is vital for constraining the physical parameters of the fireball Long-lived radio afterglow can see wide-angle jets Long-lived radio afterglow can capture NR transition Can resolve the outflow via interstellar scintillation Not sensitive to dust obscuration (dusty hosts), Lyman breaks (z>5), time of day, weather, lunar phase Energetics Circumburst Environment Host Galaxies

31 What Radio Is Not Sensitive To time of day, weather, lunar phase dust obscuration Lyman break relativistic beaming (less so)