Radio Inputs in GRB Afterglows Poonam Chandra NCRATIFR

Radio Inputs in GRB Afterglows Poonam Chandra NCRA-TIFR Academic Day 2013: 24 th October

Gamma Ray Bursts Meszaros and Rees 1997

Major afterglow breakthrough Beppo. SAX: first detection of X-ray counterpart of GRB 970228. Optical detection after 20 hours by William Herschel Telescope. Faint host galaxy detected afterglow faded but no distance measurement. GRB 970508, localized by Beppo. Sax, detected in optical 4 hours later. Z=0. 835. Confirmed cosmological distances. First radio afterglow also detected from GRB 970508. GRB 980425 associated with SN 1998 bw (massive star connection)

Multiwaveband modeling • Long lived afterglow with powerlaw decays • Spectrum broadly consistent with the synchrotron. • Measure Fm, na, nc and obtain Ek (Kinetic energy), n (density), ee, eb (micro parameters), theta (jet break), p (electron spectral index).

Where does radio fit into the picture? ENERGY CIRCUMBURST ENVIRONMENTS GEOMETRY

Detection Statistics v 304 GRBs detected in radio bands from 1997 -2011. v 123 GRBs in pre-Swift and 181 in post-Swift. v 34% detected in pre-Swift, 29% post-Swift. v. Detection rate almost unchanged unlike optical and X-ray Chandra et al. 2012, Ap. J 746, 156

Radio Detection Biases Upper limits detection Chandra et al. 2012, Ap. J 746, 156

Radio Detection Biases Chandra et al. 2012, Ap. J 746, 156 But Gaensler 2013 says different

Where does radio fit into the picture? ENERGY CIRCUMBURST ENVIRONMENTS GEOMETRY

GRBs: Energetics Erel=Egamma+Einj+Erad+Ekin Two models collapsar, magnetar, upper limit ~1 E+52 ergs Cenko et al. 2010

GRBs: Energetics Erel=Egamma+Einj+Erad+Ekin Two models collapsar, magnetar, upper limit ~1 E+52 ergs Cenko et al. 2011

Swift Complications: Soft Energy Response GRB 090902 B Swift energy response 15 -350 ke. V BAT bandpass provides limited spectral coverage Often miss Epeak Leads to large uncertainties in Eγ, iso Abdo et al. , 2009

SED GRB 070125 Chandra et al. 2008

Energetics from Radio long lived afterglow emission The outflow reaches sub-relativistic regime Quasi-spherical geometry Energetics are independent of uncertain beaming angles

Energetics: GRB 970508 Frail et al. 2000 Light curves upto 450 days. Sub-relativistic by 100 days. Derived total Energy from radio 0. 5 E 51 ergs.

Where does radio fit into the picture? ENERGY CIRCUMBURST ENVIRONMENTS GEOMETRY

GRBs: Circumstellar Environments

Density estimation GRB 070125 N=50 cm-3 or A*=2. 5 (n=3 E 35 A*r-2), Chandra et al. 2008

GRB 090423, z=8. 3 (Chandra, P. et al. 2010) GRB 050904, z=6. 3, n=600 cm-3 19 11 -09 -13

Density crucial in SHBs Current SHB models: Mergers: NS-NS, NS-BH. magnetar flares, delayed magnetar formation through WD-WD mergers. , accretion induced collapse of WD or NS. Approach to progenitor: redshift distribution, host properties, burst location within hosts. If mergers, in low density environments due to kicks. Denser environment shows the alternate scenario.

Where does radio fit into the picture? ENERGY CIRCUMBURST ENVIRONMENTS GEOMETRY

GRBs: Jets and Geometry GRB emission is not spherical but in relativistic jets Due to relativistic beaming, only small fraction of jet. As jet slows down, lateral expansion. Jet break, geometrical effect. Simultaneous in all electromagnetic bands.

Jet breaks Harrison et al. 1999

Jet breaks Panaitescu & Kumar 2001

Missing jet breaks in Swift Era Butler et al. 2009

Missing breaks in Swift Era Swift is more sensitive but has a softer energy response Median redshifts higher, shift tjet to later times. Also finding more population of fainter bursts, harder to see breaks. Lack of jet breaks in X-rays light curves masked by other effects like continuous energy injection, inverse Compton effect.

GRB 070125: Chromatic jet break Chandra, P. et al. 2008

GRB 070125: Chromatic jet break Chandra, P. et al. 2008

Other inputs in Radio Bands: Scintillation puts constraints (Goodman 1997) GRB 970508. Limit of 3 microarcsec on the angular size. R~1 E 17 cm

GRB 070125: Scintillation theta=~2. 8+/-0. 5 marcsec R~2 E 17 cm Chandra et al 2008

Other Inputs in radio bands Radio VLBI. Direct constraints on fireball size Confirmation on relativistic expansion GRB 030329: Size 0. 07 mas (0. 2 pc) 25 days and 0. 17 mas (0. 5 p) 83 days. Confirmation of relativistic fireball expansion (Taylor et al. 2004)

GRB 100418 A: Constraints on Energy injection models Moin, A. , Chandra P. et al. 2013

GRB 100418 A: Constraints on Energy injection models Moin, A. , Chandra P. et al. 2013 • Unresolved source, Size <0. 33 mas. • Upper limit on expansion speed <8 c. • Lorentz factor <7 • Multiple shells with various lorentz factor ruled out. • Prolonged activity from the central engine is causing the rebrightening in the light curve.

Other Inputs in radio bands: Detectability at high redshift Chandra et al. 2012, Ap. J 746, 156

Detectability of radio afterglows - redshift Kolmogorov-Smirnov test P=0. 61 Chandra et al. 2012, Ap. J 746, 156

GRBs detected at high redshift GRB 090423 (Chandra et al. 2010) GRB 050904 (Frail et al. 2009)

Other inputs in radio bands: Reverse Shocks

Reverse shocks in radio afterglows Only 990123 has a confirmed optical and radio reverse shock. Low incidence of optical reverse shocks, i. e. < 4% (Gomboc et al. 2009). Radio RS is 1 every 4 bursts, i. e. 6 times more than optical. Magnetization, poynting dominated, SSC, dust extinction, wind density If nm<nopt then no RS in optcal band For 021004, 021211 optical RS is seen but no radio RS emission (Synchrotron self absorbtion? ? ? )

Reverse shocks in radio: GRB 990123 Kulkarni et al. 1999

Reverse shocks in Radio Chandra et al. , 2013 -2014, to GRBs be submitted soon (hopefully ) : :

Reverse shock emission from GRB 090423 (Chandra et al. 2010) RS seen in Pd. BI data too on day 1. 87 Reverse shock seen in GRB 050904 (z=6. 26) too

GRB 130427 A: Evidence of RS Laskar et al. 2013 • Observations with VLA, GMRT, CARMA and combined with optical/IR/UV and X-ray bands. • Most detailed modeling of RS. Wind medium with low density prefered.

GRB radio afterglows GRB 970508: First radio afterglow. GRB 980425: First SN detection. Confirmation of massive stars progenitor. GRB 990123: First afterglow with reverse shock detection in radio band (Kulkarni et al. 1999). GRB 020405: evidence of a constant density medium around massive star (Berger et al. 2003). 030329: Confirmation of relativistic expansion. First cosmological burst with Sn association. GRB 050904 (Frail et al. 2005) and 090423 (Chandra et al. 2010): highest redshift bursts discovered in radio. GRB 070125: radio afterglow with scintillation, chromatic break, uniform density (Chandra et al. 2008).

Radio Afterglows: GRB 970508 Frail et al. 2000, 1997, Waxman et al. 1998 First radio afterglow detection. Relativistic expansion measurement of fireball through diffractive scintillation. Measured flux lower than spherical prediction (jet like geometry) Bright and long lived afterglow followed over a year, E 0=5 x 1050 ergs. Density ~0. 5 cm-2, Equipartition e. B~e. E~0. 5

Radio afterglows: 030329 van der Horst et al. 2008, Pihlström et al. 2007, Taylor et al. 2004 Very bright radio burst. Constant density medium. Non-relativistic transition ~ 80 -200 days VLBI- relativistic expansion of fireball.

Synthetic Light Curve ee=0. 1 e. B=1%, EKE=1053 erg, p=2. 2 • 8 GHz light curve • • matches with sample. 1. 4 GHz challenges: JVLA, ASKAP, WSRT/Apertif will not detect. Higher frequencies favored. JVLA (high freq) and ALMA ideal. Expected large increase in detection. Chandra et al. 2012, Ap. J 746, 156

Synthetic Light Curve: density ee=0. 1 e. B=1%, EKE=1053 erg, p=2. 2 • Radio sample biased for n=1 -10 cm-3. • Weak emission at lower n. • Higher selfabsorption for higher n. • Explains why some bright GRBs dim in radio. Chandra et al. 2012, Ap. J 746, 156

Summary Radio afterglows explore unique territory. Detection rate unchanged in pre- and post-Swift phase. Very crucial in determining GRB properties. Reverse shocks give information about the ejecta. JVLA and ALMA are goldmines

Questions Explosion properties and progenitors of short GRBs: Radio explosion physics and local environment, Only 2 radio detections: Composition of GRB ejecta: baryonic or magnetic: Radio reverse shocks. Diversity of GRB population. High redshift universe through GRB observations: