COLLABORATORS: Dale Frail, Derek Fox, Shri Kulkarni, Fiona Harrisson, Edo Berger, Douglas Bock, Brad Cenko and Mansi Kasliwal

Poonam ChandraRoyal Military College of Canada

The most distant Cosmological

Explosion

25th Texas symposiumHeidelbeg, GermanyDecember 10th, 2010

COLLABORATORS: Dale Frail, Derek Fox, Shri Kulkarni, Fiona Harrisson, Edo Berger, Douglas Bock, Brad Cenko and Mansi Kasliwal

Gamma Ray Bursts• Flashes of Gamma-Rays for short

duration (fraction of a second to few minutes).

• Most energetic cosmological explosions in the Universe after the Big Bang.

• A gamma ray burst can shine brighter than the rest of the gamma-ray Universe.

• Followed by long frequency counterparts lasting on longer timescales- afterglow.

Multiwaveband modeling• Long lived afterglow with powerlaw decays• Spectrum broadly consistent with the synchrotron.

• Measure Fm, nm, na, nc and obtain Ek (Kinetic energy), n (density), ee, eb (micro parameters), theta (jet break), p (electron spectral index).

Gamma Ray Bursts• Detectable at high redshift

because of their extreme luminosities.Ionized f(HI) ~ 0

Neutral f(HI) ~ 1

Reionized f(HI) ~ 1e-5

Gamma Ray Bursts• Indicative of massive star

formation

First stars in the high-z universe

Barkana and Loeb (2007)

• Initially formed from dark matter mini-halos at z=20-30 before galaxies

• Pop III: M~100 Msun L~105 Lsun T~105 K, Lifetime~2-3 Myrs

• Dominant mode of star formation below 10-3.5 Zsolar

• Can be found only via stellar deaths

Gamma Ray Bursts• Excellent probe of IGM and ISM at

high-z

GRB 090423: z=8.26

Tanvir et al. 2009

• Detected by Swift-BAT on 23rd April 2009.• At T0+73s : X-ray begins. Detection• At T0+109s: Optical begins. No detection• At T0+20min: UKIRT begins. Detection in K band.

Radio Observations of GRB 090423

• By our group:– CARMA observations, 95 GHz on day 1, 450+/-180

uJy– VLA observations starting day 1 until day 65– First VLA detection on day 7.

• By other groups:– PdBI, day 1 in 90 GHz. Detection 200 uJy.– WSRT, 5GHz. No detection– IRAM 30-m, 250 GHz. No detection

Multiwaveband modeling of GRB 090423 (Chandra et al. 2010)

Last Chandrameasurement

Semianalytic constraints:GEOMETRY OF THE OUTFLOW

€

Quasi - spherical geometry : ν m ∝ t−3 / 2, IR peak 0.08d ⇒ radio peak 50d

Jet - like outflow : ν m ∝ t−2, IR peak 0.08 d ⇒ radio peak 10d

€

Quasi - spherical geometry : ν m ∝ t−3 / 2, IR peak 0.08d ⇒ radio peak 50d

Semianalytic constraints:IMMEDIATE ENVIRONS

€

Before jet - break

For constant density : Fν , max ∝ constant

For wind - like density : Fν , max ∝ t−1/ 2

€

Before jet - break

For constant density : Fν , max ∝ constant

For wind - like density : Fν , max ∝ t−1/ 2

Semianalytic constraints:ELECTRON ENERGY INDEX

€

t−1.10

€

t−1.35

€

FIR (t) ∝ t−1.10 and FX−ray (t) ∝ t−1.35

consistent with ν IR < ν cooling < ν X -ray

and FIR (t) ∝ t−

3( p−1)

4 and FX−ray (t) ∝ t−

(3p−2)

4

for p = 2.46

Constraints:

• Negligible host extinction (Av<0.08, Tanvir et al. 2009)

• High energy burst with E/4p~2.5 x 1052 erg. (X-ray around 10 hrs, Freedman and Waxman 2001)

• Quasi-spherical outflow• In a constant-density medium• nIR < ncooling < nX-ray, electron energy index

p=2.46

Multiwaveband modeling using Yost et al. 2004

€

Ek = 3.8−1.7+9.8 ×1053 erg,

Eγ =1053 erg

n0 = 0.9 cm-3

εe = 0.28

εB = 0.02%

€

Ek > 8.4−3.7+21.6 ×1051 erg,

Eγ > 2.2 ×1051 erg

t j > 45 d, ϑ j > 0.21 rad

n0 = 0.9 cm-3,εe = 0.28,εB = 0.02%

Discussion on Progenitor star

• Signatures of Population III star:Low metalicity and the absence of dust extinction

NIR spectroscopy

Time is the enemySpectra taken 1-3.5 days later. AG has faded +5 magNeed satellite with NIR imaging and spectroscopy capabilities JANUS

Signatures of Pop III progenitor:• Hyper-energetic explosion • Low magnetic field• Low density HII region

– Strong radiation pressure from Pop III star– creates low density (1 cm-3) constant density region

(10 pc)

• Low metallicity• No published predictions on other afterglow

parameters.

Discussion on Progenitor star of GRB 090423 (z=8.26)



(10 pc)


parameters.

€

E K≈ 4 ×1053 erg

Even with jet break at t > 50 d

EK > 0.9 ×1052 erg

BUT not Unique!




(10 pc)


parameters.




(10 pc)


parameters.

€

εB (%) ≈1.6 ×10−2

BUT not Unique!




(10 pc)


parameters.




(10 pc)


parameters.

€

n ≈ 0.9 cm-3

BUT not Unique!




(10 pc)


parameters.





(10 pc)


parameters.

?€

Required Z < 10-3.5ZΘ

For GRB 090423

Z ~ 0.04 ZΘ (Salvaterra et al. 2009)

But measurement not robust and suffers from many uncertainties

(see Chandra et al. 2010 for detailed discussion on this)




(10 pc)


parameters. ?

?


• Afterglow properties not sufficient enough to suggest different kind of Progenitor for GRB 090423.

• More high-z GRBs required to make a more coherent picture.

Observational Challenge

• High z GRBs are rare–Theory. <10% Swift GRBs at z>5

(Loeb & Bromm 2006)–Only 3 GRBs with redshift > 6• GRB 090423 (z=8.2)• GRB 080913 (z=6.7)• GRB 050904 (z=6.3)

27

Reverse shock emission from GRB 090423 and implications for future observations

Reverse shock seen in GRB 050904 (z=6.26) too

RS seen in PdBI data too on day 1.87

• mm emission from RS if observed few hours after the burst is bright, redshift-independent as effects of time-dilation compensates for frequency-redshift. (no extinction or scintillation). ALMA will be ideal with 75 uJy/4 min sensitivity.

29

Inoue, Omukai, Ciardi (2007)

Reverse shock emission from high-z GRBs and implications for future observations

A seismic shift in radio afterglow studies with EVLA

• With EVLA and 20-fold increase in sensitivity, better constraints on geometry, energy and density. No assumptions of geometry required at high redshifts.

z=2.5, EVLA 3σ, Δt=1 hr

z=8.5, EVLA 3σ, Δt=1 hr

CONCLUSIONS• Radio emission discovered from the highest known

redshift object in the Universe.• The best-fit broad-band afterglow model is a quasi-

spherical (θj>12o), hyper-energetic (1052 erg) explosion in a constant, low density (n=1 cm-3) medium.

• The high energy and afterglow properties of GRB 090423 are not sufficiently different from GRBs at moderate redshift to suggest a different type of progenitor model (e.g. Pop III).

• EVLA and ALMA are coming (soon). They will be important tools for both detecting and studying the first generations of stars in the early universe.





















Comparison with other high-z GRBs

• GRB 050904 at z=6.26Both high energy bursts.

• Density environment:Density for GRB 050904 ~ 600 cm-3 (Frail et al. 2006)Density for GRB 090423 ~ 1 cm-3

• Geometry of the outflow:GRB 050904, jet break on day 2.6 (Frail et al. 2006)GRB 090423, no jet break until day 50, Quasi-

spherical


Signatures of Pop III progenitor (Heger et al. 2003):• Hyper-energetic explosion• Low magnetic field• Low density HII region


(10 pc)


parameters.

• GRB 050904 was a jet-like outflow and exploded in high density region, so most likely progenitor was a normal Pop II star.

WHAT ABOUT PROGENITOR OF GRB 090423?


Radio Observations

• Late time follow up- accurate calorimetry• Scintillation- constraint on size• VLBI- fireball expansion• Density structure- wind-type versus constant

Redshifts of important objectsObject Name Redshift

Milky Way z=0.0Virgo Cluster z=0.004Quasar 3C273 z=0.158“Era of Galaxy formation”

z=1-2

Most distant quasar z=6.43Most distant galaxy z=6.96GRB 090423 z=8.2First Stars appear z=20-30Cosmic Microwave Background (CMB)

z=1089

Big Bang z->∞40

Documents

COLLABORATORS: Dale Frail, Derek Fox, Shri Kulkarni, Fiona Harrisson, Edo Berger, Douglas Bock, Brad Cenko and Mansi Kasliwal