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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
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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.
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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).
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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
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Gamma Ray Bursts• Indicative of massive star
formation
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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
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Gamma Ray Bursts• Excellent probe of IGM and ISM at
high-z
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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.
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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
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Multiwaveband modeling of GRB 090423 (Chandra et al. 2010)
Last Chandrameasurement
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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
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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
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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
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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
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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%
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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
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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)
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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.
€
E K≈ 4 ×1053 erg
Even with jet break at t > 50 d
EK > 0.9 ×1052 erg
BUT not Unique!
Discussion on Progenitor star of GRB 090423 (z=8.26)
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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)
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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.
€
εB (%) ≈1.6 ×10−2
BUT not Unique!
Discussion on Progenitor star of GRB 090423 (z=8.26)
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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)
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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.
€
n ≈ 0.9 cm-3
BUT not Unique!
Discussion on Progenitor star of GRB 090423 (z=8.26)
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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)
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Discussion on Progenitor star of GRB 090423 (z=8.26)
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.
?€
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)
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Discussion on Progenitor star of GRB 090423 (z=8.26)
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. ?
?
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Discussion on Progenitor star of GRB 090423 (z=8.26)
• 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.
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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
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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
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• 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
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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
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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.
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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.
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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.
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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.
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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.
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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
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Discussion on Progenitor star
Signatures of Pop III progenitor (Heger et al. 2003):• 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.
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• 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?
Discussion on Progenitor star
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Radio Observations
• Late time follow up- accurate calorimetry• Scintillation- constraint on size• VLBI- fireball expansion• Density structure- wind-type versus constant
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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