Cosmological Transient Objects

Poonam Chandra

Royal Military College of Canada

Raman Research Institute14th December 2010

Cosmological Transient Objects

Supernovae and

Gamma Ray Bursts

Supernovae and Gamma Ray Bursts

• Supernova energy 1029 more than an atmospheric nuclear bomb explosion.

• At the time of explosion, the supernova can shine brighter than the host galaxy consisting of billions of stars.

• In one month, a supernova can emit as much energy as Sun would emit in its entire life span of billions of years.

• GRBs: biggest source of gamma-rays in universe and 100 times more energetic than supernovae.

Outline (Gamma Ray Bursts)

• Challenges• How to meet the challenge: multiwaveband

modeling• Importance of radio observations• Our radio campaign and some results• Future of gamma ray burst science

Gamma Ray Bursts

• A big challenge when discovered in 1960s.• Gamma-ray signals for just a fraction of

seconds to at most few minutes.• Non-terrestrial origin • BATSE: isotropic

Meszaros and Rees 1997

Major breakthrough

• BeppoSAX: first detection of X-ray counterpart of GRB 970228.

• Optical detection after 20 hours.

GRB 970508: a watershed event

• X-ray BeppoSAX• Optical , z=0.835 => Cosmological• Scintillation: fireball model• Radio, late time- energetics

• GRB 980425/SN1998bw- massive star origin

Crisis: GRB 990123

• Assuming isotropy, the -g ray energies spanned three orders of magnitude: 3×1051 to 3×1054 erg

• Central engine energy requirements??

The GRB Energy Crisis circa 1999

Astrophysics at the Extremes, Dec. 15-17, 2009, Hebrew University

10

Stan Woosley says “I’m a very troubled theorist.”

erg 102M 542sun c

Piran, Science, 08 Feb 2002

ApJ 519, L7, 1999

Jet Signatures

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radio

opticalX-ray

jtFl

ux D

ensi

ty

time

-1t

-2t

-1/3t

Harrison et al. 1999

tjet

The GRB Energy Crisis Resolved

Frail et al (2001)

That was then…• The GRB energy crisis was resolved• GRB outflows are highly beamed (θ ~ 1-10

degrees)• Geometry measured from jet break signature in

light curves• Beaming-corrected radiated energies are

narrowly distributed around a “standard” value of ~1051 erg

• A host of other measurements (X-ray afterglows, broadband modeling, calorimetry) support this energy scale

• This energy scale is consistent with models of GRB central engines

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This is now… POST-SWIFT1. The mystery of the missing jets in the Swift era.2. The emerging population of hyper-energetic

events.3. The established class of sub-energetic gamma-

ray bursts.

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).

Radio Observations

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

Multiwaveband modeling

Radio afterglow statistics: 1997-2010

•1/3rd of all GRBs seen as radio afterglows since 1997-2010.•93 out of 244•46 out of 149 (post Swift)•No strong redshift dependence.•z<2 47/88• z>2 21/43 Chandra et al. 2011

Radio afterglow statistics: post-Swift

•1/3rd of all GRBs seen as radio afterglows since 1997-2010.•93 out of 244•46 out of 149 (post Swift)•No strong redshift dependence.•z<2 47/88• z>2 21/43 Chandra et al. 2011

Canonical radio afterglow light curve

GRB 070125 (Chandra et al. 2008)

• One of the brightest Swift burst with isotropic energy of 1.1x1054 erg.

• Followed extensively in X-ray, optical, mm and radio bands.

• In radio bands, observed for more than a year.

GRB 070125: Scintillation (Chandra et al. 2008)

Jet break in GRB 070125Chandra et al. 2008

• Chromatic jet break…

• Optical band, day 3• X-ray band, day 10• Explanation—

– Inverse-Compton Mechanism

Inverse-Compton in X-rays

Inverse Compton Scattering

• Possible explanation for the delay in jet breaks or chromatic jet breaks in various GRBs.

• Does not affect radio and optical bands but dominates in X-ray bands.

• More effective in high-density environments. Radio data is crucial.

GRB 070125: Highlights (Chandra et al. 2008)

• Diffractive scintillation- constrain the fireball size

• Chromatic jet break- Inverse Compton• Collimated g-energy 2.5x1052 erg.• Kinetic energy 1.7x1051 erg.

GRB 090423

• Highest redshift GRB at z=8.2• Highest redshift object of any kind known in

our Universe.• Must have exploded just 630 million years

after the Big Bang.

GRB 090423

• X-ray observtions: 73 s after detection• Optical observations: 109 s after detection• No optical transient.• Detection in J band onwards.• Photo-z=8.06+/-0.25• Spectral-z=8.23+/-0.08

Radio observations of GRB 090423(Chandra et al. 2010)

Detections - VLA: 8.5 GHz on Apr 25-

Jun 27.– 74 +/- 22 uJy at Δt~8 d– 2-hr integrations every 2

days– Data sets averaged (in UV

plane) to improve detection sensitivity

– Undetectable after Δt~65 d

PdBI: 95 GHz on Apr 23-24

– Castro-Tirado et al. report a secure source detection of 200 uJy (no error bar given)

Non-Detections - WSRT: 4.9 GHz

on May 22-23CARMA: 95

GHz on Apr. 25

IRAM 30-m: 250 GHz on Apr 25

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Multiwaveband modeling:(Chandra et al. 2010)

Broadband modeling

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• High energy burst exploded in constant density medium.

• No jet break occurred until day 50.

Reverse shock emission in GRB 090423

• Reverse shock emission at day 9 (time dilated)• After 1+z correction, reverse shock on day 1• Seen is 250 GHz data also at around 10 hours

(1+z corrected).• Implications for high Lorentz factor

Previous high redshift GRB 050904 z=6.26

Afterglow Properties –

– GRB 050904 (z=6.26). Both are hyper-energetic (>1051 erg) but they exploded in very different environments. (in situ n=600 cm-3 for GRB 050904)

– Large energy predicted for Pop III. Not unique.

– Low, constant density predicted for Pop III. Not unique.

– No predictions for θj, εB, εe & p

– Reverse shock detection in both GRBs

Canonical radio afterglow light curve

• Swift had expected to find many RS

• At most, 1:25 optical AG have RS

• Favored explanation– Ejecta are magnetized (i.e. σ>1). – Do not need to be fully Poynting-flux

dominated – Suppresses RS emission

• Does not explain why prompt radio emission is seen more frequently.

• About 1:4 radio AG may be RS• Possible Explanation: The RS

spectral peak is shifted out of the optical band to lower frequencies

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Kul

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i et

al.

(199

9)

Reverse shock in radio GRBs Chandra et al. 2010b

A seismic shift in radio afterglow studies

• The VLA got a makeover!• More bandwidth, better receivers, frequency

coverage• 20-fold increase in sensitivity• Capabilities started in 2010

• GRBs at higher frequencies where ISS is reduced• Measure polarization and rotation measures• Absorption lines possible (CO; see Inoue et al.

2007)

Future of GRB Physics

• Expanded Very Large Array (EVLA)• 20 times more sensitive than the VLA.

Future: The EVLA- accurate calorimetry

EVLA, 3-s, z=8.5 1 hr

EVLA, 3-s, z=2.5 1 hr

Future: Atacama Large Millimeter Array (ALMA)

Accurate determination of kinetic energy

Future: ALMA Debate between wind versus ISM solved

Future: ALMAReverse Shock at high redshifts

mm emission from RS is bright, redshift-independent (no extinction or scintillation) (Inoue et al. 2007). ALMA will be ideal.

Conclusions

• Multiwaveband modeling required to understand the GRB afterglow Physics.

• New class of hyperenergetic GRBs such as GRB 070125.• Star formation taking place even at 630 million years after

the big bang.• New explanation for the delay in jet breaks in Swift bursts• Radio and mm is crucial as they are unique in estimating

the accurate energy, density and type of medium.• Future lies with the EVLA and the ALMA.

Supernovae• Chandra, Dwarkadas, et at. 2009, ApJ 699, 388

– X-rays from the explosion site: 15 years of light curves of SN 1993J.• Nymark, Chandra, Fransson 2009, A &A 494, 179

– Modeling the X-ray emission of SN 1993J.• Patat, Chandra, et al. 2007, Science 317, 924

– Detection of circumstellar material in a normal Type Ia supernova.• Chandra, Ray, et al. 2005, ApJ 629, 933

– Chandra’s tryst with SN 1995N.• Chandra, Ray, Bhatnagar 2004, ApJ 612, 974

– The late time radio emission from SN 1993J at meter wavelengths.• Chandra, Ray, Bhatnagar 2004, ApJL 604, 97

– Synchrotron aging and radio spectrum of SN 1993J.

Collaborators for GRB work

• Dale Frail• Shri Kulkarni• Brad Cenko• Derek Fox• Edo Berger• Fiona Harrison• Mansi Kasliwal

THANKS