GAMMA RAY BURSTBOOT CAMPRobert NemiroffMichigan Tech

GRB Boot Camp: AbstractGamma Ray Bursts (GRBs) are the furthest explosions known. As suchthey are valuable probes of energetic explosions and fluctuatingbeacons seen through nearly the entire intervening universe. Althoughalmost every physical mechanism behind GRBs is debated, leadingtheories will be reviewed including expansion physics and candidateprogenitor objects. The phenomenology of GRBs will be reviewedincluding prompt emission, afterglows, common light curve features,and candidate standard candles. Searches for GRB coincidences withdetectors sensitive to neutrinos, gravitational radiation, cosmicrays, and extremely high energy photons will be reviewed. Searches forgravitational lensing by intervening dark matter and Lorentzinvariance violations by intervening quantum foam will be reviewed.Relevant parts of the lecturer's own research will also be brieflymentioned.

Know Your Lecturer (Highlights)The consistency of cosmology and BATSE number versus brightness relation

• Wickramasinghe, Nemiroff, et al. 1993, Astrophys. J. 411, L55

Gross spectral differences between bright and dim GRBs• Nemiroff, Norris, et al. 1994, Astrophys. J. 435, L133

Detection of signature consistent with cosmological time dilation in GRBs• Norris, Nemiroff et al. 1994, Astrophys. J. 424, 540

The 75th Anniversary Astronomical Debate on the Distance Scale to GRBs• Nemiroff 1995, Pub. Astron. Soc. Pacific 107, 1131

The Pulse Scale Conjecture and the Case of BATSE Trigger 2193• Nemiroff 2000, Astrophys. J. 544, 805

Limits on cosmological supermassive objects from millilensing search in GRBs• Nemiroff, Marani et al. 2001, Phys. Rev. Lett 86, 580

Possible impact of GRB detector thresholds on cosmological standard candles• Shahmoradi, Nemiroff, 2011, Mon. Not. Roy. Astron. Soc. 411, 1843

Bounds on Spectral Dispersion from Fermi-Detected GRBs• Nemiroff, Connolly et al., 2012, Phys. Rev. Lett 108, 1103

GRBs: Suggested readings• Wikipedia: http://en.wikipedia.org/wiki/Gamma_ray_bursts

• Short: Astronomy Outline• http://astronomyonline.org/cosmology/grbs.asp

• Medium: Unveiling the Secrets of GRBs, Gomboc, A 2012• http://arxiv.org/abs/1206.3127

• Long: The Physics of Gamma-Ray Bursts, Piran, T. 2004,• http://arxiv.org/abs/astro-ph/0405503

GRBs: Why Study GRBs?To better understand …

• Star and galaxy evolution in universe

• Nature of the intervening universe

• Physics of the expanding fireballs

• Physics of the prompt explosion

GRBs: Outline• Phenomenology

• Prompt emission• Afterglows• Coincident emission searches

• Physical Mechanisms• Candidate progenitor objects• Physics of expansion

• Probes of the Universe • Star formation history • Cosmological expansion history• Dark matter & quantum foam

GRBs: Outline• Phenomenology

• Prompt emission• Afterglows• Coincident emission searches

• Physical Mechanisms• Candidate progenitor objects• Physics of expansion

• Probes of the Universe • Star formation history • Cosmological expansion history• Dark matter & quantum foam

GRBs: Prompt emission• GRBs are triggered in the hard X-ray and soft γ-ray

• Triggering emission episode called “prompt emission”• ~5% of GRBs have a “precursor” up to tens of seconds earlier

• Why are GRBs not triggered in optical light?• Background is too high• Occasional “orphan afterglow”

• Why are GRBs not triggered in hard γ-rays?• Signal is too low

• Prompt optical and soft X-ray sometimes also detected

GRBs: Present Missions• Swift, Fermi, AGILE, INTEGRAL• Tens of ground-based counterpart chasers

• Find and track optical, IR, radio counterpart• Find redshift

• InterPlanetary Network (IPN)• Solar system scattered satellites with small detectors• Time delays yield high precision locations• Current IPN members:

• Earth (Many: e.g. Fermi, Swift) • Mercury (MESSENGER) • Mars (Odyssey)• L1 (Konus-WIND)

GRBs: Unpredictable Flashes• What is seen:• Variability:

• Isotropy:

science.hq.nasa.gov

GRBs: The Long and the Short• Plot of time separation: Bimodal

Norris, J. P., Stanford talk

GRBs: Visible in other ways?

• Neutrinos• Ice Cube, etc.

• Gravitational radiation• LIGO, etc.

• Very High Energy Gamma Rays• Milagro, HAWC, etc.

• Visible light• “orphan afterglows”, LSST, etc.

GRBs: History• USA looking to verify nuclear test ban (in space)

• 1960s• Ian Strong: “If it scintillates, fly it!”

• First model: Stirling Colgate (predates first GRB detection)• First astronomer consulted: Vera Rubin

• Cosmology vs. Galactic debate• Paczynski vs. Lamb 1995• 75th anniversary of the Shapley – Curtis debate• Same location!

GRBs: Outline• Phenomenology

• Prompt emission• Afterglows• Coincident emission searches

• Physical Mechanisms• Candidate progenitor objects• Physics of expansion

• Probes of the Universe • Star formation history • Cosmological expansion history• Dark matter & quantum foam

GRBs: Outline• Phenomenology

• Prompt emission• Afterglows• Coincident emission searches

• Physical Mechanisms• Candidate progenitor objects• Physics of expansion

• Probes of the Universe • Star formation history • Cosmological expansion history• Dark matter & quantum foam

GRBs: Progenitor Models• Create your own GRB model

• Show off your physics prowess!• Be cited by your friends!

• But how?• Take your current field of research• Find a scenario that can generate great bursts of energy• Find a way for it to create gamma rays

• Or not!• Kludge with unknown progenitor rates• Publish!

• Hundreds of GRBs models have been published

GRB: Progenitor Models

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Leading Long GRB Progenitor ModelCore collapse supernova • Wolf-Rayet star (M > 50ish Msun)• Iron core• Seen as Type Ic• Furthest redshift ~9• Leaves a black hole (unconfirmed)

Host Galaxies • Blue, high star formation• Low metalicity

Image: Y. Grosdidier (U. Montreal) et al., WFPC2, HST, NASA

GRBs: Connection to Supernovae• Long GRBs• GRB 980425 = SN 1998bw • GRB 030329 = SN 2003dh• Many others suspected

Image: S. Holland, J. Hjorth, J. Fynbo (Survey of Host Galaxies of GRBs Team), ESA, NASA

Leading Short GRB Progenitor ModelColliding neutron stars• Less numerous than LGRBs• Not seen coincident with supernova (as yet)• Furthest redshift ~ 1

Host Galaxies• High diversity of types

Illustration: Dana Berry, NASA

GRBs: Physics of Expansion

• Many mechanisms hotly debated• Key problems

• How to liberate so much energy • How to efficiently convert kinetic energy to photons

• Expansion speeds must be relativistic• Or optically thick gamma-rays create primarily e-e+ pairs

• Synchrotron radiation• Charged particles deflected by B fields emitting photons

• Inverse Compton scattering• Charged particles up-scattering photons

GRBs: After the central engine• Beamed shocks: Internal: prompt; External: afterglow

Image: Piran, T., Nature 422, 268-269 (20 March 2003)

GRBs: Expanding Shocks• Fireball Expansion phases & the “jet break”

Image: Nakar & Piran, New Astronomy, 8, 2, 2003, Pages 141–153

GRBs: Outline• Phenomenology

• Prompt emission• Afterglows• Coincident emission searches

• Physical Mechanisms• Candidate progenitor objects• Physics of expansion

• Probes of the Universe • Star formation history • Cosmological expansion history• Dark matter & quantum foam

GRBs: Outline• Phenomenology

• Prompt emission• Afterglows• Coincident emission searches

• Physical Mechanisms• Candidate progenitor objects• Physics of expansion

• Probes of the Universe • Star formation history • Cosmological expansion history• Dark matter & quantum foam

GRBs: Probe of Star Formation History

• Direct information on stars in early universe• Unique!

• Must originate from SOME type of star• How early did massive stars form? (back to z=9 at least)• Properties of host galaxies – where do GRB stars reside?

GRBs: Star formation probe

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GRBs: Cosmological Expansion History

Candidate Standard Clocks• Duration (e.g.: T90)• Minimum fluctuation time

Candidate Standard Candles• Peak flux, Fluence• Lag (between energies)• Variability • Epeak : ”Amati Relation”• Constraints = weak

• GRB sample, detection threshold effects, need more nearby GRBs • (e.g.: Mörtsell & Sollerman 1005, JCAP)

GRBs: Cosmological Expansion History

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GRBs: Probe of Massive Dark Matter

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GRBs: Probe of Quantum Foam(Possibly significant signal well below lPlanck)

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Very Preliminary: Might interest Sabine(Signal below lPlanck unlikely)

GRBs: Destroyers of Life• Instant media attention!• Should Earthlings fear future bright GRBs?

• Needs to be within ~3000 light years for affect• Observed brightness distribution extrapolated to extremely bright

• Nearby GRB affects Earth every 5M years? 100M? • Long GRBs too metal poor to occur in our Milky Way galaxy?• Ordovician–Silurian extinction event 450M years ago (?)

• What would happen?• Depends on distance to explosion• Secondary radiation• Ozone depletion• Smog winter

GRBs: Missions

• Past: Vela(s), CGRO (BATSE), BeppoSAX

• Current: Swift, Fermi, AGILE, INTEGRAL

• Future: Space-based Variable Object Monitor (SVOM)• France & China, Launch in 2015 (?) • See: http://arxiv.org/abs/1005.5008

• Possible Future: • Lobster, Pharos, Edge, LOFT, UFFO Pathfinder

Gehrels, N. et al., Lobster presentation, GSFC, 2012

GRBs: Breaking News Sources

• AAS email list-server• GCN Circulars

• Best for latest news• Web page and email list-server• http://gcn.gsfc.nasa.gov/gcn3_archive.html

• arXiv.org• astro-ph.HE

GRBs: My Research• GRBs consistent with cosmology

• Time dilation• Spectral offsets

• Lensing searches with GRBs• Limiting cosmological dark matter

• Modeling pulses of GRBs• Searching for cosmological dispersion in GRBs

• Sometimes called “Lorentz Invariance violations”• Sometimes called “Spacetime foam effects”

Surprise: Philosophy Slide!

Why study astronomy?

• Defense: better bombs, lasers, detectors• Engineering: more underlying physics: better mousetraps• Entertainment: philosophical why, where, and how

• Of Life & the Universe