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Grossan grbtelescope+bsti


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Grossan grbtelescope+bsti

  1. 1. Understanding Prompt Emission from Gamma-Ray Bursts: Fast, Early, and Multi-Colored Bruce Grossan Energetic Cosmos Laboratory, Nazarbayev University & UC Berkeley ECL Collaborators: George Smoot, Eric Linder, Magzhan Kistubaev
  2. 2. I. What is a GRB? • GRB stands for “gamma ray burst” • This talk is almost exclusively LONG type GRBs 2
  3. 3. Long Gamma-Ray Bursts(GRBs) • 15-200 keV Swift BAT light curves (LCs) • Heterogeneous in every way • LCs by Kas McLean 3
  4. 4. Long GRB • Most Common GRB • Associated with Star- forming regions, SNe • Typical z ~ 2 • LGRBs > 2 s, softer spectrum than others 4
  5. 5. More GRB Basics • Most energetic events in the universe ‣ Distant: z = 8.2 (090423); zphoto= 9.4 (090429b) • Can be seen to z~12 with large detectors • Gamma-Ray Bursts (GRB) last msec – hr. • Measured up to GeV • Long Type GRB sometimes massive star collapse SNe ‣ GRB 980425 ==> SN1998BW 5
  6. 6. Gamma-Ray Bursts: Cosmic Mystery • We have models of: Explosion, Jets, Gravitational wave emission... But the emission mechanism remains unknown! 6 Z=12 GRB limit Farther than first stars • The Universe’s most energetic explosions • Bright: can be seen beyond even first stars
  7. 7. ~0-102 s ≳102 s Prompt Afterglow GRB Cartoon Picture Mészáros: • GRB are so bright and variable because of relativistic be
  8. 8. LogOpticalFlux-> Log Time -> Most GRB Have Optical Afterglows Prompt X/𝛾-ray light curves bright (wide field instruments), highly variable, inhomogeneous shapes LGRB typically ~ 40-100 s OPT AG MEASUREMENTS COMMON - Hundreds observed, dozens per year. (Flares ignored here) Physics well understood to be interaction of a jet with ISM. [Early or prompt phase not measured for most GRBs]
  9. 9. Optical Prompt Measurements Difficult & Rare • Hundreds of GRBs have been observed in X/𝛾 bands. • Hundreds of GRB afterglows, the interaction of the blast and surrounding ISM, have been observed in almost every band. – This is NOT the burst (jet) emission. • Prompt emission ≲ 102 s. 10 • Typical optical telescopes require ≳102 s to point... prompt optical observations rare Not Observable by Typical Optical Telescopes
  10. 10. Current Prompt Optical Observations • Conventional Telescopes Too Slow • Wide-Field Instruments – Great Successes! (e.g. Pi of the Sky, Raptor) – LIMITED SENSITIVITY~ 10th mag • Medium-Field Fast instruments – Great Successes! Polarization measurements! – Limited Sensitivity - • e.g. ROTSEIII - 45 cm - R ~ 16.9 mag 10 s ~ 3/ yr. • e.g. MASTER-NET - 40 cm - 12-14 mag 10 s w/polarization – NO OPERATIONAL SIMULTANEOUS MULTI-COLOR INSTRUMENTS • Note that filter wheels are useless for this rapidly-varying source 11
  11. 11. Either of first two could be sub-dominant, and not seen LogFlux-> Log Time -> But note, at Least 3 Opt Peaks Possible Prompt internal shocks Meszaros & Rees (Flares ignored here) Early External Rev. Shock (MR-SP) Afterglow -external forward shock
  12. 12. II. Best Available Prompt Data 13
  13. 13. 14 • 080319A was in same part of the sky just before, so many instruments were open, observing – Lucky! Prompt optical emission finished in ~ 100 s – most telescopes cannot open or point in less than minutes. • Incredibly Bright! – Nearly 5th mag! – Amazing light curve by TORTORA, vidicon instrument (Molinari+06) – Detection by Pi-of-the-sky Above instruments not sensitive to any but most exceptionally bright bursts. Best Prompt Light Curve: 080319B
  14. 14. 080319B Light Curve 15 • Racusin+08 • Two-component jet proposed, 1 (𝜞~103) for ultra- bright prompt optical, second (low 𝜞) for afterglow, consistent with decay slope breaks and mis-matches
  15. 15. Time-Resolved Optical Data • Such rich data available in NO OTHER burst in > 10 years of Swift!
  16. 16. Spectrum in 3 time periods 17 Just one optical point, doesn’t fit!!! What about in here? Fall steep or shallow? Rich data here; many channels, small errors Spectra Commonly fit by Band function, 2 PL with exponential cutoffs. 10 s integration about: Green: T0+3 s Blue: T0+ 17 s Red: To+32 s
  17. 17. GRB130427A 18 • Uncorrelated 𝛾, Opt • Opt >> 𝛾 (same as 080319b) • Vestrand+14: Reverse Shock dom- inates first ~ 50s (shock propagating backwards toward jet origin; decay slope –1.7) but… non-unique fit , several parts not fit. • ==> baryon-dominated jet (reverse shock traveling into a magnetic jet produces weak Optical*) • Note optical spectrum not available to confirm! * Zhang & Kobayashi 2005; Narayan et al. 2011; Giannios et al. 2008
  18. 18. Two more famous prompt optical • Other famous cases • Some might have 𝛾 correlation with optical, some not. – Look at 990123: Could this just be a delay, like 080319b, but longer? • Really need better optical time resolution 20
  19. 19. MOST GRBs Extinguished! • Most GRBs have little optical emission (30/77 UVOT) – BUT VIRTUALLY ALL GRBs HAVE IR EMISSION1 • Median extinction AV~0.35 mag2; range 0.5 - 5 mag1 • If you cannot study extinguished GRB, you may have some kind of bias against the most active star- forming regions • If you can detect extinguished GRB, you will detect many more, ~ 1.6X more than UVOT3! 21 1 - Perley et al. 2009; 2- Covino et al. 2013; 3-Grossan et al. 2014,
  20. 20. III. Recent Work on Spectra 22
  21. 21. 110205A - 260 s burst 23Guiriec+16: ApJL 831, L8; • Guiriec fits 3 components: nTh1, nTh2 = PL w/expo cutoff Th = Thermal (photo- shperic) • Optical is key; claims related to high energy component nTH2 • Very long, bright in Swift, Suzaku/WAM (MeV) • Fits suggest photospheric emission • Prompt UVOT (very rare!) resembles WAM (MeV)
  22. 22. 110205A - Guiriec Model • NO optical spectral data here!! • Fit is plausible …But look at -huge gap to optical! -huge band from just one point in optical! • -> Need optical Spectrum for more convincing fit. 24 Guiriec+16: ApJL 831, L8;
  23. 23. Mechanism? • “Standard” Internal Synchrotron Shock Model1 (ISS; log slope +1/3) – Equipartition roughly gives correct 𝜈 f 𝜈 peak energy(2) – Most observations inconsistent; may be unphysical(1) • Either multiple or variable slopes, components/mechanisms required – Log Slopes 20-200 keV have broad distribution, ~0.1±0.35 – Thermal photospheric component pretty clear in some GRB – Extrapolation to optical off (+ or -) by orders of mag • More recent fits explore Maxwellian vs. PL e– N(E), still disagree whether synchrotron acceptable or not. (3) • Conclusion: Not just heterogeneous, but also no consensus. 25 1. Rees & Me ́sza ́ros 1994, see Piran 2005 2. Ghisellini, Celotti, Lazzati, 2000 MNRAS 313,1 . Note they state that correct time-averaging gives slope -1/2, inconsistent with observations. 2. Burgess arXiv 1705.05718 vs. Axelsson & Borgonovo 2015 MNRAS447,3150; Yu et al. 2015 A&A, 583, A129
  24. 24. Scientific Opportunity • Optical Slope carries important information about emission mechanism • Break Frequency encodes information about the physics of the blast, including remission and electron energy. 27 Shen & Zhang 2009
  25. 25. Prompt Optical Spectrum, Light Curve Add Important Information • Test Extrapolation of 20-200 keV component – Optical Brighter than Extrapolation: Must be an added component – Optical Fainter: Must be break between optical & X • Important Tool: 𝛾 / Opt Correlation – correlated variability indicates same location, mechanism, and contrary – Want instrument with high time resolution! • Spectral Slope within Optical – Indicates mechanism of optical component • Self-absorption frequency1, 𝜈a – If synchrotron: Gives B, e- thermal Lorentz factor, radius of emission. – If photospheric: thermal Lorentz factor (energy dissipation of jet) 28(1) Shen & Zhang 2009 MNRAS 398,1936 frequency (Hz)-> 𝜈a
  26. 26. SIMPLE EXPERIMENTAL GOAL For burst sample covering wide range of properties, • measure optical-X/𝛾 light curve correlations • measure broad-band optical spectral shape, including absorption frequency 29 Not Possible with Current Instruments • limited by time resolution • limited by filter-wheel non-simultaneous colors
  27. 27. IV. How to Observe GRBs in the Prompt Phase 30
  28. 28. 32 How to Observe GRBs in Prompt Phase Swift Monitors GRBs in γ rays Blue Camera Red Camera IR Camera Sends alert via GCN (internet) in ~ 2 s, elescope Rapidly Points – Fast (< 10s response) – Simultaneous “blue”, “red”, IR cameras
  29. 29. Enabling Technologies • Faster Telescopes (direct-drive, computer-control of motors) • EMCCDs - allow high time resolution, with high QE and negligible electronic noise penalty 33
  30. 30. Modified 700mm Telescope • Can point anywhere in sky in < 8 s – Test data on sky 10/16 • CDK design with Two Nasmyth Ports – Can operate a triggered search with one instrument, have another used for other programs 34 Try movie IMG_1254.MOV
  31. 31. Multi-Channel Simultaneous Observations • Separate waveband to each camera via dichroics • High time resolution without noise penalty via Electron Multiplied CCD cameras 35 CAD design rendering
  32. 32. Burst Simultaneous Three-Channel Instrument (BSTI) • B,R Bands: EMCCD Cams + Blue, Red Filter • H-band Camera • H2RG (HgCdTe) sensor, cryostat + Lyot Stop + LPT Cooler (no consumables) – 3rd channel to identifies absorption frequency or curvature – allows study of extinguished bursts (most GRB extinguished; Prochaska+09, ApJL 691, L27) 36 Additional mirrors not shown for clarity. Dichroics EMCCD Cams IR Cam Cooler Final design Prof. Spitas NU Engineering- in progress.
  33. 33. Optics Design Complete • Ray Trace By L. Scherr Corrector Lens Corrector Lenses Dichroics Dichroics Camera sensor
  34. 34. Why EMCCD? • Electron Multiplied CCD – Each pixel’s signal is multiplied before read by up to 5000X – Effective read noise ~ 10-2 e- – Many frames co-added with negligible read noise • No penalty for sub-second time resolution • Same quantum efficiency as CCD • ~300 ms/frame 1024X1024 13 µm pixels • We estimate > 6 mag dynamic range in our operation scheme 38
  35. 35. Performance • 5-sigma Sensitivities 39 B R H 20.9 mag/10s 20.6 mag/10 s ~17.0 mag/20 s • 700 mm aperture telescope, high-QE sensors, good sampling of PSF, KPNO-like sky • Actual performance will vary.
  36. 36. Can we detect prompt emission? • Distribution of prompt brightness not well known- measurements not uniform • We do have a uniform early time (afterglow) sample from UVOT, t~ 110-170 s. Gives sensitivity required to detect prompt optical at least as bright as afterglow onset. 40 Conversion of W to R assumes: source log slope -0.75, median from Covino+13 Av=0.35 mag at source, Av=0.08 mag MW, z= 1.8, sample median. Brightness at end of prompt phase ROTSE10s Swift10s Master10s • Our Telescope will go much fainter than any afterglow in 10 s. • R ≤ 20 will detect much fainter than any afterglow in 10 s.
  37. 37. Estimated Annual Detection Rate • For a conservative, realistic rate (including clouds, etc.) we scale from ROTSE-III values, and from Early Brightness distribution – Not an accurate detection number, but, an accurate rate of measurements much more sensitive than early afterglow brightness. • We expect our IR channel to boost detection rate by factor of 1.6 due to extinction • Uncertainty dominated by weather! 41 Detections Upper Limits Total Optical 4.3 8.7 13 IR 6.9 6.1 13
  38. 38. Color-Color gives Slope, 𝜈a • Different slopes separate well on color-color plane • If between our bands, break frequency, 𝜈a, determined. 42 White = no 𝜈a feature Green = 𝜈a @ c/1.3 µm Red= 𝜈a @ c/1.0 µm 1.0 µm feature H B R 1.3 µm feature H B R No feature H B R Photometry techniques, calibration, now being optimized by M. Kistubaev, NU masters student
  39. 39. Dust Evaporation • LGRB associated with dusty star forming regions • GRB expected to vaporize dust throughout typical star forming cloud(1,2) • Typical cloud size ~ 10's of light sec • Time-dependent extinction measurement would • confirm calculations of dust density, evaporation, probe local environment • Solves excess gas absorption problem - Too much X-ray absorption for blue, low-extinction afterglow(3,4,5) • Need time-dependent spectral slope starting earlier than most previous measurements 44 t=60s t=0s t=30s t ---> 60s IR B Flux(mag)--> (1)Waxman, E., & Draine, B. 2000, ApJ, 537, 796 (2) Perna, R., Lazzati, D., & Fiore, F. 2003, ApJ, 585, 775 (3) Galama& Wijers 2001, ApJL, 549, L 209 ; (4)Stratta+04, ApJ, 608, 846 (5)Schady+07, MNRAS, 377, 273; Perley+09, AJ, 138, 1690
  40. 40. • Given extinction curve, band ratio gives extinction • Intrinsic slope given by final, unchanging colors • Extinction in individual star system at high-z for first time! (SMC Extinction; source log slope = –0.75; NGRG bands) Measuring Extinction Grossan et al. 2014, PASP, 126, 885
  41. 41. Summary: 1 Experiment, 3 Big Topics 1. Measurement of prompt optical-IR broad-band slopes, never done before, will be a substantial advance in understanding GRB emission mechanisms. 2. Measurement of the SSC absorption frequency, 𝜈a, never done before, will give new information about the physical conditions in GRB Jets, including radius of emission, magnetic field strength, electron energies, etc. 3. Measurement of dynamic dust extinction, never done before, will solve the excess X-ray absorption problem, and allow study of dust around a single star, separate from galactic dust, in star-forming regions at z> 1. 46
  42. 42. Thank You for Listening! 47