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Swift Observations of GRBs

Swift Observations of GRBs. David Burrows The Pennsylvania State University. 20 November 2004. GRBs and Swift. UVOT. BAT. BAT. XRT. UVOT. XRT. Spacecraft. Swift Instruments. Burst Alert Telescope (BAT) 15-150 keV 2 sr field of view CdZnTe detectors

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Swift Observations of GRBs

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  1. Swift Observations of GRBs David Burrows The Pennsylvania State University

  2. 20 November 2004 GRBs and Swift

  3. UVOT BAT BAT XRT UVOT XRT Spacecraft Swift Instruments • Burst Alert Telescope (BAT) • 15-150 keV • 2 sr field of view • CdZnTe detectors • Most sensitive gamma-ray imager ever • Detect ~100 GRBs per year • X-Ray Telescope (XRT) • 0.2-10 keV • Few arcsecond positions • CCD spectroscopy • UV/Optical Telescope (UVOT) • 170 – 650 nm • Sub-arcsec positions • Grism spectroscopy • 6 UV/optical broad-band filters • 22nd mag sensitivity (filtered) • Spacecraft • Autonomous re-pointing, 20 - 75 sec • Onboard and ground triggers

  4. Short GRB FRED Fast Rise Exponential Decay Short GRB Swift GRBs (> 330 so far) 88% followed up with XRT/UVOT observations

  5. Beppo-SAX afterglows: de Pasquale et al. 2006, AA, 455, 813 GRB 990806 GRB 000529 GRB 000615 GRB 991106 GRB 000926 GRB 001109 GRB 000214 GRB 010214 GRB 010222 2e4 1e6

  6. GRB 060204B GRB 060211A GRB 060306 1e2 1e6 GRB 060413 GRB 060428A GRB 060502A GRB 060510A GRB 060510B GRB 060729 Swift X-ray Afterglows ~ 225 Prompt X-ray LCs

  7. Afterglow Statistics • XRT: • All Swift GRBs: • Detected 276/293 = 94% with XRT (observed @ T < 200 ks) • > 80% of the X-ray afterglows ever detected! • ~90% have prompt slews (< 300 s, excluding Aug-Oct 2007) • LGRBs: • Detected 253/262 = 97% with XRT (observed @ T < 200 ks) • Compare with 55 LGRB afterglows before Swift launch • Handful of long GRBs not detected by XRT • SGRBs: • Detected ~23/31 = 74% with XRT (observed @ T < 200 ks) • Compare with 0 SGRB afterglows before Swift launch • Optical: • UVOT: ~ 40% detection rate • Total optical: ~ 60% detection rate, ~ 33% with redshifts

  8. Key Swift Discoveries GRBs • > 240 GRBs with arcsec positions • ~ 100 GRBs with redshifts (>70% of world total) • 80% of world X-ray afterglows • Complex X-ray lightcurves and flares – see O’Brien and Chincarini talks this PM

  9. tj ~ 400 d θj ~ 67° !! Eγ ~ 3 x 1051 erg 1 year! GRB 060729 at z=0.54 (Grupe et al. 2008) Key Swift Discoveries GRBs • > 240 GRBs with arcsec positions • ~ 100 GRBs with redshifts • 80% of world X-ray afterglows • Complex X-ray lightcurves and flares • Jet breaks (or not…)

  10. Key Swift Discoveries GRBs • > 240 GRBs with arcsec positions • ~ 100 GRBs with redshifts • 80% of world X-ray afterglows • Complex X-ray lightcurves and flares • Jet breaks (or not…) • “Naked-eye GRB”: GRB 080319B (see session on Tuesday PM) GRB 080319B (Racusin et al. 2008)

  11. GRB 060218 (Campana et al. 2006) Key Swift Discoveries GRBs • > 240 GRBs with arcsec positions • ~ 100 GRBs with redshifts • 80% of world X-ray afterglows • Complex X-ray lightcurves and flares • Jet breaks (or not…) • “Naked-eye GRB”: GRB 080319B • First shock breakout from stellar surface: GRB 060218 / SN2006aj

  12. VLT GRB 071227 (D’Avanzo et al. 2007) Key Swift Discoveries GRBs • > 240 GRBs with arcsec positions • ~ 100 GRBs with redshifts • 80% of world X-ray afterglows • Complex X-ray lightcurves and flares • Jet breaks (or not…) • “Naked-eye GRB”: GRB 080319B • First shock breakout from stellar surface: GRB 060218 / SN2006aj • Short GRBs with large and small redshifts • Arcsecond localizations => evidence for compact mergers • New data hints at subclasses in redshift, offset, and progenitors

  13. GRB 060614 at z=0.125 (Gal-Yam et al. 2006) Key Swift Discoveries GRBs • > 240 GRBs with arcsec positions • ~ 100 GRBs with redshifts • 80% of world X-ray afterglows • Complex X-ray lightcurves and flares • Jet breaks (or not…) • “Naked-eye GRB”: GRB 080319B • First shock breakout from stellar surface: GRB 060218 / SN2006aj • Short GRBs with large and small redshifts • Arcsecond localizations => evidence for compact mergers • New data hints at subclasses in redshift, offset, and progenitors • Nearby long GRBs with and without SNe • Possible new classes of GRBs

  14. GRB 050730 at z=3.97 (Chen et al. 2005) Key Swift Discoveries GRBs • > 240 GRBs with arcsec positions • ~ 100 GRBs with redshifts • 80% of world X-ray afterglows • Complex X-ray lightcurves and flares • Jet breaks (or not…) • “Naked-eye GRB”: GRB 080319B • First shock breakout from stellar surface: GRB 060218 / SN2006aj • Short GRBs with large and small redshifts • Arcsecond localizations => evidence for compact mergers • New data hints at subclasses in redshift, offset, and progenitors • Nearby long GRBs with and without SNe • Possible new classes of GRBs • Metallicities of star forming regions in galaxies to record high redshift (z=6.3) using GRBs • Includes transitions never before seen

  15. Short GRBs • Major discovery of Swift is the first localizations of short GRBs, and the discovery that they occur in different environments than long GRBs • Consistent with origin from different progenitors (merging compact objects rather than collapsar)

  16. Long Bursts: collapsars Young (few million yrs) Star-forming regions Short Bursts: mergers Old (few billion yrs) Outside galaxies GRB Classification • Bimodal distribution of durations • Short, hard GRBs: mergers • Long, soft GRBs: collapsars

  17. ~35 Short GRBs (33 from Swift BAT)

  18. GRB 050509B 100x-1000x fainter than typical AG BAT: t-1.3 XRT: t-1.1 Chandra t90 = 0.04 s, Fluence = 2E-8 ergs/cm2 XRT counterpart in first 400 s, fades rapidly. 11 photons total. Location in cluster at z=0.226, near early-type galaxy. Possible NS-NS merger? XRT error circle on VLT image. XRT position is 9.8” from a bright elliptical galaxy at z=0.226 Gehrels et al. 2005, Nature

  19. GRB050709: Second Short GRB Afterglow • Discovered by the HETE-II satellite • X-ray counterpart found by Chandra X-ray Observatory • Optical counterpart found by ground-based telescopes • Located at edge of star-forming galaxy at z=0.16 Fox et al. 2005 Danish 1.54m La Silla telescope (Jensen et al. 2005, GCN 3589; Price et al. 2005, GCN 3612)

  20. Wiersema et al. 2005, GCN 3699 GRB 050724 WHT t90 = 1 s by BATSE definition. (But long soft tail.) 30x brighter than GRB 050509B. Optical transient located on edge of an early-type galaxy at z=0.257, L=1.7L*, SFR < 0.02 Mo/yr. Another old, nearby elliptical galaxy associated with a short GRB!!

  21. Late-time bump (~1/2 day) t-0.8 GRB 050724 No evidence of jet break, θj > 0.5 rad for reasonable jet parameters Grupe et al. 2006

  22. GRB 050813 t-2.05 ~30 photons

  23. GRB 050813 Possible association with elliptical galaxies in cluster at z~ 0.722 (or 1.8 – Berger)

  24. Swift Short GRBs without afterglows • GRB 050906: • t90 = 0.13 s • XRT observations began at T+79 s • No X-ray counterpart – very unusual • GRB 050925 (short, soft) • t90 = 0.07 s • XRT observations began at T+92 s • No X-ray counterpart – very unusual • GRB 051105A • t90 = 0.03 s • XRT observations began at T+68 s • No X-ray counterpart – very unusual • GRB 051114 • t90 = 2.2 s • XRT observations began at T+126 ks • No X-ray counterpart

  25. GRB 051210 flare t-2.57 Naked GRB Mangano et al. 2006 No clear optical counterpart or redshift, but near z=0.114 cluster

  26. GRB 060313 Energy injection t-1.49 Many small flares

  27. GRB 060313 • Small flares in later optical light curve. • Many small flares in early X-ray light curve. • Interpret as variable circum-burst medium, with cooling frequency dropping through X-ray band during orbital gap. Roming et al., ApJ, 651, 985

  28. 060614 Long vs short GRB energetics Swift GRBs 1055 1054 long GRBs Long GRBs, from Panaitescu 2005) 1053 1052 Eiso (erg) 1051 1050 1049 short GRBs 1048 1047 10-2 100 10-1 101 102 103 T90 / (1+z) (s)

  29. Fundamental questions on short GRBs • What can we hope to learn about short GRBs from X-ray afterglows? • What are the progenitors of short GRBs? • Are there subclasses of short GRBs? • How do short GRB afterglows differ from long GRB afterglows? • What can we learn about short GRB environments? • What can we learn about the central engines of short GRBs?

  30. Short GRB Environments: “normal” decays t-1.15 BAT t-1.22 t-1.13 XRT 050509B 051227 060121 (HETE-2) t-1.07 t-1.2 060502B 060505 • ~ 25% of sample • No evidence for decay of prompt emission => consistent with short duration of bursts • exception: 051227, which had a soft tail to the prompt emission • Simple afterglows without energy injection phase • Afterglows commence by beginning of XRT observations (~ 100 s after burst)

  31. Short GRB Environments: “canonical afterglows” t-1.20 t-1.49 t-1.20 t-1.49 t-0.8 060313 050724 051221A t-1.93 t-0.7 t-0.5 t-2.3 t-1..9 t-1.5 t-0.1 t-2.2 t-1.8 061201 060614 061006 • ~ 25% of sample • Evidence for decay of prompt emission in 3 bursts: 050724, 060614, 061006. • - All three of these have soft tails in the BAT data • All have evidence for energy injection phases • Afterglows commence by beginning of XRT observations (~ 100 s after burst)

  32. Short GRB Environments: “Naked” GRBs t-1.2 t-2.05 t-2.57 t-5.8 051210 050813 060801 t-2.3 Short GRBs without X-ray afterglows: 050906, 050925, 051105A, 051114, 070209, 070810B, 070923, 071112B, 080121 061210 Combining with the 9 non-detections of short GRBs with prompt slews, we have >13/33 possible “naked” short GRBs, vs 5/210 possible “naked” long GRBs. => Consistent with lower density environments for short GRBs.

  33. Short GRB Summary • X-ray afterglows similar to long GRBs, but fainter and less complex • Late central engine activity implied by flares and energy injection in X-ray afterglows • High incidence of naked GRBs => low density environments • “Missing” hosts • Ejections from hosts? • High redshift? • Possible subclasses: • Extended soft tails • Late central engine activity

  34. Short/hard Horvath et al. 2002, AA, 392, 791 Long/soft E. Nakar, 2006 Donaghy et al. 2006 GRB Classification The problem with GRBs is that we have no clear-cut emperical classification scheme: • Considerable overlap in durations and spectral properties between the “long” and “short” populations • Increasing sample of “short/hard” GRBs with long soft tails (~ 33%) • 050709, 050724, 051227, 060121, 061006, 061210, 070714B, 080123, 080503 • These often have t90 >> 5s as measured by Swift/BAT Gehrels et al. 2006

  35. Long Soft Tails of Short GRBs GRB 050709 Villasenor et al. 2005, Nature, 437, 855 Norris & Bonnell 2006, ApJ, 643, 266

  36. Long Soft Tails of Short GRBs GRB 050724 GRB 051227 Barthelmy et al. 2005, Nature, 438, 994

  37. GRB060505 • Weak burst that did not trigger BAT • Ground processing revealed weak source • Late notification and slew • t90 = 4 s • Optical transient in SF region of spiral galaxy (Sc-type) • No associated SN to very low limits • Either short GRB (Ofek et al.) or long GRB (Fynbo et al.) Ofek et al.

  38. GRB060614 • Duration: t90 = 102s => “long”/Type II • Initial hard pulse with longer soft tail: similar to several “short”/Type I GRBs (though tail is brighter, harder, and more variable in this case)

  39. GRB060614 Gal-Yam et al., Nature

  40. GRB060614 Gehrels et al. 2006, Nature

  41. GRB060614 Zhang et al. 2007, ApJ, submitted

  42. The enigmatic case of GRB 060614 The problem with GRBs is that we have no clear-cut emperical classification scheme: • Considerable overlap in durations and spectral properties between the “long” and “short” populations • Increasing sample of “short/hard” GRBs with long soft tails • 050709, 050724, 051227, 060121, 061006, 061210 • These often have t90 >> 5s as measured by Swift/BAT • Case of GRB 060121 (Donaghy et al.) => argument for multidimensional classification, new terminology (“short/long population GRBs”) • Case of GRB 060614 => suggestion for Type I/Type II classification (Zhang et al 2007, ApJ; Zhang 2006, Nature) • Duration: t90 = 102s => “long”/Type II • Initial hard pulse with longer soft tail: similar to several “short”/Type I GRBs (though tail is brighter and more variable in this case) • Location: outskirts of host galaxy => “short”/Type I • Lack of SN => short/Type I or unusual “long”/Type II • Lag-luminosity relation: small lag => “short”/Type I • Eiso ~ 1051 ergs, Eγ ~ 4 x 1049 ergs => intermediate between Type I and Type II

  43. z = 4.275 • Damped Lya • N(HI)=1022 cm-2 • n ~ 102 cm-3 • Z = 0.06 ZO • Mprogenitor < 25 MO . . Metallicity vs Redshift Keck Spectroscopy of GRB 050505 Berger et al. 2005

  44. Subaru spectrum of GRB 050904: z = 6.295 ± 0.002 NH=4E21 Kawai et al. 2006

  45. The Future of Swift • Selected as #1 mission in the 2008 NASA Senior Review: • In the next 3-4 years we will obtain • more high redshift GRBs • more GRBs with good optical observations, • more short GRBs, and • more unusual cases (like 061007, 060614, 070110, …) • Starting subthreshold trigger experiment to search for weak bursts in the noise • GLAST / Swift synergy • GBM: will provide MeV-range spectral data for many Swift GRBs • LAT: will discover very high energy (GeV) GRBs that can be localized by Swift (~ 1 / month) • Investigating possibility of rapid Swift responses to LAT GRBs • Enhanced LIGO (2009) • Will double detection range, may permit detection of inspiral sirens • Long-term: Advanced LIGO (c. 2013) • Simultaneous detection of short GRB by Swift and LIGO would provide “smoking gun” for merger picture • NS-NS inspiral out to 300 Mpc – up to 3/d • NS-BH inspiral to 650 Mpc

  46. Long-Term Future • Beyond Swift: the high z universe • Swift may be detecting high z bursts, but ground-based observations are required to identify them • SVOM • JANUS: identify high z GRBs and QSOs • Reionization • Star formation at high z • Xenia: High resolution spectroscopy of GRBs • Reionization • First stars • Cosmic Structure • WHIM

  47. JANUS • SMEX mission selected for Phase A studies (launch in mid-2012) • X-ray Flash Monitor (0.5-20 keV) + NIR Telescope (0.7-1.7 μm, R=14) • Optimized for detection and identification of high-z GRBs • > 50 GRBs with 5 < z < 12 • Star formation rate, finder for ground-based followup • 20,000 sq degree spectroscopic sky survey to discover > 400 QSOs @ 6 < z < 10

  48. Xenia • Instrumentation • Wide Field Monitor (similar to Swift BAT) • Wide Field Imager (similar to Swift XRT, but > 1° x 1°) • Wide Field Spectrometer (microcalorimeter, 0.7° x 0.7°) • GRB Monitor (MeV range)

  49. Xenia Xenia

  50. Summary • Swift has compiled a large database of bursts and their X-ray and optical afterglows, discovering • Complex X-ray afterglows • X-ray flares, implying long-lived central engine activity • Prompt, accurate localization of short GRBs -> mergers • Bright, high-z bursts • Swift has increasingly become the satellite of choice for multiwavelength, rapid-response Targets of Opportunity • CVs and novae • SNe • Galactic transients • AGN and blazars • Future prospects: • Swift/GLAST synergy • Swift/LIGO synergy -> compact mergers • JANUS, SVOM, and other proposed missions will focus on high-z

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