Afterglow Population Studies from Swift Follow-up of Fermi-LAT - - PowerPoint PPT Presentation

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Afterglow Population Studies from Swift Follow-up of Fermi-LAT - - PowerPoint PPT Presentation

Jul 11, 2023 230 likes •383 views

Afterglow Population Studies from Swift Follow-up of Fermi-LAT GRBs J. L. Racusin (NASA/GSFC) S. R. Oates (MSSL-UCL) P. Schady (MPE), J. McEnery, V. Vasileiou, E. Troja, N. Gehrels (NASA/GSFC) Deciphering the Ancient Universe,

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SLIDE 1
  • J. L. Racusin (NASA/GSFC)
  • S. R. Oates (MSSL-UCL)
  • P. Schady (MPE), J. McEnery, V.

Vasileiou, E. Troja, N. Gehrels (NASA/GSFC)

Afterglow Population Studies from Swift Follow-up

  • f Fermi-LAT

GRBs

“Deciphering the Ancient Universe”, Kyoto, April 19-23, 2010

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SLIDE 2

The Fermi-Swift Era of GRB Science

  • Fermi

– GBM (8 keV - 40 MeV) - detect ~250 GRBs/year (~450 total) – LAT (20 MeV - 300 GeV) - detects ~10 GRBs/ year (17 total, <10% of GBM GRBs observed)

  • New features observed (delayed onset of

LAT emission, extra power-law spectral component, temporally extended emission) – see also Kouveliotou talk & Ohno talk

  • Swift-BAT (15 keV - 150 keV) - detects ~100 GRBs/

year

  • 65 simultaneous BAT/GBM triggers (19 w/

redshifts, as of Dec 2009)

  • nly 1 BAT/GBM/LAT detection to date (GRB

090510)

GRB 090902B: Abdo et al. (2009)

P r e l i m i n a r y

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SLIDE 3

Extended Emission

  • >50% of LAT GRBs have >100 MeV

emission that lasts significantly longer than prompt emission decaying as a power-law -> Extended Emission

  • Possible interpretations?

– Afterglow

  • Ghisellini et al. 2009
  • Kumar & Barniol Duran 2009

– Jet Photosphere

  • Toma et al. 2010

– Hadronic Models

  • Asano et al. 2009

– Leptonic Models

  • IC, SSC

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GRB 090902B: Abdo et al. (2009) GRB 090510: De Pasquale et al. (2010) GRB 080916C: Abdo et al. (2009)

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SLIDE 4

The Fermi-Swift Era of GRB Science

  • Afterglows - GRBs observed by both Swift & Fermi can have

spectral coverage over as much as 10 orders of magnitude (not including ground based NIR/radio) – currently only a simultaneous BAT/LAT trigger (e.g. GRB 090510) can have early observations – 8 detected in XRT follow-up (10 observed after > 12 hours) – 7 detected in UVOT follow-up (10 observed after > 12 hours) – all afterglows detected by XRT have led to ground based redshift measurements

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Preliminary

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SLIDE 5

Population Studies

  • XRT Swift afterglow sample

– Sample and characterization techniques from Racusin et al., 2009, ApJ, and Racusin PhD Thesis

  • UVOT Swift afterglow sample

– Sample and normalization technique from Oates et al., 2009, MNRAS, and Oates PhD Thesis

  • Compare Swift follow-up of LAT GRBs to large well studied

BAT GRB sample in order to learn about special properties of LAT bursts – Temporal properties – Luminosity – Energetics

  • Only using GRBs with redshifts
  • BAT/GBM bursts through end of 2009
  • LAT bursts include all detected bursts (including last week’s

GRB 100414A)

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Sample Statistics Sample Statistics XRT UVOT BAT 148 49 GBM/BAT 18 11 LAT/GBM 8 5

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SLIDE 6

LAT/GBM/BAT GRB Afterglows

Swift-XRT Swift-UVOT X-ray afterglows clustered in Luminosity (except SHB GRB 090510) UV/optical less clustered, tending toward bright (except SHB) *not yet corrected for host galaxy extinction

XRT afterglows analyzed in methods described in Racusin et al. (2009) UVOT afterglows analyzed in methods described in Oates et al. (2009)

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Preliminary Preliminary

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SLIDE 7

Long vs Short Bursts

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Swift-XRT Swift-UVOT short long

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SLIDE 8

LAT/GBM/BAT X-ray Afterglows

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Swift-XRT

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SLIDE 9

LAT/GBM/BAT Optical Afterglows

Swift-UVOT

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SLIDE 10

Redshift

  • No significant

differences in redshift distributions

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Energetics

  • On average LAT Eiso > GBM Eiso >

BAT Eiso

  • No jet breaks in Swift
  • bservations of LAT X-ray or
  • ptical afterglows

– maybe GRB 090510 or just short burst X-afterglow fast falling morphology – maybe GRB 090328A is all post-JB (McBreen et al., 2010, arXiv:1003.3885)

  • LAT GRB collimation corrected

energies ≳1052 ergs! – not even including extra spectral power-law component – see also Cenko et al., 2010, arXiv:1004:2900

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SLIDE 12

Energetics

Includes Jet Break Pre-Jet Break? Includes Jet Break Pre-Jet Break?

Long bursts Short bursts

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SLIDE 13

X-ray vs γ-ray - Efficiency?

  • LAT GRBs are most energetic, but

not most X-ray luminous – Why are the LAT GRBs clustered in X-ray luminosity? – Different efficiencies?

  • Why do LAT bursts have later jet

breaks than typical Swift bursts?

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SLIDE 14

Conclusions

  • Even with very small number statistics (6-7 LAT GRBs), quantifiable

similarities and differences between the LAT/GBM/BAT GRBs – LAT GRBs - brightest end of luminosity function, or a different population?

  • LAT has detected some of the most energetic (gamma-ray) prompt

emission of GRBs over the last 20 years – Where are these GRBs in the Swift sample?

  • Larger fraction are bright in X-ray/optical for LAT than BAT

– Due to simply larger initial energies? – Related to > 100 MeV extended emission?

  • X-ray afterglows of LAT bursts are brighter than average, but not at

the brightest end of Swift sample – Does this suggest brightest BAT bursts could have been bright in LAT too? (maybe not causally connected) – All of those brighter than the brightest LAT X-ray afterglow

  • ccurred before Fermi launched (include many notable well-

studied Swift GRBs)

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