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GRB Spectral-Energy correlations : perspectives and issues

G. Ghirlanda + G. Ghisellini , L. Nava , Z. Bosnjak , C. Firmani, I. Cabrera , F. Tavecchio & A. Celotti giancarlo.ghirlanda@brera.inaf.it. GRB Spectral-Energy correlations : perspectives and issues. Why ?. 1) tools for understanding GRB physics.

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GRB Spectral-Energy correlations : perspectives and issues

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  1. G. Ghirlanda + G. Ghisellini, L. Nava, Z. Bosnjak, C. Firmani, I. Cabrera, F. Tavecchio & A. Celotti giancarlo.ghirlanda@brera.inaf.it GRB Spectral-Energycorrelations: perspectives and issues Why? 1) toolsforunderstanding GRB physics 2) toolstostandardize GRB energetics cosmology G. Ghirlanda – 2008 Nanjing Gamma Ray BurstConference

  2. Epeak Eiso0.57 Epeak Eg1.05 Liso Ep1.62 T45-0.49 2red=7.2 (60 dof) s=0.2 Q. Spectral-energycorrelations: truephysics or selectioneffects? 2red=0.89 (23 dof) s=0.08 2red=0.7 (16 dof) s=0.06 Amati et al. 2002 Ghirlanda et al. 2004 Firmani et al. 2005 Physicalinterpretation (e.g. Rees & Meszaros 2006, Thomson, Meszaros & Rees 2006) Studyselectioneffects Liso t - 1.05 Liso V3.0 2red=9.6 (34 dof) 2red=100 (46 dof) Liso0.57  Epeak1.85 (I) GRBswith z (II) + GRBswithout z (IV) Thermalcomponent? Reichart et al. 2000 Ramirez-Ruiz & Fenimore 2000 Yonetokuet al. 2004 Norris et al. 2000 (III) Stillnotconvinced ? (V) news

  3. Epeak – Eiso Amati et al. 2002, 2006, Navaet al. 2006, Ghirlanda et al. 2008 … etc 76 GRBswith z and Epeak 35 before Nov. 2004 41 since Nov. 2004 9 SAX (GRBM+WFC) 5 CGRO (Batse) 15 Hete-II(Fr.+WXC) 20 Konuset al. 27(/41) Swift (BAT)

  4. Evolutionwithredshift? NO Slopeof the 76 GRBs

  5. REST FRAME GRBswith F>Flim Ep [Emin, Emax] Instrumental selectioneffcts OBSERVER FRAME obs frame Ep-fluencecorrelation : (Lloyd, Petrosian & Mallozzi 2000; Lambet al. 2005; Sakamotoet al. 2005) No segregation in z in the obs. frame

  6. obs Obs Frame  Epeak - F low fluence – intemediate/high Epeak Selectioneffects High fluence – intemediate/low Epeak

  7. Trigger threshold: whichfluxto trigger? Spectralthreshold: whichfluencetomeasureEpeak? (Band 2003, 2006) Assume GRB spectrum Background Detector response a=1 b=2.3 EpeakFbol • the error on Epeak(fit) < 100% in 97.7% ofcases • Fitwith single powerlawisexcluded at 2σ

  8. Trigger threshold: whichfluxto trigger? Spectralthreshold: whichfluencetomeasureEpeak? (Band 2003, 2006) Ghirlanda et al. 2008 BATSE couldnotdetectthisburst BATSE coulddetectedthisburst BATSE certainlydetectedthisburst and measuredEpeak

  9. CONCLUSIONS (I) 76 GRBs (updatedtoOct. 2007) with z and spectrum 1) No evolutionof the Epeak-Eisocorrelationwithredshift. 2) A correlationisfound in the observer frame 3.1) no z segregation 3.2) Instrumentalselectioneffect: a) trigger threshold notbiasing b) spectralanalysisthreshold yes on Swift no on Batse/Sax

  10. HOW ispopulated the Ep-Fluenceplane? Q: are there intermediate/low fluencebursts (i.e. betweenthosewith z and the spectralanalisyscurves)??

  11. HOW ispopulated the Ep-Fluenceplane?  AddGRBswithoutredshift From the literature Sakamotoet al. 2005 Butleret al. 2007 (freq) Kanekoet al. 2005 GCNs (Golenetskiet al. …) Navaet al. 2008 submitted

  12. ExtendtheBrightBatse GRB sample (Kanekoet al. 2005)tolowerfluences Build a complete spectral sample of BATSE bursts down to ~2x10-6 erg/cm2 Peakenergydistribution Ep = 160 keV Bright BATSE Fainter BATSE

  13. BATSE bursts

  14. Outliersof the Epeak – Eisocorrelation 6% of BATSE bursts are outliers Navaet al. 2008 submitted

  15. The Ep-Liso “Yonetoku” correlation The Ep-Eiso “Amati” correlation Isotropicluminosity Isotropicenergy

  16. The Ep-Fluxplane and the outliersof the Ep-Lisocorrelation Navaet al. 2008 submitted

  17. CONCLUSIONS (II) Ep-Fluence or Ep-Peakflux show strong correlations Addburstswithoutredshifts (+ a complete BATSE sample) Strong Ep-Fluencecorrelation Strong Ep-Peakfluxcorrelation The 20?? Ep-Eisocorrelationwillhave a differentslope & largerscatterbutmaybenotfor the Ep-Lisocorrelation 6% ofoutliersof the Ep-Eiso 0.3% ofoutliersof the Ep-Liso

  18. Stillnotconvinced ? Are the spectral-energycorrelationsrevealing a physicalprocess or simply due toselectioneffects? Liang, Dai & Wu 2004 notedthatanEp-Lisocorrelationholds WITHIN single bursts!

  19. Stillnotconvinced ? Are the spectral-energycorrelationsrevealing a physicalprocess or simply due toselectioneffects? Wehavestudied the timeresolvedspectraof BATSE GRBswithmeasuredredshifts

  20. Ep-LisoisequivalenttoEp(t)-Liso(t) Ep-Lisocorrelationfoundwithtimeintegratedspectraholdsalsowithin a burst!! Ep-Liso “Yonetoku” Physicaloriginforthis ! Bosnjaket al. 2008 (tobesubm.)

  21. (4) Interpretation – Thermal BB Interpretation of the <Epeak>Eg,iso0.5 “Geometrical” models: Eichler & lenvinson 2005a,b; Toma et al. 2005 “Radiative” models: Rees & Meszaros 2005; Tompson 2006; Thompson, Meszaros & Rees 2006 If the spectrumofGRBsisdominatedby a thermalbalck body componentthen the luminosityisnaturally LINKED to the peakenergy. EvidenceofBlack Body in GRBs: Ghirlanda, Celotti, Ghisellini 2003  980326, 970111, 911118, 910807, 910927 [Spectrumisthermalblack body in the initalphase (~2 sec), later a non-thermalcomponentdominates.] Bosnjak, Celotti, Ghirlanda 2005  990413 Ryde 2005, 2006  FitwithBlack body + Powerlaw

  22. Thermalcomponents in GRB spectra Black Body + powerlawfits Band modelfits

  23. Thermalinterpretationof the Amati relation Timeintegratedspectrum = sum oftimeresolved Timeresolvedspectra (BB+PL) 5 GRBsdetectedby BATSE and withWFC data the BB+PLfitto the BATSE data isinconsistentwith the X-ray (WFC) data. A single Band modelis the best fit. Ghirlanda et al. 2007

  24. Last slide … more News: the Ep-Egcorrlation Preswift-erabursts Swift era bursts (up to March 2007) Swift era burstsof the last year Jet Breaksfrom the Optical Ghirlanda et al. 2007

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