Was the Christmas star a gamma ray burst?

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1 Was the Christmas star a gamma ray burst? Drejc Kopač Faculty of Mathematics and Physics University of Ljubljana 20. December 2011

2 Overview 1 Star of Bethlehem 2 GRBs quick overview Prompt GRB Afterglow SNe 3 GRB A: observations Gamma-ray emission X-ray emission Optical emission 4 GRB A: explanations Models Tidal disruption Supernova Similar events? 5 Conclusion

3 Story

4 Explanations Fulfillment of prophecy, Astronomical object, Astrological event, Pious fiction

5 Gamma-ray emission: light curves short vs. long

6 X-ray emission: prompt tail & afterglow Nousek et al. 2006

7 X-ray emission: prompt tail & afterglow Zhang et al. 2006; Canonical X-ray light curve

8 X-ray emission: prompt tail & afterglow Racusin et al. 2011

9 Optical emission: afterglow Fireball scenario: external FS synchrotron emission Kann et al. 2010, 2011

10 LGRBs & SNe Ibc: core collapse Optical bump Sparre 2011

11 LGRBs & SNe Ibc: core collapse Spectrum Sparre 2011 Modjaz et al. 2006

12 GRB A: redshift z No redshift!

13 GRB A: gamma-ray emission BAT data (T 90 > 2000 s): Thöne et al kev tot. fluence erg cm 2 Spectrum fit: cutoff PL (E pk = 38 ± 20 kev) or a BB (kt = 10.1 ± 1.1 kev) low S/N

14 GRB A: X-ray emission XRT data (light curve):

15 GRB A: X-ray emission XRT data (spectrum): Campana et al Thöne et al Accretion disk black body and a boundary layer PL and BB

16 GRB A: optical emission Optical light curve: Campana et al Faint afterglow: t t 0 = 1.6 hours, R = 22.1 ± 0.1, I = 21.5 ± 0.2 Reddening at later times (t t 0 20 days)

17 GRB A: optical image Optical image from GTC (10.4m): Thöne et al Faint host galaxy : r = 26.9 ± 0.14, g = ± 0.27

18 GRB A: optical spectrum Spectrum from GTC (10.4m): Thöne et al No emission feature in spectrum at z = (smooth blue continuum).

19 GRB A: models Two models: Who is right?

20 GRB A: movie vs.

21 GRB A: Tidal disruption Comets hitting the Sun Extragalactic models (GRBs, SNe, blazars) unlikely: total energy arguments, faintness of the optical counterpart and putative host Galactic models (X-ray binaries, magnetars and flare stars) ruled out: extreme faint quiescent counterpart, relatively high Galactic latitude Disruptive event involving a compact object. But: the rate of such event is rather low: NS hardly retains its original population of small bodies due to SN event.

22 GRB A: Tidal disruption Phenomenological model of tidal disruption fit: Campana et al After 20 days 500 hours: transition of the accretion disk to a cold solution

23 GRB A: Tidal disruption SED is best fit with DiskBB + COMPTT (boundary layer): Campana et al Emission from the accretion disk and the NS surface heated by the accreting matter, which reach the slowly rotating NS at boundary layer, where a large fraction of the accretion energy is released (Comptonization of soft photons).

24 GRB A: Supernova Very strange SN and very special case: Faintest SN associated with LGRBs Faintest host galaxy at z = 0.33 Sparse data with large spread!

25 GRB A: Supernova SN model: Thöne et al Fit with template broad-line Type Ic SN 1998bw The BB evolves from K at 0.07 days to 5000 K at 18 days

26 GRB A: Supernova From SN fit, one can obtain the redshift: Thöne et al Redshift consistent with the N H analysis.

27 GRB/XRF and GRB A Thöne et al GRB A: z=0.677

28 Conclusion Maybe the star of Bethlehem wasn t a star at all. (Neil Young)

Probes of Star Formation in the Early Universe

Gamma Ray Bursts Probes of Star Formation in the Early Universe Edward P.J.van den Heuvel Universiteit van Amsterdam &KITP-UCSB KITP, March 17, 2007 Age of the Universe: 13.7 billion years Age of our Milky