Toward the Progenitors of Short-Duration Gamma-Ray Bursts

1. Toward the Progenitors of Short-Duration Gamma-Ray Bursts Edo Berger − Harvard University The Prompt Activity of Gamma-Ray Bursts: their Progenitors, Engines, and Radiation Mechanisms − March 2011

2. Outline • The discovery of short GRB afterglows & host galaxies • Redshift distribution & galaxy-scale environments • Offset distribution & sub-galactic environments • Evidence for Kicks? • Rates • Prompt emission & afterglows • mini-, macro-, kilo-novae? • Gravitational waves Kouveliotou et al. 1993 Berger, E. 2011, New Astronomy Reviews, 51, 1

3. Short vs. Long GRBs BATSE − short:long = 1:3 Swift − short:long = 1:10

4. Long GRBs: The Death of Massive Stars Fruchter et al. 2006; Wainwright, Berger, & Penprase 2007 1. Exclusively in star-forming galaxies Wainwright, EB & Penprase 2007, ApJ

5. Long GRBs: The Death of Massive Stars 2. Offsets trace star formation in an exponential disk 3. Coincident with the brightest UV regions of their hosts Fruchter et al. 2006 Bloom et al. 2002 Wainwright, EB & Penprase 2007, ApJ

6. Short GRB Progenitor Models NS-NS / NS-BH • Broad delay-time distribution • Diverse environments / redshifts • “Kicks” • “Mini-SN”? • Gravitational waves Magnetars • Young systems • Star forming galaxies / nearby? • No “kicks”

7. Short GRB Progenitor Models WD/NS AIC • Delayed magnetar / BH formation • Diverse environments • No “kicks” WD-WD merger

8. Early “Smoking Guns”? Unambiguous association with an elliptical galaxy & no accompanying supernova 050509B ⇔ z = 0.226 z = 0.257 Berger et al. 2005 Castro-Tirado et al. 2005; Gehrels et al. 2005; Hjorth et al. 2005; Bloom et al. 2006; Prochaska et al. 2006

9. Afterglows Galore... Berger et al. 2007 Fong et al. 2011 Berger et al. 2009 Soderberg et al. 2006 D’Avanzo et al. 2009

10. ... and Host Galaxies Berger et al. 2007; Berger 2009

11. Host Demographics Ell ? SF “Host-less”

12. Host Redshifts z = 0.410 z = 0.438 z = 0.827 z = 0.915 z = 0.922 z = 1.130 Berger et al. 2007; Berger 2009; Fong et al. 2011 ~1/2 of all short GRBs are located at z > 0.7 ⇒ 〈age〉≤ 7 Gyr

13. Host Redshifts Nakar 2006; Guetta et al. 2006; Berger et al. 2007 • Progenitor Ages: • P(τ) ∝ τn with n ~ −1* • τ ~ 3-4 Gyr, σ ~ 1 * MW: NS-NS systems have n ~ −1

14. Host Galaxies: Star Formation Rates Berger 2009 Short GRB hosts have lower specific star formation rates than long GRB hosts; they trace the general galaxy population

15. Host Galaxies: Metallicities Berger 2009 Short GRB hosts have higher metallicities than long GRB hosts; they trace the general galaxy population

16. Host Galaxies: Stellar Masses Leibler & Berger 2010 Short GRB hosts have higher stellar masses than long GRB hosts Do Short GRB progenitors track stellar mass alone?

17. Stellar Population Ages Leibler & Berger 2010 τshort,SF ~ 0.3 Gyr τshort,E ~ 3 Gyr τlong ~ 60 Myr Short GRB hosts (including star-forming) have older agesthan long GRB hosts

18. Do Short GRBs Track Stellar Mass? SF? Leibler & Berger 2010 Rell ~ 6×10−12 per M☉ Rsp ~ 2×10−11 per M☉ Early-type hosts track stellar mass, but star-forming hosts have lower masses than expected; star-forming dominate (1:1 expected)

19. Sub-galactic Environments • Are short GRBs associated with young or old stellar populations within their hosts? • Is the distribution of offsets indicative of “kicks”? Fong, Berger, & Fox 2010

20. Sub-galactic Environments: Light Fraction Fong, Berger, & Fox 2010 Fruchter et al. 2006; Kelley et al. 2008 Short GRBs trace low luminosity regions of their hosts; track optical (mass) better than UV (SFR)

21. Sub-galactic Environments: Offsets Fong, Berger, & Fox 2010 • Short GRB offsets are ~5x larger than for long GRBs • Good agreement with model predictions for NS-NS binaries

22. Is there Evidence for Large Kicks? Berger 2010 Of 20 short GRBs with optical afterglows, 5 have no coincident hosts to >26 mag.

23. Is there Evidence for Large Kicks? Berger 2010 • Underlying hosts >26 mag + fainter afterglows (high redshift) • No hosts + fainter afterglows (kicks / low density)

24. Is there Evidence for Large Kicks? z ~ 0.1-0.5 high-z: same galaxies ⇒ bimodal redshift distribution Offsets: low chance probability at ~10” ⇒ 50-100 kpc ⇒ Berger 2010

25. Kicks? Berger 2010 Extension to larger offsets provides better agreement with the NS-NS merger models. Not expected in other models.

26. Rates ℜSHB > 10 Gpc−3 yr−1 Nakar et al. 2007 Rell ~ 6×10−12 M☉−1 Rsp ~ 2×10−11 M☉−1 Leibler & Berger 2010 ρ* ~ 6×1017 M☉ Gpc−3 ⇒ ℜDNS ~ 17−290 Myr−1 (95%) τ−1 > 0.4-1.2 Myr−1 Kalogera et al. 2004

27. Short GRB Prompt Emission Short GRB090510 Long GRB09092B Abdo et al. 2009b Abdo et al. 2009a Fermi prompt emission properties similar to long GRBs (GeV delay)

28. Short GRB Afterglows Short GRB050724 Long GRBs Barthelmy et al. 2005 Nousek et al. 2006 X-ray afterglows are similar to those of long GRBs

29. Short GRB Afterglows Berger et al. 2000 Short GRB050724 Long GRB000301C Berger et al. 2005 Radio/optical afterglows similar to long GRBs ⇒ Afterglow & engine physics are similar to long GRBs

30. Short GRB Afterglows: 050724 Eγ,iso ≈ 4 × 1050 erg EK,iso ≈ 2 × 1051 erg θj > 25 deg n ≈ 0.01−0.1 cm−3 εe ≈ εB ≈ 0.03 Barthelmy et al. 2005 Berger et al. 2005 • Extended X-ray emission • X-ray flare @ 1 day

31. Short GRB Afterglows: 051221 Soderberg et al. 2006; Burrows et al. 2006 θj ≈ 7 deg Eγ ≈ 1.5 × 1049 erg EK ≈ 0.8 × 1049 erg n ≈ 1.5 × 10−3 cm−3 εe ≈ εB ≈ 0.2 • X-ray plateau @ 0.1 days • Radio reverse shock • No supernova

32. Short GRB Afterglows: Energetics Nakar 2007; Berger 2007; Gehrels et al. 2008; Nysewander et al. 2009 Energy scale of short GRBs is generally lower than for long GRBs

33. Short GRB Afterglows: CSM Density Soderberg et al. 2006 The circumburst densities (~0.1 pc) are lower than for long GRBs

34. Mini-SN / Macronova / Kilonova? vej ~ 0.1 c Mej ~ 10−3 − 10−1 M⊙ fr.a. ~ 10−6 } Lp ~ 1041 erg/s tp ~ 1 day • neutron-rich ejecta: • tidal tails (Mej < 0.1 M⊙) • AD outflows (Mej ~ 10-3−10-2 M⊙) Decompressing neutron-rich ejecta ⇒ R-process (A ~ 100) Li & Paczynski 1998; Janka et al. 1999; Lee & Kluzniak 1999; Ruffert & Janka 2001; Rosswog et al. 2004; McLaughlin & Surman 2005; Rosswog 2005; Shibata & Taniguchi 2006; Metzger et al. 2008; Giacomazzo et al. 2009; Lee et al. 2009; Rezzolla et al. 2010 Courtesy: Brian Metzger

35. Mini-SN / Macronova / Kilonova? EVLA Strongly suppressed if n < 1 and/or β < 1 and/or E <1051 Mildly-relativistic ejecta (or off-axis jet) will interact with ISM to produce a isotropic radio signal (cf radio SNe) * at d ~ 300 Mpc Nakar & Piran 2011

36. Gravitational Waves ⇒ ⇒ ⇒ LIGO: Blind DNS detections: ~20 Mpc Advanced LIGO: Blind DNS detections: ~0.2-0.3 Gpc Triggered Short GRB: ~0.5-1.3 Gpc ⇒ Detection rate of ~few per year Nakar et al. 2006; Berger et al. 2007

37. Summary I • The progenitors of short GRBs are not massive stars; they belong to an evolved population with a wide range of ages • The short GRB rate in star-forming galaxies is elevated relative to that in ellipticals ⇒ A channel that tracks SF? • If related to the star formation activity, the typical delay time is ~0.3 Gyr; the typical delay time in ellipticals is ~3 Gyr • The short GRB volumetric rate, combined with the inferred rate per unit stellar mass, indicate a temporal rate of >1 Myr−1 per galaxy (consistent with the MW DNS rate)

38. Summary II • The local environments of short GRBs exhibit: • large offsets (in agreement with NS-NS models) • better correlation with optical (mass) than UV (SF) • low density (~ 0.001-1 cm−3) • Short GRBs with optical afterglows and no coincident hosts are likely due to kicks (bimodal redshift distribution?) • Short and long GRB afterglows are similar, but lower E, n • Orphan afterglow and mini-SN (optical/radio) detections extremely challenging ⇒ γ-ray triggers are essential! • It is crucial to have a γ/X-ray mission capable of ~arcmin positions in conjunction with GW detectors.