1 Short GRBs - and other recent developments in GRBs Tsvi Piran ( HU, Jerusalem) Dafne Guetta (Rome Obs.)

2 92 GRBs detected (~100 per year) 92 GRBs detected (~100 per year) 72 XRT detections out of 79 observed 72 XRT detections out of 79 observed 20 UVOT detections out of 68 observed 20 UVOT detections out of 68 observed (42 detections ground-based + UVOT) (42 detections ground-based + UVOT) Swift BATUVOTXRT

3 Short GRBs

4 Short Bursts n ~ 1/3 of BATSE long bursts. n short =0.4

5 Understanding sGRBs The key to answering these questions is precise positions enabled by the discovery of long-lived afterglows. How far away are they? Redshift distribution, rates How much energy do they release? Isotropic vs. collimated (opening angles) Lifetime of the central engine Radiative efficiency / afterglow energy Non-relativistic ejecta? In what type of environment are they located? host galaxies, offsets circumburst density and profile

6 Afterglows Panaitescu et al The afterglows are expected to be fainter as a result of a lower energy deposit (and possibly lower density if large kick)

7 The Internal-External Fireball Model Internal Shocks  -rays cm External Shock Afterglow cm Relativistic Outflow Inner Engine 10 6 cm

8 Short GRB Afterglow Searches Hurley et al Pre-Swift searches limited by large error boxes and delayed triggers OpticalRadio

9 GRB b Gehrels et al F  = 9.5  erg/cm 2 T 90 = 40 msec 11 photons detected by XRT   9.3  radius (90%)

10 GRB b Swift/XRT position intersects a bright elliptical at z = (but also contains >10 higher redshift galaxies) ; No optical/radio afterglow Bloom et al Castro-Tirado et al Gehrels et al Hjorth et al IF IF elliptical host  Progenitors related to an old stellar population Kulkarni et al. 2005

11 GRB b Kulkarni et al  =0.5  =0.05 Hjorth et al. 2005

12 GRB Villasenor et al Short-hard spike Soft bump (no oscillations) Roughly equal energy in each component Hjorth et al Afterglow discovered with Chandra, followed up from ground and with HST; no radio host is an irregular, star-forming galaxy at z = 0.16 Fox et al z = 0.16 Was the progenitor a massive star? Was b a chance coincidence?

13 GRB Parameters*: E ~ 5  erg n ~ 0.01 cm -2  e ~  B ~ 1/3 Fox et al Hjorth et al Lack of SN detection supports a non-massive star origin * but, lack of radio detection  degenerate solutions

14 GRB Barthelmy al ms 100 s T 90 = 3  1 s keV keV F   6  erg/cm 2 (short peak) F   7  erg/cm 2 (soft tail) flare 1 flare 2 flare 3 t -7 t -2.5

15 GRB Berger et al Radio/optical/NIR/X-ray afterglow z = jet with  ~ 10 o E      erg  100x lower than long GRBs Blastwave & engine physics are likely the same but with a lower E Flare 3 also detected in the optical  energy injection into the FS

16 GRB Berger et al Prochaska et al Definitive association with an elliptical galaxy* Star formation rate at the position of the GRB is < 0.05 M  /yr  old stellar population (no H  >1 Gyr)  NS-NS/NS-BH merger? *The secure association lends support to the association of b with an elliptical

17 Gladders & Berger in prep. z = 0.72 Magellan PANIC+LDSS3 GRB Gladders & Berger: a cluster at the position of the X-ray afterglow, z ~ 0.72 (Berger 2005; Prochaska et al. 2005) F   = 1.24  erg/cm 2 T 90 = 0.6 s z  1.8  Age < 3 Gyr

18 GRB B BAT - 30 ms duration - very weak, 2x10 -8 erg/cm 2 Spacecraft slew in 52 sec XRT - faint source, fading - 11 cnts = 1x erg/cm 2 /s VLT image Hjorth et al. Gehrels et al Host: - cD Elliptical - K = L = 3 L* - z = SFR < 0.2 M O yr -1

19 GRB The Full Monty Host: - Elliptical - L = 1.7 L* - z = SFR < 0.02 M O yr -1 BAT ms hard spike - 6x10 -7 erg/cm 2 fluence Afterglow - bright fading x-ray afterglow with flares - detected by Chandra days after GRB - optical & radio Barthelmy et al. 2005

20 GRB BAT - T 90 = 0.6 s - weak, ~1x10 -7 erg/cm 2 Spacecraft slew in 100 sec XRT - faint source, fading - no OT or RT BAT Possible association with galaxy cluster at z = 0.722

21 Short GRB Summary Conclusions: Short GRBs have >10 3 lower E iso than long GRBs Association with low SFR hosts argues against collapsar origin Name Redshift Afteglow Host E iso ( keV ) What might it be? (erg). SHB ? no slew ? SHB050509B XT Elliptical 1x10 48 NS-NS merger SHB050709* XT, OT SF galaxy 6x10 49 NS-NS merger SHB XT, OT, RT Elliptical 3x10 50 NS-NS / NS-BH merger SHB  XT ? (cluster) 2x10 50 ? NS-NS merger SHB ? 0.03 ? ? galaxy ? ? minimal afterglow SSB ? ? in gal. plane - ? possible new SGR SHB051105A ? ? - - ? minimal afterglow * HETE Ia:CC  sGRB:lGRB (Bloom)

22

23 Pre-History n TP 92 : Bursts from mergers lag after SFR n Mao, Narayan & TP 94: short =0.4 n Cohen & TP 95, TP 94: Z max short  0.5 n Katz & Canel 96: short =0.4 Z max short  0.5 The observed short bursts are significantly nearer than the observed long ones.

24 Rates from Flux n N(>F) Number of bursts with flux >F  Rate as a function of z Luminosity function n(z) Rate as a function of z  (L)  Luminosity function {

25 Rates from Flux n Number of bursts with flux >F n Rate as a function of z n Luminosity function n Maximal redshift for detection of a burst with a luminosity L given the detector’s sensitivity p.

26 Guetta & TP 05a,b

27 Evidence for an old population From Nakar, Gal Yam & Fox 05 Kulkarn i & C ameron Red elliptical z=0.258 L=1.6 L * SFR<0.03 M  yr -1 Host of GRB Keck/LGSAO/Narrow Camera K’ band

28 Time lag p(  ) – probability for a time lag  TP 92, Ando 2004

29 Within the context of NS mergers expect p(  )  1/  (TP 92) Within the context of NS mergers expect p(  )  1/  (TP 92)

30 Selection effects ? Short Too Long

31 Comparison with Swift and HETE II short bursts ? X ? X? X X? X X X

32 From Nakar, Gal Yam & Fox 05

33

34 n What did we learn from all that:

35 Two populations???

36 Correlation between sGRBs and nearby IRAS Galaxies? Tanvir et al z < 0.025

37 Luminosity function and Rates ~10 /Gpc 3 /yr  80 mergers /Myr Galaxy* *with beaming L*~ erg/sec Comparable to the estimated rate of mergers (e.g Kalogera 04)

38 Luminosity function and Rates ~10 4 /Gpc 3 /yr  8  10 4 mergers /Myr Galaxy Nakar, Gal-Yam, Fox 05, Nakar, Gal-Yam, Fox 05, L*~ erg/sec Weakly constrained by current detectors See also Tanvir 05

39 80 Myr/Galaxy  20 (0.5) events/yr within 200Mpc 10 5 Myr/Galaxy  20 (1) events/yr within 40Mpc

40 Summary n Warning: these results are based on inverting convolved triple integrals, small number statistics & selection effects. n Rate of short bursts >10 Gpc -3 yr -1 with beaming this corresponds to the estimates of NS mergers. Time lag distribution requires a large fraction of mergers with 3<  <10 Gyr – implications to progenitors Time lag distribution requires a large fraction of mergers with 3<  <10 Gyr – implications to progenitors n The distribution of fluxes can be extrapolated to significantly lower luminosities. These bursts are weakly constrained by the current data. The event rate may be as large as 10 5 Gpc -3 yr -1

41 The END