Precursor activity in short GRBs E. Troja (NASA/GSFC/ORAU) S. - - PowerPoint PPT Presentation
Precursor activity in short GRBs E. Troja (NASA/GSFC/ORAU) S. Rosswog (Jacobs University) N. Gehrels (NASA/GSFC) Deciphering the ancient Universe with GRBs - Kyoto - April 2010 Outline brief summary of precursors in GRBs search of precursors
Deciphering the ancient Universe with GRBs - Kyoto - April 2010
brief summary of precursors in GRBs search of precursors in the sample of Swift short GRBs: method and results implications for LIV measurements precursors in the merger scenario
time since trigger [s]
Lazzati 05 Morsony et al. 07
emission preceding the GRB less intense than the main GRB non-thermal spectra delays 1-100 s ~20% of long GRBs theoretical interpretations:
fireball: optically thick optically thin
very short delays (~0.02-0.2 s)
jet breakout: collapsar progenitor
SAMPLE:
38 short GRBs (T90 < 2 s) 11 short GRBs with Extended Emission detected by Swift/BAT up to January 2010
OPERATIONAL DEFINITION
1) peak flux smaller than the main event 2) flux returns to the background level 3) same location in the sky
FIRST STEP wavelet algorithm (>3 sigma) on the BAT light curves
6 candidates, but ~2 spurious are expected
SECOND STEP cross check with other instruments (e.g. Fermi/GBM) THIRD STEP image domain (>5 sigma)
2 precursors in GRB090510
T0-0.5 s also seen by Fermi/GBM T0-13 s not seen by GBM, but consistent
5.2 in the image probability of being noise <10-5
σ
GRB 090510
high energy emission (up to 31 GeV) by Fermi/LAT z=0.903 (spectroscopic from host)
no evidence of LIV: exclude a linear energy dependence of photon-propagation speed
Abdo et al. 2009
a) DisCan method (Scargle, Norris & Bonnell 2008) b) emission time of the HE photons > onset of the low energy emission (GBM) emission in BAT starts ~13 s earlier
MQG > 1.22MP l MQG > 1.19MP l |∆t| < 859 ms MQG > 0.09MP l
τtg ≈ 62 min ǫ−4/3
c,−6
1.4 M⊙ −3 Rns 10 km 4
L ≈ 7 × 1045erg s−1
1015G 2 a 107 cm −7
Horowitz & Kadau 2009
L ≈ 1046 erg s−1 σMAX 0.1
system: old recycled pulsar + magnetar prediction: X-ray transient a few seconds before the merger (GRB) merger time scales ~ 105 yr Belczynski et al. 2002, 2006 NS flares from tidal induced crust cracking similar to SGR, not visible beyond 40-80 Mpc
A relativistic jet ploughing through a pre-ejected wind ? After the merger supermassive NS + torus neutrino-driven baryonic wind
Ruffert et al. 1997 Rosswog & Ramirez-Ruiz 2002 Dessart et al. 2009
standard BH+ torus relativistic jet
if it works: - central engine activity longer than ~2 s
~8% of short GRBs has a precursor (20% in long GRBs), no short GRB with EE delays 2-10 s, one GRB with 2 precursors implication for LIV measurements precursors in the merger scenario:
in the last case it marks the start of central engine activity
0.5 1 1.5 2 1 2 3 Precursor Hardness ratio GRB Hardness ratio
090510 − 1st 090510 − 2nd 091117 081024A 050724 080702A