Gamma Ray Bursts. Progress & Prospects. Resmi Lekshmi. Indian Institute of Space Science & Technology Trivandrum

Transcription

1 Gamma Ray Bursts Progress & Prospects Resmi Lekshmi Indian Institute of Space Science & Technology Trivandrum

2 Why study GRBs? to study GRBs end stages of massive star evolution jet launching, collimation particle acceleration in rel.shocks ISM of host galaxies faint end of galaxy population high z: probing IGM, reionization history, SFR

3 Gamma Ray Bursts (GRBs) in a nutshell Physics of burst & afterglow emission Central engine, progenitors GRBs as cosmological probes Prospects

4 Gamma Ray Bursts : briefly Short (a few seconds) flashes of! -rays Non-repetitive, from random directions in the sky E bol release : ergs Average rate : 1 event/day Longer lasting low-frequency counterparts Extragalactic, Cosmological ( )

5 Relativistic Jets in GRBs optical depth to pair production Frail+ 97, grb interstellar scintillation in radio resolving superluminal motion (VLBI : GRB030329) Taylor+ 2004; Granot Energetics : collimation (2-10 deg)! /4"

6 Prompt Emission predominantly in! -rays non-thermal spectrum millisec variability dissipation internal to the jet F ig. 23. A typical B and-function spectrum of G R B From B riggs et al. (1999). Band fn. Purely empirical Burgess : trying to obtain Band from Syn

7 Prompt Emission predominantly in! -rays non-thermal spectrum millisec variability I Band II Photospheric III Additional high energy (Zhang+ 2011) dissipation internal to the jet

8 Prompt Emission predominantly in! -rays non-thermal spectrum millisec variability " R! ~ cm Internal shock model (Narayan , Rees " &Meszaros 1994) : most discussed " Other models (eg. magnetic reconnection)are also being discussed dissipation internal to the jet

9 Prompt Emission predominantly in! -rays non-thermal spectrum millisec variability dissipation internal to the jet

10 (late) Afterglow Resmi, Multi-wavelength Misra+ modelling of GRB A afterglow 13 Lower frequency (till radio) Longer lasting No short-scale variability External dissipation Relevance 1. z estimate (and related) 2. KE of flow 3. ambient medium 4. jet collimation 5. microphysics 6. Non-relativistic transition (calorimetry)

11 Early afterglow : Transition period prompt emission afterglow

12 Early afterglow : Transition period prompt emission afterglow O brien Stratta+ 2009

13 Central engine! Should launch an " energetic( erg), " clean (E/N b >> m p c 2 ) jet! Should be intermittent Hyper-accreting stellar mass BH Rapidly spinning magnetar LGRB =!"c 2 = 1.8 x erg/s!-3 ["/(M!s -1 )] E rot = (1/2) I! 2 = 2 x erg [M/1.4M!] [R/10km] 2 [P/1ms] -2

14 Progenitor models Two types of bursts Predominantly two classes of GRBs Short Hard & Long Soft

15 Progenitor models Two types of bursts Predominantly two classes of GRBs Short Hard & Long Soft hardness duration

16 Duration : The iceberg s Tip Hjorth+2003 Long GRBs Association with supernovae Short GRBs No confirmed SN association so far

17 Duration : The iceberg s Tip Long GRBs Origin in star forming galaxies Close to the bright UV regions of host Occurs in both in late & early type Relatively larger offsets Short GRBs

18 Progenitor Models Progenitor of Long GRBs Rapidly spinning massive stars, (perhaps) of low metallicity Progenitor of Short GRBs Merger of binary compact objects (NS-NS or NS- BH) due to orbital momentum loss into GWs

19 Cosmology with GRBs Redshift distribution Berger, 2013 Do lgrbs trace star formation? (see Kistler+ 2008) Could all sgrbs be from DCO mergers? (see Virgili+ 2009)

20 Cosmology with GRBs Probes of early universe grb A photo-z : 8.t Tanvir Probing the IGM Reionization history No definite intrinsic standard candle properties have been found so far

21 Progress & Prospects cosmological relativistic jets late AG : synchrotron radiation from relativistic shocks at least 2 types of GRBs. lgrbs most likely originate from massive star collapse. jet composition? how are prompt! -rays produced? jet launching mechanism by central engine? are all sgrbs are from DCO mergers? what is the typical jet collimation?

22 Future observatories Thirty Meter Telescope (TMT) 2025 More host galaxy identification especially sgrb : more accurate offset, hence kick more high z (8-10) bursts, pop III, history of reionization SFR towards high z

23 Future observatories Square Km Array (SKA) 2020 Era of radio AG opt.thick fireball : probing ambient medium early RS : ejecta composition late afterglow : non-rel transition Orphan AG (~300/week predicted!!!)

24 Future observatories LIGO-2 : The dark side of the story short GRBs progenitor model dl

25 Future observatories svom (2018) lsst (2022) athena (late 2020s)

26 references Kumar & Zhang 2014 (arxiv physics of grbs) Berger 2013 (arxiv short bursts) Tanvir 2013 (arxiv high z bursts)