GRBs and short Xray transients observed by MAXI

GRBs and short X-ray transients observed by MAXI ― a summary of the first year ― Motoko Serino on behalf of the MAXI team 12/02/2010 The First Year of MAXI

outline Global characteristics – Prompt emissions number of events … more than expected? flux and hardness … are they special? – Afterglow and pre-burst emission search no detection … is it reasonable? Individual events – spectral analyses 12/02/2010 The First Year of MAXI 2

MAXI bursts 30 L 12 GRA 09 TE B IN 1 R * 1200 G 09 12 i 1 rm 09 Fe B * 2 R 1 G 10 09 6 B B 2 i R 90 erm G B 0 ft / F 31 R wi 8 G * S 09 i 0/ IPN B rm R* Fe G 16 events in 16 months 2009 2010 *S w ift 0 7 A A 11 A 1 A A 27 5 A 0 A 3 3 6 5 0 11 2 09 1 70 1 03 41 51 1 8 6 3 0 01 0 10 0 00 0 10 00 00 1 0 0 0 1 1 1 1 F F B B B R R R R X X G G G * 5 are simultaneously detected by other satellites 12/02/2010 The First Year of MAXI 3

event rate expected detection rate 400 total number of bursts × 0. 02 × instantaneous sky coverage of GSC 0. 4 = 3. 2 / yr observation efficiency actual detection rate 12 / yr ! – why? ? MAXI can detect soft events 12/02/2010 The First Year of MAXI 4

flux and hardness of MAXI bursts flux 2 -20 ke. V average hardness ( 8 -20 ke. V flux ) ( 2 -8 ke. V flux ) 12/02/2010 The First Year of MAXI 5

comparing with HETE’s classification HETE’s 45 bursts (Sakamoto et al. 2005) Sx /Sg = 2 -30 ke. V / 30 -400 ke. V (fluence) – 10 GRBs – 19 XRRs – 16 XRFs 12/02/2010 log(Sx/Sg) -0. 5 < log(Sx/Sg) 0. 0 < log(Sx/Sg) The First Year of MAXI -0. 5 0. 0 6

flux and hardness of MAXI bursts and XRF/XRR/GRB classification – XRFs dominate! 12/02/2010 The First Year of MAXI 7

afterglow & pre-burst emission no detection so far – to detect afterglows, GSC should scan <100 sec after the trigger – GSC scans a position every 5400 sec – probability ~ 0. 02 – studying 80 bursts → 1. 6 afterglow expected we should study more bursts! – or better luck? ! 12/02/2010 The First Year of MAXI 8

individual events Joint spectral fit – GRB 090926 B (MAXI & Fermi) narrow spectral energy distribution – GRB 100823 A (MAXI & Swift) soft spectral index – see also GRB 090831 by Ohno et al. MAXI / Fermi / Suzaku [P-53] 12/02/2010 The First Year of MAXI 9

GRB 090926 B light curve – maxi detected the first 25 seconds of the burst – no significant emission above 350 ke. V – low flux below 4 ke. V 12/02/2010 The First Year of MAXI 10

Peculiar spectrum of 090926 B spectra –low-energy power index = 0. 3 harder than a limit of the synchrotron shock model limit (-0. 67) –Epeak = 90 ke. V ↓ –narrow spectral energy distribution 12/02/2010 a: 0. 3 b: -2. 6 The First Year of MAXI 11

Peculiar spectrum of 090926 B 12/02/2010 The First Year of MAXI 12

GRB 100823 A with Swift soft power index ~ -2 – may be an upper part of Band function – X-ray flash good agreement in normalization – within 10% – common to the three bursts 12/02/2010 The First Year of MAXI 13

Summary MAXI GSC detected 16 bursts in 16 months A study of flux and hardness distribution of MAXI bursts shows that GSC efficiently detect soft bursts (XRRs and XRFs) We can see good agreement in normalization with other instruments GRB 090926 B has peculiar spectral shape and that may be a emission from photosphere of GRB fireball 12/02/2010 The First Year of MAXI 14

MAXI bursts 30 L 12 GRA 09 TE B IN 1 R * 1200 G 09 12 i 1 rm 09 Fe B * 2 R 1 G 10 09 6 B B 2 i R 90 erm G B 0 ft / F 31 R wi 8 G * S 09 i 0/ IPN B rm R* Fe G 16 events in 16 months 2009 2010 *S w ift 0 7 A A 11 A 1 A A 27 5 A 0 A 3 3 6 5 0 11 2 09 1 70 1 03 41 51 1 8 6 3 0 01 0 10 0 00 0 10 00 00 1 0 0 0 1 1 1 1 F F B B B R R R R X X G G G * 5 are simultaneously detected by other satellites 12/02/2010 The First Year of MAXI 15