X-RAY LIGHT CURVES OF GRBS WITHOUT FLARES

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1 X-RAY LIGHT CURVES OF GRBS WITHOUT FLARES MARIA GRAZIA BERNARDINI R. MARGUTTI, J. MAO, E. ZANINONI, G. CHINCARINI INAF - Osservatorio Astronomico di Brera THE X-RAY UNIVERSE 2011

2 THE X-RAY EMISSION OF GRBS: light curves differ from simple power-law behaviour some characteristic repeats in systematic way (canonical behaviour) flares superimposed to the smooth continuum Nousek et al., 2006 Chincarini et al., 2005 O Brian et al., 2006 Zhang et al., 2006 Chincarini et al. 2007, 2010 WHAT IS THE LIGHT CURVE MORPHOLOGY TELLING US?

3 SAMPLE SELECTION 64 GRBs observed by Swift/XRT from April 2005 to April 2010: with redshift measurements without flaring activity 16 Golden Sample (GS): t start 40 s, t stop 10 5 s FITTING PROCEDURE A software automatically identifies the smooth behaviour of the light curves (see Margutti, MGB et al for details) L 0 (t)=n t -α1 L I (t)=n((t/t b ) (α1/d1) +(t/t b ) (α2/d1) ) -d1 L II (t)=n((t/t b1 ) (α1/d1) +(t/t b1 ) (α2/d1) ) -d1 (1+(t/t b2 ) (α3/d2) ) -d2

4 THE LIGHT CURVE CLASSIFICATION 0 Ia Ib II 22 Type 0 (34%) 20 Type Ia (31%) 7 Type Ib (11%) 15 Type II (23%) In the GS 4 Type 0 5 Type Ia 0 Type Ib 7 Type II

5 0 Ia SPECTRAL INDEX vs. TIME Ib II 0 Ia spectral evolution in Ib and II initial decay moderate or absent in other segments Ib II

6 COMPARISON WITH LIGHT CURVES OF GRBS WITH FLARES We use the sample adopted in Margutti, MGB et al. 2011, analysed with the same procedure. We find: preferred temporal behaviour Type II 23% vs. 72%

7 COMPARISON WITH LIGHT CURVES OF GRBS WITH FLARES We use the sample adopted in Margutti, MGB et al. 2011, analysed with the same procedure. We find: preferred temporal behaviour similar energetic E FLC ISO E LC ISO E FLC X E LC X

8 COMPARISON WITH LIGHT CURVES OF GRBS WITH FLARES We use the sample adopted in Margutti, MGB et al. 2011, analysed with the same procedure. We find: preferred temporal behaviour similar energetic slightly different slope of the steep decay FLC steep =2.7 LC steep =3.2

9 THE STEEP DECAY 0 Ia Ib II KS[ Ib 1; II 1] 99%

10 THE STEEP DECAY generally consistent with high latitude emission from structured jet BUT spectral evolution... Kumar & Panaitescu, 2000 Barniol-Duran & Kumar, 2009 Zhang & Meszaros, 2002 Lyutikov, 2006 Kumar et al., 2008 Margutti, MGB et al., 2011 prolonged activity of central engine L~ t -3 or steeper ( steep =3.2) flares are perturbations in the mechanism powering the steep decay connection flares/type II

11 THE NORMAL DECAY 0 Ia Ib II KS[ 0 1; Ib 2] 46% KS[ 0 1; II 3] 12% KS[ Ia 2; II 3] 36%

12 THE NORMAL DECAY generally consistent with forward shock emission pre/post jet break supported by the absence of spectral evolution Sari 1998 Chevalier & Li 2000 Zhang & Meszaros 2004 accretion model predicts an asymptotic behaviour L~ t -( ) but does not constraint the spectral index

13 THE SHALLOW DECAY 0 Ia Ib II KS[ Ia 1; II 2] 6% KS[ Ia 1; Ib 2] 63% KS[ Ib 2; II 2] 49%

14 ENERGY INJECTION FROM SPINNING- DOWN NEWLY BORN NS INTO THE FORWARD SHOCK L(t)=kL i /T k+1 T0 T T k /(1+aT) 2 Dall Osso et al Usov, 1992 Duncan & Thompson, 1992 Dai & Lu, 1998 Zhang & Meszaros, 2001 Metzger et al., ke 0 /T 0 (T 0 /T) k+1 T 0 B P i k E 0 GRB z T (s) B (10 15 G) P (ms) k E (10 50 erg) B ± ± ± ± A ± ± ± ± ± ± ± ± A ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± A ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 0.4

15 THE LUMINOSITY vs. DURATION CORRELATION IN SHALLOW DECAY Dainotti et al., 2008, 2011 { B, σ B { a ~ B 2 /P 2 { t p =1/a P, σ P L i ~ B 2 /P 4 L p =L(t p )

16 CONCLUSIONS STEEP DECAY: slope, spectral evolution and connection with flares ORIGINATEs FROM CENTRAL ENGINE ACTIVITY. NOT SIMPLY THE TAIL OF THE PROMPT EMISSION SHALLOW DECAY: energetic, duration, slope, absence of spectral evolution, correlations and following normal decay INJECTION OF ENERGY FROM SPINNING-DOWN NS INTO THE FORWARD SHOCK

17 X-Ray Universe 2011 Berlin, June 2011! The Sample! We analysed all the Gamma-Ray Bursts (GRBs) with spectroscopic analysis observed by the X-Ray Telescope (XRT), on board Swift satellite, from its launch (November 2004) to the end of 2010 (437 GRBs of 658 GRBs detected by Swift).! In particular the sample includes:!!! 165 GRBs with redshift!!! 414 long GRBs (154 with z)!!! 23 short GRBs (11 with z)! Data Reduction!!! The XRT-data have been reduced with the method reported in Margutti et al.! (2010). We obtained the XRT light curves in the kev total energy band! and in four sub-energy bands: kev, 1-2 kev, 2-3 kev and 3-10 kev.!!! Our XRT archive contains light curves in count-rate, flux and luminosity (for! the redshift subsample).!!! The light curves in flux units are calibrated accounting for spectral evolution.! This is relevant especially during the steep decay.!!! The spectra have been measured both assuming NH constant and variable.! Complete catalogue of the POSTER Data Analysis GRBs observed by Swift/ XRT and characterisation of all the light curves and correlations Classification & Morphology! GRB050822! Flux (erg/s/cm2)!!!! We analysed the light curves in flux units.!!! The XRT light curves have been fitted with four different functions (F(t)): 0) power law; I) smoothed broken power! law; II) sum of power law and smoothed broken power law; III) sum of two smoothed broken power laws. The best fit! values were determined using the IDL Levenberg-Marquardt least-squares fit routine (MPFIT) supplied by! C. Markwardt (Markwardt 2009). All variability and fluctuations superimposed on the basic underlying light curve! have been subtracted by iteration following Margutti et al. (2011).!!! Using the fit data, we calculated the total fluence or energy of our light curves as well as the one of different parts! of the light curves (E1, E2, E3, E4).! Type! Light Curve Shape! 0! Ib! IIa Time (s)! IIb! III!... so stay tuned!!!1!!1!!1! E1! Ia!2! E1! E2! tbr1!!1!!1!!1!!2!!2!!2! E1! E2! tbr1! E15!3!!3! E1! E2! tbr1! E3! tbr2!!2! E1! E2! tbr1! E3! tbr2! E1! E2!!3! E3!!4! E4! tbr1! tbr2! tbr3!