1. GRB spectral evolution: from complex profile to basic structure1
P.Minaev А.Pozanenko
S.Grebenev S.Molkov
Space Research Institute (IKI)

2. Spectral evolution of GRBs
Spectrum analysis
Light curve analysis (spectral lag)

3. “Traditional” method of spectral lag analysis
Calculation of spectral lag between light curves in two different energy bands using cross-correlation analysis
In most cases 4 channels of BATSE are used (25-50, , , keV)
One can derive 3 values of spectral lag in the best case
One can only get a view of general behavior of spectral evolution
CCF 3-1
From Hakkila et al, 2007

4. “New” method of spectral lag analysis
Calculation of spectral lag between light curves in two different energy bands using cross-correlation analysis.
Analysis of light curves in narrow energy channels.
A number and width of energy channels depend only on GRB intensity.
In bright events a number of channels can be more than 20.
Using new method one can investigate spectral evolution in more details.

5. IBIS/ISGRI and SPI experiments
IBIS/ISGRI experiment
Array of 128х128 CdTe elements
Energy range keV
Geometrical area of detectors – 2600 cm2
Full field of view - 30о
SPI spectrometer
Array of 19 Ge detectors
Energy range keV
Geometrical area of detectors 508 cm2
Spectral resolution – MeV

6. Data analysis
GRBs from catalog of SPI transients were investigated (Minaev et al., submitted).
28 most intense bursts were selected.
6 of them have multi-pulse structure with well separated pulses (events).
43 events were investigated in total.

7. Algorithm of analysis Building a energy-time diagram
Pulse-resolving procedure in wide energy band
Forming of light curves in narrow energy channels with a high temporal resolution.
Cross-correlation analysis of light curves: calculation of spectral lag between the first (the softest) and other channels.
Fitting a dependence “spectral lag – energy”

8. Results (1) For 85% events In other cases:
GRB031203
GRB040323
GRB050525
For 85% events
In other cases:
The slope of the curve – “spectral lag index” is a new parameter characterizing spectral evolution

9. Results (2)

10. Results (3)
Duration of the pulse, s

11. Main results
New method of spectral evolution investigation was proposed. Using this method one can investigate spectral evolution in more detail.
28 GRBs were investigated in data of SPI and IBIS/ISGRI experiments.
It was found that for simple structure bursts and for well separated pulses of bursts the dependence of spectral lag on energy band is described by logarithmic function lag ~ A log(E).
Spectral lag index А is a new parameter characterizing spectral evolution of GRBs.
For simple structure bursts negative value of spectral lag index and break in the lag – energy relation were not found.
Correlation between spectral lag index and duration of the pulses was found. Short GRB obeys the correlation.

12. Thank you
for your attention!