The fast spectral variability of gamma-ray bursts (GRBs) with known redshifts is investigated using the Konus-Wind experiment data in time scale up to 2ms. Tracks of these GRBs in the luminosity-peak energy plane (Liso,EP ) in the rest-frame are obtained. The distribution of maximum values of an instantaneous luminosity in the GRB’s rest frame Liso is derived for such GRBs depending on the peak energy EP

Aptekar, R. L.

Frederiks, D. D.

Golenetskii, S. V.

Kokomov, A. A.

Mazets, E. P.

Palshin, V. D.

Ulanov, M. V.

English

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DOI 10.1393/ncc/i2005-10058-8IL NUOVO CIMENTO Vol. 28 C, N. 3 Maggio-Giugno 2005Fast spectral variability of GRBs with known redshifts(∗)M. V. Ulanov, S. V. Golenetskii, D. D. Frederiks, R. L. AptekarE. P. Mazets, A. A. Kokomov and V. D. PalshinIoffe Phisico-Technical Institute - St.Petersburg, Russia(ricevuto il 23 Maggio 2005; pubblicato online il 9 Settembre 2005)Summary. — The fast spectral variability of gamma-ray bursts (GRBs) withknown redshifts is investigated using the Konus-Wind experiment data in time scaleup to 2ms. Tracks of these GRBs in the luminosity-peak energy plane (Liso, EP ) inthe rest-frame are obtained. The distribution of maximum values of an instantaneousluminosity in the GRB’s rest frame Liso is derived for such GRBs depending on thepeak energy EP .PACS 95.85.Pw – γ-ray.PACS 98.70.Rz – γ-ray sources; γ-ray bursts.PACS 01.30.Cc – Conference proceedings.1. – IntroductionThe fast spectral variability of 30 GRBs with known redshifts is analyzed on thebase of the Konus-Wind experiment data. The advantage of such approach is that allmeasurements are performed by the same instrument. For all these events reliable valuesof the redshifts are available [1].The Konus-Wind instrument records burst time history in three energy windows G1,G2, and G3 with a variable time resolution from 2 up to 256ms. The nominal valuesof energy intervals at the beginning of the experiment were G1 (10–50 keV), G2 (50–150 keV), and G3 (150–750 keV). The boundaries increase in course of time due tothe degradation of photocathodes and by the end of 2004 the energy windows werethe following: G1 (20–70 keV), G2 (70–300 keV), and G3 (300–1300 keV). Multichannelenergy spectra are measured in the energy range 20 keV–10MeV with accumulation timesof 64ms–8 s adapted to current intensities of burst [2].2. – Data analysisIt is possible to consider time history in three energy windows as three-channel energyspectrum recorded with fine temporal resolution. The spectra are described by the power(∗) Paper presented at the “4th Workshop on Gamma-Ray Burst in the Afterglow Era”, Rome,October 18-22, 2004.c© Societa` Italiana di Fisica 351352 M. V. ULANOV, S. V. GOLENETSKII, D. D. FREDERIKS, ETC.Fig. 1. – Examples of correlation tracks in the rest frame.law with the exponential cut-off model:N(E) = A(E100keV)αexp(− EE0) [photonscm2 s keV].We determine the values of three parameters A, E0, α so that three-channel detectorresponse fits to the obsereved three-channel spectrum. The uncertainties in parametersPmaxmaxFig. 2. – Maximum isotropic luminosity Lmaxiso vs. maximum peak energy in the rest frameEPmaxrest . Circle size is proportional to the value of redshift. Several slopes of the individualcorrelation tracks are shown with dotted lines.FAST SPECTRAL VARIABILITY OF GRBs WITH KNOWN REDSHIFTS 353are estimated by propagation of counting statistics errors. The uncertainty of peak energyEP is less than E0 and α due to the strong anticorrelation between α and E0. In mostcases it is possible to verify the results using multichannel energy spectra.Table I. – Energetic properties of 30 GRBs with known redshifts detected by Konus-Wind.Date Z Fluence Peak flux EP integr EPmaxrest Eradiso Lmaxiso10−6 ergcm210−7 ergcm2skeV keV 1052 erg 1051 ergs970228 0.7 11± 4 15.7± 5.7 132± 21 298± 51 1.62± 0.59 3.9± 1.4970508 0.83 2.6± 3 – 92± 26 – 0.55± 0.65 –970828 0.96 58± 10 22± 6.4 – 803± 117 16.2± 2.8 12± 3971214 3.42 8.8± 2.4 5.2± 1.4 173± 18 1028± 186 24.2± 6.8 63± 18980703 0.97 28± 12 – 244± 36 – 7.8± 3.3 –990123 1.6 320± 21 88± 5.7 636± 25 2842± 560 238± 15 169± 11990506 1.31 194± 12 76± 4.7 350± 12 706± 67 98± 6 89± 6990510 1.62 27± 5 37± 7.2 145± 13 639± 60 20.3± 3.9 74± 14990705 0.84 102± 6 51± 3.1 318± 7 765± 57 21.7± 1.3 20± 1990712 0.43 16.9± 1.1 4.4± 2.2 – 72± 64 0.93± 0.06 0.34± 0.18991208 0.71 163± 5 185± 5.8 183± 3 537± 31 24.6± 0.8 47± 1991216 1.02 248± 12 468± 22 378± 10 992± 83 78.2± 3.7 296± 14000131 4.51 44± 6 16± 2.0 235± 20 1488± 127 188± 24 374± 48000210 0.85 76± 5 242± 15 407± 14 1015± 127 16.4± 1.0 97± 6000301 2.03 8.3± 0.6 12± 5.7 – 1213± 303 9.5± 0.7 42± 20000418 1.12 26± 4 28± 4.0 134± 10 445± 64 10.0± 1.4 22± 3000911 1.06 192± 34 100± 18 1023± 86 1647± 412 65± 12 69± 12000926 2.04 26± 4 15± 2.6 101± 6 957± 191 29.7± 5.1 53± 9010222 1.48 139± 8 87± 4.9 309± 12 941± 82 89± 5 138± 8010921 0.45 20± 3 9.2± 1.4 82± 9 290± 116 1.18± 0.18 0.80± 0.12011121 0.36 227± 25 109± 12 882± 93 1896± 678 8.56± 0.93 5.6± 0.6020124 0.69 11± 6 – 124± 18 – 1.61± 0.82 –020405 3.2 83± 6 35± 2.5 209± 6 1427± 105 206± 15 360± 26020813 1.25 141± 13 60± 5.6 315± 15 1174± 126 66± 6 63± 6021004 0.25 1.2± 14 – 84± 44 – 0.02± 0.25 –021211 1 3.6± 11 14± 6.2 80± 9 461± 170 1.1± 3.2 8.5± 3.8030226 1.99 13± 6 – 117± 14 – 13.8± 6.25 –030328 1.52 35± 8 – 132± 7 – 23.7± 5.14 –030329 0.17 197± 7 200± 7.6 104± 2 228± 14 1.53± 0.06 1.81± 0.07031203 0.11 3.7± 3 – 144± 46 – 0.011± 0.01 –Note: EP integr is the peak energy of the time-integrated energy spectrum and Eradiso is totalradiated isotropic energy during the whole burst.The peak energy EP = E0(α+ 2) and the energy fluxF =∫ 2EPEP /2EN(E)dEare determined for each spectrum. The choice of energy band depending on EP makesthe flux less sensitive to the value of EP than in the case of fixed finite boundaries.In most cases the values of peak energy and flux form a distinct track in the (F,EP )plane. For the bursts with known redshifts correlation tracks can be recalculated to therest frame of the burst source. We consider a relation between peak energy in the rest354 M. V. ULANOV, S. V. GOLENETSKII, D. D. FREDERIKS, ETC.frame EP rest = EP (1+Z) and the isotropic luminosity Liso = F ·4πD2L(Z) where DL(Z)is a luminosity distance:DL(Z) =cH0(1 + Z)∫ Z0dz√ΩM (1 + z)3 +ΩΛ.We assume a standard cosmology model with H0 = 65 km s−1Mpc−1, ΩM = 0.3, ΩΛ =0.7 [3].Most of the tracks has a sharp maximum point (fig. 1). The maximum values of Lisoand EP rest are determined on the timescale of 64ms. The distribution of these maximumvalues is shown in fig. 2. The spectral and energetic properties of the considered burstsare summarized in table I.3. – DiscussionIt is reasonable to assume that the correlation tracks reflect the properties of themechanism of energy transfer and conversion into gamma-rays. Specifically, the harderspectra corresponds to the greater luminosity. In average, the correlation tracks can beapproximated by a power lawLiso ∝ EγP restIn most cases indices γ lie within the interval of 1.8–3 (see, for example, fig. 1) havingan average value of 2.5.The plot Liso vs. EP rest for a set of bursts agrees generally with a slope of individualcorrelation tracks confirming the common radiative mechanism realized in the bursts.Deficiency of the low luminosity bursts with high redshift in the plot is undoubtedly dueto the selection effects. At the same time it is clear that Liso depends on the energystored in the source and therefore can not be considered as a standard candle.REFERENCES[1] http://www.mpe.mpg.de/∼jcg/grbgen.html.[2] Aptekar R. L. et al., Space Science Rev., 71 (1995) 265.[3] Davis T. M. and Lineweaver C. H., Publications of the Astronomical Society of Australia(PASA), 21 (2004) 97.

Fast spectral variability of GRBs with known redshifts

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Fast spectral variability of GRBs with known redshifts

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