The spectacular stellar explosion - GRB 17A: synchrotron moeling in the win an the ISM University of Johannesburg, Department of Physics, Aucklan Park 6, Johannesburg, South Africa E-mail: jessymolkt@uj.ac.za Reetanjali Moharana University of Johannesburg, Department of Physics, Aucklan Park 6, Johannesburg, South Africa E-mail: reetanjalim@uj.ac.za Soebur Razzaque University of Johannesburg, Department of Physics, Aucklan Park 6, Johannesburg, South Africa E-mail: srazzaque@uj.ac.za GRB 17A, is the spectacular gamma ray explosion ever etecte. It is believe to be originate from the core collapse of a massive star. It also achieve the recor of being one of the most fluent an the longest uration GRB in GeV gamma rays lasting for about hrs. The reshift of this GRB has been etecte as z=.. The Fermi-LAT Gamma-ray Space Telescope has etecte a 9-GeV energy photon from GRB 17A. The after glow raiation of this GRB was recore by Swift XRT, BAT an UVOT. The Spectral Energy Distribution (SED) an Light curves of the prompt emission an afterglow help us to stuy the GRBs in etail. We have explaine the afterglow SEDs an Light curve etecte by LAT, XRT-BAT an UVOT/optical observations for GRB 17A, by fitting it with the synchrotron emission moel from the accelerate electrons for the aiabatic blastwave in both the interstellar meium (ISM) an win environments. We see a better explanation of the observe ata with synchrotron moel in win environment compare to ISM for this GRB. PoS(HEASA1)8 r Annual Conference on High Energy Astrophysics in Southern Africa -HEASA1, 18- June 1 University of Johannesburg, Aucklan Park, South Africa Speaker. c Copyright owne by the author(s) uner the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives. International License (CC BY-NC-ND.). http://pos.sissa.it/
GRB 17A an its synchrotron moeling 1. Introuction It is an exciting fact that a large number of explosions take place in our mysterious universe an the most energetic explosions ever etecte are Gamma Ray Bursts. These GRBs can last from fractions of secons to hours an are accompanie by long lasting afterglows in all electromagnetic wavelengths. In GRBs, the prompt emissions reflect interactions within the system itself an the afterglows starts when the shock fronts of the jets reach the ISM. GRB 17A is a spectacular explosion happene on 7th April 1 marking one of the extremely high energetic event ever etecte. The re shift of this GRB 17A has been etecte as z =. which is only about.6 billion light years away [1] from us an is one of the nearest GRB observe. GRB 17A is recore as one of the most fluent an luminous burst. GRB 17A was first spotte by Fermi Gamma-ray Burst Monitor (GBM) on boar the Fermi Gamma Ray space telescope. The Large Area Telescope (LAT) on boar Fermi has etecte 9 GeV photon which is the maximum energy ever etecte from a GRB [1]. The X-ray an optical afterglows were so bright that it was observe for many ays. X-Ray afterglows were etecte by Swift at.-kev an NuSTAR at KeV of photon energies for more than a week []. The optical afterglows were also etecte by UVOT telescopes of swift an other robotic an optical telescopes like Liverpool Telescope, MITSuME cm telescope of Akeno Observatory, Faulkes Telescope, Okayamma Telescopes an Murikabushi 1m telescope of Ishigakijima Astronomical Observatory []. Due to these facts GRB 17A has been the center of attraction for astronomy as well as high energy astrophysics.. Synchrotron Moeling of GRB 17A. The GRB moels are usually escribe base on the synchrotron emission of the relativistically accelerate electrons [, ]. In GRBs, after the explosion relativistic shells containing matter collie to form internal shocks. Synchrotron loss of these relativistic matter prouce prompt emission. As the shock waves continue to expan outwar they interact with ISM an the win environment. The electrons in the external shocks get Fermi accelerate an prouce photons by synchrotron cooling in the magnetic fiel resulting in afterglows []. The GRB 17A has got a hyper energetic prompt emission an extremely bright afterglows in the X-ray, optical an infra-re wavebans. Here we have moele the SEDs an light curves for this GRB in both the win environment an the ISM. The ata use to plot the synchrotron spectrum moel are given in Table 1 to []. PoS(HEASA1)8 Time (s) Flux Flux error [erg/cm /s] [erg/cm /s] 19.1E-7 1.8E-7 6.81E-8.9E-8 6.E-9.8E.9E-.E- Table 1: LAT ata in the energy ban (.1- GeV) Time (s) Flux Flux error [erg/cm /s] [erg/cm /s] 19 1.E-7.E 1.99E.89E.1E-.1E-11 Table : XRT-BAT ata in the energy ban (.-kev)
GRB 17A an its synchrotron moeling Time [s] Flux [erg/cm /s] Filter..e- ±.8e-11 w1.e- ± 1.66e- u 8.9e- ±.e- b 7.e-1 ± 1.68e-1 w1 Table : UVOT ata in the wavelength range (17nm). Time [s] Flux [mjy] Filter. 7. ±.1 r. 6.97 ±. i.. ±. r Table : Optical/Faulkes Telescope North Time [s] Flux [mjy] Filter. 1.9 ±. i. 1.17 ±. r Table : Optical/MITSuME cm telescope of Akeno Observatory.1 SED an light curves for GRB 17A in win-environment. The instantaneous spectrum of low energy photons from a GRB can be moele by the synchrotron emission of a single power law istribution of electrons. However the photon spectrum will have breaks at ifferent frequencies ue to absorption an cooling effects of electrons. These break frequencies are ν m, the photon frequency corresponing to the minimum Lorentz factor γ e,min of electron, ν c, the photon frequency corresponing to the cooling Lorentz factor of electrons γ e,c, ν a, the photon frequency ue to self absorption an ν s presenting maximum energy of the electron. 1 T 9 for the GRB 17A is nearly 16s. We chose the available afterglow ata after this time so, the low energy spectra is in the slow cooling regime (γ e,c > γ e,min ). The instantaneous synchrotron spectrum F ν, from a power law istribution of electrons in the slow cooling regime can be expresse as given in []. However in our moeling we have also inclue the self absorption effect an the exponential cut-off at higher energy in the spectrum. as, F ν = F ν,max ( ν ν a ) ( ν a ν m ) 1 ; ν < ν a ; ( ν ν m ) 1 ; ν a < ν < ν m, ( ν ν m ) (p 1) ; ν m < ν < ν c, ( ν c ν m ) (p 1) ( ν ν c ) p exp( ν/ν s ); ν c < ν s The break frequencies for the win environment in equation.1 can be written following [6, 7] (.1) ν m = 9. 1 ε 1/ b,.1 ε e,.1e 1/ (1 + z)1/ t / Hz, (.) PoS(HEASA1)8 ν c =.1 1 ε / b,.1 E1/ (1 + z) / t 1/ A Hz, (.) ν a = 8. 9 ε 1/ b,.1 ε 1 e,.1 E / (1 + z) / t / A 6/ Hz, (.) ν s = 8. A 1/ E 1/ (1 + z) / t 1/ an F ν,max, the observe peak flux is given as, F ν,max =. ε 1/ b,.1 E1/ (1 + z) 1/ t 1/ φ 1 1 Hz, (.) l,8 erg/cm /s/hz. (.6) 1 T 9 of a GRB measures the uration of the time interval uring which 9% of the total observe counts have been etecte, with the interval starting by the time at which % of the total counts have been observe an ening with the time at which 9% of the total counts have been etecte.
GRB 17A an its synchrotron moeling Here, E is the initial kinetic energy of blast wave in units of erg, ε e is the electron equipartition fraction or the fraction of energy going to the relativistic electrons, ε e,.1 = ε e /.1, ε b is the fraction of energy going to the magnetic energy ε b,.1 = ε b /.1, l,8 is the luminosity istance in 8 cm unit, t is the time after prompt emission in ays, φ is the number of gyroraius neee for the electron acceleration in the magnetic fiel φ 1 = φ/ an A Ṁ /v 8 corresponing to a mass-loss rate of Ṁ w = Ṁ M yr 1 in the win of the progenitor star, with velocity v w = 8 v 8 cm/s. The SED an light curves of Win moel -7 - -11-1 -1-1 -1 for t = 19s for t = s for t = s for t = s 1 1 1 16 17 18 19 1 6 Frequency(Hz) Figure 1: Spectral Energy Distribution in Win meium - - -7 - ν =7.e16Hz ν =.18e17Hz ν =1.9e18Hz ν =.18e18Hz XRT_BAT ata - - -7 - -11 ν = MeV ν = 1 GeV ν = GeV LAT Data Figure : Light curve for LAT ata in win -7 - -11-1 -1-1 ν = e1hz ν = e1hz optical i',r',g' UVOT PoS(HEASA1)8-11 -1 6 7 Figure : Light curve for XRT-BAT ata in Win meium Figure : Light curve for optical/uv ata in win The SED in the slow cooling regime for the GRB 17A in the win meium is plotte in Fig.1, it shows the spectrum for the observe LAT, XRT-BAT an UVOT/optical ata of GRB 17A for ifferent time intervals. It also shows the fitting with synchrotron emission spectra for the aiabatic blast waves in the win environment. The fitte moel parameters we obtaine are, ε b =.1, ε e =.8, E = 1.1, p =., A = 1., z =., L,8 = L / 8 =.6 an φ 1 = φ/ =.1 We have also moele the temporal evolution of the flux in ifferent frequencies. To moel the light curves we have one the flux versus time plot of available ata [] at ifferent energy
GRB 17A an its synchrotron moeling levels an fitte it with the equation 1, as the break frequencies given in the equation are epenent on time. We have use the moel parameters obtaine from the SED to fit the ata. In Fig. the energy fluxes as a function of time from the trigger for observe LAT ata are shown. Similarly Fig. an Fig. shows XRT-BAT, UVOT/optical light curves respectively.. SED an light curves for GRB 17A in ISM. The synchrotron moeling of GRB 17A afterglow is also one for the constant ensity ISM. Equations erive for all the synchrotron frequencies, also explaine in [6] in the ISM environment are given as, ν m = 1.6 1 ε 1/ b,.1 ε e,.1e 1/ (1 + z)1/ t / Hz, (.7) ν c = 1.91 1 ε / b,.1 E 1/ (1 + z) 1/ t 1/ n 1 Hz, (.8) ν a =. 9 ε 1/ b,.1 ε 1 e,.1 E1/ (1 + z) 1 n / Hz, (.9) ν s =. n 1/8 E 1/8 (1 + z) /8 t /8 φ 1 1 Hz, (.) F ν,max = 7.9 (1 + z) 1 n 1/ l,8 E ε 1/ b erg/cm /s/hz. (.11) Here, n = 1/cm is the particle ensity in the ISM. vfv -7 - -11 The SED an light curves of ISM moel - - -7 ν = MeV ν = 1 GeV LAT Data PoS(HEASA1)8-1 -1-1 -1 for t = 19s for t = s for t = 7s for t = 666s 1 1 1 1 16 17 18 19 1 6 Frequency(Hz) - -11 Figure : Spectral Energy Distribution in ISM Figure 6: Light curve for LAT ata in ISM Fig. shows the flux versus frequency spectrum at ifferent time intervals 19s, s, s an s from early time to later time of the burst. It is observe that the spectrum in case of ISM is not fitting well as it oes in the win environment. The moel parameters that we obtaine for the ISM moel are ε b,.1 =, ε e =.8, E =.6, z =., l,8 =.6, p =., n =.1 an φ 1 =.1. Fig. 6, 7 an 8 are the light curves fitte with moel parameters obtaine from SEDs at ifferent frequencies for LAT, XRT-BAT an UVOT/optical ata respectively.
GRB 17A an its synchrotron moeling - - ν =7.e16Hz ν =.18e17Hz ν =1.9e18Hz ν =.18e18Hz XRT_BAT ata -7 ν = e1hz ν = e1hz optical i',r',g' UVOT -7 - -11 - -1-1 -1-11 Figure 7: Light curve for XRT-BAT ata in ISM. Discussion an conclusion -1 6 7 Figure 8: Light curve For UVOT/optical ata in ISM GRBs are extremely energetic explosions in the sky. GRB 17A is one of the most energetic, bright an nearby GRB ever etecte. The source of raiations from GRBs can be escribe in terms of synchrotron emission from accelerate electrons. In this article we have one the synchrotron moeling of broaban SED at ifferent time intervals an the temporal evolution of flux in ifferent frequencies for GRB 17A. The moeling is one for both cases of ISM an win environment. This GRB in t fit well with the ISM environment an is well escribe in win meia with reasonable parameters, which is expecte for GRB progenitor stars as they are thought to be massive an prouce strong win. References [1] Ackermann M et al. 1 Science [] Kouveliotou C et al. 1 Astrophys.J.Lett 779 1 [] A. Maselli et al. 1 Science Magazine 8 [] Piran T Rev. Mo. Phys. 76 11 [] B. Zhang, P. Meszaros Int. J. Mo. Phys. 19 8 [6] Razzaque S 1, Phys. Rev. D 88 [7] Granot J, Piran T, Sari R 1999 Astrophys.J. 7 6 PoS(HEASA1)8 6