J/A+A/640/A91ivo://CDS.VizieR/J/A+A/640/A91doi:10.26093/cds/vizier.36400091CDSYassine M.Piron F.Daigne F.Mochkovitch R.Longo F.Omodei N.,Vianello G.2022-03-01T07:31:05Z2020-11-20T09:55:40ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frgamma-ray-astronomygamma-ray-burstsThe physical origin of the gamma-ray burst (GRB) prompt emission is still a subject of debate. Internal shock models have been widely explored, owing to their ability to explain most of the high-energy properties of this emission phase. While the Band function or other phenomenological functions are commonly used to fit GRB prompt emission spectra, we propose a new parametric function that is inspired by an internal shock physical model. We use this function as a proxy of the model to compare it easily to GRB observations. We built a parametric function that represents the spectral form of the synthetic bursts provided by our internal shock synchrotron model (ISSM). We simulated the response of the Fermi instruments to the synthetic bursts and fit the obtained count spectra to validate the ISSM function. Then, we applied this function to a sample of 74 bright GRBs detected by the Fermi GBM, and we computed the width of their spectral energy distributions around their peak energy. For comparison, we also fit the phenomenological functions that are commonly used in the literature. Finally, we performed a time-resolved analysis of the broadband spectrum of GRB 090926A, which was jointly detected by the Fermi GBM and LAT. This spectrum has a complex shape and exhibits a power-law component with an exponential cutoff at high energy, which is compatible with inverse Compton emission attenuated by gamma-ray internal absorption. This work proposes a new parametric function for spectral fitting that is based on a physical model. The ISSM function reproduces 81% of the spectra in the GBM bright GRB sample, versus 59% for the Band function, for the same number of parameters. It gives also relatively good fits to the GRB 090926A spectra. The width of the MeV spectral component that is obtained from the fits of the ISSM function is slightly larger than the width from the Band fits, but it is smaller when observed over a wider energy range. Moreover, all of the 74 analyzed spectra are found to be significantly wider than the synthetic synchrotron spectra. We discuss possible solutions to reconcile the observations with the internal shock synchrotron model, such as an improved modeling of the shock microphysics or more accurate spectral measurements at MeV energies.2020A&A...640A..91Yhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/640/A91CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-tohttps://fermi.gsfc.nasa.gov/ssc/data/access/gbm : GBM cataloghttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/640/A91https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/640/A91http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/640/A91https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/640/A91https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/640/A91http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/640/A91GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/640/A91/tablea4 (Results of the Band and ISSM spectral fits to GBM data for the prompt emission of 74 GRBs)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/640/A91/tablea4?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/640/A91/tablea4?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/640/A91/tablea4?GETtext/xml+votable180.050000true151.29-19.260.0055555555555555566/240 2414 2540 3553 3602 3861 3881 4693 4903 6214 7890 8976 9060 9431 9662 10565 12170 13215 13779 14065 14810 16282 17464 17982 18538 18704 18784 18901 21059 21593 21737 21880 22181 22299 23576 24426 26365 27713 27811 27964 28692 28930 28959 29179 29937 30595 31270 34461 34933 35764 36442 36444 37505 37527 38092 39007 39594 40400 41541-41542 42066 42710 42718 44277 44617 45373 45391 45483 45835 46813 47116 47427 47911 48934https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/640/A91?format=asciiGamma-raydefaultJ/A+A/640/A91/tablea4Results of the Band and ISSM spectral fits to GBM data for the prompt emission of 74 GRBsdofDegree of freedomstat.fit.dofinte_EpPeak energy errorstat.errorintalphaPhoton indexstat.fit.paramfloatEpPeak energyem.energyintrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNameGRB name, GRBNNNNNNNNNmeta.id;meta.maincharModels[Band/ISSM] Model namemeta.id;stat.fitchare_alphaPhoton index errorstat.error;pos.eq.rafloatalpha10Local photon indexstat.fit.paramfloate_alpha10Local photon index errorstat.errorfloatbetaHigh-energy spectral indexstat.fit.paramfloate_betaHigh-energy spectral index errorstat.errorfloatbetabPhoton index at the break energy Eb of the Band function (1)stat.fit.paramfloate_betabPhoton index at the break energy Eb of the Band function errorstat.errorfloatAmpAmplitude parameter0.0001cm**-2.s**-1.keV**-1src.var.amplitudefloate_AmpAmplitude parameter error0.0001cm**-2.s**-1.keV**-1stat.errorfloatPGstat"Poisson-Gauss" fit statisticstat.fit.paramintSimbadSimbad column added by the CDSmeta.ref.urlchar_RARight Ascension (J2000) from SIMBAD (not part of the original data)degpos.eq.ra;meta.main_DEDeclination (J2000) from SIMBAD (not part of the original data)degpos.eq.dec;meta.main