SISSA DIGITAL LIBRARYInstitutional Research Information System (Statistiche: prodotti, OA)
Per informazioni contatta sdl@sissa.it
EnglishThe radiative process responsible for gamma-ray burst (GRB) prompt emission has not been identified yet. If dominated by fast-cooling synchrotron radiation, the part of the spectrum immediately below the nF n peak energy should display a power-law behavior with slope a2 = -3 2, which breaks to a higher value a1 = -2 3 (i.e., to a harder spectral shape) at lower energies. Prompt emission spectral data (usually available down to ∼10 20 keV) are consistent with one single power-law behavior below the peak, with typical slope a = -1, higher than (and then inconsistent with) the expected value α2= -3 2. To better characterize the spectral shape at low energy, we analyzed 14 GRBs for which the Swift X-ray Telescope started observations during the prompt. When available, Fermi-GBM observations have been included in the analysis. For 67% of the spectra, models that usually give a satisfactory description of the prompt (e.g., the Band model) fail to reproduce the 0.51000 keV spectra: lowenergy data outline the presence of a spectral break around a few keV. We then introduce an empirical fitting function that includes a low-energy power law a1, a break energy Ebreak, a second power law α2, and a peak energy Epeak. We find σ1 = -0.66 (s = 0.35), log keV 0.63 ( ) Ebreak = (s = 0.20), σ2 = -1.46 (s = 0.31), and log keV 2.1 (Epeak) = (s = 0.56). The values σ1 and σ2 are very close to expectations from synchrotron radiation. In this context, Ebreak corresponds to the cooling break frequency. The relatively small ratio Epeak break E ∼ 30 suggests a regime of moderately fast cooling, which might solve the long-lasting problem of the apparent inconsistency between measured and predicted low-energy spectral index.
Detection of Low-energy Breaks in Gamma-Ray Burst Prompt Emission Spectra / Oganesyan, Gor; Nava, Lara; Ghirlanda, Giancarlo; Celotti, Anna Lisa. - In: THE ASTROPHYSICAL JOURNAL. - ISSN 0004-637X. - 846:2(2017), pp. 1-22. [10.3847/1538-4357/aa831e]
| Titolo: | Detection of Low-energy Breaks in Gamma-Ray Burst Prompt Emission Spectra | |
| Autori: | Oganesyan, Gor; Nava, Lara; Ghirlanda, Giancarlo; Celotti, Anna Lisa | |
| Rivista: | ||
| Data di pubblicazione: | 2017 | |
| Volume: | 846 | |
| Fascicolo: | 2 | |
| Pagina iniziale: | 1 | |
| Pagina finale: | 22 | |
| Numero di Articolo: | 137 | |
| Digital Object Identifier (DOI): | http://dx.doi.org/10.3847/1538-4357/aa831e | |
| URL: | http://iopscience.iop.org/article/10.3847/1538-4357/aa831e/pdf | |
| Appare nelle tipologie: | 1.1 Journal article |
File in questo prodotto:
| File | Descrizione | Tipologia | Licenza | |
|---|---|---|---|---|
| Oganesyan_2017_ApJ_846_137.pdf | Versione Editoriale (PDF) | Non specificato | Open Access Visualizza/Apri |
http://hdl.handle.net/20.500.11767/75225
