We process the Fermi LAT data on GRB130427A using the Fermi Science Tools, and we summarize some of the key facts that render this observation truly remarkable. We then perform a search of spectral lags, of the type that has been of interest for its relevance in quantum-spacetime research. We do find some evidence of systematic soft spectral lags: when confining the analysis to photons of energies greater than 5？GeV there is an early hard development of minibursts within the burst. The effect is well characterized by a linear dependence, within such a miniburst, of the detection time on energy. We also observe that some support for these features is noticeable also in earlier Fermi-LAT GRBs. Some aspects of the comparison of these features for GRBs at different redshifts could be described within a quantum-spacetime picture, but taking into account results previously obtained by other studies we favour the interpretation as intrinsic properties of GRBs. Even if our spectral lags do turn out to have astrophysical origin their understanding will be important for quantum-spacetime research, since any attempt to reveal minute quantum-spacetime-induced spectral lags evidently requires a good understanding of intrinsic mechanisms at the sources that can produce spectral lags. 1. Introduction and Motivation The study of Gamma-Ray Bursts (GRBs) has been for some time one of the main themes of astrophysics research, and over the last 15 years it became also of interest for research on quantum gravity. These more recent developments look at GRBs as signals and hope to decode properties of quantum-spacetime from the implications of spacetime quantization for how such signals propagate from the distant source to our telescope. Even tiny quantum-spacetime effects modifying the structure of the signal could cumulate along the way, as the signal travels over cosmological distances. As we here contribute to assess, the remarkable very recent observation of GRB130427A is bound to teach us a lot about the astrophysics of GRBs and has the potential to also empower some of the quantum-spacetime studies of GRBs. This GRB130427A was extremely powerful, also thanks to the fact that it was among the nearest long GRBs observed. We here take the perspective that GRB130427A is an opportunity to look at a long GRB in “high resolution,” allowing us to notice features which could not be noticed in previous GRBs. In this study we test the potentialities of using GRB130427A in this way by focusing on a much studied class of effects, involving spectral lags with a linear dependence on
References
[1]
S. Zhu, J. Racusin, D. Kocevski et al., “Fermi-LAT detection of a burst,” GCN Circular, no. 14471, GRB 130427A, 2013.
[2]
A. von Kienli, “Fermi GBM observation,” GCN Circular, no. 14473, GRB 130427A, 2013.
[3]
A. Maselli, A. P. Beardmore, A. Y. Lien et al., “Swift detection of a very bright burst with a likely bright optical counterpart,” GCN Circular, no. 14448, GRB 130427A, 2013.
[4]
S. Golenetskii, R. Aptekar, D. Frederiks et al., “Konus-Wind observation of GRB 130427A,” GCN Circulars, no. 14487, 2013.
[5]
A. Pozanenko, P. Minaev, and A. Volnova, “SPI-ACS/INTEGRAL observations,” GCN Circulars, no. 14484, GRB 130427A, 2013.
[6]
F. Verrecchia, C. Pittori, A. Giuliani et al., “High energy gamma-ray detection by AGILE,” GCN Circulars, no. 14515, GRB 130427A, 2013.
[7]
A. Chernenko and I. Mitrofanov, “Decomposition of a cosmic gamma-ray burst into two non-correlated radiation components,” Monthly Notices of the Royal Astronomical Society, vol. 274, no. 2, pp. 361–368, 1995.
[8]
H. Flores, S. Covino, D. Xu et al., “VLT/X-shooter redshift confirmation,” GCN Circulars, no. 14491, GRB 130427A, 2013.
[9]
A. J. Levan, S. B. Cenko, D. A. Perley, and N. R. Tanvir, “Gemini-North redshift,” GCN Circulars, no. 14455, GRB 130427A, 2013.
[10]
D. Xu, C. Cao, S.-M. Hu, and C.-M. Zhang, “Weihai optical observations,” GCN Circulars, no. 14458, GRB 130427A, 2013.
[11]
L. Elenin, A. Volnova, V. Savanevych, A. Bryukhovetskiy, I. Molotov, and A. Pozanenko, “Early optical observations,” GCN Circulars, no. 14450, GRB 130427A, 2013.
[12]
M. Ackermann, M. Ajello, L. Baldini et al., “Constraints on the cosmic-ray density gradient beyond the solar circle from Fermiγ-ray observations of the third galactic quadrant,” The Astrophysical Journal, vol. 726, no. 2, article 81, 2011.
[13]
W. B. Atwood, A. A. Abdo, M. Ackermann et al., “The large area telescope on the Fermi gamma-ray space telescope mission,” The Astrophysical Journal, vol. 697, no. 2, Article ID 1071, 2009.
[14]
M. Ackermann, M. Ajello, A. Albert et al., “The Fermi large area telescope on orbit: event classification, instrument response functions, and calibration,” The Astrophysical Journal Supplement Series, vol. 203, no. 1, article 4, 2012.
[15]
G. Amelino-Camelia, J. Ellis, N. E. Mavromatos, D. V. Nanopoulos, and S. Sarkar, “Tests of quantum gravity from observations of γ-ray bursts,” Nature, vol. 393, pp. 763–765, 1998.
[16]
R. Gambini and J. Pullin, “Nonstandard optics from quantum space-time,” Physical Review D, vol. 59, no. 12, Article ID 124021, 4 pages, 1999.
[17]
J. Alfaro, H. A. Morales-Tecotl, and L. F. Urrutia, “Quantum gravity corrections to neutrino propagation,” Physical Review Letters, vol. 84, no. 11, pp. 2318–2321, 2000.
[18]
G. Amelino-Camelia and S. Majid, “Waves on noncommutative space-time and gamma-ray bursts,” International Journal of Modern Physics A, vol. 15, no. 27, article 4301, 2000.
[19]
R. C. Myers and M. Pospelov, “Ultraviolet modifications of dispersion relations in effective field theory,” Physical Review Letters, vol. 90, no. 21, Article ID 211601, 4 pages, 2003.
[20]
U. Jacob and T. Piran, “Lorentz-violation-induced arrival delays of cosmological particles,” Journal of Cosmology and Astroparticle Physics, vol. 2008, no. 1, article 031, 2008.
[21]
D. Mattingly, “Modern tests of Lorentz invariance,” Living Reviews in Relativity, vol. 8, article 5, 2005.
[22]
G. Amelino-Camelia and L. Smolin, “Prospects for constraining quantum gravity dispersion with near term observations,” Physical Review D, vol. 80, no. 8, Article ID 084017, 14 pages, 2009.
[23]
R. J. Szabo, “Quantum field theory on noncommutative spaces,” Physics Reports, vol. 378, no. 4, pp. 207–299, 2003.
[24]
A. A. Abdo, M. Ackermann, M. Ajello et al., “A limit on the variation of the speed of light arising from quantum gravity effects,” Nature, vol. 462, pp. 331–334, 2009.
[25]
A. Abdo, M. Ackermann, M. Ajello et al., “Detection of high-energy gamma-ray emission from the globular cluster 47 Tucanae with Fermi,” Science, vol. 323, no. 5942, pp. 845–848, 2009.
[26]
J. Ellis, N. E. Mavromatos, and D. V. Nanopoulos, “Probing a possible vacuum refractive index with γ-ray telescopes,” Physics Letters B, vol. 674, no. 2, pp. 83–86, 2009.
[27]
J. Bolmont and A. Jacholkowska, “Lorentz symmetry breaking studies with photons from astrophysical observations,” Advances in Space Research, vol. 47, no. 2, pp. 380–391, 2011.
[28]
R. J. Nemiroff, R. Connolly, J. Holmes, and A. B. Kostinski, “Bounds on spectral dispersion from Fermi-detected gamma ray bursts,” Physical Review Letters, vol. 108, no. 23, Article ID 231103, 4 pages, 2012.
[29]
J. Albert, E. Aliu, H. Anderhub et al., “Probing quantum gravity using photons from a flare of the active galactic nucleus Markarian 501 observed by the MAGIC telescope,” Physics Letters B, vol. 668, no. 4, pp. 253–257, 2008.
[30]
F. Aharonian, A. G. Akhperjanian, U. B. de Almeida et al., “Limits on an energy dependence of the speed of light from a flare of the active galaxy PKS 2155-304,” Physical Review Letters, vol. 101, no. 17, Article ID 170402, 5 pages, 2008.
[31]
M. Ackermann, M. Ajello, K. Asano et al., “The first Fermi-LAT gamma-ray burst catalog,” The Astrophysical Journal Supplement Series, vol. 209, no. 1, article 11, 2013.
[32]
G. Amelino-Camelia, D. Guetta, and T. Piran, “Possible relevance of quantum spacetime for neutrino-telescope data analyses,” http://arxiv.org/abs/1303.1826.
[33]
R. Abbasi, Y. Abdou, T. Abu-Zayyad et al., “An absence of neutrinos associated with cosmic-ray acceleration in γ-ray bursts,” Nature, vol. 484, pp. 351–354, 2012.
[34]
N. Whitehorne, A search for high-energy neutrino emission from gamma-ray bursts [Ph.D. thesis], University of Wisconsin-Madison, Madison, Wis, USA, 2012, https://docushare.icecube.wisc.edu/dsweb/Get/Document-60879/thesis.pdf.
[35]
D. Wanderman and T. Piran, “The luminosity function and the rate of Swift's gamma-ray bursts,” Monthly Notices of the Royal Astronomical Society, vol. 406, no. 3, pp. 1944–1958, 2010.
[36]
D. Coward, E. J. Howell, T. Piran et al., “The Swift short gamma-ray burst rate density: implications for binary neutron star merger rates,” Monthly Notices of the Royal Astronomical Society, vol. 425, no. 4, pp. 2668–2673, 2012.
