Fermi lat observations_of_the_gamma_ray_burst_grb_130427a

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  • 1. Fermi-LAT Observations of the Gamma-Ray Burst GRB 130427A M. Ackermann,1 M. Ajello,2 K. Asano,3 W. B. Atwood,4 M. Axelsson,5,6,7 L. Baldini,8 J. Ballet,9 G. Barbiellini,10,11 M. G. Baring,12 D. Bastieri,13,14 K. Bechtol,15 R. Bellazzini,16 E. Bissaldi,17 E. Bonamente,18,19 J. Bregeon,16 M. Brigida,20,21 P. Bruel,22 R. Buehler,1 J. Michael Burgess,23 S. Buson,13,14 G. A. Caliandro,24 R. A. Cameron,15 P. A. Caraveo,25 C. Cecchi,18,19 V. Chaplin,23 E. Charles,15 A. Chekhtman,26 C. C. Cheung,27 J. Chiang,15* G. Chiaro,14 S. Ciprini,28,29 R. Claus,15 W. Cleveland,30 J. Cohen-Tanugi,31 A. Collazzi,32 L. R. Cominsky,33 V. Connaughton,23 J. Conrad,34,6,35,36 S. Cutini,28,29 F. D’Ammando,37 A. de Angelis,38 M. DeKlotz,39 F. de Palma,20,21 C. D. Dermer,27* R. Desiante,10 A. Diekmann,40 L. Di Venere,15 P. S. Drell,15 A. Drlica-Wagner,15 C. Favuzzi,20,21 S. J. Fegan,22 E. C. Ferrara,41 J. Finke,27 G. Fitzpatrick,42 W. B. Focke,15 A. Franckowiak,15 Y. Fukazawa,43 S. Funk,15 P. Fusco,20,21 F. Gargano,21 N. Gehrels,41 S. Germani,18,19 M. Gibby,40 N. Giglietto,20,21 M. Giles,40 F. Giordano,20,21 M. Giroletti,37 G. Godfrey,15 J. Granot,44 I. A. Grenier,9 J. E. Grove,27 D. Gruber,45 S. Guiriec,41,32 D. Hadasch,24 Y. Hanabata,43 A. K. Harding,41 M. Hayashida,15,46 E. Hays,41 D. Horan,22 R. E. Hughes,47 Y. Inoue,15 T. Jogler,15 G. Jóhannesson,48 W. N. Johnson,27 T. Kawano,43 J. Knödlseder,49,50 D. Kocevski,15 M. Kuss,16 J. Lande,15 S. Larsson,34,6,5 L. Latronico,51 F. Longo,10,11 F. Loparco,20,21 M. N. Lovellette,27 P. Lubrano,18,19 M. Mayer,1 M. N. Mazziotta,21 J. E. McEnery,41,52 P. F. Michelson,15 T. Mizuno,53 A. A. Moiseev,54,52 M. E. Monzani,15 E. Moretti,7,6 A. Morselli,55 I. V. Moskalenko,15 S. Murgia,15 R. Nemmen,41 E. Nuss,31 M. Ohno,43 T. Ohsugi,53 A. Okumura,15,56 N. Omodei,15* M. Orienti,37 D. Paneque,57,15 V. Pelassa,23 J. S. Perkins,41,58,54 M. Pesce-Rollins,16 V. Petrosian,15 F. Piron,31 G. Pivato,14 T. A. Porter,15 J. L. Racusin,41 S. Rainò,20,21 R. Rando,13,14 M. Razzano,16,4 S. Razzaque,59 A. Reimer,60,15 O. Reimer,60,15 S. Ritz,4 M. Roth,61 F. Ryde,7,6 A. Sartori,25 P. M. Saz Parkinson,4 J. D. Scargle,62 A. Schulz,1 C. Sgrò,16 E. J. Siskind,63 E. Sonbas,41,64,30 G. Spandre,16 P. Spinelli,20,21 H. Tajima,15,56 H. Takahashi,43 J. G. Thayer,15 J. B. Thayer,15 D. J. Thompson,41 L. Tibaldo,15 M. Tinivella,16 D. F. Torres,24,65 G. Tosti,18,19 E. Troja,41,52 T. L. Usher,15 J. Vandenbroucke,15 V. Vasileiou,31 G. Vianello,15,66* V. Vitale,55,67 B. L. Winer,47 K. S. Wood,27 R. Yamazaki,68 G. Younes,30,69 H.-F. Yu,45 S. J. Zhu,52* P. N. Bhat,23 M. S. Briggs,23 D. Byrne,42 S. Foley,42,45 A. Goldstein,23 P. Jenke,23 R. M. Kippen,70 C. Kouveliotou,69 S. McBreen,42,45 C. Meegan,23 W. S. Paciesas,30 R. Preece,23 A. Rau,45 D. Tierney,42 A. J. van der Horst,71 A. von Kienlin,45 C. Wilson-Hodge,69 S. Xiong,23* G. Cusumano,72 V. La Parola,72 J. R. Cummings41,73 Affiliations are listed after the references. Gamma-ray Space Telescope. The LAT is a pair-conversion telescope that observes photons from 20 MeV to > 300 GeV with a 2.4 steradian field of view (1). The GBM consists of 12 sodium iodide (NaI, 8 keV - 1 MeV) and 2 bismuth germanate (BGO, 200 keV 40 MeV) detectors, positioned around the spacecraft to view the entire unocculted sky (2). In the standard model of GRBs, the blast wave that produces the initial, bright prompt emission later collides with the external material surrounding the GRB (the circumburst medium) and creates shocks (see, e.g., (3)). These external shocks accelerate charged particles, which produce photons through synchrotron radiation. Until this burst, the high-energy emission from LAT-detected GRBs had been well described by this model, but GRB 130427A challenges this widely accepted model. In particular, the maximum possible photon energy prescribed by this model is surpassed by the the late-time high-energy photons detected by the LAT. The LAT detected highenergy γ-ray emission from this burst for almost a day, including a 95 GeV photon (which was emitted at 128 GeV in the rest frame at redshift z = 0.34 (4)) a few minutes after the burst began and a 32 GeV photon (43 GeV in the rest frame) after more than 9 hours. These are more energetic and detected at considerably later times than the previous record holder, an 18 GeV photon detected by the Energetic Gamma Ray Experiment Telescope (EGRET) aboard the Compton Gamma Ray Observatory more than 90 min after GRB 940217 began (5). Observations At 07:47:06.42 UTC on 27 April 2013 (T0), while Fermi was in the regular survey mode, the GBM triggered on The observations of the exceptionally bright gamma-ray burst (GRB) 130427A by GRB 130427A. The burst was suffithe Large Area Telescope aboard the Fermi Gamma-ray Space Telescope provide ciently hard and intense to initiate an constraints on the nature of such unique astrophysical sources. GRB 130427A had Autonomous Repoint Request (6), a the largest fluence, highest-energy photon (95 GeV), longest γ-ray duration (20 spacecraft slewing maneuver that keeps hours), and one of the largest isotropic energy releases ever observed from a GRB. the burst within the LAT field of view Temporal and spectral analyses of GRB 130427A challenge the widely accepted for 2.5 hours, barring Earth occultation. model that the non-thermal high-energy emission in the afterglow phase of GRBs is At the time of the GBM trigger, the synchrotron emission radiated by electrons accelerated at an external shock. Swift Burst Alert Telescope (BAT) was slewing between two pre-planned targets, and triggered on the ongoing burst Gamma-ray bursts (GRBs) are thought to originate from collapsing mas- at 07:47:57.51 UTC immediately after the slew completed (7), 51.1 s sive stars or merging compact objects (such as neutron stars or black after the GBM trigger. The CARMA millimeter-wave observatory localholes), and are associated with the formation of black holes in distant ized this burst to (R.A., Dec.) = (173.1367°, 27.6989°) (J2000) with a galaxies. GRB 130427A was detected by both the Large Area Telescope 0.4′′ uncertainty (8). The Rapid Telescopes for Optical Response (LAT) and the Gamma-ray Burst Monitor (GBM) aboard the Fermi (RAPTOR) detected bright optical emission from the GRB, peaking at a *Corresponding author. E-mail: sjzhu@umd.edu (S.J.Z.); jchiang@slac.stanford.edu (J.C.); charles.dermer@nrl.navy.mil (C.D.D.); nicola.omodei@stanford.edu (N.O.); giacomov@slac.stanford.edu (G.V.); shaolin.xiong@uah.edu (S.X.) / http://www.sciencemag.org/content/early/recent / 21 November 2013 / Page 1 / 10.1126/science.1242353 Downloaded from www.sciencemag.org on December 1, 2013 Research Articles
  • 2. red-band magnitude of R = 7.03 ± 0.03 around the GBM trigger time before fading to R ~ 10 about 80 s later (9). The Gemini-North observatory reported a redshift of z = 0.34 (4), and an underlying supernova has been detected (10). A total of 58 observatories have reported observations of this burst as of September 2013. At the time of the GBM trigger, the GRB was 47.3° from the LAT boresight, well within the LAT field of view. The Autonomous Repoint Request brought the burst to 20.1° from the LAT boresight based on the position calculated by the GBM flight software. It remained in the LAT field of view for 715 s until it became occulted by the Earth, re-emerging from Earth occultation at T0 + 3135 s. Within the first ~ 80 ks after the trigger, the LAT detected more than 500 photons with energies > 100 MeV associated with the GRB; the previous record holder was GRB 090902B, with ~ 200 photons (11). In addition, the LAT detected 15 photons with energies > 10 GeV (compared to only 3 photons for GRB 090902B). Using the LAT Low Energy (LLE) event selection (12), which considerably increases the LAT effective collecting area to lowerenergy γ-rays down to 10 MeV (with adequate energy reconstruction down to 30 MeV) (13, 14), thousands of counts above background were detected between T0 and T0+100 s. Temporal Characteristics The temporal profile of the emission from GRB 130427A varies strongly with energy from 10 keV to ~ 100 GeV (Fig. 1 and Fig. 2). The GBM light curves consist of an initial peak with a few-second duration, a much brighter multipeaked emission episode lasting ~ 10 s, and a dim, broad peak at T0 + 120 s, which fades to an undetectable level after ~ 300 s (also seen in the Swift light curve (7)). The triggering pulse observed in the LLE (> 10 MeV) light curve is more sharply peaked than the NaI- and BGO-detected emission at T0. The LLE light curve between T0+4 s and T0+12 s exhibits a multipeaked structure. Some of these peaks have counterparts in the GBM energy range, although the emission episodes are not perfectly correlated (e.g., the sharp spike in the LLE light curve at T0 + 9.5 s is not relatively bright in the GBM light curves) because of the spectral evolution with energy. The LAT-detected emission, however, does not appear to be temporally correlated with either the LLE or GBM emission beyond the initial spike at T0. Photons with energies > 1 GeV are first observed ~ 10 s after T0, after the brightest GBM emission has ended, consistent with a delayed onset of the high-energy emission (13). The delayed onset is not caused by a progressively increasing LAT acceptance due to slewing, because the slew started at T0+33 s. Instead, it reflects the true evolution of the GRB emission. GRB spectra are generally well described by phenomenological models such as the Band function (15) or the smoothly broken power law (SBPL (16)). For the brightest LAT bursts, the onset of the GeV emission is delayed with respect to the keV-MeV emission and can be fit by an additional power-law component (13). This additional component usually becomes significant while the keV-MeV emission is still bright. For GRB 130427A, however, the extra power-law component becomes significant only after the GBM-detected emission has faded (Fig. 3). During the initial peak (T0−0.1 s to T0+4.5 s), there are only a few LAT-detected photons, and the emission is well-fit by an SBPL. For the brightest part of the burst (T0+4.5 s to T0+11.5 s), we did not use the GBM-detected emission because of the substantial systematic effects caused by extremely high flux (17); however, there are no photons with energies greater than 1 GeV in this time interval, and the energy spectrum > 30 MeV is well described by a single power law without a break (Fig. 3) (note that the LAT did not suffer from any pile up issues). Photons with energies greater than 1 GeV are detected in the last time interval (T0+11.5 s to T0+33.0 s), including a 73 GeV photon at T0+19 s. Unlike other bright LAT bursts, the LAT-detected emission from GRB 130427A appears to be temporally distinct from the GBM-detected emission, suggesting that the GeV and keV-MeV photons arise from different emission regions or mechanisms. Temporally Extended High-Energy Emission To characterize the temporally extended high-energy emission, we performed an unbinned maximum likelihood analysis of the LAT > 100 MeV data. We modeled the LAT photon spectrum as a power law with a spectral index α (i.e., the spectrum N(E) ∝ Eα). We found evidence of spectral evolution during the high-energy emission. In contrast to another study (18), that used longer time intervals in the spectral fits, we found that the LAT > 100 MeV spectrum of the GRB is well described by a power law at all times, but with a varying spectral index (17). During the first pulse around T0, the > 100 MeV emission is faint and soft; the pulse contains only a few photons, and their energies are all < 1 GeV (Fig. 2). This is followed by a period during which there is no significant > 100 MeV emission, while the GBM emission is at its brightest. Starting at ~ T0+5 s, the > 100 MeV emission is detectable again, but remains dim until ~ T0+12 s. The spectral index fluctuates between α ~ −2.5 and α ~ −1.7. At late times (> T0 + 300 s), we measured typical spectral indices of α ~ −2, consistent with the indices of other LAT bursts (13). During the time intervals with the hardest spectra, the LAT observed the highest energy photons—such as the 73 GeV photon at T0+19 s and the record breaking 95 GeV photon at T0+244 s— which severely restrict the possible mechanisms that could generate the high-energy afterglow emission (table S2). The temporally extended photon flux light curve is better fit by a broken power law than a power law. We found a break after a few hundred seconds, with the temporal index steepening from −0.85 ±0.08 to −1.35 ±0.08 (χ2/dof = 36/19 for a single power law, 16/17 for a broken power law). In contrast, a break is not statistically preferred in the energy flux light curve (χ2/dof = 14/18 for a single power law, 13/17 for a broken power law), probably because of the larger statistical uncertainties. For a single power-law fit to the energy flux light curve, we found a temporal index of −1.17 ±0.06, consistent with other LAT bursts (13). The GBM and Swift energy flux light curves are also shown in Fig. 2. The Swift X-Ray Telescope (XRT) began observing the burst at T0+190 s; the reported XRT+BAT (0.3 - 10 keV) light curve is a combination of XRT data and BAT-detected emission (15 - 150 keV) extrapolated down into the energy range of the XRT. The XRT+BAT light curve shows the unabsorbed flux in the 0.3 - 10 keV range (7). During the initial part of the burst, the GBM (10 keV - 10 MeV) light curve peaks earlier than both the XRT+BAT (0.3 - 10 keV) and LAT (> 100 MeV) light curves. The GBM light curve peaks again at ~ T0+120 s (see also (7)), while the LAT light curve shows a sharp and hard peak at T0+200 s. The BAT+XRT light curve peaks again as well at the same time as the LAT light curve, but the peak is much broader. Interpretation The energetics of GRB 130427A place it among the brightest LAT bursts. For GRB 130427A, the 10 keV - 20 MeV fluence measured with the GBM in the 400 s following T0 is ~ 4.2 ×10−3 erg cm−2. The issue with pulse pileup and the uncertainties in the calibration of the GBM detectors contribute to a systematic error which we estimate to be less than 20%; the statistical uncertainty [0.01 ×10−3 erg cm−2] is negligible with respect to the systematic one (17). The > 100 MeV fluence measured with the LAT in the 100 ks following T0 is (7 ±1)×10−4 erg cm−2. The total LAT fluence is therefore ≈ 20% of the GBM fluence, similar to other bright LAT GRBs (13, 19). For a total 10 keV - 100 GeV fluence of 4.9×10−3 erg cm−2, the total apparent isotropic γ-ray energy (i.e., the total energy release if there were no beaming) is Eγ,iso = 1.40×1054 erg, using a flat ΛCDM cosmology with h = 0.71 and ΩΛ = 0.73, implying a luminosity distance of 1.8 Gpc for z = 0.34. This value of Eγ,iso is only slightly less than the values for other bright LAT hyper-energetic events, / http://www.sciencemag.org/content/early/recent / 21 November 2013 / Page 2 / 10.1126/science.1242353
  • 3. which include GRB 080916C, GRB 090902B, and GRB 090926A (19). The emission region must be transparent against absorption by photon-photon pair production, which has a significant effect at the energies of the LAT-detected emission. Viable models of GRBs therefore require highly relativistic, jetted plasma outflows with bulk jet Lorentz factors Γ >~100 (20). The 73 GeV photon at T0 + 19 s (table S2) provides the most stringent limit on Γ. Assuming that the variability timescale reflects the size of the emitting region, and that the MeV and GeV emissions around the time of the 73 GeV photon at T0 + 19 s are cospatial, the requirement that the optical depth due to γγ opacity be less than 1 then implies that the minimum bulk Lorentz factor is Γ min = 455+16 . Here a −13 SBPL fit to the GBM spectrum in the 11.5 - 33.0 s interval (table S1) and a minimum variability timescale of 0.04 ±0.01 s are used (17). The cospatial assumption is, however, questionable given the different time histories in the MeV and GeV emission. Moreover, values of Γmin that are smaller by a factor of 2 - 3 can be realized for models with timedependent γ-ray opacity in a thin-shell model (21). The delayed onset of the LAT-detected emission with respect to the GBM-detected emission is an important clue to the nature of GRBs (13). For GRB 130427A, the LAT-detected emission becomes harder and more intense after the GBM-detected emission has faded (Fig. 3). This suggests that the GeV emission is produced later than the keV-MeV emission and in a different region. In particular, if the keV-MeV emission comes from interactions within the outflow itself, the GeV emission arises from the outflow’s interactions with the circumburst medium. The explosive relativistic outflow of a GRB sweeps up and drives a shock into the circumburst medium. The medium could have, for instance, a uniform density n0 (cm−3) or a n(r) ∝ r−2 density profile resulting from the stellar wind of the Type Ic supernova progenitor star associated with GRB 130427A (10). The LAT observations of GRB 130427A challenge the scenario in which the GeV photons are nonthermal synchrotron radiation emitted by electrons accelerated at the external forward shock (22, 23). In this model, the time of the brightest emission corresponds to the time tdec when most of the outflow energy is transferred to the shocked external medium. The Lorentz factor Γ(tdec) of the shock outflow in the external medium at the deceleration time tdec is a lower limit for the initial bulk outflow Lorentz factor Γ0, because a relativistic reverse shock would lower the shocked fluid Lorentz factor below Γ0, and the engine timescale TGRB can be longer than td, the deceleration timescale for an impulsive explosion. The activity of the central engine that produces the blast wave is revealed by the keV - MeV emission from particles accelerated at colliding-wind shocks. For GRB 130427A, the GeV emission starts to decay as a power law in time by t ≈ 20 s (Fig. 2), and most of the keV-MeV radiation has subsided by t ≈ 12 s (Fig. 1). The blast wave is in the self-similar deceleration phase at t > tdec = max[td,TGRB], where TGRB is the engine timescale (over which most of the outflow energy was released). Here td (s) ≈ 2.4 [(Eγ,iso/1054erg)/n0]1/3/(Γ0/1000)8/3 for a uniform external medium, and td (s) ≈ 6.3 (Eγ,iso/1055 erg) (0.1/A*)(500/Γ0)4 for a stellar wind medium of density ρ = AR−2, with A = 5×1011A* g cm−1. Most of the fluence from GRB 130427A was radiated before t ≈ 12 s, suggesting that td <~12−15 s. Defining t1 = td/(10 s) yields t1 ≈ 1 − 2, which gives Γ(tdec) ≈ 540 [E55/t13 n0(cm−3)]1/8 for the uniform density case, where E55 = Eγ,iso/(1055 erg) is the isotropic energy release of the GRB. For a wind medium, Γ(tdec) ≈ 450{E55/[(A*/0.1)t1]}1/4. Both values are close to the γγ opacity estimate of Γmin. The presence of high-energy photons at times t >> tdec (table S2) is incompatible with these γ rays having a synchrotron origin. Equating the electron energy-loss time scale due to synchrotron radiation with the Larmor timescale for an electron to execute a gyration gives a conservative limit on the maximum synchrotron photon energy Emax,syn ≈ 23/2(27/16παf) mec2 Γ(t)/(1+z) ≈ 79 Γ(t) MeV (where αf is the fine structure constant (17)). Using Γ(t) derived by Blandford and McKee (24) in the adiabatic limit, we find that the maximum synchrotron photon energy Emax,syn << 7 (E55/n0)1/8 [t/200 s]−3/8 GeV, which agrees with results from integration over surfaces of equal arrival time in the self-similar regime (25), when a scaling factor of 27/16π is included (17). The presence of a 95 GeV photon at T0+ 244 s (Fig. 4 and table S2) is incompatible with a synchrotron origin even for conservative assumptions about Fermi acceleration. This conclusion holds for adiabatic and radiative external shocks in both uniform or wind media (see also (26)). The question of a wind or uniform density model is not settled, but combined forward and reverse shock blast-wave model fits to the radio through X-ray emission from 0.67 d to 9.7 d after the GRB favor a wind medium (27), whereas inferences from Swift and LAT data suggest a uniform environment around GRB 130427A (7). Even in the extreme case where acceleration is assumed to operate on a timescale shorter than the Larmor timescale by a factor of 2π, synchrotron radiation cannot account for the presence of high-energy radiation in the afterglow. Synchrotron emission above >~100 GeV is still possible, however, if an acceleration mechanism faster than the Fermi process is acting, such as magnetic reconnection (e.g., (28)). The 95 GeV photon in the early afterglow and the 32 GeV photon at T0+34.4 ks therefore cannot originate from lepton synchrotron radiation in the standard afterglow model with shock Fermi acceleration (Fig. 4). If the emission mechanism for the GeV photons is not synchrotron radiation, the highest energy photons can still be produced by lepton Compton processes. Synchrotron self-Compton (SSC) γ-rays, made when target synchrotron photons are Compton scattered by the same jet electrons that emit the synchrotron emission, are unavoidable. SSC emission is expected to peak at TeV and higher energies during the prompt phase (although no GRB has been detected at TeV energies), and would cause the GeV light curve to flatten and the LAT spectrum to harden when the peak of the SSC component passes through the LAT waveband (29–31). Such a feature may be seen in the light curves of GRB 090902B and GRB 090926A at 15 s - 30 s after T0 (13), but no such hardening or plateau associated with the SSC component is observed in the LAT light curve of GRB 130427A, though extreme parameters might still allow an SSC interpretation; see, e.g., (32). Except for the hard flare at t ≈ 250 s and a possible softening at ~ 3000 s (and therefore not associated with a probable beaming break at t ≈ 0.8 d (7)), neither the integral photon or energy-flux light curves in Fig. 2 show much structure or strong evidence for temporal or spectral variability from t = 20 s to t = 1 d. The NuSTAR observations (33) of the late-time hard x-ray afterglow also suggest that a single spectral component produces the emission from optical to multi-GeV energies. If this emission is indeed synchrotron radiation, then the standard afterglow shock model must be modified to account for the highest energy photons detected by the LAT. These considerations suggest that other extreme high-energy radiation mechanisms may be operative, such as external Compton processes. The most intense source of target photons is the powerful engine emissions, as revealed by the GBM and XRT prompt emission. A cocoon or remnant shell is also a possible source of soft photons, but unless the target photon source is extended and radiant, it would be difficult to model the nearly structureless LAT light curve over a long period of time. Given the similarity between the XRT and LAT light curves (Fig. 2), afterglow synchrotron radiation made by electrons accelerated at an external shock would also be the favored explanation for the LAT emission, but this is inconsistent with the detection of high-energy photons at late time. The photon index of GRB 130427A, ≈ −2, is similar to those found in calculations of electromagnetic cascades created when the γ-ray opacity of ultra-high energy (UHE, > 100 TeV) photons in the jet plasma is large (34). An electromagnetic cascade induced by ultra-relativistic hadrons would be confirmed by coincident detection of neutrinos, but even for GRB 130427A with its extraordinary fluence, only a marginal / http://www.sciencemag.org/content/early/recent / 21 November 2013 / Page 3 / 10.1126/science.1242353
  • 4. detection of neutrinos is expected with IceCube, and none has been reported (35). Because the UHE γ-ray photons induce cascades both inside the radiating plasma and when they travel through intergalactic space (e.g., (36, 37)), a leptonic or hadronic cascade component in GRBs, which is a natural extension of colliding shell and blast wave models, might be required to explain the high-energy emission of GRB 130427A provided that the required energies are not excessive. The observations described in this paper demonstrate non-synchrotron emission in the afterglow phase of the bright GRB 130427A, contrary to the hitherto standard model of GRB afterglows. References and Notes 1. W. Atwood, A. A. Abdo, M. Ackermann, W. Althouse, B. Anderson, M. Axelsson, L. Baldini, J. Ballet, D. L. Band, G. Barbiellini, J. Bartelt, D. Bastieri, B. M. Baughman, K. Bechtol, D. Bédérède, F. Bellardi, R. Bellazzini, B. Berenji, G. F. Bignami, D. Bisello, E. Bissaldi, R. D. Blandford, E. D. Bloom, J. R. 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Ghirlanda, L. Nava, G. Ghisellini, A. Celotti, D. Burlon, S. Covino, A. Melandri, Gamma-ray bursts in the comoving frame. Mon. Not. R. Astron. Soc. 420, 483–494 (2012). doi:10.1111/j.1365-2966.2011.20053.x</jrn> 50. R. Sari, T. Piran, R. Narayan, Spectra and light curves of gamma-ray burst afterglows. Astrophys. J. 497, L17–L20 (1998). doi:10.1086/311269 Acknowledgments: The Fermi LAT Collaboration acknowledges support from a number of agencies and institutes for both development and the operation of the LAT as well as scientific data analysis. These include NASA and DOE in the United States, CEA/Irfu and IN2P3/CNRS in France, ASI and INFN in Italy, MEXT, KEK, and JAXA in Japan, and the K. A. Wallenberg Foundation, the Swedish Research Council and the National Space Board in Sweden. Additional support from INAF in Italy and CNES in France for science analysis during the operations phase is also gratefully acknowledged. The Fermi GBM collaboration acknowledges support for GBM development, operations and data analysis from NASA in the US and BMWi/DLR in Germany. Supplementary Materials www.sciencemag.org/cgi/content/full/science.1242353/DC1 Materials and Methods Figs. S1 and S2 Tables S1 and S2 References (38–50) 24 June 2013; accepted 21 October 2013 Published online 21 November 2013 10.1126/science.1242353 1 Deutsches Elektronen Synchrotron DESY, D-15738 Zeuthen, Germany. Space Sciences Laboratory, University of California, Berkeley, CA 94720, 3 USA. Institute for Cosmic Ray Research, University of Tokyo, 5-1-5 4 Kashiwa-no-Ha, Kashiwa City, Chiba 277-8582, Japan. Santa Cruz Institute for Particle Physics, Department of Physics, and Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 5 95064, USA. Department of Astronomy, Stockholm University, SE-106 91 6 Stockholm, Sweden. Oskar Klein Centre for Cosmoparticle Physics, 7 AlbaNova, SE-106 91 Stockholm, Sweden. Department of Physics, Royal Institute of Technology (KTH), AlbaNova, SE-106 91 Stockholm, Sweden. 8 Università di Pisa and Istituto Nazionale di Fisica Nucleare, Sezione di 9 Pisa I-56127 Pisa, Italy. Laboratoire AIM, CEA-IRFU/CNRS/Université Paris Diderot, Service d’Astrophysique, CEA Saclay, 91191 Gif sur Yvette, 10 France. Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34127 11 Trieste, Italy. Dipartimento di Fisica, Università di Trieste, I-34127 12 Trieste, Italy. Department of Physics and Astronomy, Rice University, 13 Houston, TX 77251, USA. Istituto Nazionale di Fisica Nucleare, Sezione 14 di Padova, I-35131 Padova, Italy. Dipartimento di Fisica e Astronomia 15 “G. Galilei,” Università di Padova, I-35131 Padova, Italy. W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator 16 Laboratory, Stanford University, Stanford, CA 94305, USA. Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa, Italy, . 17 Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, and Università 18 di Trieste, I-34127 Trieste, Italy. Istituto Nazionale di Fisica Nucleare, 19 Sezione di Perugia, I-06123 Perugia, Italy. Dipartimento di Fisica, 20 Università degli Studi di Perugia, I-06123 Perugia, Italy. Dipartimento di Fisica “M. Merlin” dell’Università e del Politecnico di Bari, I-70126 Bari, 21 Italy. Istituto Nazionale di Fisica Nucleare, Sezione di Bari, 70126 Bari, 22 Italy. Laboratoire Leprince-Ringuet, École Polytechnique, CNRS/IN2P3, 23 Palaiseau, France. Center for Space Plasma and Aeronomic Research, 24 University of Alabama, Huntsville, AL 35899, USA. Institut de Ciències 25 de l’Espai (IEEE-CSIC), Campus UAB, 08193 Barcelona, Spain. INAF– Istituto di Astrofisica Spaziale e Fisica Cosmica, I-20133 Milano, Italy. 26 Center for Earth Observing and Space Research, College of Science, George Mason University, Fairfax, VA 22030, USA, resident at Naval 27 Research Laboratory, Washington, DC 20375, USA. Space Science Division, Naval Research Laboratory, Washington, DC 20375, USA. 28 Agenzia Spaziale Italiana Science Data Center, I-00044 Frascati 29 (Roma), Italy. Istituto Nazionale di Astrofisica–Osservatorio Astronomico 30 di Roma, I-00040 Monte Porzio Catone (Roma), Italy. Universities Space 31 Research Association, Columbia, MD 21044, USA. Laboratoire Univers et Particules de Montpellier, Université Montpellier 2, CNRS/IN2P3, 32 Montpellier, France. NASA Postdoctoral Program Fellow, USA. 33 Department of Physics and Astronomy, Sonoma State University, 34 Rohnert Park, CA 94928, USA. Department of Physics, Stockholm 35 University, AlbaNova, SE-106 91 Stockholm, Sweden. Royal Swedish Academy of Sciences Research Fellow, funded by a grant from the K. A. 36 Wallenberg Foundation. Royal Swedish Academy of Sciences, Box 37 50005, SE-104 05 Stockholm, Sweden. INAF Istituto di 38 Radioastronomia, 40129 Bologna, Italy. Dipartimento di Fisica, Università di Udine, and Istituto Nazionale di Fisica Nucleare, Sezione di 39 Trieste, Gruppo Collegato di Udine, I-33100 Udine, Italy. Stellar Solutions Inc., 250 Cambridge Avenue, Suite 204, Palo Alto, CA 94306, 40 41 USA. Jacobs Technology, Huntsville, AL 35806, USA. NASA Goddard 2 / http://www.sciencemag.org/content/early/recent / 21 November 2013 / Page 6 / 10.1126/science.1242353
  • 7. 42 Space Flight Center, Greenbelt, MD 20771, USA. University College 43 Dublin, Belfield, Dublin 4, Ireland. Department of Physical Sciences, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan. 44 Department of Natural Sciences, Open University of Israel, Ra’anana 45 43537, Israel. Max-Planck-Institut für Extraterrestrische Physik, 85748 46 Garching, Germany. Department of Astronomy, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan. 47 Department of Physics, Center for Cosmology and Astro-Particle 48 Physics, Ohio State University, Columbus, OH 43210, USA. Science 49 Institute, University of Iceland, IS-107 Reykjavik, Iceland. CNRS, IRAP, 50 F-31028 Toulouse Cedex 4, France. GAHEC, Université de Toulouse, 51 UPS-OMP, IRAP, Toulouse, France. Istituto Nazionale di Fisica 52 Nucleare, Sezione di Torino, I-10125 Torino, Italy. Department of Physics and Department of Astronomy, University of Maryland, College 53 Park, MD 20742, USA. Hiroshima Astrophysical Science Center, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan. 54 Center for Research and Exploration in Space Science and Technology (CRESST) and NASA Goddard Space Flight Center, Greenbelt, MD 55 20771, USA. Istituto Nazionale di Fisica Nucleare, Sezione di Roma “Tor 56 Vergata,” I-00133 Roma, Italy. Solar-Terrestrial Environment Laboratory, 57 Nagoya University, Nagoya 464-8601, Japan. Max-Planck-Institut für 58 Physik, D-80805 München, Germany. Department of Physics and Center for Space Sciences and Technology, University of Maryland Baltimore 59 County, Baltimore, MD 21250, USA. Department of Physics, University 60 of Johannesburg, Auckland Park 2006, South Africa,. Institut für Astround Teilchenphysik and Institut für Theoretische Physik, Leopold61 Franzens-Universität Innsbruck, A-6020 Innsbruck, Austria. Department 62 of Physics, University of Washington, Seattle, WA 98195, USA. Space Sciences Division, NASA Ames Research Center, Moffett Field, CA 63 94035, USA. NYCB Real-Time Computing Inc., Lattingtown, NY 11560, 64 65 USA. Adyaman University, 02040 Adyaman, Turkey. Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain. 66 Consorzio Interuniversitario per la Fisica Spaziale (CIFS), I-10133 67 Torino, Italy. Dipartimento di Fisica, Università di Roma “Tor Vergata,” I68 00133 Roma, Italy. Department of Physics and Mathematics, Aoyama 69 Gakuin University, Sagamihara, Kanagawa 252-5258, Japan. NASA 70 Marshall Space Flight Center, Huntsville, AL 35812, USA. Los Alamos 71 National Laboratory, Los Alamos, NM 87545, USA. Astronomical Institute Änton Pannekoek, University of Amsterdam, 1090 GE 72 Amsterdam, Netherlands. INAF–Istituto di Astrofisica Spaziale e Fisica 73 Cosmica, Via U. La Malfa 153, I-90146 Palermo, Italy. Center for Research and Exploration in Space Science & Technology, University of Maryland, Baltimore County, Baltimore, MD 21250, USA. / http://www.sciencemag.org/content/early/recent / 21 November 2013 / Page 7 / 10.1126/science.1242353
  • 8. Fig. 1. Light curves for the Fermi-GBM and LAT detectors during the brightest part of the emission in 0.064-s bins, divided into five energy ranges. The NaI and BGO light curves were created from a type of GBM data (Continuous Time, or CTIME) that does not suffer from saturation effects induced by the extreme brightness of this GRB (17); for these light curves, we used NaI detectors 6, 9, and 10, and BGO detector 1. The open circles in the bottom panel represent the individual LAT γ Transient class photons and their energies, and the filled circles indicate photons with a > 0.9 probability of being associated with this burst (17). / http://www.sciencemag.org/content/early/recent / 21 November 2013 / Page 8 / 10.1126/science.1242353
  • 9. Fig. 2. Temporally extended LAT emission. Top: LAT energy flux (blue) and photon flux (red) light curves. The photon flux light curve shows a significant break at a few hundred seconds (red dashed line), while the energy flux light curve is well described by a single power law (blue dashed line). The 10 keV to 10 MeV (GBM, gray) and 0.3 to 10 keV (XRT+BAT, light blue) energy flux light curves are overplotted. The inset shows an expanded view of the first 50 s with a linear axes, with the photon flux light curve from the GBM (in −2 −2 −1 units of 10 ph cm s ) plotted in gray for comparison. Middle: LAT photon index. Bottom: Energies of all the photons with probabilities > 90% of being associated with the GRB (17). Filled circles correspond to the photon with the highest energy for each time interval. Note that the photons plotted here are Source class photons, whereas the photons in Figs. 1 and 3 are Transient class photons (17). The vertical gray lines indicate the first two time intervals during which the burst was occulted by the Earth. As the ARR moved the center of the LAT FoV toward the GRB position, the effective collecting area in that direction increased, so that after ~ 100 s the rate of photons increased even though the intrinsic flux decreased. / http://www.sciencemag.org/content/early/recent / 21 November 2013 / Page 9 / 10.1126/science.1242353
  • 10. Fig. 3. Time-resolved spectral models for the GBM- and LAT-detected emission. Top: The combined NaI and BGO light curve from Fig. 1 (arbitrarily scaled) with the LAT-detected photons overplotted (same as the filled circles in Fig. 1). The time intervals are colored to correspond with the spectral models in the lower plot. The GBM data between 4.5 and 11.5 s are not included because they are substantially affected by pulse pileup (17). Bottom: The models (thick lines) that best fit the data are plotted with 1-σ error contours (thin dashed lines). Each curve ends at the energy of the highest energy LAT photon detected within that time interval. An extra power law is statistically significant when fitting the data from T0 + 11.5 s to T0 + 33.0 s (17). / http://www.sciencemag.org/content/early/recent / 21 November 2013 / Page 10 / 10.1126/science.1242353
  • 11. Fig. 4. Curves of maximum synchrotron photon energy. The black dots show the LAT detection times of photons with energies > 1 GeV and > 90% probability of association with GRB 130427A. Adiabatic and radiative predictions for maximum synchrotron photon energy in uniform interstellar medium (ISM) and wind environments are plotted using the relations described in (17). Red and blue curves refer to the ISM and wind cases, respectively. The solid and dashed lines refer to the adiabatic and radiative cases with Γ0 = 1000, and the dot-dashed and double dot-dashed lines represent the adiabatic case with Γ0 = 500 and Γ0 = 2000, respectively. The dotted lines show an extreme possibility where acceleration takes place on the inverse of the Larmor angular frequency, in the case of an adiabatic blast wave with Γ0 = 1000. 55 −3 For cases with uniform external medium, Eiso(10 erg)/n0(cm ) = 1. The wind normalization was chosen to give the same value of td for both wind and ISM cases. The vertical dotted lines show periods of Earth avoidance when the LAT could not observe GRB 130427A. / http://www.sciencemag.org/content/early/recent / 21 November 2013 / Page 11 / 10.1126/science.1242353