Gamma-Ray Bursts: theoretical issues and...

Mem. S.A.It. Vol. 90, 57c© SAIt 2019 Memorie della

Gamma-Ray Bursts: theoretical issues anddevelopments

P. Meszaros1,2,3

1 Department of Astronomy & Astrophysics, Pennsylvania State University, University Park,PA 16802, USA, e-mail: [email protected]

2 Department of Physics, Pennsylvania State University, University Park, PA 16802, USA3 Center for Particle and Gravitational Astrophysics, Institute for Gravitation and the Cosmos,

Pennsylvania State University, University Park, PA 16802, USA

Abstract. I discuss some aspects of the evolution of the standard GRB model, emphasizingvarious theoretical developments in the last decade, and review the impact of some of the mostrecent observational discoveries and the new challenges they pose in the expanding realm ofmulti-messenger astrophysics.

Key words. Gamma-Ray Bursts, Theory

1. Introduction

Fireballs in astrophysics generally refer to anoptically thick plasma whose temperature ex-ceeds the electron rest mass and which canproduce e± pairs and photons in equilibriumwith a baryonic plasma. An early study of thefireball radiation physics aimed at GRBs, leav-ing aside consideration of specific sources, wasthat of Cavallo & Rees (1978). The fireballwould expand and adiabatically cool as it con-verts its internal into kinetic energy, and theysuggested that this kinetic energy could be re-converted into radiation as it impacts the ex-ternal medium, the highest efficiency (for non-relativistic expansion) being achieved whenthe fireball swept up an amount of externalmatter comparable to the fireball mass (theanalog of the start of the Sedov-Taylor phaseof SNe).

Paczynski (1986) proposed that a merg-ing binary neutron star (BNS) would liber-

ate enough energy in a short time to powera GRB at cosmological distances, and he andGoodman (1986) showed that in this casethe expansion would be relativistic, the bulkLorentz factor accelerating with radius as Γ ∝r, The initial blackbody plasma temperaturewould be of order a few MeV, which in the lin-early expanding comoving frame would dropas T ′ ∝ 1/r, but in the observer frame thiswould be boosted by the bulk Lorentz factorback to its initial few MeV value, with an ap-proximately blackbody spectrum, most of thephotons escaping when the plasma became op-tically thin to Thompson scattering.

A different aspect of BNS mergers empha-sized by Eichler et al. (1989) was their roleas emitters of gravitational waves and theirlikely role as sources of r-process heavy el-ements, at the same time as being likely toappear as GRBs. A more detailed study ofthe properties of relativistically expanding fire-balls (Paczynski 1990; Shemi & Piran 1990)

58 Meszaros P.: Gamma-Ray Bursts

Fig. 1. The standard GRB fireball shock model, e.g. from a collapsar (for compact mergers, the “collapse”region is replaced by the dynamical ejecta). Shown are the photosphere, internal shock and external shockresulting in the afterglow (Meszaros 2001).

Fig. 2. Left: Spectrum of a photosphere heated by pn decoupling (Beloborodov 2010). Right: Synchrotronspectra (e.g. internal or external shocks) accounting for time-dependence of transition between coolingregimes (Burgess et al. 2018).

showed that the bulk Lorentz factor growthΓ(r) ∝ r would saturate to a maximum valueη ∼ E f /M f c2 � 1, where E f and M f are theinitial energy of the explosion and the initialbaryonic mass entrained in the outflow. Aftera saturation radius rsat ∼ r0η, where r0 is thelaunching radius, the Lorentz factor remains

constant, but since adiabatic cooling contin-ues, the radiation energy that can escape afterthe photosphere becomes optically thin repre-sents an increasingly smaller fraction of the fi-nal kinetic energy of expansion. The dynam-ics is similar also for neutron star-black hole(NS-BH) mergers, which would also be im-

Meszaros P.: Gamma-Ray Bursts 59

portant GRB candidates (Narayan et al. 1991,1992), the latter mentioning briefly that recon-nection, ejection of cosmic rays and their col-lisions might contribute non-thermal radiationin addition to the optical thick spectrum.

There were several problems with theabove initial fireball models, namely, (1) forsimplicity, a spherical geometry was usuallytacitly assumed, and this combined with a lowradiative efficiency would require excessivelylarge explosion energies for the brighter bursts;(2) the main part of the gamma-ray spectrumpredicted is approximately blackbody, whereasobserved spectra are mainly non-thermal; and(3) for plausible baryon loads most of the ex-plosion energy would be wasted on bulk ki-netic energy, instead of radiation.

To address these issues the jet-like fire-ball shock model was developed, which in itsmain features is to this day the most widelyused model. As a natural way to resolve theinefficiency of spherical models, Meszaros &Rees (1992b) pointed out that collimation ofthe fireball would be expected in the sloweroutflow (the dynamical ejecta) resulting fromthe tidal heating and the radiation from themerging BNS system. This could be poweredby reconnection between their magnetospheresand collisions between their winds, as wellas by neutrino-antineutrino interactions goinginto pairs, which would occur preferentiallyalong the symmetry axis of the merger. Thiswould create a hot radiation bubble, whichwould escape through the wind preferentiallyalong the centrifugally rarefied axis of rota-tion, making a relativistic jet. For the caseof NS-BH binary merger, Meszaros & Rees(1992a) discussed the increased radiative effi-ciency due to gravitational focusing by the BHof the neutrino-antineutrino interactions fromthe disrupted NS debris, giving a quantitativediscussion of channeling into a jet along theaxis.

To address the problem of the thermalspectrum and the radiative inefficiency at thephotosphere due to most of the energy beingconverted into kinetic energy form, Rees &Meszaros (1992) showed that both of these is-sues are solved by considering the strong for-ward and reverse shocks produced in the decel-

eration of the relativistic ejecta by the externalmedium, which (unlike in the non-relativisticexpansion) occurs when the ejecta has sweptup an external mass which is ∼ 1/Γ of itsown mass, re-thermalizing about half of thebulk kinetic energy. The strong shock leads toa power-law relativistic electron spectrum viathe Fermi mechanism, and via synchrotron ra-diation results in non-thermal power-law spec-tra. For a brief (impulsive) initial energy in-put, the effects of the deceleration are felt ona timescale tdec ∼ rdec/2Γic2, when the ini-tial forward shock Lorentz factor has droppedto ∼ Γi/2 and the reverse shock, initiallyweak, has just become trans-relativistic. Theresults are the same whether the outflow is jet-like or spherical, for jet opening angles largerthan 1/Γ. At the photospheric radius a ther-mal spectrum is still emitted, but occurringabove the saturation radius, adiabatic coolingmakes its spectral contribution sub-dominant.The dynamics and the synchrotron and inverseCompton spectra from the forward and re-verse external shock were discussed in detailin Meszaros et al. (1993); Meszaros & Rees(1993).

A major motivation for introducing internalshocks arose after the launch of the ComptonGRO (CGRO) spacecraft in late 1991, whichfound gamma-ray light curves which showedvariabilities as short as 10−3s. Such short vari-ability can get smeared out in external shocks,which occur at relatively large radii. Rees &Meszaros (1994) showed that internal shocksat radii much smaller than those of the exter-nal shock can arise due to irregularly ejectedgas shells of different bulk Lorentz factors.These can collide and shock at intermediateradii above the photosphere but below the ex-ternal shock, leading to observable radiationwhose variability is due the variability of theejection from the central engine. Being abovethe photosphere, the shock radiation from syn-chrotron and inverse Compton is unsmearedand non-thermal.

A different power source for GRBs wasproposed by Woosley (1993), in addition toBNS and NS-BH mergers.This is the collapsarmodel, resulting from the collapse of the coreof massive stars leading to a central black hole


(or temporarily a magnetar). When the coreis rotating fast enough, the mass fallback to-wards the BH would lead to an accretion diskpowering a jet, which if fed long enough, canbreak out from the collapsing stellar envelope.The BH, accretion disk and jet resulting fromthis is similar to those expected in compactBNS or NS-BH mergers, and the shock radi-ation outside the envelope would have simi-lar properties. However the accretion can lastmuch longer, since fall-back times are long andthe outer accretion radii would be larger, lead-ing to longer total burst durations. This led to anatural explanation for the striking dichotomybetween the two populations of short (∆tγ ∼ 2sand long (2s ∼ ∆tγ ∼ 103s) GRBs identified byKouveliotou et al. (1993).

Multi-wavelength, broadband spectra areexpected in general from the external forwardand reverse shocks, the reverse shock syn-chrotron predicting optical/UV radiation andthe forward shock inverse Compton scatteringof synchrotron photons reaching GeV energiesMeszaros & Rees (1993). The latter provided amodel (Meszaros & Rees 1994) for the long-lasting GeV emissions first seen in CGRO-EGRET data, while the former provided anexplanation for the optical “prompt” opticalemission first detected by Akerlof et al. (1999).Internal shocks also lead to broadband spec-tra (Papathanassiou & Meszaros 1996), typi-cally harder than in external shocks, due to thelarger comoving magnetic fields at the smallerradii. The observation of some of the longerduration bursts, whose duration could signif-icantly exceed the expected deceleration timetdec ∼ rdec/2Γ2

i c2, motivated a more detaileddiscussion of external shocks (Sari & Piran1995; Sari 1997), distinguishing between thinshell cases (the limiting case from brief impul-sive accretion) and thick shell cases (for longeraccretion), where the reverse shock may be rel-ativistic.

The long-term afterglow of a GRB,as opposed to the “prompt” emission dis-cussed above, was first discussed quantita-tively (Meszaros & Rees 1997) in a paperwhich appeared two weeks before the firstannounced detection of an X-ray afterglowfrom GRB 970228 with the Beppo-SAX satel-

Fig. 3. The early classical paradigm of the stan-dard model (top) and the newer version giving moreemphasis to the photosphere and considering alter-native mechanisms in the internal shock or promptemission region.

lite (Costa et al. 1997). Its optical afterglowwas discovered by van Paradijs et al. (1997),and other afterglows soon followed, includ-ing GRB 970508 (Metzger et al. 1997) whichyielded the first redshift (z = 0.835), prov-ing that they were indeed cosmological. Theobservations confirmed in their main featuresthe predictions of the afterglow model, includ-ing the power law time decay, spectra andtimescale (Wijers et al. 1997). Synchrotron ra-diation, including the transition between slowand fast cooling regimes (Meszaros et al. 1998;Sari et al. 1998), provided a satisfactory fit formost of the observations in the subsequent pe-riod.

2. Standard GRB model and itsevolution

The “standard” GRB fireball shock model out-lined in the second half of the above section hasproved extremely durable, despite a numberof challenges and modifications of detail. Forcomprehensive reviews, see e.g., Piran (1999,2004); Kumar & Zhang (2015); Zhang (2019).Its simplest form, most often used for interpret-ing observations, is in Fig. 1.


The afterglow radiation, from radiothrough optical, X-ray and more recently GeVis overall well fitted, with some modifications,by the external shock synchrotron emission,e.g. Zhang et al. (2006). For the ”prompt”emission (broadly the typically MeV radiationwithin ∆tγ ' T90), however, an origin in termsof synchrotron has been criticized, e.g. Preeceet al. (1998), since the low energy slope ofsome GRB prompt spectra is harder then thelimiting synchrotron slope of -2/3 in dN/dE(harder than +1/3 in EdN/dE).

One possible solution is that the promptemission may be due to the optically thickphotosphere, whose peak can be in the MeVrange and the low energy slope is as hard as+2 (Eichler & Levinson 2000). This worksbut it requires an additional shock or othercomponent to make a high energy power law(Meszaros & Rees 2000); also, if the pho-tosphere is well above the saturation radiusadiabatic cooling makes it radiatively ineffi-cient. Radiatively efficient photospheres, how-ever, may arise naturally if the photospheresare dissipative (Rees & Meszaros 2005), e.g.by magnetic reconnection, or subphotosphericshocks. A natural sub-photospheric dissipa-tion mechanism is proton-neutron decoupling,which can produce efficient photospheric spec-tra from low energies all the way to multi-GeV(Beloborodov 2010), Fig. 2 (left).

However, the earlier critiques of the syn-chrotron low energy slopes may be unjusti-fied, having been obtained taking wide timebins or time-integrated spectra. If one consid-ers the time evolution of the shock-acceleratedelectrons, from injection through cooling, andtakes into account that electrons radiating atdifferent frequencies have different energiesand may be in different cooling regimes (fast,intermediate, slow), the spectra convolved withthe detector energy resolution and responsefunction can give various slopes, and the greatmajority of the observed GRB slopes can befitted with synchrotron, e.g. Burgess et al.(2018); Ravasio et al. (2019a), Fig. 2, right.

A critique of the simple internal shocksin which only the electrons radiate (leptonicmodels) has been that they are generally in-efficient, not dissipating enough of the me-

chanical energy in the relative motion betweensuccessively ejected shells, and Fermi accel-eration putting much of this dissipated energyin non-radiating protons. In more realistic in-ternal shocks, however, this radiative ineffi-ciency can be larger, e.g. when the dissipationis largely by magnetic instabilities and recon-nection, or if hadronic collisions and reaccel-eration of secondaries are taken into account.Thus, the early GRB paradigm based on inter-nal plus external shocks and an inefficient pho-tosphere (Fig. 3, top) has, since about 2005,evolved into one of an efficient photosphereand/or an efficient internal shock plus externalshock (Fig. 3, bottom). An example of efficientmagnetic dissipation internal shock models isthe ICMART model of Zhang & Yan (2011),while an example of an efficient hadronic in-ternal shock with secondary reacceleration isthat of Murase et al. (2012).

After the launch of the Fermi Gamma-raySpace Telescope 2008, its LAT detector startedto observe in a significant fraction of GRBsthat the so-called Band broken power law spec-trum above the MeV peak extended into theGeV range, as already found in some previ-ous EGRET spectra. Such “extended” Bandspectra can be modeled, e.g. with photosphericmodels, as seen in Fig. 2 (left). However, inmany Fermi-LAT GRBs the GeV appeared as asecond power-law component, harder than theBand β upper branch.

The question is whether this second, harderGeV component is due to inverse Compton(IC) upscattering of the Band component, or isit due to protons being accelerated and leadingto cascades with radiation from secondary lep-tons. Both types of models can give reasonablefits. Leptonic models where the Band spectrumarising in the photosphere is up-scattered byshocked electrons in internal shocks give rea-sonable results, e.g. Toma et al. (2011). An al-ternative leptonic model considers a baryonicor magnetic photosphere producing a Bandspectrum which is up-scattered in an externalshock, also giving good fits (Veres & Meszaros2012). Fig. 4 (left).

Hadronic models, on the other hand, couldin principle have substantial advantages. E.g.Murase et al. (2012) calculated an inter-


Fig. 4. Left: Leptonic model with photosphere plus external shock upscattering a GeV second componentVeres & Meszaros (2012). Right: Hadronic model with internal shock accelerating electrons and protonsleading to cascades and secondary re-acceleration, leading to self-consistent Band spectrum and secondGeV component (Murase et al. 2012).

Fig. 5. Left: fits to preliminary data showing light curves of various energy components of GRB 190114C(Wang et al. 2019). Right: fits to preliminary data at several epochs for the spectrum of GRB190114C(Ravasio et al. 2019b).

nal shock model accelerating both electronsand protons, where hadronic cascades andstochastic reacceleration of the leptonic secon-daries in the post-shock turbulence leads self-consistently to both the Band MeV and theGeV second hard component from the same re-gion, Fig. 4 (right). This model provides goodefficiency, which is one of its attractions for in-ternal shocks, and it may be applicable not only

to shocks but also, e.g. to magnetic dissipationregions, where MHD turbulence is expected.

3. Some recent developments

Recently the MAGIC imaging air fluores-cence telescope (IACT) announced the detec-tion of photons in excess of 300 GeV, and per-haps up to a TeV, in the bright GRB190114C(Mirzoyan 2019), also detected at other en-


Fig. 6. GRB/GW170817A, two opposed views on the SGRB radiation from a BNS. Left: observed radiationdominated by the cocoon, for a choked jet. Right: observed radiation dominated by an emergent top-hat jet(Kasliwal et al. 2017).

Fig. 7. Left: IceCube and Antares upper limits for GRB170817 (Albert et al. 2017), compared to BNSjet EE extended emission model (Kimura et al. 2017) for various jet offset angles. Right: Internal andcollimation shocks in trans-ejecta jet propagating through a BNS dynamical ejecta (Kimura et al. 2018).

ergies by Fermi, Swift, INTEGRAL and nu-merous other facilities. This was the first highconfidence (∼ 20σ) detection of a GRB withan IACT at such energies, a long awaited featwhich should be easier to accomplish with thefuture CTA. Preliminary analyses show that thelong lasting (∼ 103s) sub-TeV component ismostly associated with the afterglow seen atother energies, e.g. Fig. 5. The spectral slopeof the sub-TeV component appears harder thanthe usual Band component, pending furtherMAGIC analysis.

Detection of ∼ TeV emission from a GRBhas two requirements, one being that the red-shift be smallish, so that γγ absorption in theIGM external background light is not too se-vere, and the other being that the same ab-sorption is absent or at least mitigated in theGRB radiation zone and its immediate neigh-borhood. Fermi-LAT detections of GRBs haveshown source-frame emission up to severaltens of GeV and in one case even ∼ 100GeV ,but the present ∼ 300GeV can put significant


constraints on models. Much theoretical workremains to be done on this event.

The other major recent development wasthe short GRB 170817 detection both electro-magnetically (EM) through multi-wavelengthphotons, and through gravitational waves(GWs). This was very exciting, being the firsthigh significance multi-messenger detection ofa transient using GWs1. This was a short GRB(SGRB) with ∆tγ ≤ 2s), detected by Fermi,INTEGRAL, Swift and other EM instruments.These objects were long expected to arise fromBNS mergers, an interpretation for which ac-cumulating evidence, e.g. Gehrels et al. (2009),had almost but not quite reached the 100%confidence level. In this case, slightly preced-ing the EM flash, the associated detection ofGWs (Abbott et al. 2017), which were also ex-pected from BNS mergers, conclusively con-firmed that SGRBs where indeed BNS merg-ers. In addition, it also confirmed that BNSscan also produce a type of optical/IR flashknown as a kilonova, surmised to be respon-sible also for the elements heavier than the Fe-group via the r-process, e.g. Hotokezaka et al.(2018); Kasliwal et al. (2019).

The SGRB radiation of GRB/GW170817looked typical, except for being fainter andsomewhat softer than expected for its low dis-tance of 40 Mpc. The role played in GRBsby cocoons (Meszaros & Rees 2001; Ramirez-Ruiz et al. 2002) and choked jets (Meszaros &Waxman 2001) had been considered early on,and in the case of GRB/GW170817A a naturalpossibility was that its weaker γ-rays might beattributed either to a choked jet with a cocoonbreakout, or to an off-axis top-hat emergent jet,e.g. Kasliwal et al. (2017); Ioka & Nakamura(2017) and others. While a cocoon interpreta-tion may be favored over a simple top-hat jet,the observation of a superluminal jet signature(Mooley et al. 2018) and other features of theafterglow (Troja et al. 2018) indicate that eithera Gaussian structured jet or a cocoon could fitthe data.

1 The other previous high significance multi-messenger transient was SN 1987a, where besidesphotons also thermal (MeV) neutrinos were de-tected.

The next burning question, as far as GRBmulti-messenger studies, is whether GRBs canalso be detectable via neutrinos. Of course bothLGRBs (as core-collapse objects) and SGRBs(compact mergers involving at least one neu-tron star which is heated to virial temperatures)will emit a large fraction of their core bind-ing energy in thermal (5-30 MeV) neutrinos.At these energies the neutrino-nucleon detec-tion cross section is of order 10−44cm2, and atcosmological distances the flux is undetectablewith current detectors. High energy neutri-nos however have much higher cross sections(∼ 10−34cm2 around 10 TeV), and IceCubeis detecting a diffuse astrophysical flux in the10 TeV-10 PeV range (Aartsen et al. 2013;IceCube Collaboration 2013). The total num-ber of neutrinos so far is of order 50, dis-tributed isotropically in the sky, with local-ization error circles ranging from ∼ 1o (formuon neutrino tracks) to 15− 30o (for electronneutrino cascades), hence difficult to associatewith individual sources. Recently, however, ahigh energy (multi-TeV) muon neutrino wasdetected, with the blazar TXS 0506+56 withinits error circle, which was undergoing a γ-rayflaring episode in near time coincidence withthe neutrino arrival. The region also showedother previous neutrinos in the past years, butwithout coincident γ-ray flares, so the totalcoincidence significance is ∼ 3.5σ, which isinteresting but not yet considered conclusiveevidence (IceCube, and other Collaborations2018; IceCube Collaboration et al. 2018).

The possibility of GRBs being high en-ergy neutrino sources has been investigatedby IceCube using classical GRBs, i.e. bright,EM-detected, mainly LGRBs. These have beendisfavored by IceCube analyses, e.g. Aartsenet al. (2015), using particular models of theneutrino emission expected. The same con-clusion is reached by IceCube for classicalGRBs in a model-independent way using con-straints based on neutrino multiplet observa-tions (Aartsen et al. 2018), but the same studyleaves unconstrained a (theoretically plausible)origin in low-luminosity or choked GRBs, e.g.Senno et al. (2016). Low luminosity and/orchoked GRBs could be more numerous thanclassical GRBs, and at the typically high


redshifts they would be electromagneticallymissed or hard to detect, while their cumula-tive neutrino flux could add up to what IceCubesees.

SGRBs would in principle appear to beideal objects for constraining physical mod-els if in addition to GWs they also producedobservable neutrinos. At first sight it wouldseem that the expected neutrino fluxes wouldbe much lower than in LGRBs, since the SGRBprompt MeV emission is shorter and underlu-minous compared to LGRBs. However a largefraction of SGRBs also exhibit a longer tail(∼ 100s) of softer radiation in the 50 keVrange. This softer extended emission (EE) canbe modeled as a late jet emission with a bulkLorentz factor lower than the prompt, provid-ing a higher comoving density of target pho-tons for pγ photo-hadronic interactions lead-ing to neutrinos. The neutrino flux is still lowat typical redshifts, but at the redshift z ∼ 0.01(about 40 Mpc) of GBB 170817A, it couldhave been detectable by IceCube, if the jet beenhead-on (Kimura et al. 2017); however, for ahigher inclination angle θLOS ∼ 20 − 30o ofthe line of sight relative to the jet axis, as in-ferred from multi-wavelength observations, thelower Doppler boost in that direction implies amuch lower observable flux, which falls belowthe IceCube sensitivity, Fig. 7 (left).

The SGRB jet and shock structure is likelyto be more complicated as it is making its waythrough the dynamical ejecta, Fig. 7 (right).Both collimation shocks and internal shocksare expected in choked jets or before thejet emerges from the ejecta, and the inter-nal shocks occurring in the pre-collimationjet satisfy the conditions for Fermi accelera-tion of charged particles, leading to neutrinosvia photo-hadronic interactions (Kimura et al.2018). One can expect from such events a fewup-going neutrinos in IceCube from a mergerat 40 Mpc occurring in the Northern sky, if thejet is directed at Earth. For optimistic jet pa-rameters, a joint GW-IceCube detection mightbe achievable in a few years of operation, or forIce-Cube Gen 2 this would be probable evenfor moderate jet parameters.

Acknowledgements. I am grateful to K. Murase,S.S. Kimura and D.B. Fox for discussions, and theEberly Foundation for support.

References

Aartsen, M. G., Abbasi, R., Abdou, Y., et al.2013, Phys. Rev. Lett., 111, 021103

Aartsen, M. G., Ackermann, M., Adams, J.,et al. 2015, ApJ, 805, L5

Aartsen, M. G., Ackermann, M., Adams, J.,et al. 2018, arXiv:1807.11492

Abbott, B. P., Abbott, R., Abbott, T. D., et al.2017, ApJ, 848, L13

Akerlof, C., Balsano, R., Barthelmy, S., et al.1999, Nature, 398, 400

Albert, A., Andre, M., Anghinolfi, M., et al.2017, ApJ, 850, L35

Beloborodov, A. M. 2010, MNRAS, 407, 1033Burgess, J. M., Begue, D., Bacelj, A., et al.

2018, arXiv:1810.06965Cavallo, G. & Rees, M. J. 1978, MNRAS, 183,

359Costa, E., Frontera, F., Heise, J., et al. 1997,

Nature, 387, 783Eichler, D., et al. 1989, Nature, 340, 126Eichler, D. & Levinson, A. 2000, ApJ, 529,

146Gehrels, N., Ramirez-Ruiz, E., & Fox, D. B.

2009, ARA&A, 47, 567Goodman, J. 1986, ApJ, 308, L47Hotokezaka, K., Beniamini, P., & Piran,

T. 2018, International Journal of ModernPhysics D, 27, 1842005

IceCube Collaboration 2013, Science, 342, 1IceCube, and other Collaborations 2018,

Science, 361, eaat1378IceCube Collaboration, Aartsen, M. G.,

Ackermann, M., et al. 2018, Science, 361,147

Ioka, K. & Nakamura, T. 2017, e-printarXiv:1710.05905

Kasliwal, M. M., Nakar, E., Singer, L. P., et al.2017, Science, 358, 1559

Kasliwal, M. M., Kasen, D., Lau,R. M., et al. 2019, MNRAS in press,arXiv:1812.08708

Kimura, S. S., et al. 2017, ApJ, 848, L4Kimura, S. S., Murase, K., Bartos, I., et al.

2018, Phys. Rev. D, 98, 043020


Kouveliotou, C., Meegan, C. A., Fishman,G. J., et al. 1993, ApJ, 413, L101

Kumar, P. & Zhang, B. 2015, Phys. Rep., 561,1

Meszaros, P. 2001, Science, 291, 79Meszaros, P. & Rees, M. J. 1992a, MNRAS,

257, 29PMeszaros, P. & Rees, M. J. 1992b, ApJ, 397,

570Meszaros, P., Laguna, P., Rees, M. J. 1993,

ApJ, 415, 181Meszaros, P. & Rees, M. J. 1993, ApJ, 418,

L59Meszaros, P. & Rees, M. J. 1994, MNRAS,

269, L41Meszaros, P. & Rees, M. J. 1997, ApJ, 476, 232Meszaros, P., Rees, M. J., & Wijers, R. A. M. J.

1998, ApJ, 499, 301Meszaros, P. & Rees, M. J. 2000, ApJ, 530, 292Meszaros, P. & Rees, M. J. 2001, ApJ, 556,

L37Meszaros, P. & Waxman, E. 2001,

Phys. Rev. Lett., 87, 171102Metzger, M. R., Djorgovski, S. G., Kulkarni,

S. R., et al. 1997, Nature, 387, 878Mirzoyan, R. 2019, The Astronomer’s

Telegram, 12390Mooley, K. P., Frail, D. A., Dobie, D., et al.

2018, ApJ, 868, L11Murase, K., et al. 2012, ApJ, 746, 164Narayan, R., Piran, T., & Shemi, A. 1991, ApJ,

379, L17Narayan, R., Paczynski, B., & Piran, T. 1992,

ApJ, 395, L83Paczynski, B. 1986, ApJ, 308, L43Paczynski, B. 1990, ApJ, 363, 218Papathanassiou, H. & Meszaros, P. 1996, ApJ,

471, L91Piran, T. 1999, Phys. Rep., 314, 575Piran, T. 2004, Reviews of Modern Physics,

76, 1143Preece, R. D., Briggs, M. S., Mallozzi, R. S.,

et al. 1998, ApJ, 506, L23Ramirez-Ruiz, E., Celotti, A., & Rees, M. J.

2002, MNRAS, 337, 1349Ravasio, M. E., Ghirlanda, G., Nava, L., &

Ghisellini, G. 2019a, arXiv:1903.02555Ravasio, M. E., Oganesyan, G., Salafia, O. S.,

et al. 2019b, arXiv:1902.01861Rees, M. J. & Meszaros, P. 1992, MNRAS,

258, 41PRees, M. J. & Meszaros, P. 1994, ApJ, 430,

L93Rees, M. J. & Meszaros, P. 2005, ApJ, 628, 847Sari, R. 1997, ApJ, 489, L37Sari, R. & Piran, T. 1995, ApJ, 455, L143Sari, R., Piran, T., & Narayan, R. 1998, ApJ,

497, L17Senno, N., Murase, K., & Meszaros, P. 2016,

Phys. Rev. D, 93, 083003Shemi, A. & Piran, T. 1990, ApJ, 365, L55Toma, K., Wu, X.-F., & Meszaros, P. 2011,

MNRAS, 415, 1663Troja, E., Piro, L., Ryan, G., et al. 2018,

MNRAS, 478, L18van Paradijs, J., Groot, P. J., Galama, T., et al.

1997, Nature, 386, 686Veres, P. & Meszaros, P. 2012, ApJ, 755, 12Wang, Y., Li, L., Moradi, R., & Ruffini, R.

2019, arXiv:1901.07505Wijers, R. A. M. J., Rees, M. J., & Meszaros,

P. 1997, MNRAS, 288, L51Woosley, S. E. 1993, ApJ, 405, 273Zhang, B. 2019, The Physics of Gamma-Ray

Bursts (Cambridge Univ. Press, Cambridge,UK)

Zhang, B., Fan, Y. Z., Dyks, J., et al. 2006, ApJ,642, 354

Zhang, B. & Yan, H. 2011, ApJ, 726, 90

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