Lorentz invariance violation induced threshold anomaly versus very-high energy cosmic photon emission from GRB 221009A

2025-04-27 0 0 975.9KB 5 页 10玖币

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Lorentz invariance violation induced threshold anomaly versus very-high energy

cosmic photon emission from GRB 221009A

Hao Lia, Bo-Qiang Maa,b,c,∗

aSchool of Physics, Peking University, Beijing 100871, China

bCenter for High Energy Physics, Peking University, Beijing 100871, China

cCollaborative Innovation Center of Quantum Matter, Beijing, China

Abstract

It has been reported that the Large High Altitude Air Shower Observatory (LHAASO) observed very high energy

photons from GRB 221009A, with the highest energy reaching 18 TeV. We ﬁnd that observation of such high energy

photons is quite nontrivial since extragalactic background light could absorb these photons severely and the ﬂux is too

weak to be observed. Therefore we discuss a potential mechanism for us to observe these photons, and suggest that

Lorentz invariance violation induced threshold anomaly of the process γγ →e−e+provides a candidate to explain this

phenomenon.

Keywords:

Lorentz invariance violation, threshold anomaly, very high energy photons, gamma-ray burst

On 9 October 2022, a special gamma-ray burst (GRB)

was reported ﬁrst by Fermi and Swift and is numbered

as GRB 221009A [1–7]. This burst, located at around

RA = 288.282 and Dec = 19.495 [4], is a long burst but

with a very small redshift z= 0.1505 [8,9] compared to

most other long bursts. More remarkably, the extraor-

dinary brightness of this burst immediately makes this

burst a very interesting object for studying various as-

pects of physics and astronomy. The highest energy pho-

ton observed by Fermi-LAT reaches 99.3 GeV [4], while

more strikingly, the Large High Altitude Air Shower Ob-

servatory (LHAASO) reported more than 5000 very high

energy photon events with energies above 500 GeV, in-

cluding photons with the energy up to 18 TeV, making

these photons the most energetic GRB photons ever ob-

served [10]. This unexpected observation of 18 TeV pho-

tons immediately brings a new question: can we observe

photons with this energy if we consider only the standard

knowledge of the Universe and particle physics? In the fol-

lowing we study the background light absorption of such

photons in the Universe, show that we may need to invoke

new mechanism to explain this observation. We also argue

that Lorentz invariance violation (LIV) induced threshold

anomaly [11–19] provides a potential solution.

The Fermi Gamma-Ray Burst Monitor was triggered at

13:16:59.99 UT on 9 October 2022, and then located GRB

221009A [1,2]. LHAASO also joined in the observation of

this GRB. Since LHAASO is designed for gamma-ray as-

∗Corresponding author

Email addresses: haolee@pku.edu.cn (Hao Li),

mabq@pku.edu.cn (Bo-Qiang Ma)

tronomy in the energy band between 1011 and 1015 eV [20–

23], it eventually reveals the very high energy property of

this burst. The most intriguing result of LHAASO is that

there are photons of about 18 TeV [10]. These photons

can be used to help us understand the features of GRBs,

and also we can utilize them to study the propagation of

high energy photons in the Universe. According to the

standard model of particle physics, two photons can an-

nihilate with each other and produce an electron-positron

pair: γγ →e−e+. This annihilation process then prohibits

high energy photons from propagating a long distance in

the Universe since they can react with background photons

such as those from cosmic microwave background (CMB)

and extragalactic background light (EBL). Let Eand εb

be the energies of the high energy photon and the back-

ground photon respectively, then according to special rel-

ativity we can easily derive the threshold for this reaction

to happen [18,19]:

E≥Eth =m2

εb

,(1)

where meis the mass of electrons. For CMB photons, the

mean energy is εb'6.35×10−4eV, resulting in a threshold

energy ECMB

th '411 TeV [18,19], which indicates that

CMB is almost transparent to the LHAASO photon of

18 TeV. However, for EBL photons the situation could

be more complicated. As a rough estimate, we can take

εb'10−3eV to 1 eV according to the distribution of EBL,

leading to the corresponding thresholds Eth '261 GeV to

261 TeV [19]. As a result, EBL photons do matter to

cause an attenuation of cosmic photon propagation in the

analysis of the LHAASO photons of above 10 TeV [19]. In

Preprint submitted to Astroparticle Physics 148 (2023) 102831 doi:10.1016/j.astropartphys.2023.102831 March 7, 2023

arXiv:2210.06338v6 [astro-ph.HE] 4 Mar 2023

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Lorentzinvarianceviolationinducedthresholdanomalyversusvery-highenergycosmicphotonemissionfromGRB221009AHaoLia,Bo-QiangMaa,b,c,aSchoolofPhysics,PekingUniversity,Beijing100871,ChinabCenterforHighEnergyPhysics,PekingUniversity,Beijing100871,ChinacCollaborativeInnovationCenterofQuantumMatter,Beijing,C...

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Lorentz invariance violation induced threshold anomaly versus very-high energy cosmic photon emission from GRB 221009A

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