Seminars

Tsvi PIRAN

(COLLOQUIUM)

05 Jun 2025, 11:30, Aula Jappelli

GeV-TeV Emission from GRBs: Insights from Recent Observations

Recent observations by MAGIC, HESS, and LHASSO have detected several gamma-

ray bursts (GRBs) as GeV–TeV sources. These findings offer a fresh perspective on

the longstanding GRB puzzle. In this talk, I will review these high-energy detections,

with particular focus on GRB 190114A and the exceptionally bright GRB 221009A

(the “BOAT”). A key insight emerging from these observations is that the extremely

high-energy photons do not originate during the prompt emission phase. Rather,

they are produced during the very early afterglow stage, likely through synchrotron

self-Compton (SSC) processes. This realization compels us to revisit conventional

models of particle acceleration in relativistic shocks. At the same time, these

observations provide a rare window into an otherwise unexplored stage of GRB

evolution—the initial interaction of the blast wave with the ambient medium.

Additionally, the detection of such high-energy photons carries intriguing

implications for constraints on quantum gravity theories. Finally, I will touch on a

novel class of gravitational wave signals that may be associated with GRBs, offering

new possibilities for multi-messenger astronomy.

Prof. Tsvi Piran is the Schwarzmann Chair for theoretical physics at the Hebrew University of

Jerusalem. He graduated in 1976 at the Hebrew University and was a research fellow at

Oxford, UT Austin, and Princeton. He was also visiting Professor at Harvard, Columbia, and

NYU and distinguished Moore Scholar at Caltech. One of the most highly cited

astrophysicists with over 500 scientific papers and a dozen books, Piran also obtained

three ERC Advanced Grants and received prestigious Prizes including the Lagrange, EMET,

and Marcell Grossman awards.

Piran is best known for his major contributions on gamma-ray bursts (GRBs), from their

extragalactic origin and the possibility of a binary neutron star merger progenitor to the

seminal work on the fireball model, afterglow theory, and the physics of GRB jets.

Nonetheless, his research spans many other topics in theoretical astrophysics ranging from

numerical relativity, accretion, inflation, cosmic censorship, tidal disruption events, and

more.

NOTE: In the afternoon the speaker will meet at 4.30 pm with students and post-docs in sala della Madonna for a new format called "Spritz&Tramezzino" that is meant as a moment between young people and speaker to discuss their mutual scientific interests, the career path of the speaker, future perspectives, and the secret recipe of the perfect Spritz. 

Join Zoom Meeting

https://unipd.zoom.us/j/85273198731?pwd=V1ZiNE9ZWUN4ZTdIUzJsTFo0Z3U2Zz09

Meeting ID: 852 7319 8731

Passcode: 208186

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Next scheduled seminars:

June 19th - David Izquierdo-Villalba

and many more!!

Colloquia: 

June 5th - Tsvi PIRAN

CONTAMINATION Seminars: 

Juen 6th - Federica Cacciatore (ISPRA)