Discovery of VHE gamma rays from GRB 190114C Koji Noda (ICRR, U. - - PowerPoint PPT Presentation

Discovery of VHE gamma rays from GRB 190114C

Koji Noda (ICRR, U. Tokyo)

• A. Berti, S. Covino, S. Fukami, S. Inoue, 

• D. Miceli, E. Moretti, L. Nava, Y. Suda, I. Vovk 

• n behalf of the MAGIC Collaboration

12 Sep 2019 TAUP 2019 @ Toyama

Koji Noda (ICRR) TAUP 2019 @ Toyama

Gamma Ray Bursts

• GRBs are the most violent explosions in the Universe
• Long (>~2 s): collapse of a massive star (supernova) 


Short (<~2 s): (probably) merger of binary neutron stars

• Prompt emission by internal shock, seen in keV-MeV, followed

by afterglow by external shock, seen in more wavebands

(c) NASA

Koji Noda (ICRR) TAUP 2019 @ Toyama

>~GeV γ from GRBs

• Ex.) 130427A by Fermi-LAT: 95 GeV after ~4 min, 32 GeV ~9 h

Ackermann et al. (2014)

Naturally thinking, GeV γ is probably not from the main synchrotron component, but it was not confirmed even with the monster burst... With a delay, mostly in late prompt - early afterglow

Koji Noda (ICRR) TAUP 2019 @ Toyama

MAGIC

• 17 m φ, 2 Imaging Atmospheric Cherenkov Telescopes since 2009


at ORM, La Palma, Canaries, Spain. 2200 m a.s.l.

• Sensitivity (50 h, 5σ, >220 GeV): ~0.66% Crab, E resolution: ~15% @ 


1 TeV, ~23% @ 100 GeV, E threshold: ~50 GeV, ~30 GeV (SumTrig)

• Slewing speed: 7 deg/s (~25 s for 180 deg) The best IACT for GRB

Koji Noda (ICRR) TAUP 2019 @ Toyama

Efforts to catch the guy

• "Good GRBs are always with Sun, bright Moon, or bad 

• weather. Too unlucky..." ? No, just a low duty cycle ~10% 


=> Observation under Moon is "standard-ized" in MAGIC 


Ahnen, et al. Astropart. Phys. 94, 29–41 (2017)

• Not like "trials & errors, and wait for a good result" 


Active selection (filtering) is crucial not to waste time and 
 efforts with useless alerts => Automatic alert system

• Strategy (Zd & time ranges) tuned with newest knowledge
• Added late time GRB (soon after 130427A), and more 


recently HEν and GW alerts

• Telescope should respond to the alerts correctly 


Carosi, et al., ICRC, 809 (2015); Berti, et al. IAU Symposium, 70–73 (2017)

Koji Noda (ICRR) TAUP 2019 @ Toyama

History of MAGIC GRBs

Known z 
 distribution Delay vs. Zenith angle

• 105 GRBs observed since

2005 (not all analysed)

– 24 with delay <100 s – out of which 15 stereo – out of which 5 known z <1.5

• Fastest: 24 s = 160821B, 


z = 0.16 (closest as well)

• second closest 160623A:

z=0.367, but delay 7.6e4 s

• z<1 && delay < 1h

Koji Noda (ICRR) TAUP 2019 @ Toyama

Hint from GRB 160821B

• Triggered by Swift-BAT 


T90 ~0.5 s Short GRB

• Swift-XRT: t < 300 s extended 


emission + decay + plateau?

• MAGIC covered this period 


24 s - 4 hr (14.4 ks)

– Bright moon, adverse weather – >4 (pre-trial), 3.1 sigma (post-trial) 
 hint of detection in >600-800 GeV – No candidate source around – No detection ~1 yr later (not steady)

• No detection by Fermi-LAT.
• Kilonova (Troja+, Lamb+) "the best-


sampled kilonova LC w/o a GW trigger"

• Shown in mtgs. Publication in prep.

Koji Noda (ICRR) TAUP 2019 @ Toyama

GRB190114C

ATel #12390 (and also GCN #23701)

• Long GRB with T90 = 361 s


triggered by Swift-BAT
 "very bright" "half 130427A"

• The 3rd closest (z=0.42) in 


MAGIC GRBs

• Not the fastest (~50 s) but 


well within T90

• Zenith angle from 55 deg
• moderate moon (again!) 


=> Eth ~= 300 GeV

• First clear detection of a 


GRB in VHE regime

• I was the burst advocate, 


coordinated following analyses, and analysed the data by myself. Accepted in Nature, to be published soon.

Koji Noda (ICRR) TAUP 2019 @ Toyama

How DAQ started

ToDo list in the manual after the inquiry call from the operators

• "Don't panic!" ✓ 


but, well, too calm first (sleepy), then in a panic :)

• Check coordinates ✓
• Check system: 


automatic procedure, stable DAQ and its rate, mirrors, pointing, calibration, and

• nline analysis ✓ 


but, in the phone we did not talk about significance. We were too much used to non-detections... :)

Operator writing it: 


• M. Takahashi (ICRR)

(in Japan Time)

<Phone call here> Me

(OK,,, but want a bit more sleep)

Koji Noda (ICRR) TAUP 2019 @ Toyama

~0.1 "kCrab" @ 0.3 TeV

Note the Y scale difference by a factor 10 Very strong signal, almost BG free

Koji Noda (ICRR) TAUP 2019 @ Toyama

First a few min

• System worked perfectly. Stable pointing, threshold, DAQ
• Alert received 22 s after the burst, + 28 s to point & start to track, 


+ 7 s to start DAQ, + 5 s for valid data (with a safe margin of 1-2 s)

P r e l i m i n a r y E M B A R G O

Crab Nebula flux

"Embargo" for following plots 
 until published in Nature

Koji Noda (ICRR) TAUP 2019 @ Toyama

P r e l i m i n a r y E M B A R G O P r e l i m i n a r y E M B A R G O

First runs

• 1st run (~20 mins): 


ATel ">20 sigma in the first 20 min for >300 GeV" 
 >50 sigma with the offline analyses

• 1st & 2nd runs (~40 mins): 


Monotonic decay, no hint 


• f break. Most probably, 


in the afterglow phase from the beginning

• power-law decay in MeV-

GeV starts from 6 s after T0, even if T90 >300 s

Ravasio, et al., A&A 626, A12 (2019)

Koji Noda (ICRR) TAUP 2019 @ Toyama

P r e l i m i n a r y E M B A R G O

First clear detection of 
 a component beyond synchrotron

• Bottom curves: the expected max. photon energy of electron synchrotron

radiation in the standard afterglow theory, for two extreme cases

• isotropic-equivalent blast wave kinetic energy Ek,aft = 3 x 1055 erg
• dotted – n = const., dashed – n ~ 1/R²

cf.) 130427A
 Ackermann et al. (2014)

Up to 1 TeV

Koji Noda (ICRR) TAUP 2019 @ Toyama

Integrated SED for 40 mins

• No sign of any break up to 1 TeV
• Evolution of spectrum? and finally,,, what is the probable

mechanism of the component beyond synchrotron?

• MWL study ongoing (accepted in Nature, yesterday)

P r e l i m i n a r y E M B A R G O

Koji Noda (ICRR) TAUP 2019 @ Toyama

GRB 190114C is 
 not a monster

• Monster 130427A: 


Eγ,iso ~=1.4e54 erg

• More recently, HESS

also reported a 5σ 
 γ-ray emission up to 400 GeV from GRB 180720B (z=0.653), 
 ~10 h after the burst

• Another, 2 weeks ago

(190829A, z=0.0785)

• For VHE-γ detections, 


no need to be an exceptional GRB, 
 but just need to be relatively close

Koji Noda (ICRR) TAUP 2019 @ Toyama

Summary

• MAGIC clearly detected afterglow of GRB 190114C

from redshift z=0.4245. This is a component not seen previously, different from the synchrotron, extending from 300 GeV up to 1 TeV (at least)

• This is the brightest source ever detected by IACTs, the

peak rate of gamma-rays was ~0.1 kCrab !

• MWL study to dig into the mechanism ongoing
• Most GRBs may have TeV components similar to

GRB 190114C, which may be detectable as long as redshift is low and the observing conditions are suitable

• This is just the beginning of the GRB era with IACTs