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 
 on behalf of the MAGIC Collaboration 12 Sep 2019 TAUP 2019 @ Toyama

Gamma Ray Bursts (c) NASA • 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 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) With a delay, mostly in late prompt - early afterglow Naturally thinking, GeV γ is probably not from the main synchrotron component, but it was not confirmed even with the monster burst... 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, 5 σ , >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 HE ν 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 • 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: Delay vs. Zenith angle z=0.367, but delay 7.6e4 s • z<1 && delay < 1h Known z 
 distribution 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 • Long GRB with T 90 = 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 T 90 • Zenith angle from 55 deg • moderate moon (again!) 
 => Eth ~= 300 GeV • First clear detection of a 
 GRB in VHE regime ATel #12390 (and also GCN #23701) • 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 Operator writing it: 
 M. Takahashi (ICRR) ToDo list in the manual after the (in Japan Time) inquiry call from the operators <Phone call here> "Don't panic!" ✓ 
 • but, well, too calm first Me (sleepy), then in a panic :) Check coordinates ✓ • Check system: 
 • automatic procedure, stable DAQ and its rate, mirrors, pointing, calibration, and online analysis ✓ 
 (OK,,, but want a bit more sleep) but, in the phone we did not talk about significance. We were too much used to non-detections... :) 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) y r a n i m O i l e G r R P A B M E "Embargo" for following plots 
 Crab Nebula flux until published in Nature Koji Noda (ICRR) TAUP 2019 @ Toyama

First runs • 1st run (~20 mins): 
 y r a n i m ATel ">20 sigma in the first O i l e G r R P 20 min for >300 GeV" 
 A B M E >50 sigma with the offline analyses • 1st & 2nd runs (~40 mins): 
 Monotonic decay, no hint 
 of break. Most probably, 
 in the afterglow phase from the beginning y r a n i m • power-law decay in MeV- O i l e G r R P A GeV starts from 6 s after B M E T 0 , even if T 90 >300 s Ravasio, et al., A&A 626, A12 (2019) Koji Noda (ICRR) TAUP 2019 @ Toyama

First clear detection of 
 a component beyond synchrotron cf.) 130427A 
 Up to 1 TeV Ackermann et al. (2014) y r a n i m O i l e G r R P A B M E • 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 E k,aft = 3 x 10 55 erg • dotted – n = const., dashed – n ~ 1/R ² Koji Noda (ICRR) TAUP 2019 @ Toyama

Integrated SED for 40 mins y r a n i m O i l e G r R P A B M E • 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) Koji Noda (ICRR) TAUP 2019 @ Toyama

GRB 190114C is 
 not a monster • Monster 130427A: 
 E γ ,iso ~=1.4e54 erg • More recently, HESS also reported a 5 σ 
 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 Koji Noda (ICRR) TAUP 2019 @ Toyama