The variable gamma-ray sky Observing astrophysical accelerators in real time Rolf Bühler • 2nd June 2017 • Ginzburg Centennial • Moscow

Counts >800 MeV

Counts ~1 GeV ~100 GeV Selig et al. A&A 2015

Std. deviation >800 MeV

Max. variation >800 MeV

Particle acceleration UV X-rays Su el al. Nature Physics 9 2013 From Steven J. Schwartz. Astrophysical Plasmas The most studied acceleration mechanisms are shock acceleration and magnetic reconnection

Shock acceleration Sironi et al. SSRv 1 2015 Upstream 𝑑𝑁 𝑑γ ∝ γ − 𝑠 γ Sironi and Spitkovsky ApJ 726 2011 Theoretically studies since the 70's, more recently with 2D/3D Particle In Cell simulations

Magnetic reconnection Sironi and Spitkovsky ApJ 783 2014 B X-point Magnetic islands Kagan et al. SSRv 1 2015 Particles are accelerated predominantly at X-points and by scattering on magnetic islands sγ = 1.5 sγ = 2.0 sγ = 3.0 sγ = 4.0

Fermi All-sky Variability Analysis Photometric Analysis 100 – 800 MeV r95 ≈ 0.2° 0.8 – 2000 GeV r95 ≈ 0.1° Likelihood Analysis Applied all-sky in weekly time bins in two energy bins over 7.4 years. 4547 flares detected above 6σ.

The red crosses represent the x – sources circles are flares The red crosses represent the 2FAV sources. The flares used to construct the 2FAV are also shown: yellow circles are flares with the best determined position from the TS maps. Flares with worse TS map positioning are in orange, if they have been assigned to a cluster, or cyan otherwise. Flares with only FAVA positions are in magenta if they have been assigned to a cluster, green if they constitute a separate cluster. For all the flares, the radius of the drawn circles is equal to r 95 .

2FAV catalog 518 sources Matteo Giomi 77 Abdollahi et al., sub. ApJS, arXiv:1612.03165 https://fermi.gsfc.nasa.gov/ssc/data/access/lat/fava_catalog/

See Maxim Lyutikov’s talk Source classes AGNs are the dominant source class GRBs detected on a week time scale Galactic flaring sources are binaries (HMXB, Novae, pulsars) Crab nebula is still the only flaring Pulsar Wind Nebula See Maxim Lyutikov’s talk

Another Crab nebula? Sensitivity in the Galaxy F ≈ 2 10-7 ph cm-2 s-1 Preliminary MSPs Radio loud Radio quiet Sensitivity in the Galaxy F ≈ 2 10-7 ph cm-2 s-1 Crab flare with F ≈ 0.5 10-5 ph cm-2 s-1 would be detected in a large fraction of our Galaxy (≈10 kpc). Possibly PWN N157B in the Large Magelanic cloud Saito et al. AIP Proc. 2017

Spectral properties “Harder when brighter” for FSRQs and BL Lacs. FSRQs softer. Photon index always harder than 1.5 Isotropic Thompson

Spectra Crab and HMXB typically softer than for other sources Spectral properties Spectra Crab and HMXB typically softer than for other sources

Summary & Outlook Cosmic accelerators energize particles rapidly in many different source classes The second catalog of flaring sources was recently released by the LAT collaboration: AGNs dominate the variable sky: FSRQS have softer flaring spectra than BL LACs In no case is the index of the flare photon spectrum significantly harder than 1.5 In the Galaxy binaries are the dominant population. The Crab remains the only PWN for which flares are observed. FAVA is run in real time (typical 12h processing delay) and publicly available...

FAVA online https://fermi.gsfc.nasa.gov/ssc/data/access/lat/FAVA/ Dan Kocevski https://fermi.gsfc.nasa.gov/ssc/data/access/lat/FAVA/

Backup slides

Transition of the binary PSR J1023+0038 Pulsar detected in radio only (P = 1.7ms, 4.8hr eclipsing binary system) Gamma-ray flux and X-ray flux increase as radio pulsations disappear and double peaked optical lines appear This is interpreted as transition from a millisecond pulsar to a Low Mass X-ray Binary This phenomenology was already detected in the case of two redback systems, PSR J1023+0038 and PSR J1227−4853, for which we present here a dedicated stud Stappers et al. ApJ 790 2014

State transition of PSR J1021+4026 Pulsar detected in gamma rays only (P = 0.26s, τ = 77 kyr) Gamma-ray flux decreases as spin-down frequency rate increases Allafort et al. ApJL 777 2013

Fermi Gamma-ray Space Telescope Large Area Telescope (LAT): FoV: 2.4 sr FoV (20% sky) Energy range: 20 MeV to 2 TeV Angular resolution: 0.8o @ 1GeV Dead time: 15 % (SAA) + 9% (trigger) gamma e+ e- Gamma-ray Burst Monitor (GBM) FoV: Complete unocculted sky Energy range: 8 KeV- 40 MeV Positional accuracy: 4o-8o