LOFAR Observations of Galaxy Clusters The Toothbrush Radio Relic Reinout van Weeren Harvard-Smithsonian Center for Astrophysics M. Brüggen, G. Brunetti, H. Röttgering F. de Gasperin, A. Bonafede, W. Forman, G. Ogrean, C. Jones, F. Andrade-Santos, Galaxy Clusters Surveys KSP
OUTLINE Introduction LOFAR observations Toothbrush Other clusters Summary
RADIO RELICS Reviews: Brunetti & Jones 2014; Feretti+ 2012 Radio (WSRT) + X-rays (XMM) Radio Relics Radio Luminosity (1.4 GHz): 10 24-25 W Hz -1 Radio spectral index (F ν α ): -0.8 to -1.5 Polarization: 10-60 % Size: Distance to cluster center: 0.5-2 Mpc ~1-2 Mpc 1 Mpc Morphology: usually elongated MACS J1752.0+4440 (van Weeren+ 2012; Bonafede+ 2012)
QUESTIONS Physics of shocks Origin of Cosmic Rays and magnetic fields in the ICM Particle acceleration mechanisms Acceleration efficiency of shocks Magnetic field amplification Contribution of CRs and B-fields to the ICM pressure budget
Origin of the radiating electrons Radiative lifetime of electrons is 10 7 yr << diffusion timescale (Jaffe 1977) electrons are accelerated in-situ Guo+ 2014ab Bonafede+ 2014 Shock acceleration Particles accelerated by multiple crossings of a shock front (diffusive shock acceleration) Problem: low acceleration efficiency PIC simulations show efficient electron acceleration (shock drift acceleration) for low-mach shocks Re-acceleration Guo+ 2014; Caprioli & Spitkovsky 2014 XMM GMRT 325 MHz Relativistic particles accumulated over the lifetime of a cluster Morphological connection between some relics and radio galaxies Efficient re-acceleration for low- Mach shocks Markevitch+ 2005; Giacintucci+ 2008; Kang & Ryu 2011; Kang+ 2012; Shimwell+ 2015
MACS J0717.5+3745 Radio Xray SZ Radio/X-ray: van Weeren+. SZ: Mroczkowski+ 2012 Optical: HST FF images
LOFAR HBA LBA
Low and High band Antennas : 10-250 MHz LBA 10-80 MHz HBA 110-250 MHz
quiet ionosphere wild ionosphere Note: these images have 3 arcmin resolution... Ger de Bruyn & LOFAR EoR team
TOOTHBRUSH RX J0603.3+4214
Non-thermal component of the ICM (cosmic rays) Radio Relic ( Toothbrush ) Radio Halo RX J0603.3+4214 (z=0.225) Found by inspecting 1.4 GHz NVSS & 325 MHz WENSS survey images XMM X-ray image (+radio contours) Thermal component of the ICM 1 Mpc GMRT radio image (325 MHz) XMM observations by Ogrean+2013: LX ~10 45 erg s -1, T = 8 kev main merger event in the NS direction evidence for shocks (M~1.5) via surface brightness jumps Puzzle: no shock at the Toothbrush relic Ogrean+2013; van Weeren+2012
LOFAR 120-180 MHz One pointing full FOV 4 x 4 degr
LOFAR HBA 93 microjy/beam, 6 arcsec resolution GMRT 1.1 mjy/beam, 22 arcsec resolution
45 arcsec 22 arcsec 4 arcsec
shock: particle injection Spectral index energy losses GMRT 610 MHz LOFAR 150 MHz energy losses energy losses GMRT 610 MHz image
Temperature map Chandra 0.5-2.0 kev (243 ks) 5000 counts per bin Chandra + LOFAR
northern kink cold front radio relic emission M ~ 1.2? southern shock radio halo emission M = 1.4±0.06 M = 1.7±0.4 (temperature jump)
Shock at the northern Toothbrush relic? M = 1.2 M = 1.5 M = 2.8 Chandra: Mach number < 1.6 DSA αinj < -1.8 (!) Measured LOFAR/GMRT/JVLA spectral index: αinj - 0.8 Conclusion: radio spectral index strongly overestimates the Mach number!
Radio spectral index for re-acceleration Markevitch+ 2005; Giacintucci+ 2008; Kang & Ryu 2011; Kang+ 2012 Re-acceleration case I Fossil particle population has a steeper spectrum than what would be produced by DSA Spectral index follows DSA spectral index of fossil population erased Re-acceleration case II Fossil particle population has a flatter spectrum than produced by DSA Spectral index of fossil population maintained The case for weak shocks shock shock αfossil αfossil αfossil
Relic - Halo connection Spectral index: JVLA 1.5 GHz LOFAR 150 MHz Re-acceleration of pre-accelerated shock electrons due to turbulence??
ABELL 2256, VIR-A (M87)
LBA 60 MHz,; van Weeren+ 2012 ABELL 2256 HBA 150-158 MHz (to do: 120-180 MHz) 1 arcmin resolution 25 arcsec resolution 7 arcsec resolution
VIR-A / M87 Work by Francesco de Gasperin 46 MHz (22-70 MHz) dynamic range ~ 10 4 17x16 arcsec resolution
SUMMARY First ultra-deep LOFAR cluster image (factor of 10 deeper than anything done before in this frequency band) Toothbrush relic is not associated with a strong shock: Mach 1.6 Toothbrush relic spectrum can be explained by re-acceleration of a flat spectrum fossil population? Toothbrush halo: CR electrons from shocks re-accelerated by merger induced turbulence? LBA 60 MHz observations: see poster Kimberly Emig