GR SIMULATIONS OF BINARY NEUTRON STARS AND BINARY BLACK HOLES WITH WHISKY. Bruno Giacomazzo University of Trento, Italy

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1 GR SIMULATIONS OF BINARY NEUTRON STARS AND BINARY BLACK HOLES WITH WHISKY Bruno Giacomazzo University of Trento, Italy

2 PART I: BINARY NEUTRON STAR MERGERS

3 WHY SO INTERESTING? Due to their duration and dynamics, NS-NS and NS-BH binaries are very good sources for gravitational wave detectors such as Virgo (Italy) and Ligo (USA) Virgo (Pisa, Italy) They are also possible sources for short gamma-ray bursts. Tori formed after the merger could power GRBs via neutrino or magnetic fields. Credit: Rezzolla, Giacomazzo, et al 2011 To study these sources we use our fully GRMHD code Whisky

4 BNS MERGER OUTCOME Depending on mass and EOS several postmerger scenarios: BH+torus HMNS BH+torus NS-NS SMNS NS+torus BH+torus? NS+torus Magnetic fields play fundamental role in post-merger dynamics (jets from BH/NS+torus, NS collapse to BH,...) All these scenarios may lead to SGRBs with different properties

5 Giacomazzo, Rezzolla, Baiotti 2011, PRD 83, Visualization by Koppitz, Giacomazzo, Rezzolla

6 JETS FROM BNS MERGERS? Rezzolla, Giacomazzo, Baiotti, Granot, Kouveliotou, Aloy 2011, ApJL 732, L6

7 BNSs AND SHORT GRBs Rezzolla, Giacomazzo et al 2011 EM signal switches on at the end of GW signal magnetic field amplified by several orders of magnitude by KH and then MRI instabilities

8 COMPACT BINARY PROGENITORS OF SHORT GAMMA-RAY BURSTS Giacomazzo, Perna, Rezzolla, Troja, Lazzati 2013, ApJL 762, L18 BNS and NS-BH can produce tori around spinning BHs. When NSs are magnetized this can lead to the production of relativistic jets. Energy extraction from the disk can power short GRBs. Can we link SGRBs observations with numerical simulations?

9 We considered the current sample of SGRBs with measured energies We made the following assumptions: SGRBs are powered via magnetic fields SGRBs energy is provided by the disk Efficiency is constant E,iso = M torus c 2 jet jet = 10% = 50% εjet is inferred from disk simulations (Fragile, McKinney, Tchekhovskoy,...) εᵧ is derived from observations (e.g., Zhang et al 2007)

10 We then considered a sample of 25 accurate GR BNS simulations Mtorus /M % 25% 29% 33% 4% M BNS /M max And we compared their torus masses with the distribution derived from observations ideal fluid APR APR4 SLy H3 H4 ALF2 PS Giacomazzo et al 2013 Note that most SGRBs requires tori with masses <~0.1 M

11 low-energy SGRBs (<~1e51 erg) high-energy SGRBs (>~1e51 erg) high-mass BNSs low-mass BNSs Simultaneous GW/EM detection will help validate this model

12 MAGNETAR FORMATION Giacomazzo & Perna 2013, ApJ Letters, 771, L26 NSs of ~2.0 M have been observed, hence low-mass BNSs may produce stable NSs. Investigated merger of two 1.2 M NSs (with and without magnetic fields). Used Ideal Fluid, Gamma=2.75, k=30000 (similar to Shen et al EOS at high densities, e.g., Oechslin et al 2007).

13 MAGNETAR FORMATION Giacomazzo & Perna 2013, ApJ Letters, 771, L26 Produced a stable ultraspinning NS surrounded by a disk of ~0.1 M. Magnetic fields will redistribute angular momentum and produce an uniformly rotating NS surrounded by a magnetized disk (e.g., Duez et al 2006).

14 MAGNETAR FORMATION Giacomazzo & Perna 2013, ApJ Letters, 771, L26 Difference in the GW signal are small and present only in the postmerger phase Magnetic fields could emit EM counterparts in radio, optical, X- ray, and gamma rays. EM signal could be used to confirm magnetar formation and to provide constraints on NS EOS. A stable magnetar could be used to explain X-ray plateaus and extended emissions from SGRBs (e.g., Dai et al 2006, Fan et al 2013, Rowlinson et al 2013). GWs publicly available for download at

15 MAGNETIC FIELD AMPLIFICATION AT MERGER Giacomazzo, Duffell, MacFadyen, Perna, Zrake, in prep. In our sims, KH instability causes the magnetic field to grow exponentially of only ~1 order of magnitude. Local very high-res simulations shows that magnetic fields could be amplified up to magnetar levels (Zrake & MacFadyen 2013). Is it possible to include small scale effects in global simulations? 1e+18 1e+17 dx=225m (standard) dx=225m new run max(b) [G] 1e+16 1e+15 1e+14 PRELIMINARY Baiotti et al e+13 standard run 1e Giacomazzo et al 2014

16 PART II: MAGNETIZED PLASMAS AROUND MERGING SUPERMASSIVE BHs Giacomazzo, Baker, Miller, Reynolds, van Meter 2012, ApJ Letters, 752, L15

17 WHY ARE THEY INTERESTING? Supermassive BBHs are the results of the merger of galaxies and are powerful sources of GWs. The Mice Credit: NASA/ESA Gas accreting onto the BHs could produce EM signals. Sgr A* observed with NuStar Credit: NASA To study these sources we use our GRMHD code Whisky

18 INITIAL DATA We considered equal-mass non-spinning BBHs with different magnetic fields: model Pmag/Pgas B0 0 B2 2.5x10-2 Initial separation of the BHs sufficient for ~3 orbits before merger. The gas is initially uniform and the magnetic field is aligned w i t h t h e t o t a l a n g u l a r momentum: B=B z. Outer boundary at r~1540m, 11 refinement levels ranging from h~0.0375m to h~38.4m. Used Whisky, but spacetime evolution decoupled from matter. No constraint on the evolution of the magnetic and gas pressures.

19 CASE B0 (NO MAGNETIC FIELD) Visualization by Philip Cowperthwaite

20 CASE B2 (Pmag/Pgas~0.01) Visualization by Philip Cowperthwaite

21 B0 vs B2: rest-mass density comparison B0 B2 Visualization by Philip Cowperthwaite High magnetic pressure in B2 evacuates the region above the BH creating a funnel. No spherical accretion in this case.

22 POYNTING VECTOR Giacomazzo et al 2012 Emission is mainly collimated along the z axis. No signs of dominant quadrupole emission. Note that the jet is not propagating in vacuum.

23 LUMINOSITIES Poynting flux computed across a surface at rex=10m. Values computed for a 10 8 solar mass BBH, g/cm 3 gas, and B(t=0)~10 4 G. Giacomazzo et al 2012 Luminosity increases at merger and then decreases by a factor ~2. Behavior qualitatively similar to Palenzuela et al, but much larger luminosities.

24 EM EMISSION Emission at merger and computed for a BBH of 10 7 M, Te=100keV, and optical depth of order unity Schnittman 2013, arxiv: Luminosity E L E (erg/s) radio IR/optical UV X-ray total with inverse Compton synchrotron seeds PRELIMINARY bremsstrahlung seeds E (kev) Figure produced by Jeremy Schnittman using our results Possible EM emission from radio up to X-ray

25 CONCLUSIONS GRMHD simulations of BNSs now able to study all phases of merger Magnetic fields can be strongly amplified Magnetized BNSs may produce jets and power SGRBs Magnetic fields have an important role in the post-merger dynamics Most SGRBs may be produced by high-mass BNSs Possible to form stable magnetars+disk from BNS mergers Large magnetic field amplifications are expected, but difficult to resolve in global simulations, unless implementing a subgrid-scale model (work in progress) First GRMHD study of magnetized plasmas around BBHs Magnetized plasmas around merging BHs can produce collimated jets Luminosity ~4 orders of magnitude larger than in the force-free sims Possible EM emission from radio up to X-ray (work in progress)