Possible Multi-Messenger Sources of Gravitational Waves and Particle Radiation

Transcription

1 Possible Multi-Messenger Sources of Gravitational Waves and Particle Radiation 1. High Energy Neutrinos 2. Gamma-Ray Bursts and Gravitational Waves 3. Pulsars and Magnetars 4. Diffuse GW Flux from Cosmological Supernovae 5. Diffuse GW Backgrounds from Accretion Günter Sigl II. Institut theoretische Physik, Universität Hamburg 1

2 The All Particle Cosmic Ray Spectrum 1.5 sr -1 s -1 ev -2 / m Akeno (J.Phys.G18(1992)423) AGASA (ICRC 2003) HiResI (PRL100(2008)101101) HiResII (PRL100(2008)101101) AUGER SD (Phys.Lett.B 685(2010)239) EAS-TOP (Astrop.Phys.10(1999)1) KASCADE (Astrop.Phys.24(2005)1) TIBET-III (ApJ678(2008)1165) GAMMA (J.Phys.G35(2008)115201) TUNKA (Nucl.Phys.B,Proc.Sup.165(2007)74) Yakutsk (NewJ.Phys11(2008)065008) KASCADE-Grande (QGSJET II) Nch-Nµ-unfolding 2.5 E direct data dif. flux dn/de LHC center of mass KASCADE-Grande collaboration, arxiv: primary energy E/eV 21 2

3 Very High High Energy Neutrinos The grand unified differential neutrino number spectrum From Physics Today 3

4 Summary of neutrino production modes From Physics Today 4

5 A.Karle, IceCube collaboration, arxiv:

6 But now two PeV energy candidate neutrinos observed by IceCube 103 data sum of atmospheric background atmospheric µ atmospheric conventional atmospheric prompt cosmogenic Ahlers et al. E2 ( e+ µ+ ) = 3.6x10-8 GeV sr -1 cm-2 s Number of events log NPE 10 IceCube collaboration, arxiv:

7 and a total of 37 events above 30 TeV deposited energy: IceCube collaboration, arxiv:

8 A possible Correlation of IceCube Neutrinos with the Cosmic Ray Excess seen by Telescope Array? Telescope Array Collaboration, arxiv: Fang, Olinto et al., arxiv:

9 Cosmogenic Neutrinos Produced during Propagation of Primary Cosmic Rays can not explain these Events Including secondary photons strong source evolution is here constrained by Fermi-LAT results Auger skimming final IceCube final Roulet, Sigl, van Vliet, Mollerach, JCAP 1301, 028 9

10 Discrete Extragalactic High Energy Neutrino Sources Prog enitor Pre burst Burst Afterglow E~10 erg Shock form ation loc al medium n~10 cm 3 T = R = s ~100 s ~3*10 s ~10 s cm (photons) neutrinos? soft photons (X ra ys) neutrinos? X ra ys, opt, radio,... neutrinos? ~3*10 cm ~10 cm ~3*10 cm active galaxies gamma ray bursts Figures from J. Becker, Phys.Rep. 458 (2008)

11 Neutrino Fluxes from Gamma-Ray Bursts GRBs are optically thick to charged cosmic rays and nuclei are disintegrated => only neutrons escape and contribute to the UHECR flux by decaying back into protons Diffuse neutrino flux from GRBs can thus be linked to UHECR flux (if it is dominantly produced by GRBs) (E ) 1 where ' 0.1 is average neutrino energy in units of the parent proton energy. p E, Above ~ ev neutrino spectrum is steepened by one power of E ν muons interact before decaying because pions/ 11

12 GRBs as UHECR sources now strongly constrained by neutrino fluxes observed by IceCube Waxman & Bahcall IC40 limit IC40 Guetta et al. IC40+59 Combined limit IC40+59 Guetta et al. E n 2 f cm -2 s -1 sr -1 D NeuCosmA 2012 IC40 IC40+59 NFC prediction GRB, all GRB, z known stat. error astrophysical uncertainties f e 10 5 Neutrino Energy (GeV) IceCube collaboration, Nature 484 (2012) 351 IC86, 10y HextrapolatedL E but re-evaluation of diffuse neutrino flux from GRBs gave factor ~10 smaller fluxes Hümmer, Baerwald, Winter, PRL 108 (2012)

13 GRBs as Multi-Messenger GW Sources Non-GW emission of GRBs are well described by the fireball model which does not specify the detailed nature of the central engine short GRBs (duration < 2 sec) are thought to be due to neutron star-neutron star or neutron star-black hole inspiral -> relatively strong and well understood GW signal, visible out to 30 Mpc (initial) and 440 Mpc (advanced) long GRBs (duration > 2 sec) are thought to be due to stellar collapse -> weaker, less well understood GW signal 13

14 Detection of high energy neutrino and GW signal candidates in coincidence in time and/or arrival direction, possibly along with a γ ray signal, can considerably suppress the backgrounds, in particular since the latter are uncorrelated for neutrinos, γ rays and GWs. An external trigger of a GW detector network by neutrinos or γ rays can also considerably suppress random coincidences of background noise fluctuations in separate GW detectors. For a more detailed discussion see e.g. arxiv:

15 Soft Gamma-Repeaters energy release up to erg, but likely only a small fraction in GWs, < erg best f-mode limit is 1.4x10 47 erg at 1.09 khz at 1 kpc distance [Abadie et al. ApJL 734 (2011) L35] 15

16 Pulsar Spin-Down Rotation frequency f r and its derivative can be measured for pulsars which gives the spin-down time which for a star of mass M and radius R with rotational energy E r =2M(2πRf r ) 2 /5 gives the spin-down luminosity The quadrupole moment induced by two opposite mountains of mass m leads to a gravitational wave spin-down time L s = gw,s E r L gw Ėr = 2E r s f 4 r G N MR 2 2. with ϵ=5m/(2m) the ratio of inertial moments of the star and the mountains. 16

17 For the Crab pulsar f r =30 Hz and τ s =2500 yr. If spin-down dominated by gravitational waves, this would imply ϵ ~ 10-3 (which is unsustainable anyway) and a gravitational wave strain h 4G NM 5r at a distance r ~ 2 kpc. This is about a factor 10 higher than the measured upper limit and thus gravitational waves can at most contribute ~ 1% to the total spin-down power [Aasi et al. Ap.J. 785 (2014) 119]. The main contribution could come from magnetic dipole radiation with power for magnetic moment p m, and spin-down time which leads to B s ~ p m /R 3 ~ G. (2 Rf r ) 2 ' , L em ' 2 3 p m 2 (2 f r ) 4 em,s E r L em 17 3MR 2 10 p m 2 (2 f r ) 2,

18 X-Ray Binaries X-ray binaries consist of a compact star such as a white dwarf, a neutron star or a black hole that accretes matter and gas from its companion star. A fraction η X of the accreted matter is emitted in X-rays. The torque due to angular momentum accreted from a radius r acc is where v c is the circular velocity at r acc. This can be compensated by the torque from GW wave emission due to a small asphericity of the rotating accreting compact star, G gw = L gw = I(2 f r )= I(2 f r) = L gw I(2 f r )= L gw. s 2E r 2 f r where f r = rotation frequency, I=moment of inertia, τ s = spin-down time, E r = rotational energy, L gw =GW power. 18

19 Balancing the two torques gives a GW strain related to the locally observed X-ray energy flux F X 2 p 2 1/2 MF X h G N X f r 28 1/4 ' /2 X 1/2 M 1.4M 1/2 1/2 1/2 F X 1 khz 10 8 erg cm 2 s 1, f r where α is r acc in units of the Schwarzschild radius. This can reach which could be observable with next-generation interferometers, provided that spin and orbital parameters are all known such that matched filtering techniques can be applied. 19

20 General Issues: Individual Signals The dimensionless characteristic GW strain h c (f) for a single event at redshift z is related to the energy per frequency interval (de gw /df)(f) by h 2 c(f) = 15G N 16 2 (1 + z) 2 d 2 L de gw df [(1 + z)f], where d L is the luminosity distance. individual event is then defined as 2 S =2Z N The signal to noise ratio (SNR) of an d ln f h2 c(f) fs n (f), where S n (f) is the spectral noise power per frequency. 20

21 General Issues: Diffuse Signals In terms of cosmology dt = dz/[(1 + z)h(z)] and an event rate per comoving volume R(z), the time-averaged GW energy density per logarithmic frequency interval is Z d 1 gw d ln f = dz R(z) dt 1+z dz f de gw z df (f z). 0 One can then define the spectral density and the characteristic strain for di use backgrounds by S h (f) h2 c f = 4G N 1 d gw f 3 d ln f. 21

22 Event rates and Duty Cycles 22

23 Onion structure of a supernova Janka, Mueller Convection, turbulence 23

24 Supernovae as Neutrino and Gravitational Wave Sources Anisotropic mass motion and neutrino emission in collapse of massive stars leads to gravitational wave emission. At low frequencies anisotropic neutrino emission of luminosity L ν (t) and anisotropy q(t) dominates and leads to the dimensionless strain at luminosity distance d L (gravitational wave memory) t D 2G h ( t) = N dt$ L ( t$ ) q( t$ ) ν dl Individual supernovae (SN) in our Galaxy can give prominent signals in neutrinos in Super-Kamiokande, Amanda, ICECUBE, Uno and in gravitational waves in Virgo/EGO, LIGO, but are rare events. However, backgrounds from cosmological SN may soon be detectable by gadolinium upgrade of Super-K in neutrinos and by gravitational wave 24 detectors such as the Big Bang Observatory (BBO).

25 Illustration for a particular rotating core collapse model by Mueller et al., Astrophys. J. 603 (2004) 221. for average <q> ~0.45% for time dependent q Fully 2D axisymmetric rotating 15 solar mass progenitor, 1.8x10-8 solar masses released in GWs during simulation. 25

26 However, note dependence on progenitor model average <q> ~3x10-5 Fully 2D axisymmetric rotating 15 solar mass progenitor, 1.6x10-10 solar masses released in GWs during simulation. 26

27 SN rate + very massive PopIII stars at z 15 input from SWIFT and other large scale surveys neutrino spectra + s i m u l a t i o n s 100Msun PopIII ordinary SN gravitational wave spectra 27

28 => diffuse neutrino spectra Ando and Sato, astro-ph/ stochastic gravitational wave background 28 Buonanno, Sigl, Raffelt, Janka, Mueller, Phys.Rev.D 72 (2005)

29 At low frequency gravitational wave spectrum always dominated by anisotropic neutrino emission. At high frequency f > 100 Hz convective mass motion dominates. Note that simulations stop after ~250 msec, during which only about 1/6 of the total 3x10 53 erg in neutrinos radiated during cooling phase has been emitted Possible enhancement factors in the GW amplitude between ~ 6 and ~6 (bands in previous figure) Red vs blue band are different type II SN redshift evolutions 29

30 For events with rate R and processes that loose phase coherence after one cycle, at frequencies f < R the signal becomes «stochastic», or «gaussian», i.e. more than one event is «on» at any given time. Individual events are also unresolvable at such frequencies because SNR < 1. The rate of ordinary supernovae is R ~ 1/sec. Thus, for f < 1Hz the signal should be gaussian. For Pop III events related to a few hundred solar mass stars the rate R III is related to the fraction of baryons converted into Pop III stars f III by R III & f $ % 10 1 III 0.2 s 3 # " If metals are released, f III has to be <10-5. There were speculations (now largely ruled out) that an observed infrared background exess could be explained by efficient Pop III formation correponding to f III ~ 0.1. Metallicity constraints in this case would have to be circumvented by fall into black hole. 30

31 By using more optimistic SFR, Sandick et al, Phys.Rev.D 73 (2006) obtain more optimistic estimates 31

32 Compare this with upper limits, sensitivities, and cosmological predictions BBO BBO correlated SN and PopIII By the way: Accelerated expansion could decrease conventional inflation signal by factor 100 This makes astrophysical sources more important. Giovannini 32

33 General Consequence: Gravitational Wave Background from type II supernovae and PopIII stars could mask inflationary background 33

34 Active Galactic Nuclei as Photon and Gravitational Wave Sources The bolometric luminosity L bol of an AGN with central black hole of mass M is related to the accretion rate L acc and the Eddington rate L Edd by of which a fraction f X is in X-rays between 2 and 10 kev, L X = f X L bol. Assume that a fraction f co of accretion is in the form of compact objects of typical mass m ~ 100 M sun. These objects release a fraction η gw ~ 0.2 of their mass m in gravitational waves during inspiral to the last stable orbit: Thus, from the observed X-ray luminosity function dn/dl X for AGNs, we can compute the cosmological gravitational wave background. 34

35 Define fractions of critical density: Ω SMBH = SMBHs, Ω acc = accreted gas, Ω X = X-rays in the 2-10 kev band. f acc = fraction of SMBH mass due to accreted gas, f obsc = fraction of obscured emission ~ 0.3, one has f acc Ω SMBH ~ (1 η em ) Ω acc Ω X ~ <(1+z) -1 > f obsc f X η em Ω acc Since Ω X /Ω SMBH ~ 1.3x10-3, <(1+z) -1 > ~ 0.4 from AGN evolution data, one obtains the condition f obsc f acc f X η em ~ 3x10-3 Observations suggest that η em is not much smaller than 0.1, and that SMBH build-up is dominated by accretion f acc ~ 1 and NOT by mergers f X ~ 0.1: bolometric emission dominated by infrared. This will be our standard case. 35

36 The universal photon spectrum 36

37 AGN+galaxy Diffuse X-ray background Compton thin Compton thick unobscured 37 Comastri, Gilli, Hasinger. astro-ph/

38 The X-ray background between ~1 and ~100 kev is explained by AGNs. X-ray luminosity function 38

39 SNR of a 100 M sun object spiraling into central black holes of various masses at distance = 1Gpc Individual events 10 7 M sun 10 6 M sun 10 5 M sun 39 Sigl, Schnittman, Buonanno, Phys.Rev. D75 (2007)

40 f X = 0.03, η em = 0.2, (infrared emission dominated) f acc = 1, f co = 0.01, black hole spin a/m = 0.95, for which η gw ~ 0.2 Confusion noise Noise induced by subtracting resolvable events with SNR > 15 Time-averaged total signal, including resolvable part 40

41 The duty factor is the event rate times the time t coh ~ f/(df/dt) ~ f -8/3 spent emitting at frequency f. Sigl, Schnittman, Buonanno, Phys.Rev. D75 (2007) Below a few milli-hertz > 1 event contributes at any given time and the signal is gaussian. At higher frequencies one would see individual events at final stages of inspiral. These events also have sufficient SNR to be resolved. 41

42 The observable total (solid) and resolvable (dashed) chirp rate as function of frequency f. 42 Sigl, Schnittman, Buonanno, Phys.Rev. D75 (2007)

43 43

44 Conclusions 1 1.) There is a deep connection between neutrino and gravitational wave emission by collapsing massive stars. Both signals have good chances to be seen by future experiments. 2.) Such astrophysical backgrounds could partially mask the inflationary background in the BBO (~0.1 Hz) frequency range. In the ground based frequency range ~100 Hz, these backgrounds would only be detectable by the most advanced third generation detectors. 3.) The supernova type II background is gaussian below ~1 Hz, however the neutron star phase transition background would be pop-corn type. 44

45 Conclusions 2 5.) The accretion powering Active Galactic Nuclei gives rise to electromagnetic emission from the infrared to γ-rays and at the same time to gravitational waves from inspiral of compact objects. 6.) If > 1% of the accreted matter fueling AGNs is in form of compact objects, a continuous background detectable by LISA results below 1 mhz. If the typical compact object masses are > 10 solar masses, individual inspirals should be resolvable above a few mhz with a rate of a few hundred per year. 45