Ultrahigh Energy Cosmic Rays from Tidal Disruption Events: Origin, Survival, and Implications

arxiv: 1706.00391 accepted by PRD Ultrahigh Energy Cosmic Rays from Tidal Disruption Events: Origin, Survival, and Implications Bing T. Zhang Peking University, Penn State University Collaborator: Kohta Murase, Foteini Oikonomou, Zhuo Li

1/14 Ultrahigh-Energy Cosmic Rays - Spectrum Cut-off Review of Particle Physics, Chin. Phys., 2016

Ultrahigh-Energy Cosmic Rays - Spectrum UHECRs: cosmic rays with energy larger than 10 18 ev What is the composition? Cut-off Where are the sources? How can they be accelerated to ultrahigh energy? Review of Particle Physics, Chin. Phys., 2016 1/14

2/14 What is the composition? A trend toward heavy nuclei Air Shower H He C N O Ne Mg Si Fe The Auger Collaboration, ICRC, 2017

Combined fit spectrum and composition data Spectrum The Auger Collaboration, 2017, JCAP Injection spectrum Composition data Source evolution Proton Helium m = 0 Nitrogen Iron 3/14

Combined fit spectrum and composition data Implications for the sources: heavy nuclei Intermediate mass, CNO, Ne, Mg, Si, Hard spectra Spectral index less than 2 Source evolution Prefer no evolution or negative evolution 3/14

Where are the sources? Gamma ray bursts Air Shower Heavy nuclei from the interior of progenitor stars Survival of nuclei : For GRBs, it is difficult in high-luminosity GRBs but easy in low-luminosity GRBs. Murase et al, 2006; Murase et al, 2008; Wang et al, 2007; Chakraborti et al, 2010; Liu et al, 2011; Horiuchi et al, 2012; Globus et al, 2014; Biehl et al, 2017 O Si Fe He P Data from Talys1.8 and Gent4 4/14

Where are the sources? Gamma ray bursts Air Shower Heavy nuclei from the interior of progenitor stars Survival of nuclei : For GRBs, it is difficult in high-luminosity GRBs but easy in low-luminosity GRBs. Murase et al, 2006; Murase et al, 2008; Wang et al, 2007; Chakraborti et al, 2010; Liu et al, 2011; Horiuchi et al, 2012; Globus et al, 2014; Biehl et al, 2017 Active galactic nuclei Heavy nuclei from the interstellar medium The fraction of heavy nuclei is too low Re-acceleration (galactic CRs) model Kimura, Murase, BTZ, 2017 4/14

Heavy nuclei in Tidal disruption events Main-sequence stars Solar composition White dwarfs Composed of heavy nuclei He, C, O, Ne, Mg Helium White dwarfs Carbon-oxygen White dwarfs Oxygen-neon-magnesium White dwarfs 5/14

CR acceleration in jetted TDEs t dyn R/ c Forward shock t acc = E A ZeBc First order Fermi acceleration Reverse shock Internal shock Wind Constrain maximum energy t acc apple min(t dyn,t syn,t A ) Energy loss time scale Photodisintegration or photomeson 6/14

7/14 Internal shock model CRs can be accelerated to ultrahigh energy Difficult for UHECR nuclei to survive in luminous TDE jets such as Swift J1644+57 A int UHECR nuclei mainly lose one nucleon in each interaction Inelasticity apple A ( ") E E = N N Interaction time scale A int / A ( ") Energy loss time scale A A / A ( ")apple A ( ")

Internal shock model CRs can be accelerated to ultrahigh energy Difficult for UHECR nuclei to survive in luminous TDE jets such as Swift J1644+57 The survival is allowed for less powerful TDE jets A int A int A A 7/14

Forward shock model UHECR nuclei can survive at forward shock such as Swift J1644+57 Si He O A int P Optical depth Fe f A A / dyn A P He O Si Fe Reverse shock: CRs can be accelerated to ultrahigh energy and survive Non relativistic wind: CRs cannot be accelerated to ultrahigh energy 8/14

9/14 Cosmic rays escaping from sources Acceleration spectral index s acc s esc Escape spectral index CRs can be confined and lose their energies during diffusive escape A harder spectrum s esc <s acc =2 Direct escape of CRs in internal shock Escape from a relativistic decelerating blast wave Two assumptions: The spectral index of escaped particles: s esc = s acc ( min (s acc 2) + E )/ max Baerwald, Bustamante and Winter, 2013 Katz, Meszaros and Waxman, 2010 The number of ejected CRs is similar to the number of particles at radius R "N esc (") "N(",R "max =") The minimum, maximum and total cosmic ray energies are power low functions of the radius E A,min ' 2 Am p c 2 / r min E A,max ' ZeBr / r max E CR / r E

UHECR nuclei injection spectrum UHECR nuclei follow a power-law distribution with an exponential cutoff Number fraction of different UHECR nuclei Maximum acceleration energy dn A 0 de 0 = f A 0N 0 E 0 ZE 0 sesc exp E 0 ZE 0 p,max E iso CR = CR E iso rad Normalization Depend on the total CR energy of TDEs CR 100 Spectral index Cosmic ray loading factor 10/14

11/14 Results of MS - SMBH tidal disruptions Solar composition ZE p,max = Z 2 10 19 ev s esc =1 CR 100 Q CR,44.6 0 1 10.5 E 1 rad,53 Propagate with CRPropa 3-1D EBL: Gilmore 12 Proton dominated in nearly all the energy range

12/14 Results of CO WD - IMBH tidal disruptions X C =0.5,X O =0.5 ZE p,max =6.3 10 18 Z ev s esc =1 CR 100 Q CR,44.6 0 1 10.2 E 1 rad,53 Propagate with CRPropa 3-1D EBL: Gilmore 12 Poor fit to the UHECR spectrum

Results of ONeMg WD - IMBH tidal disruptions X O =0.12,X Ne =0.76,X Mg =0.12 ZE p,max =6.3 10 18 Z ev s esc =1 CR 1000 Q CR,44.6 0 1 11.7 E 1 rad,53 Propagate with CRPropa 3-1D EBL: Gilmore 12 Consistent with Auger data 13/14

Summary, conclusion and implications The production of UHECRs in TDEs accompanied by relativistic jets Internal shock Forward shock Reverse shock Non-relativistic wind Examine different composition models for TDEs MS-SMBH CO-IMBH ONeMg-IMBH WD-IMBH with ignition Secondary gamma rays and neutrinos signals are of interest to test the model Cosmogenic neutrinos flux High energy gamma rays The survival is allowed for less powerful TDEs Production and survival of UHECRs Production and survival of UHECRs CRs can only be accelerated to ~ PeV Proton dominate in nearly all the energy range Poor fit to the spectrum ~ 1/30 CO WDs The number density of ONeMg WDs is lower than CO WDs Difficult to reconcile Auger data E 2 10 10 GeV cm 2 sr 1 s 1 Gamma rays can escape from sources Neutron pion decay, photodeexcitation, Bethe-Heitler process Simulation resolution 14/14