Observing Massive Black Hole Binary Coalescence with LISA

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1 Observing Massive Black Hole Binary Coalescence with LISA Joan Centrella John Baker NASA/GSFC GSFC - JPL 5 th International LISA Symposium ESTEC July 12-15, 2004

2 Massive Black Hole Mergers MBHs lurk at the centers o all galaxies with bulges Chandra X-ray observatory ound the irst known system o 2 MBHs starting to merge in the galaxy NGC 6240 Most galaxies are believed to have undergone at least one merger ΛCDM models o cosmic structure ormation eature hierarchical build-up o galaxies rom smaller structures binary black hole mergers Merger rates depend on size o seed black holes, accretion, stellar eects,... Rates: expect ~ 10s (more or less) per year (Sesana et al., Islam et al.) Detectable by LISA to high z 2

3 Final coalescence o MBH binary Binary separation << 1 pc (to coalesce within a Hubble time) Gravitational radiation reaction dominates energy losses Waveorms & dynamics scale with BH masses and spins strong-ield spacetime dynamics, spin lips and couplings measure masses and spins o binary BHs detect normal modes o ringdown to identiy inal Kerr BH (graphic courtesy o Kip Thorne) 3

4 MBH inspirals and LISA symbols at 10 years, 1 year, 1 month, & 1 day beore the onset o merger. the merger itsel and subsequent ringdown occur at higher requencies 4

5 Observing MBH binary inspirals Parameter estimation: how well can we learn the masses, spins, binary orientation, sky position, luminosity distance to do astronomy LISA measures redshited masses (1+z)M Need good measurement o sky position & orientation to obtain D L Cutler (1998): 1 st detailed analysis o parameter extraction with LISA Hughes (2002): detailed estimates o LISA s precision or MBH binary parameters Use knowledge o cosmological parameters (WMAP) to get z rom D L Assume steep wall in sensitivity curve or < 10-4 Hz need to observe MBH inspiral or ~ 1 radian (~ 2 months) o its orbit or a good measurement o D L and z to study merger history o MBHs Vecchio (2003): eects o spin-induced precession o orbital plane; more in progress Holz & Hughes (2003): move cuto rom 10-4 Hz to Hz 2-month rule-o-thumb: need to observe MBH inspiral or ~ 2 mos in band Good measurement o source parameters, GW astronomy Enable LISA to be used as a cosmological probe o galaxy merger history 5

6 Characterizing MBH binary inspirals Which MBH binary systems are observable or T = 2 months, or various candidate low-requency sensitivities? Orientation-averaged SNR (FH 1998, matched iltering) h ( ) 2 ρ where and n = S = requency observed by the detector h ( ) = d h ( ( 2 char 0 2 hn = (1 z) ) ) 2(1 + z) de h char = [(1 + π D ( z) d and emitted (source) GW requency e + L z) ] m = m 1 + m 2 Binary total mass and chirp mass M = µ c 3/ 5 m 2 /5 Use Newtonian quadrupole approximation (agrees with PN expressions to within 25% or better or M c < M sun ) de d 1 2/3 5/3 1/ 3 π M c e = 3 6

7 Characterizing MBH binary inspirals At time T beore inal coalescence, LISA observes the MBH binary at requency M c( Msun with characteristic strain amplitude z) 5/8 T 2mos. 3/8 h char DL( z) 1Gpc 1 T 2mos. 1/ 2 10 Hz 4 3/ 2 Plot h char vs. requency Colored lines: systems at T = 2 mos beore inal coalescence or speciied redshits z h char ~ -3/2 parallel to baseline sensitivity curve < S h ()> 1/2 ~ -3/2 Black lines: systems with ixed chirp masses M c at T = 2 months 7

8 Low requency sensitivity o LISA LISA s sensitivity below 0.1 mhz aects observations o MBH binaries Assume baseline sensitivity above 0.1 mhz ( Examine candidate low requency sensitivity curves below 0.1 mhz: Baseline: extends baseline with white accel noise, so (S h ()) 1/2 ~ -2 Bender: (S h ()) 1/2 ~ -2.5 rom 10-4 Hz to 10-5 Hz, -3 out to Hz, then -6 below Hz Relaxed: (S h ()) 1/2 ~ -3.5 Wall: (S h ()) 1/2 ~ -20 Also consider relaxed sensitivity at 0.1 mhz 0.1-mHz x5: relaxed by actor o 5 rom baseline Minimum mission: degrading the Bender curve by actor o 10 Note: sensitivity curves to be shown include WD background noise 8

9 Science Reach MBH inspirals An MBH binary with chirp mass M c at redshit z can be observed or 2 months in band i it is above a given sensitivity curve 9

10 Science Reach MBH inspirals An MBH binary with chirp mass M c at redshit z can be observed or 2 months in band i it is above a given sensitivity curve 10

11 Caveats and comments. These results apply to an average source 2-month rule based on Monte Carlo simulations with random orientations Any real system will have a speciic orientation that will increase or decrease its detectability somewhat relative to these plots More extensive parameter estimation studies would be useul Spin eects (Vecchio, in progress) Eects o expected noise (not just averaged sensitivity curves) Eects o actual LISA perormance, TDI, etc. Is the 2-month rule-o-thumb modiied? How realistic are these low-requency sensitivity curves? Experimental, observational eects Cost o implementation 11

12 MBH mergers. BHs leave their quasi-circular orbits to begin inal plunge & merger near innermost stable circular orbit or ISCO at separation ~ 6M isco Msun 4 10 (1+ z) M Common EH orms distorted BH emits GW in quasinormal ringing Expect l = m = 2 mode will be dominant: longest lived, bar-like qnr Merger and ringdown are burst signals, at higher requencies than inspiral Zero-signal solution w/ TDI (Tinto & Larson 2004) may help w/ source location How well can we estimate MBH binary parameters using merger & ringdown? Knowledge o merger waveorms, phenomenology (GSFC, UTB.) Hz 6 3/10 10 M [ (1- a) ] Hz, 0 a 1 2 sun (1 + z) M Occur at higher requencies less sensitive to low requency perormance 12

13 Observing MBH binary inspirals. Overall, expect younger (higher z) MBHs to have smaller masses than older (lower z) systems, which have had more time to grow Current observations revealing more quasars (and thus MBHs) at higher redshits Bromm & Loeb (2003): scenario or ormation o SMBHs inside the irst galaxies ~ 5 x 10 6 M sun MBH ormation at z > 10 MBHs may orm in binary system source o GWs or LISA What are the rates? Merger rates depend on assumptions about the size o seed black holes, accretion, stellar eects, Sesana, et al.(2004): merger tree Alicea-Muñoz, Baker, Centrella, and Matzner (in progress) Test eects o assumptions about mergers, accretion Various low requency sensitivities 13

14 Summary Low requency sensitivity o LISA is important or parameter estimation o MBH binaries at high redshits Parameter estimation How robust is 2 month rule-o-thumb? Eects o spin, higher harmonics Data analysis issues: realistic noise, account or TDI. Astrophysical issues Rates, MBH scenarios in early universe Balance with instrumental issues, cost Science payo rom good low requency sensitivity is substantial MBH demographics Merger history and relation to hierarchical structure ormation. Outstanding probe o early universe 14