A new model for emission from Microquasar jets Based on works by Asaf Peer (STScI) In collaboration with Piergiorgio Casella (Southampton) March 2010 Peer & Casella, 2009, ApJ, 699, 1919 Casella & Peer, 2009, ApJ, 703, L63 Outline Background - Jets in Microquasars Flat radio spectrum: the model of Blandford & Konigl Our model: emission from jets with decaying magnetic field Results & condition for flat radio spectra Key result #1: No need for electron re-acceleration for flat radio spectra Key result #2: Strong B suppression of radio flux Microquasars:Accreting Binary Systems Stellar size accreting objects -Similar to Quasars: basic ingredients- (1) spinning BH, (2) accr. disk, (3) jets Emission in Radio -- X/ rays Activity varies on ~weeks -~20 known; F x ~tens mJy Mirabel & Rodriguez, 1998 M BH >~ 10 6 M ; M BH ~ 10M T disk ~10 3 deg; T disk ~10 6 deg Activity states in the X-ray GX339-4 Various activity states; Time scale: ~days - months S 6-10 /s 3-6 S 6-10keV Dunn et. al., 2008 Activity states in the X-ray McClintock & Remillard, 2006, 2008 High/Soft Very high Low/Hard Cyg X-1 (Stirling+, 2001) 1E (Mirabel & Rodriguez 1999) Radio emission High/soft state: Radio emission suppressed Low/Hard state: 1) Compact jets obs. in radio; 2) Flat radio spectrum 3) L radio (5GHz) ~ L x 0.6 (2-10keV) M BH 0.8 (Fundamental plane) VLBA, 8.4GHz 15.4 GHz marc-sec -> 10s A.U. Corbel et. al., 2000; Gallo et. al., 2003 Merloni et. al., 2003; Falcke et. al., 2004 Basic model for emission from jets: Blandford & Konigl (1979) 1. Basic assumptions: n=c -p ~r -2 B(r ) ~ r Basic Synchrotron Theory: a) e - P.L. distribution -> broken power law spectra (from jet segment) b) B decays -> break decays Flat radio spectrum Aim: to explain flat radio spectrum. Idea: optically thick synchrotron emission from partially self-absorbed jet Fitting broad band spectrum of XTE J using disk-Jet model Markoff, Falcke &Fender, 2001 L disk ~0.001L Edd q j =L j /L disk ~0.01 p=2.6 Study physical properties of the system/jet: A short break: Jets in GRBs Basic assumption Microquasars GRBs Source of B field Central object dissipation (shock waves) B~r -1 u B = B u Electron distribution power law Power law above min (entire spectrum) Radiative Cooling Assumed to be Inherent replenished Implementing ideas from GRBs to Microquasars n=c -p ~r -2 1) There must be a heating mechanism (e.g., internal shocks..) Separated from cooling ! 2) B~r -1 --> B-field is Poynting flux dominated -- origin of B field 3) Power law is limited only between min.. max 4) For flat radio spectrum - Jet must be conical ? A new toy model: basic assumptions Single acceleration episode at the jet base Jet geometry - free parameter: r(x) ~ x a B=B 0 (r/r 0 ) -1 Constant velocity: v j Acceleration: limited to min.. max Cooling: Synchrotron + adiabatic energy losses x r(x) X 0,t 0 dx Key result #1: Electron cooling along the jet Only synchrotron 1) a>1/2, only sync, t>>t 0 ~ t 0 -Can explain B&K result; no need for reacceleration !! 2) a>3/8, t>>t 0 ~ t -2a/3 3) Narrow jets, t>>t 0 ~ t 2a-1 (Kaiser, 2006) 1) Initial rapid cooling - close to the jet base 2) Asymptotic expansion B 0 < B cr,1 - electrons at min dont cool B 0 < B cr,0 - electrons at max dont cool Critical values of B field (1) Spectrum from a Maxwellian: only sync.,B < B cr,1 peak ~ B min 2 ~r -1 break = | =1~ min -1 F ~B 0 1-1/a For conical jet (a=1), flat radio spectra Same result as in BK79 but different physical origin ! No need for e - power law distribution! Two frequencies at the jet base: Spectrum from a Maxwellian: only sync.,B >~ B cr,1 Rapid cooling close to the jet base: F ~ B el 0 x ; ~ el 2 ~ x -2 F ~ -1/2 F ~ -1/2 between fast.. peak,0 (Optic - X); ROBUST Critical values of B field (2) peak ~ B min 2 break = | =1~ min -1 Two frequencies at the jet base: B 0 > B cr,2 - break,f > peak,f (close to the jet base) Radio flux is suppressed !! F ~B /a Key result #2: Suppression of radio flux at high B (Spectrum from a Power law:only sync.) When B 0 increases: Radio flux increases and then decreases; Optical-UV flux becomes F ~ -1/2 X- ray flux steepens, from F ~ -(p-1)/2 to F ~ -p/2 Universal radio - X correlation in XRBs Gallo (2007); Casella & Peer (2009) Comparison with observations Casella & Peer (2009) Outliers - always low radio flux High B-field - Natural explanation to outliers Part of The fundamental plane (with mass) Summary Evidence for jets in the Low/Hard state of microquasars Flat radio spectra can be obtained without the need for re-acceleration ! without the need for e - power law ! Increase of B 0 above B cr,2 leads to a decay of the radio flux (but not the X!) -possible explanation to the outliers In strong B field, F ~ -1/2 in optical/UV- X; Peer & Casella, 2009, ApJ, 699, 1919; Casella & Peer, 2009, ApJ, 703, L63 Key result #3: limited region for flat radio spectra Inclusion of adiabatic energy losses: tras peak ~ B min 2 min ~ r -2/3 peak ~x -7a/3 break = | =1~ x -2a/3 Regardless of B-field, At x trans, peak = break = trans Three spectral regimes: < trans - optically thick; F ~ (13-3/a)/7 trans < < fast - optically thin; F ~ (3/7)(1-1/a) fast < < peak,0 - fast cooling; F ~ -1/2 Key result #3: limited region for flat radio spectra Spectrum from Power law: Sync + adiabatic At x trans, peak = break = trans ; At x low > x trans, max = break = low (< trans ) low < < trans - peak,0 < break < max F ~ ; depends on power law index!! For 2.0 < p < 2.5 flat radio spectra for a jet 3/8 (w/adiabatic), or a>1/2 Spectrum from a Maxwellian: Sync + adiabatic If B>B cr,2 trans = fast (degeneracy)