A new model for emission from Microquasar jets Based on works by Asaf Pe’er (STScI) In collaboration with Piergiorgio Casella (Southampton) March 2010 Pe’er & Casella, 2009, ApJ, 699, 1919 Casella & Pe’er, 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 -> 10’s 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 GRB’s 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 GRB’s 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 don’t cool B 0 < B cr,0 - electrons at  max don’t 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 XRB’s Gallo (2007); Casella & Pe’er (2009) Comparison with observations Casella & Pe’er (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; Pe’er & Casella, 2009, ApJ, 699, 1919; Casella & Pe’er, 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 <~2/3 Total of 5(!) transition frequencies

Narrow jets: Flat radio spectra - impossible Requirement: a > 3/8 (w/adiabatic), or a>1/2

Spectrum from a Maxwellian: Sync + adiabatic If B>B cr,2  trans = fast (degeneracy)