A Study of Sgr A* and Non-thermal Radio Filaments

F. Yusef-Zadeh

X-Ray

(XMM)• G. Belanger

Radio

(VLA+ATCA) • D. Roberts

Near-IR

(HST)• H. Bushhouse•C. Heinke•M. Wardle•S. Shapiro•A, Goldwurm

Sub-millimeter (CSO, SMT)•D. Dowel•B. Vila Vilaro•L. Kirby

Non-thermal FilamentsS. Boldyrev

• Sgr A*

– Light curves in NIR wavelengths – Sub-mm emission is variable – Cross correlation – Power spectrum of NIR emission

• Non-thermal Filamen ts– Recent observations– Global vs local origin– Strong vs weak magnetic field

– a new turbulent model

Outline

X-rayNIRSub-mm

XMM

ATCA

SMT

VLA

CSO

HST

XMM

March Campaign

September Campaign

Two Epochs of Observations of SgrA* in 2004

VLA

BIMANMA

INTEGRAL

INTEGRAL

CSO Sub-mm

mm

Radio

X/ray

X/ray

Sub-mm

Radio

NIR

Near-IR Line and Continuum (NICMOS /HST)

• Observations:– 32 orbits of Camera 1 NICMOS in three bands:

• F160:W Broad band at 1.6m (1.4-1.8mum) • F187:N Narrow band at 1.m(1.865-1.885) (P line)• F190N: Narrow band at 1.m (continuum)

– Each cycle: Alternating between the three bands for about 7-8 min

– Six observing time intervals

1.6 m image

• Pixel size 0.043”• Field of view 11”• Sigma=0.002

mJy after 30sec

• The position of S2 wrt SgrA* estimated from orbit calculations (Ghez et al. 2003)

• S2 offset from SgrA* is 0.13”N and 0.03”E

• PSF has a four pixel diameter

• S2 is a steady source (PSF contamination)

• Great instrument because of background and PSF stability

PSF has a 4-pixel diameter

• Near-IR Light Curves of SgrA* (blue, red, green)

• Amp: 10 % to 25% or 3 to 5 times the quiescent flux (11-14 mJy)

• Duration: multiple peaks, lasting from 20 minutes to hours

• Flare activity: overall fraction of activity is about 30-40% of the observed time (background 8.9 mJy)

a

b

c

ed

Near-IR variability in 1.6, 1.87 (Paline), 1.9m

Submillimeter 0.87mm and 0.45mm Emission (CSO) September Campaign

•Variability with maximum: 4.6Jy and minimum: 2.7 Jy

•Likely to be due to hourly than daily variability

IR (1.6-1.9m) vs. X-Ray (September Campaign)

NIR

X-ray

X-ray

NIR

Simultaneous X-ray and NIR flare

• NIR due to Synchrotron: nir= 40min, Beq=10G, Ee=1.1 GeV

• X-Rays due to Synchrotron: nir=1min, B=10G, Ee=10 GeV

• X-Rays due to ICS: diameter=10Rsch, F850m=4Jy, Ee=1GeV

• Ex=2x10-12 erg/cm2/s/keV, Eobs=1.2x10-12 erg/cm2/s/keV

• Spectral index between near-IR and X-rays is = -1.35 bu in near-IR and X-rays , =-0.6

• If is flatter by 0.2, the X-ray flux is reduced by a factor of 2, so no X-ray counterpart is detected.

• ICS with =-0.6 produces soft ray emission with L = 7.6x1034 erg/s (2-20 keV) which is 5 times lower than observed

• Lomb-Scargle periodogram searches for periodicity

• Significant power with a period of ~ 1.3h and ~ 30min

• a/M=0

• (r/M)orbit = 6Rsch

• The same scale size as the region of the seed photons for ICS

Radio (7mm) vs X-ray (March Campaign)

• Lag time between X-ray/NIR flare and sub-mm peak 4-5 hours

• Time delay between X-ray/NIR and radio peak is one day

• The flux variation in sub-mm is about 30% whereas at 7mm is 10%

• An expanding synchrotron source in

an optically thick medium

X-ray

NIR

Sub-mm

Radio

Sub-mm and Radio Time Lags

D.P. Marrone, 2005

Conclusions I

• Flare correlation: simultaneous vs delayed

• Correlation between a near-IR and X-ray flare: consistent with SSC (Eckart et al. 2004)

• An expanding synchrotron self-absorbed blob: radio and NIR wavelengths

• Evidence for a NIR flare with quasi-periodic 1-1.3h and 30min behavior

• The flow always fluctuates even in its quiescent phase

• Non-thermal radio continuum emission is significant (40-50%) – Excess SNRs– Stellar clusters (Arches cluster, Sgr B2)– Diffuse background emission– Magnetized Filaments

Law et al. (2005)

The ripple filament: total intensity (top), polarized intensity at 6cm (bottom)

X-ray (2-8 keV) and Radio (15GHz) Images of SgrA-E

X-ray Radio

Sakano et al. 2003

Lu et al. 2003

Yusef-Zadeh et al. 2005

The spectrum is similar in both radio and X-ray

Using the 1200, 862 and 442 micron flux and RJ tail of Planck function

Tdust= 30-50 K

(dust) = 0.008-0.004

Using 25 mJy flux at 15 GHz with =0.75, ICS flux can match the observed X-ray flux 3.2x10-14 ergs/ cm2/s/keV if:

Tdust =50 K, B=100 G

Beq =140 G for a cutoff of 10MeV

Distribution of Radio Filaments

Origin of the Filaments

Models:• Loop ejection from a central differentially rotating engine at the Galactic

center (Heyvaerts, Norman and Pudritz 1988)

• Induced electric field by the motion of molecular clouds with respect to organized poloidal magnetic field (Benford 1988)

• Contraction of a rotating nuclear disk in a medium threaded by poloidal magnetic field

• Cosmic Strings oscillating in a magnetized medium

• Interaction of a magnetized galactic wind with molecular clouds (Shore and LaRosa 1999)

• Reconnection of the magnetic field at the interaction site of molecular clouds and large-scale magnetic field (Serabyn and Morris 1994)

Magnetic Field in the Galactic Center

Standard Picture for the last 20 years: The field has a global, poloidal geometry due to the filaments orientation The field has a milli-Gauss strength due to dynamical interaction and

morphology

Some Recent Problems: A number of filaments don’t run perpendicular to the Galactic plane Zeeman and Faraday measurements plus synchrotron lifetime Anisotropy of scatter broadened OH/IR stars Diffuse non-thermal emission places a limit of pervasive field < 10mG

Diffuse X-ray emission due to ICS with Tdust=30K requires B~10 G

Filaments not representative of the large-scale Field

A Turbulent Model of the Nonthermal Radio Filaments

• The mean field is weak but strong turbulent activity amplifies the field locally Turbulent energy is ~ two orders of magnitude higher than the disk

High velocity dispersion Hyper-scattering medium

Analogous to hydro turbulence with vorticity and MHD simulations B increases, produces filamentary structure until it reaches equipartition

Generation: Amplification rate ~ eddy turnover time scale ~ 106-7 yrs The length of the filament ~ outer scale of turbulence ~10s pcs

Expulsion:

Turbulent region is confined in GC, the field is expelled by turbulece Diffusion time scale ~ (diffusion) ~ L2 / ~ 10 times the eddy turnover time scale

In the disk: The region not confined, (diffusion) >> eddy turnover time scale in the disk Turbulent energy is much smaller than in the GC

ordlund et al. (1992)B field vectors of flux tubes (yellow and red); Vortes tube (grey)

Conclusions II

• ICS of the seed photons from dust cloud can explain some of the diffuse X-ray features in the GC

• Although non-thermal radio filaments may have strong magnetic field,

they can not be representative of the large-scale filed in the GC

• A turbulent dynamo model in a highly turbulent region of the GC may explain the origin of nonthermal radio filaments

6 and 1.2cm VLA images of the Galactic Center

• The dispersion plot is minimum at ~20min

• An expanding self-

absorbed synchrotron source with a delay of 20min implies plasma ejection took place 54min before the 7mm peak (van der Laan 1966).

• No near-IR or sub-

millimeter data)

• Continuous ejection?

SMT Observations (870micorn)March Campaign

Submillimeter 7mm and 0.45mm Emission (CSO) March Campaign

IR (1.6-1.9m) vs. Radio (7mm) (September Campaign)

Radio (7mm) vs X-ray (September Campaign)

IR (1.6-1.9m) vs. X-Ray (September Campaign)

Radio (7mm) vs X-ray (March Campaign)

40, 56 or 65min delay

Spectrum of Sgr A*

36 9Radio-submm Edd

35 10IR Edd

33 11X Edd

~ 10 erg/s ~ 3 10

~10 erg/s ~ 3 1

(brighter during flare

0

~ 2 10 erg/s 10

s)

L L

L L

L L

~

Sgr A*

Sub-millimeter Spectrum is Flat or Falling

optically thin?

Radio (7mm) vs X-ray (September Campaign)

• Assuming the P= 1.3h variability is due to circular motion:

• a/M=0 no spin – (r/M)orbit = (P/2 M)2/3 = 6Rsch

– (for comparison rISCO =2Rsch

• The same scale size as the region where sub-mm emission is expected to peak

Power Spectrum

Light Curve of SgrA* at 1.6, 1.87 and 1.90 microns

• The variation is similar in all three filters

• Great instrument because of background and PSF stability