A Distinctive Disk-Jet Coupling in the Seyfert-1 AGN NGC 4051

0.37 MB·English

by  Ashley L. King

The Astrophysical Journal
PreprinttypesetusingLATEXstyleemulateapjv.11/10/09
A DISTINCTIVE DISK-JET COUPLING IN THE SEYFERT-1 AGN NGC 4051
A. L. King1, J. M. Miller1, E. M. Cackett2, A. C. Fabian2, S. Markoff3, M. A. Nowak4, M. Rupen5, K.
Gu¨ltekin1, M. T. Reynolds1
Received 2010 July 28; accepted 2010 December2
ABSTRACT
We report on the results of a simultaneous monitoring campaign employing eight Chandra X-ray
1 (0.5–10 keV) and six VLA/EVLA (8.4 GHz) radio observations of NGC 4051 over seven months.
1 Evidence for compact jets is observed in the 8.4 GHz radio band; This builds on mounting evidence
0
thatjetproductionmaybe prevalenteveninradio-quietSeyferts. Assuming comparativelynegligible
2 local diffuse emission in the nucleus, the results also demonstrate an inverse correlation of L ∝
n L−0.72±0.04. If the A configuration is excluded in the case that diffuse emission plays a signriafidcioant
X−ray
a role, the relation is still L ∝ L−0.12±0.05. Current research linking the mass of supermassive
J radio X−ray
black holes and stellar-mass black holes in the “low/hard” state to X-ray luminosities and radio
3
luminositiessuggesta“fundamentalplaneofaccretionontoblackholes”thathasapositivecorrelation
1
of Lradio ∝ LX0.−67r±ay0.12. Our simultaneous results differ from this relation by more than 11 σ (6 σ
] excludingtheAconfiguration),indicatingthataseparatemodeofaccretionandejectionmayoperate
E
in this system. A review ofthe literature shows that the inversecorrelationseen in NGC 4051is seen
H in three other black hole systems, all of which accrete at near 10% of their Eddington luminosity,
. perhaps suggesting a distinct mode of disk-jet coupling at high Eddington fractions. We discuss our
h
results in the context of disk and jets in black holes and accretion across the black hole mass scale.
p
-
o
r 1. INTRODUCTION radialdependenceofthetemperatureassociatedwiththe
t accretion disk. In SMBH accretion disks, this spectrum
s With evidence of supermassive black holes
a (SMBH) lurking at the center of nearly all galax- is thought to peak in the UV and is associated with the
[ “BigBlueBump”(Elvis et al.1994). Unfortunately,UV
ies (Richstone et al. 1998), it is pertinent to examine

2 andunderstandtheir propertiesaswellastheirimpacts. flux is extremely susceptible to scattering by dust and
modeling to correct for this can induce large uncertain-
v Studies have shown a critical relation between SMBHs
ties. In X-rays, emission from inverse-Compton scatter-
2 and their host galaxies in the form of the M–L and
ing, magnetic flares and magnetic reconnection events
6 M–σ relations. The M–L relation between the mass of
associatedwith the accretion disk are characterizedwell
7 the SMBH and the luminosity of the bulge suggests an
by a non-thermal power-law (e.g. McHardy et al. 2004).
0 intrinsiclinkbetweentheSMBHandtheamountofmass
Accordingly,X-rayfluxcanbeanotherproxyforobserv-
. in the bulge assuming a particular mass-to-light ratio
2 ing accretion disks.
(e.g. Magorrianet al. 1998; Kormendy & Richstone
1 In accreting systems, as material migrates toward the
1995; Gu¨ltekin et al. 2009b) The M–σ relation between
0 center, a fraction is also ejected into outflows that have
SMBH mass and the velocity dispersion of the host
1
both radiative and mechanical influences on their en-
: galaxy also implies a physical coupling between forma-
v tion and growth of the black hole and its surroundings vironments. The exact physical nature has not yet
Xi (e.g Ferrarese & Merritt 2000; Gebhardt et al. 2000). been observationally determined, but outflows are seen
in all types of accreting systems, i.e., proto-stellar ob-
The driving mechanism behind these couplings and the
r jects (e.g. Mundt 1985), neutron stars and stellar-
a M–σ relation especially, is thought to be the result of
mass black holes (e.g. Margon 1982), and SMBHs (e.g.
mergers that drive accretion onto the SMBH, which
Cohen et al. 1979). These outflows can reach super-
can quench star formation as energy released from
sonic speeds when collimated into jets, eventually de-
the central engine drives the gas out (Di Matteo et al.
positing significant energy into their surroundings (e.g.
2005).
Cohen et al. 1979; Fabian et al. 2002; Allen et al. 2006).
In particular, the study of an accretion disk around a
Materialmovingoutwardintotheirhostgalaxiesalsobe-
SMBH begins with observations of the extended black-
gins to cool via synchrotron radiation (e.g. Jones et al.
bodyspectrumemittedbythedisk;aconsequenceofthe
1974). Observed in the radio frequencies, this non-
1Department of Astronomy, University of Michigan, 500 thermalprocessemitted in the coreofthe systemis pre-
ChurchStreet, AnnArbor,MI48109,[email protected] dictedto havea flatspectrum, independent offrequency
2InstituteofAstronomy,UniversityofCambridge,Madingley (Blandford & Konigl 1979) making it a great observa-
Road,CambridgeCB30HA,UK
3Astronomical Institute ’Anton Pannekoek’, University of tional tool for characterizing jet emission.
Amsterdam,SciencePark904,1098XH,Amsterdam Utilizing these two wavelength regimes, Merloni et al.
4Chandra X-ray Science Center, Massachusetts Institute of (2003), Falcke et al. (2004), and Gu¨ltekin et al. (2009a)
Technology,NE80-6077,77MassachusettsAve.,Cambridge,MA
have all suggested a “fundamental plane” of black hole
02139
5ArrayOperationsCenter,NationalRadioAstronomyObser- activity connecting black hole mass, X-ray luminosity
vatory, 1003LopezvilleRoad,Socorro,NM87801 and radio luminosity. The plane spans over 9 orders of
2
magnitude in mass, 12 orders of magnitude in radio lu- which can mislead analysis by making the spectrum ap-
minosityand13ordersofmagnitudeinX-rayluminosity pear harderthanit actually is. To avoidphoton pile-up,
(Merloni et al.2003). This planesuggeststhataccretion weusedthemodewiththeminimalintegrationtime,i.e.
(traced by X-ray luminosity) and jet production (traced the Continuous Clocking mode, with integration times
by radio luminosity) are fundamentally linked together. of only 2.85 ms. Such a fast integration time helps to
Although the exact coupling is not understood, this re- prevent against multiple photons being counted as one
lation implies accretion must be driving jet production. higher energy photon, but does so at the expense of one
A known problem with the relation is the large scat- spatialdimension. Theresultingimageis1×1024pixels
ter of the data about the plane, (σ = 0.88dex with a resolution < 1′′, and an effective field of view of
radio
Gu¨ltekin et al.2009a). This scattercanbe attributedto 8.3′×8.3′,withspatialresolutioninonlyonedimension.
observational errors or the result of non-simultaneouty We used HEASOFT version 6.7, FTOOLS version 6.7,
between the observations themselves. Measuring the X- XSPEC version 12.5.1, CALDB version 4.1 and CIAO ver-
ray and radio luminosities at different times may have sion 4.1 in the data reduction and analysis of these im-
sampled different fluctuations in the accretion rate in ages. The CIAO psextract routine was used to extract
individual sources, driving them away from the rela- a spectrum and backgroundfor a point source as well as
tion. The time between X-ray and radio observations the companion auxiliary response functions (ARF) and
of Merloni et al. (2003) and Gu¨ltekin et al. (2009a) are response matrix functions (RMF). To do so, we used
known to span a few years to a decade. a circular extraction region of diameter 2′′ centered at
To address these issues, and in order to examine disk- 12h03m09.6s, +44◦31′52′.′5, while another 2′′ diameter
jet coupling at high mass accretion rates, we undertook circular extraction region was used approximately 20′′
a simultaneous X-ray and radio monitoring campaign of off-source for the background. This aperture size en-
the Seyfert-1 AGN NGC 4051. This galaxy is relatively sured encapsulation of the source, assuming it was a
nearby (z=0.002336), and the central black hole mass point source and not elongated, but not so large as to
has been determined through reverberation mapping include effects from the background.
techniques ((1.91±0.78)×106M⊙ Petersonet al. 2004; We analyzed X-ray data between the energy range of
Denney et al. 2009, (1.73±0.55)×106M⊙). NGC 4051 0.5–10.0 keV with a minimum of 10 counts per bin. A
is typically observed to accrete at approximately 5% of power-law component modeling the continuum was ini-
its Eddington luminosity (Peterson et al. 2004). The in- tially fit to the data. To check for pile-up in our source
nermostorbitaltimescaleofNGC4051isontheorderof before further modeling was attempted, we also used an
afewminutestohours,definedast ∼R/v ,whereR annulus with inner radius of 0′.′9 and outer radius of 1′.′7
dyn φ
istheradiusassumedtobeonlyafewgravitationalradii to obtain an additional spectrum from each observation
from the black hole and v is the orbital velocity. While using psextract. Again, requiring a minimum of 10
φ
the viscous timescales are on order of days to weeks for counts per bin, we fit power-law models to the annu-
typical parameters, defined as t ∼ t α−1(H/R)−2, lar spectra for comparison. If pile-up was present, the
vis dyn
where α is the viscosity parameter in the standard α- spectra from the annuli would be softer than those ex-
disk prescription (Shakura & Sunyaev 1973), and H is tracted from the central region. In general, we found
the scale-height of the disk. Variations in the accretion that the two spectra were equivalent, within errors,sug-
rate of NGC 4051 are thought to occur on these viscous gesting that any pile-up is minimal in all observations.
timescales of a day to weeks. This is further supported A description of the line-of-sight absorption is as fol-
byits highlyvariablespectrum,whichismostnotablein lowsand was included in allmodeling. The Galactic ab-
X-raysthatvaryuptoafactorof10onweeklytimescales sorption was modeled as an effective H column density
(Uttley et al. 1999). The variability seen in NGC 4051 of 1.15x1020 cm−2 (Kalberla et al. 2005) using phabs.
was essential for our simultaneous monitoring campaign Twoabsorptionedgestypicalto SeyfertAGN(Reynolds
to probe different accretion rates. 1997) at K-shell rest energies of O VII and O VIII of
In this paper, we present the simultaneous X-ray and 0.739 and 0.871 keV respectively, were modeled using
radio observations of NGC 4051, in effort to shed light zedge. These three rest-frame values were frozen, while
ontheimplicationsofthefundamentalplaneofaccretion individual normalizations were allowed to vary.
onto black holes, and to explore jet-production in this Figure 1 shows a sample spectrum fit with a simple
Seyfert galaxy. power-law model. This attempt at fitting the data re-
sulted in a poor fit for all spectra and in particular the
2. DATAREDUCTIONANDANLAYSIS spectrum presented in Figure 1 had a χ2/ν of 1770/366.
By looking at the ratio of the data to the model, one
2.1. X-ray
can see the obvious excess at low energies typical of
The Advanced CCD Image Spectrometer (ACIS) on Seyfert galaxies(Reynolds 1997). To better characterize
the Chandra X-ray telescope was used to collect eight the source flux, a disk blackbody component was added
observations of NGC 4051 between 1 Jan 2009 (MJD shownin Figure 2. Typically, it is thought that this soft
54848.2) and 31 Jul 2009 (MJD 55043.1). We list these excessis notthe resultof thermalblackbody component
observationsofapproximately10ksexposuresinTable1. butofanatomicprocessthatisnottrivialtomodel(e.g.
X-ray observations are subject to photon pile-up. Pho- Gierlinski & Done 2004; Crummy et al. 2006). Figure 3
ton pile-up is when multiple low-energy photons arrive plots the temperature and flux from the putative disk
at the same CCD pixel in a single frame and register component. We find thatthe temperature does notvary
identically to one higher energy photon. It reduces the with flux, suggesting it is not a blackbody thermal com-
numberofsoft,i.e. lowenergy,photonsthataredetected ponent. However, the addition of the disk blackbody
whileincreasingthehard,i.e. highenergy,photoncounts does produce a formally better fit.
3
In Figure 2, we not only include a power-law compo- to set 3C 286 as the flux calibrator, while the routine
nent and a disk blackbody but also an unresolvedGaus- gaincal set the gain calibration incorporating both the
sianthatmodelsanarrowFeKαlineandabroadFeKα phase calibrator source located at 12h21m4s +44◦1′4′′
line. The fit is improved to χ2/ν=368.3/353. It should and 3C 286 as references. Either antenna VA06, VA08,
be noted that the Fe Kα lines are not detected at more VA10, or VA12 was used as the reference antennae for
than the 2σ level of confidence, except in the last two these calibrations. Antennae that were off or showed
exposures. However,they were included inthe modeling discontinuities that werenot characteristicofthe overall
for completeness (see Table 2). In Seyferts and AGN, data in either phase or amplitude were excluded, result-
Fe K-shell emission due to fluorescence and recombina- inginonlyoneortwoEVLAantennaeperdataset. The
tion is the most prominent of the X-ray emission lines CLEAN algorithm was then run to create an image, us-
(e.g. Miller 2007). The shape and broadening of the Fe ing a threshold of 0.1 mJy as well as Briggs weighting
Kα line, initially modeled by Fabian et al. (1989) for a and robust parameter of 0.5. Briggs weighting provides
zero-spin Schwarzschild black hole and Laor (1991) for asmoothtransitionbetweennaturalanduniformvisibil-
a maximally spinning black hole, is dependent on the ityweightingandischaracterizedby arobustparameter
spin of the black hole, the inner and outer radius of the where 2.0 is approximatelynatural weighting and -2.0 is
emitting region,the inclinationangleofthe diskandthe approximatelyuniform(Briggs1995). Noself-calibration
efficiency of the disk emissivity. With this in mind, we wasdone because the sourcewas too faint, whichis con-
modeled the broad Fe Kα line with XSPEC model laor sistent with methods described by Giroletti & Panessa
thatproducesanemissionlinefromanaccretiondiskand (2009), who also observed NGC 4051 at 8.4 GHz. Fig-
includes generalrelativistic effects (Laor1991). Keeping ure 5 shows an example of the type of images that were
the emissivity asa function ofradius(∝R−3), the outer produced.
radius fixed at 400 GM/c2, and the inclination fixed at After the CLEAN algorithm was run, the flux density
30◦, we let the inner radius vary. was measured using CASA’s imfit, which fit Gaussian
Finally, in order to compare to the fundamental curvestothe peakintensities. Becauseofthe fourdiffer-
plane of accretion onto black holes as described by entconfigurations,wewereonlyabletoresolvestructures
Gu¨ltekin et al. (2009a), just the power-law component intheAconfiguration,asseeninFigure5,whichafforded
within the energy range of 2–10 keV was used to com- the best resolution. In order to make a fair comparison
putethetotalfluxassociatedwitheachobservation. This betweenallthemeasurements,theGaussianfitswerere-
component contributes to more than 95% of the total strictedtoanareaofapproximately8′′×6′′,ensuringthe
flux in the 2–10keV range, with the broad Fe Kα line inclusionofallthestructurespresentintheimages. For-
contributing 2–5% of the total flux. We plot this light tunately,asseenintheworkdonebyGiroletti & Panessa
curve in Figure 4, and list the results for each spectrum (2009), there does not appear to be any extensive large
in Table 1. The continuum flux varies by almost a fac- scalediffuseemissionthatwouldberesolvedoutinhigher
tor of 3, which can be attributed to fluctuations in mass resolution configurations. If this were the case, the flux
accretion rate. would decrease with higher resolution, when in fact Ta-
ble3demonstratesthatthefluxintheBconfiguration,a
higher resolution, is larger than the flux in the C config-
2.2. Radio
uration, a lower resolution. This strongly suggests that
AcombinationoftheVeryLargeArray(VLA)andEx- the radio variability observedbetween the B and C con-
tendedVeryLargeArray(EVLA)antennaewereusedto figurations is intrinsic, not instrumental. However, it is
observeNGC 4051six times between 31Dec 2008(MJD unclear if the diffuse emission has been resolved out in
54831.3)and 31 July 2009 (MJD 55043.1). These obser- theAconfiguration. Forthisreason,wequoteourresults
vations were approximately 1 hour integrations centered with and without the A array measurements. The mea-
at8.4GHz withabandwidthof50MHz intwochannels surements including the integral flux densities as well as
with two polarizations. We chose this frequency to en- the peak flux densities arelistedinTable 3andthe light
sure self-absorption of the synchrotronemission was not curveis showninFigure 6. The errorsin these measure-
a problem. Exposure dates and times are listed in Ta- ments also include a systematic error of 3% of the total
ble 3. During each observation, the antennae switched flux, added in quadrature,to accountfor the calibration
from on source, located at 1h203m1s +44◦31′8′′, to a errors. These measurements do vary by a factor of 3,
phase calibrator located at 12h21m4s +44◦11′4′′ every whichis comparable to the X-rayvariations. In order to
3.33 s. 3C 286 was used as the flux calibrator with 3.33 compare to Gu¨ltekin et al. (2009a), we scaled the fluxes
s of integration at the end of each observation. Dur- as F ∝ν−0.5 from 8.4 GHz to 5 GHz as Ho (2002) did.
ν
ing the seven months spanning the observations, the Inspection of the image produced in the A configu-
VLA/EVLAevolvedfromits Aconfiguration,whichhas ration reveals evidence of jet production. As shown in
its longest baseline of 36.4 km, to its C configuration Figure 5, three structures are present: a central source
with a maximum baseline of only 3.4 km. This signif- and two extended lobes. The central radio lobe is likely
icantly changed the resolution of the resulting images, associated with the black hole, while the northwest and
and steps were taken to ensure a consistent comparison southeastlobes may be associatedwith the endpoints of
among the six observations. The resolution during each the outflows in this system. The alignment and vary-
configuration is listed in Table 3. ing brightness between the three lobes suggests this is
The Common Astronomy Software Applications a jet structure where the jet is partially projected into
(CASA)package,version3.0.0,developedbyNationalRa- our line-of-sight, placing the northwest lobe closer and
dioAstronomyObservatory(NRAO)wasusedtoreduce less obscured then the southeast lobe. We also note
the radio observations. The routine setjy was used
4
thatthese lobesarenotseeninthe antennaepsfandare A configuration, and 6.5σ, while not including it, when
therefore not artifacts of the Clean algorithm. Observa- dividing the difference between the power-laws by the
tionsbyChristopoulou et al.(1997),Giroletti & Panessa largerofthetwoerrors. Thefundamentalplaneisknown
(2009), and Kukula et al. (1995) note similar structures to have a large scatter, and NGC 4051 lies close to the
as well as the potential evidence for jet production. plane. This exercise, however, makes clear how different
the X-ray and radio coupling in NGC 4051 appears to
2.3. Comparison be.
These measurements by themselves can give insights Finally,weattempttoquantifywhetherornotthereis
into the physical processes that occur in AGN, but asignificanttimedelaybetweenfluctuationsintheX-ray
throughacomparisonoftheX-rayandradioluminosities andradioluminosities,whichcanbe seeninFigures4&
we can explore how accretion is coupled to jet produc- 6respectively. We usedadiscretecross-correlationfunc-
tion. To quantifyany correlationbetweenthe X-rayand tion (DCCF) as described by Edelson & Krolik (1988)
radio fluxes, we calculated the Spearman’s rank coeffi- to quantify this delay. The sparse and uneven sam-
cient (ρ). This ρ describes how well a data set exhibits pling of the all six observations poses a natural limi-
a monotonic behavior between two variables; ρ < 0 cor- tation on the results of this analysis. This led us to
responds to variables that are anti-correlated. We find a linearly interpolate the data within the seven month pe-
ρ of −0.66,with a probability of only 16% of zero corre- riod with uniform spacing. The time steps between in-
lation. terpolated points were 17 days, corresponding to the
Figure7plotstheX-rayvs. radioluminosities. Weas- shortest time between observations. White & Peterson
sumed a distance of 10.0 Mpc derived from the redshift, (1994) and Gaskell & Peterson (1987) describe similar
z = 0.002336 (Peterson et al. 2004), and cosmological techniquesforinterpolatingandcross-correlatingdatain
parameterH◦=70kms−1 Mpctoobtaintheseluminosi- their respective variability studies of AGN. The results,
shown in Figure 9, place the minimum of the DCCF of
ties. Figure 7 also includes the least-squaresfit of a first
-0.48 ±0.1 at -2.5±5.3 days, suggesting that X-ray dips
order polynomial to the data points, described by the
are leading the radio flares.
following relation:
logLradio =(−0.72±0.04)logLX−ray+(64±2) (1) 3. DISCUSSION
Inthispaper,wepresenteightChandra X-rayobserva-
Totesttherobustnessoftheanti-correlation,weusedan
tions and six VLA/EVLA radio observations of Seyfert-
F-testtocomparetheresultsofthefirstorderpolynomial
1 NGC 4051 taken over a seven month period. By si-
givenabovetofitswithazerothorderpolynomialaswell
as the fundamental plane relation of L ∝ L0.64 . multaneously measuring in X-ray and radio bands ev-
radio X−ray ery two to four weeks apart, we are able to probe vari-
At an 81% confidence level, we were able to rule out
ations in the accretion rate that occur on the viscous
the flat model. However, at a 96% confidence level, the
timescale of a few days to weeks in NGC 4051. The
fundamental plane relation is excluded by our model.
observations reveal significant variability in both X-ray
We also looked at the correlation between the data
andradiobands. The first8.4 GHz observationon MJD
points excluding the A configuration, in the case that
54831.3alsoshowsevidenceofjetproductionintheform
this array resolved out a substantial amount of flux.
of two distinct radio lobes, contrary to the idea that ra-
We found that the correlationwas still inversely propor-
dio quiet galaxies like NGC 4051 lack jet production.
tional, described as,
In fact, work by Falcke et al. (2001) and Nagar et al.
logLradio =(−0.12±0.05)logLX−ray+(40±2) (2) (2002) suggest that elongated, non-thermal emission is
commonin Seyfertand LLAGN.The lobes appearto be
Using the same F-test, our secondmodel may be consis-
resolved into compact impact regions at very high reso-
tentwithbeingflat,foritonlyexcludesaflatdistribution
lution (Giroletti & Panessa2009). A variability analysis
at the 60% confidence level. However, the positive fun-
shows that the 2–10 keV X-ray luminosity and 8.4 GHz
damentalplanerelationwasagainexcluded, thistime at
radio luminosity are inversely correlated according to
a 98% confidence level. L ∝L−0.72±0.04. This differs by 11.6σ from the cur-
ToplacethedatafromNGC4051incontextofthefun- radio X−ray
rentfundamentalplanerelationswhichcorrelatesthera-
damentalplane of accretiononto black holes, we plotted
dioluminositytoX-rayluminosityasL ∝L0.67±0.12
ourdataandbestfitlineagainstthedataandthebestfit radio X−ray
linedescribedinGu¨ltekin et al.(2009a)inFigure8. The for a fixed mass (Gu¨ltekin et al. 2009a). Furthermore,
bestfitlinefoundbyGu¨ltekin et al.(2009a)isdescribed if extended emission is resolved out in the highest res-
as follows, olution image, then excluding the A configuration data
point, the correlation is L ∝ L−0.12±0.05. This still
radio X−ray
logLradio =(0.67±0.12)logLX−ray+ differs fromthe fundamentalplane by more than6σ and
(3) is not consistent with the relation.
(0.78±0.27)logM +(4.80±0.24)
BH The results help to shed light on the fundamental
One should notice that our data are not described plane of accretion onto black holes (Merloni et al. 2003;
by the positive correlation of L ∝ L0.67±0.12 de- Falcke et al. 2004; Gu¨ltekin et al. 2009a). This plane
radio X−ray demonstrates that accretion is linked to jet production,
noted by the solid line, but instead by the dashed line
and dotted line described by L ∝ L−0.72±0.04 and as evidenced by the positive correlation between X-ray
radio X−ray and radio luminosity. The measurements in the funda-
Lradio ∝ L−X−0.r1a2y±0.05, respectively. In fact, our relation mental plane are generally not simultaneous, and one
differs from this relation by 11.6σ, while including the goal of this study was to understand if simultaneity be-
5
tween X-ray and radio measurements would reduce the fractions. This would go beyond a simple quenching of
scatter in the plane. NGC 4051 was found to lie near jet production, as discussed by Maccarone et al. (2003)
to the fundamental plane, but showed a negative corre- andGallo et al.(2003),sincethejetproductiondoesnot
lationbetween X-rayandradio luminosities, contraryto turnoffentirely(evidencedbycontinuousradioemission
thepositivecorrelationoftheplane. Theinversecorrela- and jet structures, especially in NGC 4051 and 3C 120;
tion suggeststhat some systems may lie nearto the fun- Giroletti & Panessa 2009; Chatterjee et al. 2009). This
damental plane, but vary like NGC 4051, moving across is the first study to probe a Seyfert galaxy in X-ray and
the plane and thus increasing the total scatter. radiobandsonviscoustimescalesofitsinnerdisk. Inthe
At least a few other case studies have also shown a future, we will undertake an extended monitoring cam-
separateandinversecorrelationdeviating fromthe posi- paign of NGC 4051 to further characterize this relation
tivecorrelationsuggestedbythefundamentalplane. The as well as determine any time lags between X-rays and
first is 3C 120, a SMBH with a mass of approximately radio fluxes.
5.5×107M⊙ thatisobservedtoaccreteatapproximately
10% L (Peterson et al. 2004). Chatterjee et al.
Edd TheauthorsgratefullyacknowledgeJoanWrobel,Phil
(2009) present a five year study of 3C 120 using RXTE
Uttley, and Ian McHardy, and the anonymous referee
and VLBI to obtain X-ray and radio data respectively.
for their insights and comments that improved this pa-
Theyuseadiscretecross-correlationfunctiontodescribe
per. They gratefully acknowledge Steven T. Myers for
the correlationbetweenthe X-rayat2.4–10keVandthe
hishelpwiththe CASAsoftwarepackage. J.M.M.grate-
radio at 37 GHz. They find that the greatest amplitude
inthe DCCFtobe −0.68±0.11,correspondingtoanin- fully acknowledges support through the Chandra guest
observerprogram. S.M.gratefullyacknowledgessupport
verse correlation at a 90% confidence level. This ampli-
from a Netherlands Organization for Scientific Research
tudeisconsistentwiththeresultsofthecross-correlation
(NWO)VidiFellowshipandfromtheEuropeanCommu-
analysisinNGC 4051. The minimum in ofthe DCCF of
nity’s Seventh Framework Programme (FP7/2007-2013)
3C120citedinChatterjee et al.(2009)correspondsto a
time lag of120days±30days,withthe X-raydips lead- under grantagreementnumber ITN 215212”BlackHole
Universe”. E. M. C. gratefully acknowledges support
ing leading the radioflares. This time delaycorresponds
providedbyNASAthroughtheChandra FellowshipPro-
to approximately 4 days in NGC 4051 when scaled us-
gram.
ing their respective masses, which is consistent with our
NOTE ADDED IN PROOF:While our paper was be-
data.
ing reviewed, a separate paper on radio and X-ray ob-
Attheoppositeendofthe massscale,the 14M⊙ black
servations of NGC 4051 was accepted for publication
holeGRS1915+105(Greiner et al.2001)sometimesalso
(Jones et al. 2010). Our paper was accepted for pub-
shows an inverse relation between simultaneous X-ray
lication only days later. Jones et al. (2010) report on
and radio observations. Rau & Greiner (2003) present
many more radio observations, and employed RXTE to
a survey of X-ray and radio observations using RXTE
obtain X-ray flux points. Treating the possibility of dif-
and the Ryle Telescope between 1996 November to 2000
fusenuclearemissionwithgreatcare,Jones et al.(2010)
September. The 1–200 keV X-ray flux showed no corre-
findanearlyflatradio-X-raycorrelation. Ourresultsare
lation to the 15 GHz radio observations. However, the
broadlyconsistentwiththatfindingwhentheEVLAob-
20–200keVcontinuumdidshowaninversecorrelationto
servation in the A configuration is excluded. The main
the 15 GHz flux described by a Spearman’s rank-order
advantagesofour work arethe close timing ofradio and
correlation coefficient of -0.75. The hard X-ray band in
X-ray observations, and the ability to separate distinct
GRS 1915+105 excludes direct emission from the disk,
X-rayflux componentsinChandraspectra. Bothpapers
whichisconsistentwithusingX-rayemissioninsteadUV
show that NGC 4051 lies significantly below the Funda-
emission in NGC 4051 and 3C 120.
mental Plane. Within the context of other black holes
The prototypical stellar-mass black hole, Cygnus X-
accreting at high Eddington fractions (a point of em-
1, may also show an inverse trend at high luminosity.
phasis in this paper), both sets of results support the
Gallo et al. (2003) study the disk-jet connections in this
possibility that the coupling between the disk and jet in
stellar-massblackholebyanalyzingRXTEAllSkyMon-
NGC4051maybe differentthaninlow-luminosityAGN
itoringX-raydatafrom2–11keVandtheRyleTelescope
and other extremely sub-Eddington sources. We thank
radiodataat15GHzbetween1996JanuaryandJanuary
2003. Cygnus X-1 does follow L ∝ L0.7 , until Ian McHardy and Phil Uttley for helpful conversations
Radio X−ray regarding NGC 4051 and diffuse nuclear radio flux.
itreachesapproximately2%ofits Eddingtonluminosity
whentheradiofluxdensityturnovers. Gallo et al.(2003)
describe departures from this relation at high X-ray lu-
minosity as quenching of its jet production as Cygnus
X-1 moves into its “high/soft” state.
Observations of NGC 4051, 3C 120, GRS 1915+105,
and Cygnus X-1 all show that X-ray and radio flux fol-
low an inverse relation when observing at nearly simul-
taneous times when the sources are emitting at 1–10%
of Eddington. Given that an inverse correlation is seen
in a quasar, a Seyfert, and two stellar-mass black holes
at high Eddington fractions, it is possible that a dis-
tinct mode of disk-jet coupling holds at high Eddington
6
TABLE 1
X-rayObservations
Dateof Exposure Count Γ ΓFlux DiskBlackbody DiskBlackbody χ2/ν
Observation Time Rate (2–10keV) Temperature Flux(2–10keV)
(MJD) (ks) (counts s−1) (10−11 ergs−1 cm−2) (keV) (10−15 ergss−1 cm−2)
54838.2 10.2 15.6±0.04 2.24+−00..0033 3.27+−00..0099 0.18+−00..0022 10.7+−63..37 646.1/426
∗ 54874.9 1.1 16.3±0.12 2.39+−00..1019 2.58+−00..1270 0.17+−00..0043 6.1−+141.1.8 244.6/213
54898.3 10.1 5.3±0.02 1.73+−00..0083 1.59+−00..1005 0.17+−00..0012 4.3+−21..70 394.0/381
∗ 54943.1 10.1 4.7±0.02 2.10+−00..0057 1.14+−00..0058 0.18+−00..0033 3.7+−41..44 368.0/353
54988.0 10.1 4.6±0.02 1.33+−00..0067 1.67+−00..0192 0.19+−00..0011 16.0+−23..11 370.0/394
55005.8 10.1 5.6±0.02 2.01+−00..0067 1.23+−00..0078 0.18+−00..0011 8.1+−32..24 501.8/364
55025.4 10.1 13.1±0.04 2.29+−00..0033 2.57+−00..0067 0.18+−00..0022 5.1+−42..12 578.7/411
55043.1 10.1 14.9±0.04 2.29+−00..0032 2.97+−00..0076 0.17+−00..0022 3.5+−21..35 627.7/420
Note. — This table shows the X-ray observations made by Chandra in the continuous clocking mode. The data was modeled using
Xspecandunabsorbedfluxesforboththepower-lawanddiskblackbodyarepresentedhere. Thepower-lawusedintheanalysisvariesby
afactorof3. The∗ referstotheobservationsthatwerenotusedinthisanalysisbecauseofthelackofsimultaneousradiomeasurements.
TABLE 2
X-rayFe Kα line
Narrow Broad
Dateof FeKα Equivalent Flux BroadFeKα Rin Equivalent Flux
Observation(MJD) (keV) Width(keV) (10−13ergs−1 cm−2) line(keV) (GMc−2) Width(keV) (10−13ergs−1 cm−2)
54838.2 6.40+−0N.0A4 0.04+−00..0044 1.36+−11..2296 6.95+−N0.6A1 8.2+−753 0.31+−00..2148 7.07+−54..4181
∗ 54874.9 – – – 6.34+−0N.4A2 5.6+−2N0A 0.54+−00..8409 10.1−+195.1.08
54898.3 6.45+−00..0097 0.04+−0N.0A7 0.84+−1N.3A1 6.62+−N0.3A2 25+−1N6A5 0.15+−0N.3A8 2.27+−5N.7A6
∗ 54943.1 6.40+−00..0054 0.14+−00..0077 1.81+−00..9968 6.91+−N0.5A6 3.1+−1N3A 0.70+−00..4435 5.67+−33..5636
54988.0 6.39+−0N.0A5 0.06+−00..0055 1.32+−11..2205 6.35+−0N.1A3 1.2+−6N9A 0.39+−00..2268 6.59+−44..5725
55005.8 6.36+−0N.0A3 0.12+−00..0170 1.73+−11..0454 6.34+−0N.6A1 3.3+−3N1A 0.32+−00..2267 3.94+−33..2203
55025.4 6.40+−0N.1A1 0.03+−0N.0A4 1.02+−1N.3A1 6.43+−0N.1A3 44+−2302 0.30+−00..1121 6.60+−22..7429
55043.1 6.67+−00..0078 0.02+−00..0051 0.64+−10..4155 6.34+−0N.1A5 20+−295 0.29+−00..1122 7.29+−22..9886
Note. —ThistableshowsthetwoFeKαlinesincludedintheX-raymodels. TocalculatethenarrowFeKαlines,zgausswithenergy
restrictedbetween 6.35-6.97, awidthof σ=0(unresolved), redshiftofz=0.002336 andvaryingnormalizationwas used. ForthebroadFe
Kαline,laortheenergywasrestrictedtovaryfrom6.34-6.95keV,thepower-lawdependencewasfrozenat3,theinneredgewasallowed
tovaryfrom1.235to400GM/c2,theouterradiuswasfrozenat400GM/c2,theinclinationanglewasfrozenat30◦ andthenormalization
was allowed to vary. Allthe lines were at leastmarginallydetected and therefore included inmodelingtechniques, except the narrow Fe
Kα on MJD 54874.9, where it registered 0 flux for the best fit parameters. The ∗ refers to the observations that were not used in this
analysisbecause ofthelackofsimultaneousradiomeasurements.
TABLE 3
Radio Observations
DateofObservation ExposureTime Configuration Resolution FluxDensity PeakFluxDensity
(MJD) (ksec) (arcsec) (pc) (mJy) (mJy)
54831.3 3.6 A 0.3×0.2 15×10 1.73±0.06 0.65±0.02
54899.2 3.5 B 0.9×0.7 44×34 5.99±0.20 1.13±0.04
54987.1 3.6 BnC 2.2×0.9 110×44 5.66±0.20 1.47±0.05
55005.2 3.6 C 3.1×2.3 150×110 4.97±0.17 2.22±0.08
55027.0 2.4 C 2.5×2.0 120×97 4.99±0.20 2.08±0.08
55043.1 3.6 C 3.1×2.2 150×110 4.78±0.16 2.22±0.08
Note. — Thistablegivestheradioobservationstakenat8.4GHzwitha50MHzbandwidthintwochannels. TheVLA/EVLAwasin
4different configurations duringthe entirecampaign, starting inthe A with longest baselineand ending at C withthe shortest baseline.
Intheanalysis,wescaledtheobservations to5GHzasHo(2002)didusingthetotalfluxdensitiesgivenincolumn5.
7
1
V−1
e
k
s −1
nts 0.1
u
o
c
d
e
z
mali 0.01
or
n
10−3
2
atio 1.5
r
1
0.5 1 2 5 10
Energy (keV)
Fig.1.— This is a sample spectrum from MJD 54943.1 modeled with just a power-law component, in red, as the Xspec model
phabs(po)*zedge*zedge. The Galactic absorption was modeled as an effective H column density of 1.15x1020 cm−2 (Kalberlaetal.
2005) and the K-shell absorption edges of OVII and OVIII were frozen at their respective rest energies of 0.739 keV and 0.871 keV. We
initiallyfitthespectrumfrom2–10keVandthenextended themodeltolowerenergies. Thefitproducedaχ2/ν=1770/366.
1
V−1
e
k
s −1
s
nt 0.1
u
o
c
d
e
z
ali
m
or 0.01
n
10−3
2
o 1.5
ati
r
1
0.5
1 2 5
Energy (keV)
Fig.2.— This is the same spectrum as Figure 1 but now includes a power-law, disk blackbody, a narrow Fe Kα line and a broad Fe
Kαline,modeledwithXspecmodelphabs(po+diskbb+zgauss+laor)*zedge*zedge. WeusedthesameGalacticabsorptionandabsorption
edgesasinFigure1. Thepower-lawisthereddashedline. Thediskblackbodyisthebluedot-dashedline. ThenarrowFeKαlineisthe
greendottedline. ThebroadFeKαlineistheblacktripledotted-dashedline. Finally,thesolidblacklineisthesumofallthecomponents.
Thefitproducedaχ2/ν=368.0/353.
8
0.25
V) 0.20
e
k
p (
m
e
T
b
b
k
Dis 0.15
0.10
0 5.0•10−15 1.0•10−14 1.5•10−14 2.0•10−14
Diskbb Flux (ergs s−1 cm−2 )
Fig.3.— This figure shows the comparison between the soft-excess disk blackbody temperature and its blackbody flux. A constant
temperatureindependent offluxasseenheresuggests apurelyphenomenological interpretationofthediskblackbodycomponent.
4•10−11
)
−2
m
3•10−11
c
−1
s

s
g
er 2•10−11
(

x
u
Fl

ay 1•10−11
r
−
X
0
5.48•104 5.49•104 5.50•104 5.51•104
Modified Julian Date
Fig.4.— ThisistheX-raylightcurvetakenbyChandra inthecontinuousclockingmodebetween2–10keV.Itshowsavariabilityofa
factorof3. Thepoints inreddonothavesimultaneousradioobservations andarenotusedinthecorrelationanalysis.
9
Fig. 5.—Shownhereisaradioobservation madebyVLA/EVLAintheA-configuration on31Dec2009(MJD 54831.3). Thecontours
are[0.2,0.4,0.6,0.8]×0.6mJybeam−1. Thebeampattern(3′′×2′′)isalsoshowninthelowerleftcorner. Thecenterisassociatedwith
theblackhole,whiletheextended lobesnorthwestandsoutheastareassociatedwiththeendpoints ofjetsofthesystem.
0.008
0.006
)
y
J
(

x
u
Fl 0.004

o
di
a
R
0.002
0.000
5.48•104 5.49•104 5.50•104 5.51•104
Modified Julian Date
Fig.6.— Thisfigureshowsthe8.4GHzlightcurvetakenbytheVLA/EVLA.Theradiofluxdensityvariesbymorethanafactorof3.
10
35.5
35.0
)

]
1
−
s

s
g
r
e
[ 34.5

o
di
a
R
L
(
g
o
l
34.0
33.5
41.0 41.2 41.4 41.6 41.8
log(L [ergs s−1 ])
Fig. 7.— This figure shows the inverse correlation between X-rayX−aRndayr adio luminosities. We used the continuum flux from 2–10 keV,
and we scaled the radio flux as Fν ∝ ν−0.5 (Ho 2002) from 8.4 GHz to 5 GHz in order to correctly compare to Gu¨ltekinetal. (2009a).
Thedashed lineisafittoour data givenbythe relation,logLradio =(−0.72±0.04)logLX−ray+(64±2). Thedotted lineexcludes the
Aconfiguration datapoint,andisdescribedbytherelation,logLradio=(−0.12±0.05)logLX−ray+(40±2).