impulsive brightening and variability timescales in the m87 jet
TRANSCRIPT
Variability Timescales inthe M87 Jet
D. E. Harris (SAO)C. C. Cheung (GSFC)
L. Stawarz (KIPAC)
INTRODUCTION, METHODS, & PROBLEMSINTRODUCTION, METHODS, & PROBLEMS THE TEV CONNECTION: SITE OF EXCESSTHE TEV CONNECTION: SITE OF EXCESS SIGNATURES OF ESIGNATURES OF E22 LOSSES LOSSES IMPULSIVE BRIGHTENING IN HST-1IMPULSIVE BRIGHTENING IN HST-1
Chandra RG workshop 2008 July
BACKGROUND
• Nucleus: varies between 0.2and 1.5 keV/s
• HST-1 at 0.86” (60pcprojected) is the site of giantflare: more than factor of 50!
• Knot D is affected by HST-1• Knot A shows ACIS
contamination
Chandra RG workshop 2008 July
BACKGROUND: RADIO
• From VLBA observations at 1.5 GHz, we findsuperluminal proper motions in HST-1 (~4c).
• For no acceleration, component was ‘emitted’(from upstream end) ~ 2002 (prior to peak ofmajor flare).
Chandra RG workshop 2008 July
Methods: Intensities for light curves:-pileup mitigation-
• Filter evt1 for GTI, but not grade (recover migration)• Multiply each event by its energy; sum from 0.2 - 17 keV• For the nucleus, subtract 5% of HST-1
Chandra RG workshop 2008 July
Problem: Pileup can produce a secondarypeak in PSF from release of trapped charge
at readout time
Chandra RG workshop 2008 July
Problem: Cross-talk from HST-1• The PA of the secondary
peak rotates during theobserving season.
• Before mid-March themajor effect is on thenucleus; after that date itaffects mainly knot D.
• For this reason, the bestdata for the nucleus isrestricted to times whenHST-1 < 4 keV/s
Chandra RG workshop 2008 July
Methods: First Derivative of LC• To study timescales, we
calculate the slope betweenadjacent (black) and everyother (red) observation.
• The fractional change per yearfor increasing intensities isfpy(+) = [(I2/I1) -1] / ΔT,and for decreasing intensitiesfpy(-) = [1 - (I1/I2)] / ΔT
• Thus a value of fpy=±1corresponds to a change by afactor of 2 in a year.
Chandra RG workshop 2008 July
The TeV connectionThe HESS group reported a
higher gamma ray flux in2005. They argued thatbecause of rapidvariability, the likely originwas the nucleus (close toSMBH) in spite of thesimilarity of their γ-raylight curve to the X-raylight curve of HST-1.
Chandra RG workshop 2008 July
Comparing variability timescales betweenthe nucleus and HST-1
• Both the 2005 HESS ‘event’and the 2008 Feb (MAGIC &VERITAS) TeV flaringdisplayed variability over a fewdays.
• The Chandra data indicate thatalthough the nucleus neverexperienced a giant flare likethat in HST-1, its ‘flickering” ischaracterized by larger valuesof fractional change per year.
Chandra RG workshop 2008 July
The First TeV Event2005 Apr (peak of HST-1
flare): Although there ispossible contamination ofthe nucleus by HST-1di/dt(nucleus) reached+50 (doubling time of < 7days). [During a shortcampaign of weeklyChandra observations]
Chandra RG workshop 2008 July
The Second TeV Event
2008 Feb: At the time ofthe TeV flaringobserved by MAGICand VERITAS thenucleus reached itshighest observed leveland di/dt = 11.8±0.5.[Normal monitoring;every 6 weeks]
Chandra RG workshop 2008 July
The TeV Connection: Summary
In favor of the nucleus:
• Easier to get source size ~ fewlight days
• Faster flickering in X-rays• Coincidence in 2008 Feb TeV
flaring with X-ray level and di/dt
In favor of HST-1:
• The observed (radio) size of HST-1 is of order 0.7 light years andthe inferred size from the X-rayvariability is of order 0.2 lightyears (∗δ).
• Coincidence of peaks in lightcurve (2005).
• With an SSC model, we expect toget IC scattering at TeVfrequencies.
• There is much less of a problemgetting TeV photons out of HST-1than out of the nucleus.
Chandra RG workshop 2008 July
Signatures of E2 Losses for HST-1
• If all frequencies decaytogether, expansionlosses dominate or thebeaming factor ischanging.
• If E2 losses (synchrotron& IC) are important, weexpect longer decaytimes for lowerfrequencies.
Chandra RG workshop 2008 July
The 2005 Decay• During the decay of the
giant flare, there is ashoulder in the UV lightcurve.
• fpy = -3.5±0.2 for X-raysfpy = -0.85 ± 1.16 for UV
• If the X-ray value were toarise from synchrotronlosses, B ≈ 1 mG for δ=4,the same field strengthfound by equipartitioncalculations.
Chandra RG workshop 2008 July
Comparative di/dt values: X-ray, UV, &Radio
• Granted the large error bars &poor sampling in the radio, themost negative values of fpyare -5 for X-rays; -2 for UV,and -1 for radio.
• We suspect that whileexpansion losses play asignificant role, E2 lossescontribute to the frequencydependence.
• These data are inconsistentwith a simple expansion for asimple power law.
Chandra RG workshop 2008 July
Discovery of impulsive brighteningin HST-1
Chandra RG workshop 2008 July
The River Analogy
• A jet is like a smoothly flowing river; observableemission arises only where there is white water.
• Even though HST-1 increased its emission bymore than a factor of 50, the power sodissipated is less than one percent of the totalpower believed to be flowing down the jet.
• A large rock may have been dropped into theriver; or perhaps there was a release of waterfrom an upstream dam………
Chandra RG workshop 2008 July
A Wager
Although I have not been able to identify acriterion for deciding the outcome, I wagerthe classical bottle of wine that:
The oscillations in brightening and fading ofHST-1 arise from a local instability ornaturally occurring characteristicfrequency rather than from a change in thepower flow of the entire jet.
[this is a personal wager, and does not involve my co-authors!]
FIN