Radio-to-Gamma Ray Monitoring of Mkn 421 and Mkn 501: Source Variability N. Nowak, D. Paneque, U. Barres de Almeida, N. Strah, D. Tescaro On behalf of the Fermi-LAT, MAGIC, VERITAS and other collaborations and groups involved in the multiwavelength campaigns
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Radio-to-Gamma Ray Monitoring of Mkn 421 and Mkn 501: Source Variability
N. Nowak, D. Paneque, U. Barres de Almeida, N. Strah, D. Tescaro
On behalf of the Fermi-LAT, MAGIC, VERITAS and other collaborations and groups involved in the multiwavelength campaigns
Outline
• Introduction
• 2009 MWL campaigns on Mrk 421 and Mrk 501:
- SEDs
- Lightcurves
- Variability
- Correlations
• Conclusions & Outlook
Motivation
Blazars: - AGN with relativistic jet pointing directly towards us
- highly variable at all wavelengths
- SEDs dominated by jet emission, two non-thermal bumps at low (radio-optical-Xray) and high (X/γ-rays) energies respectively. Origin of high-energy
bump not yet identified unambiguously.
➡ simultaneous observations of blazars over the whole wavelength range (Radio - TeV) over a long time period needed (mostly in low state).
Mrk 421 and Mrk 501:- luminous gamma ray sources
- nearby blazars (z~0.03) which implies a low EBL absorption
➡ ideal candidates for multiwavelength studies
2009 MWL campaigns on Mrk421 and Mrk501
4.5 months long multiwavelength campaigns in 2009 (PI: David Paneque):
• Mrk421: Jan 19, 2009 (MJD 54850) - June 1st, 2009 (MJD 54983)
• Mrk501: Mar 15, 2009 (MJD 54905) - Aug 1st, 2009 (MJD 55044)
• monitored regardless of activity. However, both sources were in a relatively low state throughout the campaigns
high-energy bump of the SED well covered by Fermi-LAT + MAGIC + VERITAS
Modelling the Mrk 421 and Mrk 501 SEDs
• can be well described by standard one-zone synchrotron self-Compton model with 2 breaks in the electron spectrum
• model parameters (e.g. Doppler factor, size of emitting blob, magnetic field, properties of the electron population, ...) are very similar for both objects
➡ common properties of jets and acceleration mechanisms in blazars
108 1011 1014 1017 1020 1023 1026 1029
[Hz]
10-14
10-13
10-12
10-11
10-10
10-9
10-8
F [e
rg s-1
cm
-2]
Mrk 421 SED with SSC model fits
Abdo et al., 2011, ApJ, 736, 131!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Swift/XRT PC mode (0.3 - 2 keV)Swift/XRT PC mode (2 - 10 keV)
PRELIMINARY
PRELIMINARY
PRELIMINARY
Lightcurves Mrk 501 − γ-rays and VHE
Large flare in VHE around MJD 54952 (May 1st, 2009). No obvious correlation with other wavelengths.
54900 54940 54980 55020 55060
]-1 s
- 2Flu
x [ph
oton
s cm
10
20
30
40
50
-910!
Fermi (15 day bins)Fermi (30 day bins) ]-1 s
-2Flu
x [ph
oton
s cm
0
0.05
0.1
0.15
0.2-910!
MAGICVERITAS
MJD54900 54940 54980 55020 55060
]Flu
x [ph
oton
s/minu
te
0
0.5
1
1.5
2 WhippleMJD
Fermi MAGIC Whipple
E>300MeV E>300GeV
E>400GeV
PRELIMINARY
PRELIMINARY
PRELIMINARY
Lightcurves Mrk 501 − γ-rays and VHE
Large flare in VHE around MJD 54952 (May 1st, 2009). No obvious correlation with other wavelengths.
Flarewithout X-ray counterpart
54900 54940 54980 55020 55060
]-1 s
- 2Flu
x [ph
oton
s cm
10
20
30
40
50
-910!
Fermi (15 day bins)Fermi (30 day bins) ]-1 s
-2Flu
x [ph
oton
s cm
0
0.05
0.1
0.15
0.2-910!
MAGICVERITAS
MJD54900 54940 54980 55020 55060
]Flu
x [ph
oton
s/minu
te
0
0.5
1
1.5
2 WhippleMJD
Fermi MAGIC Whipple
E>300MeV E>300GeV
E>400GeV
PRELIMINARY
Flarewithout X-ray counterpart
PRELIMINARY
PRELIMINARY
Lightcurves Mrk 501 − γ-rays and VHE
optical linear polarisation: -steady and then drops by ~15% after flare-much larger than in March 2009
EVPA:-continuous increase from ~15o to ~30o
in 3 days before flare- rotation stops when flare occurs
➡ indicates common origin for optical and γ-ray emission (e.g., Marscher et al. 2010)
]-1 s-2
Flux [
phot
ons c
m
0
0.05
0.1
0.15
0.2-910!
MAGICVERITAS
MJD54900 54940 54980 55020 55060
]Flu
x [ph
oton
s/minu
te
0
0.5
1
1.5
2 Whipple
P (%
)
123456
54900 54940 54980 55020 55060
°EV
PA( )
1520253035
MJD
Steward Observatory
PRELIMINARY
Flarewithout X-ray counterpart
PRELIMINARY
PRELIMINARY
Lightcurves Mrk 501 − γ-rays and VHE
optical linear polarisation: -steady and then drops by ~15% after flare-much larger than in March 2009
EVPA:-continuous increase from ~15o to ~30o
in 3 days before flare- rotation stops when flare occurs
➡ indicates common origin for optical and γ-ray emission (e.g., Marscher et al. 2010)
]-1 s-2
Flux [
phot
ons c
m
0
0.05
0.1
0.15
0.2-910!
MAGICVERITAS
MJD54900 54940 54980 55020 55060
]Flu
x [ph
oton
s/minu
te
0
0.5
1
1.5
2 Whipple
P (%
)
123456
54900 54940 54980 55020 55060
°EV
PA( )
1520253035
MJDFurther details on this flaring event can be found inPichel & Paneque, Proc. ICRC 2011, arXiv:1110.2549v1
Steward Observatory
log(frequency [Hz])10 12 14 16 18 20 22 24 26 28
var
F
0
0.2
0.4
0.6
0.8
1
Fermi
ROVOR NMSkies
MITSuME
GRT
GASPOAGH
UVOT
WiroEffelsberg
Metsähovi
Medicina
OVRO
Whipple
MAGIC
PCAASM
BAT
XRTa
XRTb
Steward V
Variability of Mrk 421 and Mrk 501
Largest variability in X-rays
PRELIMINARY
Low but significant variability at all wavelengths
Mrk 421Fvar =
!
S2! < !2
err >
< F! >2
Fractional variability Fvar (Vaughan et al. 2003)
open circles:host galaxy subtracted(R band; Nilsson et al. 2007)
log(frequency [Hz])10 12 14 16 18 20 22 24 26 28
0
0.2
0.4
0.6
0.8
1
Fermi (15 day)Fermi (30 day)
ROVOR
GASP
GRT
MITSuMEOAGH
UVOTWiroMetsähoviGASP
SMA
OVRO
MAGIC
PCAASM
BAT
XRTaXRTb
Steward V
VERITAS
Whipple
Whipple(flare removed)
VERITAS (flare removed)va
rF
PRELIMINARY Largest variability in VHE due to flare in May
2009
Mrk 501
Variability increases with frequency
Variability of Mrk 421 and Mrk 501
open circles:host galaxy subtracted(R band; Nilsson et al. 2007)
Fermi-LAT: dominated by
variability at 30 day timescales
• unevenly sampled lightcurves, gaps• each lightcurve has a different sampling, different number of data points
What is the error in Fvar introduced by this? How many flux measurements are needed to obtain a reliable Fvar estimate?
Unequally & unevenly sampled lightcurves
• unevenly sampled lightcurves, gaps• each lightcurve has a different sampling, different number of data points
What is the error in Fvar introduced by this? How many flux measurements are needed to obtain a reliable Fvar estimate?
Unequally & unevenly sampled lightcurves
log(frequency [Hz])10 12 14 16 18 20 22 24 26 28
var
F
0
0.2
0.4
0.6
0.8
1varF and its uncertainty calculated using Vaughan et al. 2003
delete-d jackknife estimate and variance, d=sqrt(n)
Fermi
UVOTMetsähovi
OVRO
Whipple
MAGIC
PCA
ASM
BAT
XRTa
XRTb
PRELIMINARY
d randomly selected flux measurements removed from eachlightcurve without replacement (Jackknife)
Mrk 421
• unevenly sampled lightcurves, gaps• each lightcurve has a different sampling, different number of data points
What is the error in Fvar introduced by this? How many flux measurements are needed to obtain a reliable Fvar estimate?
Unequally & unevenly sampled lightcurves
log(frequency [Hz])10 12 14 16 18 20 22 24 26 28
var
F
0
0.2
0.4
0.6
0.8
1varF and its uncertainty calculated using Vaughan et al. 2003
delete-d jackknife estimate and variance, d=sqrt(n)
Fermi
UVOTMetsähovi
OVRO
Whipple
MAGIC
PCA
ASM
BAT
XRTa
XRTb
PRELIMINARY
d randomly selected flux measurements removed from eachlightcurve without replacement (Jackknife)
Mrk 421
➡no significant change in the Fvar values
• unevenly sampled lightcurves, gaps• each lightcurve has a different sampling, different number of data points
What is the error in Fvar introduced by this? How many flux measurement are needed to obtain a reliable Fvar estimate?
PRELIMINARY
d randomly selected flux measurements removed from eachlightcurve without replacement (Jackknife)
log(frequency [Hz])10 12 14 16 18 20 22 24 26 28
0
0.2
0.4
0.6
0.8
1va
rF
varF and its uncertainty calculated using Vaughan et al. 2003delete-d jackknife estimate and variance, d=sqrt(n)
Fermi
UVOTMetsähoviOVRO
MAGIC
PCAASM
BAT
XRTa
XRTb
VERITAS
Whipple
Mrk 501
Unequally & unevenly sampled lightcurves
➡no significant change in the Fvar values
PRELIMINARY
• d = 1 ... n-2 flux values removed from each lightcurve
• Fvar measurements reliable for all but the smallest (n 10) samples
nn-d
0.2 0.4 0.6 0.8 1
Fvar
-0.1
0
0.1
0.2
0.3
0.4
0.5 ASM
nn-d
0 0.2 0.4 0.6 0.8 1
Fvar
0
0.1
0.2
0.3
0.4
0.5 PCAn
n-d0 0.2 0.4 0.6 0.8 1
Fvar
0
0.05
0.1
0.15
0.2
0.25
0.3 GASP
nn-d
0 0.2 0.4 0.6 0.8 1
Fvar
0.2
0.25
0.3
0.35
0.4 UVOT W2n
n-d0 0.2 0.4 0.6 0.8 1
Fvar
00.05
0.10.15
0.20.25
0.30.35
0.40.45 Whipple
nn-d
0 0.2 0.4 0.6 0.8 1
Fvar
0
0.1
0.2
0.3
0.4
0.5
0.6 Metsähovi
!
Mrk
421
Unequally & unevenly sampled lightcurves
PRELIMINARY
• d = 1 ... n-2 flux values removed from each lightcurve
• Fvar measurements reliable for all but the smallest (n 10) samples!
ASM
PCA
GASP
UVOT W2
Whipple
Metsähovi
nn-d
0 0.2 0.4 0.6 0.8 1
Fvar
0.050.060.070.080.09
0.10.110.120.13
nn-d
0 0.2 0.4 0.6 0.8 1
Fvar
00.020.040.060.08
0.10.120.140.160.18
nn-d
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Fvar
-0.3-0.2-0.1
00.10.20.30.4
nn-d
0 0.2 0.4 0.6 0.8 1
Fvar
-0.05
0
0.05
0.1
0.15
0.2
0.25
nn-d
0 0.2 0.4 0.6 0.8 1
Fvar
0.2
0.4
0.6
0.8
1
1.2
nn-d
0 0.2 0.4 0.6 0.8 1
Fvar
0
0.05
0.1
Mrk
501
Unequally & unevenly sampled lightcurves
P R E L I M I N A R Y
P R E L I M I N A R Y
Correlations
Mrk 421: clear correlation between VHE and X-raysDiscrete correlation function (Edelson & Krolik 1988)
Mrk 501: no correlation between VHE and X-rays
Mkn 421MAGIC – Whipple
–200 –100 0 100 200–1.0
0.5
–0.0
–0.5
1.0
!! [d]
DC
F
Mkn 421ASM – PCA
–200 –100 0 100 200–1.0
0.5
–0.0
–0.5
1.0
!! [d]
DC
F
Mkn 421MAGIC – PCA
–200 –100 0 100 200–1.0
0.5
–0.0
–0.5
1.0
!! [d]
DC
FMkn 501
Whipple – PCA
–200 –100 0 100 200–1.0
0.5
–0.0
–0.5
1.0
!! [d]
DC
FMkn 501
XRT – PCA
–200 –100 0 100 200–1.0
0.5
–0.0
–0.5
1.0
!! [d]
DC
F
Mkn 501VERITAS – Whipple
–200 –100 0 100 200–1.0
0.5
–0.0
–0.5
1.0
!! [d]
DC
F Mrk 501
Mrk 421
Conclusions & Outlook• 2009 MWL campaings on Mrk 421 and Mrk 501
• preliminary results on variability:
- both sources in low activity state
- Mrk 421: - Fractional variability Fvar low but significant at all frequencies, largest in
X-rays
- Mrk 501: - flare in VHE in May 2009, accompanied by changes in optical
polarisation and EVPA- Mrk 501: Fractional variability Fvar increases with frequency, largest in
VHE due to flare
• Problem of unevenly and unequally sampled lightcurves: first quick test shows that Fvar is not significantly affected by sampling, gaps and different number of flux measurements
• more detailed analysis of the variability and correlation studies (discrete correlation functions) under way
SED fitting parameters
Mrk 501: Stawarz’s codeAbdo et al., 2011, ApJ, 727, 129
Mrk 421: Finke’s codeAbdo et al., 2011, ApJ, 736, 131
log(frequency [Hz])10 12 14 16 18 20 22 24 26 28
0
0.2
0.4
0.6
0.8
1 and its uncertainty calculated using Vaughan et al. 2003varF
moving block jackknife estimate and variance
var
F
Fermi
UVOTMetsähovi
OVRO
Whipple
MAGIC
PCA
ASM
BAT
XRTa
XRTb
• removed block of m consecutive flux measurements, m=n1/3
• somewhat larger errors
PRELIMINARY
Mrk 421
Unequally & unevenly sampled lightcurves
PRELIMINARY
log(frequency [Hz])10 12 14 16 18 20 22 24 26 28
0
0.2
0.4
0.6
0.8
1 and its uncertainty calculated using Vaughan et al. 2003varF
moving block jackknife estimate and variance
var
F
Fermi
UVOTMetsähovi
OVRO
MAGIC
PCA
ASM
BAT
XRTa
XRTb
VERITAS
WhippleMrk 501
Unequally & unevenly sampled lightcurves
• removed block of m consecutive flux measurements, m=n1/3