Transcript Diapositiva 1

Multiwavelength observations of the
gamma-ray blazars detected by AGILE
Filippo D’Ammando
INAF - Istituto di Astrofisica Spaziale e Fisica Cosmica Roma
Università degli Studi di Roma “Tor Vergata”
Ph.D in Astronomy - Cycle XXII
Roman Young Researchers Meeting 2009
Active Galactic Nuclei - Unification Model
• central Black Hole (106 -109 Mʘ)
• accretion disk rotating around
the SMBH
• clouds
of
gas
gravitational
attracted by the black hole and
illuminated by the disk radiation
• optically thick torus of molecular
gas and dust
• two collimated relativistic jets
Urry and Padovani 1995
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Almost all galaxies contains a
massive black hole but 99% of
them are silent and 1% is active
(mostly radio-quiet AGNs)... and
only 0.1% is radio-loud AGNs
Blazar characteristics:
- compact radio
inverted spectrum
core,
flat
or
- apparent superluminal motion
- irregular, rapid and often very
large variability at all frequencies
- high and variable polarization at
optical and radio frequencies
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Emission mechanisms in blazars
Leptonic processes:
- synchrotron emission
- inverse Compton where seed
photons
came
from
the
internal synchrotron radiation
- inverse Compton where seed
photons came from external
radiation (accretion disk, BLR
and/or torus)
Hadronic processes:
- synchrotron emission
- proton-initiated cascades
- proton-synchrotron emission
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Synchrotron Self-Compton (SSC)
Electrons in a magnetic field can work twice: first producing
synchrotron radiation, and then Comptonizing it (SSC)
Synchrotron
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SSC
21 July 2009
Sikora, Begelman
and Rees 1994
In External Compton model the seed photons come from outside to the jet
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The blazar (spectral) sequence
Epk of synchrotron and Compton components inversely correlated with L
FSRQ
L
BL Lac
Fossati et al. 1998
Donato et al. 2001
npeak
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Low power
slow
cooling
large ɣpeak
Big power
fast
cooling small ɣpeak
Ghisellini et al. 1998, 2002
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First AGILE multi-λ campaign: 3C 279
Giuliani, D’Ammando, Vercellone, et al. 2009, A&A, 494, 509
First extragalactic source detected in gamma-ray by AGILE-GRID, monitored
simultaneously in optical band by REM telescope and in X-rays by Swift
<Fɣ> = (210  38) 10-8 ph cm-2 s-1 E > 100 MeV
Gamma-ray flux similar to the EGRET high state but soft spectrum
The soft spectrum during a flaring episode could be an indication of a
dominant contribution of EDC emission compared to ECC emission model
9 - 13 July 2007
ECC
ECD
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R-band light curve between December
2006 and December 2007: a strong
minimum occurred about 2 months
before the AGILE observation
This optical minimum might be
correlated with a low accretion
state of the disk and then with a
ECC component deficit, delayed
of about two months
Hartman et al. 2001
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PKS 1510-089
Pucella, Vittorini, D’Ammando, et al. 2008,
A&A, 491, L21
<Fɣ> = (195  30) 10-8 ph cm-2 s-1
E >100 MeV
Possible correlation between optical and gamma-ray
bands: contemporaneous decrease in fluxes
The IC contribution from the BLR can explain the
observed hard gamma-ray spectrum
23 August - 1 September 2007
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PKS 1510-089: a rapid gamma-ray flare in March 2008
17 - 21 March 2008
D’Ammando, Pucella, Raiteri, et al.,
submitted to A&A
Serendipitous detection during an AGILE
pointing towards the Galactic Center
3 ToO by Swift/XRT: the spectrum becomes
harder when the source is brighter
GASP-WEBT observed intense optical activity
between January and April 2008
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Between January and
April 2008, the blazar
PKS 1510-089 showed
intense optical activity
with several episodes of
fast variability detected
by GASP - WEBT
Peaks was detected in
the optical band on 15
February, 29 March and
11 April 2008
After two episodes of
medium intensity the
source was not detected
for some days in
gamma-ray band and
suddenly a rapid flare
was observed by AGILE
on 18-19 March 2008
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Radio-to-optical behaviour
The light curve at 230-345 GHz
suggests that the mechanism
producing
the flaring event
observed in optical in the second
half of February and in late
March-April 2008 also interested
the millimetric emitting zone,
with some delay
At 22-43 GHz a hint of flux
increase is visible in the
second part of the light
curve, while the radio flux
at 5-15 GHz shows no trend
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Spectral Energy Distribution - March 2008
Likely signatures of the
little and big blue bumps
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hard X-ray spectrum:
soft X-ray excess?
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21 July 2009
PKS 1510-089 March 2009
PKS 1510-089 showed an extraordinary gamma-ray activity
during March 2009, with several flaring episodes
D’Ammando et al., in preparation
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GASP observations of PKS 1510-089
During March 2009 the optical activity of PKS 1510-089
is greatly increased with a peak on 26 March 2009
D’Ammando et al., in preparation
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S5 0716+714 in September - October 2007
Chen, D’Ammando, Villata, et al. 2008,
A&A, 489, L37
<Fɣ> = (97  15) 10-8 ph cm-2 s-1 E >100 MeV
with a peak level of (193  42) 10-8 ph cm-2 s-1
z = 0.31  0.08 (Nilsson et al., 2008)
Total power transported in the jet is extremely
high ( Ltot > 3 x 1045 erg s-1) , at the limit of the
maximum power generated by a spinning black
hole of 109 Mʘ
4 - 23 September 2007
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The Discrete Correlation Function
(DCF) displays a significant peak for
a time-lag of -1 day
Possible delay in the gamma-ray flux
variations with respect to optical
variations of the order of 1 day
To fit the SED we use 2 different SSC
components:
- the first component reproduces the
ground state
- the second components dominates
the optical and gamma-ray bands
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Swift and AGILE simultaneous obs. in October - November 2007
23 October - 13 November 2007
Giommi, Colafrancesco, Cutini, et al., 2008, A&A, 487, L49
<Fɣ> = (47 ± 11) 10-8 ph cm-2 s-1
E >100 MeV
The gamma-ray flux is about a factor of 2 lower than in September
Strong variability in soft X-ray, moderate variability at optical/UV
and approximately constant behavior in hard X-rays
The SED is consistent with a two-components SSC model
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3C 273: simultaneous detection by GRID & SA
Pacciani, Donnarumma, Vittorini, et al.
2009, A&A, 494, 49
<Fɣ> = (22  6) 10-8 ph cm-2 s-1
E >100 MeV
Fɣ [peak] = (33 11) 10-8 ph cm-2s-1 E >100 MeV
Multi-wavelength campaign: REM, Swift, RXTE,
INTEGRAL and AGILE
No optical variability during the entire campaign.
Hint of a possible anti-correlated variability
between X-rays and gamma-rays
SSC + EC: spectral variability consistent with an
acceleration episode of the electron population
16 December 2007 – 8 January 2008
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3C 454.3: July 2007
24 - 30 July 2007
Vercellone, Chen, Giuliani, et al. 2008, ApJL, 676, 13
AGILE repointing the source during a period of strongly enhanced optical emission
<Fɣ> = (280 ± 40) 10-8 ph cm-2 s-1
E >100 MeV
Highest gamma-ray flux from this source in the last 15 years but see Fermi obs.
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MW Observations of 3C 454.3 in November 2007
Vercellone, Chen, Vittorini, Giuliani, D’Ammando et al. 2009, ApJ, 690, 1018
<Fɣ> = (170  13) 10-8 ph cm-2 s-1, with a peak of ~400 x 10-8 ph cm-2 s-1 E >100 MeV
Rapid variability in the optical band
Emission in the optical range appears to be correlated with that at gamma-ray energies
10 November - 1 December 2007
The DCF indicate a moderate correlation
with no lag between gamma-ray and
optical flux variations
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ECC
ECD
The contribution of ECD radiation
alone cannot account for the
hardness
of
the
spectrum.
The gamma-ray emission seems
to be dominated by IC scattering
of the external photons from the
broad line region clouds
ECC
ECD
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MW Observations of 3C 454.3 in December 2007
Donnarumma et al., 2009, submitted to ApJ
Simultaneous
multi-wavelength
campaign
with the contribution of Spitzer, REM, GASPWEBT, MITSuME, Swift, Suzaku and AGILE
<Fɣ> = ~ 250 x 10-8 ph cm-2 s-1 E >100 MeV
A leptonic EC model is considered, with also a
contribution of EC on a hot corona (T=106 K),
to account for the hard ɣ-ray spectrum
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21 July 2009
DCF analysis shows a (possible)
delay of the gamma-ray flux
variations with respect to the
optical ones of about 10 hours
Vercellone et al., in preparation
The longest monitor so far of a
blazar in the gamma-ray band
A factor of about 10 in dynamic
range in about 2 years with a
possible spectral trend (harder
when brighter)
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21 July 2009
Mrk 421: WEBT + AGILE + VERITAS + MAGIC = …
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21 July 2009
Mrk 421 from optical to TeV energies
Donnarumma, Vittorini, Vercellone et al., 2009, ApJ 691, L13
<Fɣ> = (42 ± 13) 10-8 ph cm-2 s-1 E >100 MeV
Swift/XRT: Flux (2 - 10 keV) = 2.6 x 10-9 ph cm-2 s-1
Possible correlated variability between optical, X-rays
and high-energy parts of the spectrum
SSC model: hardening/softening of electron energy
distribution caused by particle acceleration process
Summary and remarks
• Gamma-ray astronomy is still a largely unexplored territory,
in particular for the class of blazars
• AGILE (and EGRET) detected only few objects with flux
greater than 100 x 10-8 ph cm-2 s-1? Why? Selection effects
or there is a subclass of blazar with peculiar characteristics?
• SSC vs EC vs more complex models? How to distinguish?
• AGILE observations has brought to light a more complex
behaviour of blazars with respect to the standard models:
- the presence of two emission components in any BL Lacs
- the possible contributions of an hot corona as source of
seed photons for the EC in FSRQs
• The study of multi-wavelength correlations is the key to
understanding the structure of the inner jet and the origin
of the seed photons for the IC process
• The study of sources in different activity states, not only
during flaring states, could provide new informations
Thanks for your attention!!!