FERMI Large Area Telescope and multi-wavelength observations of the flaring activity of PKS 1510-089 between 2008 september and 2009 june

TLDR: In this article, the authors report on the multi-wavelength observations of PKS 1510-089 (a flat spectrum radio quasar) at z = 0.361 during its high activity period between 2008 September and 2009 June.

Abstract: We report on the multi-wavelength observations of PKS 1510-089 (a flat spectrum radio quasar (FSRQ) at z = 0.361) during its high activity period between 2008 September and 2009 June. During this 11 month period, the source was characterized by a complex variability at optical, UV, and gamma-ray bands, on timescales down to 6-12 hr. The brightest gamma-ray isotropic luminosity, recorded on 2009 March 26, was similar or equal to 2 x 1048 erg s-1. The spectrum in the Fermi Large Area Telescope energy range shows a mild curvature described well by a log-parabolic law, and can be understood as due to the Klein-Nishina effect. The. -ray flux has a complex correlation with the other wavelengths. There is no correlation at all with the X-ray band, a weak correlation with the UV, and a significant correlation with the optical flux. The. -ray flux seems to lead the optical one by about 13 days. From the UV photometry, we estimated a black hole mass of similar or equal to 5.4 x 10(8)M(circle dot) and an accretion rate of similar or equal to 0.5M(circle dot) yr(-1). Although the power in the thermal and non-thermal outputs is smaller compared to the very luminous and distant FSRQs, PKS 1510-089 exhibits a quite large Compton dominance and a prominent big blue bump (BBB) as observed in the most powerful gamma-ray quasars. The BBB was still prominent during the historical maximum optical state in 2009 May, but the optical/ UV spectral index was softer than in the quiescent state. This seems to indicate that the BBB was not completely dominated by the synchrotron emission during the highest optical state. We model the broadband spectrum assuming a leptonic scenario in which the inverse Compton emission is dominated by the scattering of soft photons produced externally to the jet. The resulting model-dependent jet energetic content is compatible with a scenario in which the jet is powered by the accretion disk, with a total efficiency within the Kerr black hole limit.

Figures

Table 1 Flaring Activity of PKS 1510-089 from 2008 August Until 2009 June

Figure 1. Upper panel: the γ -ray photon index (αγ ), as a function of time, for weekly and daily binning. In the case of daily binning, only observations with a test statistic > 10 are taken into account. The test statistic is defined as TS = −2 log(L0/L1), where L1 and L0 are the likelihood of whether the source is included or not. Lower panel: light curves of weekly and daily (TS > 10) fluxes.

Figure 14. Scatter plot of the Fermi-LAT flux (E > 200 MeV) vs. the UVOT νF(ν) in the UVW2 filter. The red dashed line represents the best-fit power-law model. The correlation coefficient of the logarithm of the UV and γ -ray fluxes is r = 0.2 with a 95% confidence interval of 0.05 r 0.34.

Figure 13. Panels (a) and (b): UVOT light curves. Panel (c): hardness ratio of the UVOT spectra (UVW2/UVV) evaluated as a function of the time.

Figure 24. Red solid circles correspond to simultaneous optical/UV data representing the intermediate state during the γ -ray integration period. Blue and green circles correspond to the highest and lowest flux states, respectively, observed during the same integration period. The Swift-XRT data (orange points) are integrated during the same interval of the LAT data, and the SwiftBAT data represent the five year fluxes discussed in Section 4.1. The black squares represent GASP radio data, integrated during the flares. The cyan points correspond to the LAT quiescent state SED. The magenta points represent the γ -ray SED integrated during the flare. The blue, green, and red dotted lines represent the PL best fit of the γ -ray data, for a daily integration and simultaneous to the optical/UV data with the same color. The thin black dotted line represents the flaring synchrotron emission. The thin black dashed line corresponds to flaring SSC emission. The red and blue thick dotted lines correspond to the dusty torus and BBB emission, respectively. The red and blue thin dashed lines correspond to the ERC/DT and ERC/BLR flaring emission, respectively. The solid black thick line represents the sum of all the flaring model components. The thick dot-dashed line represents the sum of all the model components for the quiescent state alone.

Figure 25. Upper panel: the SEDs for the different values of the highenergy electron distribution index. The black dashed lines represent the synchrotron emission without self-absorption. The black dotted line represents the synchrotron self-adsorbed emission. The black solid lines correspond to SSC emission. The red and blue dotted lines correspond to the dusty torus and BBB emission, respectively. The red and blue solid lines correspond to the ERC/DT and ERC/BLR emission, respectively. Lower panel: optical/γ -ray flux correlations for ERC/BLR (blue solid circles), ERC/DT (red solid circles), and SSC (black solid circles); dashed lines are the power-law relations.

Full text

Physics
Physics Research Publications
Purdue University Year 
Fermi large area telescope and
multi-wavelength observations of the
flaring activity of PKS 1510-089 between
2008 September and 2009 June
A. A. Abdo, M. Ackermann, I. Agudo, M. Ajello, A. Allafort, H. D. Aller,
M. F. Aller, E. Antolini, A. A. Arkharov, M. Axelsson, U. Bach, L. Baldini,
J. Ballet, G. Barbiellini, D. Bastieri, K. Bechtol, R. Bellazzini, A. Berdyugin,
B. Berenji, R. D. Blandford, D. A. Blinov, E. D. Bloom, M. Boettcher, E.
Bonamente, A. W. Borgland, A. Bouvier, J. Bregeon, A. Brez, M. Brigida, P.
Bruel, R. Buehler, C. S. Buemi, T. H. Burnett, S. Buson, G. A. Caliandro, R.
A. Cameron, P. A. Caraveo, D. Carosati, S. Carrigan, J. M. Casandjian, E.
Cavazzuti, C. Cecchi, O. Celik, A. Chekhtman, W. P. Chen, C. C. Cheung,
J. Chiang, S. Ciprini, R. Claus, J. Cohen-Tanugi, J. Conrad, S. Corbel, L.
Costamante, C. D. Dermer, A. de Angelis, F. de Palma, D. Donato, E. D. E.
Silva, P. S. Drell, R. Dubois, D. Dumora, C. Farnier, C. Favuzzi, S. J. Fegan, E.
C. Ferrara, W. B. Focke, E. Forne, P. Fortin, Y. Fukazawa, S. Funk, P. Fusco,
F. Gargano, D. Gasparrini, N. Gehrels, S. Germani, B. Giebels, N. Giglietto, F.
Giordano, M. Giroletti, T. Glanzman, G. Godfrey, I. A. Grenier, J. E. Grove,
S. Guiriec, M. A. Gurwell, C. Gusbar, J. L. Gomez, D. Hadasch, V. A. Hagen-
Thorn, M. Hayashida, E. Hays, D. Horan, R. E. Hughes, G. Johannesson, A.
S. Johnson, W. N. Johnson, T. Kamae, H. Katagiri, J. Kataoka, N. Kawai, G.
Kimeridze, J. Knodlseder, T. S. Konstantinova, E. N. Kopatskaya, E. Koptelova,
Y. Y. Kovalev, O. M. Kurtanidze, M. Kuss, A. Lahteenmaki, J. Lande, V. M.
Larionov, E. G. Larionova, L. V. Larionova, S. Larsson, L. Latronico, S. H.
Lee, P. Leto, M. L. Lister, F. Longo, F. Loparco, B. Lott, M. N. Lovellette,
P. Lubrano, G. M. Madejski, A. Makeev, E. Massaro, M. N. Mazziotta, W.
McConville, J. E. McEnery, I. M. McHardy, P. F. Michelson, W. Mitthumsiri,
T. Mizuno, A. A. Moiseev, C. Monte, M. E. Monzani, D. A. Morozova, A.
Morselli, I. V. Moskalenko, S. Murgia, M. Naumann-Godo, M. G. Nikolashvili,
P. L. Nolan, J. P. Norris, E. Nuss, M. Ohno, T. Ohsugi, A. Okumura, N. Omodei,
E. Orlando, J. F. Ormes, M. Ozaki, D. Paneque, J. H. Panetta, D. Parent, M.

Pasanen, V. Pelassa, M. Pepe, M. Pesce-Rollins, F. Piron, T. A. Porter, A.
B. Pushkarev, S. Raino, C. M. Raiteri, R. Rando, M. Razzano, A. Reimer, O.
Reimer, R. Reinthal, J. Ripken, S. Ritz, M. Roca-Sogorb, A. Y. Rodriguez, M.
Roth, P. Roustazadeh, F. Ryde, H. F. W. Sadrozinski, A. Sander, J. D. Scargle,
C. Sgro, L. A. Sigua, P. D. Smith, K. Sokolovsky, G. Spandre, P. Spinelli, J. L.
Starck, M. S. Strickman, D. J. Suson, H. Takahashi, T. Takahashi, L. O. Takalo,
T. Tanaka, B. Taylor, J. B. Thayer, J. G. Thayer, D. J. Thompson, L. Tibaldo,
M. Tornikoski, D. F. Torres, G. Tosti, A. Tramacere, C. Trigilio, I. S. Troitsky,
G. Umana, T. L. Usher, J. Vandenbroucke, V. Vasileiou, N. Vilchez, M. Villata,
V. Vitale, A. P. Waite, P. Wang, B. L. Winer, K. S. Wood, Z. Yang, T. Ylinen,
and M. Ziegler
This paper is posted at Purdue e-Pubs.
http://docs.lib.purdue.edu/physics articles/1130

The Astrophysical Journal, 721:1425–1447, 2010 October 1 doi:10.1088/0004-637X/721/2/1425
C
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2010. The American Astronomical Society. All rights reserved. Printed in the U.S.A.
FERMI LARGE AREA TELESCOPE AND MULTI-WAVELENGTH OBSERVATIONS OF THE FLARING
ACTIVITY OF PKS 1510-089 BETWEEN 2008 SEPTEMBER AND 2009 JUNE
A. A. Abdo
1,2,79
, M. Ackermann
3
, I. Agudo
4,5
, M. Ajello
3
, A. Allafort
3
, H. D. Aller
6
, M. F. Aller
6
, E. Antolini
7,8
,
A. A. Arkharov
9
, M. Axelsson
10,11,12
, U. Bach
13
, L. Baldini
14
, J. Ballet
15
, G. Barbiellini
16,17
, D. Bastieri
18,19
,
K. Bechtol
3
, R. Bellazzini
14
, A. Berdyugin
20
, B. Berenji
3
, R. D. Blandford
3
,D.A.Blinov
21
, E. D. Bloom
3
,
M. Boettcher
22
, E. Bonamente
7,8
, A. W. Borgland
3
, A. Bouvier
3
, J. Bregeon
14
,A.Brez
14
, M. Brigida
23,24
,P.Bruel
25
,
R. Buehler
3
,C.S.Buemi
26
, T. H. Burnett
27
,S.Buson
18,19
, G. A. Caliandro
28
, R. A. Cameron
3
, P. A. Caraveo
29
,
D. Carosati
30
, S. Carrigan
19
, J. M. Casandjian
15
, E. Cavazzuti
31
, C. Cecchi
7,8
,
¨
O. ¸Celik
32,33,34
, A. Chekhtman
1,35
,
W. P. Chen
36
, C. C. Cheung
1,2
, J. Chiang
3
,S.Ciprini
8
,R.Claus
3
, J. Cohen-Tanugi
37
, J. Conrad
12,38,80
, S. Corbel
15,39
,
L. Costamante
3
, C. D. Dermer
1
, A. de Angelis
40
, F. de Palma
23,24
, D. Donato
32
, E. do Couto e Silva
3
, P. S. Drell
3
,
R. Dubois
3
, D. Dumora
41,42
, C. Farnier
37
, C. Favuzzi
23,24
, S. J. Fegan
25
, E. C. Ferrara
32
, W. B. Focke
3
, E. Forn
´
e
43
,
P. Fortin
25
, Y. Fukazawa
44
,S.Funk
3
,P.Fusco
23,24
, F. Gargano
24
, D. Gasparrini
31
, N. Gehrels
32
, S. Germani
7,8
,
B. Giebels
25
, N. Giglietto
23,24
, F. Giordano
23,24
, M. Giroletti
45
, T. Glanzman
3
, G. Godfrey
3
,I.A.Grenier
15
,
J. E. Grove
1
,S.Guiriec
46
,M.A.Gurwell
47
, C. Gusbar
22
,J.L.G
´
omez
4
, D. Hadasch
48
, V. A. Hagen-Thorn
21,49
,
M. Hayashida
3
,E.Hays
32
, D. Horan
25
,R.E.Hughes
50
,G.J
´
ohannesson
3
,A.S.Johnson
3
,W.N.Johnson
1
, T. Kamae
3
,
H. Katagiri
44
, J. Kataoka
51
, N. Kawai
52,53
, G. Kimeridze
54
,J.Kn
¨
odlseder
55
, T. S. Konstantinova
21
, E. N. Kopatskaya
21
,
E. Koptelova
36
, Y. Y. Kovalev
13,56
, O. M. Kurtanidze
54
,M.Kuss
14
, A. Lahteenmaki
57
,J.Lande
3
, V. M. Larionov
9,21,49
,
E. G. Larionova
21
, L. V. Larionova
21
, S. Larsson
10,12,38
, L. Latronico
14
,S.-H.Lee
3
,P.Leto
26
,M.L.Lister
58
,
F. Longo
16,17
, F. Loparco
23,24
, B. Lott
41,42
, M. N. Lovellette
1
, P. Lubrano
7,8
, G. M. Madejski
3
, A. Makeev
1,35
,
E. Massaro
59
, M. N. Mazziotta
24
, W. McConville
32,60
,J.E.McEnery
32,60
, I. M. McHardy
61
, P. F. Michelson
3
,
W. Mitthumsiri
3
, T. Mizuno
44
, A. A. Moiseev
33,60
, C. Monte
23,24
, M. E. Monzani
3
, D. A. Morozova
21
, A. Morselli
62
,
I. V. Moskalenko
3
, S. Murgia
3
, M. Naumann-Godo
15
, M. G. Nikolashvili
21
, P. L. Nolan
3
, J. P. Norris
63
,E.Nuss
37
,
M. Ohno
64
, T. Ohsugi
65
, A. Okumura
64
, N. Omodei
3
, E. Orlando
66
,J.F.Ormes
63
, M. Ozaki
64
, D. Paneque
3
, J. H. Panetta
3
,
D. Parent
1,35
, M. Pasanen
20
, V. Pelassa
37
, M. Pepe
7,8
, M. Pesce-Rollins
14
, F. Piron
37
, T. A. Porter
3
,
A. B. Pushkarev
9,13,67
,S.Rain
`
o
23,24
, C. M. Raiteri
68
, R. Rando
18,19
, M. Razzano
14
,A.Reimer
3,69
,O.Reimer
3,69
,
R. Reinthal
20
, J. Ripken
12,38
,S.Ritz
70
, M. Roca-Sogorb
4
, A. Y. Rodriguez
28
,M.Roth
27
, P. Roustazadeh
22
, F. Ryde
12,71
,
H. F.-W. Sadrozinski
70
, A. Sander
50
, J. D. Scargle
72
,C.Sgr
`
o
14
,L.A.Sigua
54
,P.D.Smith
50
, K. Sokolovsky
13,56
,
G. Spandre
14
, P. Spinelli
23,24
, J.-L. Starck
15
, M. S. Strickman
1
,D.J.Suson
73
, H. Takahashi
65
, T. Takahashi
64
,
L. O. Takalo
20
, T. Tanaka
3
, B. Taylor
74
, J. B. Thayer
3
, J. G. Thayer
3
, D. J. Thompson
32
, L. Tibaldo
15,18,19,81
,
M. Tornikoski
57
, D. F. Torres
28,48
, G. Tosti
7,8
, A. Tramacere
3,75,76
, C. Trigilio
26
, I. S. Troitsky
21
, G. Umana
26
,
T. L. Usher
3
, J. Vandenbroucke
3
, V. Vasileiou
33,34
, N. Vilchez
55
, M. Villata
68
, V. Vitale
62,77
,A.P.Waite
3
,P.Wang
3
,
B. L. Winer
50
,K.S.Wood
1
,Z.Yang
12,38
,T.Ylinen
12,71,78
, and M. Ziegler
70
1
Space Science Division, Naval Research Laboratory, Washington, DC 20375, USA
2
National Academy of Sciences, Washington, DC 20001, USA
3
W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology,
Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305, USA; tramacer@slac.stanford.edu
4
Instituto de Astrof
´
ısica de Andaluc
´
ıa, CSIC, Apdo. 3004, Granada 18080, Spain
5
Institute for Astrophysical Research, Boston University, Boston, MA 02215, USA
6
Department of Astronomy, University of Michigan, Ann Arbor, MI 48109-1042, USA
7
Istituto Nazionale di Fisica Nucleare, Sezione di Perugia, I-06123 Perugia, Italy
8
Dipartimento di Fisica, Universit
`
a degli Studi di Perugia, I-06123 Perugia, Italy
9
Pulkovo Observatory, 196140 St. Petersburg, Russia
10
Department of Astronomy, Stockholm University, SE-106 91 Stockholm, Sweden
11
Lund Observatory, SE-221 00 Lund, Sweden
12
The Oskar Klein Centre for Cosmoparticle Physics, AlbaNova, SE-106 91 Stockholm, Sweden
13
Max-Planck-Institut f
¨
ur Radioastronomie, Auf dem H
¨
ugel 69, 53121 Bonn, Germany
14
Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa, Italy
15
Laboratoire AIM, CEA-IRFU/CNRS/Universit
´
e Paris Diderot, Service d’Astrophysique, CEA Saclay, 91191 Gif sur Yvette, France
16
Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34127 Trieste, Italy
17
Dipartimento di Fisica, Universit
`
a di Trieste, I-34127 Trieste, Italy
18
Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I-35131 Padova, Italy
19
Dipartimento di Fisica “G. Galilei,” Universit
`
a di Padova, I-35131 Padova, Italy
20
Tuorla Observatory, University of Turku, FI-21500 Piikki
¨
o, Finland
21
Astronomical Institute, St. Petersburg State University, St. Petersburg, Russia
22
Department of Physics and Astronomy, Ohio University, Athens, OH 45701, USA
23
Dipartimento di Fisica “M. Merlin” dell’Universit
`
a e del Politecnico di Bari, I-70126 Bari, Italy
24
Istituto Nazionale di Fisica Nucleare, Sezione di Bari, 70126 Bari, Italy
25
Laboratoire Leprince-Ringuet,
´
Ecole polytechnique, CNRS/IN2P3, Palaiseau, France
26
Osservatorio Astrofisico di Catania, 95123 Catania, Italy
27
Department of Physics, University of Washington, Seattle, WA 98195-1560, USA
28
Institut de Ciencies de l’Espai (IEEC-CSIC), Campus UAB, 08193 Barcelona, Spain
29
INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica, I-20133 Milano, Italy
30
EPT Observatories, Tijarafe, La Palma, Spain
1425

1426 ABDO ET AL. Vol. 721
31
Agenzia Spaziale Italiana (ASI) Science Data Center, I-00044 Frascati (Roma), Italy
32
NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
33
Center for Research and Exploration in Space Science and Technology (CRESST) and NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
34
Department of Physics and Center for Space Sciences and Technology, University of Maryland Baltimore County, Baltimore, MD 21250, USA
35
George Mason University, Fairfax, VA 22030, USA
36
Graduate Institute of Astronomy, National Central University, Jhongli 32054, Taiwan
37
Laboratoire de Physique Th
´
eorique et Astroparticules, Universit
´
e Montpellier 2, CNRS/IN2P3, Montpellier, France
38
Department of Physics, Stockholm University, AlbaNova, SE-106 91 Stockholm, Sweden
39
Institut universitaire de France, 75005 Paris, France
40
Dipartimento di Fisica, Universit
`
a di Udine and Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, Gruppo Collegato di Udine, I-33100 Udine, Italy
41
CNRS/IN2P3, Centre d’
´
Etudes Nucl
´
eaires Bordeaux Gradignan, UMR 5797, Gradignan, 33175, France
42
Universit
´
e de Bordeaux, Centre d’
´
Etudes Nucl
´
eaires Bordeaux Gradignan, UMR 5797, Gradignan, 33175, France
43
Agrupaci
´
oAstron
`
omica de Sabadell, 08206 Sabadell, Spain
44
Department of Physical Sciences, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan
45
INAF Istituto di Radioastronomia, 40129 Bologna, Italy
46
Center for Space Plasma and Aeronomic Research (CSPAR), University of Alabama in Huntsville, Huntsville, AL 35899, USA
47
Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
48
Instituci
´
o Catalana de Recerca i Estudis Avan¸cats (ICREA), Barcelona, Spain
49
Isaac Newton Institute of Chile, St. Petersburg Branch, St. Petersburg, Russia
50
Department of Physics, Center for Cosmology and Astro-Particle Physics, The Ohio State University, Columbus, OH 43210, USA
51
Research Institute for Science and Engineering, Waseda University, 3-4-1, Okubo, Shinjuku, Tokyo 169-8555, Japan
52
Department of Physics, Tokyo Institute of Technology, Meguro City, Tokyo 152-8551, Japan
53
Cosmic Radiation Laboratory, Institute of Physical and Chemical Research (RIKEN), Wako, Saitama 351-0198, Japan
54
Abastumani Observatory, Mt. Kanobili, 0301 Abastumani, Georgia
55
Centre d’
´
Etude Spatiale des Rayonnements, CNRS/UPS, BP 44346, F-30128 Toulouse Cedex 4, France
56
Astro Space Center of the Lebedev Physical Institute, 117810 Moscow, Russia
57
Mets
¨
ahovi Radio Observatory, Helsinki University of Technology TKK, FIN-02540 Kylmala, Finland
58
Department of Physics, Purdue University, West Lafayette, IN 47907, USA
59
Physics Department, Universit
`
a di Roma “La Sapienza,” I-00185 Roma, Italy; enrico.massaro@uniroma1.it
60
Department of Physics and Department of Astronomy, University of Maryland, College Park, MD 20742, USA
61
School of Physics and Astronomy, University of Southampton, Highfield, Southampton, SO17 1BJ, UK
62
Istituto Nazionale di Fisica Nucleare, Sezione di Roma “Tor Vergata,” I-00133 Roma, Italy
63
Department of Physics and Astronomy, University of Denver, Denver, CO 80208, USA
64
Institute of Space and Astronautical Science, JAXA, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-8510, Japan
65
Hiroshima Astrophysical Science Center, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526, Japan
66
Max-Planck Institut f
¨
ur extraterrestrische Physik, 85748 Garching, Germany
67
Crimean Astrophysical Observatory, 98409 Nauchny, Crimea, Ukraine
68
INAF, Osservatorio Astronomico di Torino, I-10025 Pino Torinese (TO), Italy
69
Institut f
¨
ur Astro- und Teilchenphysik and Institut f
¨
ur Theoretische Physik, Leopold-Franzens-Universit
¨
at Innsbruck, A-6020 Innsbruck, Austria
70
Santa Cruz Institute for Particle Physics, Department of Physics and Department of Astronomy and Astrophysics, University of California at Santa Cruz,
Santa Cruz, CA 95064, USA
71
Department of Physics, Royal Institute of Technology (KTH), AlbaNova, SE-106 91 Stockholm, Sweden
72
Space Sciences Division, NASA Ames Research Center, Moffett Field, CA 94035-1000, USA
73
Department of Chemistry and Physics, Purdue University Calumet, Hammond, IN 46323-2094, USA
74
Lowell Observatory, Flagstaff, AZ 86001, USA
75
Consorzio Interuniversitario per la Fisica Spaziale (CIFS), I-10133 Torino, Italy
76
INTEGRAL Science Data Centre, CH-1290 Versoix, Switzerland
77
Dipartimento di Fisica, Universit
`
a di Roma “Tor Vergata,” I-00133 Roma, Italy
78
School of Pure and Applied Natural Sciences, University of Kalmar, SE-391 82 Kalmar, Sweden
Received 2010 April 30; accepted 2010 July 2; published 2010 September 10
ABSTRACT
We report on the multi-wavelength observations of PKS 1510-089 (a flat spectrum radio quasar (FSRQ) at z =
0.361) during its high activity period between 2008 September and 2009 June. During this 11 month period, the
source was characterized by a complex variability at optical, UV, and γ -ray bands, on timescales down to 6–12 hr.
The brightest γ -ray isotropic luminosity, recorded on 2009 March 26, was  2 × 10
48
erg s
−1
. The spectrum in
the Fermi Large Area Telescope energy range shows a mild curvature described well by a log-parabolic law, and
can be understood as due to the Klein–Nishina effect. The γ -ray flux has a complex correlation with the other
wavelengths. There is no correlation at all with the X-ray band, a weak correlation with the UV, and a significant
correlation with the optical flux. The γ -ray flux seems to lead the optical one by about 13 days. From the UV
photometry, we estimated a black hole mass of  5.4 × 10
8
M

and an accretion rate of  0.5 M

yr
−1
. Although
the power in the thermal and non-thermal outputs is smaller compared to the very luminous and distant FSRQs, PKS
1510-089 exhibits a quite large Compton dominance and a prominent big blue bump (BBB) as observed in the most
powerful γ -ray quasars. The BBB was still prominent during the historical maximum optical state in 2009 May,
but the optical/UV spectral index was softer than in the quiescent state. This seems to indicate that the BBB was
not completely dominated by the synchrotron emission during the highest optical state. We model the broadband
spectrum assuming a leptonic scenario in which the inverse Compton emission is dominated by the scattering of
soft photons produced externally to the jet. The resulting model-dependent jet energetic content is compatible with
a scenario in which the jet is powered by the accretion disk, with a total efficiency within the Kerr black hole limit.
Key words: galaxies: active – galaxies: jets – gamma rays: galaxies – quasars: individual (PKS 1510-089)
Online-only material: color figures

No. 2, 2010 FERMI-LAT AND MULTI-WAVELENGTH OBSERVATIONS OF PKS 1510-089 1427
1. INTRODUCTION
Among blazars, flat spectrum radio quasars (FSRQs) are those
objects characterized by prominent emission lines in the optical
spectra. The typical spectral energy distribution (SED) of blazars
has a two bump shape. According to current models, the low-
energy bump is interpreted as synchrotron emission from highly
relativistic electrons, and the high-energy bump is interpreted
as inverse Compton (IC) emission. In FSRQs, the IC bump
can dominate over the synchrotron one by more than an order
of magnitude. It is widely believed that in these sources the
IC component is dominated by the scattering of soft photons
produced externally to the jet (Sikora et al. 1994;Dermer&
Schlickeiser 2002), rather than by the synchrotron self-Compton
(SSC) emission (Jones et al. 1974; Ghisellini & Maraschi 1989).
In the external radiation Compton (ERC) scenario, the seed
photons for the IC process are typically UV photons generated
by the accretion disk surrounding the black hole (BH), and
reflected toward the jet by the broad line region (BLR) within
a typical distance from the disk in the subparsec scale. If the
emission occurs at larger distances, the external radiation is
likely to be provided by a dusty torus (DT; Sikora et al. 2002).
In this case, the radiation is typically peaked at IR frequencies.
The study of the SEDs of blazars and their complex variability
has been greatly enriched since the 2008 August start of
scientific observations by the Large Area Telescope (LAT;
Atwood et al. 2009)ontheFermi Gamma-ray Space Telescope
(Ritz 2007), thanks to its high sensitivity and survey mode.
One of the most active blazars observed in this period was
the FSRQ PKS 1510-089. This object has an optical spectrum
characterized by prominent emission lines overlying a blue
continuum (Tadhunter et al. 1993) at a redshift z = 0.361
(Thompson et al. 1990). Radio images show a bright core with
a jet that has a large misalignment between the arcsecond and
milliarcsecond scales; superluminal velocity up to  20c are
also reported (Homan et al. 2002).
PKS 1510-089 was already detected in γ -rays by EGRET
(Hartman et al. 1999) and exhibited a very interesting activity
at all wavelengths. It was also detected by AGILE during 10
days of pointed observations from 2007 August 23 to 2007
September 1 (Pucella et al. 2008). In the period 2008–2009,
PKS 1510-089 was observed to be bright and highly variable
in several frequency bands. In gamma rays, it was detected in
2008 March by AGILE (D’Ammando et al. 2008) and other
bright phases were observed in the subsequent months by both
Fermi-LAT and AGILE (Tramacere 2008; Ciprini & Corbel
2009; D’Ammando et al. 2009b; Pucella et al. 2009; Vercellone
et al. 2009; Cutini & Hays 2009). High states in X-rays and
in optical were reported by Krimm et al. (2009), Villata et al.
(2009a), and Larionov et al. (2009a, 2009b). In a recent paper,
Marscher et al. (2010a) presented data from a multi-wavelength
(MW) campaign concerning the same flaring period of PKS
1510-089. In that paper, the authors focus on analysis of the
parsec-scale behavior and correlation of rotation of the optical
polarization angle with the dramatic γ -ray activity.
In the present paper, we describe the results of the LAT mon-
itoring together with the related MW campaigns covering the
entire electromagnetic spectrum. We present a detailed analysis
79
National Research Council Research Associate
80
Royal Swedish Academy of Sciences Research Fellow, funded by a grant
from the K. A. Wallenberg Foundation.
81
Partially supported by the International Doctorate on Astroparticle Physics
(IDAPP) program.
of the γ -ray spectral shape and spectral evolution, and of the
MW SED modeling and interpretation. This paper is organized
as follows: in Section 2, we report results on the γ -ray obser-
vation of PKS 1510-089 and we study the spectral shape and
its evolution. In Section 3, we summarize multifrequency data
obtained through simultaneous optical–UV–X-ray Swift obser-
vations and radio–optical observatories. In Section 4, we present
the results of the multifrequency data and their connection with
the γ -ray activity. In Section 5, we report our conclusions about
the MW data, and we use a phenomenological analysis to esti-
mate some of the physical fundamental parameters, such as the
BH mass, the accretion disk bolometric luminosity, the shape
of the electron distribution, and the beaming factor. We then
model the observed SEDs and comment on the jet energetics.
Furthermore, we compare PKS 1510-089 with other powerful
FSRQs observed by Fermi. In Section 6, our final remarks are
reported.
In the following, we use a ΛCDM (concordance) cosmology
with values given within 1σ of the Wilkinson Microwave
Anisotropy Probe (WMAP) results (Komatsu et al. 2009),
namely, h = 0.71, Ω
m
= 0.27, and Ω
Λ
= 0.73, and a Hubble
constant value H
0
= 100 h km s
−1
Mpc
−1
, the corresponding
luminosity distance (d
L
)is 1.91 Gpc ( 5.9 × 10
27
cm).
2. FERMI-LAT DATA AND RESULTS
The LAT data presented here were collected from 2008 Au-
gust 4 to 2009 July 1. Only events with energies greater than
200 MeV were selected to minimize the systematic uncertain-
ties. To have the highest probability that collected events are
photons, the diffuse class selection was applied. A further se-
lection on the zenith angle >105
◦
was applied to avoid con-
tamination from limb gamma rays. The analysis was performed
using the Science Tools package
82
(v9r15p5). The instrument
response functions (IRFs) P6_V3_DIFFUSE were used. These
IRFs provide a correction for the pile-up effect. To produce light
curves and spectral analysis the standard tool gtlike was used.
The photons were extracted from a region of interest (ROI) cen-
tered on the source, within a radius of 7
◦
.Thegtlike model
includes the PKS 1510-089 point source component and all the
point sources form the first LAT catalog (Abdo et al. 2010a)
that fall within 12
◦
from the source. The model also includes
a background component of the Galactic diffuse emission and
an isotropic component, both of which are the standard models
available from the Fermi Science Support Center
83
(FSSC). The
isotropic component includes both contribution from the extra-
galactic diffuse emission and from the residual charged particle
backgrounds. The estimated systematic uncertainty of the flux
is 10% at 100 MeV, 5% at 500 MeV, and 20% at 10 GeV.
2.1. Temporal Behavior
We extracted light curves from the entire data set, to investi-
gate the flaring activity. To take into account possible biases or
systematics when the source flux is faint, we used two differ-
ent time binnings of 1 day and 1 week. The light curves were
extracted using gtlike, fitting the source spectrum by means
of a power-law (PL) distribution (dN/dE ∝ E
−α
γ
), where
α
γ
is the photon index, following the prescription given in the
previous section. The flux was evaluated by integrating the fit-
ted model above 0.2 GeV. The lower panel of Figure 1 clearly
82
http://fermi.gsfc.nasa.gov/ssc/data/analysis/documentation/Cicerone/
83
http://fermi.gsfc.nasa.gov/ssc/data/access/lat/BackgroundModels.html

Frequently asked questions

Q1. What are the contributions mentioned in the paper "Fermi large area telescope and multi-wavelength observations of the flaring activity of pks 1510-089 between 2008 september and 2009 june" ?

The authors report on the multi-wavelength observations of PKS 1510-089 ( a flat spectrum radio quasar ( FSRQ ) at z = 0. 361 ) during its high activity period between 2008 September and 2009 June. 

Q2. What could be the cause of the lags in the light curve?

temporal lags could be related to the internal source photon absorption, to the cooling time of the radiating particles, or to inhomogeneities in the emitting region. 

Q3. What is the UV peak in a quasar?

The UV peak, as in many quasars, is likely due to the BBB that usually is understood as thermal emission from the accretiondisk surrounding the BH. 

Q4. What is the best-fit parameter for the LP model?

Due to the nonderivable character of the BPL law, the authors used also the loglikelihood profile method to determine the best-fit parameter for this model. 

Q5. Why is the -ray luminosity smaller than other distant FSRQs?

Due to the low redshift of the source, the bolometric isotropic γ -ray luminosity is also smaller compared to other distant FSRQs observed by Fermi. 

Q6. How is the source size calculated without beaming effects?

without beaming effects, the source size estimated from the observed variability timescale (Rrad = cΔt/(1 + z)) makes the source opaque to the photon–photon pair production process, provided that γ -ray and X-ray photons are produced cospatially. 

Q7. How did the authors analyze the XRT data?

The authors analyzed XRT (Burrows et al. 2005; Gehrels et al. 2004) data using the xrtpipeline tool provided by the HEADAS v6.7 software package, for data observed in photon counting mode. 

Q8. What is the correlation coefficient of the UV and ray fluxes?

The correlation coefficient of the logarithms of the UV and γ -ray fluxes, obtained through the Monte Carlo method described in Section 2.2.1, is r = 0.2 with a 95% confidence interval of 0.05 r 0.34. 

Q9. What is the correlation coefficient of the optical and ray fluxes?

The correlation coefficient of the logarithm of the optical and γ -ray fluxes, evaluated through the Monte Carlo method described in Section 2.2.1, is r = 0.42 with a 95% confidence interval 0.36 r 0.46, higher than that found for the UV band. 

Q10. Why do the authors prefer to present light curves in terms of F?

The authors prefer to present light curves in terms of νF (ν) to make easier the comparison between the various bands and the SED changes. 

Q11. What is the way to compare the flux and photon index?

The plot of the flux in 0.3–10.0 keV range versus the photon index (see Figure 8) is compatible with a harder when brighter trend. 

Q12. How is the MW SED compared to the fast variability estimate?

In this regard, the authors note that since the authors are describing flare-averaged states, with integration times of the order of a few weeks, the discrepancy with the fast variability estimate is not problematic.