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AGILE detection of intense gamma-ray activity from the blazar PKS 0537-441 in October 2008

Authors :
Marco Feroci
Luigi Pacciani
F. Boffelli
G. De Paris
E. Vallazza
Martino Marisaldi
Claudio Labanti
C. Pittori
T. Froysland
Domenico Impiombato
Ennio Morelli
A. Zambra
A. Morselli
F. Longo
A. Treves
Fulvio Gianotti
A. W. Chen
P. Caraveo
M. Fiorini
L. Salotti
G. Di Cocco
Francesco Lazzarotto
F. Perotti
E. Del Monte
G. Pucella
M. Perri
Filippo D'Ammando
G. Barbiellini
V. Vittorini
M. Prest
P. Santolamazza
M. Galli
G. Piano
F. Verrecchia
Marco Tavani
P. Giommi
P. W. Cattaneo
A. Argan
I. Donnarumma
Y. Evangelista
Andrea Bulgarelli
A. Pellizzoni
Sandro Mereghetti
Enrico Costa
Maura Pilia
Elena Pian
E. Striani
Alessio Trois
P. Picozza
I. Lapshov
S. Colafrancesco
M. Trifoglio
S. Sabatini
A. Giuliani
D. Zanello
Hans A. Krimm
Massimo Rapisarda
L. A. Antonelli
V. Cocco
A. Rappoldi
Paolo Lipari
F. Fuschino
D. Fugazza
Paolo Soffitta
P. Romano
S. Vercellone
Pucella G
DAmmando F
Romano P
Treves A
Pian E
Vercellone S
Vittorini V
Piano G
Impiombato D
Fugazza D
Verrecchia F
Krimm HA
Donnarumma I
Tavani M
Bulgarelli A
Chen AW
Giuliani A
Longo F
Pacciani L
Argan A
Barbiellini G
Boffelli F
Caraveo P
Cattaneo PW
Cocco V
Costa E
Del Monte E
De Paris G
Di Cocco G
Evangelista Y
Feroci M
Fiorini M
Froysland T
Fuschino F
Galli M
Gianotti F
Labanti C
Lapshov I
Lazzarotto F
Lipari P
Marisaldi M
Mereghetti S
Morelli E
Morselli A
Pellizzoni A
Perotti F
Picozza P
Pilia M
Prest M
Rapisarda M
Rappoldi A
Sabatini S
Soffitta P
Striani E
Trifoglio M
Trois A
Vallazza E
Zambra A
Zanello D
Perri M
Pittori C
Santolamazza P
Giommi P
Antonelli LA
Colafrancesco S
Salotti L
G., Pucella
F., D'Ammando
P., Romano
A., Treve
E., Pian
S., Vercellone
V., Vittorini
G., Piano
D., Impiombato
D., Fugazza
F., Verrecchia
H. A., Krimm
I., Donnarumma
M., Tavani
A., Bulgarelli
A. W., Chen
A., Giuliani
Longo, Francesco
L., Pacciani
A., Argan
G., Barbiellini
F., Boffelli
P., Caraveo
P. W., Cattaneo
V., Cocco
E., Costa
E. D., Monte
G. D., Pari
G. D., Cocco
Y., Evangelista
M., Feroci
M., Fiorini
T., Froysland
F., Fuschino
M., Galli
F., Gianotti
C., Labanti
I., Lapshov
F., Lazzarotto
P., Lipari
M., Marisaldi
S., Mereghetti
E., Morelli
A., Morselli
A., Pellizzoni
F., Perotti
P., Picozza
M., Pilia
M., Prest
M., Rapisarda
A., Rappoldi
S., Sabatini
P., Soffitta
E., Striani
M., Trifoglio
A., Troi
E., Vallazza
A., Zambra
D., Zanello
M., Perri
C., Pittori
P., Santolamazza
P., Giommi
L. A., Antonelli
S., Colafrancesco
L., Salotti
Publication Year :
2010

Abstract

Context. We report the detection by the AGILE satellite of intense gamma-ray activity from the source 1AGL J0538-4424, associated with the low-energy-peaked BL Lac PKS 0537-441, during a target of opportunity (ToO) observation performed on 2008 October 10-17, triggered by a Fermi-LAT alert, together with REM and Swift observations. Aims. The quasi-simultaneous near-infrared, optical, UV, X-ray, and gamma-ray coverage allowed us to investigate the behaviour of the source in different energy bands and study the spectral energy distribution and a theoretical model that can describe the gamma-ray state observed in mid-October. Methods. AGILE observed the source with its two co-aligned imagers: the Gamma-Ray Imaging Detector (GRID) and the hard X-ray imager (SuperAGILE), sensitive in the 30 MeV-30 GeV and 18-60 keV ranges, respectively. During the AGILE observation, the source was monitored simultaneously in the UV and X-ray bands by the Swift satellite through 6 ToO observations carried out between 2008 October 8 and 17. Moreover, the source was observed in the near-infrared and optical bands by the REM telescope on 2008 October 7, 8, and 9. Results. During 2008 October 10-17, AGILE-GRID detected gamma-ray emission from PKS 0537-441 at a significance level of 5.3-sigma with an average flux of (42 +/- 11) x 10(-8) photons cm(-2) s(-1) for energies higher than 100 MeV. A significant increase in the gamma-ray activity was detected between the first and the second halves of the observing period. REM and Swift/XRT detected the source in near-infrared/optical and X-rays during a relatively low and intermediate activity state, respectively, with no signs of evident variability in the different observations. However, Swift/UVOT detected an increase between the first and the second parts of the observing period, smaller than in the gamma-rays. Conclusions. The average gamma-ray flux of PKS 0537-441 detected by AGILE is close to the average flux observed for this source by the EGRET and Fermi-LAT instruments, with an increase of a factor 3 throughout the observation period up to a flux level slightly lower than the highest flux observed by Fermi-LAT during the first 11 months of operation. The spectral energy distribution of PKS 0537-441 in mid-October 2008 seems to require two synchrotron self-Compton components to be modelled, to account for both the near-infrared/optical bump and the X-ray data, together with the information on the gamma-ray flux level observed by AGILE. An alternative model based on the external Compton radiation, which requires an accretion disk with a relatively high luminosity, is also proposed.

Details

Database :
OpenAIRE
Accession number :
edsair.doi.dedup.....ad3a98b6f7a030f0e354e4c325a5970e