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Astron. Astrophys. 348, 63-70 (1999)


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The blazar PKS 0528+134: new results from Beppo SAX observations

G. Ghisellini 1, L. Costamante 1,2, G. Tagliaferri 1, L. Maraschi 3, A. Celotti 4, G. Fossati 5, E. Pian 6, A. Comastri 7, G. De Francesco 8, L. Lanteri 8, C.M. Raiteri 8, G. Sobrito 8, M. Villata 8, I.S. Glass 9, P. Grandi 10, C. Perola 11 and A. Treves 12

1 Osservatorio Astronomico di Brera, V. Bianchi 46, I-23807 Merate, Italy
2 Univ. di Milano, V. Celoria 16, I-20100 Milano, Italy
3 Osservatorio Astronomico di Brera, V. Brera 28, I-20100 Milano, Italy
4 S.I.S.S.A., V. Beirut 2-4, I-34014 Trieste, Italy
5 CASS/UCSD, La Jolla, CA 92093-0424, USA
6 TESRE, Bologna, Italy
7 Osservatorio Astronomico di Bologna, V. Zamboni 33, I-40126 Bologna, Italy
8 Osservatorio Astronomico di Torino, Strada Osservatorio 20, I-10025 Pino Torinese, Italy
9 South African Astron. Observ.
10 IAS/CNR, Frascati, Roma, Italy
11 University of Rome III, Italy
12 University of Como, Como, Italy

Received 15 December 1998 / Accepted 4 June 1999

Abstract

Beppo SAX observed 8 times the [FORMULA]-ray bright blazar PKS 0528+134 in Feb. and Mar. 1997, during a multiwavelength campaign involving EGRET, onboard CGRO, and ground based telescopes. The source was in its faintest X-ray state observed so far, with an unabsorbed [2-10] keV flux of [FORMULA] erg cm- 2 s-1. The spectrum can be fitted with a power law, with energy index [FORMULA] between 0.1 and 10 keV. The high energy instrument PDS detected a flux in the 15-100 keV band which appears disconnected from the lower X-ray energies, most likely due to a contaminating source. We consider our findings in the context of the overall spectral energy distribution and discuss their implications for synchrotron and inverse Compton models.

Key words: galaxies: BL Lacertae objects: general – galaxies: BL Lacertae objects: individual: PKS 0528+134 – X-rays: general

Send offprint requests to: G. Ghisellini

© European Southern Observatory (ESO) 1999

Online publication: July 16, 1999

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