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Issue A&A
Volume 450, Number 1, April IV 2006
Page(s) 77 - 81
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20064804

A&A 450, 77-81 (2006)
DOI: 10.1051/0004-6361:20064804

A short hard X-ray flare from the blazar NRAO 530 observed by INTEGRAL

L. Foschini1, E. Pian2, L. Maraschi3, C. M. Raiteri4, F. Tavecchio3, G. Ghisellini3, G. Tosti5, G. Malaguti1 and G. Di Cocco1

1  INAF/IASF-Bologna, via Gobetti 101, 40129 Bologna, Italy
    e-mail: foschini@iasfbo.inaf.it
2  INAF, Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, 34131, Trieste, Italy
3  INAF, Osservatorio Astronomico di Brera, via Bianchi 46, 23807, Merate, Italy
4  INAF, Osservatorio Astronomico di Torino, via Osservatorio 20, 10025, Pino Torinese, Italy
5  Osservatorio Astronomico, Università di Perugia, via B. Bonfigli, 06126 Perugia, Italy

(Received 22 November 2005 / Accepted 5 January 2006 )

Abstract
We report about a short flare from the blazar NRAO 530 occurred on 17 February 2004 and detected serendipitously by the IBIS/ISGRI detector on board INTEGRAL. In the 20-40 keV energy range, the source, that is otherwise below the detection limit, is detected at a level of $\approx$2 $\times$ 10-10 erg cm-2 s-1 during a time interval of less than 2000 s, which is about a factor 2 above the detection threshold. At other wavelengths, only nearly-simultaneous radio data are available (1 observation at 2 cm on 11 February 2004), indicating a moderate increase of the polarization. This appears to be the shortest time variability episode ever detected in a high luminosity blazar at hard X-rays, unless the blazar is contaminated by the presence of an unknown unresolved rapidly varying source.


Key words: galaxies: quasars: general -- galaxies: quasars: individual: NRAO 530 -- X-rays: galaxies

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© ESO 2006


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