ROXA J081009.9+384757.0: a erg s blazar with hard X-ray synchrotron peak or a new type of radio loud AGN?

¹ ASI Science Data Center, ESRIN, 00044 Frascati, Italy e-mail: paolo.giommi@asi.it
² Dipartimento di Fisica, Università “La Sapienza”, P.le A. Moro 2, 00185 Roma, Italy
³ European Southern Observatory, Karl Schwarzschild-Str. 2, Garching bei München, Germany
⁴ Università degli studi di Roma, Tor Vergata, Dip. Fisica, via della ricerca scientifica 1, 00133 Roma, Italy
⁵ Dipartimento di Fisica, Universitá di Perugia, via A. Pascoli, Perugia, Italy
⁶ INAF - Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio, Italy
⁷ INAF - Osservatorio Astronomico di Brera, via Bianchi 46, 23807 Merate, Italy
⁸ Department of Astronomy and Astrophysics, Pennsylvania State University, USA
⁹ NASA/Goddard Space Flight Center, Greenbelt, Maryland 20771, USA

Received: 14 October 2006
Accepted: 13 March 2007

Abstract

We report the discovery of ROXA J081009.9+384757.0 = SDSS J081009.9+384757.0, a  blazar with a highly unusual Spectral Energy Distribution. This object was first noticed as a probable high , high-luminosity blazar within the error region of a ≈10^-12 erg cm^-2 s^-1 ROSAT source which, however, also included a much brighter late-type star. We describe the results of a recent Swift observation that establishes beyond doubt that the correct counterpart of the X-ray source is the flat spectrum radio quasar. With a luminosity well in excess of 10⁴⁷ erg s^-1 ROXA J081009.9+384757.0 is therefore one of the most luminous blazars known. We consider various possibilities for the nature of the electromagnetic emission from this source. In particular, we show that the SED is consistent with that of a blazar with synchrotron power peaking in the hard X-ray band. If this is indeed the case, the combination of high-luminosity and synchrotron peak in the hard-X-ray band contradicts the claimed anti-correlation between luminosity and position of the synchrotron peak usually referred to as the “blazar sequence”. An alternative possibility is that the X-rays are not due to synchrotron emission, in this case the very peculiar SED of ROXA J081009.9+384757.0 would make it the first example of a new class of radio loud AGN.