INTEGRAL and XMM-Newton observations towards the unidentified MeV source GRO J1411-64

¹ Institut de Ciències de l'Espai (IEEC/CSIC), Campus UAB, Facultat de Ciències, Torre C5-parell, 2 planta, 08193 Barcelona, Spain e-mail: dtorres@ieec.uab.es
² Laboratory for Particle Astrophysics, Institute of High Energy Physics, Beijing 100049, China
³ W. W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305, USA
⁴ Instituto de Física de Cantabria (CSIC-UC), 39005 Santander, Spain
⁵ Universitat de Barcelona, Av. Diagonal 647, 08028 Barcelona, Spain
⁶ Instituto Argentino de Radioastronomia, CC5, 1894 Villa Elisa, Argentina
⁷ Max-Planck-Institut für extraterrestrische Physik, PO Box 1603, 85740 Garching, Germany
⁸ Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA

Received: 3 April 2006
Accepted: 16 June 2006

Abstract

Aims.We investigate the nature of the COMPTEL unidentified source GRO J1411-64.

Methods.The source was observed by INTEGRAL. Its central part was also observed by XMM-Newton.

Results.The data analysis shows no hint for new detections at hard X-rays. The upper limits in flux herein presented constrain the energy spectrum of whatever was producing GRO J1411-64, imposing, in the framework of earlier COMPTEL observations, the existence of a peak in power output located somewhere between 300–700 keV for the so-called low state. The Circinus Galaxy is the only source detected within the 4σ location error of GRO J1411-64, but can be safely excluded as the possible counterpart: the extrapolation of the energy spectrum is well below the one for GRO J1411-64 at MeV energies. 22 reliable and statistically significant sources (likelihood ) were extracted and analyzed from XMM-Newton data. Only one of these sources, XMMU J141255.6-635932, is spectrally compatible with GRO J1411-64 although the fact the soft X-ray observations do not cover the full extent of the COMPTEL source position uncertainty make an association hard to quantify and thus risky.

Conclusions.The unique peak of the power output at high energies (hard X-rays and gamma-rays) resembles that found in the SED seen in blazars or microquasars, and might suggest that a similar scenario is at work. However, an analysis using a microquasar model consisting on a magnetized conical jet filled with relativistic electrons which radiate through synchrotron and inverse Compton scattering with star, disk, corona and synchrotron photons shows that it is hard to comply with all observational constrains. This fact and the non-detection at hard X-rays introduce an a-posteriori question mark upon the physical reality of this source, which is discussed in some detail.