Letter to the Editor

First INTEGRAL observations of GRS 1915+105^*

¹ Observatory, PO Box 14, 00014, University of Helsinki, Finland
² INTEGRAL Science Data Center, Chemin d'Écogia 16, 1290 Versoix, Switzerland
³ Centre d'Études de Saclay, DAPNIA/Service d'Astrophysique (CNRS FRE 2591), Bât. 709, Orme des Merisiers, 91191 Gif-sur-Yvette Cedex, France
⁴ Danish Space Research Institute, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
⁵ INAF - Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate (LC), Italy
⁶ Instituto de Astrofísica de Andalucía (IAA-CSIC), PO Box 03004, 18080 Granada, Spain
⁷ Dept. of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, UK
⁸ Astronomical Institute, “Anton Pannekoek”, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
⁹ Istituto Astrofisica Spaziale e Fisica Cosmica, Sezione di Roma, CNR, via Fosso del Cavaliere, 00133 Roma, Italy
¹⁰ School of Physics, University of Sydney, NSW 2006, Australia
¹¹ Theoretical Astrophysics Group, University of Leicester, Leicester LE1 7RH, UK
¹² Astrophysics Group, Cavendish Laboratory, University of Cambridge, Madingley Road, Cambridge CB3 0HE, UK
¹³ Astronomy Division, PO Box 3000, 90014 University of Oulu, Finland
¹⁴ MSSL, University College London, Holmbury St. Mary, Surrey RH5 6NT, UK
¹⁵ Nicolaus Copernicus Astronomical Center, Bartycka 18, 00-716 Warszawa, Poland

Corresponding author: D. Hannikainen, diana@astro.helsinki.fi

Received: 7 July 2003
Accepted: 16 September 2003

Abstract

We present data from the first of six monitoring Open Time observations of GRS 1915+105 undertaken with the orbiting INTEGRAL satellite. The source was clearly detected with all three X-ray and gamma-ray instruments on board. GRS 1915+105 was in a highly variable state, as demonstrated by the JEM X-2 and ISGRI lightcurves. These and simultaneous RXTE/PCA lightcurves point to a novel type of variability pattern in the source. In addition, we fit the combined JEM X-2 and ISGRI spectrum between 3–300 keV with a disk blackbody + powerlaw model leading to typical parameter values found earlier at similar luminosity levels. A new transient, IGR J19140+098, was discovered during the present observation.