Multi-wavelength observations of IGR J17544-2619 from quiescence to outburst

¹ ISDC Data Centre for Astrophysics, Chemin d’Ecogia 16, 1290 Versoix, Switzerland
e-mail: enrico.bozzo@unige.ch
² Inter-University Center for Astronomy and Astrophysics, Post Bag 4, Ganeshkhind, 411007 Pune, India
³ St. Josephs College, Singamari, 734104 Darjeeling, West Bengal, India
⁴ North Bengal University, Raja Rammohanpur, 734013 District Darjeeling, West Bengal, India
⁵ Space Sciences Laboratory, 7 Gauss Way, University of California, Berkeley, CA 94720-7450, USA
⁶ INAF, Istituto di Astrofisica Spaziale e Fisica Cosmica – Palermo, via U. La Malfa 153, 90146 Palermo, Italy
⁷ Laboratoire AIM, UMR 7158, CEA/DRF/Irfu/SAp-CNRS-Université Paris Diderot, Centre de Saclay, L’Orme des Merisiers, Bât. 709, 91191 Gif-sur-Yvette Cedex, France
⁸ Institut Universitaire de France, 103 boulevard Saint-Michel, 75005 Paris, France
⁹ Institut für Physik und Astronomie, Universität Potsdam, Karl-Liebknecht-Str. 24/25, 14476 Potsdam, Germany
¹⁰ Centrum Astronomiczne im. M. Kopernika, Bartycka 18, 00-716 Warszawa, Poland
¹¹ International Space Science Institute (ISSI), Hallerstrasse 6, 3012 Bern, Switzerland
¹² International Space Science Institute in Beijing, No. 1 Nan Er Tiao, Zhong Guan Cun, Beijing 100190, PR China
¹³ INAF – Osservatorio Astronomico di Brera, via Emilio Bianchi 46, 23807 Merate (LC), Italy
¹⁴ INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00044 Rome, Italy
¹⁵ Ruhr-Universität Bochum, 44780 Bochum, Germany
¹⁶ Instituto de Astronomía, Universidad Católica del Norte, Avenida Angamos 0610, Antofagasta, Chile

Received: 14 July 2016
Accepted: 9 October 2016

Abstract

In this paper we report on a long multi-wavelength observational campaign of the supergiant fast X-ray transient prototype IGR J17544-2619. A 150 ks-long observation was carried out simultaneously with XMM-Newton and NuSTAR, catching the source in an initial faint X-ray state and then undergoing a bright X-ray outburst lasting approximately 7 ks. We studied the spectral variability during outburst and quiescence by using a thermal and bulk Comptonization model that is typically adopted to describe the X-ray spectral energy distribution of young pulsars in high mass X-ray binaries. Although the statistics of the collected X-ray data were relatively high, we could neither confirm the presence of a cyclotron line in the broad-band spectrum of the source (0.5−40 keV), nor detect any of the previously reported tentative detections of the source spin period. The monitoring carried out with Swift /XRT during the same orbit of the system observed by XMM-Newton and NuSTAR revealed that the source remained in a low emission state for most of the time, in agreement with the known property of all supergiant fast X-ray transients being significantly sub-luminous compared to other supergiant X-ray binaries. Optical and infrared observations were carried out for a total of a few thousand seconds during the quiescence state of the source detected by XMM-Newton and NuSTAR. The measured optical and infrared magnitudes were slightly lower than previous values reported in the literature, but compatible with the known micro-variability of supergiant stars. UV observations obtained with the UVOT telescope on-board Swift did not reveal significant changes in the magnitude of the source in this energy domain compared to previously reported values.