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

Creators: Bozzo, E.; Bhalerao, V.; Pradhan, P.; Tomsick, J.; Romano, P.; Ferrigno, C.; Chaty, S.; Oskinova, L.; Manousakis, A.; Walter, R.; Falanga, M.; Campana, S.; Stella, L.; Ramolla, M.; Chini, R.

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.

Additional Information

© 2016 ESO. Article published by EDP Sciences. Received 14 July 2016; Accepted 9 October 2016; Published online 22 November 2016. We warmly thank the XMM-Newton and NuSTAR teams for their efforts in scheduling the simultaneous observations of IGR J17544-2619. This work was supported under NASA Contract No. NNG08FD60C, and made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA). We also made use of observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. This publication was motivated by a team meeting sponsored by the International Space Science Institute in Bern, Switzerland. E.B., L.O., and A.M. thank ISSI for their financial support during their stay in Bern. V.B. and J.A.T. thank Brian Grefenstette and Kristin Madsen for help with planning the NuSTAR observations and Lorenzo Natalucci and David Smith for useful discussions. P.R. acknowledges contract ASI-INAF I/004/11/0 and financial contribution from the agreement ASI-INAF I/037/12/0. A.M. acknowledges support from the Polish NCN grant 2013/08/A/ST9/00795. S.C. is grateful to the Centre National d'Études Spatiales (CNES) for the funding of MINE (Multi-wavelength INTEGRAL Network). We thank the anonymous referee for detailed and useful referee report that helped improve the paper.

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