THE FAINT "HEARTBEATS" OF IGR J17091−3624: AN EXCEPTIONAL BLACK HOLE CANDIDATE

• Main Authors: Altamirano, D. (Author), Belloni, Tomaso M. (Author), Linares, Manuel Alegret (Contributor), van der Klis, M. (Author), Wijnands, R. (Author), Curran, P. A. (Author), Kalamkar, M. (Author), Stiele, H. (Author), Motta, S. (Author), Munoz-Darias, T. (Author), Casella, P. (Author), Krimm, H. A. (Author)
• Other Authors: MIT Kavli Institute for Astrophysics and Space Research (Contributor)
• Format: Article
• Language: English
• Published: Institute of Physics/American Astronomical Society, 2015-02-27T17:06:38Z.
• Subjects: Article
• Online Access: Get fulltext

We report on the first 180 days of Rossi X-Ray Timing Explorer observations of the outburst of the black hole candidate IGR J17091-3624. This source exhibits a broad variety of complex light curve patterns including periods of strong flares alternating with quiet intervals. Similar patterns in the X-ray light curves have been seen in the (up to now) unique black hole system GRS 1915+105. In the context of the variability classes defined by Belloni et al. for GRS 1915+105, we find that IGR J17091-3624 shows the ν, ρ, α, λ, β, and μ classes as well as quiet periods which resemble the χ class, all occurring at 2-60 keV count rate levels which can be 10-50 times lower than observed in GRS 1915+105. The so-called ρ class "heartbeats" occur as fast as every few seconds and as slow as ~100 s, tracing a loop in the hardness-intensity diagram which resembles that previously seen in GRS 1915+105. However, while GRS 1915+105 traverses this loop clockwise, IGR J17091-3624 does so in the opposite sense. We briefly discuss our findings in the context of the models proposed for GRS 1915+105 and find that either all models requiring near Eddington luminosities for GRS 1915+105-like variability fail, or IGR J17091-3624 lies at a distance well in excess of 20 kpc, or it harbors one of the least massive black holes known (<3 M ☉).
Netherlands Organization for Scientific Research (NWO Rubicon fellowship)
European Union (European Community's Seventh Framework Programme (FP7/2007-2013) grant agreement number ITN 215212 "Black Hole Universe")
Spain. Ministerio de Educación y Ciencia (Spanish MEC, Consolider-Ingenio 2010 Programme grant CSD2006- 00070: "First Science with the GTC")