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Title: | First INTEGRAL Observations of V404 Cygni during the 2015 Outburst: Spectral Behavior in the 20-650 keV Energy Range | Authors: | Roques, Jean-Pierre Jourdain, Elisabeth BAZZANO, ANGELA FIOCCHI, MARIATERESA NATALUCCI, LORENZO UBERTINI, PIETRO |
Issue Date: | 2015 | Journal: | THE ASTROPHYSICAL JOURNAL LETTERS | Number: | 813 | Issue: | 1 | First Page: | L22 | Abstract: | In 2015 June, the source V404 Cygni (= GS2023+38) underwent an extraordinary outburst. We present the results obtained during the first revolution dedicated to this target by the INTEGRAL mission and focus on the spectral behavior in the hard X-ray domain, using both SPI and IBIS instruments. The source exhibits extreme variability and reaches fluxes of several tens of Crab. However, the emission between 20 and 650 keV can be understood in terms of two main components, varying on all the observable timescales, similar to what is observed in the persistent black hole system Cyg X-1. The low-energy component (up to ∼200 keV) presents a rather unusual shape, probably due to the intrinsic source variability. Nonetheless, a satisfactory description is obtained with a Comptonization model, if an unusually hot population of seed photons (kT<SUB>0</SUB> ∼ 7 keV) is introduced. Above this first component, a clear excess extending up to 400-600 keV leads us to investigate a scenario where an additional (cutoff) power law could correspond to the contribution of the jet synchrotron emission, as proposed in Cyg X-1. A search for an annihilation feature did not provide any firm detection, with an upper limit of 2 × 10<SUP>-4</SUP> ph cm<SUP>-2</SUP> s<SUP>-1</SUP> (2σ) for a narrow line centered at 511 keV, on the averaged obtained spectrum. <P />Based on observations with INTEGRAL, an ESA project with instruments and science data center funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Spain, and Switzerland), Czech Republic, and Poland with the participation of Russia and USA. | Acknowledgments: | The INTEGRAL SPI project has been completed under the responsibility and leadership of CNES. The Italian co-authors acknowledge the Italian Space Agency (ASI) for financial support under ASI/INAF agreement No. 2013-025-R.0. We are grateful to ASI, CEA, CNES, DLR, ESA, INTA, NASA, and OSTC for support. Note: Results on the two next revolutions are reported in Rodriguez et al. ( 2015 ), with a different spectral description. All the SPI spectra presented in our paper are made available in a fits format on the site given in footnote 2 in order to allow anybody to test different models. | URI: | http://hdl.handle.net/20.500.12386/30916 | URL: | https://iopscience.iop.org/article/10.1088/2041-8205/813/1/L22 | ISSN: | 2041-8205 | DOI: | 10.1088/2041-8205/813/1/L22 | Bibcode ADS: | 2015ApJ...813L..22R | Fulltext: | open |
Appears in Collections: | 1.01 Articoli in rivista |
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File | Description | Size | Format | |
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1510.03197.pdf | preprint | 462.91 kB | Adobe PDF | View/Open |
Roques_2015_ApJL_813_L22.pdf | Pdf editoriale | 164.62 kB | Adobe PDF | View/Open |
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