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The Ultraluminous X-Ray Sources Population of the Galaxy NGC 7456

Pintore, F. and Marelli, M. and Salvaterra, R. and Israel, G. L. and Rodríguez Castillo, G. A. and Esposito, P. and Belfiore, A. and De Luca, A. and Wolter, A. and Mereghetti, S. and Stella, L. and Rigoselli, M. and Earnshaw, H. P. and Pinto, C. and Roberts, T. P. and Walton, D. J. and Bernardini, F. and Haberl, F. and Salvaggio, C. and Tiengo, A. and Zampieri, L. and Bachetti, M. and Brightman, M. and Casella, P. and D’Agostino, D. and Dall’Osso, S. and Fürst, F. and Harrison, F. A. and Mapelli, M. and Papitto, A. and Middleton, M. (2020) The Ultraluminous X-Ray Sources Population of the Galaxy NGC 7456. Astrophysical Journal, 890 (2). Art. No. 166. ISSN 1538-4357.

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Ultraluminous X-ray sources (ULXs) are a class of accreting compact objects with X-ray luminosities above 10³⁹ erg s⁻¹. The ULX population counts several hundred objects but only a fraction are well studied. Here we present a detailed analysis of all ULXs hosted in the galaxy NGC 7456. It was observed in X-rays only once in the past (in 2005) by XMM-Newton. but the observation was short and strongly affected by high background. In 2018, we obtained a new, deeper (~90 ks) XMM-Newton observation that allowed us to perform a detailed characterization of the ULXs hosted in the galaxy. ULX-1 and ULX-2, the two brightest objects (L_X ~ 6−10 × 10³⁹ erg s⁻¹), have spectra that can be described by a model with two thermal components, as often found in ULXs. ULX-1 also shows one order of magnitude in flux variability on short-term timescales (hundreds to thousands of kiloseconds). The other sources (ULX-3 and ULX-4) show flux changes of at least an order of magnitude, and these objects may be candidate transient ULXs, although longer X-ray monitoring or further studies are required to ascribe them to the ULX population. In addition, we found a previously undetected source that might be a new candidate ULX (labeled as ULX-5), with a luminosity of ~10³⁹ erg s⁻¹ and hard power-law spectral shape, whose nature is still unclear and for which a background active galactic nucleus cannot be excluded. We discuss the properties of all the ULXs in NGC 7456 within the framework of super-Eddington accretion onto stellar-mass compact objects. Although no pulsations were detected, we cannot exclude that the sources host neutron stars.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Marelli, M.0000-0002-8017-0338
Salvaterra, R.0000-0002-9393-8078
Israel, G. L.0000-0001-5480-6438
Esposito, P.0000-0003-4849-5092
Belfiore, A.0000-0002-2526-1309
Mereghetti, S.0000-0003-3259-7801
Stella, L.0000-0002-0018-1687
Earnshaw, H. P.0000-0001-5857-5622
Roberts, T. P.0000-0001-8252-6337
Walton, D. J.0000-0001-5819-3552
Bernardini, F.0000-0001-5326-2010
Haberl, F.0000-0002-0107-5237
Tiengo, A.0000-0002-6038-1090
Zampieri, L.0000-0002-6516-1329
Bachetti, M.0000-0002-4576-9337
Brightman, M.0000-0002-8147-2602
D’Agostino, D.0000-0003-2649-0071
Fürst, F.0000-0003-0388-0560
Harrison, F. A.0000-0003-2992-8024
Mapelli, M.0000-0001-8799-2548
Papitto, A.0000-0001-6289-7413
Middleton, M.0000-0002-8183-2970
Additional Information:© 2020 The American Astronomical Society. Received 2019 December 12; revised 2020 January 14; accepted 2020 January 20; published 2020 February 26. The scientific results reported in this article are based on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. L.S. acknowledges support from the research grant "iPeska" (P.I. Andrea Possenti) funded under the INAF national call Prin-SKA/CTA approved with the Presidential Decree 70/2016. G.R. acknowledges the support of high performance computing resources awarded by CINECA (MARCONI and GALILEO), under the ISCRA initiative and the INAF-CIENCA MoU; and also the computing centers of INAF—Osservatorio Astronomico di Trieste and Osservatorio Astrofisico di Catania, under the coordination of the CHIPP project, for the availability of computing resources and support. C.P. is supported by ESA Research Fellowships. D.J.W. and M.M. acknowledges support from STFC in the form of an Ernest Rutherford Fellowship. H.P.E. acknowledges support under NASA contract NNG08FD60C. F.B. is funded by the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska Curie grant agreement No. 664931. This research was supported by high performance computing resources at New York University Abu Dhabi. H.P.E. acknowledges support under NASA contract NNG08FD60C. T.P.R. acknowledges support from STFC as part of the consolidated grant ST/K000861/1. A.P. acknowledges financial support from the Italian Space Agency and National Institute for Astrophysics, ASI/INAF, under agreements ASI–INAF I/037/12/0 and ASI–INAF n.2017-14-H.0. We acknowledge funding in the framework of the project ULTraS ASI–INAF contract No. 2017-14-H.0, and project ASI–INAF contract I/037/12/0.
Group:Space Radiation Laboratory, Astronomy Department
Funding AgencyGrant Number
Istituto Nazionale di Astrofisica (INAF)UNSPECIFIED
European Space Agency (ESA)UNSPECIFIED
Science and Technology Facilities Council (STFC)ST/K000861/1
Marie Curie Fellowship664931
Agenzia Spaziale Italiana (ASI)I/037/12/0
Agenzia Spaziale Italiana (ASI)2017-14-H.0
Subject Keywords:X-ray astronomy; X-ray binary stars; X-ray sources; Neutron stars; Pulsars
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: X-ray astronomy (1810); X-ray binary stars (1811); X-ray sources (1822); Neutron stars (1108); Pulsars (1306)
Record Number:CaltechAUTHORS:20200226-134844778
Persistent URL:
Official Citation:F. Pintore et al 2020 ApJ 890 166
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:101591
Deposited By: Tony Diaz
Deposited On:26 Feb 2020 21:59
Last Modified:04 Jun 2020 20:09

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