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Nustar and Xmm-Newton Observations of 1E1743.1-2843: Indications of a Neutron Star Lmxb Nature of the Compact Object

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Nustar and Xmm-Newton Observations of 1E1743.1-2843: Indications of a Neutron Star Lmxb Nature of the Compact Object NUSTAR AND XMM-NEWTON OBSERVATIONS OF 1E1743.1-2843: INDICATIONS OF A NEUTRON STAR LMXB NATURE OF THE COMPACT OBJECT The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. Citation Lotti, Simone; Natalucci, Lorenzo; Mori, Kaya; Baganoff, Frederick K.; Boggs, Steven E.; Christensen, Finn E. et al. "NUSTAR AND XMM-NEWTON OBSERVATIONS OF 1E1743.1-2843: INDICATIONS OF A NEUTRON STAR LMXB NATURE OF THE COMPACT OBJECT." Astrophysical Journal 882, no. 1 (May 2016): 57 © 2016 The American Astronomical Society. As Published http://dx.doi.org/10.3847/0004-637X/822/1/57 Publisher IOP Publishing Version Final published version Citable link http://hdl.handle.net/1721.1/109849 Terms of Use Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. The Astrophysical Journal, 822:57 (8pp), 2016 May 1 doi:10.3847/0004-637X/822/1/57 © 2016. The American Astronomical Society. All rights reserved. NUSTAR AND XMM-NEWTON OBSERVATIONS OF 1E1743.1-2843: INDICATIONS OF A NEUTRON STAR LMXB NATURE OF THE COMPACT OBJECT Simone Lotti1, Lorenzo Natalucci1, Kaya Mori2, Frederick K. Baganoff3, Steven E. Boggs4, Finn E. Christensen5, William W. Craig4,3, Charles J. Hailey3, Fiona A. Harrison6, Jaesub Hong7, Roman A. Krivonos4,8, Farid Rahoui9,10, Daniel Stern11, John A. Tomsick4, Shuo Zhang3, and William W. Zhang12 1 INAF-IAPS Roma, Via fosso del cavaliere 100, Rome I-00133, Italy; [email protected] 2 Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027, USA 3 MIT Kavli Institute for Astrophysics and Space Research, Cambridge, MA 02139, USA 4 Space Sciences Laboratory, 7 Gauss Way, University of California, Berkeley, CA 94720-7450, USA 5 DTU Space, National Space Institute, Elektrovej 327, DK-2800 Lyngby, Denmark 6 Cahill Center for Astronomy and Astrophysics, Caltech, Pasadena, CA 91125, USA 7 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA 8 Space Research Institute, Russian Academy of Sciences, Profsoyuznaya 84/32, 117997 Moscow, Russia 9 Department of Astronomy, Harvard University, 60 Garden Street, Cambridge, MA 02138, USA 10 European Southern Observatory, Karl Schwarzschild-Strasse 2, D-85748 Garching bei München, Germany 11 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA 12 NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA Received 2015 October 16; accepted 2016 March 4; published 2016 May 5 ABSTRACT We report on the results of NuSTAR and XMM-Newton observations of the persistent X-ray source 1E1743.1-2843, located in the Galactic Center region. The source was observed between 2012 September and October by NuSTAR and XMM-Newton, providing almost simultaneous observations in the hard and soft X-ray bands. The high X-ray luminosity points to the presence of an accreting compact object. We analyze the possibilities of this accreting compact object being either a neutron star (NS) or a black hole, and conclude that the joint XMM-Newton and NuSTAR spectrum from 0.3 to 40 keV fits a blackbody spectrum with kT ~ 1.8 keV emitted from a hot spot or an equatorial strip on an NS surface. This spectrum is thermally Comptonized by electrons with kTe ~ 4.6 keV. Accepting this NS hypothesis, we probe the low-mass X-ray binary (LMXB) or high-mass X-ray binary (HMXB) nature of the source. While the lack of Type-I bursts can be explained in the LMXB scenario, the absence of pulsations in the 2 mHz–49 Hz frequency range, the lack of eclipses and of an IR companion, and the lack of a Ka line from neutral or moderately ionized iron strongly disfavor interpreting this source as a HMXB. We therefore conclude that 1E1743.1-2843 is most likely an NS-LMXB located beyond the Galactic Center. There is weak statistical evidence for a soft X-ray excess which may indicate thermal emission from an accretion disk. However, 23- 2 the disk normalization remains unconstrained due to the high hydrogen column density (NH ~´1.6 10 cm ). Key words: accretion, accretion disks – stars: neutron – X-rays: binaries – X-rays: individual (1E1743.1-2843) 1. INTRODUCTION analysis, Porquet tested several single-component spectral models (i.e., absorbed power law, absorbed blackbody, The X-ray source 1E1743.1-2843 was discovered during the absorbed disk blackbody) but could not distinguish between first soft X-ray imaging observation of the Galactic Center, ( these models due to the narrow bandpass from 2 to 10 keV. In which was performed by the Einstein Observatory Watson ’ et al. 1981), and has been detected in all of the subsequent this regard, NuSTAR s ability to perform high-resolution, observations performed by X-ray satellites with imaging broadband spectroscopy allows us to probe more deeply the capabilities above 2 keV (Kawai et al. 1988; Sunyaev nature of the high-energy emission from this source. et al. 1991; Pavlinsky et al. 1994; Lu et al. 1996; Cremonesi The presence of an accreting object is required to explain the et al. 1999; Porquet et al. 2003; Muno et al. 2009; Bird et al. unabsorbed source luminosity, which is of the order of 36 2 -1 2010). Its position has been determined with Chandra to be L210keV- ~ 10d10 kpc erg s , where d10 kpc is the source hms distance expressed in units of 10 kpc, while the absence of aJ2000 = 17 46 21. 09, dJ2000 =-28 43¢ 42. 67 with a reported 0 21 1σ accuracy (Evans et al. 2010). Because of periodic oscillations and eclipses favors a scenario in which a 23- 2 compact object (either a neutron star (NS) or a black hole) its high column absorption (NH =´1.3 0.1 10 cm ; see Cremonesi et al. 1999), the source is likely in the Galactic accretes matter from a low-mass companion (LMXB systems). Center (d =7.9 0.3 kpc; McNamara et al. 2000) or LMXBs in this luminosity range which contain an NS are beyond, while the orbital inclination is smaller than 70° usually characterized by thermonuclear flashes of accreted (Cowley et al. 1983). The analysis performed by Porquet et al. matter that ignites on the NS surface (Type 1 X-ray bursts), but (2003) detected no pulsations or quasi-periodic oscillations in these bursts have never been observed for 1E1743.1-2843 in 20 the 2.4 mHz–2.5 Hz frequency range using EPIC-MOS and the years of X-ray observations. So far, this has led to the PN fullframe mode (time resolution 2.6 s and 200 ms, conclusion that (1) the accretion rate is high enough to allow respectively). However, since many X-Ray binaries present stable burning of the accreted material, which would imply an quasi-periodic variations above 2.5 Hz, the XMM-Newton data M˙ value comparable to the Eddington limit (Bildsten 2000), were not suitable to probe the millisecond pulsations that could and thus a distance greater than 8 kpc, (2) the bursts are indicate a low-mass X-ray binary (LMXB) nature. In their suppressed by the presence of intense magnetic fields (at least 1 The Astrophysical Journal, 822:57 (8pp), 2016 May 1 Lotti et al. Figure 1. Images from NuSTAR focal plane modules in the 3–79 keV energy band, FPMA (left) and FPMB (right); the target source is ~7¢ off-axis during the observation. FPMB is highly contaminated by stray light, and moreover the source is cut in half by two different stray light zones, and therefore only data from FPMA were used in the analysis. Table 1 NuSTAR and XMM-Newton observations of 1E1743.1-2843 Obs.Id Revolution Satellite Start (UTC) End (UTC) Exposure Time (s) 40010005001 K NuSTAR 2012 Oct 15 13:31:07 2012 Oct 16 05:41:07 25993 0694640401a 2332 XMM-Newton 2012 Sep 02 19:33:02 2012 Sep 03 11:20:55 24830 0694640501 2334 XMM-Newton 2012 Sep 05 21:16:14 2012 Sep 06 09:46:55 29581 0694641201 2344 XMM-Newton 2012 Sep 26 06:17:37 2012 Sep 26 17:24:59 35540 Note. a Data from obs. 0694640401 were not used in the analysis. 109 G), and (3) the accreting compact object is a black hole The observation was performed on 2012 October 15th, and the (Porquet et al. 2003; Del Santo et al. 2006). The presence of total exposure time was 26ks. The source was ~7¢ off-axis in strong magnetic fields (>1012 G), however, should be accom- the NuSTAR observation and appears distorted due to the panied by cyclotron absorption features and pulsations, neither asymmetric point-spread function (PSF) shape at a large off- of which have been observed in 1E1743.1-2843. The source axis angle (Madsen et al. 2015), as can be seen in Figure 1. showed marginal variability on month timescales in the NuSTAR is the first X-ray satellite with multilayer hard X-ray 20–40 keV range (Del Santo et al. 2006), some variability on optics and is operational in the energy range 3–79 keV ( – ) – hour timescales 10% 20% in the 1.3 10 keV energy range (Harrison et al. 2013). The mission carries two identical ( ) Cremonesi et al. 1999 , and less than 18% of variability telescopes with grazing incidence optics, each one focusing on −4 – between 10 and 2.5 Hz in the 2 10 keV energy range separate detector modules, Focal Plane Modules A and B (Porquet et al. 2003). (FPMA, FPMB), at a distance of 10m. These CdZnTe Here, we present the results of four observations of detectors have a total field of view (FOV) of 13¢´ 13¢ 1E1743.1-2843 performed with the NuSTAR and XMM-Newton – (Harrison et al.
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