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Title: NuSTAR J163433-4738.7: A fast X-ray transient in the galactic plane

During hard X-ray observations of the Norma spiral arm region by the Nuclear Spectroscopic Telescope Array (NuSTAR) in 2013 February, a new transient source, NuSTAR J163433-4738.7, was detected at a significance level of 8σ in the 3-10 keV bandpass. The source is consistent with having a constant NuSTAR count rate over a period of 40 ks and is also detected simultaneously by Swift at lower significance. The source is not significantly detected by NuSTAR, Swift, or Chandra in the days before or weeks after the discovery of the transient, indicating that the strong X-ray activity lasted between ∼0.5 and 1.5 days. Near-infrared imaging observations were carried out before and after the X-ray activity, but we are not able to identify the counterpart. The combined NuSTAR and Swift energy spectrum is consistent with a power law with a photon index of Γ=4.1{sub −1.0}{sup +1.5} (90% confidence errors), a blackbody with kT = 1.2 ± 0.3 keV, or a Bremsstrahlung model with kT=3.0{sub −1.2}{sup +2.1} keV. The reduced-χ{sup 2} values for the three models are not significantly different, ranging from 1.23 to 1.44 for 8 degrees of freedom. The spectrum is strongly absorbed with N{sub H}=(2.8{sub −1.4}{sup +2.3})×10{sup 23} cm{sup –2}, (9{submore » −7}{sup +15})×10{sup 22} cm{sup –2}, and (1.7{sub −0.9}{sup +1.7})×10{sup 23} cm{sup –2}, for the power-law, blackbody, and Bremsstrahlung models, respectively. Although the high column density could be due to material local to the source, it is consistent with absorption from interstellar material along the line of sight at a distance of 11 kpc, which would indicate an X-ray luminosity >10{sup 34} erg s{sup –1}. Although we do not reach a definitive determination of the nature of NuSTAR J163433-4738.7, we suggest that it may be an unusually bright active binary or a magnetar.« less
Authors:
; ; ; ; ;  [1] ; ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [7] ;  [8] ;  [9] ;  [10] ;  [11]
  1. Space Sciences Laboratory, 7 Gauss Way, University of California, Berkeley, CA 94720-7450 (United States)
  2. Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027 (United States)
  3. European Southern Observatory, Karl Schwarzschild-Strasse 2, D-85748 Garching bei München (Germany)
  4. Núcleo de Astronomía de la Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército 441, Santiago (Chile)
  5. Instituto de Astrofísica, Facultad de Física, Pontifica Universidad Católica de Chile, 306, Santiago 22 (Chile)
  6. DTU Space, National Space Institute, Technical University of Denmark, Elektrovej 327, DK-2800 Lyngby (Denmark)
  7. Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 (United States)
  8. Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States)
  9. Istituto Nazionale di Astrofisica, INAF-IAPS, via del Fosso del Cavaliere, I-00133 Roma (Italy)
  10. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)
  11. NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
Publication Date:
OSTI Identifier:
22357210
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 785; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; BINARY STARS; BREMSSTRAHLUNG; COUNTING RATES; DEGREES OF FREEDOM; DENSITY; DISTANCE; ENERGY SPECTRA; ERRORS; GALAXIES; HARD X RADIATION; KEV RANGE; LUMINOSITY; NEUTRON STARS; PHOTONS; STARS; TELESCOPES; TRANSIENTS