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Title: Discovery of the third transient X-ray binary in the galactic globular cluster Terzan 5

We report and study the outburst of a new transient X-ray binary (XRB) in Terzan 5, the third detected in this globular cluster, Swift J174805.3-244637 or Terzan 5 X-3. We find clear spectral hardening in Swift/XRT data during the outburst rise to the hard state, thanks to our early coverage (starting at L{sub X} ∼ 4 × 10{sup 34} erg s{sup –1}) of the outburst. This hardening appears to be due to the decline in relative strength of a soft thermal component from the surface of the neutron star (NS) during the rise. We identify a Type I X-ray burst in Swift/XRT data with a long (16 s) decay time, indicative of hydrogen burning on the surface of the NS. We use Swift/BAT, MAXI/GSC, Chandra/ACIS, and Swift/XRT data to study the spectral changes during the outburst, identifying a clear hard-to-soft state transition. We use a Chandra/ACIS observation during outburst to identify the transient's position. Seven archival Chandra/ACIS observations show evidence for variations in Terzan 5 X-3's nonthermal component but not the thermal component during quiescence. The inferred long-term time-averaged mass accretion rate, from the quiescent thermal luminosity, suggests that if this outburst is typical and only slow cooling processes aremore » active in the NS core, such outbursts should recur every ∼10 yr.« less
Authors:
; ; ;  [1] ; ;  [2] ;  [3] ;  [4] ;  [5] ;  [6]
  1. Department of Physics, University of Alberta, CCIS 4-183, Edmonton, AB T6G 2E1 (Canada)
  2. Astronomical Institute "Anton Pannekoek," University of Amsterdam, Science Park 904, 1098 XH Amsterdam (Netherlands)
  3. Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, 70 Vassar Street, Cambridge, MA 02139 (United States)
  4. Instituto de Astrofísica de Canarias, c/Vía Láctea s/n, E-38205 La Laguna, Tenerife (Spain)
  5. Department of Physics, Sam Houston State University, Huntsville, TX 77341 (United States)
  6. Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States)
Publication Date:
OSTI Identifier:
22348262
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 780; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BINARY STARS; GALAXY CLUSTERS; HARDENING; HYDROGEN BURNING; LUMINOSITY; MASS; NEUTRON STARS; NEUTRONS; SPECTRAL HARDENING; SURFACES; TRANSIENTS; VARIATIONS; X RADIATION