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Title: SAX J1808.4$-$3658, an accreting millisecond pulsar shining in gamma rays?

We report the detection of a possible gamma-ray counterpart of the accreting millisec- ond pulsar SAXJ1808.4–3658. The analysis of ~6 years of data from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope (Fermi-LAT) within a re- gion of 15° radius around the position of the pulsar reveals a point gamma-ray source detected at a significance of ~6σ (Test Statistic TS = 32), with position compatible with that of SAXJ1808.4–3658 within 95% Confidence Level. The energy flux in the energy range between 0.6 GeV and 10 GeV amounts to (2.1 ± 0.5) × 10 -12 erg cm -2 s -1 and the spectrum is well-represented by a power-law function with photon index 2.1±0.1. We searched for significant variation of the flux at the spin frequency of the pulsar and for orbital modulation, taking into account the trials due to the uncertain- ties in the position, the orbital motion of the pulsar and the intrinsic evolution of the pulsar spin. No significant deviation from a constant flux at any time scale was found, preventing a firm identification via time variability. Nonetheless, the association of the LAT source as the gamma-ray counterpart of SAXJ1808.4–3658 would match the emission expected frommore » the millisecond pulsar, if it switches on as a rotation-powered source during X-ray quiescence.« less
 [1] ;  [1] ;  [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [5] ;  [4] ;  [4]
  1. Consejo Superior de Investigaciones Cientificas (CSIC), Barcelona (Spain)
  2. Consejo Superior de Investigaciones Cientificas (CSIC), Barcelona (Spain); Univ. of Amsterdam (Netherlands)
  3. Consejo Superior de Investigaciones Cientificas (CSIC), Barcelona (Spain); Univ. Autonoma de Barcelona (Spain). Inst. Catalana de Recerca i Estudis Avancats (ICREA)
  4. Univ. degli Studi di Cagliari (Italy)
  5. Univ. of Palermo (Italy)
Publication Date:
Grant/Contract Number:
Accepted Manuscript
Journal Name:
Monthly Notices of the Royal Astronomical Society
Additional Journal Information:
Journal Volume: 456; Journal Issue: 3; Journal ID: ISSN 0035-8711
Royal Astronomical Society
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
Country of Publication:
United States
OSTI Identifier: