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    • Keywords


      Stars: neutron; pulsars: individual: EXO 2030?375; X-rays: stars.

    • Abstract


      We present the results obtained from timing and spectral studies of Be/X-ray binary pulsar EXO 2030$+$375 using observations with the Large Area Xenon Proportional Counters and Soft X-ray Telescope of AstroSat, at various phases of its Type-I outbursts in 2016, 2018, and 2020. The pulsar was faint during these observations as compared to earlier observations with other observatories. At the lowest luminosity of $2.5\times10^{35}$ erg s$^{-1}$ in 0.5–30 keV energy range, $\approx$41.3 s pulsations were clearly detected in the X-ray light curves. This finding establishes the first firm detection of pulsations in EXO 2030$+$375 at anextremely low mass accretion rate to date. The shape of the pulse profiles is complex due to the presence of several narrow dips. Though pulsations were detected up to $\sim$80 keV when the source was brighter, pulsations were limited up to $\sim$25 keV during the third AstroSat observation at lowest source luminosity. A search for quasi-periodic oscillations in $2\times 10^4$ Hz to 10 Hz yielded a negative result. Spectral analysis of the AstroSat data showed that the spectrum of the pulsar was steep with a power-law index of $\sim$2. Thevalues of photon-indices at observed low luminosities follow the known pattern in sub-critical regime of the pulsar.

    • Author Affiliations



      1. National Space Institute, Technical University of Denmark, Elektrovej 327-328, DK 2800 Lyngby, Denmark.
      2. Astronomy and Astrophysics Division, Physical Research Laboratory, Navrangpura, Ahmedabad 380 009, India.
      3. Department of Astronomy and Astrophysics, Tata Institute of Fundamental Research, Colaba, Mumbai 400 005, India.
      4. Indian Institute of Technology, Gandhinagar, Palaj 382 355, India.
      5. School of Physics and Technology, Wuhan University, Wuhan 430072, China.
    • Dates

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