Browsing by Author "Huppenkothen, D."

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    Identification of an X-Ray Pulsar in the BeXRB System IGR J18219-1347
    (IOP Publishing, 2022) O'Connor, B.; Göğüş, E.; Huppenkothen, D.; Kouveliotou, C.; Gorgone, N.; Townsend, L.J.; Calamida, A.; Fruchter, A.; Buckley, D.A.H.; Baring, M.G.; Kennea, J.A.; Younes, G.; Arzoumanian, Z.; Bellm, E.; Cenko, S.B.; Gendreau, K.; Granot, J.; Hailey, C.; Harrison, F.; Hartmann, D.; Kaper, L.; Kutyrev, A.; Slane, P.O.; Stern, D.; Troja, E.; Horst, A.J. van der; Wijers, R.A.M.J.; Woudt, P.
    We report on observations of the candidate Be/X-ray binary (BeXRB) IGR J18219−1347 with the Swift/X-ray Telescope, the Nuclear Spectroscopic Telescope ARray, and the Neutron Star Interior Composition Explorer during Type-I outbursts in 2020 March and June. Our timing analysis revealed the spin period of a neutron star with P spin = 52.46 s. This periodicity, combined with the known orbital period of 72.4 days, indicates that the system is a BeXRB. Furthermore, by comparing the spectral energy distribution of the infrared counterpart to that of known BeXRBs, we confirm this classification and set a distance of approximately 10–15 kpc for the source. The broadband X-ray spectrum (1.5–50 keV) of the source is described by an absorbed power law with a photon index Γ ∼ 0.5 and a cutoff energy at ∼13 keV.
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    Time resolved spectroscopy of SGR J1550−5418 bursts detected with Fermi/gamma-ray burst monitor
    (The American Astronomical Society, 2014) Younes, G.; Kouveliotou, C.; van der Horst, A.J.; Baring, M.G.; Granot, J.; Watts, A.L.; Bhat, P.N.; Collazzi, A.; Gehrels, N.; Gorgone, N.; Gogus, E.; Gruber, D.; Grunblatt, S.; Huppenkothen, D.; Kaneko, Y.; von Kienlin, A.; van der Klis, M.; Lin, L.; Mcenery, J.; van Putten, T.; Wijers, R.A.M.J.
    We report on a time-resolved spectroscopy of the 63 brightest bursts of SGR J1550–5418, detected with the Fermi/Gamma-ray Burst Monitor during its 2008-2009 intense bursting episode. We performed spectral analysis down to 4 ms timescales to characterize the spectral evolution of the bursts. Using a Comptonized model, we find that the peak energy, E peak, anti-correlates with flux, while the low-energy photon index remains constant at ~ – 0.8 up to a flux limit F ≈ 10–5 erg s–1 cm–2. Above this flux value, the E peak–flux correlation changes sign, and the index positively correlates with the flux reaching ~1 at the highest fluxes. Using a two blackbody model, we find that the areas and fluxes of the two emitting regions correlate positively. Further, we study here for the first time the evolution of the temperatures and areas as a function of flux. We find that the area–kT relation follows the lines of constant luminosity at the lowest fluxes, R 2vpropkT –4, with a break at the higher fluxes (F > 10–5.5 erg s–1 cm–2). The area of the high-kT component increases with the flux while its temperature decreases, which we interpret as being due to an adiabatic cooling process. The area of the low-kT component, on the other hand, appears to saturate at the highest fluxes, toward R max ≈ 30 km. Assuming that crust quakes are responsible for soft gamma repeater (SGR) bursts and considering R max as the maximum radius of the emitting photon-pair plasma fireball, we relate this saturation radius to a minimum excitation radius of the magnetosphere, and we put a lower limit on the internal magnetic field of SGR J1550–5418, B int gsim 4.5 × 1015 G.