Browsing by Author "Kaspi, Victoria M."

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    Contemporaneous X-Ray Observations of 30 Bright Radio Bursts from the Prolific Fast Radio Burst Source FRB 20220912A
    (2024) Cook, Amanda M.; Scholz, Paul; Pearlman, Aaron B.; Abbott, Thomas C.; Cruces, Marilyn; Gaensler, B. M.; Dong, Fengqiu Adam; Michilli, Daniele; Eadie, Gwendolyn; Kaspi, Victoria M.; Stairs, Ingrid; Tan, Chia Min; Bhardwaj, Mohit; Cassanelli, Tomas; Curtin, Alice P.; Ibik, Adaeze L.; Lazda, Mattias; Masui, Kiyoshi W.; Pandhi, Ayush; Rafiei-Ravandi, Masoud; Sammons, Mawson W.; Shin, Kaitlyn; Smith, Kendrick; Stenning, David C.
    We present an extensive contemporaneous X-ray and radio campaign performed on the repeating fast radio burst (FRB) source FRB 20220912A for 8 weeks immediately following the source's detection by CHIME/FRB. This includes X-ray data from XMM-Newton, NICER, and Swift, and radio detections of FRB 20220912A from CHIME/Pulsar and Effelsberg. We detect no significant X-ray emission at the time of 30 radio bursts with upper limits on a 0.5-10.0 keV X-ray fluence of (1.5-14.5) x 10(-10) erg cm(-2) (99.7% credible interval, unabsorbed) on a timescale of 100 ms. Translated into a fluence ratio eta(x/r) = FX-ray/F-radio, this corresponds to eta(x/r) < 7 x 10(6). For persistent emission from the location of FRB 20220912A, we derive a 99.7% 0.5-10.0 keV isotropic flux limit of 8.8 x 10(-15) erg cm(-2) s(-1) (unabsorbed) or an isotropic luminosity limit of 1.4 x 10(41) erg s(-1) at a distance of 362.4 Mpc. We derive a hierarchical extension to the standard Bayesian treatment of low-count and background-contaminated X-ray data, which allows the robust combination of multiple observations. This methodology allows us to place the best (lowest) 99.7% credible interval upper limit on an FRB eta(x/r) to date, eta(x/r) < 2 x 10(6), assuming that all 30 detected radio bursts are associated with X-ray bursts with the same fluence ratio. If we instead adopt an X-ray spectrum similar to the X-ray burst observed contemporaneously with FRB-like emission from the Galactic magnetar SGR 1935+2154 detected on 2020 April 28, we derive a 99.7% credible interval upper limit on eta(x/r) of 8 x 10(5), which is only 3 times the observed value of eta(x/r) for SGR 1935+2154.
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    PHASE-RESOLVED NuSTAR AND SWIFT-XRT OBSERVATIONS OF MAGNETAR 4U 0142+61
    (2015) Tendulkar, Shriharsh P.; Hascoeet, Romain; Yang, Chengwei; Kaspi, Victoria M.; Beloborodov, Andrei M.; An, Hongjun; Bachetti, Matteo; Boggs, Steven E.; Christensen, Finn E.; Craig, William W.; Guiilot, Sebastien; Hailey, Charles A.; Harrison, Fiona A.; Stern, Daniel; Zhang, William
    We present temporal and spectral analysis of simultaneous 0.5-79 keV Swift-XRT and Nuclear Spectroscopic Telescope Array observations of the magnetar 4U 0142+61. The pulse profile changes significantly with photon energy between 3 and 35 keV. The pulse fraction increases with energy, reaching a value of approximate to 20%, similar to that observed in 1E 1841-045 and much lower than the approximate to 80% pulse fraction observed in 1E 2259+586. We do not detect the 55 ks phase modulation reported in previous Suzaku-HXD observations. The phase-averaged spectrum of 4U 0142+61 above 20 keV is dominated by a hard power law (PL) with a photon index Gamma(H) similar to 0.65, and the spectrum below 20 keV can be described by two blackbodies, a blackbody plus a soft PL, or by a Comptonized blackbody model. We study the full phase-resolved spectra using the e(+/-) outflow model of Beloborodov. Our results are consistent with the parameters of the active j-bundle derived from INTEGRAL data by Hascoet et al. We find that a significant degeneracy appears in the inferred parameters if the footprint of the j-bundle is allowed to be a thin ring instead of a polar cap. The degeneracy is reduced when the footprint is required to be the hot spot inferred from the soft X-ray data.