Browsing by Author "Koljonen, Karri"
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- Investigating the Mini and Giant Radio Flare Episodes of Cygnus X-3
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2020-12-29) Egron, Elise; Pellizzoni, Alberto; Righini, Simona; Giroletti, Marcello; Koljonen, Karri; Pottschmidt, Katja; Trushkin, Sergei; Lobina, Jessica; Pilia, Maura; Wilms, Joern; Corbel, Stéphane; Grinberg, Victoria; Loru, Sara; Trois, Alessio; Rodriguez, Jérome; Lähteenmäki, A.; Tornikoski, M.; Enestam, Sissi; Järvelä, E.The microquasar Cygnus X-3 underwent a giant radio flare in 2017 April, reaching a maximum flux of ∼16.5 Jy at 8.5 GHz. We present results from a long monitoring campaign carried out with Medicina at 8.5, 18.6, and 24.1 GHz, parallel to the Metsähovi radio telescope at 37 GHz, from 2017 April 4 to 11. We observe a spectral steepening from α = 0.2 to 0.5 (with S ν ∝ ν α) within 6 hr of the epoch of the flare's peak maximum, and rapid changes in the spectral slope in the following days during brief enhanced emission episodes while the general trend of the radio flux density indicated the decay of the giant flare. We further study the radio orbital modulation of Cyg X-3 emission associated with the 2017 giant flare and with six mini-flares observed in 1983, 1985, 1994, 1995, 2002, and 2016. The enhanced emission episodes observed during the decline of the giant flare at 8.5 GHz coincide with the orbital phase φ ∼ 0.5 (orbital inferior conjunction). On the other hand, the light curves of the mini-flares observed at 15-22 GHz peak at φ ∼, except for the 2016 light curve, which is shifted 0.5 w.r.t. the other ones. We attribute the apparent phase shift to the variable location of the emitting region along the bent jet. This might be explained by the different accretion states of the flaring episodes (the 2016 mini-flare occurred in the hypersoft X-ray state). - Joint XMM-Newton and NuSTAR observations of the reflection spectrum of III Zw 2
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2020-03-30) Chamani, Wara; Koljonen, Karri; Savolainen, TuomasDetecting and modeling the reprocessed hard X-ray emission component in the accretion flow, the so-called reflection spectrum, is a main tool used to estimate black hole spins in a wide range of astrophysical black holes, regardless of their mass or distance. In this work, we study the X-ray spectra of the Seyfert I galaxy III Zw 2 by using multiepoch XMM-Newton, NuSTAR, and Suzaku observations. The X-ray spectra exhibit a soft-excess below 1 keV and a prominent excess at the location of the broad FeKff line at 6.4 keV. To account for these spectral features, we fit the spectra with multiple models including an ionized partially covering absorber and an accretion disk reflection model. To fully resolve the reflection component, we analyzed jointly the XMM-Newton and NuSTAR observations taken in 2017 and archival XMM-Newton data from 2000. Assuming the reflection scenario, the resulting model fits support for a rapidly spinning black hole (a ≥ 0.98) in this radio-intermediate source. The X-ray spectra in 2000 and 2017 are remarkably similar; the only difference pertains to the reflection fraction, which is possibly due to a change in the geometry of the accretion flow. However, the Suzaku observation is markedly different, and we suggest this could be an effect of a jet contribution in the X-ray band, which is supported by the elevated radio flux during this observation. - Multiwavelength Spectral Analysis of Accretion Disk and Astrophysical Jet Connection in Low-Mass X-ray Binaries
Sähkötekniikan korkeakoulu | Master's thesis(2020-10-19) Binios, AlexandrosX-ray binaries (XRBs) are powerful double star systems where a normal star feeds through accretion a compact object, e.g. a black hole, and the liberation of accretion energy results in strong radiation throughout the electromagnetic spectrum. Performing multiwavelength observations of XRBs allow us to study their fundamental astrophysical properties and processes, which are ultimately governed by the mass flow rate from the donor star to the accretor. The primary objective of this master's thesis was to perform multiwavelength spectral studies of known XRBs focusing on the accretion disk and astrophysical jet connection, i.e. the disk--jet connection, and to determine their spectral models and states at different observation periods. The data sets used in this master's thesis comprised of (quasi-)simultaneous multiwavelength observations. The principal instrument of this thesis was the Very Large Telescope's X-shooter, and its observations constituted the foundation of the collected (quasi-)simultaneous data sets. This thesis examines four different low-mass X-ray binary (LMXB) targets including MAXI J1820+070, a recently discovered LMXB. This master's thesis ultimately presents novel and unprecedented broadband observations and results for the main target MAXI J1820+070. Based on the spectral modelling of the observations, the results show how the MAXI J1820+070 first was in the low/hard state in mid-April 2018, then had entered the high/soft state in following observations in mid-July 2018, and finally in late September had transitioned to the intermediate-hard state. During mid-April 2018, the astrophysical jets were dominating and extended from the radio to the near-infrared spectrum. In mid-July, the astrophysical jets were no longer detected, and the accretion disk governed the emission spectrum in the X-shooter band. Additionally, this master’s thesis presents two novel value pairs for the jet break frequency ν_b as a function of the X-ray power law photon index Γ for black hole systems. - A Multiwavelength Study of GRS 1716-249 in Outburst: Constraints on Its System Parameters
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä(2022-06-01) Saikia, Payaswini; Russell, David M.; Baglio, M. C.; Bramich, D. M.; Casella, Piergiorgio; Trigo, Maria Diaz; Gandhi, Poshak; Jiang, Jiachen; Maccarone, Thomas; Soria, Roberto; Al Noori, Hind; Al Yazeedi, Aisha; Alabarta, Kevin; Belloni, Tomaso; Bel, Marion Cadolle; Ceccobello, Chiara; Corbel, Stéphane; Fender, Rob; Gallo, Elena; Homan, Jeroen; Koljonen, Karri; Lewis, Fraser; Markoff, Sera B.; Miller-Jones, James C.A.; Rodriguez, Jerome; Russell, Thomas D.; Shahbaz, Tariq; Sivakoff, Gregory R.; Testa, Vincenzo; Tetarenko, Alexandra J.We present a detailed study of the evolution of the Galactic black hole transient GRS 1716-249 during its 2016-2017 outburst at optical (Las Cumbres Observatory), mid-infrared (Very Large Telescope), near-infrared (Rapid Eye Mount telescope), and ultraviolet (the Neil Gehrels Swift Observatory Ultraviolet/Optical Telescope) wavelengths, along with archival radio and X-ray data. We show that the optical/near-infrared and UV emission of the source mainly originates from a multi-temperature accretion disk, while the mid-infrared and radio emission are dominated by synchrotron emission from a compact jet. The optical/UV flux density is correlated with the X-ray emission when the source is in the hard state, consistent with an X-ray irradiated accretion disk with an additional contribution from the viscous disk during the outburst fade. We find evidence for a weak, but highly variable jet component at mid-infrared wavelengths. We also report the long-term optical light curve of the source and find that the quiescent i′ -band magnitude is 21.39 ± 0.15 mag. Furthermore, we discuss how previous estimates of the system parameters of the source are based on various incorrect assumptions, and so are likely to be inaccurate. By comparing our GRS 1716-249 data set to those of other outbursting black hole X-ray binaries, we find that while GRS 1716-249 shows similar X-ray behavior, it is noticeably optically fainter, if the literature distance of 2.4 kpc is adopted. Using several lines of reasoning, we argue that the source distance is further than previously assumed in the literature, likely within 4-17 kpc, with a most likely range of ∼4-8 kpc.