Browsing by Author "Koljonen, Karri I.I."
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Item Association of the IceCube neutrinos with blazars in the CGRaBS sample(EDP Sciences, 2024-10-01) Kouch, Pouya M.; Lindfors, Elina; Hovatta, Talvikki; Liodakis, Ioannis; Koljonen, Karri I.I.; Nilsson, Kari; Kiehlmann, Sebastian; Max-Moerbeck, Walter; Readhead, Anthony C.S.; Reeves, Rodrigo A.; Pearson, Timothy J.; Jormanainen, Jenni; Ramazani, Vandad Fallah; Graham, Matthew J.; Metsähovi Radio Observatory; University of Turku; Institute of Astrophysics; Universidad de Chile; California Institute of Technology; Universidad de Concepción; Norwegian University of Science and Technology; Ruhr University BochumThe origin of high-energy (HE) astrophysical neutrinos has remained an elusive hot topic in the field of HE astrophysics for the past decade. Apart from a handful of individual associations, the vast majority of HE neutrinos arise from unknown sources. While there are theoretically motivated candidate populations, such as blazars – a subclass of active galactic nuclei with jets pointed toward our line of sight – they have not been convincingly linked to HE neutrino production yet. Here, we perform a spatio-temporal association analysis between a sample of blazars (from the CGRaBS catalog) in the radio and optical bands and the most up-to-date IceCube HE neutrino catalog. We find that if the IceCube error regions are enlarged by 1◦ in quadrature, to account for unknown systematic errors at a maximal level, a spatio-temporal correlation between the multiwavelength light curves of the CGRaBS blazars and the IceCube HE neutrinos is hinted at, least at a 2.17σ significance level. On the other hand, when the IceCube error regions are taken as their published values, we do not find any significant correlations. A discrepancy in the blazar-neutrino correlation strengths, when using such minimal and enlarged error region scenarios, was also obtained in a recent study by the IceCube collaboration. In our study, this difference arises because several flaring blazars – coinciding with a neutrino arrival time – happen to narrowly miss the published 90%-likelihood error region of the nearest neutrino event. For all of the associations driving our most significant correlations, the flaring blazar is much less than 1◦ away from the published error regions. Therefore, our results indicate that the question of the blazar-neutrino connection is highly sensitive to the reconstruction of the neutrino error regions, whose reliability is expected to improve with the next generation of neutrino observatories.Item Microquasar Cyg X-3 - a unique jet-wind neutrino factory?(Oxford University Press, 2023-09-01) Koljonen, Karri I.I.; Satalecka, Konstancja; Lindfors, Elina J.; Liodakis, Ioannis; Metsähovi Radio Observatory; University of TurkuThe origin of astrophysical neutrinos is one of the most debated topics today. Perhaps the most robust evidence of neutrino counterpart comes from supermassive black holes in active galactic nuclei associated with strongly collimated outflows, or jets, that can accelerate particles to relativistic energies and produce neutrinos through hadronic interactions. Similar outflows can also be found from X-ray binaries, or 'microquasars', that consist of a neutron star or a stellar-mass black hole accreting matter from a non-degenerate companion star. In some cases, these systems can accelerate particles up to GeV energies implying an efficient acceleration mechanism in their jets. Neutrino production in microquasar jets can be expected with suitable conditions and a hadronic particle population. Microquasar Cyg X-3 is a unique, short orbital period X-ray binary hosting a Wolf-Rayet companion star with a strong stellar wind. The interaction of the dense stellar wind with a relativistic jet leads to particle collisions followed by high-energy gamma-ray and potentially neutrino emission. Here, using the 10-yr neutrino candidate sample of the IceCube neutrino observatory, we find that the events with the highest spatial association with Cyg X-3 occur during short-lived high-energy gamma-ray flaring periods indicating the possible astrophysical nature of these events.Item Optical Precursors to Black Hole X-Ray Binary Outbursts: An Evolving Synchrotron Jet Spectrum in Swift J1357.2-0933(2018-01-10) Russell, David M.; Qasim, Ahlam Al; Bernardini, Federico; Plotkin, Richard M.; Lewis, Fraser; Koljonen, Karri I.I.; Yang, Yi Jung; Metsähovi Radio Observatory; New York University Abu Dhabi; Curtin University; Cardiff University; Sun Yat-sen UniversityWe present six years of optical monitoring of the black hole (BH) candidate X-ray binary Swift J1357.2-0933, during and since its discovery outburst in 2011. On these long timescales, the quiescent light curve is dominated by high amplitude, short-term (seconds-days) variability spanning ∼2 mag, with an increasing trend of the mean flux from 2012 to 2017 that is steeper than in any other X-ray binary found to date (0.17 mag yr-1). We detected the initial optical rise of the 2017 outburst of Swift J1357.2-0933, and we report that the outburst began between 2017 April 1 and 6. Such a steep optical flux rise preceding an outburst is expected according to disk instability models, but the high amplitude variability in quiescence is not. Previous studies have shown that the quiescent spectral, polarimetric, and rapid variability properties of Swift J1357.2-0933 are consistent with synchrotron emission from a weak compact jet. We find that a variable optical/infrared spectrum is responsible for the brightening: a steep, red spectrum before and soon after the 2011 outburst evolves to a brighter, flatter spectrum since 2013. The evolving spectrum appears to be due to the jet spectral break shifting from the infrared in 2012 to the optical in 2013, then back to the infrared by 2016-2017 while the optical remains relatively bright. Swift J1357.2-0933 is a valuable source to study BH jet physics at very low accretion rates and is possibly the only quiescent source in which the optical jet properties can be regularly monitored.Item The Radio/X-Ray Correlation in X-Ray Binaries - Insights from a Hard X-Ray Perspective(IOP PUBLISHING LTD, 2019-01-20) Koljonen, Karri I.I.; Russell, David M.; Metsähovi Radio Observatory; New York University Abu DhabiThe radio/X-ray correlation is one of the most important pieces of observational evidence of the disk-jet connection in accreting compact objects. However, a growing number of X-ray binaries (XRB) seem to present deviations from the universal radio/X-ray correlation, and the origin of these outliers are still very much debated. In previous studies, the X-ray bolometric luminosity used in the radio/X-ray correlation has been estimated using a narrow, soft X-ray band. We study how estimating the X-ray bolometric luminosity using broadband observations of XRB affects the radio/X-ray correlation. We found that the ratio between the broadband (3-200 keV) and narrowband (3-9 keV) luminosities varies between 5 and 10 in the hard X-ray state. Overall, the resulting radio/X-ray correlation slopes and normalizations did not present a very significant change, suggesting that they are not affected greatly by observational biases but are caused by real physical effects. We found that all sources that reach high enough luminosity change their correlation slopes from the universal slope to a much steeper one. In addition, sources in the steeper radio/X-ray track show a distinct cutoff in the high-energy X-ray spectrum at tens of keV. These results suggest that the accretion flow presents a morphological change at a certain critical luminosity during the outburst rise from radiatively inefficient to radiatively efficient flow that is in turn more efficient in cooling the hot accretion flow producing the hard X-ray emission. This change could also affect to the jet launching properties in these systems.Item A Wildly Flickering Jet in the Black Hole X-Ray Binary MAXI J1535-571(2018-11-10) Cristina Baglio, Maria; Russell, David M.; Casella, Piergiorgio; Al Noori, Hind; Al Yazeedi, Aisha; Belloni, Tomaso; Buckley, David A.H.; Cadolle Bel, Marion; Ceccobello, Chiara; Corbel, Stephane; Coti Zelati, Francesco; Díaz Trigo, Maria; Fender, Rob P.; Gallo, Elena; Gandhi, Poshak; Homan, Jeroen; Koljonen, Karri I.I.; Lewis, Fraser; Maccarone, Thomas J.; Malzac, Julien; Markoff, Sera; Miller-Jones, James C.A.; O'Brien, Kieran; Russell, Thomas D.; Saikia, Payaswini; Shahbaz, Tariq; Sivakoff, Greg R.; Soria, Roberto; Testa, Vincenzo; Tetarenko, Alexandra J.; Van Den Ancker, Mario E.; Vincentelli, Federico M.; Metsähovi Radio Observatory; New York University Abu Dhabi; Osservatorio Astronomico di Roma; Osservatorio Astronomico di Brera; South African Astronomical Observatory; SIXT Leasing SE; Chalmers University of Technology; French Alternative Energies and Atomic Energy Commission; European Southern Observatory; University of Oxford; University of Michigan, Ann Arbor; University of Southampton; Eureka Scientific, Inc.; Cardiff University; Texas Tech University; IRAP; University of Amsterdam; Curtin University; Durham University; Instituto de Astrofísica de Canarias; University of AlbertaWe report on the results of optical, near-infrared (NIR), and mid-infrared observations of the black hole X-ray binary candidate (BHB) MAXI J1535-571 during its 2017/2018 outburst. During the first part of the outburst (MJD 58004-58012), the source shows an optical-NIR spectrum that is consistent with an optically thin synchrotron power law from a jet. After MJD 58015, however, the source faded considerably, the drop in flux being much more evident at lower frequencies. Before the fading, we measure a dereddened flux density of 100 mJy in the mid-infrared, making MAXI J1535-571 one of the brightest mid-infrared BHBs known so far. A significant softening of the X-ray spectrum is evident contemporaneous with the infrared fade. We interpret it as being due to the suppression of the jet emission, similar to the accretion-ejection coupling seen in other BHBs. However, MAXI J1535-571 did not transition smoothly to the soft state, instead showing X-ray hardness deviations associated with infrared flaring. We also present the first mid-IR variability study of a BHB on minute timescales, with a fractional rms variability of the light curves of ∼15%-22%, which is similar to that expected from the internal shock jet model, and much higher than the optical fractional rms (≲7%). These results represent an excellent case of multiwavelength jet spectral timing and demonstrate how rich, multiwavelength time-resolved data of X-ray binaries over accretion state transitions can help in refining models of the disk-jet connection and jet launching in these systems.