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Item Green Bank Telescope observations of ³He⁺: planetary nebulae(American Astronomical Society, 2021-03) Bania, Thomas M.; Balser, Dana S.We use the Green Bank Telescope to search for ³He⁺ emission from a sample of four Galactic planetary nebulae: NGC 3242, NGC 6543, NGC 6826, and NGC 7009. During the era of primordial nucleosynthesis the light elements ²H, ³He, ⁴He, and ⁷Li were produced in significant amounts and these abundances have since been modified primarily by stars. Observations of ³He⁺ in H II regions located throughout the Milky Way disk reveal very little variation in the ³He/H abundance ratio -- the "³He Plateau" -- indicating that the net effect of ³He production in stars is negligible. This is in contrast to much higher ³He/H abundance ratios reported for some planetary nebulae. This discrepancy is known as the "³He Problem". We use radio recombination lines observed simultaneously with the ³He⁺ transition to make a robust assessment of the spectral sensitivity that these observations achieve. We detect spectral lines at ∼ 1 -- 2 mK intensities, but at these levels instrumental effects compromise our ability to measure accurate spectral line parameters. We do not confirm reports of previous detections of ³He⁺ in NGC 3242 nor do we detect ³He⁺ emission from any of our sources. This result calls into question all reported detections of ³He⁺ emission from any planetary nebula. The ³He/H abundance upper limit we derive here for NGC 3242 is inconsistent with standard stellar production of ³He and thus requires that some type of extra mixing process operates in low-mass stars.Item A VLA census of the Galactic H II region population(American Astronomical Society, 2021-03) Armentrout, W.P.; Anderson, L.D.; Wenger, Trey V.; Balser, Dana S.; Bania, Thomas M.The Milky Way contains thousands of H ii region candidates identified by their characteristic mid-infrared morphology, but lacking detections of ionized gas tracers such as radio continuum or radio recombination line emission. These targets thus remain unconfirmed as H ii regions. With only ∼2500 confirmed H ii regions in the Milky Way, Galactic surveys are deficient by several thousand nebulae when compared to external galaxies with similar star formation rates. Using sensitive 9 GHz radio continuum observations with the Karl G. Jansky Very Large Array, we explore a sample of H ii region candidates in order to set observational limits on the actual total population of Galactic H ii regions. We target all infrared–identified “radio-quiet” sources from the Wide-field Infrared Survey Explorer Catalog of Galactic H ii regions between 245° ≥ ℓ ≥ 90° with infrared diameters less than 80′′. We detect radio continuum emission from 50% of the targeted H ii region candidates, providing strong evidence that most of the radio-quiet candidates are bona fide H ii regions. We measure the peak and integrated radio flux densities and compare the inferred Lyman continuum fluxes using models of OB stars. We conclude that stars of approximately spectral type B2 and earlier are able to create H ii regions with similar infrared and radio continuum morphologies as the more luminous H ii regions created by O stars. From our 50% detection rate of “radio-quiet” sources, we set a lower limit of ∼7000 for the H ii region population of the Galaxy. Thus the vast majority of the Milky Way’s H ii regions remain to be discovered.Item The Galactic H II region luminosity function at radio and infrared wavelengths(American Astronomical Society, 2021-04) Mascoop, J.L.; Anderson, L.D.; Wenger, Trey V.; Makai, Z.; Armentrout, W.P.; Balser, Dana S.; Bania, Thomas M.The Galactic H ii region luminosity function (LF) is an important metric for understanding global star formation properties of the Milky Way, but only a few studies have been done, and all use relatively small numbers of H ii regions. We use a sample of 797 first Galactic quadrant H ii regions compiled from the Wide-field Infrared Survey Explorer Catalog of Galactic H ii Regions to examine the form of the LF at multiple infrared and radio wavelengths. Our sample is statistically complete for all regions powered by single stars of type O9.5V and earlier. We fit the LF at each wavelength with single and double power laws. Averaging the results from all wavelengths, the mean of the best-fit single power-law index is 〈α〉 = −1.75 ± 0.01. The mean best-fit double power-law indices are 〈α 1〉 = −1.40 ± 0.03 and 〈α 2〉 = −2.33 ± 0.04. We conclude that neither a single nor a double power law is strongly favored over the other. The LFs show some variation when we separate the H ii region sample into subsets by heliocentric distance, physical size, Galactocentric radius, and location relative to the spiral arms, but blending individual H ii regions into larger complexes does not change the value of the power-law indices of the best-fit LF models. The consistency of the power-law indices across multiple wavelengths suggests that the LF is independent of wavelength. This implies that infrared and radio tracers can be employed in place of Hα.Item The GBT diffuse ionized gas survey (GDIGS): survey overview and first data release(American Astronomical Society, 2021-06) Anderson, L.D.; Luisi, Matteo; Liu, Bin; Wenger, Trey V.; Balser, Dana S.; Bania, Thomas M.; Haffner, L.M.; Linville, Dylan J.; Mascoop, J.L.The Green Bank Telescope (GBT) Diffuse Ionized Gas Survey (GDIGS) traces ionized gas in the Galactic midplane by measuring 4–8 GHz radio recombination line (RRL) emission. The nominal survey zone is 32.°3 > ℓ > − 5°, ∣b∣ < 0.°5, but coverage extends above and below the plane in select fields and additionally includes the areas around W47 (ℓ ≃ 37.°5) and W49 (ℓ ≃ 43°). GDIGS simultaneously observes 22 Hnα (15 usable), 25 Hnβ (18 usable), and 8 Hnγ RRLs (all usable), as well as multiple molecular line transitions (including those of H_2^13CO, H2CO, and CH3OH). Here, we describe the GDIGS survey parameters and characterize the RRL data, focusing primarily on the Hnα data. We produce sensitive data cubes by averaging the usable RRLs, after first smoothing to a common spectral resolution of 0.5 km s−1 and a spatial resolution of 2.′65 for Hnα, 2.′62 for Hnβ, and 2.′09 for Hnγ. The average spectral noise per spaxel in the Hnα data cubes is ∼10 mK (∼5 mJy beam−1). This sensitivity allows GDIGS to detect RRLs from plasma throughout the inner Galaxy. The GDIGS Hnα data are sensitive to emission measures EM ≳ 1100 cm^−6 pc, which corresponds to a mean electron density ⟨n_e⟩ ≳ 30 cm^−3 for a 1 pc path length or ⟨n_e〉 ≳ 1 cm^−3 for a 1 kpc path length.Item Statistical inference with stochastic gradient algorithms(2022-11-14) Negrea, Jeffrey; Yang, Jun; Feng, Haoyue; Roy, Daniel; Huggins, JonathanThe tuning of stochastic gradient algorithms (SGAs) for optimization and sampling is often based on heuristics and trial-and-error rather than generalizable theory. We address this theory–practice gap by characterizing the large-sample statistical asymptotics of SGAs via a joint step-size–sample-size scaling limit. We show that iterate averaging with a large fixed step size is robust to the choice of tuning parameters and asymptotically has covariance proportional to that of the MLE sampling distribution. We also prove a Bernstein–von Mises-like theorem to guide tuning, including for generalized posteriors that are robust to model misspecification. Numerical experiments validate our results and recommendations in realistic finite-sample regimes. Our work lays the foundation for a systematic analysis of other stochastic gradient Markov chain Monte Carlo algorithms for a wide range of models.Item Imaging X-ray polarimetry explorer: prelaunch(SPIE-Intl Soc Optical Eng, 2022-04-14) Weisskopf, Martin C.; Soffitta, Paolo; Baldini, Luca; Ramsey, Brian D.; O’Dell, Stephen L.; Romani, Roger W.; Matt, Giorgio; Deininger, William D.; Baumgartner, Wayne H.; Bellazzini, Ronaldo; Costa, Enrico; Kolodziejczak, Jeffery J.; Latronico, Luca; Marshall, Herman L.; Muleri, Fabio; Bongiorno, Stephen D.; Tennant, Allyn; Bucciantini, Niccolò; Dovčiak, Michal; Marin, Frederic; Marscher, Alan; Poutanen, Juri; Slane, Pat; Turolla, Roberto; Kalinowski, William; Di Marco, Alessandro; Fabiani, Sergio; Minuti, Massimo; La Monaca, Fabio; Pinchera, Michele; Rankin, John; Sgro’, Carmelo; Trois, Alessio; Xie, Fei; Alexander, Cheryl; Allen, D. Zachery; Amici, Fabrizio; Andersen, Jason; Antonelli, Angelo; Antoniak, Spencer; Attinà, Primo; Barbanera, Mattia; Bachetti, Matteo; Baggett, Randy M.; Bladt, Jeff; Brez, Alessandro; Bonino, Raffaella; Boree, Christopher; Borotto, Fabio; Breeding, Shawn; Brienza, Daniele; Bygott, H. Kyle; Caporale, Ciro; Cardelli, Claudia; Carpentiero, Rita; Castellano, Simone; Castronuovo, Marco; Cavalli, Luca; Cavazzuti, Elisabetta; Ceccanti, Marco; Centrone, Mauro; Citraro, Saverio; D’Amico, Fabio; D’Alba, Elisa; Di Gesu, Laura; Del Monte, Ettore; Dietz, Kurtis L.; Di Lalla, Niccolò; Persio, Giuseppe Di; Dolan, David; Donnarumma, Immacolata; Evangelista, Yuri; Ferrant, Kevin; Ferrazzoli, Riccardo; Ferrie, MacKenzie; Footdale, Joseph; Forsyth, Brent; Foster, Michelle; Garelick, Benjamin; Gunji, Shuichi; Gurnee, Eli; Head, Michael; Hibbard, Grant; Johnson, Samantha; Kelly, Erik; Kilaru, Kiranmayee; Lefevre, Carlo; Roy, Shelley Le; Loffredo, Pasqualino; Lorenzi, Paolo; Lucchesi, Leonardo; Maddox, Tyler; Magazzu, Guido; Maldera, Simone; Manfreda, Alberto; Mangraviti, Elio; Marengo, Marco; Marrocchesi, Alessandra; Massaro, Francesco; Mauger, David; McCracken, Jeffrey; McEachen, Michael; Mize, Rondal; Mereu, Paolo; Mitchell, Scott; Mitsuishi, Ikuyuki; Morbidini, Alfredo; Mosti, Federico; Nasimi, Hikmat; Negri, Barbara; Negro, Michela; Nguyen, Toan; Nitschke, Isaac; Nuti, Alessio; Onizuka, Mitch; Oppedisano, Chiara; Orsini, Leonardo; Osborne, Darren; Pacheco, Richard; Paggi, Alessandro; Painter, Will; Pavelitz, Steven D.; Pentz, Christina; Piazzolla, Raffaele; Perri, Matteo; Pesce-Rollins, Melissa; Peterson, Colin; Pilia, Maura; Profeti, Alessandro; Puccetti, Simonetta; Ranganathan, Jaganathan; Ratheesh, Ajay; Reedy, Lee; Root, Noah; Rubini, Alda; Ruswick, Stephanie; Sanchez, Javier; Sarra, Paolo; Santoli, Francesco; Scalise, Emanuele; Sciortino, Andrea; Schroeder, Christopher; Seek, Tim; Sosdian, Kalie; Spandre, Gloria; Speegle, Chet O.; Tamagawa, Toru; Tardiola, Marcello; Tobia, Antonino; Thomas, Nicholas E.; Valerie, Robert; Vimercati, Marco; Walden, Amy L.; Weddendorf, Bruce; Wedmore, Jeffrey; Welch, David; Zanetti, Davide; Zanetti, FrancescoLaunched on 2021 December 9, the Imaging X-ray Polarimetry Explorer (IXPE) is a NASA Small Explorer Mission in collaboration with the Italian Space Agency (ASI). The mission will open a new window of investigation—imaging x-ray polarimetry. The observatory features three identical telescopes, each consisting of a mirror module assembly with a polarization-sensitive imaging x-ray detector at the focus. A coilable boom, deployed on orbit, provides the necessary 4-m focal length. The observatory utilizes a three-axis-stabilized spacecraft, which provides services such as power, attitude determination and control, commanding, and telemetry to the ground. During its 2-year baseline mission, IXPE will conduct precise polarimetry for samples of multiple categories of x-ray sources, with follow-on observations of selected targets.Item Juno Plasma Wave Observations at Ganymede.(American Geophysical Union (AGU), 2022-12-16) Kurth, W.S.; Sulaiman, A.H.; Hospodarsky, G.B.; Menietti, J.D.; Mauk, B.H.; Clark, G.; Allegrini, F.; Valek, P.; Connerney, J.E.P.; Waite, J.H.; Bolton, S.J.; Imai, M.; Santolik, O.; Li, Wen; Duling, S.; Saur, J.; Louis, C.The Juno Waves instrument measured plasma waves associated with Ganymede's magnetosphere during its flyby on 7 June, day 158, 2021. Three distinct regions were identified including a wake, and nightside and dayside regions in the magnetosphere distinguished by their electron densities and associated variability. The magnetosphere includes electron cyclotron harmonic emissions including a band at the upper hybrid frequency, as well as whistler-mode chorus and hiss. These waves likely interact with energetic electrons in Ganymede's magnetosphere by pitch angle scattering and/or accelerating the electrons. The wake is accentuated by low-frequency turbulence and electrostatic solitary waves. Radio emissions observed before and after the flyby likely have their source in Ganymede's magnetosphere.Item Equations of motion near cyclotron resonance(2022-06-16) Albert, J.M.; Artemyev, A.; Li, Wen; Gan, Longzhi; Ma, Q.This work compares several versions of the equations of motion for a test particle encountering cyclotron resonance with a single, field-aligned whistler mode wave. The gyro-averaged Lorentz equation produces both widespread phase trapping (PT) and “positive phase bunching” of low pitch angle electrons by large amplitude waves. Approximations allow a Hamiltonian description to be reduced to a single pair of conjugate variables, which can account for PT as well as phase bunching at moderate pitch angle, and has recently been used to investigate this unexpected bahavior at low pitch angle. Here, numerical simulations using the Lorentz equation and several versions of Hamiltonian-based equations of motion are compared. Similar behavior at low pitch angle is found in each case.Item Dependence of nonlinear effects on whistler-mode chorus wave bandwidth and amplitude: a perspective from diffusion coefficients(2021-12-17) Gan, Longzhi; Li, Wen; Ma, Q.; Artemyev, A.; Albert, J.M.The electron resonant interaction with whistler-mode waves is characterized by transport in pitch angle–energy space. We calculate electron diffusion and advection coefficients (a simplified characterization of transport) for a large range of electron pitch angle and energy using test particle simulations. Nonlinear effects are analyzed by comparing the diffusion coefficients using test particle simulations and quasilinear theory, and by evaluating the advection rates. Dependence of nonlinear effects on the wave amplitude and bandwidth of whistler-mode waves is evaluated by running test particle simulations with a broad range of wave amplitude and bandwidth. The maximum amplitudes where the quasilinear approach is valid are found to increase with increasing bandwidth, from 50 pT for narrowband waves to 300 pT for broadband waves at L-shell of 6. Moreover, interactions between intense whistler-mode waves and small pitch angle electrons lead to large positive advection, which limits the applicability of diffusion-based models. This study demonstrates the parameter range of the applicability of quasilinear theory and diffusion model for different wave amplitudes and frequency bandwidths of whistler-mode waves, which is critical for evaluating the effects of whistler-mode waves on energetic electrons in the Earth’s magnetosphere.Item Dependence of nonlinear effects on whistler-mode wave bandwidth and amplitude: a perspective from diffusion coefficients(2022-05-16) Gan, L.; Li, Wen; Ma, Q.; Artemyev, A.; Albert, J.M.The electron resonant interaction with whistler-mode waves is characterized by transport in pitch angle–energy space. We calculate electron diffusion and advection coefficients (a simplified characterization of transport) for a large range of electron pitch angle and energy using test particle simulations. Nonlinear effects are analyzed by comparing the diffusion coefficients using test particle simulations and quasilinear theory, and by evaluating the advection rates. Dependence of nonlinear effects on the wave amplitude and bandwidth of whistler-mode waves is evaluated by running test particle simulations with a broad range of wave amplitude and bandwidth. The maximum amplitudes where the quasilinear approach is valid are found to increase with increasing bandwidth, from 50 pT for narrowband waves to 300 pT for broadband waves at L-shell of 6. Moreover, interactions between intense whistler-mode waves and small pitch angle electrons lead to large positive advection, which limits the applicability of diffusion-based models. This study demonstrates the parameter range of the applicability of quasilinear theory and diffusion model for different wave amplitudes and frequency bandwidths of whistler-mode waves, which is critical for evaluating the effects of whistler-mode waves on energetic electrons in the Earth’s magnetosphere.Item Energetic charged particle observations during Juno's close flyby of Ganymede(American Geophysical Union (AGU), 2022-12-16) Clark, G.; Kollmann, P.; Mauk, B.H.; Paranicas, C.; Haggerty, D.; Rymer, A.; Smith, H.T.; Saur, J.; Allegrini, F.; Duling, S.; Ebert, R.W.; Kurth, W.S.; Gladstone, R.; Greathouse, T.K.; Li, W.; Bagenal, F.; Connerney, J.E.P.; Bolton, S.J.; Szalay, J.R.; Sulaiman, A.H.; Hansen, C.J.; Turner, D.L.On 7 June 2021, NASA's Juno mission obtained unique measurements of Ganymede's magnetosphere during a close flyby that brought the spacecraft within ∼1,000 km of its surface. Here Jupiter Energetic particle Detector Instrument observations are presented and analyzed. The electron pitch angle distributions reveal distinct regions of Ganymede's magnetosphere that can be characterized as inbound and outbound magnetospheric boundaries, a magnetotail/wake region, and Ganymede's open field line region. Evidence for energy dependent electron pitch angle structuring is also documented both outside and within Ganymede's magnetosphere. Electron precipitation is observed and mapped to Ganymede's surface along Juno's magnetic footpoint.Item Analytical results for phase bunching in the pendulum model of wave-particle interactions(2022-07-15) Albert, J.M.; Artemyev, A.; Li, Wen; Gan, L.; Ma, Q.[Radiation belt electrons are strongly affected by resonant interactions with cyclotron-resonant waves. In the case of a particle passing through resonance with a single, coherent wave, a Hamiltonian formulation is advantageous. With certain approximations, the Hamiltonian has the same form as that for a plane pendulum, leading to estimates of the change at resonance of the first adiabatic invariant I, energy, and pitch angle. In the case of large wave amplitude (relative to the spatial variation of the background magnetic field), the resonant change in I and its conjugate phase angle ξ are not diffusive but determined by nonlinear dynamics. A general analytical treatment of slow separatrix crossing has long been available and can be used to give the changes in I associated with “phase bunching,” including the detailed dependence on ξ, in the nonlinear regime. Here we review this treatment, evaluate it numerically, and relate it to previous analytical results for nonlinear wave-particle interactions. “Positive phase bunching” can occur for some particles even in the pendulum Hamiltonian approximation, though the fraction of such particles may be exponentially small.]Item An event of extreme relativistic and ultra-relativistic electron enhancements following the arrival of consecutive corotating interaction regions: coordinated observations by Van Allen Probes, Arase, THEMIS and Galileo satellites(2022-08-30) Nasi, A.; Katsavrias, C.; Daglis, Ioannis A.; Sandberg, I.; Aminalragia-Giamini, S.; Li, Wen; Miyoshi, Y.; Evans, H.; Mitani, T.; Matsuoka, A.; Shinohara, I.; Takashima, T.; Hori, T.; Balasis, G.[During July to October of 2019, a sequence of isolated Corotating Interaction Regions (CIRs) impacted the magnetosphere, for four consecutive solar rotations, without any interposed Interplanetary Coronal Mass Ejections. Even though the series of CIRs resulted in relatively weak geomagnetic storms, the net effect of the outer radiation belt during each disturbance was different, depending on the electron energy. During the August-September CIR group, significant multi-MeV electron enhancements occurred, up to ultra-relativistic energies of 9.9 MeV in the heart of the outer Van Allen radiation belt. These characteristics deemed this time period a fine case for studying the different electron acceleration mechanisms. In order to do this, we exploited coordinated data from the Van Allen Probes, the Time History of Events and Macroscale Interactions during Substorms Mission (THEMIS), Arase and Galileo satellites, covering seed, relativistic and ultra-relativistic electron populations, investigating their Phase Space Density (PSD) profile dependence on the values of the second adiabatic invariant K, ranging from near-equatorial to off equatorial mirroring populations. Our results indicate that different acceleration mechanisms took place for different electron energies. The PSD profiles were dependent not only on the μ value, but also on the K value, with higher K values corresponding to more pronounced local acceleration by chorus waves. The 9.9 MeV electrons were enhanced prior to the 7.7 MeV, indicating that different mechanisms took effect on different populations. Finally, all ultra-relativistic enhancements took place below geosynchronous orbit, emphasizing the need for more Medium Earth Orbit (MEO) missions.]Item Unraveling the formation region and frequency of chorus spectral gaps(2022-09-29) Li, J.; Bortnik, Jacob; Li, Wen; An, X.; Lyons, L.Electromagnetic ion cyclotron (EMIC) waves could cause a simultaneous dropout of radiation belt electrons and ring current protons. However, their effects on the dropout of both plasma populations have not been quantified in previous studies. In this paper, we model the simultaneous dropout of MeV electrons and hundreds of keV protons observed by Van Allen Probes within ∼40 min on 27 February 2014. The wave and particle measurements during the period of most intense EMIC waves at 𝐿 ∼ 5.2 are used to calculate the quasilinear diffusion coefficients and simulate the evolution of both energetic electrons and protons. Our model well captures the dropout of electrons with energies >1 MeV and pitch angles <75°, and the concurrent dropout of protons with energies >200 keV and pitch angles >40°. This is the first modeling work quantitatively reproducing the simultaneous dropout of both populations due to EMIC wave scattering.Item Multi-fluid simulation of solar chromospheric turbulence and heating due to the Thermal Farley-Buneman Instability(American Astronomical Society, 2023-06-01) Evans, Samuel; Oppenheim, Meers; Dimant, Yakov; Martinez- Sykora, JuanModels fail to reproduce observations of the coldest parts of the Sun’s atmosphere, where interactions between multiple ionized and neutral species prevent an accurate MHD representation. This paper argues that a meter-scale electrostatic plasma instability develops in these regions and causes heating. We refer to this instability as the Thermal Farley–Buneman Instability (TFBI). Using parameters from a 2.5D radiative MHD Bifrost simulation, we show that the TFBI develops in many of the colder regions in the chromosphere. This paper also presents the first multifluid simulation of the TFBI and validates this new result by demonstrating close agreement with theory during the linear regime. The simulation eventually develops turbulence, and we characterize the resulting wave-driven heating, plasma transport, and turbulent motions. These results all contend that the effects of the TFBI contribute to the discrepancies between solar observations and radiative MHD models.Item Unified fluid-model theory of EXB instabilities in low-ionized collisional plasmas with arbitrarily magnetized multi-species ions(2022-11-22) Dimant, Yakov; Oppenheim, Meers; Evans, Samuel; Martinez-Sykora, JuanThis paper develops a unified linear theory of local cross-field plasma instabilities, such as the Farley-Buneman, electron thermal, and ion thermal instabilities, in collisional plasmas with fully or partially unmagnetized multi-species ions. Collisional lasma instabilities in low-ionized, highly dissipative, weakly magnetized plasmas play an important role in the lower Earth's ionosphere and may be of importance in other planet ionospheres, star atmospheres, cometary tails, molecular clouds, accretion disks, etc. In the solar chromosphere, macroscopic effects of collisional plasma instabilities may contribute into significant heating -- an effect originally suggested from spectroscopic observations and relevant modeling. Based on a simplified 5-moment multi-fluid model, the theoretical analysis produces the general linear dispersion relation for the combined Thermal-Farley-Buneman Instability (TFBI). Important limiting cases are analyzed in detail. The analysis demonstrates acceptable applicability of this model for the rocesses under study. Fluid-model simulations usually require much less computer resources than do more accurate kinetic simulations, so that the apparent success of this approach to the linear theory of collisional plasma instabilities makes it possible to investigate the TFBI (along with its possible macroscopic effects) using global fluid codes originally developed for large-scale modeling of the solar and planetary atmospheres.Item Relation between magnetosonic waves and pitch angle anisotropy of warm protons(Frontiers Media SA, 2022-11-24) Joseph, J.; Jaynes, A.N.; Ma, Q.; Hartley, D.P.; Usanova, M.E.; Li, WenIn the past decade, many observations of transversely heated low energy protons were reported in the inner magnetosphere. Interestingly, most of the time heated protons were observed along with magnetosonic waves. Due to the strong correlation, it was often assumed that magnetosonic waves were responsible for the heating of low energy protons. By performing a case study under unusually disturbed geomagnetic conditions, this paper unravels the controversial relationship between the observed pitch angle anisotropy of warm protons and the accompanying magnetosonic waves in the inner magnetosphere. We perform a comparative analysis involving two nearly identical cases of pitch angle anisotropy of warm protons in low L-shell region–one with magnetosonic waves and one without them. It is found that magnetosonic waves are not responsible for primary heating of low-energy protons and may just marginally alter the shape of the distribution of heated protons in the events analyzed. Based on the recent Cluster and POLAR observations, we also show how the recirculated polar wind plasma in the Earth’s magnetosphere can cause the concurrent appearance of heated protons and magnetosonic waves.Item The X-ray polarimetry view of the accreting pulsar Cen X-3(American Astronomical Society, 2022-12-01) Tsygankov, Sergey S.; Doroshenko, Victor; Poutanen, Juri; Heyl, Jeremy; Mushtukov, Alexander A.; Caiazzo, Ilaria; Marco, Alessandro Di; Forsblom, Sofia V.; González-Caniulef, Denis; Klawin, Moritz; Monaca, Fabio La; Malacaria, Christian; Marshall, Herman L.; Muleri, Fabio; Ng, Mason; Suleimanov, Valery F.; Sunyaev, Rashid A.; Turolla, Roberto; Agudo, Iván; Antonelli, L.A.; Bachetti, Matteo; Baldini, Luca; Baumgartner, Wayne H.; Bellazzini, Ronaldo; Bianchi, Stefano; Bongiorno, Stephen D.; Bonino, Raffaella; Brez, Alessandro; Bucciantini, Niccolò; Capitanio, Fiamma; Castellano, Simone; Cavazzuti, Elisabetta; Ciprini, Stefano; Costa, Enrico; Rosa, Alessandra De; Monte, Ettore Del; Gesu, Laura Di; Lalla, Niccolò Di; Donnarumma, Immacolata; Dovčiak, Michal; Ehlert, Steven R.; Enoto, Teruaki; Evangelista, Yuri; Fabiani, Sergio; Ferrazzoli, Riccardo; Garcia, Javier A.; Gunji, Shuichi; Hayashida, Kiyoshi; Iwakiri, Wataru; Jorstad, Svetlana G.; Karas, Vladimir; Kitaguchi, Takao; Kolodziejczak, Jeffery J.; Krawczynski, Henric; Latronico, Luca; Liodakis, Ioannis; Maldera, Simone; Manfreda, Alberto; Marin, Frédéric; Marinucci, Andrea; Marscher, Alan P.; Matt, Giorgio; Mitsuishi, Ikuyuki; Mizuno, Tsunefumi; Ng, C.-Y.; O'Dell, Stephen L.; Omodei, Nicola; Oppedisano, Chiara; Papitto, Alessandro; Pavlov, George G.; Peirson, Abel L.; Perri, Matteo; Pesce-Rollins, Melissa; Petrucci, Pierre-Olivier; Pilia, Maura; Possenti, Andrea; Puccetti, Simonetta; Ramsey, Brian D.; Rankin, John; Ratheesh, Ajay; Romani, Roger W.; Sgrò, Carmelo; Slane, Patrick; Soffitta, Paolo; Spandre, Gloria; Tamagawa, Toru; Tavecchio, Fabrizio; Taverna, Roberto; Tawara, Yuzuru; Tennant, Allyn F.; Thomas, Nicolas E.; Tombesi, Francesco; Trois, Alessio; Vink, Jacco; Weisskopf, Martin C.; Wu, Kinwah; Xie, Fei; Zane, SilviaCen X-3 is the first X-ray pulsar discovered 50 years ago. Radiation from such objects is expected to be highly polarized due to birefringence of plasma and vacuum associated with propagation of photons in presence of the strong magnetic field. Here we present results of the observations of Cen X-3 performed with the Imaging X-ray Polarimetry Explorer. The source exhibited significant flux variability and was observed in two states different by a factor of ~20 in flux. In the low-luminosity state no significant polarization was found either in pulse phase-averaged (with the 3𝜎 upper limit of 12%) or phase-resolved data (the 3𝜎 upper limits are 20-30%). In the bright state the polarization degree of 5.8% ± 0.3% and polarization angle of $49.°6 ±1.°5 with significance of about 20σ was measured from the spectro-polarimetric analysis of the phase-averaged data. The phase-resolved analysis showed a significant anti-correlation between the flux and the polarization degree as well as strong variations of the polarization angle. The fit with the rotating vector model indicates a position angle of the pulsar spin axis of about 49° and a magnetic obliquity of 17°. The detected relatively low polarization can be explained if the upper layers of the neutron star surface are overheated by the accreted matter and the conversion of the polarization modes occurs within the transition region between the upper hot layer and a cooler underlying atmosphere. A fraction of polarization signal can also be produced by reflection of radiation from the neutron star surface and the accretion curtain.Item The X-ray polarization view of Mrk~421 in an average flux state as observed by the Imaging X-ray Polarimetry Explorer(2022-09-15) Gesu, Laura Di; Donnarumma, Immacolata; Tavecchio, Fabrizio; Agudo, Ivan; Barnounin, Thibault; Cibrario, Nicolò; Lalla, Niccolò Di; Marco, Alessandro Di; Escudero, Juan; Errando, Manel; Jorstad, Svetlana G.; Kim, Dawoon; Kouch, Pouya M.; Lindfors, Elina; Liodakis, Ioannis; Madejski, Grzegorz; Marshall, Herman L.; Marscher, Alan P.; Middei, Riccardo; Muleri, Fabio; Myserlis, Ioannis; Negro, Michela; Omodei, Nicola; Pacciani, Luigi; Paggi, Alessandro; Perri, Matteo; Puccetti, Simonetta; Antonelli, L.A.; Bachetti, Matteo; Baldini, Luca; Baumgartner, Wayne H.; Bellazzini, Ronaldo; Bianchi, Stefano; Bongiorno, Stephen D.; Bonino, Raffaella; Brez, Alessandro; Bucciantini, Niccolò; Capitanio, Fiamma; Castellano, Simone; Cavazzuti, Elisabetta; Ciprini, Stefano; Costa, Enrico; Rosa, Alessandra De; Monte, Ettore Del; Doroshenko, Victor; Dovčiak, Michal; Ehlert, Steven R.; Enoto, Teruaki; Evangelista, Yuri; Fabiani, Sergio; Ferrazzoli, Riccardo; Garcia, Javier A.; Gunji, Shuichi; Hayashida, Kiyoshi; Heyl, Jeremy; Iwakiri, Wataru; Karas, Vladimir; Kitaguchi, Takao; Kolodziejczak, Jeffery J.; Krawczynski, Henric; Monaca, Fabio La; Latronico, Luca; Maldera, Simone; Manfreda, Alberto; Marin, Frédéric; Marinucci, Andrea; Massaro, Francesco; Matt, Giorgio; Mitsuishi, Ikuyuki; Mizuno, Tsunefumi; Ng, C.-Y.; O'Dell, Stephen L.; Oppedisano, Chiara; Papitto, Alessandro; Pavlov, George G.; Peirson, Abel L.; Pesce-Rollins, Melissa; Petrucci, Pierre-Olivier; Pilia, Maura; Possenti, Andrea; Poutanen, Juri; Ramsey, Brian D.; Rankin, John; Ratheesh, Ajay; Romani, Roger W.; Sgrò, Carmelo; Slane, Patrick; Soffitta, Paolo; Spandre, Gloria; Tamagawa, Toru; Taverna, Roberto; Tawara, Yuzuru; Tennant, Allyn F.; Thomas, Nicolas E.; Tombesi, Francesco; Trois, Alessio; Tsygankov, Sergey; Turolla, Roberto; Vink, Jacco; Weisskopf, Martin C.; Wu, Kinwah; Xie, Fei; Zane, SilviaParticle acceleration mechanisms in supermassive black hole jets, such as shock acceleration, magnetic reconnection, and turbulence, are expected to have observable signatures in the multi-wavelength polarization properties of blazars. The recent launch of the Imaging X-ray Polarimetry Explorer (IXPE) enables us, for the first time, to use polarization in the X-ray band (2-8 keV) to probe the properties of the jet synchrotron emission in high-frequency-peaked BL Lac objects (HSPs). We report the discovery of X-ray linear polarization (degree 𝛱_x =15% and electric-vector position angle ψ_x = 35° ± 4°) from the jet of the HSP Mrk~421 in an average X-ray flux state. At the same time, the degree of polarization at optical, infrared, and millimeter wavelengths was found to be lower by at least a factor of 3. During the IXPE pointing, the X-ray flux of the source increased by a factor of 2.2, while the polarization behavior was consistent with no variability. The higher level of 𝛱_x compared to longer wavelengths, and the absence of significant polarization variability, suggest a shock as the most likely X-ray emission site in the jet of Mrk 421 during the observation. The multiwavelength polarization properties are consistent with an energy-stratified electron population, where the particles emitting at longer wavelengths are located farther from the acceleration site, where they experience a more disordered magnetic field.Item Polarization properties of the weakly magnetized neutron star X-ray binary GS 1826-238 in the high soft state(American Astronomical Society, 2023-02-01) Capitanio, Fiamma; Fabiani, Sergio; Gnarini, Andrea; Ursini, Francesco; Ferrigno, Carlo; Matt, Giorgio; Poutanen, Juri; Cocchi, Massimo; Mikusincova, Romana; Farinelli, Ruben; Bianchi, Stefano; Kajava, Jari J.E.; Muleri, Fabio; Sanchez-Fernandez, Celia; Soffitta, Paolo; Wu, Kinwah; Agudo, Ivan; Antonelli, L.A.; Bachetti, Matteo; Baldini, Luca; Baumgartner, Wayne H.; Bellazzini, Ronaldo; Bongiorno, Stephen D.; Bonino, Raffaella; Brez, Alessandro; Bucciantini, Niccolò; Castellano, Simone; Cavazzuti, Elisabetta; Ciprini, Stefano; Costa, Enrico; Rosa, Alessandra De; Monte, Ettore Del; Gesu, Laura Di; Lalla, Niccolo Di; Marco, Alessandro Di; Donnarumma, Immacolata; Doroshenko, Victor; Dovčiak, Michal; Ehlert, Steven R.; Enoto, Teruaki; Evangelista, Yuri; Ferrazzoli, Riccardo; Garcia, Javier A.; Gunji, Shuichi; Hayashida, Kiyoshi; Heyl, Jeremy; Iwakiri, Wataru; Jorstad, Svetlana G.; Karas, Vladimir; Kitaguchi, Takao; Kolodziejczak, Jeffery J.; Krawczynski, Henric; Monaca, Fabio La; Latronico, Luca; Liodakis, Ioannis; Maldera, Simone; Manfreda, Alberto; Marin, Fréedèric; Marinucci, Andrea; Marscher, Alan P.; Marshall, Herman L.; Mitsuishi, Ikuyuki; Mizuno, Tsunefumi; Ng, C.-Y.; O'Dell, Stephen L.; Omodei, Nicola; Oppedisano, Chiara; Papitto, Alessandro; Pavlov, George G.; Peirson, Abel L.; Perri, Matteo; Pesce-Rollins, Melissa; Petrucci, Pierre-Olivier; Pilia, Maura; Possenti, Andrea; Puccetti, Simonetta; Ramsey, Brian D.; Rankin, John; Ratheesh, Ajay; Romani, Roger W.; Sgrò, Carmelo; Slane, Patrick; Spandre, Gloria; Tamagawa, Toru; Tavecchio, Fabrizio; Taverna, Roberto; Tawara, Yuzuru; Tennant, Allyn F.; Thomas, Nicholas E.; Tombesi, Francesco; Trois, Alessio; Tsygankov, Sergey S.; Turolla, Roberto; Vink, Jacco; Weisskopf, Martin C.; Xie, Fei; Zane, SilviaThe launch of the Imaging X-ray Polarimetry Explorer (IXPE) on 2021 December 9 has opened a new window in X-ray astronomy. We report here the results of the first IXPE observation of a weakly magnetized neutron star, GS 1826-238, performed on 2022 March 29-31 when the source was in a high soft state. An upper limit (99.73% confidence level) of 1.3% for the linear polarization degree is obtained over the IXPE 2-8 keV energy range. Coordinated INTEGRAL and NICER observations were carried out simultaneously with IXPE. The spectral parameters obtained from the fits to the broad-band spectrum were used as inputs for Monte Carlo simulations considering different possible geometries of the X-ray emitting region. Comparing the IXPE upper limit with these simulations, we can put constraints on the geometry and inclination angle of GS 1826-238.