Bulletin of the American Physical Society
Mid-Atlantic Section 2022 Meeting
Volume 67, Number 20
Friday–Sunday, December 2–4, 2022; University Park, PA, Pennsylvania State University
Session C04: Astrophysics I |
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Chair: Tiffany Lewis, NASA Goddard Space Flight Center Room: Pennsylvania State University Osmond 106 |
Saturday, December 3, 2022 9:00AM - 9:35AM |
C04.00001: Magnetars and Physics in Strong Magnetic Fields Invited Speaker: Zorawar Wadiasingh Neutron stars serve as useful laboratories to study physics under conditions of extreme density, gravity, and magnetic fields inaccessible terrestrially. Magnetars are a topical subclass of neutron stars with surface fields exceeding 10^10 Tesla, a regime where exotic untested QED processes may operate. Magnetars in our galaxy are largely observed through their X-ray/gamma-ray emission via bursts and persistent emission. In magnetars, the magnetic field is in the quantum electrodynamic (QED) domain where the cyclotron energy approaches or exceeds the electron rest mass. This defines the Schwinger or critical field of 4.41x10^9 Tesla and is a regime where exotic aspects of standard (but nonlinear and nonperturbative) QED are important. In this talk I will detail advanced spectral modeling of magnetars. Principal QED opacity processes will be discussed, namely magnetic pair production and photon splitting, which attenuate spectra at hard X-ray and higher energies. Opacity to photon splitting can be significant above 100 keV, introducing strong polarization that can be probed by future hard X-ray polarimetry instruments such as X-Calibur, or a future Compton telescope like AMEGO and COSI. Such instruments may finally confirm photon splitting can occur in nature, and inform on its selection rules and the non-pertubative regime of QED. |
Saturday, December 3, 2022 9:35AM - 9:47AM |
C04.00002: Discovery of extraordinary X-ray emission from magnetospheric interaction in the unique binary stellar system Epsilon Lupi Barnali Das, Véronique Petit, Michael Corcoran, Yael Naze, Asif ud-Doula, Ernst Paunzen, Gregg Wade, Alexandre David-Uraz, Coralie Neiner, Maurice Leutenegger, Poonam Chandra, Ayan Biswas, David Cohen, Matthew Shultz Magnetic massive stars are unique stellar laboratories to understand magnetospheric physics. This is due to the fact that their magnetic fields are strong, extremely stable, and can very often be approximated as a simple dipole, which makes it relatively easy to characterize. So far there have been several studies exploring different magnetospheric phenomena occurring in solitary magnetospheres, and their effects on stellar evolution. However, only a handful of studies exist that attempt to answer the question of what happens when binarity and magnetism are acting together. The unique stellar system Epsilon Lupi is probably one of the best test-beds to investigate this effect. It is the only known short-period binary where both stars are magnetic massive stars. The orbit is mildly eccentric so that variable magnetospheric interactions (if there are any) are expected. In order to investigate this aspect, we observed the system using the Neutron Star Interior Composition Explorer Mission (NICER, an X-ray telescope on the International Space Station) at orbital phases that are close to periastron and away from the periastron. Our NICER observations revealed the presence of strong and persistent inter-star magnetospheric interaction leading to an enhanced X-ray flux at periastron, especially over the more energetic part of the spectrum. I will discuss potential scenarios that can explain these observations, and further investigations that will be needed to rule out/confirm these scenarios. |
Saturday, December 3, 2022 9:47AM - 9:59AM |
C04.00003: Exploring the Initial B-Field Function of massive stars by simulating magnetic detectability in stars clusters Victor A Ramirez Delgado, Véronique Petit, Mary Oksala, James MacDonald, Zsolt Keszthelyi, Ylva Götberg, Shaquann S Seadrow, Pinar Cerrahoglu
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Saturday, December 3, 2022 9:59AM - 10:11AM |
C04.00004: An XMM-Newton Study of Narrow-Line Seyfert 1 Galaxies at z = 0.35−0.92 Zhibo Yu, Jiachen Jiang, Cosimo Bambi, Luigi Gallo, Dirk Grupe, Andrew C Fabian, Christopher Reynolds, William N Brandt We report a detailed analysis of the XMM-Newton spectra of six Narrow-Line Seyfert 1 (NLS1) galaxies at redshift z = 0.35−0.92. Their spectra all show soft X-ray excess emission below 2 keV with respect to the extrapolation of the 2−10 keV continuum. We compare our sources with a sample of NLS1s and BLS1s at lower redshifts in the literature. Our measurements show that our sample has a softer hard X-ray continuum than the lower-redshift sources at similar Eddington ratios. However, the quantified soft excess strength does not show an obvious discrepancy from previous studies of the lower-redshift sample. The systematic effect mainly lies in the bolometric correction factor. We further fit the spectra assuming two more physical models for the soft excess: warm Comptonization and relativistic reflection from the inner accretion disk. In the first scenario, we confirm the ubiquity of a warm (kTe,w ≈ 0.1−1 keV) and optically thick (τ ≈ 5−20) corona. In the second scenario, we find that a significant fraction of the energy of the accretion disk is released to the hot corona in order to explain the best-fit electron density parameter. These two models provide similarly good fits to the data. Due to the low signal-to-noise ratio in the iron emission band, we could not obtain good constraints on some of the parameters in the reflection model. Future X-ray missions like the Athena and self-consistent hybrid models for the soft excess emission might provide new insights about our NLS sample. |
Saturday, December 3, 2022 10:11AM - 10:23AM |
C04.00005: Investigating the Magnetic Incidence of Be Stars Patrick J Stanley, Federico Villadiego Forero, Robin Moore, Dax Moraes, Marisol Catalen Olais, Colin Folsom, Mary Oksala, Véronique Petit, Gregg Wade The current understanding of stellar magnetic fields is centered on the convective envelope of low mass stars and the resulting magnetic dynamo. However, it was discovered that 10% of massive O-, B-, and A-type stars, which are lacking large convective envelopes, are host to strong, globally organized magnetic fields. The 10% magnetic incidence is seemingly not present for a certain subset of massive stars known as Be stars. Be stars are B-type stars with Balmer emission lines that originate from a Keplerian disk. Additionally, they rotate at a significant fraction of their critical rotation rate. For these reasons, measuring magnetic fields in Be stars is incredibly difficult and none have been found to possess unambiguously-detected fields. Those difficulties could also mean that Be stars might possess magnetic fields but their signatures are completely masked by noise. Using a novel method that combines observation and synthetic models, we are able increase the signal to noise ratio of spectropolarimetric observations, allowing stricter constraints to be put on the upper limits of possible magnetic fields and gain a better understanding of the observational biases in the sample of 78 Be stars that have been observed in the context of the MiMeS Survey. We will then be able to determine whether the lack of known magnetic Be stars is compatible or not with the 10% incidence of magnetism in massive stars. |
Saturday, December 3, 2022 10:23AM - 10:35AM |
C04.00006: BlackCAT: A CubeSat for Detecting High-Redshift Gamma-Ray Bursts and Multi-Messenger Counterparts Joseph M Colosimo, Abe D Falcone, Tyler Anderson, Logan D Baker, Jacob Buffington, David N Burrows, Michael Betts, Zachary Catlin, Derek B Fox, Hannah M Grzybowski, Frederic Hancock, Evan C Jennerjahn, Jordan Josties, David M Palmer, Lukas R Stone, Mitchell Wages, Daniel Washington BlackCAT is a 6U CubeSat mission designed to monitor the soft x-ray sky, searching for distant gamma-ray bursts (GRBs), counterparts to gravitational-wave events, and other high-energy transient phenomena. The instrument makes use of an array of four event-driven X-ray hybrid CMOS detectors and a coded-aperture mask. This design provides a large field of view (~0.9 sr) while enabling sub-arcminute localization of sources, making BlackCAT an effective tool for finding bursts and flare events. BlackCAT’s sensitivity in the soft x-ray band will make it a particularly valuable detector of high-redshift GRBs, which can serve as powerful probes of star formation and reionization in the early universe. Ground and space-based follow-up observations of GRB afterglows, enabled by rapid alerts from BlackCAT, will allow measurements of redshifts and characterization of the environments in which bursts occurred. BlackCAT will also serve to complement various multi-messenger observatories, helping to identify and localize X-ray counterparts to gravitational-wave and neutrino events. In this presentation, we discuss the design of the BlackCAT CubeSat and its expected science capabilities. |
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