12:00–1:00 pm ERC 501
Host: Jeff McMahon
Vikram Dwarkadas "UltraLuminous X-Ray Sources, and an Intriguing New Source"
UltraLuminous X-Ray Sources, and an Intriguing New Source. Abstract: Ultraluminous X-ray sources (ULXs) are point-like sources found far from the nucleus of external galaxies, with X-ray luminosities that exceed 1e39 erg/s. Observations and modelling suggest that the majority of ULXs could be highly magnetized neutron stars undergoing super-Eddington accretion, although the brightest ones could contain intermediate mass black holes. I will give a very brief overview of ULXs. I will then proceed to describe an intriguing new transient ULX that we discovered in one of my Chandra observations, which faded by a factor > 7 in luminosity in about 2 months, and discuss possibilities that could explain its transient nature.
Erin Healy "The Simons Observatory Design and Calibration"
The Simons Observatory is an upcoming ground-based experiment located in the Atacama Desert in Chile, designed to study the cosmic microwave background (CMB) across a range of angular scales and frequencies. The observatory will consist of both large-and small-aperture telescopes, each with unique science goals. The large-aperture (6m) telescope will observe the CMB at small angular scales, addressing a host of cosmological and astrophysical topics, including probing for new particles and interactions, constraining the sum of the neutrino masses, and providing insights into galaxy formation and the transient universe. The small-aperture (0.5m) telescopes, will make degree-scale measurements of the CMB, with the aim of constraining the primordial gravity wave signal. To achieve its scientific goals, the Simons Observatory will field over 60,000 transition-edge sensors, sensitive to both temperature and polarization. To obtain precise measurements of the CMB, exquisite control of the systematics is required. I will describe ongoing efforts to study a broad range of instrument systematics with a test cryostat at Chicago. I will also describe a novel approach to calibrating the absolute polarization angle of the small-aperture telescopes. This calibration is essential for constraining primordial gravitational waves, and it will also contribute to an improved constraint on cosmic birefringence.
