The optical counterpart of an Ultra-luminous X-Ray Source in NGC 5204

Ultra-luminous X-Ray sources are extra-nuclear point sources in external galaxies with $L_X=10^{39}$--$10^{41}$ erg/s and are among the most poorly understood X-ray sources. To help understand their nature, we are trying to identify their optical counterparts by combining images from the Hubble Space Telescope and the Chandra Observatory. Here we report upon the optical counterpart for the ULX in NGC 5204, which has average X-ray luminosity of $\sim3\times10^{39}$ erg/s and has varied by a factor of 50% over the last 10 years. A unique optical counterpart to this ULX is found by carefully comparing the Chandra ACIS images and HST WFPC2 and ACS/HRC images. The spectral energy distribution and the HST/STIS FUV spectrum of this object show that it is a B0 Ib supergiant star with peculiarities, including the $\lambda$1240 N V emission line that is uncommon in B stellar spectra but has been predicted for X-ray illuminated accretion disks and seen in some X-ray binaries. Study of its FUV spectrum leads to a binary model for this ULX in which the B0 Ib supergiant is overflowing its Roche Lobe and accreting onto the compact primary, probably a black hole. This picture predicts an orbital period of $\sim10$ days for different black hole mass, which can be tested by future observations

Low-background performance of a monolithic InSb CCD array

A 20 element monolithic InSb charge coupled device (CCD) detector array was measured under low background conditions to assess its potential for orbital astronomical applications. At a temperature of 64 K, previous results for charge transfer efficiency (CTE) were reproduced, and a sensitivity of about 2 x 10 to the minus 15th power joules was measured. At 27 and 6 K, extended integration times were achieved, but CTE was substantially degraded. The noise was approximately 6000 charges, which was in excess of the level where statistical fluctuations from the illumination could be detected. A telescope demonstration was performed showing that the array sensitivity and difficulty of operation were not substantially different from laboratory levels. Ways in which the device could be improved for astronomical applications were discussed

Different Methods of Forming Cold Fronts in Non-Merging Clusters

Sharp edges in X-ray surface brightness with continuous gas pressure called cold fronts have been often found in relaxed galaxy clusters such as Abell 496. Models that explain cold fronts as surviving cores of head-on subcluster mergers do not work well for these clusters and competing models involving gas sloshing have been recently proposed. Here, we test some concrete predictions of these models in a combined analysis of density, temperature, metal abundances and abundance ratios in a deep Chandra exposure of Abell 496. We confirm that the chemical discontinuities found in this cluster are not consistent with a core merger remnant scenario. However, we find chemical gradients across a spiral "arm" discovered at 73 kpc north of the cluster center and coincident with the sharp edge of the main cold front in the cluster. Despite the overall SN Ia iron mass fraction dominance found within the cooling radius of this cluster, the metal enrichment along the arm, determined from silicon and iron abundances, is consistent with a lower SN Ia iron mass fraction (51% +- 14%) than that measured in the surrounding regions (85% +- 14%). The "arm" is also significantly colder than the surroundings by 0.5-1.6 keV. The arm extends from a boxy colder region surrounding the center of the cluster, where two other cold fronts are found. This cold arm is a prediction of current high resolution numerical simulations as a result of an off-center encounter with a less massive pure dark matter halo and we suggest that the cold fronts in A496 provide the first clear corroboration of such model, where the closest encounter happened ~ 0.5 Gyr ago. We also argue for a possible candidate dark matter halo responsible for the cold fronts in the outskirts of A496.Comment: 11 ApJ pages, 1 Table, 16 Figures, accepted for publication in the Astrophysical Journal. For full version with all hi-res figures click on http://www.astro.lsa.umich.edu/~rdupke/a496sub.pd

Estimated National and Regional Impact of COVID-19 on Elective Case Volume in Aesthetic Plastic Surgery.

BACKGROUND:In efforts to help alleviate the strain placed on healthcare during the COVID-19 pandemic, The American Society of Plastic Surgery (ASPS) recommended suspending elective procedures on March 19, 2020. When this suspension was enacted, it was unknown when cases would resume. OBJECTIVES:This analysis aims to estimate the regional economic impact of the pandemic specifically with regards to elective, aesthetic surgical procedures. As knowledge regarding the effects of the pandemic has grown, the authors then evaluated the accuracy of our projected estimates when compared to actual events. METHODS:Using the ASPS 2018 Plastic Surgery Statistics Report, regional case volume and surgeons\u27 fees were obtained for the top five aesthetic procedures. Models developed by the Institute for Health Metrics and Evaluation (IHME) were used to estimate the anticipated duration of suspension by using the date that no ventilators would be required to for COVID-19 patients. This duration was used to calculate the volume of cases that would not occur. RESULTS:These estimates predict up to 1.3 billion fewer dollars will be collected in surgeons\u27 fees, representing a 20% loss compared to 2018. The South Atlantic region is predicted to have the greatest number of OR days lost; However, the Mountain and Pacific regions are estimated to have the greatest loss in case volume and surgeons\u27 fees. CONCLUSIONS:The cumulative impact of the pandemic on life, society, and the economy is tremendous. This analysis may help guide surgeons\u27 responses during and after the crisis

The Effect of Environment on the X-Ray Emission from Early-Type Galaxies

In order to help understand the phenomena of X-ray emission from early-type galaxies, we obtained an optically flux-limited sample of 34 early-type galaxies, observed with ROSAT. A previous analysis of this sample suggested that the most X-ray luminous galaxies were in rich environments. Here we investigate environmental influences quantitatively, and find a positive correlation between L_B/L_X and the local galaxy density. We suggest that this correlation occurs because the X-ray luminosity is enhanced either through accretion of the intergalactic gas or because the ambient medium stifles galactic winds. When the ambient medium is unimportant, partial or global galactic winds can occur, reducing L_B/L_X. These effects lead to the large observed dispersion in L_X at fixed L_B. We argue that the transition from global winds to partial winds is one of the principle reasons for the steep relationship between L_X and L_B. We discuss details of the data reduction not previously presented, and examine the dependence of L_X on the choice of outer source radius and background location. Effects of Malmquist bias are shown not to be important for the issues addressed. Finally, we compare the temperature deduced for these galaxies from different analyses of ROSAT and ASCA data.Comment: 29 pages, including 6 figures (ps); AASTeX 12pt,aaspp4 format; submitted to Ap

A Two Hour Quasi-Period in an Ultra-luminous X-Ray source in NGC628

Quasi-periodic oscillations and X-ray spectroscopy are powerful probes of black hole masses and accretion disks, and here we apply these diagnostics to an ultraluminous X-ray source (ULX) in the spiral galaxy NGC628 (M74). This object was observed four times over two years with the Chandra X-ray Observatory and XMM-Newton, with three long observations showing dramatic variability, distinguished by a series of outbursts with a quasi-period (QPO) of 4,000-7,000 seconds. This is unique behavior among both ULXs and Galactic X-ray binaries due to the combination of its burst-like peaks and deep troughs, its long quasi-periods, its high variation amplitudes of $>90$%, and its substantial variability between observations. The X-ray spectra is fitted by an absorbed accretion disk plus a power-law component, suggesting the ULX was in a spectral state analogous to the Low Hard state or the Very High state of Galactic black hole X-ray binaries. A black hole mass of $\sim2$--$20\times10^3 M_\odot$ is estimated from the $f_b$--$M_\bullet$ scaling relation found in the Galactic X-ray binaries and active galactic nuclei.Comment: 12 pages, 3 figures. accepted for publication in ApJ Lette

Fast Primal-Dual Gradient Method for Strongly Convex Minimization Problems with Linear Constraints

In this paper we consider a class of optimization problems with a strongly convex objective function and the feasible set given by an intersection of a simple convex set with a set given by a number of linear equality and inequality constraints. A number of optimization problems in applications can be stated in this form, examples being the entropy-linear programming, the ridge regression, the elastic net, the regularized optimal transport, etc. We extend the Fast Gradient Method applied to the dual problem in order to make it primal-dual so that it allows not only to solve the dual problem, but also to construct nearly optimal and nearly feasible solution of the primal problem. We also prove a theorem about the convergence rate for the proposed algorithm in terms of the objective function and the linear constraints infeasibility.Comment: Submitted for DOOR 201