Deep Chandra Survey of the Small Magellanic Cloud. III. Formation Efficiency of High-mass X-Ray Binaries

We have compiled the most complete census of high-mass X-ray binaries (HMXBs) in the Small Magellanic Cloud with the aim to investigate the formation efficiency of young accreting binaries in its low-metallicity environment. In total, we use 123 X-ray sources with detections in our Chandra X-ray Visionary Program (XVP), supplemented by 14 additional (likely and confirmed) HMXBs identified by Haberl & Sturm that fall within the XVP area, but are neither detected in our survey (nine sources) nor matched with any of the 127 sources identified in the XVP data (five sources). Specifically, we examine the number ratio of the HMXBs [N(HMXBs)] to (a) the number of OB stars, (b) the local star formation rate (SFR), and (c) the stellar mass produced during the specific star formation burst, all as a function of the age of their parent stellar populations. Each of these indicators serves a different role, but in all cases we find that the HMXB formation efficiency increases as a function of time (following a burst of star formation) up to similar to 40-60 Myr, and then gradually decreases. The formation efficiency peaks at similar to 30-40 Myr with average rates of N(HMXB)/SFR = 339(-83)(+78) (M-circle dot/yr)(-1), and N(HMXB)/M-* = (8.74(-0.92)(+1.0)) x 10(-6) M-circle dot(-1,) in good agreement with previous estimates of the average formation efficiency in the broad similar to 20-60 Myr age range

Concordance: in-flight calibration of X-ray telescopes without absolute references

We describe a process for cross-calibrating the effective areas of X-ray telescopes that observe common targets. The targets are not assumed to be “standard candles” in the classic sense, in that we assume that the source fluxes have well-defined, but a priori unknown values. Using a technique developed by Chen et al. (2019) that involves a statistical method called shrinkage estimation, we determine effective area correction factors for each instrument that brings estimated fluxes into the best agreement, consistent with prior knowledge of their effective areas. We expand the technique to allow unique priors on systematic uncertainties in effective areas for each X-ray astronomy instrument and to allow correlations between effective areas in different energy bands. We demonstrate the method with several data sets from various X-ray telescopes