Bogdanov, Slavkovan den Berg, MaureenServillat, MathieuHeinke, Craig O.Grindlay, Jonathan E.Stairs, Ingrid H.Ransom, Scott M.Freire, Paulo C. C.Bégin, SteveBecker, Werner2019-09-252011Bogdanov, Slavko, Maureen van den Berg, Mathieu Servillat, Craig O. Heinke, Jonathan E. Grindlay, Ingrid H. Stairs, Scott M. Ransom, Paulo C. C. Freire, Steve Bégin, and Werner Becker. 2011. “CHANDRAX-RAY OBSERVATIONS OF 12 MILLISECOND PULSARS IN THE GLOBULAR CLUSTER M28.” The Astrophysical Journal 730 (2): 81. https://doi.org/10.1088/0004-637x/730/2/81.0004-637X1538-4357http://nrs.harvard.edu/urn-3:HUL.InstRepos:41399768We present a Chandra X-ray Observatory investigation of the millisecond pulsars in the globular cluster M28 (NGC 6626). In what is one of the deepest X-ray observations of a globular cluster, we firmly detect seven and possibly detect two of the 12 known M28 pulsars. With the exception of PSRs B1821-24 and J1824-2452H, the detected pulsars have relatively soft spectra, with X-ray luminosities 10(30)-10(31) erg s(-1) (0.3-8 keV), similar to most "recycled" pulsars in 47 Tucanae and the field of the Galaxy, implying thermal emission from the pulsar magnetic polar caps. We present the most detailed X-ray spectrum to date of the energetic PSR B1821-24. It is well described by a purely non-thermal spectrum with spectral photon index Gamma = 1.23 and luminosity 1.4x10(33)Theta (D/5.5 kpc)(2) erg s(-1) (0.3-8 keV), where Theta is the fraction of the sky covered by the X-ray emission beam(s). We find no evidence for the previously reported line emission feature around 3.3 keV, most likely as a consequence of improvements in instrument calibration. The X-ray spectrum and pulse profile of PSR B1821-24 suggest that the bulk of unpulsed emission from this pulsar is not of thermal origin, and is likely due to low-level non-thermal magnetospheric radiation, an unresolved pulsar wind nebula, and/or small-angle scattering of the pulsed X-rays by interstellar dust grains. The peculiar binary PSR J1824-2452H shows a relatively hard X-ray spectrum and possible variability at the binary period, indicative of an intrabinary shock formed by interaction between the relativistic pulsar wind and matter from its non-degenerate companion star.en-USJournal Article2019-09-2510.1088/0004-637X/730/2/81