Search for hard x-ray emission from millisecond pulsars and compact binaries in the globular cluster 47 Tuc

X-ray binaries in globular clusters provide a powerful tool for the exploration of the evolution of compact binaries and their host globular clusters. Recent x-ray and optical studies of these systems have yielded long-sought binary periods and fundamental properties for two sources (in NGC 6624 and M 15). It appears that tidal capture formation of compact binaries in globular clusters can proceed by several different routes and lead to exotic systems such as the white dwarf-neutron star binary with an 11-minute period recently discovered in NGC 6624. Combined with previously reported long-term periods for several globular cluster (and field) x-ray sources, this suggests again that many of these systems may in fact be hierarchical triple systems. The prospects for forming these in the dense cores of clusters undergoing core collapse is discussed, and searches for color gradients in the cores of globular clusters showing cusps in their central surface brightness distribution are presented. A program to test for the high central density of binaries (and triples) expected in cusp clusters by searching for diffuse line emission from their constituent cataclysmic variables is briefly described. Finally, the case for globular cluster disruption and the formation of galactic x-ray burst source is reviewed in light of recent developments.

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High-Resolution X-ray Imaging of a Globular Cluster Core: Compact Binaries in 47Tuc

Science ◽

10.1126/science.1061135 ◽

2001 ◽

Vol 292 (5525) ◽

pp. 2290-2295 ◽

Cited By ~ 162

Author(s):

J. E. Grindlay

Keyword(s):

High Resolution ◽

Globular Cluster ◽

Cluster Core ◽

X Ray ◽

Compact Binaries ◽

X Ray Imaging

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Chandra and HST studies of six millisecond pulsars in the globular cluster M13

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab117 ◽

2021 ◽

Vol 502 (2) ◽

pp. 1596-1604

Author(s):

Jiaqi Zhao ◽

Yue Zhao ◽

Craig O Heinke

Keyword(s):

Globular Cluster ◽

White Dwarf ◽

Hubble Space Telescope ◽

X Rays ◽

Power Law Model ◽

Millisecond Pulsars ◽

X Ray ◽

V Band ◽

Upper Limit ◽

Single Power

ABSTRACT We analyse 55 ks of Chandra X-ray observations of the Galactic globular cluster (GC) M13. Using the latest radio timing positions of six known millisecond pulsars (MSPs) in M13 from Wang et al. (2020), we detect confident X-ray counterparts to five of the six MSPs at X-ray luminosities of LX(0.3–8 keV)∼3 × 1030–1031 erg s−1, including the newly discovered PSR J1641+3627F. There are limited X-ray counts at the position of PSR J1641+3627A, for which we obtain an upper limit LX < 1.3 × 1030 erg s−1. We analyse X-ray spectra of all six MSPs, which are well described by either a single blackbody (BB) or a single power-law model. We also incorporate optical/UV imaging observations from the Hubble Space Telescope (HST) and find optical counterparts to PSR J1641+3627D and J1641+3627F. Our colour–magnitude diagrams indicate the latter contains a white dwarf, consistent with the properties suggested by radio timing observations. The counterpart to J1641+3627D is only visible in the V band; however, we argue that the companion to J1641+3627D is also a white dwarf, since we see a BB-like X-ray spectrum, while MSPs with non-degenerate companions generally show non-thermal X-rays from shocks between the pulsar and companion winds. Our work increases the sample of known X-ray and optical counterparts of MSPs in GCs.

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Multi-epoch X-ray imaging of globular cluster M62 with Chandra

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2462 ◽

2020 ◽

Vol 498 (1) ◽

pp. 292-303

Author(s):

Kwangmin Oh ◽

C Y Hui ◽

K L Li ◽

A K H Kong

Keyword(s):

Globular Cluster ◽

Globular Clusters ◽

Imaging Data ◽

Short Term ◽

Observation Window ◽

X Ray ◽

Compact Binaries ◽

X Ray Imaging ◽

Low Mass

ABSTRACT Using archival spectral-imaging data with a total exposure of ∼144 ks obtained by Chandra, 43 X-ray sources are detected within the half-light radius of globular cluster M62 (NGC 6266). Based on the X-ray colour–luminosity diagram or the positional coincidences with known sources, we have classified these sources into different groups of compact binaries including cataclysmic variable (CV), quiescent low-mass X-ray binary (qLMXB), millisecond pulsar, and black hole (BH). Candidates of the X-ray counterparts of 12 CVs, 4 qLMXBs, 2 MSPs, and 1 BH are identified in our analysis. The data used in our analysis consist of two frames separated by 12 yr, which enable us to search for the long-term variability as well as the short-term X-ray flux variability within each observation window. Evidence for the short-term variability and long-term variability have been found in 7 and 12 sources, respectively. For a number of bright sources with X-ray luminosities Lx ≳ 1032 erg s−1, we have characterized their spectral properties in further details. By comparing the X-ray population in M62 with those in several other prototypical globular clusters, we found the proportion of bright sources is larger in M62 that can possibly be a result of their active dynamical formation processes.

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QPOs in compact binaries from small scale eruptions in an inner magnetized disk

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3410 ◽

2020 ◽

Author(s):

Nicolas Scepi ◽

Mitchell C Begelman ◽

Jason Dexter

Keyword(s):

Rapid Heating ◽

Small Scale ◽

Type B ◽

Periodic Oscillations ◽

X Ray ◽

Compact Binaries ◽

Heating And Cooling ◽

Low Mass ◽

X Ray Binaries ◽

Standard Disk

Abstract Dwarf novæ (DNe) and low mass X-ray binaries (LMXBs) are compact binaries showing variability on time scales from years to less than seconds. Here, we focus on explaining part of the rapid fluctuations in DNe, following the framework of recent studies on the monthly eruptions of DNe that use a hybrid disk composed of an outer standard disk and an inner magnetized disk. We show that the ionization instability, that is responsible for the monthly eruptions of DNe, is also able to operate in the inner magnetized disk. Given the low density and the fast accretion time scale of the inner magnetized disk, the ionization instability generates small, rapid heating and cooling fronts propagating back and forth in the inner disk. This leads to quasi-periodic oscillations (QPOs) with a period of the order of 1000 s. A strong prediction of our model is that these QPOs can only develop in quiescence or at the beginning/end of an outburst. We propose that these rapid fluctuations might explain a subclass of already observed QPOs in DNe as well as a, still to observe, subclass of QPOs in LMXBs. We also extrapolate to the possibility that the radiation pressure instability might be related to Type B QPOs in LMXBs.

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