J/ApJ/892/16 X-ray mass segregation effect in GCs. III. M28 (Cheng+, 2020)
Exploring the mass segregation effect of X-ray sources in globular clusters.
III. Signs of binary disruption in M28.
Cheng Z., Mu H., Li Z., Xu X., Wang W., Li X.
<Astrophys. J., 892, 16-16 (2020)>
=2020ApJ...892...16C 2020ApJ...892...16C (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular; X-ray sources
Keywords: Globular star clusters; X-ray binary stars; Stellar dynamics
Dynamical friction; Tidal disruption
Abstract:
Using archival Chandra observations with a total effective exposure of
323ks, we derive an updated catalog of point sources in the bulge
globular cluster M28. The catalog contains 502 X-ray sources within an
area of ∼475arcmin2, and more than 90% of these sources are first
detected in this cluster. We find significant dips in the radial
distribution profiles of X-ray sources in M28, and the projected
distance and width of the distribution dip for bright
(LX≳4.5x1030erg/s) X-ray sources are larger than for faint
(LX≲4.5x1030erg/s) sources. Fitting with the "generalized King
model" gives a slightly larger average mass for the bright sources
(1.30±0.15M☉) than for the faint ones (1.09±0.14M☉),
which supports a universal delay in mass segregation between heavy
objects in globular clusters. We show that the dynamical age of M28 is
comparable to that of Terzan 5 and much smaller than that of 47 Tuc,
but M28 is evolving faster (i.e., with a shorter two-body relaxation
timescale) than 47 Tuc. These features may suggest an acceleration
effect of cluster dynamical evolution by tidal shock in M28. Besides,
we find an abnormal deficiency of X-ray sources in the central region
(R≲1.5') of M28 compared with its outskirts, which indicates that M28
may have suffered an early phase of primordial binary disruption
within its central region, and the mass segregation effect will erase
such a phenomenon as clusters evolve to an older dynamical age.
Description:
We use eight Chandra observations of M28, all taken with the Advanced
CCD Imaging Spectrometer (ACIS) taken between 2002 September 9 and
2015 Aug 11 (ObsIDs: 2683, 2684, 2685, 9132, 9133, 16748, 16749 and
16750).
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
18 24 32.73 -24 52 13.0 M28 = NGC 6626
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 230 502 Main Chandra source catalog
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See also:
B/chandra : The Chandra Archive Log (CXC, 1999-2014)
VII/195 : Globular Clusters in the Milky Way (Harris, 1996)
VII/202 : Globular Clusters in the Milky Way (Harris, 1997)
J/AJ/121/916 : HST obs. of NGC 2298, 5897, 6535, and 6626 (Testa+, 2001)
J/ApJS/166/249 : Stellar dynamics & PMs in 47Tuc (McLaughlin+, 2006)
J/MNRAS/482/5138 : Galactic GC mean PMs & velocities (Baumgardt+, 2019)
J/ApJ/876/59 : Chandra X-ray sources in 47 Tuc (Cheng+, 2019)
J/ApJ/883/90 : X-ray mass segregation effect in GCs. II. (Cheng+, 2019)
J/A+A/632/A3 : MUSE binaries in NGC 3201 (Giesers+, 2019)
J/A+A/651/A47 : Variable stars in VVV globulars. II. (Alonso-Garcia+, 2021)
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Seq [1/502] X-ray catalog sequence number,
RA sorted
5- 22 A18 --- Name IAU designation (HHMMSS.ss+DDMMSS.s; J2000)
24- 33 F10.6 deg RAdeg [275.88/276.42] Right Ascension (J2000)
35- 44 F10.6 deg DEdeg [-25.1/-24.7] Declination (J2000)
46- 48 F3.1 arcsec PosErr [0/1.6] 1σ positional uncertainty
50- 54 F5.1 arcsec R [1.8/924] Projected distance
from cluster center (1)
56- 62 E7.2 --- PB [0/0.051] logarithmic Poisson probability
of a detection not being a source
64- 70 F7.1 ct Cnet-t [4.6/11352] Full (0.5-8keV) band
aperture-corrected source counts
72- 78 F7.1 ct b_Cnet-t [0.2/11245] 1σ lower bound of Cnet-t
80- 86 F7.1 ct B_Cnet-t [8.3/114560] 1σ upper bound of Cnet-t
88- 94 F7.1 ct Cnet-s [-5.7/10737] Soft (0.5-2 keV) band
aperture-corrected source counts
96-102 F7.1 ct b_Cnet-s [0/10633]? 1σ lower bound of Cnet-s
104-110 F7.1 ct B_Cnet-s [2/10842] 1σ upper bound of Cnet-s
112-117 F6.1 ct Cnet-h [-5.2/3713] Hard (2-8keV) band
aperture-corrected source counts
119-124 F6.1 ct b_Cnet-h [0/3652]? 1σ lower bound of Cnet-h
126-131 F6.1 ct B_Cnet-h [1/3774] 1σ upper bound of Cnet-h
133-140 E8.2 ph/cm2/s Flux-t [6e-8/0.00014] Full (0.5-8keV) band
photon flux
142-150 E9.2 ph/cm2/s Flux-s [-1.1e-7/7.8e-5] Soft (0.5-8keV) band
photon flux
152-160 E9.2 ph/cm2/s Flux-h [-7.6e-8/5.1e-5] Hard (2-8keV) band
photon flux
162-169 E8.2 10-7W Lum-tc [8.8e+29/1.5e+33] Absorption-corrected
intrinsic 0.5-8.0keV luminosity; erg/s (2)
171-178 E8.2 10-7W Lum-sc [2.6e+29/1.2e+33] Absorption-corrected
intrinsic 0.5-2.0keV luminosity; erg/s (2)
180-187 E8.2 10-7W Lum-hc [6.1e+29/1.2e+33] Absorption-corrected
intrinsic 2.0-8.0keV luminosity; erg/s (2)
189-193 F5.2 [cm-2] logNH [21.3/22.7] Log of absorption column density
195-199 F5.2 [cm-2] b_logNH [21.3/22.6]? 1σ lower bound of logNH (3)
201-205 F5.2 [cm-2] B_logNH [21.4/22.8]? 1σ upper bound of logNH (3)
207-210 F4.2 --- Gamma [0.09/3.3] Photon index of power-law model
212-215 F4.2 --- b_Gamma [0.2/3.2]? 1σ lower bound of Gamma (3)
217-220 F4.2 --- B_Gamma [0.5/3]? 1σ upper bound of Gamma (3)
222-225 I4 --- dof [1179/1183] Cstatistic degrees of freedom
227-230 I4 --- CStat [249/1909] Cstatistic values using
1192 PHA bins
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Note (1): The cluster center coordinates adopted is
RAJ2000=18:24:32.73,DEJ2000=-24:52:13.07 (Miocchi+ 2013ApJ...774..115M 2013ApJ...774..115M).
Note (2): X-ray luminosities were derived from the model spectrum, assuming
a distance of 5.5kpc (Harris, 1996, Cat. VII/195).
Note (3): A blank in these columns indicates a NaN value.
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History:
From electronic version of the journal
References:
Cheng et al. Paper I. 2019ApJ...876...59C 2019ApJ...876...59C Cat. J/ApJ/876/59
Cheng et al. Paper II. 2019ApJ...883...90C 2019ApJ...883...90C Cat. J/ApJ/883/90
Cheng et al. Paper III. 2020ApJ...892...16C 2020ApJ...892...16C This catalog
Cheng et al. Paper IV. 2020ApJ...904..198C 2020ApJ...904..198C
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 10-Aug-2021