J/MNRAS/511/5964 X-ray study of MSPs in globular clusters (Zhao+, 2022)
A census of X-ray millisecond pulsars in globular clusters.
Zhao J., Heinke C.O.
<Mon. Not. R. Astron. Soc. 511, 5964-5983 (2022)>
=2022MNRAS.511.5964Z 2022MNRAS.511.5964Z (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Clusters, globular ; Pulsars ; Binaries, X-ray ;
Binaries, eclipsing ; Stars, faint ; Spectroscopy ; Photometry ;
X-ray sources
Keywords: stars: neutron; pulsars: general - Galaxy: centre -
globular clusters: general - X-rays: stars
Abstract:
We present a comprehensive census of X-ray millisecond pulsars (MSPs)
in 29 Galactic globular clusters (GCs), including 68 MSPs with
confirmed X-ray luminosities and 107 MSPs with X-ray upper limits. We
compile previous X-ray studies of GC MSPs, and add new analyses of six
MSPs (PSRs J1326-4728A, J1326-4728B, J1518+0204C, J1717+4308A,
J1737-0314A, and J1807-2459A) discovered in five GCs. Their X-ray
spectra are well described by a single blackbody model, a single
power-law model, or a combination of them, with X-ray luminosities
ranging from 1.9 * 1030 to 8.3 * 1031 erg/s. We find that most
detected X-ray MSPs have luminosities between ∼1030 and 3 * 1031
erg/s. Redback pulsars are a relatively bright MSP population with
X-ray luminosities of ∼2 * 1031 - 3 * 1032 erg/s. Black widows
show a bimodal distribution in X-ray luminosities, with eclipsing
black widows between ∼7 * 1030 and 2 * 1031 erg/s, while the two
confirmed non-eclipsing black widows are much fainter, with LX of
1.5-3 * 1030 erg/s, suggesting an intrinsic difference in the
populations. We estimate the total number of MSPs in 36 GCs by
considering the correlation between the number of MSPs and stellar
encounter rate in GCs, and suggest that between 600 and 1500 MSPs
exist in these 36 GCs. Finally, we estimate the number of
X-ray-detectable MSPs in the Galactic bulge, finding that 1-86 MSPs
with LX > 1033 erg/s, and 20-900 MSPs with LX > 1032 erg/s
should be detectable there.
Description:
Galactic globular clusters (GCs) are ideal birthplaces for low-mass
X-ray binaries (LMXBs), since the high stellar densities in GC cores
provide significant chances for stellar interactions, such as tidal
capture and exchange interactions. LMXBs are the progenitors of
millisecond pulsars (MSPs), where the neutron star (NS) is spun up by
accreting mass and angular momentum from its companion to a period of
a few milliseconds. Therefore, it is not surprising that GCs show an
overabundance of MSPs compared to the Galactic field, and many MSPs
exist in binary systems. In this paper, we present an X-ray survey for
all the radio-detected MSPs in Galactic GCs which have Chandra X-ray
observatory data, and which lack the confusion of bright LMXBs. We
also report the X-ray spectral analyses of two newly found MSPs in the
cluster Omega Centauri, using archival Chandra observations, and
statistically study the X-ray properties of GC MSPs, with particular
attention to the implications for X-ray studies of the population of
MSPs in the Galactic Centre, (i.e see section Introduction).
Based on the catalogue of pulsars in GCs (230 pulsars in 36 GCs to
date),we first produced a list of MSPs in GCs by defining their
spinning periods of P ≲ 25 ms. The boundary of rotational periods
between normal pulsars and MSPs is not solid and may vary depending on
the research of interests. Here, we chose ∼25 ms as the upper limit.
This initial filtering gave 210 MSPs in total, and each GC in the
catalogue harbours at least one MSP. To obtain the X-ray luminosities
of these MSPs, we looked into Chandra X-ray Observatory (CXO)
observations. Next, we proceed to data reduction on our selected MSPs
via Chandra tools for photometric data. Then, we set upper limits on
luminosities of 107 faint MPCs as explained along the section 2 Data
collection and reduction, we present our collection results in the
tablea1.dat. Secondly, for MPCs having well defined data, as
explicited in the section 3 Analysis and results, we extracted
luminosities with spectral models (BB and PL) on X-ray 0.3-8 KeV
Chandra spectra, we present these results in the table10.dat.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table10.dat 59 68 Determined X-ray 0.3-8 keV luminosities LX
of GC MSPs
tablea1.dat 52 107 Upper limits of X-ray luminosities for GC MSPs
not eligible to specific X-ray spectral analysis
refs.dat 206 46 References of GC MSPs with upper limits of
X-ray luminosities
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See also:
J/MNRAS/472/3706 : Globular cluster 47 Tuc Chandra studies (Bhattacharya+,2017)
J/ApJ/687/1019 : Chandra X-ray observations of M71 (Elsner+, 2008)
J/ApJ/625/796 : X-ray sources in the globular cluster 47 Tuc (Heinke+, 2005)
J/MNRAS/479/2834 : 233 X-ray sources in omega Centauri (Henleywillis+, 2018)
IX/45 : The Chandra Source Catalog, Release 1.1 (Evans+ 2012)
IX/57 : The Chandra Source Catalog (CSC), Release 2.0 (Evans+, 2019)
IX/70 : Chandra Source Catalog Release 2 (CSC 2.1) (Evans+, 2024)
B/chandra : The Chandra Archive Log (CXC, 1999-2014)
Byte-by-byte Description of file: table10.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 A12 --- Pulsar Pulsar Name designation (PulsarName)
14- 22 A9 --- GC Globular cluster name
24- 28 F5.2 ms Period Spinning period of the pulsar (Period)
30- 32 A3 --- Type Types of MSP systems obtained from Paulo
Freire's GC Pulsar Catalog, Freire
2013IAUS..291..243F 2013IAUS..291..243F (Type) (1)
34- 38 A5 --- SpMod Spectral model used to fit the LX emission
from MSPs, blackbody BB and power-law PL
models as explained in the section 3 Analysis
and results (Spectralmodel) (2)
40- 45 F6.1 10+23W LX X-ray luminosity estimated from 0.3 to 8 keV
which are unabsorbed at the distances to
corresponding GCs (LX)
47- 50 F4.1 10+23W E_LX Upper error of LX
52- 55 F4.1 10+23W e_LX Lower error of LX
57- 59 A3 --- rLX Reference of LX (Ref) (2)
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Note (1): Types of MSP systems encoded as follows:
B = Binary pulsar, 21 sources in our sample
BW = Black widow pulsar, 4 sources in our sample
I = Isolated pulsar, 23 sources in our sample
eBW = Eclipsing black widow pulsar, 9 sources in our sample
eRB = Eclipsing redback, 10 sources in our sample
O = Others MSP type, 1 source in our sample
Note (2): Reference of LX as coded as follows:
1 = Bogdanov et al. 2006ApJ...646.1104B 2006ApJ...646.1104B
2 = Bhattacharya et al. 2017MNRAS.472.3706B 2017MNRAS.472.3706B, Cat. J/MNRAS/472/3706
3 = Ridolfi et al. 2016MNRAS.462.2918R 2016MNRAS.462.2918R
4 = In our work
5 = Pavlov et al. 2007ApJ...664.1072P 2007ApJ...664.1072P
6 = Zhao et al. 2021MNRAS.502.1596Z 2021MNRAS.502.1596Z
7 = Oh et al. 2020MNRAS.498..292O 2020MNRAS.498..292O
8 = Bogdanov et al. 2010ApJ...709..241B 2010ApJ...709..241B, J/ApJ/709/241
9 = Pichardo Marcano et al. 2021MNRAS.503L..51P 2021MNRAS.503L..51P
10 = Bogdanov et al. 2021ApJ...912..124B 2021ApJ...912..124B
11 = Bogdanov et al. 2011ApJ...730...81B 2011ApJ...730...81B
12 = Linares et al. 2014MNRAS.438..251L 2014MNRAS.438..251L
13 = Amato et al. 2019MNRAS.486.3992A 2019MNRAS.486.3992A
14 = Forestell et al. 2014MNRAS.441..757F 2014MNRAS.441..757F
15 = Cohn et al. 2021MNRAS.508.2823C 2021MNRAS.508.2823C
16 = Elsner et al. 2008ApJ...687.1019E 2008ApJ...687.1019E, Cat. J/ApJ/687/1019
17 = Zhao et al. 2020MNRAS.499.3338Z 2020MNRAS.499.3338Z
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Byte-by-byte Description of file: tablea1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 A12 --- Pulsar Pulsar Name designation (PulsarName)
14 A1 --- n_Pulsar MSPs with precise timing positions
16- 35 A20 --- GC Globular cluster name (GCName)
37- 41 F5.2 ms Period Spinning period of the pulsar (Period)
43- 45 A3 --- Type Types of MSP systems obtained from Paulo
Freire's GC Pulsar Catalog, Freire
2013IAUS..291..243F 2013IAUS..291..243F (Type) (1)
47- 49 I3 10+23W LX X-ray luminosity upper limit estimated from
0.3 to 8 keV criteria of determining upper
limits have been discussed in section 2 Data
collection and reduction (LX)
51- 52 I2 --- r_Pulsar References of pulsar data in refs.dat file
(References)
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Note (1): Types of MSP systems encoded as follows:
B = Binary pulsar, 41 sources in our sample
BW = Black widow pulsar, 8 sources in our sample
I = Isolated pulsar, 50 sources in our sample
eBW = Eclipsing black widow pulsar, 2 sources in our sample
eRB = Eclipsing redback, 5 sources in our sample
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Byte-by-byte Description of file: refs.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 --- Ref Reference number
4-206 A203 --- Text Authors and bibcodes
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History:
From electronic version of the journal
(End) Luc Trabelsi [CDS] 05-Feb-2025