J/ApJ/709/241 Characterisation of X-rays sources in NGC 6397 (Bogdanov+, 2010)
A Chandra X-ray observatory study of PSR J1740-5340 and candidate millisecond
pulsars in the globular cluster NGC 6397.
Bogdanov S., van den Berg M., Heinke C.O., Cohn H.N., Lugger P.M.,
Grindlay J.E.
<Astrophys. J., 709, 241-250 (2010)>
=2010ApJ...709..241B 2010ApJ...709..241B
ADC_Keywords: Clusters, globular ; X-ray sources ; Pulsars
Keywords: globular clusters: general - globular clusters:
individual (NGC 6397) - pulsars: general - pulsars:
individual (PSR J1740-5340) - stars: neutron - X-rays: stars
Abstract:
We present a deep Chandra X-ray Observatory study of the peculiar
binary radio millisecond pulsar (MSP) PSR J1740-5340 and candidate
millisecond pulsars in the globular cluster NGC 6397. The X-rays from
PSR J1740-5340 appear to be non-thermal and exhibit variability at the
binary period. These properties suggest the presence of a relativistic
intrabinary shock formed due to interaction of a relativistic
rotation-powered pulsar wind and outflow from the unusual
"red-straggler/sub-subgiant" companion. We find the X-ray source U18
to show similar X-ray and optical properties to those of
PSR J1740-5340, making it a strong MSP candidate. It exhibits
variability on timescales from hours to years, also consistent with an
intrabinary shock origin of its X-ray emission. The unprecedented
depth of the X-ray data allows us to conduct a complete census of MSPs
in NGC 6397. Based on the properties of the present sample of
X-ray-detected MSPs in the Galaxy, we find that NGC 6397 probably
hosts no more than six MSPs.
Description:
The Chandra data discussed herein were acquired during two separate
observations in Cycle 8, on 2007 June 22 (ObsID 7461) and 2007 July 16
(ObsID 7460) for 90 and 160ks, respectively. We also make use of two
Cycle 3 ACIS-S observations, on 2002 May 13 and 15, for 28.5ks and 27ks
(ObsIDs 2668 and 2669, respectively), and a single Cycle 1 ACIS-I
(ObsID 79) observation of 49ks, on 2000 Jul 31.
For the purposes of optical matching of the X-ray sources using the
set of Hubble Space Telescope Advanced Camera for Surveys Wide-Field
Channel (HST ACS/WFC) observations (GO-10257) in F435W (B), F625W (R),
and F658N (Hα), we computed a boresight correction for the
Chandra source coordinates (see H. Cohn et al., 2010ApJ...722...20C 2010ApJ...722...20C,
for details).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 73 79 X-ray sources in NGC 6397
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See also:
B/chandra : The Chandra Archive Log (CXC, 1999-)
B/hst : HST Archived Exposures Catalog (STScI, 2007)
J/A+A/505/L13 : Lithium in globular NGC 6397 (Gonzalez Hernandez+, 2009)
J/A+A/503/545 : Equivalent widths of Li, Na, Fe, Ca in NGC 6397 (Lind+, 2009)
J/A+A/490/777 : Abundances of Population II stars in NGC 6397 (Lind+, 2008)
J/A+A/425/509 : VI photometry of NGC 6397 (Andreuzzi+, 2004)
J/A+AS/122/1 : BV photometry of variables in NGC 6397 (Kaluzny, 1997)
J/AJ/110/1699 : F-P observations of globular clusters (Gebhardt+ 1995)
J/A+A/287/769 : UV photometry of NGC 6397 (Burgarella+ 1994)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [5,123] Source names based on the X-ray source
list from Grindlay et al. (2001ApJ...563L..53G 2001ApJ...563L..53G;
<[GHE2001b] UNNN> in Simbad)
5- 19 A15 --- CXOGlb CXOGlb name (HHMMSS.s+DDMMSS; J2000)
21- 22 I2 h RAh Hour of right ascension (J2000) (1)
24- 25 I2 min RAm Minute of right ascension (J2000)
27- 32 F6.3 s RAs Second of right ascension (J2000)
34 A1 --- DE- Sign of declination (J2000) (1)
35- 36 I2 deg DEd Degree of declination (J2000) (1)
38- 39 I2 arcmin DEm Arcminute of declination (J2000)
41- 45 F5.2 arcsec DEs Arcsecond of declination (J2000)
47- 50 F4.2 arcsec r95 The 95% positional uncertainty radius (2)
52- 55 I4 ct Scts Soft X-ray counts in 0.5-1.5keV band (3)
57- 60 I4 ct Hcts Hard X-ray counts in 1.5-6keV band (3)
62- 67 F6.1 10-19W/m2 Flux Flux in 0.5-6keV band (4)
69- 73 A5 --- Type Probable source identifications (5)
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Note (1): J2000.0 acis_extract derived positions of each source boresighted to
the frame of the HST ACS data set.
Note (2): The 95% positional uncertainty radius based on Hong et al.
(2005ApJ...635..907H 2005ApJ...635..907H)
Note (3): Background-subtracted source counts in the 0.3-1.5 and 1.5-6keV
bands.
Note (4): Source flux in the 0.5-6keV band in units of 10-16ergs/cm2/s,
assuming a power-law model with spectral photon index Γ=2.5.
Note (5): Probable source identifications based on optical counterpart
properties (from H. Cohn et al. 2010ApJ...722...20C 2010ApJ...722...20C).
Flag as follows:
AB = active binary,
CV = cataclysmic variable,
GLX = background galaxy,
qLMXB = quiescent low-mass X-ray binaries (LMXB),
MS = main-sequence star,
MSTO = main-sequence turnoff star,
MSP = millisecond pulsar,
? = ambiguous or unknown optical counterpart,
None = no optical counterpart.
Sources marked with an additional "?" are probable but less certain
classifications.
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History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 27-Feb-2012