A search for diffuse X-ray emission from GeV-detected Galactic globular clusters

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Table 1

The GC sample and Chandra observations.

GC	Reference⁽¹⁾	r_h⁽²⁾	ObsID⁽³⁾	Coverage⁽⁴⁾	Net exposure⁽⁵⁾	Sensitivity⁽⁶⁾
name		(′′)		(%)	(ks)	(10^-15 erg cm^-2 s^-1)

M 62	A10	74	2677 (ACIS-S)	98	62.2	0.6
NGC 6388	A10	40	5505 (ACIS-S)	99	44.7	1.0
NGC 6541	A10, T11	71	3779 (ACIS-S)	80	44.9	0.7
M 28	A10	94	9132 (ACIS-S)	63	141.9	0.5
M 80	T11	37	1007 (ACIS-S)	99	48.6	1.0
NGC 6139	T11	51	8965 (ACIS-S)	83	18.1	2.0

47 Tuc	A09, A10	190	r_h too large
ω Cen	A10	134	r_h too large
NGC 6440	A10	35	bright point source
NGC 6441	A10, T11	34	bright point source
NGC 6624	T11	49	only grating or low exposure
NGC 6652	A10	29	only low exposure
M 15	A10	60	bright point source
NGC 6752	A10, T11	115	r_h large, known diffuse source in region (Okada et al. 2007)
Liller 1	T11	48	only grating

Notes. Summary of GeV-bright GCs that were considered (top section) or not considered (bottom section) in this work.

⁽¹⁾

Fermi/LAT reference: A09 (Abdo et al. 2009b), A10 (Abdo et al. 2010), T11 (Tam et al. 2011).

⁽²⁾

Half-mass-radius (r_h) from Harris (1996, 2010 edition).

⁽³⁾

Chandra observation identifier and instrument mode, or reason for exclusion.

⁽⁴⁾

Fraction of the area between one and three r_h within the FoV.

⁽⁵⁾

Remaining exposure after GTI screening. Owing to low background activity this is identical to the total exposure in most cases (see Sect. 2.2).

⁽⁶⁾

Sensitivity for point-source detection (0.5–7.0 keV).

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