We initiated in November 2014 a Swift-XRT monitoring of selected GCs in order to: i) find new low-luminosity transient LMXBs, ii) detect short and faint outbursts from known transient NS LMXBs and iii) monitor the X-ray activity of the known MSP population to search for more MSP-LMXB transition pulsars. Even if the angular resolution of Swift-XRT cannot resolve the X-ray sources in the core of GCs, with typical luminosities Lx~1E29-1E32 erg/s, their integrated emission can reveal subtle changes in the unexplored Lx = 1E33-1E34 erg/s regime.
We have selected the following GCs, which have large numbers of known MSPs, no persistent bright X-ray sources and are relatively nearby and not strongly absorbed (comparing Harris' and Freire's catalogs). The data products are made public here after the observations take place.
47Tuc: Contains 23 known MSPs. D=4.5 kpc; NH=0.01E22 cm2. REFS: Heinke et al. (2005ApJ...625..796H).
Ter5: Contains 34 known MSPs and three known neutron star transients. D=6.9 kpc; NH=1.2E22 cm2. REFS: Heinke et al. (2006ApJ...651.1098H).
M28: Contains 12 known MSPs and two known neutron star transients. D=5.5 kpc; NH=0.24E22 cm2. REFS: Becker et al. (2003ApJ...594..798B).
M62(since March 2016): Contains 6 known MSPs and one binary BH
candidate. D=6.9kpc; NH=0.28E22
cm2. REFS: Pooley et
al. (2003ApJ...591L.131P), Chomiuk et al. (2013ApJ...777...69C).
If these data have been useful to you please include the following acknowledgement: "This research has made use of the Swift-XRT Globular Cluster Monitoring page (http://www.iac.es/proyecto/SwiftGloClu) maintained by M. Linares & J. Chenevez."
We thank the Swift team for having made these observations possible
We acknowledge support from the COST Action MP1304 "NewCompStar"
Manu LINARES & Jérôme CHENEVEZ
July 2015 (automatic updates; last upgrade April 2016)