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tokens: all but one observation the exposure time was particularly low (i.e. 0.5–1 ks). We estimated the Bayesian 95 per cent upper limit (Kraft et al. ( 1991 ) to the source count rate from the observation with the longer exposure (4.2 ks, n. 4, obs ID 00087498001). It was equal to 0.0025 count s −1 . Using WebPIMMS, it converts into an observed (unabsorbed) 0.3–10 keV flux of ∼4 × 10 −13 erg cm −2 s −1 (∼7.6 × 10 −13 erg cm −2 s −1 ). We assumed the same spectral model as from the Swift / XRT observation n. 3. 3.4.3 Investigation at lower frequencies with archival data Halpern et al. ( 2007 ), using the precise Chandra localization of XTE J1829–098, individuated its probable infrared counterpart through images in the K and H bands as obtained with the MDM 2.4 m telescope on 2005 June 17. The measured magnitudes were H ∼ 13.9 and K ∼ 12.7, no measurement was obtained in the J band. Back in 2005, no additional infrared measurements were available from other infrared surveys, e.g. the UKIDSS survey started on 2005. Currently, we note that the infrared counterpart proposed by Halpern et al. ( 2007 ) has been also detected during the UKIDSS GPS data release 6 with magnitudes J = 16.147 ± 0.009, H = 14.064 ± 0.003, and K = 12.591 ± 0.002. If we use the reddening-free NIR diagnostic Q (Negueruela Schurch 2007 ) with the extinction law of Fitzpatrick ( 1999 ), we note that it has a Q value of –0.7 which is very typical of early-type OB stars. In particular, the negative value strongly indicates an infrared excess. Adopting the UKIDSS infrared magnitudes of such proposed counterpart, we can obtain a rough idea about its distance: if we assume a supergiant B0.5Ib star (with M V = −6.8 mag, V − K = −0.7 and V − J = −0.54), the source should be located at a distance d ∼ 18 kpc (with A V ∼ 21 mag). This implies a V magnitude fainter than V ∼ 30–31 mag. A main-sequence B0 star (assuming M V = −4 mag, V − K = −0.9 and V − J = −0.7), would imply a distance d ∼ 4.5 kpc (with A V ∼ 22 mag), while a giant B0 star (assuming M V = −5 mag, V − K = −0.8 and V − J = −0.7), would be located at about 8 kpc. 3.5 Search for periodicities We performed a timing analysis using the Lomb–Scargle method (Lomb 1976 ; Scargle 1982 ) of the long term INTEGRAL -IBIS and Swift -BAT light curves of the sources under study, in order to search for periodicities which could eventually be ascribed to their orbital periods. For all four sources, the long term IBIS/ISGRI ScW light curves (18–60 keV) cover the observational period from 2003 March to 2015 January. We applied standard optimum filtering in order to exclude poor quality data points which could eventually disrupt the periodic signal (see Goossens et al. 2013 and Sguera et al. 2007 for details). Periodicities were searched for in the range 1–100 d, but none were found. The public access Swift /BAT light curves (15–50 keV) on daily time-scale of all sources but IGR J12341–6143 were also searched for periodic signals in the range 2–250