GX 1+4, KS 1731-260, GRS 1741.9-2853, A1524-62

R. Sunyaev, on the behalf of the Granat team (Space Research Institute, Moscow; Centre d'Etude Spatiale des Rayonnements, Toulouse; Service d'Astrophysique, Centre d'Etudes Nucleaires de Saclay, Gif sur Yvette), reports: "The field of the well-known pulsar GX 1+4 was observed with the Granat observatory on Aug. 23. The pulsations with period 114.60 +/- 0.05 s (at solar barycenter) were detected both by ART-P (2-60 keV) and SIGMA (> 35 keV) instruments. Comparison with the Mir-Kvant measurements in 1988 yields the following value of the average spindown rate during the elapsed period: P-dot/P = 1.0 x 10E-2 yrE-1. This value is remarkably lower than that observed with Ginga and Kvant in 1987- 1988 (P-dot/P = 1.3 x 10E-2 yrE-1). The source luminosity (3-20 keV) was found to be (2.3 +/- 0.2) x 10E36 erg/s (for distance 8.5 kpc). In the same field, ART-P detected the transient x-ray burster KS 1731-260 (IAUC 4839), with the 3- to 20-keV luminosity being 1.2 x 10E37 erg/s (for distance 8.5 kpc). During these observations, the source was two times weaker than during Apr. 4 Granat observations (the 3- to 20-keV luminosity being 2.1 x 10E37 erg/s) and similar to that observed in 1989 Aug.-Sept. by Mir-Kvant (the 3- to 20-keV luminosity being 1.5 x 10E37 erg/s). Further analysis of 1990 Mar. 24 and Apr. 8 observations of the Galactic Center by ART-P (IAUC 5032) improves the error box of x-ray source to within 10' of Sgr A. Previously this source was tentatively identified with 1E 1741.7-2850. Now the 99-percent- confidence error circle (1'.6 radius) does not overlap with error boxes of 1E 1741.7-2850 and GS 1741.2-2859/GS 1741.6-289. The coordinates of the new transient x-ray source GRS 1741.9-2853 (GRanat Source) are: R.A. = 17h41m52s, Decl. = -28 52'55" (equinox 1950.0). The 4- to 20-keV averaged luminosity of this source was 1.3 x 10E36 erg/s (for distance 8.5 kpc). A bremsstrahlung fit to the spectrum gives a temperature of 8 keV. During the Aug. 27-28 observations, the SIGMA telescope detected a hard x-ray source whose 2' error box contains the soft x-ray transient A1524-62. The 30- to 100-keV luminosity was 2.5 x 10E35 erg/s (for a distance of 2 kpc). This result implies the presence of a hard component in the source spectrum, like that observed for GS 2000+25 and A0620+00."