A new outburst from XTE J1858+034. Improving the source position.

ATel #274; S. V.Molkov (IKI/SAI, Moscow), A. M.Cherepashchuk (SAI, Moscow), M. G.Revnivtsev (IKI Moscow/MPA Garching), A. A.Lutovinov (IKI Moscow), K. A.Postnov (SAI Moscow), P. Kretschmar (ISDC Versoix, MPE Garching), R. A.Sunyaev (IKI Moscow, MPA Garching)
on 29 Apr 2004; 10:29 UT
Distributed as an Instant Email Notice Request For Observations
Credential Certification: A.Lutovinov (aal@hea.iki.rssi.ru)

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We report on the detection of a new X-Ray outburst from the X-Ray transient pulsar XTE J1858+034 and improvement of its coordinates.

INTEGRAL observations of the Sgr Arm Tangent field in the end of March 2004 detected a weak source (~2 mCrab in the 18-60 keV energy band, the ISGRI/IBIS telescope) near the position of XTE J1858+034 (~5.5' offset). Subsequent INTEGRAL observations of this region on April 21-24 showed that the source flux increased to ~8 mCrab (18-60 keV). On April 24-27 the source was also clearly detected by the JEM-X telescope in the 3-15 keV energy band. The flux of the source averaged over these observations was ~20 mCrab and ~15 mCrab in 3-15 keV and 18-60 keV energy bands, respectively. The position of the source from the JEM-X data is R.A.=18h58m44s, Decl.=3d26m02s (equinox J2000.0; 1' uncertainty), the ISGRI/IBIS yields R.A.=18h58m43s, Decl.=3d26m06s (equinox J2000.0; 2' uncertainty). Both positions are consistent with each other.

To determine the nature of this source (a new one or the known pulsar) RXTE observations were carried out on April 28. Strong pulsations with a period of 222+/-1.5 s (3-20 keV) were found from the source. Pulsations with the same period were previously detected from XTE J1858+034 (IAUC 6826 ). This fact proves that we are observing now a new outburst from XTE J1858+034. The raster scan observations allowed us to localize the source with PCA/RXTE at the position of R.A.=18h58m52s, Decl.=3d28m19s (equinox J2000.0; 2.5' uncertainty). This localization does not contradict that of INTEGRAL.

We are thankful to the RXTE team for quick scheduling of the observations.

Follow-up observations in different wavelengths are encouraged.