National Aeronautics and Space Administration

XTE J0111.2-7317

D. Chakrabarty, A. M. Levine, and G. W. Clark, Massachusetts Institute of Technology; and T. Takeshima, Goddard Space Flight Center, NASA, and Universities Space Research Association, write: "Multiple observations of the SMC X-1 field with the Proportional Counter Array (PCA) on the Rossi X-ray Timing Explorer between Oct. 29 and Nov. 7 have revealed a previously unknown 31-s x-ray pulsar, designated XTE J0111.2-7317, about 30' from SMC X-1. Raster scans of the region on Nov. 6 and 7 have yielded the following position for the new pulsar: R.A. = 1h11m.2, Decl. = -73o17'.4 (equinox 2000.0), with an error radius of 1'.5 (90-percent confidence). The 2-10-keV x-ray intensities of XTE J0111.2-7317 and SMC X-1 on Nov. 6.6 UT were 36(7) and 51(4) mCrab, respectively, and the pulsed fraction of XTE J0111.2-7317 was roughly 45 percent. If XTE J0111.2-7317 is located in the SMC, its x-ray intensity implies a luminosity of order 10E38 erg/s. The source was not detected during a series of six PCA observations of the field between Oct. 16 and 27. Observations at other wavelengths are encouraged in order to identify the binary companion."

C. A. Wilson and M. H. Finger, Marshall Space Flight Center, NASA, report: "Hard-x-ray observations with the BATSE all-sky monitor on the Compton Gamma Ray Observatory first detected XTE J0111.2-7317 on Oct. 30, with a barycentric pulse frequency of 0.0322275(8) Hz on Oct. 30.5 UT. The 20-50-keV pulsed intensity increased from 18(3) mCrab on Oct. 30 to 37(3) mCrab on Nov. 5 and remained steady through Nov. 9. The pulse profile in the band 20-50 keV consists of a single asymmetric peak. BATSE pulse-phase measurements during Nov. 2-8 are consistent with a barycentric pulse frequency of 0.03225181(3) Hz on Nov. 5.0 and a constant pulse frequency derivative of 5.58(4) x 10E-11 Hz/s. If this rate is primarily due to the accretion torque on the pulsar, it implies a luminosity of at least 10E38 erg/s, consistent with the distance to the SMC."

1ES 2005-489

R. Remillard reports for the ASM instrument teams at the Massachusetts Insitute of Technology and Goddard Space Flight Center: "The RXTE All Sky Monitor has detected increased x-ray flux from the BL Lac object 1ES 2005-489 = PKS 2005-489 (R.A. = 20h09m25s.39, Decl. = -48o49'53".8, equinox 2000.0). During the interval Oct. 11-28, the flux has been in the range of 4 to 10 mCrab at 2-12 keV, which is a factor of 2-3 above its typical intensity during 1996-1998. Observations at other wavelengths are strongly encouraged."

XTE J1906+09

T. Takeshima, Goddard Space Flight Center and Universities Space Research Association; and T. Murakami, Institute of Space and Astronautical Science, on behalf of the RXTE Science Operations Center and ASCA team, report: "Simultaneous observations of SGR 1900+14 with ASCA (Sept. 16.794-17.831 UT) and RXTE/PCA (Sept. 16.826-16.988 and 17.281-17.388) confirmed that the 89-s pulsar XTE J1906+09 (Marsden et al. 1998, Ap.J. 502, L129) is a separate source from SGR 1900+14 (IAUC 7008). While RXTE/PCA detected significant 89-s pulsations, ASCA saw only 5.17-s pulsations from SGR 1900+14. Scans with the RXTE/PCA on Sept. 21.45 localized the 89-s pulsar to R.A. = 19h05m20s, Decl. = +9 02'.5 (equinox 2000.0), which was about 2' outside the ASCA/GIS field-of-view. The error radius of 2'.0 (90-percent confidence level) is dominated by systematic uncertainties due to intensity variations of the 89-s pulsar and of nearby sources during the scans. The average flux of XTE J1906+09 and its pulse fraction during the scan observation were 4.1 mCrab (2-10 keV) and 66 percent, respectively. The pulsating x-ray flux declined below 0.3 mCrab (2-10 keV) by Oct. 2, but observations at other wavelengths to identify the counterpart are encouraged."

XTE J1550-564

J. McClintock and G. Sobczak, Harvard-Smithsonian Center for Astrophysics; R. Remillard, E. Morgan, and A. Levine, Massachusetts Institute of Technology; C. Bailyn, Yale University; and J. Orosz, Pennsylvania State University, communicate: "XTE J1550-564 was observed with the RXTE PCA during the Sept. 19-20 x-ray flare reported on IAUC 7019. The source intensity during the 3000-s exposure was above 6 Crab. Fourier analysis of the lightcurve from the full energy range of the PCA (effectively 2-30 keV in this case) reveals a high-frequency quasiperiodic oscillation (QPO) at 183.6 Hz, with a width (FWHM) of 46 Hz and an rms amplitude of 0.45 percent of the mean x-ray flux. The statistical significance of the feature is above 8 sigma. The QPO is not seen during other PCA observations at lower flux. This is the third blackhole candidate known to exhibit x-ray QPOs above 50 Hz, following the 67-Hz QPO in GRS 1915+105 (Morgan et al. 1997, Ap.J. 482, 993) and the 298-Hz QPO in GRO J1655-40 (Remillard et al. 1998, http://xxx.lanl.gov/abs/astro-ph/?9806049). The QPO is likely to be an effect of general relativity, with the QPO frequency dependent on both the mass and spin of the accreting black hole, but there are competing models for such oscillations. Meanwhile, recent ASM and PCA observations made between Sept. 25 and Oct. 5 indicate intensities (2-12 keV) in the range of 1.2 to 1.4 Crab."

XTE J1550-564

R. Remillard and E. Morgan, Massachusetts Institute of Technology; and J. McClintock and G. Sobczak, Harvard-Smithsonian Center for Astrophysics, write: "The x-ray nova and blackhole candidate XTE J1550-564 has brightened dramatically since its discovery at 0.07 Crab (2-12 keV) on Sept. 7 (IAUC 7008). Observations with the RXTE All Sky Monitor show a steady rise to 1.7 Crab on Sept. 15. Thereafter, there is increased variability, with the intensity reaching 3.2 Crab on Sept. 18.7 UT. On Sept. 19 and 20, a large flare peaked at 6.8 Crab, and the intensity fell back to the range of 2.7-3.6 Crab on Sept. 20 and 21. PCA observations on Sept. 22.15 indicate a flux of 2.0 Crab at 2-30 keV. The long-term trend shows a steeper x-ray spectrum with increased brightness, while a local hardening of the spectrum was observed during the Sept. 19-20 flare. This x-ray nova is the brightest yet observed by RXTE, and observations at other wavelengths are strongly encouraged."

J. D. Hawley, S. M. Petrinec, and D. L. Chenette, Lockheed Martin Missiles and Space ATC Space Physics, communicate: "XTE J1550-564 (IAUC 7008) has been observed by the PIXIE instrument onboard the NASA/POLAR spacecraft since it first became visible on Sept. 7. The first PIXIE observation with adequate counting statistics was at Sept. 7.7 UT. The object is visible for about 5.5 hr every orbit (18-hr period, apogee over north pole at 9 earth radii). Although the primary mission of PIXIE is to study the bremsstrahlung x-rays of the earth's auroral regions, we also have the opportunity to observe celestial x-ray sources that appear off the limb of the earth. Averaged x-ray flux measurements (E = 2-12- keV, 64 logarithmically spaced energy channels) for each apogee pass show a nearly-linear slope of +0.8 photon sE-1 cmE-2 dayE-1 for Sept. 7-16. On Sept. 16, the x-ray flux dipped but then rose rapidly (flux of 5.8 photons sE-1 cmE-2 on Sept. 16.0, versus 24 photons sE-1 cmE-2 on Sept. 19.5), with the flux peaking on Sept. 20. PIXIE also measures Cir X-1, and on Sept. 12 the intensity of XTE J1550-564 surpassed the typical level of Cir X-1. Preliminary analysis shows similar spectral shapes for Cir X-1 and XTE J1550-564. Spectra along with more detailed information and plots can be found on the PIXIE home page, http://pixie.spasci.com."

XTE J1946+274 AND 3A 1942+274

T. Takeshima, NASA/Goddard Space Flight Center and Universities Space Research Association; and D. Chakrabarty, Massachusetts Institute of Technology, report: ``Scans of the region containing this transient x-ray pulsar (IAUC 7014) with the Proportional Counter Array (PCA) onboard RXTE on Sept. 16.23 UT have yielded the following improved position for the x-ray source: R.A. = 19h45m34s, Decl. = +27o23'.0 (equinox 2000.0). The error radius of 2'.4 (90-percent confidence level) is dominated by systematic uncertainties due to source intensity variations during the scans. The error circle almost includes the overlap of the RXTE/ASM error box for XTE J1946+274 (IAUC 7014) and the long Ariel V error strip for 3A 1942+274 (Warwick et al. 1981, MNRAS 197, 865). This strongly suggests that the two sources are identical. During the PCA observations on Sept. 16.24 and 17.57, the average source flux level and the pulse fraction stayed at about 110 mCrab and about 30 percent, respectively (2-60 keV). Observations at other wavelengths are encouraged in order to identify the mass donor."

Corrigendum. On IAUC 7014, line 30, for 2.2(2) x 10E-12 Hz/s read 8.7(9) x 10E-12 Hz/s

XTE J1946+274 = GRO J1944+26

D. A. Smith, Massachusetts Institute of Technology (MIT); and T. Takeshima, Goddard Space Flight Center (GSFC), NASA, on behalf of the RXTE/ASM and PCA teams at MIT and GSFC, communicate: "The ASM on RXTE has detected emission from a location that overlaps the previous localization of the 1976 Ariel V transient 3A 1942+274 (Warwick et al. 1981, MNRAS 197, 865; galactic latitude +1.7 deg). The corners of the ASM 6' x 26' error region are at R.A. = 19h47m.1, Decl. = +27o16'; 19h46m.2, +27o25'; 19h45m.5, +27o25'; 19h46m.2, +27o18' (equinox 2000.0; 90-percent-confidence total error). The source first came to our attention at about 90 mCrab (2-12 keV) on Sept. 15.91 UT, with a very hard spectrum. A retroactive search reveals that the 1-day average intensity has been rising from 13 mCrab on Sept. 5 to 60 mCrab on Sept. 15. The RXTE/PCA observed this location on Sept. 16.02 and recorded an intensity of about 110 mCrab (2-60 keV) with a very strong 15.83-s (+/- 0.02 s) pulsation. The pulse profile is double-peaked, with a pulse fraction of about 29 percent. There is, to our knowledge, no previous report of pulsations from 3A 1942+274. If this is a reoccurrence of the Ariel source, the 8' x 52' Ariel position restricts the location to the westernmost 5' of the ASM region (see http://xte.mit.edu/~dasmith/x1946_map.gif). Further PCA observations are in progress. Observations at other wavelengths are encouraged."

C. A. Wilson, M. H. Finger, R. B. Wilson, and D. M. Scott, Marshall Space Flight Center, NASA, report for the BATSE team: "Pulsations from a previously-uncatalogued x-ray pulsar in the Vul- Cyg region have been detected with BATSE in the energy band 20-50 keV from Sept. 8 through Sept. 14. A preliminary location (95- percent confidence) is bounded by R.A. = 19h34m to 19h54m and Decl. = +22o.5 to +30o.5 (equinox 2000.0). GRO J1944+26 rose from a 20- 50-keV rms pulsed flux of < 15 mCrab on Sept. 7 to 27 +/- 3 mCrab on Sept. 13. Observations between Sept. 8 and 14 are consistent with a barycentric pulse frequency of 0.06315331(6) Hz on Sept. 11.0 UT, with a frequency derivative of 2.2(2) x 10E-12 Hz/s. The pulse profile in the band 20-50 keV has a single asymmetric peak."

XTE J1550-564

D. A. Smith, Massachusetts Institute of Technology (MIT), on behalf of the RXTE/ASM teams at MIT and Goddard Space Flight Center (GSFC), reports: "A transient x-ray source has been detected with the RXTE/ASM near R.A. = 15h50m41s, Decl. = -56o27'.6 (equinox 2000.0). The source was first detected at an intensity of about 70 mCrab (2-12 keV; 5-sigma significance) in an observation at Sept. 7.0927 UT. At Sept. 7.4282, the source was observed to have a strength of 170 +/- 20 mCrab. Crossed lines of position were obtained; from these, the source is estimated to be located within a region (90-percent confidence) defined by a box of width 4'.3 and length 11'.0 with corners at R.A. = 15h51m31s, -56o33'.4; 15h50m19s, -56o26'.1; 15h49m52s, -56o19'.3; 15h50m57s, -56o25'.1."

F. E. Marshall, GSFC; and E. A. Smith, Hughes STX and GSFC, write: "An RXTE PCA observation on Sept. 7.72 UT of the transient XTE J1550-564 shows a highly-variable source with an average 2-10- keV flux of 6 x 10E-8 erg sE-1 cmE-2. Aperiodic variability of about a factor of two was seen on timescales of less than a second. The source is likely to be a black-hole transient."

XTE J1906+09

T. Takeshima and R. H. D. Corbet, Goddard Space Flight Center (GSFC) and Universities Space Research Association; and J. H. Swank, GSFC, on behalf of the RXTE Science Operations Center, report: SFC, on behalf of the RXTE Science Operations Center, report: "During a series of pointed observations of SGR 1900+14 with the Proportional Counter Array on RXTE, a coherent pulsation at period of 89.178 +/- 0.003 s (not barycenter-corrected) was detected, in addition to 5.16-s pulsations (IAUC 7001, 7002, 7003, 7004, 7005), in data obtained on Aug. 31.34-31.52, Sept. 1.24-1.52, and 2.41-2.52 UT. However, the 89-s pulsations were not seen in observations on Aug. 29.41-29.59 and 30.28-30.46. This period and the 2-10-keV pulse profile are consistent with those reported by Marsden et al. (1998, Ap.J. 502, L129) for XTE J1906+09. The average pulsed PCA count rates were 1.6, 2.5, and 4.3 counts/s (2-10 keV) in the three observations, respectively. As SGR 1900+14 pulses at a 5.16-s period, XTE J1906+09 with its 89-s period is probably a transient pulsar and not associated with the soft gamma-ray repeater itself. Offset pointed observations with the PCA are scheduled to attempt to determine the source position."

XTE J0053-724

J. C. Lochner, Goddard Space Flight Center and Universities Space Research Association, writes: "The transient x-ray system XTE J0053-724 (= 1WGA J0053.8-7226; cf. IAUC 6788, 6789, 6803) was detected in an observation by RXTE on Aug. 31. The measured 2-10- keV flux was estimated to be 3.0 x 10E-11 erg sE-1 cmE-2, with a photon index of 0.82 and a cutoff energy of 12.5 keV. Pulsations of 46.6 +/- 0.1 s were observed, with a pulse fraction of about 25 percent. This source was last detected in an observation on Apr. 8 while monitoring the second outburst of AX J0051-722 (IAUC 6858). This, along with the previous detection from late Nov. through mid- Dec. 1997, suggests a possible orbital period of this Be/neutron star system of about 139 days. Continued optical monitoring is encouraged."

SGR 1900+14

F. E. Marshall, T. Cline, and D. Palmer, Goddard Space Flight Center, NASA; E. P. Mazets, Ioffe Physical-Technical Institute, St. Petersburg; K. Hurley, University of California at Berkeley; and A. P. Beardmore, Keele University, write: "The x-ray transient of Aug. 27.432148 UT, initially reported on IAUC 7002, has been localized using the relative arrival times at RXTE, Global Geo- Science Wind, Near Earth Asteroid Rendezvous, and Ulysses. The six different two-spacecraft annuli are consistent with the location of SGR 1900+14, as expected (see IAUC 7004), with errors from about 1' to 12'. This event appears to be the brightest soft gamma-ray repeater in the four years of GGS-Wind operation. The maximum intensity is difficult to determine, since this event saturated both the RXTE PCA and the GGS-Wind detector and triggered an automatic turn-off of the NEAR gamma-ray experiment."

M. Feroci, P. Soffitta, and E. Costa, Istituto di Astrofisica Spaziale, CNR, Rome; and F. Frontera, Istituto Tecnologie e Studio Radiazioni Extraterrestri, CNR, Bologna, on behalf of the BeppoSAX/GRBM team; and M. Tavani, Istituto di Fisica Cosmica, CNR, Milan, and Columbia Astrophysics Laboratory, report: "The Gamma-Ray Burst Monitor (GRBM) onboard BeppoSAX was triggered by the event reported by Cline et al. (IAUC 7002) on Aug. 27.4321259 UT. The event showed a fast rise (< 1 s) and an exponential-like decay, lasting > 300 s. The event was observed at an offset angle of about 56 deg from the axis of GRBM unit 1, and showed a peak intensity in 40-700 keV of about 64 000 counts/s. The event was clearly detected above 100 keV. A preliminary analysis shows that the spectrum is hard during the initial 1 s, followed by a sudden softening. Subsequent spectral evolution shows a progressive hardening. The near-5-s periodicity reported by Cline et al. is evident in the GRBM data for the entire duration of the event. In addition, starting from about 35 s after the event onset, the GRBM clearly detected a periodic pattern of subpulses for each near-5-s oscillation. The repetitive pattern is made of four subpulses of period near 1 s. More detailed temporal and spectral analyses are in progress."

SGR 1900+14

C. Kouveliotou, Universities Space Research Association (USRA) at Marshall Space Flight Center (MSFC), NASA; T. Strohmayer, Goddard Space Flight Center (GSFC), NASA; T. Takeshima, USRA at GSFC; J. H. Swank, GSFC; and P. Woods, University of Alabama in Huntsville, report on behalf of a larger collaboration: "We have observed SGR 1900+14 with the RXTE/PCA and RXTE/HEXTE, following the possible RXTE/ASM detection of this source (Remillard et al., IAUC 7002); reactivation of the source has been observed with BATSE/CGRO. The RXTE observation started on Aug. 28.55 UT and lasted for 5760 s. We detect a source with average persistent flux of 6 mCrab, which was strongly pulsed (roughly 23-percent peak-to- valley amplitude) at 5.16 s (not yet corrected to the barycenter). During the observation, multiple short-duration bursts were observed (< 0.125 s), one with intensity above 1.4 Crab. Analysis of scans carried out to localize the source is hampered by its variability. While no improvement on the ASM position has been obtained, the pulse period and the bursts identify the source as SGR 1900+14, the pulsing burst source observed in June 1998 (IAUC 7001), but with 10 times the persistent flux. No evidence was seen of the 89.17-s pulse period reported in data of a 1996 obervation of SGR 1900+14 (IAUC 6882). Additional observations are being carried out."

C. Kouveliotou, USRA; G. J. Fishman, NASA/MSFC; and P. Woods and M. Kippen, UAH, communicate on behalf of the BATSE/CGRO team: "BATSE did not detect the burst of Aug. 27.432148 UT (Cline et al., IAUC 7002) due to earth occultation of the source. However, we have detected a dozen short (about 1-s) bursts starting on about Aug. 27.4456 UT and continuing to the present. Several of these bursts have been intense (BATSE did not trigger because the trigger channels were set to 300-1000 keV). On Aug. 29.4282 UT, BATSE triggered (no. 7031) on a very intense event with fluence about 7 x 10E-6 erg cmE-2 (25-300 keV); the event lasted roughly 3.5 s and exhibited two main peaks, after which weak evidence of pulses during its decay can be seen. We have reset the BATSE trigger energy channels to 25-100 keV in anticipation of further activity from SGR 1900+14."

SGR 1900+14

T. L. Cline, Goddard Space Flight Center (GSFC); and E. P. Mazets and S. V. Golenetskii, Ioffe Physical-Technical Institute, St. Petersburg, write: "A > 50-keV transient of intensity comparable to a strong gamma-ray burst triggered the GRB monitor on the Global Geo-Science Wind spacecraft on Aug. 27.432148 UT, exhibiting a persistent periodicity of 5.15 +/- 0.02 s. This is the first gamma-ray transient seen to clearly exhibit a periodic response in an uncollimated GRB detector since the 1979 March 5 event, itself the progenitor of the first known soft gamma-ray repeater (SGR). This transient is assumed to originate from SGR 1900+14, in view of its current state of activity (see, e.g., IAUC 6929), although there is no directional information from the Konus instruments other than a north-ecliptic-hemisphere indication, consistent with SGR 1900+14. Since the GGS-Wind spacecraft is not in a near-earth orbit, comparison with other observations may be able to provide a source directional annulus and confirmation of this identity."

R. Remillard, D. A. Smith, and A. Levine, Massachusetts Institute of Technology (MIT), report on behalf of the RXTE/ASM teams at MIT and at NASA/GSFC: "The RXTE All Sky Monitor has detected an x-ray flare at a location consistent (+/- 0o.2 deg) with the position of the candidate x-ray counterpart for SGR 1900+14 (Hurley et al. 1996, Ap.J. 463, L13). Two consecutive detections were made in each of two cameras on Aug. 27, showing a 2-12-keV intensity of 78 +/- 12 mCrab at Aug. 27.5174 UT and 114 +/- 11 mCrab at Aug. 27.5185. During the preceeding week, there were no significant detections made, and on Aug. 26, the average of 13 measurements implies a 3-sigma upper limit of 14 mCrab. On the day following the flare, seven measurements indicate a mean intensity 18 +/- 5 mCrab. During all of the 90-s exposures associated with ASM detections, the time-series data indicate steady emission with no evidence of SGR bursts."

SGR 1900+14

K. Hurley, Space Sciences Laboratory, on behalf of the Ulysses Gamma-Ray Burst Team; C. Kouveliotou, Universities Space Research Association (USRA); T. Murakami, Institute of Space and Astronautical Science; and T. Strohmayer, Goddard Space Flight Center (GSFC), report on behalf of a larger collaboration: "We have derived a preliminary triangulation error box for SGR 1900+14 using bursts observed in common with Ulysses and BATSE/CGRO from May through July. The corners of the box are (equinox 2000.0): R.A. = 19h07m16s, Decl. = +9o23'.8; 19h06m52s, +9o06'.5; 19h07m45s, +9o39'.1; 19h07m21s, +9o21'.9. This error box includes the ROSAT source previously suggested as the quiescent x-ray counterpart to the soft gamma-ray repeater (Hurley et al. 1996, Ap.J. 463, L13). We observed SGR 1900+14 with the ASCA satellite in April, and find that it has a hard spectrum consistent with a power law with index 2.2, and flux 1.3 x 10E-11 erg cmE-2 sE-1 (2-10 keV). We detect coherent pulsations from the source at a high significance with a period of 5.16 s. The similarity of the period of this source to the one of 7.47 s detected from SGR 1806-20 (Kouveliotou et al. 1998, Nature 393, 235), indicates that the newly detected pulsar is the soft gamma-ray repeater. The centroid of the error box of the source is at R.A. = 19h07m14s, Decl. = +9o19'.3, close to the supernova remnant G42.8+0.6. As the source is still active, we urge monitoring at other wavelengths."

C. Kouveliotou, USRA; T. Strohmayer, GSFC; K. Hurley, University of California at Berkeley; J. van Paradijs, University of Amsterdam and University of Alabama in Huntsville (UAH); and P. Woods, UAH, report on behalf of a larger collaboration: "We initiated Target of Opportunity Observations of SGR 1900+14 with the RXTE/PCA after the source triggered BATSE/CGRO on May 30 (IAUC 6929). Our observations took place between June 2.604 and 9.045, during which we obtained 41 700 s on source. We confirm the pulsations detected with ASCA (see item above); a comparison of the ASCA and the PCA data establishes that the period is increasing at a rate of dP/dt = 6 x 10E-11 s/s. The period and period derivative of SGR 1900+14 are very similar to those detected for SGR 1806-20 and strongly suggest that SGR 1900+14 is also a magnetar with B = 5 x 10E14 Gauss and characteristic age P/(dP/dt) about 1500 yr. We strongly encourage further infrared and radio observations of the source."

XTE J1710-281 = 1RXS J171012.3-280754

C. B. Markwardt, National Research Council and Goddard Space Flight Center (GSFC); F. E. Marshall and J. Swank, GSFC; and T. Takeshima, Universities Space Research Association and GSFC, report: "A transient x-ray source was serendipitously detected with the RXTE PCA in two slews, first on July 22.0 UT at a level of 24 counts/s, and on Aug. 12.7 at a level of 64 counts/s (per five PCUs). In subsequent PCA scans on Aug. 19.3, the source had decreased to 23 counts/s (5 x 10E-11 erg sE-1 cmE-2 over 2-10 keV). The best-fit position is R.A. = 17h10m12s, Decl. = -28o07'.1 (equinox 2000.0), with a position uncertainty of +/- 2' in R.A. and +/- 4' in Decl. (90-percent confidence), and it is consistent with the location of the unidentified source 1RXS J171012.3-280754 of the ROSAT All-Sky Survey Bright Source Catalogue. The spectrum on Aug. 19.3 is consistent with either thermal bremsstrahlung (kT = 14 +/- 3 keV) or a power law (photon index 1.8 +/- 0.1), with interstellar absorption < 2 x 10E22 cmE-2. No spectral lines are apparent. No short-timescale variability was observed, although the 400-s pointed observation only provided a 3-sigma upper limit of 14 percent for the best case of coherent oscillations. Further observations at other wavelengths are desirable."

2S 1711-339

R. Remillard reports for the RXTE ASM team at Massachusetts Institute of Technology and Goddard Space Flight Center, NASA: "The RXTE All-Sky Monitor has detected x-ray emission at a position consistent with the recurrent transient 2S 1711-339 (e.g., Greenhill et al. 1979, Nature 279, 620). The ASM error circle (4' radius) is centered 1' north of the more accurate SAS position at R.A. = 17h14m19s, Decl. = -34o02'.9 (equinox 2000.0). Retrospective analysis indicates that the x-ray flux (2-12 keV) began to increase on July 21, reaching 25 +/- 4 mCrab on July 22 and 54 +/- 5 mCrab on July 27. Thereafter, the ASM results are consistent with a slow decline to 33 +/- 6 mCrab on Aug. 4. Radio and optical observations are needed."

XTE J2123-058

J. Casares, M. Serra-Ricart, C. Zurita, A. Gomez, and D. Alcalde, Instituto de Astrofisica de Canarias; and P. Charles, University of Oxford, report the discovery of optical eclipses in the x-ray transient XTE J2123-058 (IAUC 6955): "R-band images were obtained between July 2 and 12 with the European Space Agency's Optical Ground Station 1-m telescope at the Observatorio del Teide. Our light curves show triangular-shaped minima with a central depth of 0.65 mag, repeating each night, indicating a periodicity of roughly 1 day. The dips, which we interpret as eclipses of the accretion disk by the companion star, have a total duration of 0.16 day. Preliminary analysis, using phase-dispersion minimization, yields a strong peak at 1.99 days. After phase folding on this period and submultiples of it, we favor an orbital period of 0.993 or 0.993/2 day. A provisional ephemeris for the time of mid- eclipse is HJD 24451001.685(2) + 0.993(2)E. Observations at other wavelengths (especially in x-rays) to monitor the decline are strongly encouraged. Optical monitoring from widely-distributed sites is particularly important to disentangle 1-day aliases and search for the secondary minimum."

J. Homan, M. van der Klis, J. van Paradijs, and M. Mendez, Astronomical Institute 'Anton Pannekoek', University of Amsterdam, communicate: "We report the discovery, using RXTE PCA data from July 14.4 to 14.8 UT, of two high-frequency quasiperiodic oscillations (QPOs) in the persistent x-ray flux of the newly discovered x-ray transient XTE J2123-058 (IAUC 6955). The QPOs have frequencies of 855 +/- 5 and 1123 +/- 7 Hz, widths of 33.5 +/- 11.8 and 51.5 +/- 15.1 Hz, and rms amplitudes of 6.3 +/- 0.8 and 7.4 +/- 0.9 percent (2-11 keV). Both QPOs get stronger with photon energy and are detected at count rates below about 640 counts/s (2-60 keV, including background), but undetected above. Two x-ray bursts were examined for oscillations, but none were found. We recommend further RXTE observations when the PCA level drops below about 640 counts/s."

GRB 980703

A. Levine, E. Morgan, and M. Muno, Massachusetts Institute of Technology (MIT), report on behalf of the RXTE ASM team at MIT and Goddard Space Flight Center: "A gamma-ray burst that occurred on about July 3.182 UT (BATSE trigger 6891) was in the field-of-view of two ASM cameras. The resulting detection yielded a position of R.A. = 23h59m05s, Decl. = +8o33'.6 (equinox 2000.0), with an uncertainty of about 4' radius (90-percent confidence). The burst peak intensity was roughly 1.7 Crab (2-12 keV)."

XTE J1748-288

D. Fox and W. Lewin, Massachusetts Institute of Technology, report on behalf of a large collaboration: "We have examined the Rossi X-ray Timing Explorer June 6.4 UT observation of the x-ray and radio transient source XTE J1748-288 (IAUC 6932, 6934, 6937, 6938); the count rate of the source at this time was about 5100 counts/s in the Proportional Counter Array (2-60 keV). The power- density spectrum shows two quasi-periodic oscillation (QPO) peaks, at about 0.5 and 32 Hz respectively, superposed on a 5.8-percent- r.m.s. (0-100 Hz) 'double flat-top/power law' noise spectrum with a -2.2 power-law slope between 1.6 and 2.0 Hz and above a 5.9-Hz break frequency. The 0.5-Hz QPO moves from 0.35 to 0.50 Hz and strengthens over the course of the 2700-s observation; its FWHM is about 0.5 Hz and its average r.m.s. strength is 3.4 percent. The 32-Hz QPO, by contrast, is relatively stationary, with a FWHM of 5.4 Hz and an r.m.s. strength of 3.3 percent. The x-ray colors of the source (2.0-4.6:4.6-9.4:9.4-18.3-keV counts ratio of 3.2:4.1:1) are typical for black-hole candidates in the 'low state', and in particular this source's spectral and timing properties are reminiscent of low- or very-high-state behavior in GX 339-4."

SGR 1621-47

S. Dieters and P. Woods, University of Alabama, Huntsville (UAH); C. Kouveliotou, Universities Space Research Association; and J. van Paradijs, UAH and University of Amsterdam, report: "We have analyzed 9200 s of RXTE pointed observations made on June 26 of SGR 1627-41 (IAUC 6944), which were centered on the possibly-associated supernova remnant G337.0-0.1 (cf. IAUC 6948, 6950). We detected one burst, confirming flux detection from the new source and strengthening the association of the two sources. Power spectral analysis of the observations reveals a quasi-periodic oscillation (QPO) peak centered at 0.15 Hz (about 6.7 s), with an r.m.s. of at least 3.2 percent, depending upon background and source contributions to the signal. Also within the RXTE field-of-view is the black-hole candidate 4U 1630-47, from which QPOs have been observed (IAUC 6823). However, no QPOs near the above frequency have been reported, and the intensity of 1630-47 was low during our observations. Further observations are required to determine which source is the origin of the QPO."

XTE J2123-058

T. Takeshima, Goddard Space Flight Center (GSFC) and Universities Space Research Association; and T. E. Strohmayer, GSFC, on behalf of the RXTE Science Operations Center, write: "We report an improved position for this transient (IAUC 6955) of R.A. = 21h23m16s, Decl. = -5 47'.5 (equinox 2000.0), with an uncertainty of 1', based on scans across the source with the Proportional Counter Array on RXTE on June 29.04 UT. This is consistent with the position of the candidate of an optical counterpart reported on IAUC 6957. Two weak bursts were seen during the pointed observations on June 27.98 and 29.70. Preliminary spectral analysis suggests that they are type-I (thermonuclear) bursts; thus the system is likely a low-mass x-ray binary with a neutron star. The He II emission reported by Tomsick et al. (IAUC 6957) also supports this hypothesis. The observed steady fluxes (2-10 keV) on June 27.09, 29.04, and 29.70 were 65, 67, and 56 mCrab, respectively. The observed burst peak fluxes above the steady flux level (2-10 keV) were 50 and 88 mCrab."

XTE J2123-058

A. Levine, Massachusetts Institute of Technology (MIT); and J. Swank and E. Smith, Goddard Space Flight Center (GSFC), NASA, report on behalf of the RXTE ASM and PCA teams at MIT and GSFC: "A transient x-ray source has been detected with the RXTE/ASM at R.A. = 21h23m.1, Decl. = -5o49' (equinox 2000.0), corresponding to l = 46.4 deg, b = -36.2 deg. The position uncertainty is about 10' along an axis with p.a. 20 deg (i.e., northeast-southwest) and about 5' in the perpendicular direction (90-percent confidence). The flux was measured to be about 100 mCrab (2-12 keV) in each of five measurements on June 27-28. The strength of the source has been confirmed with PCA observations June 27.95, in which the count rate varied from 600 to 1000 counts/s. Additional PCA observations, including a determination of the source location, will be undertaken. The appearance of a new transient x-ray source at high galactic latitude is unusual; we urge observers to carry out additional observations at all wavelengths."

SGR 1627-41

D. A. Smith and A. M. Levine report on behalf of the RXTE/ASM teams at Massachusetts Institute of Technology and Goddard Space Flight Center: "Three short (< about 1 s) burst events, most likely produced by the new soft gamma-ray repeater SGR 1627-41 (IAUC 6944), were detected in SSC 3 of the RXTE/ASM at May 17.943917, 17.954243, and 18.010803 UT. These bursts are not associated with the times of any reported BATSE triggers. Due to low signal-to-noise, our standard blind-search analysis procedure did not yield a position of the source, so we performed a search, assuming that the source is located within a 1-degree-long segment of the IPN annulus (Hurley et al., IAUC 6948) centered on the supernova remnant G337.0-0.1 noted by Woods et al. on IAUC 6948. We find a maximum reduction in chi^2 for sources located at R.A. = 16h35m.8, Decl. = -47o32' for event 1 and R.A. = 16h35m.8, Decl. = -47o39' for event 2 (1-sigma error of 4' in Decl. in both cases). Both positions are consistent with the location of G337.0-0.1. If we assume that these two bursts came from G337.0-0.1, their fluences are 2 and 3 x 10E-7 erg/cm^2 (5-12 keV). No flux was detected in the band 1.5-5 keV with 2-sigma upper limits of 1 x 10E-7 erg/cm^2 for both events."

XTE J1748-288

T. Strohmayer and F. E. Marshall, Goddard Space Flight Center, on behalf of the RXTE Science Operations Center, report an improved position for this x-ray transient (IAUC 6932) of R.A. = 17h48m08s, Decl. = -28o29'.2 (equinox 2000.0) with an estimated uncertainty of 1' based on scans across the source with the Proportional Counter Array on the Rossi X-ray Timing Explorer on June 5.13 UT. The observed 2-10-keV flux of about 600 mCrab indicates a continued brightening of the source.
R. M. Hjellming and M. P. Rupen, National Radio Astronomy Observatory (NRAO); and A. J. Mioduszewski, Joint Institute for VLBI in Europe and NRAO, report: "Very Large Array observations on June 7.40 UT of the field of XTE J1748-288 show the presence of an unresolved radio source with flux densities of 50 +/- 3 and 28 +/- 2 mJy at 1.46 and 4.86 GHz, respectively. Its position is R.A. = 17h48m05s.06, Decl. = -28o28'25".8 (equinox 2000.0; uncertainty 0".6), which is 1' from the center of the 1' uncertainty region for XTE J1748-288 (see above). It is a candidate for the radio counterpart of the x-ray transient because it is much stronger than the usual background radio source, but variability still needs to be established."

XTE J1748-288

D. A. Smith, A. Levine, and A. Wood, Massachusetts Institute of Technology (MIT), report for the RXTE ASM team at MIT and NASA Goddard Space Flight Center: "The RXTE All-Sky Monitor has detected a transient x-ray source at R.A. = 17h48m08s, Decl. = -28o28'.8 (equinox 2000.0; error radius 5', to better than 90-percent confidence). The source was observed in each of two detector systems in two contiguous 90-s exposures on June 4.69 UT, and again in two more observations 1.8 hr later. The spectrum is hard, with typical fluxes of 90, 300, and 470 mCrab in the bands 1.5-3, 3-5, and 5-12 keV, respectively."

XTE J1855-026

R. Corbet, Goddard Space Flight Center (GSFC) and Universities Space Research Association, reports on behalf of the RXTE ASM team at GSFC and the Massachusetts Institute of Technology: "An analysis of the RXTE All Sky Monitor light curve of the 362-s pulsar XTE J1855-026 (IAUC 6904) obtained between 1996 Jan. 6 and 1998 May 28 reveals a modulation at a period of about 6.1 days. A sine-wave fit yields 6.074 +/- 0.004 days, with an amplitude of 0.15 counts/s and time of maximum flux of JD 2450289.6 +/- 0.2. The mean count rate during this period was 0.5 counts/s, which corresponds to about 7 mCrab (2-12 keV). This combination of pulse and orbital parameters raises the possibility that this may be a supergiant, rather than a Be star system, as earlier suggested. If this is a Be star system, then a 6-day orbital period would be the shortest known for this class."

XTE J2012+381

F. E. Marshall and T. Strohmayer, Goddard Space Flight Center, on behalf of the RXTE Science Operations Center, report an improved position for this x-ray transient: R.A. = 20h12m43s, Decl. = +38o11'.0 (equinox 2000.0); the estimated uncertainty is 1', based on scans across the source with the Proportional Counter Array on the Rosssi X-ray Timing Explorer on May 27.68 UT. This error circle is consistent with the larger region determined with the RXTE All-Sky Monitor but does not contain the star suggested by Wagner et al. (IAUC 6920). The observed 2-10-keV flux of about 110 mCrab indicates a continued brightening of the source. M. R. Garcia, J. E. McClintock, P. Berlind, and E. Barton, Harvard-Smithsonian Center for Astrophysics; and P. Callanan, University College, Cork, report: "Spectra and photometry of the possible counterpart to XTE J2012+381 (Wagner et al., IAUC 6920) with the Mt. Hopkins 1.5-m and 1.2-m telescopes show that this star is a heavily reddened M giant. Photometry on May 28.312-28.469 UT yields V = 19.7 +/- 0.2, R = 16.3 +/- 0.1, and I = 12.2 +/- 0.1, with no detected variability. The apparent brightening described on IAUC 6920 is most probably an artifact of the extreme red colors and the mismatch in the bandpasses of the LONEOS images (which used an unfiltered CCD) and the DSS images. Neither our photometry nor that on IAUC 6920 provides any evidence that this star is the counterpart to XTE J2012+381."

XTE J2012+381

R. Remillard, A. Levine, and A. Wood, Massachusetts Institute of Technology (MIT), reporting for the RXTE ASM team at MIT and Goddard Space Flight Center (GSFC), write: "The RXTE All-Sky Monitor has detected a transient x-ray source at R.A. = 20h12m.6, Decl. = +38o11' (equinox 2000.0). The position uncertainty (90-percent confidence) is approximately +/- 10' in R.A. and +/- 4' in Decl. In daily averages, the ASM count rate (2-12 keV) was 23 mCrab on May 24.6 UT and 28 on May 25.4, rising to 55 mCrab on May 26.5 and to 88 on May 27.3. The spectrum is becoming softer as the source brightens. Observations at other wavelengths are urgently needed."
R. M. Wagner, Ohio State University; S. Starrfield, Arizona State University; C. Shrader, GSFC; and E. Bowell, B. Skiff, and B. Koehn, Lowell Observatory, on behalf of the Lowell Observatory Near Earth Object Search (LONEOS) collaboration, report: "We obtained several unfiltered images of the RXTE/ASM error box with the LONEOS Schmidt telescope and CCD camera (field 3.2 x 1.6 deg; scale 2".8/pixel) on May 27.34 UT. Comparison of these images with the Digital Sky Survey (DSS) reveals a variable stellar object and possible optical counterpart of XTE J2012+381 within the ASM error box at R.A. = 20h12m30s.3, Decl. = +38 08'59" (equinox 2000.0; uncertainty 1" in both coordinates). The object appears on the DSS at mag about 17-17.5 and is distinctly fainter than a star located 15" to the south. However, the object appears 2-3 mag brighter on the LONEOS images and comparable in brightness to the stellar object 15" to the south. No other obviously variable objects or new objects not present on the DSS were found in the LONEOS images of the error box."

NGC 6814

K. Mukai, Goddard Space Flight Center (GSFC), NASA, and Universities Space Research Association; G. Madejski, GSFC and University of Maryland; and C. Hellier, University of Keele, write: "We have observed the Seyfert galaxy NGC 6814 with the Rossi X-ray Timing Explorer. On May 18.54 UT, it was detected at a rate of about 15 counts/s in 5 PCUs (subject to background uncertainties of about 5 counts/s), or 3 x 10E-11 erg cmE-2 sE-2 at 2-10 keV. Thus, NGC 6814 appears to be in an unusually high state, an order of magnitude brighter than in 1993 May (1.2 x 10E-12 erg cmE-2 sE-1 at 2-10 keV; George et al. 1998, Ap.J. Supp. 114, 73), and arguably brighter than in any previous x-ray observations. We have also observed the magnetic cataclysmic variable, V1432 Aql (which contaminated previous non-imaging x-ray data on the Seyfert), located 37' away, and confirmed that cross-contamination in our data is minimal. We will be monitoring both sources at about 4-day intervals until early September (see http://asd.gsfc.nasa.gov/~mukai/v1432.html); coordinated observations at other wavelengths are strongly encouraged."

XTE J1806-246

F. E. Marshall and T. Strohmayer, Goddard Space Flight Center; and R. Remillard, Massachusetts Institute of Technology, on behalf of the RXTE Science Operations Center, report the detection with the Rosssi X-ray Timing Explorer of a bright, soft x-ray transient (designated XTE J1806-246) at a position consistent with that of the SAS source 2S 1803-245 and a possibly related source of isolated bursts, SAX J1806.8-2435 (IAUC 6867): "The 2-12-keV flux measured with the All-Sky Monitor increased as follows: Apr. 16.66 UT, 31 mCrab; 18.27, 60; 22.42, 131; 24.45, 356; 28.93, 417. The 3-20-keV spectrum measured with the Proportional Counter Array (PCA) on Apr. 28.81 is well described as thermal bremsstrahlung emission with kT = 4.3 keV. The source position determined with the PCA is R.A. = 18h06m51s, Decl. = -24o35'.1 (equinox 2000.0) with an estimated uncertainty of 1'.5. Observations at other wavelengths are encouraged."

XTE 1909+06

D. Marsden and R. Rothschild, Center for Astrophysics and Space Sciences, University of California at San Diego, report for the RXTE/HEXTE team: "We report the discovery of a pulsating x-ray source designated XTE 1909+06 during observations with RXTE of a 1 deg (FWHM) region on 1996 Aug. 16-19 containing the soft gamma- ray repeater SGR 1900+14. The RXTE field-of-view was centered at R.A. = 19h05m43s, Decl. = +8o58'.8 (equinox 2000.0). Coherent pulsations were detected from the source by both the PCA and HEXTE instruments at a fundamental period of 89.17 +/- 0.02 s, with higher-order harmonics visible in the 2-10-keV power spectrum. The folded pulsar lightcurve is energy dependent, with a multipeaked morphology (2-20 keV) at lower energies that becomes singly peaked in the energy range 20-200 keV. After correcting for instrumental, sky, and Galactic ridge backgrounds, the pulsed fractions are 16, 6, and 4 percent in the energy ranges 2-10, 10-20, and 20-300 keV, respectively. The phase-averaged spectrum is well fitted over the entire energy range by either a power law of photon index 1.9 +/- 0.1 or a thermal bremsstrahlung model of temperature kT = 20 +/- 5 keV, with a 2-10-keV flux of about 1.5 x 10E-11 erg cmE-2 sE-1. The column density implied by the spectral fits is N_H about 1 x 10E23 cmE-2, implying a distance to the source of about 10-20 kpc. We encourage observations at other wavelengths to refine the position and search for a counterpart."

SAX J1808.4-3658 = XTE J1808-369

W. Heindl, D. Marsden, and P. Blanco, Center for Astrophysics and Space Sciences, University of California at San Diego, report for the RXTE/HEXTE team: "Pointed observations of XTE J1808-369 (IAUC 6876, 6877) with the RXTE/HEXTE on Apr. 11.85-11.89 and 13.08-13.10 UT reveal that this unusual source has a very hard, power-law spectrum extending to at least 120 keV. This makes XTE J1808-369 one of the hardest binary x-ray pulsars. No spectral variability was observed between the two observations, and the 15-250-keV spectrum is well-fitted by a power law with photon index of 2.02 +/- 0.05. The average flux from both days is 89.5 +/- 0.6 mCrab (15-250 keV), which corresponds to 1.3 x 10E-9 erg cmE-2 sE-1 (2-10 keV), in good agreement with the RXTE/PCA value from the Apr. 11.8 observation reported by Marshall et al. (IAUC 6876). Using the orbital model of Chakrabarty and Morgan (IAUC 6877), we confirm pulsations at their period, although with low significance due to limited statistics. The very hard nature of this object further motivates additional observations at hard-x-ray and other wavelengths."

SAX J1808.4-3658 = XTE J1808-369

D. Chakrabarty and E. H. Morgan, Massachusetts Institute of Technology, report for the Rossi XTE team: "The pulsations from XTE J1808-369 (= SAX J1808.4-3658) recently discovered in RXTE observations (IAUC 6876) show clear evidence for a binary orbit. Using RXTE/PCA data from Apr. 11.81-11.82, 11.86-11.89, and 13.07- 13.09 and assuming a constant pulsar-spin frequency for all these data, we find the following provisional orbital parameters for the neutron star: an orbital period of 7251(1) s, a projected semimajor axis of 0.0632(3) lt-s, and an orbital epoch (time of 90 degrees mean longitude) of JD 2450915.3995(1). The corresponding barycentric spin frequency is 400.9753(1) Hz. The orbital parameters give a pulsar mass function of 3.9 x 10E-5 solar mass, one of the smallest mass functions for any x-ray binary. Since x-ray heating of the mass donor and/or the accretion disk in such a low-mass x-ray binary is likely to be very strong, observations at other wavelengths are urgently required to identify the counterpart while the x-ray source is still active."

SAX J1808.4-3658 = XTE J1808-369

XTE J0421+560

D. Smith and R. Remillard, Massachusetts Institute of Technology; and J. Swank, T. Takeshima, and E. Smith, Goddard Space Flight Center, NASA, report: "The RXTE All-Sky Monitor has detected a bright and rapidly rising x-ray transient, which we designate XTE J0421+560. The best-fit position is R.A. = 4h21m.01, Decl. = +56o03'.5 (equinox 2000.0), with an error radius (90-percent confidence) of 4'. The ASM countrate (2-12 keV) was below 40 mCrab (at 3 sigma) on Mar. 31.36 UT, rising rapidly thereafter to 139 (Mar. 31.64), 504 (31.77), and 1880 mCrab (Apr. 1.04). An RXTE PCA observation, which began on Apr. 1.08, confirms the presence of a new source with a flux near 2 Crab. The ASM spectrum appears very hard, but the PCA light curve shows no obvious pulsations at periods longer than 0.25 s. Observations at other wavelengths are urgently needed."

eta CARINAE

M. F. Corcoran, Goddard Space Flight Center (GSFC) and Universities Space Research Association; J. H. Swank and R. Petre, GSFC; and K. Ishibashi and K. Davidson, University of Minnesota, report: "Continuing observation of this peculiar luminous star with the RXTE PCA shows that the star may be emerging from the x-ray 'low state' that began in early Dec. 1997. During the low state, the PCA countrate in the band 2-10 keV dropped from > 70 to 15 PCU counts/s in a period of about 1 month. Recent RXTE observations show that the observed x-ray emission has risen by about a factor of 2 since 1998 Feb. 2. After correcting for the permanent sky background, the countrate due to eta Car itself has increased by a factor close to 6. Since Feb. 16, the average rate of increase in the x-ray emission has been Delta(R) = +0.7 PCU counts sE-1 dayE-1. This is still considerably less than the rate of decline to x-ray minimum, Delta(R) = -1.6 PCU counts sE-1 dayE-1 during the interval 1997 Nov. 11-Dec. 18. Using a conversion factor of 3.22 x 10E-12 erg sE-1 cmE-2 per PCA count in the band 2-10 keV suggests that at present the rate of increase in 2-10-keV flux is about 2.25 x 10E-12 erg cmE-2 sE-1 dayE-1. If the rate of increase remains constant, then the x-ray flux from eta Car should reach or exceed the previous maximum flux level on May 8. The recent x-ray brightening could also be associated with episodic flaring previously reported (IAUC 6668), since the next flare maximum is expected to occur on Mar. 17."

V1333 AQUILAE

J. H. Swank and E. Smith, Goddard Space Flight Center (GSFC); and A. M. Levine and R. Remillard, Massachusetts Institute of Technology (MIT), on behalf on the RXTE ASM team at GSFC and MIT, report that the low-mass x-ray binary Aql X-1 (= V1333 Aql) has started another x-ray outburst. In real-time results from the RXTE All Sky Monitor, the daily average flux levels in the band 2-12 keV are: Feb. 27, about 22 mCrab; 28, 36; Mar. 1, 59; 2, 100; 3, 127. Pointed observations with the PCA began on Mar. 3 and confirm the ASM results. Observations at other wavelengths are encouraged.

XTE J1858+034

F. E. Marshall, Goddard Space Flight Center; D. Chakrabarty, Massachusetts Institute of Technology; and M. H. Finger, Marshall Space Flight Center, report an improved position for XTE J1858+034 (IAUC 6826) of R.A. = 18h58m.6, Decl. = +3o21' (equinox 2000.0), with an estimated 90-percent confidence error radius of 2'.5, based on repeated scans across the source with the PCA on RXTE. The flux (2-10 keV) on Feb. 28.9 UT was 4 mCrab.

XTE J1858+034

R. Remillard and A. Levine, Massachusetts Institute of Technology (MIT), report, for the RXTE ASM team at MIT and NASA Goddard Space Flight Center (GSFC): "The RXTE All Sky Monitor has detected a new, hard x-ray transient, which we designate XTE J1858+034. The source was detected in a correlation map constructed by superposing data collected during Feb. 6-12. The source is located at R.A. = 18h58m41s, Decl. = +3d24'.0 (equinox 2000.0), with an estimated uncertainty (90-percent confidence) of 6'. Reanalysis of recent ASM observations shows that the source flux (2-12 keV) was 15 mCrab on Jan. 30, 24 mCrab on Feb. 7, 15 mCrab on Feb. 16 and 10 mCrab on Feb. 26. The spectrum is very hard, resembling that of an x-ray pulsar."

T. Takeshima and R. H. D. Corbet, GSFC and Universities Space Research Association; F. E. Marshall and J. H. Swank, GSFC; and D. Chakrabarty, MIT, report: "PCA/RXTE observations of XTE J1858+034 were performed on Feb. 20 (1 ks duration) and 24 (8 ks). The source flux (2-10 keV) was 13 and 12 mCrab on Feb. 20 and Feb. 24, respectively. The identification of this source as a pulsar is confirmed by the detection of pulsations in both observations, and a period of 221.0 +/- 0.5 s was determined from the Feb. 24 observations. The pulse profile is nearly sinusoidal with a pulsed fraction of about 25 percent (peak to peak). The pulsations and transient nature of XTE J1858+034 suggest that this is a Be/neutron star binary. Optical observations are strongly encouraged."

4U 1630-47

S. Dieters, University of Alabama in Huntsville; T. Belloni, Astronomical Institute 'Anton Pannekoek', University of Amsterdam; E. Kuulkers, Oxford University; A. Harmon, Marshall Space Flight Center, NASA; and R. Sood, Australian Defence Force Academy, University of New South Wales, report: "We have analyzed RXTE/PCA observations of the present outburst of the x-ray transient 4U 1630-47 (IAUC 6822) taken on Feb. 9.07 and 9.7 UT. We report the discovery of two strong quasiperiodic oscillation (QPO) peaks and band-limited noise in the power spectrum of the 2-14-keV x-ray flux. During our observations, the source flux (2-60 keV) was about 60 and about 140 mCrab, respectively. The first QPO peak is asymmetric and has centroid frequencies of 2.67 +/- 0.01 and 3.19 +/- 0.01 Hz, FWHM of 0.19 +/- 0.02 and 0.33 +/- 0.02 Hz, and fractional rms amplitudes of 16 +/- 4 and 14 +/- 3 percent, during the first and second observations, respectively. The second QPO peak has centroid frequencies of 5.59 +/- 0.07 and 6.53 +/- 0.07 Hz, FWHM of 1.2 +/- 0.2 and 1.3 +/- 0.3 Hz, and fractional rms amplitudes of 5.5 +/- 2 and 6 +/- 2 percent, during the first and second observations, respectively. The second peak is most likely a harmonic of the first. The band-limited noise component has a break frequency between 2 and 5 Hz and a fractional rms amplitude of about 30 percent. Our results indicate that 4U 1630-47 is in a rare state (so-called very high state) seen previously only in two other blackhole x-ray transients (GX 339-4 and GS 1124-68)."

4U 1630-47

4U 1608-52

W. Cui, Center for Space Research, Massachusetts Institute of Technology; and J. Swank, Goddard Space Flight Center, report on behalf of the ASM team at MIT and RXTE Science Operation Facility: "The real-time ASM lightcurve indicates that 4U 1608-52, a recurrent soft x-ray transient source, started an x-ray outburst on Jan. 29. Rough daily-averaged 1.3-12-keV fluxes: Jan. 29, 25 mCrab; 31, 21; Feb. 1, 28; 2, 121; 3, 261; 4, 491. A pointed observation was carried out with the PCA and HEXTE detectors aboard RXTE on Feb. 3.82 UT, and the measured flux was consistent with the ASM results. More pointed RXTE observations have been planned. Observations at other wavelengths are encouraged."

XTE J0055-724 = 1SAX J0054.9-7226

F. E. Marshall, Goddard Space Flight Center (GSFC); and J. C. Lochner, GSFC and Universities Space Research Association (USRA), report the discovery of a transient x-ray source, designated XTE J0055-724, that was pulsating with a period of 59.0 +/- 0.2 s during an observation of the Small Magellanic Cloud (SMC) with the RXTE on Jan. 20: "Based on scans across the source on Jan. 22, we estimate a position of R.A. = 0h55m.3, Decl. = -72o29' (equinox 2000.0; estimated error circle 10'). The average flux was about 6 x 10E-11 erg sE-1 cmE-2 in the band 2-10 keV, with approximately sinusoidal variations of +/- 30 percent. The source was not seen during an observation on Jan. 12."

A. Santangelo and G. Cusumano, Istituto di Fisica Cosmica ed Applicazioni dell'Informatica del CNR, Palermo; G. L. Israel, Osservatorio Astronomico di Roma; D. Dal Fiume, M. Orlandini, and F. Frontera, Istituto di Tecnologie e Studio delle Radiazioni Extraterrestri, Bologna; A. N. Parmar, Space Science Department, European Space Agency, ESTEC; F. E. Marshall, Goddard Space Flight Center (GSFC); and J. C. Lochner and R. H. D. Corbet, GSFC and Universities Space Research Association, report: "A BeppoSAX Narrow Field Instruments Target Of Opportunity observation in the direction of the SMC was performed on Jan. 28. The BeppoSAX MECS detected a pulsating source located at R.A. = 0h54m54s.8, Decl. = -72o26'41" (equinox 2000.0; uncertainty radius 50"), which we have designated as 1SAX J0054.9-7226. The source had a flux of 1.9 x 10E-11 erg sE-1 cmE-2 (2-10 keV) and exhibited pulsations of period 58.969 +/- 0.001 s. Our position for 1SAX J0054.9-7226 is consistent with that of the ROSAT WGACAT source 1WGA J0054.9-7226 and of the Einstein source 2E 0053.2-7242. A periodicity search of archival data from the October 1991 ROSAT observation of 1WGA J0054.9-7226 reveals a strong pulsation with period 59.072 +/- 0.001 s; the same source was not detected in four ROSAT PSPC pointings performed between April and November 1993. Our preliminary conclusion is that 2E 0053.2-7242 = XTE J0055-724 = 1WGA J0054.9-7226 is a newly-recognized 59-s transient x-ray pulsar that is likely to be in a Be/high-mass-x-ray-binary system and unrelated to the three x-ray pulsars reported on IAUC 6788, 6803, and 6814. At least four other sources are now in the MECS field- of-view. Analysis of these sources is currently underway."

MXB 1730-335

R. Guerriero, D. Fox and W. Lewin, Massachusetts Institute of Technology; R. Rutledge, University of California at Berkeley; C. Moore, Kapteyn Institute; M. van der Klis, Astronomical Institute 'Anton Pannekoek', University of Amsterdam (UA); and J. van Paradijs, University of Alabama in Huntsville and UA, report: "The All-Sky Monitor of the Rossi X-ray Timing Explorer indicates the beginning of a new x-ray outburst of this rapid burster. Discovery of a likely radio counterpart (IAUC 6813) makes timely radio and infrared observations extremely valuable."

XTE J0054-720

J. C. Lochner, Goddard Space Flight Center (GSFC) and Universities Space Research Association (USRA); F. E. Marshall, GSFC; L. A. Whitlock, GSFC and USRA; and N. Brandt, Pennsylvania State University, note: "RXTE detected a new pulsating object (period 169.30 s) on 1997 Dec. 17 in the direction of the Small Magellanic Cloud; the object has a 2-10-keV flux of 6.0 x 10E-11 erg sE-1 cmE-2. Scans made across the region on Dec. 20 revealed a single source located at R.A. = 0h54m.6, Decl. = -72o04', (equinox 2000.0; estimated error circle 10'). By this time, the source had brightened to 8.3 x 10E-11 erg sE-1 cmE-2. Pulsations have persisted in observations taken through 1998 Jan. 12, with a monotonic decrease in the period to 168.40 s, and a decrease in the flux to 3.3 x 10E-11 erg sE-1 cmE-2. Pulsations from XTE J0053-724 (IAUC 6788, 6789) and AX J0051-722 (IAUC 6803) persist in a number of these observations. Simultaneous BeppoSAX and RXTE observations of the region are planned for Jan. 28."

NGC 2060

G. Cusumano, M. C. Maccarone, T. Mineo, and B. Sacco, Istituto di Fisica Cosmica con Applicazioni all'Informatica, CNR, Palermo, report: "Analysis of archival data acquired with the MECS instrument onboard the BeppoSAX X-ray Observatory confirms the RXTE detection of pulsations in NGC 2060 (IAUC 6810). BeppoSAX observed the LMC field on 1996 Oct. 25-26, and NGC 2060 was 16' off-axis in the MECS field-of-view. In the energy band 2-10 keV, a pulsed signal was detected with a period of 0.016114775(4) s (in agreement with the extrapolated RXTE value); the folded lightcurve is has a single peak; the observed pulsed countrate, 0.0037 +/- 0.0006 counts/s, corresponds to a flux of 5.9 x 10E-13 erg cmE-2 sE-1."

NGC 2060

XTE J0053-724 AND AX J0051-722

R. Corbet, Goddard Space Flight Center (GSFC) and Universities Space Research Association (USRA); F. E. Marshall, GSFC; J. C. Lochner, GSFC and USRA; and M. Ozaki and Y. Ueda, Institute of Space and Astronautical Science, report: "Further analysis of the ASCA observation of 1WGA J0053.8-7226 = XTE J0053-724 (IAUC 6788, 6789) reveals that there are two transient pulsing sources in this image. 1WGA J0053.8-7226, whose location was given on IAUC 6788, in fact has a period of 46.63 +/- 0.04 s, rather than about 92 s as initially reported. A second source, AX J0051-722, located at R.A. = 0h51m04s, Decl. = -72o13'44" (equinox 2000.0; +/- 1'.2, 90- percent confidence) with a 2-10-keV flux of 1.05 x 10E-11 erg sE-1 cmE-2, exhibits the 91.12-s (+/- 0.05 s) pulsations first detected with RXTE. Initial misidentification arose due to the approximate 2 to 1 ratio of these periods. Additional analysis of the first RXTE observation (IAUC 6777) shows, in addition to the 46.6-s and 91.1-s pulsations, an indication of additional modulation at a period of 74.8 +/- 0.4 s from a possible third pulsar within the 2-deg FWZI field-of-view centered on SMC X-3. However, no corresponding ASCA source can be identified. A ROSAT observation on 1997 Dec. 11 detected both AX J0051-722 and 1WGA J0053.8-7226 at R.A. = 0h50m55s.8, Decl. = -72o13'38", and at R.A. = 0h53m55s.0, Decl. = -72o26'47" (+/- 10"), respectively."