XTE J1908+094 P. M. Woods, C. Kouveliotou, M. H. Finger, and E. Gogus, National Space Science and Technology Center; and J. Swank, C. Markwardt, and T. Strohmayer, Goddard Space Flight Center, report the serendipitous discovery of a new x-ray transient, XTE J1908+094, in RXTE PCA observations of the soft-gamma-ray repeater SGR 1900+14, triggered following the burst activity on Feb. 17-18 (GCN 1253). These observations failed to detect the 5.2-s SGR pulsations, pointing towards a possible new source as the origin of the high x-ray flux. An RXTE PCA scan of the region around SGR 1900+14 on Feb. 21 was consistent with emission only from known sources (and no new sources). However, the scans required SGR 1900+14 to be 20 times brighter than its quiescent flux level (GCN 1256). A Director's Discretionary Time Chandra observation on Mar. 11 showed that the SGR was quiescent and did not reveal any new source within the Chandra ACIS field-of-view. A subsequent RXTE PCA scan on Mar. 17, taken in combination with the first scan, required that a new 19h08m50s, Decl. = +9 22'.5 (equinox J2000.0; estimated 2' systematic error radius), or approximately 24' away from the SGR source. The source spectrum (2-30 keV) can be best fit with a power-law function including photoelectric absorption (column density N_h = 2.3 x 10**22, photon index = 1.55). Iron line emission is present, but may be due to the Galactic ridge. Between Feb. 19 and Mar. 17, the source flux (2-10 keV) has risen from 26 to 64 mCrab. The power spectrum is flat between 1 mHz and 0.1 Hz, falling approximately as 1/f**0.5 up to 1 Hz. At 1 Hz is seen a broad quasiperiodic oscillation peak and a break to a 1/f^2 power law, which continues to 4 Hz. The fractional rms amplitude from 1 mHz to 4 Hz is 43 percent. No coherent pulsations are seen between 0.001 and 1024 Hz. The authors conclude that XTE J1908+094 is a new blackhole candidate. (C) Copyright 2002 CBAT 2002 March 21 (7856) Daniel W. E. Green ----- XTE J1908+094 M. Feroci, Istituto di Astrofisica Spaziale e Fisica Cosmica, CNR, Rome; and L. Reboa, BeppoSAX Science Operation Center, Telespazio, Rome, on behalf of the BeppoSAX team, report: "As a part of the follow-up program on soft gamma-ray repeaters, BeppoSAX serendipitously observed the new x-ray transient XTE J1908+094 (IAUC 7856). Due to technical problems with the battery system of the spacecraft, the source was observed only with the Phoswich Detection System (PDS) in the nominal energy range 15-300 keV. The observation started on Mar. 9.386 UT and lasted until Mar. 12.210, for a net observing time of about 48 000 s. Attributing all the counts detected in the collimated field-of-view of the PDS (1.3 deg, full width at half maximum) to the new source, we can derive a high-energy spectrum for the new x-ray transient. The source is well detected up to > 250 keV, with a net count rate of (18.24 +/- 0.04) counts/s at 15-300 keV. The hard x-ray spectrum is not consistent with an extension of the absorbed power law (photon Instead, our data require the introduction of a high-energy cut-off at about 100 keV (but still resulting in an unacceptable fit, with chi**2 of about 5 per degree of freedom). Based on this model, taking into account the 24' off-axis location of the source, we derive a source flux of about 2.9 x 10**-9 erg cm**-2 s**-1 in the energy range 15-100 keV. The BeppoSAX/PDS detection of the source up to 250 keV strongly supports the interpretation of the new x-ray transient as a new blackhole candidate." (C) Copyright 2002 CBAT 2002 March 26 (7861) Daniel W. E. Green ----- XTE J1908+094 J. J. M. in 't Zand, Astronomical Institute, Utrecht University, and Space Research Organization Netherlands; and M. Capalbi and M. Perri, ASI Science Data Center, Frascati, report on behalf of a larger team that two target-of-opportunity observations were carried out with BeppoSAX on the proposed black-hole x-ray transient XTE J1908+094 (Woods et al., IAUC 7856; Feroci et al., IAUC 7861): "The second observation was with the Medium-Energy Concentrator Spectrometer on Apr. 2.4-3.8 UT and resulted in an order-of-magnitude improvement of the positional accuracy. We localize the source at R.A. = 19h08m52s.6, Decl. = +9d23'07" (equinox 2000.0; uncertainty 17", 90-percent confidence). This is 0'.9 from the position determined by Woods et al. but consistent within its 2' accuracy." (C) Copyright 2002 CBAT 2002 April 10 (7873) Brian G. Marsden XTE J1908+094 P. Garnavich, J. Quinn (University of Notre Dame) and P. Callanan (University College, Cork) report that images of the X-ray error circle of XTE J1908+094 (IAUC 7856, 7873) were obtained with the 1.8m Vatican Advanced Technology Telescope (VATT) on 2002 Apr. 8 and 9 (UT). Total exposures of 1500s in I-band and 2100s in R-band were accumulated. We found no obvious new sources within the error circles compared with the red Digitized Sky Survey and no strongly varying sources between the two nights. Six stars from the USNO A-2.0 provide a coordinate accuracy of 0.2" and we find no sources to a limit of I=22.0 within 3" of the radio position of Rupen, Dhawan & Mioduszewski (IAUC 7874). A finder chart of the field can be found at: http://www.nd.edu/~pgarnavi/xtej1908/vatt.jpg ------------------------------------------------------------------------------ The Astronomer's Telegram http://atel.caltech.edu/ ------------------------------------------------------------------------------ Posted: Thu Apr 4 03:30:00 PST 2002 -- Sat Apr 13 03:30:01 PDT 2002 ============================================================================== ATEL #86 ATEL #86 Title: Search for an Optical Counterpart of XTE J1908+094 Author: R. M. Wagner (LBTO) and S. Starrfield (ASU) Queries: rmw@as.arizona.edu Posted: 13 Apr 2002; 7:30 UT Subjects: Radio, Infra-Red, Optical, X-ray, Black Holes, Cataclysmic Variables, Neutron Stars, Transients, Stars We obtained R-band imagery of the X-ray error box of the black hole candidate XTE J1908+094 (IAUC #7856, #7861, and #7873) on 2002 April 11.44 UT with the Hiltner 2.4-m telescope and 8K CCD camera at the MDM Observatory on Kitt Peak. At the location of the possible radio counterpart reported by Rupen, Dhawn, and Mioduszewski (IAUC #7874), we do not find an optical counterpart brighter than R ~ 23. A R ~ 20 mag star (RA = 09:08:52.75, DEC = +09:23:03.9, J2000) lies 4.8 arcsec west and 1.0 arcsec south of the radio position. Further observations will be useful, particularly at infrared wavelengths. ------------------------------------------------------------------------------ Password Certification: R. Mark Wagner (rmw@as.arizona.edu) XTE J1908+094 S. Chaty, Open University; and R. P. Mignani, European Southern Observatory (ESO), Garching, report on the detection in the near-infrared of a likely counterpart to the blackhole candidate XTE J1908+094 (IAUC 7856). Target-of-opportunity observations performed by L. Vanzi (ESO) with the ESO New Technology Telescope on Apr. 25 and 29 show an infrared source that is coincident (within an uncertainty of +/- 0".17 in each coordinate) with the position of the radio counterpart (IAUC 7874). The magnitudes of the source on Apr. 25 were J = 18.7 +/- 0.3, H = 17.2 +/- 0.3, K_s = 16.4 +/- 0.2. Although the source was also visible on Apr. 29, the data do not allow an accurate determination of the magnitude and therefore prevent any variability measurement. Taking the value of column density given on IAUC 7856, and assuming that the source is located near the Galactic center, absolute magnitudes of J = 0.4, H = 0.3, and K = 0.3 are derived. Chaty and Mignani add: "If the source is indeed the actual counterpart of XTE the accretion disk. In this case, the derived upper limits show that the source is a low-mass system with a companion star of spectral type later than A. Further photometric observations are encouraged to search for variability of this source." Circular No. 7874 Central Bureau for Astronomical Telegrams INTERNATIONAL ASTRONOMICAL UNION Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A. IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions) CBAT@CFA.HARVARD.EDU (science) URL http://cfa-www.harvard.edu/iau/cbat.html ISSN 0081-0304 Phone 617-495-7440/7244/7444 (for emergency use only) XTE J1908+094 M. P. Rupen, V. Dhawan and A. J. Mioduszewski, National Radio Astronomy Observatory, report: "We have detected a possible radio counterpart to the black-hole candidate XTE J1908+094. Observations with the Very Large Array on Mar. 21 and 22 show a radio source (flux 1.1 +/- 0.1 mJy at 4860 MHz, 0.84 +/- 0.08 mJy at 8460 MHz) at R.A. = 19h08m53s.077, Decl. = +9d23'04".90 (J2000.0, uncertainty about 0".1 in each coordinate), within the 17" error box reported from BeppoSAX (IAUC 7873) and about 8" from its center. The radio spectrum is consistent with this identification, extension in the images (resolution 0".20). Further monitoring is underway." although no variability has yet been seen, and there is no obvious extension in the images (resolution 0".20). Further monitoring is underway."