Документ взят из кэша поисковой машины. Адрес оригинального документа : http://hea-www.harvard.edu/~garcia/xtej1908iauc.txt Дата изменения: Wed Feb 9 00:13:42 2011 Дата индексирования: Mon Oct 1 21:24:50 2012 Кодировка: Поисковые слова: infrared

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."