XTE J1118+480 = KV UMa

ASCA - VSNET multiwavelength campaign on 2000 May 11

(CCD image by Denis Buczynski, taken on 2000 Mar. 30.83)

(CCD image by Yasuo Sano, taken on 2000 Apr. 8)

(close-up CCD image by Trondal and Granslo)

Alert from the RXTE team

(vsnet-alert 4501)

The RXTE All-Sky Monitor has detected X-ray emission from a new source, XTE J1118+480. The ASM position (equinox 2000.0, with a 90% confidence radius of 6') is centered at R.A. = 11h 18m 17s, Decl. = +48o 03'.0 The average X-ray intensity (2-12 keV) is 39(8) mCrab on March 29. Retrospective ASM analysis indicates that the X-ray flux has been slowly rising since March 5. Another modest outburst had pviously occurred during Jan 29 2000, peaking at 37(3) mCrab on Jan 6. The SIMBAD database lists only an unremarkable guide star (V~11) near the X-ray position. The source was confirmed in an 800 s RXTE pointed observation beginning on 23:14 UT March 29. Rapid flares (e.g. 10 s) were seen, reaching a factor of 5 above the baseline flux near 25 mCrab and suggesting a Galactic X-ray source. No pulsations were deteed. The X-ray spectrum does not vary appciably during intense flares. Preliminary spectral analysis indicates a power-law visible to 30 keV. The photon index is roughly 1.8, which is similar to Cyg X-1 in its hard state. The high galactic latitude (62o) and X-ray properties present a puzzling combination, and observations at other wavelengths are urgently needed.

Optical counterpart

(vsnet-alert 4503)

We started CCD observation on the field of XTE J1118+480 at Kyoto from 17:00 (UT).

There is an object brighter than 15 mag located at 1' from RXTE detected position (R.A. = 11h 18m 17s, Decl. = +48o 03'.0). In the DSS images, there are only faint objects near the position of this possible optical counterpart of XTE J1118+480.

The follow-up observations are strongly urged.

Makoto Uemura and Taichi Kato

(vsnet-alert 4505)

I have observed the field of XTE1118+480 at 2000 March 30 20:43:04 UT with the 33cm F/3 automatic reflector+SXL8 CCD unfiltered+90s exp at Conder Brow Observatory (iau978) and have imaged a bright object at the the location indicated by Uemura in VSNET alert 4503 and have derived the follwing results:

XTE1118+480                    12.91
GSC3451-1542 comparision star  12.8
GSC3451-974  check star        12.22
Observations of this interesting object are continuing.

Best wishes

Visual and CCD observation

(vsnet-alert 4507)

Norwegian Astronomical Society - Variable Star Section

           ***** 1112+48  XTE J1118+480 *****
I have alerted Odd Trondal about this event, and he was able to observe this new x-ray object, both visually and using CCD. His visual observation - in VSNET format - is as follows:
Object         YYMMDD(UT)   Mag  Obs  Instrum.  Note
XTE_J1118+480  000330.867  12.5  TOL  M610      Seq. revised GSC
He observed the object around 20h48m, and estimated it as 0.5 mag. brighter than GSC 3451-0938, which is at magnitude 12.91, according to Guide Star Catalogue. According to Brian Skiff [vsnet-alert 4506] the GSC are only about 0.1 mag. brighter than standard V in this field. Trondal's observed magnitude was thus 12.9+0.1-0.5=12.5.

According to his CCD images (using MX5_16), the object was located about 1'.5 SW from the position reported by RXTE. The RXTE position (2000.0) is RA = 11h18m17s, Decl.=+48o03'.0 (ref. [vsnet-alert 4501] and IUAC 7389).

This observation confirms the optical detections by Makoto Uemura and Taichi Kato [vsnet-alert 4503] and Denis Buczynski [vsnet-alert 4505].

Observer: TOL = O. Trondal (Oslo, Norway). Instrument: 61-cm f/4
  reflector (M610). Clear sky.

                                 Yours sincerely,
                                 Bjorn H. Granslo


(vsnet-alert 4508)

Dear all,

>There is an object brighter than 15 mag located at 1' from 
>RXTE detected position (R.A. = 11h 18m 17s, Decl. = +48o 03'.0). 
>In the DSS images, there are only faint objects near the position 
>of this possible optical counterpart of XTE J1118+480.

I have examined Kyoto image, then am awared that the position of this bright object is fairly close to:

  USNO_A1.0 1350.08089912  11:18:10.826  +48:02:12.55  18.8r 20.1b
= USNO_A2.0 1350.07924726  11:18:10.851  +48:02:12.78  18.8r 19.4b
There is no USNO star within 1' from this star, but on DSS R image (either generation), several fainter objects can be seen. More precise astrometry is in progress.

Sincerely Yours,
Hitoshi Yamaoka, Kyushu Univ., Japan

(vsnet-alert 4509)

The astrometry of the bright (C about 13.0) object using seven GSC-ACT stars gave that R.A. = 11h18m10s.79, Decl. = +48o02'11".2 (equinox 2000.0). The accuracy for R.A. is about 0s.03 (standard deviation), besides the one for Decl. is slightly poor (sigma = 0".6).

It is strongly suggested that USNO_A1.0 1350.08089912 = USNO_A2.0 1350.07924726 is the precurser of XTE J1118+480. On DSS2 images, no other object can be seen within 10" from this USNO star.

Sincerely Yours,
Hitoshi Yamaoka, Kyushu Univ., Japan

(vsnet-alert 4510)

This star is still about magnitude 13 - essentially equal in brightness to GSC 3451:938 on the monitor but no photometry yet - I just started imaging and will continue only for a short while.

Regards, Lew 

Optical spectroscopy

(vsnet-alert 4512)

Dear Colleagues:

Spectra obtained at the FLWO 60" with the FAST spectrograph of the optical counterpart to XTE J1118+48 show weak (~2 Angstrom equivalent width) H-alpha emission, which has a double peaked structure with a FWZI of ~70 Angstroms. There is a complex absorption structure immediately to the blue of the H-alpha emission.

Sincerely, Mike Garcia, Warren Brown, Mike Pahre, Jeff McClintock, Harvard/Smithsonian Center for Astrophysics.

(vsnet-alert 4527)

Dear Colleagues:

We have submitted the following to the IAUC:

M. Garcia, W. Brown, M. Pahre, J. McClintock (Harvard/Smithsonian Center for Astrophysics, P. Callanan (University College, Cork), and P. Garnavich (Notre Dame) report:

Optical spectroscopy of XTE J1118+38 on the night of March 31 (UT) reveals a spectrum typical of an x-ray nova in outburst (ie, Shafer et al 1994 ApJ 434, 698). A series of spectra obtained with the FLWO 1.5m telescope and FAST spectrograph show H-alpha, H-beta, and HeII 468.6 nm emission with equivalent widths (nm) and FWHM (km/sec), accurate to 10%, of 0.19, 2200; 0.01, --; 0.12, 2690, respectively. The H-alpha FWHM we find in this x-ray nova is approximately equal to the largest seen in quiescent black-hole x-ray novae. The H-alpha line shows two blue-ward absorption features, and the H-beta line shows red-ward and blue-ward absorption features. The NaD 589.0 nm line has an equivalent width of 0.004 nm, indicating very low interstellar absorption. The column density out of the plane in this direction (Dickey & Lockman, 1990, ARAA. 28, p215) corresponds to an E(B-V)~0.024. Differential V-band photometry from the FLWO 1.2m telescope, relative to USNO A2.0 1350_08091237 with V=10.91, finds magnitudes of 12.80(0.1) and 13.05(0.1) on March 31.151 and 31.396, respectively. The surprisingly low x-ray to optical flux ratio (ie, V~13, Fx~40 mCrab, IAUC 7389) may be due to a nearly edge-on viewing angle.

Prediscovery optical activity!

(vsnet-alert 4515()

Kesao Takamizawa (Nagano, Japan) reports the examination of his previous photographs has revealed that the optical counterpart of the X-ray transinet XTE J1118+480 was already active since January, which is very consisent with the reported source activity peaking on 2000 January 6 (IAUC 7389).

Photographic magnitude estimates by VSOLJ members

object         YYYYMMDD(UT)   mag  code
XTEJ1118+480   19941104.804  <154p  Tmz.VSOLJ
XTEJ1118+480   19941130.760  <154p  Tmz.VSOLJ
XTEJ1118+480   19950226.587  <154p  Tmz.VSOLJ
XTEJ1118+480   19951118.790  <154p  Tmz.VSOLJ
XTEJ1118+480   19960309.503  <154p  Tmz.VSOLJ
XTEJ1118+480   19970426.476  <154p  Tmz.VSOLJ
XTEJ1118+480   19970528.562  <150p  Tmz.VSOLJ
XTEJ1118+480   19971026.779  <150p  Tmz.VSOLJ
XTEJ1118+480   19971109.759  <154p  Tmz.VSOLJ
XTEJ1118+480   19980417.503  <154p  Tmz.VSOLJ
XTEJ1118+480   19981024.804  <154p  Tmz.VSOLJ
XTEJ1118+480   19981115.803  <154p  Tmz.VSOLJ
XTEJ1118+480   19990112.700  <150p  Tmz.VSOLJ
XTEJ1118+480   19990404.485  <154p  Tmz.VSOLJ
XTEJ1118+480   19991207.774  <154p  Tmz.VSOLJ
XTEJ1118+480   20000108.743  127p  Tmz.VSOLJ
XTEJ1118+480   20000108.747  127p  Tmz.VSOLJ
XTEJ1118+480   20000131.621  138p  Tmz.VSOLJ
XTEJ1118+480   20000131.626  138p  Tmz.VSOLJ
XTEJ1118+480   20000227.617  138p  Tmz.VSOLJ
XTEJ1118+480   20000227.621  138p  Tmz.VSOLJ
XTEJ1118+480   20000324.481  122p  Tmz.VSOLJ
XTEJ1118+480   20000324.487  129p  Tmz.VSOLJ

Observer's code:
  Tmz: K.Takamizawa (Saku-machi,Nagano,Japan)
       Inst.: 10cmR F4 twin patrol cameras  T-Max400 120
       Comparison stars mag.:GSC

(vsnet-alert 4521()

The observations indicates the presence of a previously unrecognized outburst, with a sharp rise to Jan. 28.

Photographic magnitude estimates by VSOLJ members

object         YYYYMMDD(UT)   mag  code
XTEJ1118+480   20000127.595  133p  Tmz.VSOLJ
XTEJ1118+480   20000127.600  133p  Tmz.VSOLJ
XTEJ1118+480   20000127.606  134p  Tmz.VSOLJ
XTEJ1118+480   20000127.610  133p  Tmz.VSOLJ
XTEJ1118+480   20000128.599  125p  Tmz.VSOLJ
XTEJ1118+480   20000128.604  123p  Tmz.VSOLJ

Observer's code:
  Tmz: K.Takamizawa(Saku-machi,Nagano, Japan)
       Inst.25cm F2.8 Baker-Schmidt camera T-Max400 120

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