XTE J0421+560 = CI Cam

(Outburst CCD image provided by M. Watanabe)

(vsnet-alert 1620)

Interim report to interested parties:

I know some of you are planning observations at other wavelengths or are anxious about how the observations will be planned, what we know about the source and who will have access to the data. I should inform you of some developments.

1.) Source intensity

Last night the source reached the equivalent of ~ 2 Crab in the PCA, ~ 1 Crab in HEXTE. But it has declined till it is less than 0.5 Crab recently in the ASM.

2.) We think the position needs correcting, but do not have an accurate one for you. The position given in the cirular (which has not come out) is 65.253, 56.058, with an error of ~4'. Last night we executed 4 raster scans over the source. It is clear that the dec pretty good, but the ra looks closer to 65.0 than to 65.25 degrees, so that the error is underestimated.

We should be able to get a position to a couple of arc minutes from the scans. By an accident of where the satellite was and the data streams, we seem to be missing, so far, the real time per detector rates (called Standard 1 and 2). We are attempting to get these data as soon as possible. A few more concidences slowed this progress, such as fall out from a need to change passwords and tighten computer security.

The disposition of the observations I will comment more on shortly.

Ron has been in transit between GSFC and MIT.


CI Cam

(vsnet-alert 1621)

First, sorry for mis-labelling in vsnet-alert relaying as "Haswell" as the sender; it should be "Swank".

The new error box seems to contain a cataloged symbiotic? - Be star, CI Cam = MWC 84.

041942.0 +555957 (2000.0) CAMCI ZAND: 12.31 13.08 B - - - -
041938.8 +560012 (2000.0) MWC84 11.5 Bep
041942.4 +560000 (2000.0) MWC84
Taichi Kato

Note on CI Cam

(vsnet-alert 1631)

Note on CI Cam (Re: XTE J0421+560)

More information on the known variable star, CI Cam, which is located within the new error circle of XTE J0421+560. Our library has fortunately received the original article on CI Cam: Odessa Astronomical Publications, 7, part 1, p. 76 by A. S. Miroshnichenko (anat@gaoran.spb.su).

According to this literature, spectroscopy of the B[e] star MWC 84 = CI Cam revealed absorption features typical for late-type stars. Photometric observations revealed 11.7-d periodicity with an amplitude of 0.3 mag. The best fit for the SED is B0V + G8II plus a dense gas and dust shell.

Hope this information would help for further investigations.

Taichi Kato


(vsnet-alert 1632)

Dear Colleagues:

Attached is the text of our submittion to the IAUC. Good luck observing tonight!


M.R. Garcia, P. Berlind, E. Barton, J.E. McClintock (Center for Astrophysics), P.J. Callanan and J. McCarthy, (UCC Ireland),


Photometric and spectroscopic observations of CI CAM, the possible counterpart of XTE J0421+56 (IAUC 6855, 6857), were obtained with the 1.2m and 1.5m telescopes at the Whipple Observatory during 1998 April 3.08-3.17 UT. Conditions were photometric with variable 2" seeing. We find V=9.25 +/- 0.1, B=10.25 +/- 0.1. This implies a brightening of more than 2 magnitudes in each band, relative to the levels measured by Bergner et al (1995 A&A Suppl 112 221). Relative photometry of 3 B and 4 V frames yields an upper limit to any short term photometric variability of <2% during our observations. Our spectra, obtained at 3.0 and 0.75 angstrom resolution (covering 4000-7000 angstroms and 6000-7000 angstroms), appear similar to those of Downes (1984 PASP 96 807), but the level of Fe II and He I emission has strengthened in comparison to H-Balmer. He II (4685.3 angstroms) and He I (4712.9 angstroms) are detected with equivalent widths of 15+/-5 angstroms and 30+/-10 angstroms respectively, confirming the new HeII emission reported by Wagner et al. (IAUC 6857). The forest of strong H, He I, and Fe II emission lines obscures the continuum to the extent that it is unclear if any photospheric absorption lines are present. None of the lines in our spectra show any evidence for the type of double peaked emission typically arising in x-ray binary or cataclysmic variable accretion disks. Our data are consistent with the association of CI Cam with XTE J0421+56, but imply that this might then be an unusual symbiotic-type x-ray binary, perhaps akin to GX1+4 or 2A1704+241(=HD154791).

(vsnet-alert 1633)

The following submission to the IAU Circulars describes our current conclusion from the VLA data of April 2 and 3. There will be a long VLBA imaging run on this source tomorrow.

If you plot the radio spectra you will see why this is an EXCEPTIONALLY quickly evolving synchrotron radiation source.

>Date: Fri, 03 Apr 1998 17:38:13 -0700
>From: "Robert M. Hjellming (Bob)" 
>Subject: IAU Circular submission on XTE J0421+560 (= CI Cam)
>Cc: rhjellmi, amiodusz
> R. M. Hjellming and A. J. Mioduszewski, National Radio
>Astronomy Observatory, report: "VLA observations of 
>CI Cam on Apr 3.83 UT reveal the presence of an 
>unresolved point source with preliminary flux densities 
>of 120, 470, 650, 500, and 420 mJy at 1.4, 4.9, 8.4, 
>14.9, and 22.5 GHz, respectively.  This indicates that 
>it was optically thick at the two lower frequencies 
>and close to optically thin at the two higher frequencies. 
>The size of the source is less than 0.1" at 22.5 GHz.
>We reanalyzed the 1.4 GHz data for April 2.63 UT (IAUC 6827) 
>and were able to also image the source at 4.9 and 8.4 GHz, 
>so we can report preliminary flux densities of 20, 150, and 
>280 mJy at these three frequencies on April 2.63 UT; at 
>that time the spectrum was optically thick with a spectral 
>index of about 1.5. The rapid variability of factors of ~6, 
>~3, and ~2.3 at 1.4, 4.9, and 8.4 GHz, respectively, 
>indicates that this is synchrotron radio emission which 
>is probably related to the X-ray transient XTE J0421+560 
>(IAUC 6855,6857).  Since the position of the unusual
>radio source coincides with the "symbiotic" star CI Cam, 
>the radio emission and X-ray transient can both be 
>identified with CI Cam."  
(vsnet-alert 1634)

Just an informal note to everyone to report that we took some images with WIYN - given the 3.5m aperture, CI Cam was saturated, but visual inspection suggests that there are no other objects above 20th magnitude which have brightened significantly with respect to the sky survey and are compatible with the RXTE X-ray coordinates. The complete data will arrive in New Haven tomorrow, and we will take a closer look, but I don't think anything else is there.

Charles Bailyn

(vsnet-alert 1638)

I am convinced enough to be willing to tell people we have preliminary VLA evidence for twin jets from CI Cam. This is derived from VLA imaging April 5.08 UT. A 10 hour VLBA run was occuring at the same time, so that (and the April 1 VLBA run) will really tell us what is going on.

We want confirming evidence Monday or Tuesday before we would put it in an IAUC.

The jets shows up best at 1.3 cm where the half-power beam is 0.07", but we see extensions at the same position angle (-45d) on both sides in the 2cm images also.

I am letting people know early, even though there is some chance that I will end up with "egg on my face," because the right spectroscopy/imaging might bring out signs of optical emission from the jets.

Assuming a start when the XR rise began on March 31.06, and a location 0.1" from the center on April 5.08 UT, if the distance is 1 kpc as suggested by Chkhikvadze (and quoted in Bergner et al. 1995) this is ~0.1c apparent lateral motion. Both sides have roughly the same flux so there is no large doppler boosting, which is reasonable if that is the ballpark of the physical velocity.

The radio spectrum continues to evolve from an optically thick to thin state, and at the time of the observations just mentioned preliminary fluxes were 220, 500, 532, 370, and 320 mJy at 1.4, 4.9, 8.4, 14.9, and 22.5 GHz. So the spectrum peaked at 4.9 GHz, whereas on April 3.83 UT it peaked at 8.6 GHz.

The public domain GBI data up to about April 5.0 shows the source rising at 2.25 GHz and staying at about the same flux levels at 8.3 GHz, We had enough time span in the April 3.83 UT VLA run to confirm that the GBI measurements on April 3 correctly observed the hourly flux changes, and there were even signs of the same fluctuation in the high frequencies that seemed present in the GBI 8.3 GHz data.

If you look at the GBI public data, ignore the April 1-2 data for J0421+56 and j0420+56; it needs special processing to shift the visibilities to the correct position and correct for beam sensitivity effects before we will have data on those (critical!) portions of the radio light curves.

Keep up the observing! The radio variations are vary rapid so all aspects of this event in CI Cam are probably short in lifetime, as was spectacularly true for its X-ray emission.


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