The 2002 Outburst of GK Persei

The spin profile of GK Per during the second visit (in blue, I also show the spin profile from the first visit; NB. the relative phasing is arbitrary, and that I tried to align the minimum to phase zero by eye for both). Even allowing for phase shifts due to a lack of ephemeris, and the overall normalization change, the profile seems to have changed.

The unfolded spectrum of GK Per from the second observation, plotted with the best-fit model for the first observation (plotted in blue). The absorption has increased noticeably between the two (now about 1.6 x 10²³ cm^-2), while the differences are minimal above 10 keV.

The spin profile of GK Per during the third visit, overplotted with those from the first (blue) and the second (red) visits. I has evolved into a strong single-peaked pulse.

However, the raw light curve shows that the shoulder may still be there in individual pulses.

Since all 5 PCUs were on for this observation (which is highly unusual nowadays; NB I have not actually used data from PCU0, which is not calibrated well enough for sources of this brightness since it lost its propane layer), I extracted light curves in 3 bands: 2.5-5 keV (red), 5-10 keV (green), and 10-20 keV (blue). The above plot shows 2 things: one, that there is an energy dependence in the spin modulation (deeper at lower energies); two, that the modulation is pronounced even above 10 keV. The former may suggest that photoelectric absorption does play a role; the latter, however, suggests that that's far from the whole story, since X-ray photons above 10 keV are not easily absorbed.

The unfolded spectrum of GK Per from the third observation. It's hard to be certain due to the interplay of calibration uncertainties with the true spectral shape, there may be a hint of a "soft excess" in the lowest channel included in this plot.

The spin profile of GK Per during the roufth visit, overplotted with those from the first (blue), the second (red), and the third (green) visits.

The unfolded spectrum of GK Per from the fourth observation; the best fit simple continuum model is identical to that for the third (green).

The spin profile of GK Per during the fiffth visit, overplotted with those from the first (blue), the second (red), the third (green), and the fourth (magenta) visits. It was noticeably brighter during this observation, not sure if this was part of the overall evolution of the outburst or a fluctuation.

The unfolded spectrum of GK Per from the fifth observation.

The spin profile of GK Per during the sixth visit: note the change of scale (this plot goes down to zero, previous ones did not).

The unfolded spectrum of GK Per from the sixth observation. Both the spin profile and the spectrum show that GK Per was fainter in X-rays during the 6th RXTE visit, even though it is just peaking in the optical.

The spin profile of GK Per during the seventh visit. The flux level has recovered to the level seen earlier (the dashed blue line is the profile from the sixth observation).

The unfolded spectrum of GK Per from the seventh observation. This observation was almost exactly 48 hrs after the sixth observation --- thus we can rule out orbital modulation as the cause of the "dip."

The raw and spin-folded light curves of GK Per during the eighth visit.

The spin-folded light curves of GK Per during the ninth visit, compared with all the previos profiles (above); and the spin-folded light curves during the two halves of the ninth visit (below). Note that they were separated by about 3 hrs.

The unfolded spectrum of GK Per from the ninth observation, the most absorved so far.

The spin-folded light curves of GK Per during the second half of the tenth visit, compared with all the previos profiles (above); and the spin-folded light curves during the two halves of the tenth visit (below). Note the drastic changes in two halves.

The unfolded spectrum of GK Per from the tenth observation (new Y scale). The second half is the most absorbed so far, while the first half is buried in the cluster of colored lines represnting earlier data.

The spin-folded light curves of GK Per during the eleventh visit.

The unfolded spectrum of GK Per from the eleventh observation. In the visible band, GK Per seems to have started a slow decline, but it's still going strong in the X-rays.

The spin-folded light curves of GK Per during the twelfth visit.

The unfolded spectrum of GK Per from the twelfth observation, still strong in the X-rays despite the optical decline.

The spin-folded light curves of GK Per during the thirteenth visit.

The unfolded spectrum of GK Per from the thirteenth observation. When will it start to decline in the X-rays? Will we be able to catch the decline with RXTE, or will it wait until after it gets too close to the Sun even for RXTE? The last date on which we can observe GK Per with RXTE is extimated to be May 3rd.

The spin-folded light curves of GK Per during the fourteenth visit.

The unfolded spectrum of GK Per from the fourteenth observation. Although the flux level remains high, and the spin profile unchanged, the level of absorption has gone done considerably in this visit. This may well be a sign that the X-ray outburst is finally approaching its end.

The raw and the spin-folded light curves of GK Per during the fifteenth visit. Although the count rate is still high, the spin modulation is shallower and there is now a hint of an interpulse.

The unfolded spectrum of GK Per from the fifteenth observation. There is a slight decline in the flux level above 10 keV, although it's still quite bright compared with the quiescent level.

The raw and the spin-folded light curves of GK Per during the sixteenth visit. Although the count rate is still high, the spin modulation has all but disappered in the folded version, although it is still there in the raw curve.

The unfolded spectrum of GK Per from the sixteenth observation. There is a slight decline in the flux level above 10 keV, accompanied by a marked decline in absorption.

Last updated 2002 May 5.