OPTICAL TRANSIENT NEAR HX PEG
A description of my discovery of a new variable star
The evening of Sep 19, 2003 was a typical one for me. After working on my PhD research, I was at home
and relaxing as I usually did by visually observing variable stars for the AAVSO. At the time, I was a
typical economically challenged graduate student, living in a roach and termite infested room
on 9th Ave in the Kaimuki section of Honolulu, Hawaii. But I was fortunate to have a small lanai
and it allowed me to setup my 14.5" reflector telescope on it, and observe a narrow strip of sky between the
trees and buildings. That evening, around 10PM local time I was estimating the brightness of HX Peg,
a well known cataclysmic variable. I was quite familiar with the field surrounding it, and as I approached
my target, I noticed a new stellar object nearby, which I had never seen there before. After checking
for any motion, and MPChecker for minor planets, and online for any recent reports, and all coming up
negative, my excitement began to build rapidly! Could this be a new nova? I quickly sent an email message to
an observer colleague of mine in Michigan, who was just able to confirm my finding before his break of
dawn. Confident of my new object, I posted it to the AAVSO discussion list, and it was thus distributed
worldwide.
I continued to observe it over the next 2 hours, and was surprised to notice it fading at an accelerating rate! By 1:30AM local time, it had faded below my limit. This was quite atypical behavior for a nova. While it was conceivable that some rapid or eclipsing variable star could behave in this way, there was no such bright variable known at this location. Surely, if it was such an object, it would have been discovered decades ago I thought, so it seemed improbable to be an undiscovered variable.
Therefore, my new hypothesis was that this was a possible GRB optical afterglow caught fading from maximum light. These types of newly discovered high-energy cosmological events were a hot area of research at the time, and catching the optical afterglow visually by pure luck like this, would have been a first in Astronomy!!
GRB afterglows typically fade very rapidly, and a few hours later may no longer be detectable, except by the largest telescopes. Therefore, I attempted to engage as many professional astronomers as I could, via the internet, to image the field as quickly as possible. Henden was able to image the field approximately 16 hours after my last observation using a 1m telescope, and nothing obvious was apparent near the center of my error circle. A deeper image using the 10m Keck on Mauna Kea, made 4 hours after that, really didn't show anything definitive either.
There was a magnitude 15.5 star just within my error circle, and based upon his suspicions, Henden subsequently obtained accurate photometry of it. This clearly showed a characteristic light curve (Fig 5) of an RR Lyrae type variable with a nearly exactly integral-day period!
This strange coincidence resulted in the variable essentially always appearing the same brightness to a given observer at the same time of night, and thus escaped detection as a variable star up until my discovery!
REFERENCE
IBVS 5521
Last modified: Dec 13, 2008