CCD Image

CCD Image of the GRB000926 optical transient

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Annotated image from 28-September 2000 UT, center part of image showing the OT, black stars, light background.
Blown-up image from 28-September 2000 UT, white stars, black background.
Full frame image from 28-September 2000 UT, white stars, black background.
Follow-up image from 3-October 2000 UT, center part of image (approximately same scale as the annotated version from 28-Sept), black stars, light background.
Joe Dellinger’s account of the imaging the GRB000926 afterglow.

The image below is a stack of best seven (out of eleven), unfiltered, four-minute CCD images taken by Joe Dellinger at the George Observatory, using the Fort Bend Astronomy Club’s 18-inch (46 cm) f/4.5 reflector and Rice University’s ST-9e camera (on generous loan). The mid-point of the image stack 03:16:16 UT, 28 September, 2000. The image is roughly 20 arcminutes on a side. North is up, East is to the left.

I processed the images using MaxIm DL. The images were dark subtracted and flat fielded (using a week-old flat, none was taken on the 28th). A “Flatten background” was then applied. An attempt was made to remove hot/cold pixels in the kernel option before stack, but some have made it through, giving rise to a streaky grain. Thanks go to Dennis Borgman for advice and help when problems were encountered in doing the image stack. A blowup of the central part of the image is displayed below the main image. I’ve also added an annotated version of this image as a “negative” (black stars, light sky) with the optical transient (OT) bracketed with red bars to its left and above.

Using the Astrometrica software package and 10 USNO-A2.0 reference stars, I derived a J2000 position of:

RA 17h 04m 09.76s,
DEC +51d 47′ 10.6″

for the optical transient. The “magnitude” was 19.1, but this is rather uncertain, due to the faintness of the OT, the non-standard magnitudes of the USNO stars, and our lack of standard filter.

On 3 October 2000, Randy Pepper and I shot a follow-up series of images. Our follow-up stack shown below consists of the best 31 one-minute images (out of 41 taken) which were started at 03:52:20 UT. The image is a blowup of the center part of the full image, with black stars on a light sky. We used the same telescope and camera as Joe did. This image did not go quite as deep, because the night was hazier and we were shooting through a bit greater air mass. Even so, the OT appears to have faded from view. We may try to shoot this area again at the next dark moon.

Blowup of the central part of the image above.

Annotated version, optical transient bracketed with red bars to the left and above.

Follow up image 3 October 2000.