Astronomy Montage


Sunday, September 03, 2006

Biography of GRB 060218

At 03:34:30 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 060218A(trigger=191157). Swift slewed immediately to the burst. The BAT on-board calculated location is RA,Dec 50.404, +16.866 deg {RA 03h 21m 37s, DEC +16d 51' 58"} (J2000) with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The TDRSS lightcurve shows nothing, which is consistent and common for an image trigger.

The XRT began taking data at 03:37:04 UT, 153 seconds after the BAT trigger. The XRT on-board centroid algorithm did not find a source in the image and no prompt position is available. We are waiting for down-linked data to detect and determine a position for the source.

The UVOT began taking data 152 seconds after the BAT trigger. There is an indication of an afterglow candidate at RA,Dec RA 03h 21m 39.8s,DEC +16d 52' 06" +/- 1 arcsec with an estimated B magnitude of 19.4.

The orbiting NASA telescope Swift picked up the gamma-ray burst (GRB) in a star-forming galaxy about 440 million light years away, towards the constellation of Aries. As it swivelled in the direction of the blast, Swift also relayed its discovery to major ground-based and space-based observatories. The combined data from their sensors has been pieced together to give a picture about what happened over the next 17 days.
GRBs have long been associated with the aftermath of supernovae. They are typically huge releases of energy. In a few seconds, they can spew out more energy than the sun will do in its entire expected lifetime of 10 billion years. This GRB was highly unusual. It lasted almost 40 minutes, whereas a typical GRB only lasts a few milliseconds or tens of seconds at the most, and it was remarkably weak, too - a mild type of GRB known as an X-ray flash.

The astronomers believe that this burst was a high-energy jet that pierced through the doomed star from its collapsing core. In essence, it was sending out a warning that a supernova was imminent. Suddenly, as the GRB faded away, the massive star blew itself into smithereens, sending out a "slightly aspherical" shock wave that rocketed across the galaxy. The star's glowing remains were confirmed optically two days later and classified as supernova SN 2006aj. Britain's Particle Physics and Astronomy Research Council (PPARC) operates an ultra-violet/optical telescope aboard Swift.
For further info to find out how the GCN GRB CooRdinate Network works

Saturday, September 02, 2006

Dark Matter in Bullet Cluster

The "bullet cluster" is a galaxy cluster denoted 1E 0657-56 which was formed after the collision of two large clusters of galaxies(ie individual groups of galaxies)

This monumental energetic collision can only get surpassed by The Big Bang in terms of energy output, and has resulted in tearing apart dark matter from normal matter as an outcome of the collision.

The spectacular bullet cluster is composed of a hundred million degree bullet shaped cloud of gas, which is due to wind produced by the high speed collision of the two galactic clusters.

Because dark mater does not interact with the hot gas it was not slowed by the collisional drag force, wheras normal matter was slowed due to the collisonal drag force due to its interaction with the hot gas.

Xray imaging by the Chandra XRay Telescope showed this separation and thus provided the first direct evidence for dark matter.

It is formally known as 1E0657-56 and has coordinates: RA 06h 58m 37.9s | Dec -55ยบ 57' 0". It is about 4 billion light years from Earth in the constellation of Carina. The subcluster passed through the cluster center 150 million years ago creating a "bow-shaped shock wave located near the right side of the cluster" formed as "70 million degree Celsius gas in the sub-cluster plowed through 100 million degree gas in the main cluster at a speed of about 6 million miles per hour". Strictly speaking, the name Bullet cluster refers to the smaller subcluster, moving away from the larger one.