GRB 090817: INTEGRAL/OMC's unlucky gamma-ray burst
On 17 August 2009, INTEGRAL caught another long Gamma-Ray Burst (GRB) in the field of view of IBIS/ISGRI. This one was special as it was also in the smaller field of view of the X-ray monitor JEM-X 1 and (almost) of the optical camera OMC.
On 2009-08-17 at 2:51 a.m. (00:51 GMT) INTEGRAL caught another Gamma-Ray Burst
(GRB) in the field of view of IBIS/ISGRI. Although this happens about 10 times a
year, this GRB was special, as it was not only within the field of view of the
imager IBIS/ISGRI and of the spectrograph SPI, but also in the smaller field of
view of the X-ray monitor JEM-X 1 and (almost) of the optical camera OMC.
Usually not all the data of OMC are downloaded from the satellite to the ground,
but in case of a GRB in its field of view, a command is sent to the spacecraft
to download the data around the burst position. This worked fine. But OMC was
unlucky again (see INTEGRAL
Picture of the Month of July 2005) - the burst was just outside its detector
area. This is illustrated in the image to the left showing the IBIS/ISGRI error
circle ontop of the OMC image.
Nevertheless GRB 090817 provides a lot of data to analyse. Both the IBIS/ISGRI
and the JEM-X 1 light curves show two prominent peaks and a comparably long
duration of about 250 seconds. The combined INTEGRAL spectrum covers the whole
range of a gamma-ray burst, from 3 keV to several hundreds of keV, but, unluckily,
not simultaneously the optical range.
Other observations of this GRB were reported and can be accessed on the GCN site.