MBCAA Observatory

GRB041211: Search for an optical transient

Observation: 11 Dec 2004

Creation: 25 Dec 2004

Abstract

10 hours after the burst, no optical counterpart down to mag 17.8.

Introduction

The gamma ray burst GRB041211 was discovered by the HETE satellite, with a circular error box of 80" radius. It is a classical hard GRB with a duration >100s and a 30-400 keV fluence of 1.0 x 10-5 ergs cm-2 [Dezalay et al (GCN 2839)].

Observation

I observed the gamma ray burst field 10 h 18 mn after the event with a 203 mm SC telescope fitted with a Clear filter and a SBIG ST7E camera. The galactic coordinates are around b=7.5 l=195 and there was no Moon. I obtained 10 one-minute exposure images that I stacked.

Analysis

I did not blink the resulting image against e.g. the DSS. Instead, I used the AstroMB software to scan the image and to match the detected sources against catalogs:

  • AstroMB is parametrized to be a very sensitive source detector. 764 sources are then detected;
  • 38 sources are considered to be defects (hot pixels, cosmic, etc) because their FWHM is significantly smaller than the average FWHM;
  • 28 sources are considered as extended because of their large FWHM;
  • the sources are matched against the GSC 1.1, the USNO-A2 catalog, the USNO-B1 and 2MASS catalogs over the Internet;
  • 12 very faint sources remain without a catalog match. One of them lies in the error box;
  • profiling theses sources show that they are not real. AstroMB found them because it was parametrized to be very sensitive.

  • Therefore no optical counterpart are detected.

    The image is here.

    To evaluate the sensitivity of the search, the sequence from Henden (GCN 2844) is used. The limit magnitude is estimated as 17.8. (This is not very precise because the observation is done with no filter).

    Note

    No other observer found an optical counterpart.

    Technical notes

    Telescope and camera configuration.

    Computer and software configuration.

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