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Register a new userRising optical afterglows seen by TAROT
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Authors
B. Gendre
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We present the multi-wavelength study of those gamma-ray bursts observed by TAROT. These events are characterized by the presence at early time of a rising in their optical light curves lasting a few hundred of seconds. In one case (GRB 060904B), a flare occurs at similar time in the X-ray band, while in the other cases the X-ray light curves appear smooth during the optical rise. We investigate the possible nature of this behavior and conclude th at a multi-component emission is mandatory to explain the optical-to-X-ray afterglow.
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We present the time-resolved optical emission of gamma-ray bursts GRB 060904B and GRB 070420 during their prompt and early afterglow phases. We used time resolved photometry from optical data taken by the TAROT telescope and time resolved spectroscopy at high energies from the Swift spacecraft instrument. The optical emissions of both GRBs are found to increase from the end of the prompt phase, passing to a maximum of brightness at t_{peak}=9.2 min and 3.3 min for GRB 060904B and GRB 070420 respectively and then decrease. GRB 060904B presents a large optical plateau and a very large X-ray flare. We argue that the very large X-flare occurring near t_{peak} is produced by an extended internal engine activity and is only a coincidence with the optical emission. GRB 070420 observations would support this idea because there was no X-flare during the optical peak. The nature of the optical plateau of GRB 060904B is less clear and might be related to the late energy injection.
The TAROT telescopes (Telescopes a Action Rapide pour les Objets Transitoires) are two robotic observatories designed to observe the prompt optical emission counterpart and the early afterglow of gamma ray bursts (GRBs). We present data acquired between 2001 and 2008 and discuss the properties of the optical emission of GRBs, noting various interesting results. The optical emission observed during the prompt GRB phase is rarely very bright: we estimate that 5% to 20% of GRBs exhibit a bright optical flash (R<14) during the prompt gamma-ray emission, and that more than 50% of the GRBs have an optical emission fainter than R=15.5 when the gamma-ray emission is active. We study the apparent optical brightness distribution of GRBs at 1000 s showing that our observations confirm the distribution derived by other groups. The combination of these results with those obtained by other rapid slewing telescopes allows us to better characterize the early optical emission of GRBs and to emphasize the importance of very early multi-wavelength GRB studies for the understanding of the physics of the ejecta.
TAROT-1 is an automatic, autonomous ground based observatory whose primary goal is the rapid detection of the optical counterparts of cosmic gamma-ray burst sources. It will be able to begin imaging any GRB localization 8 seconds after receipt of an alert from CGRO/BATSE or HETE-2. TAROT-1 will reach the 17th V magnitude in 10 seconds, at a 10$sigma$ confidence level. TAROT will be able to observe GRB positions given by Beppo-SAX or RXTE, EUV transients from ALEXIS alerts, etc. TAROT will also study a wide range of secondary objectives and will feature a complete automatic data analysis system, and a powerful scheduling software. TAROT will be installed this fall on the Plateau du Calern, 1200m above sea level. We report on the status of the project.
The TAROT telescope has for primary goal the search for the prompt optical counterpart of Cosmic Gamma-Ray Bursts. It is a completely autonomous 25cm telescope installed near Nice (France), able to point any location of the sky within 1-2 seconds. The control, scheduling, and data processing activities are completely automated, so the instrument is completely autonomous. In addition to its un-manned modes, we added recently the possibility to remotely control the telescope, as a request of the Hands-On Universe (HOU) program for exchange of time within automatic telescopes for the education and public outreach. To this purpose we developed a simple control interface. A webcam was installed to visualize the telescope. Access to the data is possible through a web interface. The images can be processed by the HOU software, a program specially suited for use within the classroom. We experienced these feature during the open days of the University of California Berkeley and the Astronomy Festival of Fleurance (France). We plan a regular use for an astronomy course of the Museum of Tokyo, as well as for French schools. Not only does Hands-On TAROT gives the general public an access to professional astronomy, but it is also a more general tool to demonstrate the use of a complex automated system, the techniques of data processing and automation. Last but not least, through the use of telescopes located in many countries over the globe, a form of powerful and genuine cooperation between teachers and children from various countries is promoted, with a clear educational goal.
When a planet inspirals into its host star, it releases gravitational energy which is converted into an expanding bubble of hot plasma. We study the radiation from the bubble and show that it includes prompt optical-infrared emission and a subsequent radio afterglow. The prompt emission from M31 and Large Magellanic Cloud is detectable by optical-near infrared transient surveys with a large field of view. The subsequent radio afterglows are detectable for $10^{3-4}$~years. The event rate depends on uncertain parameters in the formation and dynamics of giant planets. Future observation of the rate will constrain related theoretical models. If the event rate is high (> a few events per year), the circumstellar disk must typically be massive as suggested by recent numerical simulations.
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