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We report on our program for multiband photometry observations of Optical Transients of Gamma-Ray Bursts at the 152 cm telescope in Loiano. 40 Km south of Bologna, Italy. Observations in the four semesters starting on July 1st, 2001, were performed for 13 events and allowed positive detections for six of them. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The study of the color indices of 23 optical afterglows (OAs) of GRBs shows that the color variations during the decline of the OAs are very small during t - T0 < 10 days. The colors in the observer frame concentrate at (B - V)0 = 0.45 ± 0.15, (V - R)0 = 0.41 ± 0.09, (R - I)0 = 0.46 ± 0.13, (I - J)0 = 0.88 ± 0.15, but are more scattered in (U - B)0. These findings entirely confirm our previous ones, determined from a smaller ensemble of the OAs with a smaller range of the redshifts z. The strong concentration of the color indices of most OAs also suggests that the intrinsic reddening (i.e. inside their host galaxies) must be quite similar and relatively small for these events. The maximum reddening which can be allowed by the scatter of the colors of the individual OAs is about EB-V = 0.2. This suggests that they are not deep inside the star-forming regions or, alternatively, that the dust is destroyed by the energetic initial flash. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

We present here the soft X-ray All-Sky Monitor (ASM). It is based on the current technological capabilities, sensitive in the ∼ 0.1 – 10.0 keV range with angular resolution of ∼ 3 – 4 arcmin, and has a limiting detectable flux ∼ 10-12 erg/s/cm2 for daily scans in the mentioned energy range. The ASM will play a key role in studying transient X-ray sources like XRBs, GRBs, XRFs, X-ray novae, as well as in the study of the long term variability of X-ray sources like XRBs, AGN, or stellar X-ray flares. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The High Energy Transient Explorer (HETE) mission is devoted to the study of gamma-ray bursts (GRBs) using soft X-ray, medium X-ray, and gamma-ray instruments mounted on a compact spacecraft. The METE satellite was launched into equatorial orbit on 9 October 2000. A science team from France, Japan, Brazil, India, Italy, and the US is responsible for the METE mission, which was completed for ∼ 1/3 the cost of a NASA Small Explorer (SMEX). The METE mission is unique in that it is entirely "self-contained," insofar as it relies upon dedicated tracking, data acquisition, mission operations, and data analysis facilities run by members of its international Science Team. A powerful feature of METE is its potential for localizing GRBs within seconds of the trigger with good precision (∼ 10') using medium energy X-rays and, for a subset of bright GRBs, improving the localization to ∼ 30' accuracy using low energy X-rays. Real-time GRB localizations are transmitted to ground observers within seconds via a dedicated network of 14 automated "Burst Alert Stations," thereby allowing prompt optical, IR, and radio follow-up, leading to the identification of counterparts for a large fraction of METE -localized GRBs. METE is the only satellite that can provide near-real time localizations of GRBs, and that can localize GRBs that do not have X-ray, optical, and radio afterglows, during the next two years. These capabilities are the key to allowing METE to probe further the unique physics that produces the brightest known photon sources in the universe. To date (December 2002), HETE has produced 31 GRB localizations. Localization accuracies are routinely in the 4'-20' range; for the five GRBs with SXC localization, accuracies are ∼1-2'. In addition, METE has detected ∼ 25 bursts from soft gamma repeaters (SGRs), and >600 X-ray bursts (XRBs). [ABSTRACT FROM AUTHOR]

The BAN (Burst Alert Network) is comprised by an equatorial belt of VHF receiving stations dedicated to relaying via the internet HETE burst alerts and spacecraft status reports to the MIT Operations Center. Messages created by the satellite are sent to the GCN within seconds. Each of the 14 BAN stations consists of low cost (total is less than $3000) components: a simple antenna, a preamplifier, a PC, and a receiver. HETE broadcasts a repeated VHF message stream to minimize the data corruption due to low signal level and varying local noise conditions. This low technology approach has proven to be successful for HETE operations. Real time coverage of the satellite has steadily increased from the time of the launch in 2000 to a value near 80% in 2002. [ABSTRACT FROM AUTHOR]

The study of the color indices and luminosities of 17 optical afterglows (OAs) of GRBs, including the most recent one, GRB010222, showed that the color variations during the decline of OAs are quite small during t - T[sub 0] < 10 days and allow a comparison among them, even for the less densely sampled OAs. The colors in the observer frame concentrate at (V - R)[sub 0] = 0.40 ± 0.13, (R - I)[sub 0] = 0.46 ± 0.18, (B - V)[sub 0] = 0.47 ± 0.17, except for GRB000131 and GRB980425. However, large scatter is observed in (U- B)[sub 0]. The color evolution of the OAs is negligible although their brightness declines by several magnitudes during t - T[sub 0] < 10 days. Such a strong concentration of the color indices also suggests that the intrinsic reddening (inside their host galaxies) must be quite similar and relatively small for all these events. The absolute brightness of OAs in the observer frame lies within M[sub R[sub 0]] = -26.5 to -22.2 for (t - T[sub 0])[sub rest] = 0.25 days. The general decline rate of the OA sample considered here seems to be independent of the absolute optical brightness of the OA, measured at some t - T[sub 0] identical for all OAs, and the light curves of all events are almost parallel, when corrected for the redshift-induced time dilation. [ABSTRACT FROM AUTHOR]

We present results of the study of the comprehensive properties of optical afterglows of gamma-ray bursts (GRBs) using the color indices determined from published multicolor photometry. Suitable data for nine afterglows are available. We found that the color variations, detectable for the well-covered events (usually reddening on late decline), are generally small enough to allow for a comparison of the respective afterglows (especially for t-T[sub 0]<10 days). Most afterglows concentrate at V-R=0.4, R-I=0.6, B-V=0.5. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Gamma-Ray Bursts are now detected at redshifts even as large as eight. In the present note we try to find changes due to redshift in the well known 'Amati Relation' between the restframe peak and isoptropic energies in the prompt phase of the events. [ABSTRACT FROM AUTHOR]

The measurement of redshift for a number of Gamma-Ray Bursts or their hosts now makes it possible to estimate their isotropic total radiation and its dependence on redshift, as it has been done by. I discuss whether or not it is already possible, from the available data, to prove that there is a dependence of the properties of Gamma-Ray Bursts on redshift. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The 57 cm telescope of the Klef Observatory has been used for follow-up observations of selected GRBs. Limiting magnitudes as deep as mag 22 have been obtained. The results obtained are presented and discussed. We also address the capabilities of the current system for GRB analyses as well as further improvements including the newly developed 1.06 m aperture CCD telescope. [ABSTRACT FROM AUTHOR]