The GLAST-AGILE Support Program (GASP)

1. The GLAST-AGILE Support Program (GASP) Massimo Villata & Claudia M. Raiteri for the WEBT collaboration November 1997: birth of the Whole Earth Blazar Telescope, an international consortium of optical, NIR, and radio observers. Up to now, 23 multiwavelength campaigns organized, usually including high-energy observations by satellites. Since the CGRO operation in 1991-2000, one of the primary unresolved questions about the blazar gamma-ray emission has been its possible correlation with the low-energy (in particular optical) emission. To help answer this problem, the Whole Earth Blazar Telescope (WEBT) consortium has organized the GLAST-AGILE Support Program (GASP) to provide the optical-to-radio monitoring data to be compared with the gamma-ray detections by the AGILE and GLAST satellites. This new WEBT project started in early September 2007, just before a strong gamma-ray detection of 0716+714 by AGILE. http://www.oato.inaf.it/blazars/webt/ The GASP on 0716+714 (Villata et al. 2008, A&A 481, L79) R-band data collected by the GASP and WEBT in August-November 2007. Green boxes indicate the periods of the first AGILE pointings in September 2007, including the strong gamma-ray detection reported by Giuliani et al. 2007 (Atel 1221; red box). In the same period, we observed a noticeable optical flare. In mid October the optical flux started to rise, reaching a peak of R = 12.15, comparable to the brightest states ever observed. This triggered intensive observations at all wavelengths and in particular AGILE (blue box) and Swift ToO pointings. 37 GHz and optical R-band flux densities in August-November 2007 together. The optical and radio outbursts appear roughly contemporaneous. However, when seen in detail, the two events show a different behaviour. A contemporaneous optical-radio event has sometimes been observed in blazars. However, usually radio events are observed to lag behind the optical ones by several weeks or months. In the case of 0716+714, Raiteri et al.(2003, A&A 402, 151) noticed that in the 1994-2001 observing period, major optical outbursts may have modest radio counterparts. Thus, the optically-emitting jet region is sometimes not completely opaque to the high radio frequencies. In particular, it is quite transparent to them in the case of the 2007 outburst. Lower radio frequencies are at least partially absorbed, as the 14.5 GHz delay and the strongly-inverted radio spectrum indicate. Source SEDs built with V B U W1 M2 W2 data from Swift-UVOT and B V R I J H K data from GASP-WEBT, at three epochs characterized by different brightness levels. Data were corrected for Galactic extinction. The SEDs show two main features: the bluer-when-brighter behaviour (especially in the UV band), which is typical of BL Lac objects, and the wavy shape of the spectra. We note that the dip in the W1 band resembles an analogous feature found in the optical-UV SEDs of AO 0235+16 by Raiteri et al.(2008, A&A 480, 339), who interpreted it as anomalous absorption, or as a UV excess at higher frequencies. However, in our case the drop, though systematic, is within the uncertainties, and might be due to calibration problems and/or uncertainties on the extinction. A cross-correlation analysis between the GASP-WEBT data and the AGILE data is under way.