TITLE: GCN CIRCULAR NUMBER: 19167 SUBJECT: Konus-Wind observation of GRB 160310A (possible ultra-long GRB?) DATE: 16/03/11 17:33:47 GMT FROM: Dmitry Frederiks at Ioffe Institute D. Frederiks, S. Golenetskii, R.Aptekar, P. Oleynik, M. Ulanov, D. Svinkin, A. Tsvetkova, A.Lysenko, A. Kozlova, and T. Cline, on behalf of the Konus-Wind team, report: The long GRB 160310A (Fermi/LAT detection: Vianello et al., GCN 19158; Fermi/GBM detection: Toelge & Hui, GCN 19161) triggered Konus-Wind at T0=1391.997 s UT (00:23:11.997). The light curve shows a multi-peaked pulse which started at ~T0-14 s and lasted until ~T0+15 s (the total duration is ~30 s). The emission is seen up to ~4 MeV. As observed by Konus-Wind, the burst had a fluence of (6.8 ± 1.5)x10^-6 erg/cm2 and a 64-ms peak energy flux, measured from T0-0.192, of (2.1 ± 0.4)x10^-6 erg/cm2 (both in the 20 keV - 10 MeV energy range). The spectrum of the burst (measured from T0 to T0+8.448 s) is best fit in the 20 keV - 10 MeV range by a cutoff power-law (CPL) function with the following model parameters: the photon index alpha = -1.40(-0.16,+0.21), and the peak energy Ep = 316(-95,+206) keV, chi2 = 89/85 dof. Fitting this spectrum with the GRB (Band) function yields the same alpha and Ep with only an upper limit on beta of -2.0, chi2 = 89/94 dof. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB160310_T01391/ In the KW waiting mode data, GRB 160310A was preceded by a weaker, GRB-like event lasting from ~T0-1510 s to ~T0-1418 s (the total duration is ~90 s). Modeling the KW 3-channel spectrum for this episode by the CPL function yields alpha = -1.23 ± 0.24, Ep = 142 ± 57 keV, and a 20--1500 keV fluence of (7.7 ± 1.7)x10^-6 erg/cm2. The KW ecliptic latitude response for this event is consistent with that for GRB 160310A. Taking this into account, we suggest a possibility that GRB 160310A is, in fact, a double-episode, ultra-long GRB with a total duration of ~1500 s. All the quoted errors are estimated at the 1 sigma confidence level. All the presented results are preliminary.