Letter to the Editor

Spectral evolution of weak bursts from SGR 1806–20 observed with INTEGRAL^*

¹ Istituto di Astrofisica Spaziale e Fisica Cosmica – CNR, Sezione di Milano “G. Occhialini”, via Bassini 15, 20133 Milano, Italy
² Dipartimento di Fisica, Università degli Studi di Milano Bicocca, P.zza della Scienza 3, 20126 Milano, Italy
³ Service d'Astrophysique, CEA/Saclay, Orme des Merisiers, Bât. 709, 91191 Gif-sur-Yvette, France
⁴ Instituto de Astronomia y Fisica del Espacio / CONICET, cc67, suc 28, 1428 Buenos Aires, Argentina
⁵ UC Berkeley Space Sciences Laboratory, Berkeley CA 94720-7450, USA

Corresponding author: D. Götz, diego@mi.iasf.cnr.it

Received: 28 January 2004
Accepted: 29 February 2004

Abstract

We report on bursts from the Soft Gamma-Ray Repeater SGR 1806–20 detected with INTEGRAL in October 2003, during a period of moderate activity of the source. The spectral and temporal properties of 21 short bursts are consistent with those found in previous observations, even if these bursts are among the faintest observed in the 15–200 keV range from this source. During some of the bursts a clear spectral evolution is visible. The data also show, for the first time, evidence for a hardness-intensity anti-correlation within SGR 1806–20 bursts.