Our data agree with results from RATAN-600 (Fig.1) obtained by Trushkin S.A. [3]. Results from RT-32 allowed us making the following estimations: the.
Radio observations of GR B source s with IAA RA S telesc ope s in 2003- 2009 Kharinov M.A. (1), Gnedin Yu.N. (2), Finkelstein A.M. (1), Ipatov A.V. (1), Tsiopa O.A. (2), Piotrovich M.Yu. (2), D'yakov А.А. (1), Rakhimov I.A. (1), Sergeev R.Yu. (1) (1) Institute of Applied Astronomy (IAA) RAS , Russia: (2) Central (Pulkovo) Astronomical Observatory, Russia. GRB sources are accompanied with afterglows in radio bands in few days after an initial burst. The carrying out of regular radio observations at various frequencies gives important information for construction of GRB physical models. The objective of our observations is to detect radio emission from a maximum possible quantity of GRB sources. The known problem is the extremely weak flux densities - about 0.1÷1 mJy. Rare radio afterglows achieve few tens mJy what could be detected with the IAA RAS RT-32 radio telescopes. Preliminary methods of observation and reduction, and first results of GRB observations with the RT-32 radio telescopes are presented. OBSERVATIONS Observations were carried out with the IAA RAS RT-32 radio telescopes at the observatories Svetloe (SV), Zelenchukskaya (ZC) and Badary (BD) at the frequencies 8.45, 4.85 and 2.33 GHz. For observations we used the drift scanning by elevation or azimuth – the antenna follows a source in one coordinate and scans it in the second coordinate. To integrate signal, the scanning of each GRB source was repeated during one hour (Fig.4). Parameters of drift scans for our frequency bands are presented in Table 1 [1]: Table 1. Band (GHz)
8.45
4.85
2.33
Amplitude (arc min)
10
20
30
Fig.2. Light curve of SGR1806-20 from RT-32 at ZC, 8.45 GHz.
GRB080319B was observed from 26 March to the end of September 2008 with RT-32 at SV and ZC at 8.45 GHz [5] (Fig.3). During 17 May we have detected a week rebrightening of radio flux slightly over 2σ (Fig.3 and 4). Additional observations in June, July and September 2008 did not The list of GRB sources for our radio observations are regularly updated by messages from "The detect flux densities exceeding 2σ. Gamma-ray bursts Coordinates Network Circulars" (GCN Cir.) and "The Astronomer's Telegram" (ATel). Totally 47 GRB sources were observed in points of detection of radio afterglow. Radio monitoring of SN2000AG, GRB030329, GRB051111 and GRB060218 was carried out during a period from several months to few years. The rest sources were observed during few weeks or mos. Velocity (arc sec/sec)
30
40
40
Observations were carried out on elevations from 45 to 70°. Function of antenna efficiency from elevation was defined by observations of reference sources 3C295, 3C48, 3C286 and 3С147. The daily session was formed in such a manner that between hour observations of investigated sources the observations of reference sources for ten minutes were placed. REDUCTION Observation of each source was recorded to a separate file. The processing of these files was made with a special program package developed in IAA RAS. During preprocessing all scans have been filtered from random interferences. Leaving of signal zero level on receiver output because of atmosphere noise temperature was considered by linear approximation on everyone separate scan. At drift scanning by elevation a two kinds of scans turns out: from up to down and from down to up. The integration of scans was made according to scan direction. Then both integrated scans were fitted with function of Gauss. Mean of Fig.3. Light curve of GRB080319B from RT-32 at SV and ZC, 8.45 GHz. maximums was accepted as the result in antenna temperature units. Obtained ant. temperatures of sources have been added to the database of single dish observations. In the database the ant. temperatures were converted to flux densities using antenna efficiency, previously calculated on reference sources [1]. RESULTS Radio afterglows were detected from GRB030329, SGR1806-20 and GRB080319B. GRB030329 was observed on 11-13 April 2003 with the IAA RAS radio telescopes RT-32 at 8.45 GHz and 4.85 GHz [2]. Our data agree with results from RATAN-600 (Fig.1) obtained by Trushkin S.A. [3]. Results from RT-32 allowed us making the following estimations: the total GRB energy in case of isotropy emission Е = 1051 erg [4]; the plasma density of preSN star wind n = 3 sm-3 [4]; the magnetic field of proto-neutron star В ~ 1015 G [5]. According to additional sessions in 2007-2008, the flux densities did not exceed a mean uplimit of 6 mJy at 8.45 GHz and 4.85 GHz. Fig.4. Drift scans of GRB080319B during 17 May 2008. Only up-limits were obtained for remaining 44 sources (see, for example, Fig.5): SN2000AG, GRB050507, GRB050509, GRB051111, GRB060124, GRB060218, GRB060806, GRB061126, SN2006BT, SN2006GY, GRB070125, GRB070129, GRB070208, GRB070306, GRB070311, SN2007BG, SN2007I, GRB081022, GRB080310, GRB080602, GRB080604, GRB080625, GRB080928, GRB081011, GRB081022, GRB081024, GRB081025, GRB081028, GRB081102, GRB081128, GRB081203A, GRB081203B, GRB090111, GRB090113, GRB090306B, GRB090313, GRB090323, GRB090401, GRB090404, GRB090417B, GRB090418, GRB090424, SN2009LS, SN2009NA, SN2009FY.
Fig.5. Light curve of GRB051111 from RT-32, 8.45 GHz, = 0 ± 7 mJy. Fig.1. RT-32 and RATAN-600 light curves of GRB030329 (grbblog.org).
Investigations of the increase of integration time from 1 to 2-4 hours are planned. This can help SGR1806-20 was observed at the beginning of February 2005 with RT-32 of ZC at 8.45 GHz [6]. us to reduce errors and to increase the number of GRB sources we could detect. An interesting result of the international monitoring of SGR1806-20 is the detection of its rebrightening at 4.85 GHz in 25 days after the initial GRB. This event lasted about 5 days. Our REFERENCES results of 5-10 February show a similar rebrightening (Fig.2). The elevation of SGR1806–20 was 1. A.V.Ipatov et al., Trudy IAA RAS, 12, 93 (2005). too low (max ~ 26 deg) for our stations, so we've got a low accuracy. But obtained flux densities 2. A.M.Finkelstein, A.V.Ipatov, Yu.N.Gnedin, GCN Circ. No. 2161 (2003). are still in agreement with theoretical calculations of fluxes (few tens of mJy) made in [7]. From 3. S. A.Trushkin, GCN Circ. No. 2282 (2003). our observations the magnetic field on the surface of neutron star was estimated in the paper [6] 4. Yu.N.Gnedin et al., Astronomy Letters, 30, 6, 368-375 (2004). 5. A.M.Finkelstein et al., Trudy IAA RAS, 12, 36 (2005). as B ≥ 1015 G. 6. Yu.N.Gnedin et al., Astronomy Reports 51, 10, 863-868 (2007). 7. J. Granot et al., astro-ph/0503251 (2005).
