TITLE: GCN CIRCULAR NUMBER: 3141 SUBJECT: GRB050319, color indices DATE: 05/03/25 10:50:15 GMT FROM: Rene Hudec at AIO This is a multi-part message in MIME format. --------------010903040009000401050606 Content-Type: multipart/alternative; boundary="------------020908080103070301090909" --------------020908080103070301090909 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit <> V. Simon, R. Hudec (Astronomical Institute AV CR, Ondrejov, Czech Republic) and G. Pizzichini, N. Masetti (INAF/IASF Bologna, Italy) report: <> We have determined the color indices of the optical afterglow (OA) of GRB050319 in its very early phase from the available data (GCN 3124, 3129). The interpolation method described in Simon et al. (2001, A&A, 377, 450) was used. Since the Swift UVOT magnitudes need a confirmation of their calibration, we determined the indices separately for UVOT and ground-based observations. The indices of the OA from UVOT are: t-To=0.0044 d: B-V=0.68; 0.0119: -0.10; 0.0625: 0.85; 0.1968: 0.64, while those of the ground-based observations (GCN 3124) are: t-To(d)= 0.331 d: B-R=0.73; 0.448: 1.12. The typical error of these indices is about 0.10 mag. The Galactic reddening E(B-V)=0.011, determined from the maps by Schlegel et al. (1998, ApJ, 500, 525), is comparable to the errors of the measurements. We note that the variations in B-V, with a peak at t-To=0.01 days, are caused by a plateau in B while the V magnitude was already steadily decreasing. The last two measurements from UVOT can suggest that B-V reached the value roughly consistent with the typical one for the ensemble of 23 OAs, defined by Simon et al. (2001; 2004, AIP Conf. Proc., Vol.727, p.487), not later than at t-To=0.06 days. The indices of the OA of GRB050319 for t-To > 0.06 days thus appear to be plausibly consistent with the mean values of the ensemble (B-V)o=0.45+/-0.15, (B-R)o=0.86+/-0.17. This suggests that the shape of the spectrum of the afterglow of GRB050319 is similar to the other afterglows and that its intrinsic reddening (that is inside the host galaxy) must be again small (Simon et al. 2001; 2004, AIP Conf. Proc., Vol.727, p.487). Also the redshift of GRB050319 z=3.24 (GCN 3136) suggests that this GRB appears to be another member of the above-mentioned ensemble of the OAs with z < 3.5. The search for the host galaxy and the determination of its type are also encouraged. This message may be cited. --------------020908080103070301090909 Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit

<> V. Simon, R. Hudec (Astronomical Institute AV CR, Ondrejov, Czech

Republic) and G. Pizzichini, N. Masetti (INAF/IASF Bologna, Italy) report:

<> We have determined the color indices of the optical afterglow (OA) of

GRB050319 in its very early phase from the available data (GCN 3124,

3129). The interpolation method described in Simon et al. (2001, A&A,

377, 450) was used. Since the Swift UVOT magnitudes need a confirmation

of their calibration, we determined the indices separately for UVOT and

ground-based observations. The indices of the OA from UVOT are:

t-To=0.0044 d: B-V=0.68; 0.0119: -0.10; 0.0625: 0.85; 0.1968: 0.64,

while those of the ground-based observations (GCN 3124) are: t-To(d)=

0.331 d: B-R=0.73; 0.448: 1.12. The typical error of these indices is

about 0.10 mag.

The Galactic reddening E(B-V)=0.011, determined from the maps by

Schlegel et al. (1998, ApJ, 500, 525), is comparable to the errors

of the measurements.

We note that the variations in B-V, with a peak at t-To=0.01 days,

are caused by a plateau in B while the V magnitude was already

steadily decreasing. The last two measurements from UVOT can

suggest that B-V reached the value roughly consistent with the

typical one for the ensemble of 23 OAs, defined by Simon et al.

(2001; 2004, AIP Conf. Proc., Vol.727, p.487), not later than at

t-To=0.06 days.

The indices of the OA of GRB050319 for t-To > 0.06 days thus appear

to be plausibly consistent with the mean values of the ensemble

(B-V)o=0.45+/-0.15, (B-R)o=0.86+/-0.17. This suggests that the shape

of the spectrum of the afterglow of GRB050319 is similar to the other

afterglows and that its intrinsic reddening (that is inside the host

galaxy) must be again small (Simon et al. 2001; 2004, AIP Conf.

Proc., Vol.727, p.487). Also the redshift of GRB050319 z=3.24 (GCN

3136) suggests that this GRB appears to be another member of the

above-mentioned ensemble of the OAs with z < 3.5.

The search for the host galaxy and the determination of its type

are also encouraged.

This message may be cited.

--------------020908080103070301090909-- --------------010903040009000401050606 Content-Type: text/x-vcard; charset=utf-8; name="rhudec.vcf" Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename="rhudec.vcf" begin:vcard fn:Rene Hudec n:Hudec;Rene org:Astronomical Institute, CZ-251 65 Ondrejov, Czech Republic;High Energy Astrophysics Group adr:;;Observatory Ondrejov;Ondrejov;;CZ-251 65;Czech Republic email;internet:rhudec@asu.cas.cz tel;work:00420 323 620128 tel;fax:00420 323 620263 tel;home:00420 323 649011 tel;cell:00420 737 137396 url:http://www.asu.cas.cz version:2.1 end:vcard --------------010903040009000401050606--