TITLE: GCN CIRCULAR NUMBER: 40173 SUBJECT: GRB 250419A: Swift-XRT refined Analysis DATE: 25/04/19 08:09:20 GMT FROM: Phil Evans at U of Leicester pae9@star.le.ac.uk
K.L. Page (U. Leicester), B. Sbarufatti (INAF-OAB), C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU), A.P. Beardmore (U. Leicester) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:
We have analysed 2.0 ks of XRT data for the SVOM/ECLAIRs-detected burst GRB 250419A (SVOM burst-id sb25041901), from 3.8 ks to 9.6 ks after the SVOM/ECLAIRs trigger. The data are entirely in Photon Counting (PC) mode. The light curve is consistent with a constant source of mean count rate 1.1e-01 ct/sec. A power-law fit gives an index of 0.3 (+0.6, -0.5). Despite a constant count rate, we are likely detecting the GRB afterglow. The source is consistent with the position of the optical afterglow detected by the SVOM/COLIBRÍ (FM-GFT) telescope (Lopez et al., GCN 40169), SVOM/VT (Xin et al., GCN 40170), KAIT (Zheng et al., GCN 40171), GOTO (Kumar et al., GCN 40172).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.9 (+0.4, -0.3). The best-fitting absorption column is 7.7 (+9.9, -5.5) x 10^20 cm^-2, consistent with the Galactic value of 2.2 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.5 x 10^-11 (4.1 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus: Total column: 7.7 (+9.9, -5.5) x 10^20 cm^-2 Galactic foreground: 2.2 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.9 (+0.4, -0.3)
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00019724.
This circular is an official product of the Swift-XRT team.
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