GRB 220107A: Swift-XRT afterglow detection
Abstract
Swift-XRT has performed follow-up observations of the Swift/BAT-GUANO-detected burst GRB 220107A (DeLaunay et al. GCN Circ. 31402), collecting 699 s of Photon Counting (PC) mode data between T0+26.7 ks and T0+27.4 ks. An uncatalogued X-ray source is detected and is above the RASS 3-sigma upper limit at this position, and is therefore likely the GRB afterglow. Using 698 s of PC mode data and 1 UVOT image, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 169.80648, +34.17014 which is equivalent to: RA (J2000): 11h 19m 13.55s Dec(J2000): +34d 10' 12.5" with an uncertainty of 2.3 arcsec (radius, 90% confidence). This position is 3.0 arcmin from the Swift/BAT-GUANO position. The light curve can be modelled with a power-law decay with a decay index of alpha=2.5 (+0.5, -2.4). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.84 (+0.27, -0.18). The best-fitting absorption column is 3.1 (+6.1, -0.9) 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 (3.7 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.1 (+6.1, -0.9) x 10^20 cm^-2 Galactic foreground: 2.2 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.84 (+0.27, -0.18) If the light curve continues to decay with a power-law decay index of 2.5, the count rate at T+24 hours will be 0.054 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.9 x 10^-12 (2.0 x 10^-12) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00021476. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/ToO_GRBs/00021476. This circular is an official product of the Swift-XRT team.
- Publication:
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GRB Coordinates Network
- Pub Date:
- January 2022
- Bibcode:
- 2022GCN.31410....1B