V. Mangano (PSU) and S.T. Holland (STScI) for the Swift team
Sonbas et al. (GCN Circ. 15640) reported the GRB detection. At 04:45:16.08 on Dec 31, 2013, Fermi LAT detected high energy emission from GRB 131231A, which was also detected by Fermi-GBM (trigger 410157919/131231198). Table 1 contains the best reported positions from Swift.
Malesani et al. (GCN Circ. 15642) reported the position from NOT for the optical afterglow of this GRB. Xu et al. (GCN Circ. 15645) determined a redshift of 0.642 from VLT, and Cucchiara (GCN Circ. 15652) determined a redshift of 0.6439 from Gemini. Table 2 is a summary of GCN Circulars about this GRB from observatories other than Swift.
BAT did not observe this burst.
We have analysed 23 ks of XRT data for the Fermi/LAT-detected burst: GRB 131231A, from 52.1 ks to 431.2 ks after the Fermi/LAT trigger. The data are entirely in Photon Counting (PC) mode. An X-ray source is detected within the Fermi/LAT error circle.
The light curve (Figure 2) can be modelled with a power-law decay with a decay index of α=1.47 ± 0.06.
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.86 ± 0.13. The best-fitting absorption column is 1.4 (+0.7, -0.6) x 1021 cm-2, at a redshift of 0.642, in addition to the Galactic value of 2.6 x 1020 cm-2 (Kalberla et al. 2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.1 x 10-11 (3.7 x 10-11) erg cm-2 count-1.
A summary of the PC-mode spectrum is thus:
Galactic foreground: 2.6 x 1020 cm-2
Intrinsic column: 1.4 (+0.7, -0.6) x 1021 cm-2 at z=0.642
Photon index: 1.86 ± 0.13
The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00020336.
The Swift/UVOT began observations of the field of GRB 131231A 136.5 ks after the Fermi/LAT trigger (Sonbas et al., 2013, GCN Circ. 15640) (Holland and Mangano GCN Circ. 15673). The preliminary UVOT position is Table 3 gives preliminary magnitudes using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc., 1358, 373). No correction has been made for the expected extinction in the Milky Way corresponding to a reddening of EB-V of 0.02 mag. in the direction of the GRB (Schlegel et al. 1998).
Figure 1. The BAT light curve is not available.
Figure 2. The XRT light curve.
Any data from a cross-hatched region are not included in the fit.
RA (J2000) | Dec (J2000) | Error | Note | Reference |
---|---|---|---|---|
00h42m21.66s | -01°39'10.6" | 0.43" | UVOT-refined | Holland and Mangano GCN Circ. 15673 |
00h42m21.70s | -01°39'06.7" | 3.5" | XRT-final | UKSSDC |
00h42m21.70s | -01°39'06.7" | 3.5" | XRT | Mangano et al. GCN Circ. 15648 |
Band | Authors | GCN Circ. | Subject | Observatory | Notes |
---|---|---|---|---|---|
Optical | Xu et al. | 15641 | Nanshan afterglow candidate | Xinjiang Astro.Obs. | detection |
Optical | Malesani et al. | 15642 | afterglow confirmation from the NOT | NOT | detection |
Optical | Singer et al. | 15643 | iPTF optical afterglow candidate coincident with Nanshan detection |
Xinjiang Astro.Obs. | detection |
Optical | Xu et al. | 15645 | VLT/X-shooter redshift | VLT | redshift |
Optical | Halpern | 15646 | MDM afterglow observation | MDM | |
Optical | Xin et al. | 15647 | xinglong TNT optical observation | TNT | |
Optical | Perley | 15650 | P60 observations | Palomar 60-inch | detection |
Optical | Cucchiara | 15652 | Gemini-South Redshift | Gemini | redshift |
Optical | Pandey et al. | 15676 | Optical Observations | Nainital | detection |
Optical | Huang and Urata | 15681 | Lulin Optical Observations | Lulin | |
Optical | Volnova et al. | 15711 | AAO optical observations | Abastumani | detection |
Radio | Perley | 15680 | CARMA 3mm detection | CARMA | detection |
Gamma-ray | Sonbas et al. | 15640 | Fermi-LAT detection of a burst | Fermi LAT | detection |
Gamma-ray | Jenke and Xiong | 15644 | Fermi GBM detection | Fermi GBM | Epeak = 146 ± 3 keV |
Gamma-ray | Golenetskii et al. | 15670 | Konus-Wind observation | Konus-Wind | Epeak = 163 ± 6 keV |
Gamma-ray | Jenke | 15672 | Fermi GBM correction to GCN Circ. 15644 | Fermi GBM |
Filter | Tstart | Tstop | Exposure | Mag | Err |
---|---|---|---|---|---|
u | 246,875 | 248,554 | 1652 | 19.57 | 0.10 |
white | 136,762 | 138,942 | 1650 | 19.37 | 0.05 |
white | 228,985 | 231,172 | 1639 | 20.07 | 0.07 |
Table 3. UVOT observations reported by Holland and Mangano (GCN Circ. 15673). The start and stop times of the exposures are given in seconds since the BAT trigger. The preliminary detections and 3-σ upper limits are given. No correction has been made for extinction in the Milky Way.
January 15, 2014