P.A. Evans (U. Leicester), K.L. Page (U. Leicester) and S.W.K. Emery (UCL-MSSL) for the Swift team
Evans et al. (GCN Circ. 22381) reported the initial Swift results. BAT has detected GRB 180205A (trigger #808625), leading to a slew and follow-up observations by Swift. Table 1 contains the best reported positions from Swift, and the latest XRT position can be viewed at http://www.swift.ac.uk/xrt_positions.
Evans et al. (GCN Circ. 22381) reported the discovery with UVOT of an optical afterglow. Tanvir et al. (GCN Circ. 22384) determined a redshift of 1.409 from VLT. Table 2 is a summary of GCN Circulars about this GRB from observatories other than Swift.
Standard analysis products for this burst are available at https://gcn.gsfc.nasa.gov/swift_gnd_ana.html.
As reported by Krimm et al. (GCN Circ. 22393),
the BAT ground-calculated position is RA, Dec = 126.819, 11.536 deg which is RA(J2000) = 0
The mask-weighted light curve (Figure 1) shows a multi-peaked structure that starts at ~T-7 s and ends at ~T+11 s.
The two major peaks occur at ~T-5 s and ~
The time-averaged spectrum from T-7.04 to T+10.87 s is best fit by a simple power-law model.
The power law index of the time-averaged spectrum is 2.04 ± 0.13.
The fluence in the 15-150 keV band is 1.0 ± 0.1 x 1
The results of the batgrbproduct analysis are available at https://gcn.gsfc.nasa.gov/notices_s/808625/BA/.
Analysis of the initial XRT data was reported by Page et al. (GCN Circ. 22394). We have analysed 47 ks of XRT data for GRB 180205A, from 160 s to 918.7 ks after the BAT trigger. The data comprise 85 s in Windowed Timing (WT) mode (the first 10 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode.
The late-time light curve (Figure 2) (from T0+5.0 ks) can be modelled with a power-law decay with a decay index of α=1.11 (+0.07, -0.06).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.72 (+0.18, -0.17). The best-fitting absorption column is 8.7 (+2.8, -2.5) x 1
A summary of the PC-mode spectrum is thus:
Galactic foreground: 3.4 x 1
Intrinsic column: 3.1 (+3.0, -2.6) x 1
Photon index: 1.89 (+0.15, -0.14)
The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00808625.
The Swift/UVOT began settled observations of the field of GRB 180205A 182 s after the BAT trigger
(Emery and Evans GCN Circ. 22396).
A fading source consistent with the XRT position (Page et al., GCN Circ. 22394), also detected by (Zheng et al. GCN Circ. 22382; Bolmer et al. GCN Circ. 22383; Tanvir et al. GCN Circ. 22384; Volnova et al. GCN Circ. 22387; Falcon et al. GCN Circ. 22390; Xin et al. 22392; Zhu et al. GCN Circ. 22395) is detected in the initial UVOT exposures.
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
Figure 1. The BAT
mask-weighted light curve in the four individual and total
energy bands. The units are counts
Figure 2. The XRT light curve.
Any data from a crosshatched region are not included in the fit.
| RA (J2000) | Dec (J2000) | Error | Note | Reference |
|---|---|---|---|---|
| 0 |
+11°32'30.9" | 0.42" | UVOT-refined | Emery and Evans GCN Circ. 22396 |
| 0 |
+11°32'31.6" | 1.5" | XRT-final | UKSSDC |
| 0 |
+11°32'31.6" | 1.5" | XRT-refined | Page et al. GCN Circ. 22394 |
| 0 |
+11°32'11.1" | 1.1' | BAT-refined | Krimm et al. GCN Circ. 22393 |
| Band | Authors | GCN Circ. | Subject | Observatory | Notes |
|---|---|---|---|---|---|
| Optical | Zheng and Filippenko | 22382 | KAIT optical afterglow confirmation | KAIT | detection |
| Optical | Bolmer and Kann | 22383 | GROND detection of the NIR/optical afterglow |
GROND | detection |
| Optical | Tanvir et al. | 22384 | VLT/X-shooter redshift | VLT | redshift |
| Optical | Volnova et al. | 22387 | Mondy optical observations | Mondy | detection |
| Optical | Wiersema and Covino | 22388 | VLT polarimetry | VLT | |
| Optical | Falcon et al. | 22390 | Nickel telescope optical observations | KAIT | detection |
| Optical | Bolmer and Kann | 22391 | Further GROND Observations reveal Afterglow is still bright |
GROND | light curve |
| Optical | Xin et al. | 22392 | Xinglong TNT optical observation | TNT | detection |
| Optical | Zhu et al. | 22395 | Nanshan-1m optical observations | Xinjiang Astro. Obs. | detection |
| Optical | Oksanen and Malesani | 22401 | optical observations | detection | |
| Optical | Mazaeva et al. | 22403 | AbAO optical observations | Abastumani Astro. Obs. | detection |
| Optical | Choi et al. | 22404 | Optical observations with DOAO 1m telescope |
DOAO | |
| Optical | Volnova et al. | 22411 | BAO optical observations | detection | |
| Optical | Cunningham et al. | 22414 | SEDM Observations | Spectral Energy Distribution Machine at Palomar | |
| Optical | Mazaeva et al. | 22430 | Mondy optical observations | Mondy | detection |
| Gamma-ray | von Kienlin | 22386 | Fermi GBM observation | Fermi GBM | Fluence=1.5±1.4x1 (2 |
| Other | Im et al. | 22397 | Optical observations |
| Filter | Exp(s) | Mag | ||
|---|---|---|---|---|
| whit |
182 | 331 | 147 | 15.75 ± 0.02 |
| white | 540 | 732 | 36 | 16.33 ± 0.02 |
| v | 158 | 612 | 52 | 16.11 ± 0.09 |
| b | 515 | 710 | 39 | 16.65 ± 0.07 |
| u | 490 | 686 | 39 | 16.82 ± 0.07 |
| uvw1 | 466 | 661 | 39 | 16.04 ± 0.10 |
| uvm2 | 441 | 636 | 39 | 16.32 ± 0.15 |
| uvw2 | 391 | 585 | 39 | 17.06 ± 0.17 |
Table 3. UVOT observations reported by Emery and Evans (GCN Circ. 22396). 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.
February 22, 2018