E. Troja (NASA/GSFC/UMCP), A. Tohuvavohu (PSU) and M.H. Siegel (PSU) for the Swift team
At 14:23:33 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 190311A (trigger=892607) (Troja et al. GCN Circ. 23946). Swift slewed immediately to the burst. At the time of the trigger, the initial BAT position was 120° from the Sun (9.3 hours West) and 113° from the 22%-illuminated Moon. 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.
Troja et al. (GCN Circ. 23946) reported the discovery with UVOT of an optical afterglow. Zhu et al. (GCN Circ. 23948) reported the position for the optical afterglow of this GRB. 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 Cummings et al. (GCN Circ. 23961),
the BAT ground-calculated position is RA, Dec = 212.067, 53.486 deg which is RA(J2000) = 1
The mask-weighted light curve (Figure 1) shows a single-pulse structure that starts at ~T-2 s, peaks at ~T+1 s, and ends at ~T+20 s.
The time-averaged spectrum from T-2.22 to T+20.78 s is best fit by a simple power-law model.
The power law index of the time-averaged spectrum is 1.80 ± 0.17.
The fluence in the 15-150 keV band is 9.1 ± 0.9 x 1
The results of the batgrbproduct analysis are available at https://gcn.gsfc.nasa.gov/notices_s/892607/BA/.
Analysis of the initial XRT data was reported by Tohuvavohu et al. (GCN Circ. 23952). We have analysed 15 ks of XRT data for GRB 190311A, from 67 s to 200.8 ks after the BAT trigger. The data comprise 80 s in Windowed Timing (WT) mode (the first 9 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Goad et al. (GCN Circ. 23950).
The light curve (Figure 2) can be modelled with a series of power-law decays. The initial decay index is α=2.26 (+0.18, -0.15). At T+389 s the decay flattens to an α of 0.54 (+0.06, -0.05) before breaking again at T+19.0 ks to a final decay with index α=1.17 (+0.25, -0.18).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.80 (+0.25, -0.24). The best-fitting absorption column is 2.1 (+1.2, -1.1) x 1
A summary of the PC-mode spectrum is thus:
Total column: 3.8 (+0.8, -0.7) x 1
Galactic foreground: 1.2 x 1
Excess significance: 8.5 σ
Photon index: 2.00 (+0.16, -0.15)
The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00892607.
The Swift/UVOT began settled observations of the field of GRB 190311A 88 s after the BAT trigger
(Siegel and Troja GCN Circ. 23965).
A source consistent with the XRT position (Goad et al., GCN Circ. 23950) 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 |
|---|---|---|---|---|
| 1 |
+53°30'02.9" | 0.49" | UVOT-refined | Siegel and Troja GCN Circ. 23965 |
| 1 |
+53°30'01.6" | 1.4" | XRT-final | UKSSDC |
| 1 |
+53°30'01.3" | 1.8" | XRT-enhanced | Goad et al. GCN Circ. 23950 |
| 1 |
+53°29'09.2" | 1.3' | BAT-refined | Cummings et al. GCN Circ. 23961 |
| Band | Authors | GCN Circ. | Subject | Observatory | Notes |
|---|---|---|---|---|---|
| Optical | Pozanenko et al. | 23947 | Mondy optical observations | Mondy | detection |
| Optical | Zhu et al. | 23948 | NEXT-0.6m optical afterglow detection | Xinjiang Astro. Obs. | detection |
| Optical | Gorbovskoy et al. | 23949 | MASTER Global Robotic Net OT optical observation |
MASTER | |
| Optical | Belkin et al. | 23951 | TSHAO optical observations | Zeiss-1000 | |
| Optical | Mao et al. | 23954 | GMG observation | Gao-Mei-Gu | detection |
| Optical | Mazaeva et al. | 23958 | Mondy optical observations | Mondy | |
| Optical | Selsing et al. | 23962 | NOT optical counterpart | NOT | detection |
| Optical | Blazek et al. | 23963 | Liverpool Telescope observations | Liverpool Telescope | detection |
| Optical | Mazaeva et al. | 23964 | Mondy optical observations | Mondy | |
| Optical | Blazek et al. | 23966 | OSN optical afterglow detection | Obs.de Sierra Nevada | detection |
| Optical | Iida et al. | 23968 | MITSuME Akeno optical observation | MITSuME Akeno | detection |
| Gamma-ray | Veres and Meegan | 23953 | Fermi GBM observation | Fermi GBM | Fluence=1.40±0.18x1 (2 |
| Other | Peris and Fernandez-Soto | 23959 | OAO observations | detection |
| Filter | Exp(s) | Mag | ||
|---|---|---|---|---|
| white | 88 | 238 | 147 | 19.59 ± 0.10 |
| white | 5678 | 7314 | 393 | >21.42 |
| white | 51260 | 58205 | 2454 | >22.45 |
| u | 301 | 550 | 246 | 19.85 ± 0.20 |
| u | 6704 | 18770 | 1081 | >21.08 |
| b | 6910 | 19082 | 493 | >20.89 |
| v | 6089 | 12525 | 1164 | >20.42 |
| uvw1 | 6500 | 28478 | 1676 | >20.98 |
| uvm2 | 6294 | 23285 | 1557 | >20.87 |
| uvw2 | 5884 | 7521 | 393 | >20.16 |
Table 3. UVOT observations reported by Siegel and Troja (GCN Circ. 23965). 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.
March 16, 2019