P.A. Evans (U. Leicester) and K.K. Simpson (PSU) for the Swift team
At 07:05:17 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 200416A (trigger=966554) (Evans et al. GCN Circ. 27591). Swift slewed immediately to the burst. At the time of the trigger, the initial BAT position was 52° from the Sun (3.3 hours West) and 24° from the 37%-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.
Evans et al. (GCN Circ. 27591) reported the discovery with UVOT of an optical afterglow. 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.
Analysis of the BAT data was reported by Lien et al. (GCN Circ. 27601).
A. Evans et al., GCN Circ. 27591).
The BAT ground-calculated position is RA, Dec = 335.691, -7.525 deg which is RA(J2000) = 2
The mask weighted light curve (Figure 1) shows multi-peaked structure.
The overall structure starts at ~T-2 s and lasts till ~T+6 s.
The time-averaged spectrum from T-1.31 to T+4.69 s is best fit by a simple power-law model.
The power law index of the time-averaged spectrum is 1.76 ± 0.15.
The fluence in the 15-150 keV band is 8.7 ± 0.8 x 1
The results of the batgrbproduct analysis are available at https://gcn.gsfc.nasa.gov/notices_s/966554/BA/.
Analysis of the initial XRT data was reported by Evans (GCN Circ. 27594). We have analysed 677 s of XRT data for GRB 200416A, from 84 s to 773 s after the BAT trigger. The data comprise 43 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 light curve (Figure 2) can be modelled with an initial power-law decay with an index of α=2.9 ± 0.5, followed by a break at T+167 s to an α of 0.25 (+0.19, -0.25).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.83 (+0.20, -0.16). The best-fitting absorption column is 8.5 (+5.4, -2.0) x 1
A summary of the PC-mode spectrum is thus:
Total column: 8.5 (+5.4, -2.0) x 1
Galactic foreground: 6.5 x 1
Excess significance: <1.6 σ
Photon index: 1.83 (+0.20, -0.16)
The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00966554.
The Swift/UVOT began settled observations of the field of GRB 200416A 102 s after the BAT trigger
(Simpson and Evans GCN Circ. 27602).
A source consistent with the XRT position (Evans GCN Circ. 27594) 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 |
---|---|---|---|---|
2 |
-07°31'06.0" | 0.43" | UVOT-refined | Simpson and Evans GCN Circ. 27602 |
2 |
-07°31'04.4" | 3.5" | XRT-final | UKSSDC |
2 |
-07°31'04.3" | 3.5" | XRT-refined | Evans GCN Circ. 27594 |
2 |
-07°31'29.5" | 1.4' | BAT-refined | Lien et al. GCN Circ. 27601 |
Band | Authors | GCN Circ. | Subject | Observatory | Notes |
---|---|---|---|---|---|
Gamma-ray | Bissaldi | 27592 | Fermi GBM observation | Fermi GBM | Fluence=1.43±0.08x1 (2 |
Filter | Exp(s) | Mag | ||
---|---|---|---|---|
white | 102 | 252 | 147 | 16.57 ± 0.03 |
v | 644 | 664 | 19 | 17.05 ± 0.32 |
b | 570 | 590 | 20 | 17.48 ± 0.20 |
u | 314 | 564 | 246 | 16.44 ± 0.04 |
w1 | 694 | 714 | 20 | 16.59 ± 0.23 |
m2 | 668 | 688 | 19 | >16.3 |
w2 | 620 | 640 | 19 | >17.5 |
Table 3. UVOT observations reported by Simpson and Evans (GCN Circ. 27602). 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.
April 19, 2020