A. Tohuvavohu (PSU), V. D'Elia (ASDC) and N.P.M. Kuin (UCL-MSSL) for the Swift team
At 12:40:50 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 190706B (trigger=913302) (Tohuvavohu et al. GCN Circ. 24993). Swift slewed immediately to the burst. At the time of the trigger, the initial BAT position was 52° from the Sun (0.1 hours East) and 65° from the 19%-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.
Kuin and Tohuvavohu (GCN Circ. 25023) reported the detection 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.
As reported by Markwardt et al. (GCN Circ. 25003),
the BAT ground-calculated position is RA, Dec = 107.443, -29.575 deg which is RA(J2000) = 0
The mask-weighted light curve (Figure 1) shows a multi-peaked structure that starts at ~
The time-averaged spectrum from T-0.25 to T+27.48 s is best fit by a simple power-law model.
The power law index of the time-averaged spectrum is 1.90 ± 0.23.
The fluence in the 15-150 keV band is 5.8 ± 0.9 x 1
The results of the batgrbproduct analysis are available at https://gcn.gsfc.nasa.gov/notices_s/913302/BA/.
Analysis of the initial XRT data was reported by D'Elia et al. (GCN Circ. 24999). We have analysed 11 ks of XRT data for GRB 190706B, from 98 s to 40.0 ks after the BAT trigger. The data comprise 26 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Beardmore et al. (GCN Circ. 24994).
The light curve (Figure 2) can be modelled with an initial power-law decay with an index of α=5.3 (+1.0, -0.9), followed by a break at T+160 s to an α of 0.77 ± 0.05.
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.99 (+0.22, -0.21). The best-fitting absorption column is 3.4 (+1.0, -0.9) x 1
A summary of the PC-mode spectrum is thus:
Total column: 3.4 (+1.0, -0.9) x 1
Galactic foreground: 2.4 x 1
Excess significance: 1.8 σ
Photon index: 1.99 (+0.22, -0.21)
The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00913302.
The Swift/UVOT began settled observations of the field of GRB 190706B 100 s after the BAT trigger
(Kuin and Tohuvavohu GCN Circ. 25023).
No optical afterglow consistent with the XRT position (Beardmore et al. GCN Circ. 24995) 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 |
-29°33'10.3" | 1.5" | XRT-final | UKSSDC |
0 |
-29°33'10.5" | 1.8" | XRT-enhanced | Beardmore et al. GCN Circ. 24995 |
0 |
-29°34'30.7" | 2.2' | BAT-refined | Markwardt et al. GCN Circ. 25003 |
Band | Authors | GCN Circ. | Subject | Observatory | Notes |
---|
Filter | Exp(s) | Mag | ||
---|---|---|---|---|
whit |
100 | 250 | 147 | 20.35 ± 0.27 |
312 | 562 | 246 | >19.86 | |
white | 100 | 5778 | 519 | >20.9 |
v | 642 | 17542 | 561 | >19.9 |
b | 568 | 5644 | 292 | >20.6 |
u | 312 | 13071 | 647 | >19.9 |
w1 | 691 | 11551 | 1204 | >20.0 |
m2 | 666 | 7285 | 490 | >19.6 |
w2 | 618 | 17284 | 1199 | >20.5 |
Table 3. UVOT observations reported by Kuin and Tohuvavohu (GCN Circ. 25023). 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.
July 8, 2019