T.N. Ukwatta (LANL), M.G. Bernardini (INAF-OAB) and K.K. Simpson (PSU) for the Swift team
At 23:52:59 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 190630C (trigger=912239) (Ukwatta et al. GCN Circ. 24927). Swift slewed immediately to the burst. At the time of the trigger, the initial BAT position was 164° from the Sun (11.0 hours West) and 142° from the 4%-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.
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. 24941),
the BAT ground-calculated position is RA, Dec = 293.890, -32.759 deg which is RA(J2000) = 1
The mask-weighted light curve (Figure 1) shows a single FRED-shaped burst, beginning at ~T-5 s, peaking at T+0 s, and declining to background by ~T+40 s.
A spacecraft slew took the burst position out of the BAT field of view just before T+500 s.
The time-averaged spectrum from T-1.92 to T+50.23 s is best fit by a simple power-law model.
The power law index of the time-averaged spectrum is 1.96 ± 0.11.
The fluence in the 15-150 keV band is 2.3 ± 0.2 x 1
The results of the batgrbproduct analysis are available at https://gcn.gsfc.nasa.gov/notices_s/912239/BA/.
Analysis of the initial XRT data was reported by Bernardini et al. (GCN Circ. 24958).
We have analysed 5.7 ks of XRT data for GRB 190630C, from 155 s to 57.3 ks after the BAT trigger. The data comprise 56 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Goad et al. (GCN Circ. 24930).
The light curve (Figure 2) can be modelled with an initial power-law decay with an index of α=4.3 (+0.7, -0.5), followed by a break at T+310 s to an α of 1.06 (+0.12, -0.23).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 3.09 (+0.33, -0.29). The best-fitting absorption column is 2.7 ± 0.7 x 1
A summary of the PC-mode spectrum is thus:
Total column: 2.0 (+1.0, -0.9) x 1
Galactic foreground: 1.1 x 1
Excess significance: 1.7 σ
Photon index: 2.2 ± 0.3
The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00912239.
The Swift/UVOT began settled observations of the field of GRB 190630C 136 s after the BAT trigger
(Simpson and Ukwatta GCN Circ. 24945).
No optical afterglow consistent with the XRT position (Goad et al. GCN Circ. 24930) 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 |
-32°44'38.9" | 1.8" | XRT-final | UKSSDC |
1 |
-32°44'38.6" | 1.9" | XRT-enhanced | Goad et al. GCN Circ. 24930 |
1 |
-32°45'32.5" | 1.1' | BAT-refined | Krimm et al. GCN Circ. 24941 |
Band | Authors | GCN Circ. | Subject | Observatory | Notes |
---|---|---|---|---|---|
Optical | Zheng and Filippenko | 24944 | KAIT Optical Upper Limit | KAIT | upper limits |
Optical | Belkin et al. | 24947 | ISON-Castelgrande optical upper limit | upper limits | |
Gamma-ray | Sharma et al. | 24939 | AstroSat CZTI detection | CZTI |
Filter | Exp(s) | Mag | ||
---|---|---|---|---|
whit |
157 | 307 | 147 | >20.5 |
white | 157 | 307 | 147 | >20.5 |
v | 136 | 412 | 32 | >18.1 |
w2 | 367 | 387 | 19 | >20.1 |
Table 3. UVOT observations reported by Simpson and Ukwatta (GCN Circ. 24945). The start and stop times of the exposures are given in seconds since the BAT trigger. The preliminary 3-σ upper limits are given. No correction has been made for extinction in the Milky Way.
July 2, 2019