M.J. Moss (George Washington University), A.P. Beardmore (U. Leicester) and M.H. Siegel (PSU) for the Swift team
At 16:04:21 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 190515B (trigger=903845) (Moss et al. GCN Circ. 24553). Swift slewed immediately to the burst. At the time of the trigger, the initial BAT position was 49° from the Sun (3.1 hours East) and 93° from the 87%-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. 24564),
the BAT ground-calculated position is RA, Dec = 98.826, 52.322 deg which is RA(J2000) = 0
The mask-weighted light curve (Figure 1) shows a single-pulse structure that starts at ~T-30 s, peaks at ~
The time-averaged spectrum from T-30.84 to T+31.02 s is best fit by a simple power-law model.
The power law index of the time-averaged spectrum is 1.74 ± 0.15.
The fluence in the 15-150 keV band is 1.6 ± 0.1 x 1
The results of the batgrbproduct analysis are available at https://gcn.gsfc.nasa.gov/notices_s/903845/BA/.
Analysis of the initial XRT data was reported by Beardmore et al. (GCN Circ. 24561). We have analysed 11 ks of XRT data for GRB 190515B, from 73 s to 90.4 ks after the BAT trigger. The data comprise 66 s in Windowed Timing (WT) mode (the first 8 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 Osborne et al. (GCN Circ. 24554).
The light curve (Figure 2) can be modelled with a series of power-law decays. The initial decay index is α=3.95 (+0.20, -0.19). At T+294 s the decay flattens to an α of 0.39 (+0.09, -0.10) before breaking again at T+9885 s to a final decay with index α=1.20 (+0.25, -0.20).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 3.3 ± 0.3. The best-fitting absorption column is 2.1 (+0.6, -0.5) x 1
A summary of the PC-mode spectrum is thus:
Total column: 1.34 (+0.69, -0.07) x 1
Galactic foreground: 1.3 x 1
Excess significance: <1.6 σ
Photon index: 1.97 (+0.24, -0.15)
The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00903845.
The Swift/UVOT began settled observations of the field of GRB 190515B 93 s after the BAT trigger
(Siegel and Moss GCN Circ. 24568).
No optical afterglow consistent with the XRT position (Osborne et al. GCN Circ. 24557) 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 |
+52°19'02.3" | 1.5" | XRT-final | UKSSDC |
0 |
+52°18'59.9" | 2.3" | XRT-enhanced | Osborne et al. GCN Circ. 24557 |
0 |
+52°19'17.6" | 1.5' | BAT-refined | Krimm et al. GCN Circ. 24564 |
Band | Authors | GCN Circ. | Subject | Observatory | Notes |
---|---|---|---|---|---|
Optical | Belkin et al. | 24556 | Kitab Observatory optical upper limit | upper limits | |
Optical | de Ugarte Postigo et al. | 24558 | Optical observations from OSN | Obs.de Sierra Nevada | |
Optical | Hu et al. | 24567 | BOOTES-4/MET and 2.2m CAHA optical limits |
BOOTES-4 | upper limits |
Filter | Exp(s) | Mag | ||
---|---|---|---|---|
whit |
93 | 242 | 147 | >19.9 |
305 | 555 | 246 | >19.4 | |
white | 93 | 605 | 167 | >20.0 |
v | 636 | 4442 | 216 | >18.9 |
b | 561 | 754 | 39 | >18.7 |
u | 305 | 730 | 265 | >19.5 |
w1 | 685 | 4722 | 88 | >18.9 |
m2 | 661 | 4647 | 216 | >19.6 |
w2 | 612 | 4237 | 216 | >19.0 |
Table 3. UVOT observations reported by Siegel and Moss (GCN Circ. 24568). 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.
May 17, 2019