J.D. Gropp (PSU), P.A. Evans (U. Leicester) and F.E. Marshall (NASA/GSFC) for the Swift team
At 08:02:59 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 180410A or a Galactic transient (trigger=824063) (Gropp et al. GCN Circ. 22620). Swift slewed immediately to the source. At the time of the trigger, the initial BAT position was 76° from the Sun (5.2 hours East) and 142° from the 31%-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 Lien et al. (GCN Circ. 22628),
the BAT ground-calculated position is RA, Dec = 95.974, 12.804 deg which is RA(J2000) = 0
The mask-weighted light curve (Figure 1) shows a weak-long pulse that starts and peak at ~ T+25 s, and ends at ~T+150 s.
The time-averaged spectrum from T+25.16 to T+153.67 s is best fit by a simple power-law model.
The power law index of the time-averaged spectrum is 1.46 ± 0.13.
The fluence in the 15-150 keV band is 2.2 ± 0.2 x 1
The results of the batgrbproduct analysis are available at https://gcn.gsfc.nasa.gov/notices_s/824063/BA/.
Analysis of the initial XRT data was reported by Evans et al. (GCN Circ. 22629).
We have analysed 6.8 ks of XRT data for GRB 180410A, from 176 s to 45.6 ks after the BAT trigger. The data comprise 201 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Evans et al. (GCN Circ. 22622).
The light curve (Figure 2) can be modelled with a series of power-law decays. The initial decay index is α=1.39 (+0.22, -0.28). At T+321 s the decay steepens to an α of 2.9 (+0.4, -0.3) before breaking again at T+866 s to a final decay with index α=1.48 (+0.15, -0.13).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.87 (+0.07, -0.05). The best-fitting absorption column is consistent with the Galactic value of 6.6 x 1
A summary of the PC-mode spectrum is thus:
Total column: 7.7 (+2.3, -1.2) x 1
Galactic foreground: 6.6 x 1
Excess significance: <1.6 σ
Photon index: 1.45 (+0.21, -0.19)
The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00824063.
The Swift/UVOT began settled observations of the field of GRB 180410A 179 s after the BAT trigger
(Marshall and Gropp GCN Circ. 22627).
No optical afterglow consistent with the enhanced XRT position (Evans et al. GCN Circ. 22622) 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 |
+12°48'41.1" | 1.5" | XRT-final | UKSSDC |
0 |
+12°48'41.1" | 1.8" | XRT-enhanced | Evans et al. GCN Circ. 22622 |
0 |
+12°48'15.2" | 1.9' | BAT-refined | Lien et al. GCN Circ. 22628 |
Band | Authors | GCN Circ. | Subject | Observatory | Notes |
---|---|---|---|---|---|
Optical | Itoh et al. | 22623 | MITSuME Akeno optical upper limits | MITSuME Akeno | upper limits |
Optical | Watson et al. | 22631 | RATIR Optical Observations | RATIR | upper limits |
Gamma-ray | Bissaldi | 22636 | Fermi GBM observation | Fermi GBM | Fluence=3.1±0.4x1 (4 |
Filter | Exp(s) | Mag | ||
---|---|---|---|---|
whit |
179 | 329 | 147 | >20.6 |
338 | 587 | 246 | >20.0 | |
white | 179 | 2068 | 450 | >20.9 |
v | 669 | 1943 | 156 | >19.2 |
b | 594 | 2043 | 156 | >20.1 |
u | 338 | 2017 | 382 | >20.4 |
w1 | 718 | 1993 | 136 | >20.1 |
m2 | 693 | 1968 | 136 | >20.3 |
w2 | 644 | 2093 | 175 | >19.9 |
Table 3. UVOT observations reported by Marshall and Gropp (GCN Circ. 22627). 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.
April 13, 2018