J.D. Gropp (PSU), A.P. Beardmore (U. Leicester) and M.H. Siegel (PSU) for the Swift team
At 14:54:48 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 230328B (trigger=1162001) (Gropp et al. GCN Circ. 33527). Swift slewed immediately to the burst. At the time of the trigger, the initial BAT position was 85° from the Sun (5.1 hours West) and 72° from the 46%-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.
Gropp et al. (GCN Circ. 33527) reported the detection with UVOT of an optical afterglow. Pankov et al. (GCN Circ. 33528) reported the position from Mondy for the optical afterglow of this GRB. 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 Markwardt and Barthelmy (GCN Circ. 33541).
The mask weighted light curve (Figure 1) has a double peaked structure.
The light curve (Figure 1) does not show an early afterglow as was stated in the original GCN.
The time-averaged spectrum from T-7.38 to T+25.49 s is best fit by a power law
The results of the batgrbproduct analysis are available at https://gcn.gsfc.nasa.gov/notices_s/1162001/BA/.
Analysis of the initial XRT data was reported by Beardmore et al. (GCN Circ. 33533). We have analysed 59 ks of XRT data for GRB 230328B, from 94 s to 896.1 ks after the BAT trigger. The data comprise 14 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 enhanced XRT position for this burst was given by Osborne et al. (GCN Circ. 33529).
The late-time light curve (Figure 2) (from T0+4.3 ks) can be modelled with an initial power-law decay with an index of α=0.71 (+0.28, -0.44), followed by a break at T+10.0 ks to an α of 1.35 ± 0.04.
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.89 ± 0.08. The best-fitting absorption column is 1.40 (+0.24, -0.23) x 1
A summary of the PC-mode spectrum is thus:
Total column: 1.40 (+0.24, -0.23) x 1
Galactic foreground: 6.3 x 1
Excess significance: 5.5 σ
Photon index: 1.89 ± 0.08
The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01162001.
The Swift/UVOT began settled observations of the field of GRB 230328B 114 s after the BAT trigger
(Siegel and Gropp GCN Circ. 33556).
A source consistent with the XRT position (Osborne et al. GCN Circ. 33529) is detected in the initial UVOT exposures, confirming the initial optical detections (Pankov et al., GCN Circ. 33528; Catapano & Izzo, GCN Circ. 33535; Suresh et al., GCN Circ. 33536; Adami et al., GCN Circ. 33537; Komesh et al., GCN Circ. 33539).
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 |
+80°00'34.6" | 0.44" | UVOT-refined | Siegel and Gropp GCN Circ. 33556 |
| 1 |
+80°00'34.4" | 1.9" | XRT-final | UKSSDC |
| 1 |
+80°00'34.3" | 2.1" | XRT-enhanced | Osborne et al. GCN Circ. 33529 |
| 1 |
+80°00'45.3" | 1.0' | BAT-refined | Markwardt and Barthelmy GCN Circ. 33541 |
| Band | Authors | GCN Circ. | Subject | Observatory | Notes |
|---|---|---|---|---|---|
| Optical | Pankov et al. | 33528 | Mondy optical afterglow confirmation | Mondy | detection |
| Optical | Belkin et al. | 33530 | Mondy, AbAO and Kitab optical observations |
Abastumani Astro. Obs. | detection |
| Optical | Lu et al. | 33534 | Nanshan/NEXT optical upper limit | Xinjiang Astro. Obs. | upper limits |
| Optical | Catapano and Izzo | 33535 | OASDG optical observations | S.Di Giacomo Obs. | |
| Optical | Suresh et al. | 33536 | GIT optical follow-up | GROWTH-India Tel. | detection |
| Optical | Adami et al. | 33537 | OHP/T120 optical observations | Obs.de Haute-Provence | |
| Optical | Gompertz et al. | 33538 | Liverpool Telescope afterglow detection | Liverpool Telescope | detection |
| Optical | Komesh et al. | 33539 | NUTTelA-TAO / BSTI Early Measurements | NUTTelA | |
| Optical | Lu et al. | 33540 | Nanshan/NEXT 2nd optical observation | Xinjiang Astro. Obs. | |
| Optical | Ror et al. | 33547 | 3.6m DOT multiband optical observation | DOT | detection |
| Optical | Kugel et al. | 33550 | GRANDMA/Kilonova-Catcher optical detection |
GRANDMA | detection |
| Optical | Pankov et al. | 33559 | Multa observatory optical afterglow observation |
ISON-Multa | detection |
| Gamma-ray | Fermi | 33526 | Fermi GBM Final Real-time Localization | Fermi GBM | |
| Gamma-ray | Dalessi and Meegan | 33531 | Fermi GBM observation | Fermi GBM | Fluence=9.4±0.3x1 (brighter than 74% of long GRBs) |
| Gamma-ray | Waratkar et al. | 33532 | AstroSat CZTI detection | CZTI | |
| Gamma-ray | Dafcikova et al. | 33543 | GRBAlpha detection | GRBAlpha | |
| Gamma-ray | Svinkin et al. | 33544 | Konus-Wind detection | Konus-Wind | Duration=~12 seconds Fluence=7.12(-0.51,+0.58)x1 |
| Other | Minaev and Pozanenko | 33609 | redshift lower limit estimating | redshift |
| Filter | Exp(s) | Mag | ||
|---|---|---|---|---|
| white (fc) | 114 | 264 | 147 | 18.38 ± 0.05 |
| White | 5537 | 5735 | 196 | 20.16 ± 0.14 |
| white | 28147 | 28879 | 713 | 21.88 ± 0.32 |
| v | 655 | 849 | 39 | >17.6 |
| b | 582 | 774 | 39 | >18.3 |
| u (fc) | 326 | 576 | 246 | 19.20 ± 0.16 |
| w1 | 705 | 725 | 19 | >18.5 |
| w2 | 805 | 825 | 19 | >18.0 |
Table 3. UVOT observations reported by Siegel and Gropp (GCN Circ. 33556). 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 5, 2023