Swift Observations of GRB 180407A

A. Deich (PSU) for the Swift team

1. Introduction

At 01:54:49 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 180407A (trigger=823001) (Deich et al. GCN Circ. 22612). Swift could not slew to the location due to an observing constraint. At the time of the trigger, the initial BAT position was 32° from the Sun (1.3 hours East) and 127° from the 62%-illuminated Moon. Table 1 contains the best reported positions from Swift.

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.

2. BAT Observations and Analysis

Analysis of the BAT data was reported by Krimm et al. (GCN Circ. 22616). Note that due to the Sun constraint, Swift could not slew to the burst location, and no data were collected for the burst after ~ T+144 s. The BAT ground-calculated position is RA, Dec = 35.236, 33.513 deg which is RA(J2000) = 02h20m56.6s Dec(J2000) = +33°30'48.4" with an uncertainty of 1.8 arcmin, (radius, sys+stat, 90% containment). The partial coding was 52%.

The mask-weighted light curve (Figure 1) shows a weak pulse that starts at ~ T-20 s and ends at ~ T+110 s. The pulse consists of several overlapping peaks. The largest peak occurs at ~ T+2 s. T90 (15-350 keV) is 95.9 ± 29.8 s (estimated error including systematics). Note that because the burst went out of the BAT field of view at T+144 s, T90 reported here might not capture the entire burst duration.

The time-averaged spectrum from T-20.58 to T+107.48 s is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.94 ± 0.20. The fluence in the 15-150 keV band is 1.4 ± 0.2 x 10-6 erg cm-2. This fluence is larger than that of 49% of the long GRBs in the Second BAT GRB Catalog (Sakamoto et al. 2011). The 1-s peak photon flux measured from T+2.18 s in the 15-150 keV band is 0.9 ± 0.2 ph cm-2 s-1. All the quoted errors are at the 90% confidence level.

The results of the batgrbproduct analysis are available at https://gcn.gsfc.nasa.gov/notices_s/823001/BA/.

3. XRT Observations and Analysis

XRT refined results are not available.

4. UVOT Observations and Analysis

UVOT results are not available.

BAT light curve

Figure 1. The BAT mask-weighted light curve in the four individual and total energy bands. The units are counts s-1 illuminated-detector-1. The vertical green dash-dotted lines show the T50 interval, the vertical black dashed lines show the T90 interval, and vertical blue (orange) solid lines show the start (stop) of slews.

RA (J2000) Dec (J2000) Error Note Reference
02h20m56.6s +33°30'48.4" 1.8' BAT-refined Krimm et al. GCN Circ. 22616

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes
Optical Watson et al. 22614 COATLI Upper Limits COATLI upper limits

Table 2. Summary of GCN Circulars from other observatories sorted by band and then circular number.

April 9, 2018