Swift Observations of GRB 140818A

Swenson (PSU) for the Swift team

1. Introduction

Honda et al. (GCN Circ. 16702) reported the GRB detection. The MAXI/GSC nova alert system triggered a bright uncatalogued X-ray transient source at 2014-08-18T08:31:56 UT. Table 1 contains the best reported positions from Swift.

Swenson et al. (GCN Circ. 16706) reported the detection with UVOT of an optical afterglow. Table 2 is a summary of GCN Circulars about this GRB from observatories other than Swift.

2. BAT Observations and Analysis

BAT did not observe this burst.

3. XRT Observations and Analysis

XRT results are not available.

4. UVOT Observations and Analysis

The Swift/UVOT began settled observations of the field of GRB 140818A 10467 s after the MAXI trigger (Swenson et al. GCN Circ. 16706). A source consistent with the XRT position 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 E_B-V of 0.04 mag. in the direction of the GRB (Schlegel et al. 1998).

Figure 1. The BAT light curve is not available.

RA (J2000) Dec (J2000) Error Note Reference

13^h18^m15.08^s +06°55'22.6" 0.50" UVOT-refined Swenson et al. GCN Circ. 16706

13^h18^m15.06^s +06°55'21.1" 2.1" XRT Swenson et al. GCN Circ. 16706

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes

Optical Knust et al. 16726 GROND confirmation of afterglow
candidate GROND detection

X-ray Honda et al. 16702 MAXI/GSC detection MAXI detection

Gamma-ray Roberts 16708 Fermi GBM Detection Fermi GBM E_peak=181±8 keV
T₉₀=109 seconds
Fluence=2.95±0.06x10^-5erg cm^-2
(91^st percentile for long GRBs)

Gamma-ray Golenetskii et al. 16719 Konus-Wind observation Konus-Wind E_peak=219 (-21,+26) keV
Fluence=3.68(-0.21,+0.22)x10^-5erg cm^-2

Negoro and Honda 16705 Correction to GCN Circ. 16702 corrects Circ. 16702

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

Filter T_start(s) T_stop(s) Exp(s) Mag

u 10467 11094 617 19.21 ą 0.12

RA (J2000)	Dec (J2000)	Error	Note	Reference
13^h18^m15.08^s	+06°55'22.6"	0.50"	UVOT-refined	Swenson et al. GCN Circ. 16706
13^h18^m15.06^s	+06°55'21.1"	2.1"	XRT	Swenson et al. GCN Circ. 16706

Band	Authors	GCN Circ.	Subject	Observatory	Notes
Optical	Knust et al.	16726	GROND confirmation of afterglow candidate	GROND	detection
X-ray	Honda et al.	16702	MAXI/GSC detection	MAXI	detection
Gamma-ray	Roberts	16708	Fermi GBM Detection	Fermi GBM	E_peak=181±8 keV T₉₀=109 seconds Fluence=2.95±0.06x10^-5erg cm^-2 (91^st percentile for long GRBs)
Gamma-ray	Golenetskii et al.	16719	Konus-Wind observation	Konus-Wind	E_peak=219 (-21,+26) keV Fluence=3.68(-0.21,+0.22)x10^-5erg cm^-2
	Negoro and Honda	16705	Correction to GCN Circ. 16702		corrects Circ. 16702

Filter	T_start(s)	T_stop(s)	Exp(s)	Mag
u	10467	11094	617	19.21 ą 0.12

Table 3. UVOT observation reported by Swenson et al. (GCN Circ. 16706). The start and stop time of the exposure are given in seconds since the BAT trigger. The preliminary detection is given. No correction has been made for extinction in the Milky Way.

May 22, 2015