Swift Observations of GRB 190829A

S. Dichiara (NASA/GSFC/UMCP), J.P. Osborne (U. Leicester) and S.R. Oates (U.Warwick) for the Swift team

1. Introduction

At 19:56:44.60 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 190829A (trigger=922968) (Dichiara et al. GCN Circ. 25552). Swift slewed immediately to the burst. At the time of the trigger, the initial BAT position was 114° from the Sun (7.5 hours West) and 108° from the 1%-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.

Xu et al. (GCN Circ. 25555) reported the position for the optical afterglow of this GRB. Oates and Dichiara (GCN Circ. 25570) reported the detection with UVOT of an optical afterglow. Heintz et al. (GCN Circ. 25563) determined a redshift of 0.08 from NOT, Valeev et al. (GCN Circ. 25565) determined a redshift of 0.0785 from GTC, and De et al. (GCN Circ. 25595) determined a redshift of 0.078 from Keck. 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

As reported by Lien et al. (GCN Circ. 25579), the BAT ground-calculated position is RA, Dec = 44.542, -8.958 deg which is RA(J2000) = 02^h58^m10.0^s Dec(J2000) = -08°57'28.4" with an uncertainty of 1.9 arcmin, (radius, sys+stat, 90% containment). The partial coding was 5%.

The mask-weighted light curve (Figure 1) shows an early peak centered at T-50 s, coincident with the Fermi/GBM trigger (Lesage, et al., GCN Circ. 25575). This early peak shows more counts in the higher energy bands (> 50 keV) than is typical for a precursor. This was followed by the main peak of emission from T-5 to T+10 s, peaking at the trigger time. Finally, there was a weak, hard peak between T+15 and T+20 s. T₉₀ (15-350 keV) is 58.2 ± 8.9 s (estimated error including systematics).

The time-averaged spectrum from T-51.9 to T+7.2 s is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.56 ± 0.21. The fluence in the 15-150 keV band is 6.4 ± 0.7 x 10^-6 erg cm^-2. This fluence is larger than that of 87% of the long GRBs in the Second BAT GRB Catalog (Sakamoto et al. 2011). The 1-s peak photon flux measured from T-0.01 s in the 15-150 keV band is 18.0 ± 2.7 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/922968/BA/.

3. XRT Observations and Analysis

Analysis of the initial XRT data was reported by Osborne et al. (GCN Circ. 25568). We have analysed 52 ks of XRT data for GRB 190829A, from 87 s to 786.7 ks after the BAT trigger. The data comprise 711 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 Evans et al. (GCN Circ. 25567).

The late-time light curve (Figure 2) (from T0+4.8 ks) can be modelled with an initial power-law decay with an index of α=1.60 ± 0.05, followed by a break at T+23.2 ks to an α of 1.038 (+0.023, -0.022).

A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.17 (+0.20, -0.19). The best-fitting absorption column is 7.4 (+1.7, -1.5) x 10²¹ cm^-2, in excess of the Galactic value of 5.6 x 10²⁰ cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 2.09 (+0.08, -0.07) and a best-fitting absorption column of 1.12 (+0.08, -0.07) x 10²² cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.8 x 10^-11 (9.9 x 10^-11) erg cm^-2 count^-1.

A summary of the PC-mode spectrum is thus:
Total column: 1.12 (+0.08, -0.07) x 10²² cm^-2
Galactic foreground: 5.6 x 10²⁰ cm^-2
Excess significance: 24.0 σ
Photon index: 2.09 (+0.08, -0.07)

The results of the XRT team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00922968.

4. UVOT Observations and Analysis

The Swift/UVOT began settled observations of the field of GRB 190829A 106 s after the BAT trigger (Oates and Dichiara GCN Circ. 25570). An optical afterglow consistent with the XRT position (Evans et al. GCN Circ. 25567) and the optical afterglow reported by Dabancheng-0.5m (Xu et al. GCN Circ. 25555), MASTER-net (Lipunov et al. GCN Circ. 25558), GROWTH (Kumar et al. GCN Circ. 25560), NOT (Heintz et al. GCN Circ. 25563), GTC (Valeev et al. GCN Circ. 25565) and GROND (Chen et al. GCN Circ. 25569) 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 0.05 mag. in the direction of the GRB (Schlegel et al. 1998).

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.

XRT light curve

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

02^h58^m10.51^s -08°57'29.3" 1.4" XRT-final UKSSDC

02^h58^m10.57^s -08°57'30.1" 1.8" XRT-enhanced Evans et al. GCN Circ. 25567

02^h58^m10.0^s -08°57'28.4" 1.9' BAT-refined Lien et al. GCN Circ. 25579

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes

Optical Xu et al. 25555 Dabancheng-0.5m optical afterglow
detection detection

Optical Lipunov et al. 25558 MASTER-net bright and decay OT detection MASTER detection

Optical Kumar et al. 25560 GROWTH India detection of afterglow GROWTH-India detection

Optical Heintz et al. 25563 NOT optical afterglow detection and
spectroscopy NOT spectroscopy

Optical Valeev et al. 25565 10.4m GTC spectroscopy GTC spectroscopy

Optical Chen et al. 25569 GROND detection of the Optical/NIR
Afterglow GROND detection

Optical Lipunov et al. 25573 Global MASTER-net optical clear and
polarization observations scheduler
and some spiculations MASTER

Optical Zheng and Filippenko 25580 KAIT Detection of the Optical Afterglow KAIT detection

Optical Fong et al. 25583 MMT detection of the optical afterglow MMT detection

Optical Paek and Im 25584 UKIRT detection of the NIR Afterglow UKIRT detection

Optical Perley and Cockeram 25585 Liverpool Telescope optical photometry Liverpool Telescope detection

Optical D'Avanzo et al. 25591 TNG imaging of the NIR afterglow TNG detection

Optical Blazek et al. 25592 Liverpool Telescope observations Liverpool Telescope detection

Optical De et al. 25595 Keck LRIS spectroscopy of the optical
afterglow Keck spectroscopy

Optical Perley and Cockeram 25597 Continued fading inferred from
Liverpool Telescope photometry Liverpool Telescope

Optical Perley and Cockeram 25623 Flattening of optical light curve from
continued Liverpool Telescope
photometry Liverpool Telescope light curve

Optical Strausbaugh and Cucchiara 25641 LCO Optical Afterglow Detection LCO detection

Optical Bolmer et al. 25651 GROND detection of the accompanying SN GROND

Optical Lipunov et al. 25652 MASTER confirmation of GROND SN GROND

Optical Perley and Cockeram 25657 Liverpool Telescope observations of a
slow supernova rise Liverpool Telescope light curve

Optical Terreran et al. 25664 Keck LRIS spectroscopic confirmation of
the accompanying supernova Keck

Optical Vagnozzi and Nesci 25667 optical observation

Optical de Ugarte Postigo et al. 25677 GTC confirmation of an associated Type
Ic-BL Supernova GTC

Optical Volnova et al. 25682 observations in CrAO, photometry of the
SN CrAO

Radio Dado and Dar 25581 Follow up VLA and VLBI radio
observations urged VLA

Radio de Ugarte Postigo et al. 25589 NOEMA detection of the mm afterglow NOEMA detection

Radio Chandra 25627 Detection of radio afterglow with the
uGMRT GMRT detection

Radio Monageng et al. 25635 MeerKAT radio observation detection

Radio Laskar et al. 25676 ATCA cm-band detection ATCA detection

Gamma-ray Fermi 25551 Fermi GBM Final Real-time Localization Fermi GBM

Gamma-ray Piron et al. 25574 Fermi-LAT Upper Limits Fermi LAT

Gamma-ray Lesage et al. 25575 Fermi GBM detection Fermi GBM E_peak=130±20 keV
T₉₀=63 seconds

Gamma-ray Pittori et al. 25577 AGILE ratemeters detection and MCAL
upper limits AGILE

Gamma-ray Piano et al. 25578 AGILE-GRID upper limits AGILE

Gamma-ray Tsvetkova et al. 25660 Konus-Wind observation Konus-Wind

Other de Naurois 25566 Detection of VHE gamma-ray emission
with H.E.S.S. detection

Other Coleiro and Dornic 25582 No Neutrino Counterpart detected with
ANTARES detection

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

white_FC 106 256 147 20.05 ± 0.17

u_FC 264 514 246 19.95 ± 0.27

white 546 566 19 19.48 ± 0.30

v 771 791 19 17.52 ± 0.28

b 1149 1168 19 17.29 ± 0.15

u 845 865 19 18.40 ± 0.36

w1 1099 1638 78 18.54 ± 0.35

m2 1075 1614 78 > 18.5

w2 1026 1565 78 > 18.7

RA (J2000)	Dec (J2000)	Error	Note	Reference
02^h58^m10.51^s	-08°57'29.3"	1.4"	XRT-final	UKSSDC
02^h58^m10.57^s	-08°57'30.1"	1.8"	XRT-enhanced	Evans et al. GCN Circ. 25567
02^h58^m10.0^s	-08°57'28.4"	1.9'	BAT-refined	Lien et al. GCN Circ. 25579

Band	Authors	GCN Circ.	Subject	Observatory	Notes
Optical	Xu et al.	25555	Dabancheng-0.5m optical afterglow detection		detection
Optical	Lipunov et al.	25558	MASTER-net bright and decay OT detection	MASTER	detection
Optical	Kumar et al.	25560	GROWTH India detection of afterglow	GROWTH-India	detection
Optical	Heintz et al.	25563	NOT optical afterglow detection and spectroscopy	NOT	spectroscopy
Optical	Valeev et al.	25565	10.4m GTC spectroscopy	GTC	spectroscopy
Optical	Chen et al.	25569	GROND detection of the Optical/NIR Afterglow	GROND	detection
Optical	Lipunov et al.	25573	Global MASTER-net optical clear and polarization observations scheduler and some spiculations	MASTER
Optical	Zheng and Filippenko	25580	KAIT Detection of the Optical Afterglow	KAIT	detection
Optical	Fong et al.	25583	MMT detection of the optical afterglow	MMT	detection
Optical	Paek and Im	25584	UKIRT detection of the NIR Afterglow	UKIRT	detection
Optical	Perley and Cockeram	25585	Liverpool Telescope optical photometry	Liverpool Telescope	detection
Optical	D'Avanzo et al.	25591	TNG imaging of the NIR afterglow	TNG	detection
Optical	Blazek et al.	25592	Liverpool Telescope observations	Liverpool Telescope	detection
Optical	De et al.	25595	Keck LRIS spectroscopy of the optical afterglow	Keck	spectroscopy
Optical	Perley and Cockeram	25597	Continued fading inferred from Liverpool Telescope photometry	Liverpool Telescope
Optical	Perley and Cockeram	25623	Flattening of optical light curve from continued Liverpool Telescope photometry	Liverpool Telescope	light curve
Optical	Strausbaugh and Cucchiara	25641	LCO Optical Afterglow Detection	LCO	detection
Optical	Bolmer et al.	25651	GROND detection of the accompanying SN	GROND
Optical	Lipunov et al.	25652	MASTER confirmation of GROND SN	GROND
Optical	Perley and Cockeram	25657	Liverpool Telescope observations of a slow supernova rise	Liverpool Telescope	light curve
Optical	Terreran et al.	25664	Keck LRIS spectroscopic confirmation of the accompanying supernova	Keck
Optical	Vagnozzi and Nesci	25667	optical observation
Optical	de Ugarte Postigo et al.	25677	GTC confirmation of an associated Type Ic-BL Supernova	GTC
Optical	Volnova et al.	25682	observations in CrAO, photometry of the SN	CrAO
Radio	Dado and Dar	25581	Follow up VLA and VLBI radio observations urged	VLA
Radio	de Ugarte Postigo et al.	25589	NOEMA detection of the mm afterglow	NOEMA	detection
Radio	Chandra	25627	Detection of radio afterglow with the uGMRT	GMRT	detection
Radio	Monageng et al.	25635	MeerKAT radio observation		detection
Radio	Laskar et al.	25676	ATCA cm-band detection	ATCA	detection
Gamma-ray	Fermi	25551	Fermi GBM Final Real-time Localization	Fermi GBM
Gamma-ray	Piron et al.	25574	Fermi-LAT Upper Limits	Fermi LAT
Gamma-ray	Lesage et al.	25575	Fermi GBM detection	Fermi GBM	E_peak=130±20 keV T₉₀=63 seconds
Gamma-ray	Pittori et al.	25577	AGILE ratemeters detection and MCAL upper limits	AGILE
Gamma-ray	Piano et al.	25578	AGILE-GRID upper limits	AGILE
Gamma-ray	Tsvetkova et al.	25660	Konus-Wind observation	Konus-Wind
Other	de Naurois	25566	Detection of VHE gamma-ray emission with H.E.S.S.		detection
Other	Coleiro and Dornic	25582	No Neutrino Counterpart detected with ANTARES		detection

Filter	T_start(s)	T_stop(s)	Exp(s)	Mag
white_FC	106	256	147	20.05 ± 0.17
u_FC	264	514	246	19.95 ± 0.27
white	546	566	19	19.48 ± 0.30
v	771	791	19	17.52 ± 0.28
b	1149	1168	19	17.29 ± 0.15
u	845	865	19	18.40 ± 0.36
w1	1099	1638	78	18.54 ± 0.35
m2	1075	1614	78	> 18.5
w2	1026	1565	78	> 18.7

Table 3. UVOT observations reported by Oates and Dichiara (GCN Circ. 25570). 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.

September 8, 2019