Swift Observations of GRB 190530A

A. Melandri (INAF-OAB) and M.H. Siegel (PSU) for the Swift team

1. Introduction

Longo et al. (GCN Circ. 24679) reported the GRB detection. At 10:19:08 UT on 2019-05-30, Fermi-LAT triggered on high-energy emission from long GRB 190530A, which was also detected by Fermi-GBM (GCN Circ. 24676) and AGILE-MCAL (GCN Circ. 24678). Table 1 contains the best reported positions from Swift.

Izzo et al. (GCN Circ. 24687) reported the position from Obs. Astro. de Javalambre for the optical afterglow of this GRB. Siegel (GCN Circ. 24703) 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

Analysis of the initial XRT data was reported by Melandri et al. (GCN Circ. 24689).

The light curve (Figure 2) can be modelled with a power-law decay with a decay index of α=2.2 ± 0.4.

A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.70 ± 0.11. The best-fitting absorption column is 1.1 (+0.4, -0.3) x 1021 cm-2, in excess of the Galactic value of 5.1 x 1020 cm-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.6 x 10-11 (4.1 x 10-11) erg cm-2 count-1.

4. UVOT Observations and Analysis

The Swift/UVOT began settled observations (Siegel GCN Circ. 24703) of the field of GRB 190530A 33.8 ks after the LAT trigger (GCN Circ. 24676). A fading source consistent with the optical counterpart first reported by Lipunov et al. (GCN Circ. 24680) 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 EB-V of 0.05 mag. in the direction of the GRB (Schlegel et al. 1998).

Figure 1. The BAT light curve is not available.

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
08h02m07.70s +35°28'46.8" 0.49" UVOT-refined Siegel GCN Circ. 24703
08h02m07.78s +35°28'46.1" 1.4" XRT Melandri et al. GCN Circ. 24689

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes
Optical Lipunov et al. 24680 MASTER OT detection MASTER detection
Optical Kann et al. 24684 Bright afterglow confirmed by OSN Obs.de Sierra Nevada detection
Optical Lipunov et al. 24685 Fermi GRB190530.43 Global MASTER-Net
observations report 		MASTER
Optical Heintz et al. 24686 NOT photometry and spectroscopy NOT spectroscopy
Optical Izzo et al. 24687 OAJ optical detection Obs. Astro. de Javalambre detection
Optical Xin et al. 24688 GWAC-F30 optical detection Xinglong Obs. detection
Optical Watson et al. 24690 COATLI Optical Detection of the Fading
Afterglow		 COATLI detection
Optical Lipunov et al. 24693 optical afterglow detection by 5 MASTER
telescopes		 MASTER detection
Optical Xin et al. 24697 Xinglong 2.16m optical observation Xinglong detection
Optical Belkin et al. 24698 AbAO optical observations Abastumani Astro. Obs.
Optical Kann et al. 24700 Steep afterglow decay found by OSN Obs.de Sierra Nevada light curve
Optical Moskvitin and Uklein 24708 SAO RAS optical observations SAO RAS detection
Optical Vinko et al. 24709 Konkoly optical observations of the
afterglow		 Konkoly marginal detection
Optical Belkin et al. 24712 Mondy and AbAO optical observations Abastumani Astro. Obs.
Optical Kumar et al. 24729 R-band observation from HCT Himalayan Chandra Telescope
Optical Nandi et al. 24745 Photometric follow-up with GROWTH-India
telescope		 GROWTH-India
Optical Vinko et al. 24751 optical follow-up observations at
Konkoly		 Konkoly
Optical Kann et al. 24763 Further OAJ/OSN photometry and analysis Obs. Astro. de Javalambre detection
Radio de Ugarte Postigo et al. 24978 Observation of the afterglow by NOEMA NOEMA detection
Gamma-ray Fermi 24676 Fermi GBM Final Real-time Localization Fermi GBM
Gamma-ray Biltzinger et al. 24677 Fermi Trigger 580904353 / GRB
190530430 / GRB190530A: BALROG
localization		 BALROG
Gamma-ray Lucarelli et al. 24678 AGILE-MCAL detection AGILE
Gamma-ray Longo et al. 24679 Fermi-LAT detection Fermi LAT Emax=8.7 GeV
Gamma-ray Verrecchia et al. 24683 AGILE/GRID analysis AGILE
Gamma-ray Bissaldi and Meegan 24692 Fermi GBM observation Fermi GBM Epeak=900±10 keV
T90=18.4 seconds
Fluence=3.72±0.01x10-4erg cm-2
(99.9 percentile for long GRBs)
Gamma-ray Ghumatkar et al. 24694 AstroSat CZTI detection CZTI T90=23.9 seconds
Gamma-ray Yi et al. 24714 Insight-HXMT/HE detection Insight-HXMT T90=20.31 seconds
Gamma-ray Frederiks et al. 24715 Konus-Wind observation of extremely
bright GRB 190530A		 Konus-Wind Epeak=848 (-33,+44) keV

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

Filter Tstart(s) Tstop(s) Exp(s) Mag
v 56532 56734 199 18.49 ± 0.23
b 38334 38490 153 18.06 ± 0.09
u 38132 38329 194 17.09 ± 0.06
w1 37734 38128 388 16.89 ± 0.06
w2 44276 44610 329 17.39 ± 0.08

Table 3. UVOT observations reported by Siegel (GCN Circ. 24703). 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, 2019