Swift Observations of GRB 201015A

V. D'Elia (SSDC), A. D'Ai (INAF-IASFPA) and F.E. Marshall (NASA/GSFC) for the Swift team

1. Introduction

At 22:50:13 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 201015A (trigger=1000452) (D'Elia et al. GCN Circ. 28632). Swift did not slew immediately to the burst due to an observing constraint. At the time of the trigger, the initial BAT position was 131° from the Sun (10.2 hours East) and 124° 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.

Malesani et al. (GCN Circ. 28637) reported the position from NOT for the optical afterglow of this GRB. Marshall and D'Elia (GCN Circ. 28662) reported the detection with UVOT of an optical afterglow. de Ugarte Postigo et al. (GCN Circ. 28649) determined a redshift of 0.426 from GTC, and Izzo et al. (GCN Circ. 28661) determined a redshift of 0.423. 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 Markwardt et al. (GCN Circ. 28658), the BAT ground-calculated position is RA, Dec = 354.310, 53.446 deg which is RA(J2000) = 23^h37^m14.4^s Dec(J2000) = +53°26'45.0" with an uncertainty of 2.9 arcmin, (radius, sys+stat, 90% containment). The partial coding was 30%.

The mask-weighted light curve (Figure 1) shows a short-soft structure with several overlapping pulses that start at ~T₀ and end at ~T+1 s, followed by a weak-soft tail that lasts till ~T+10 s. T₉₀ (15-350 keV) is 9.78 ± 3.47 s (estimated error including systematics).

The time-averaged spectrum from T+0.02 to T+10.35 s is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 3.03 ± 0.68. The fluence in the 15-150 keV band is 2.0 ± 0.6 x 10^-7 erg cm^-2. This fluence is larger than that of 6.3% of the long GRBs in the Second BAT GRB Catalog (Sakamoto et al. 2011). The 1-s peak photon flux measured from T+0.08 s in the 15-150 keV band is 1.8 ± 0.4 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/1000452/BA/.

3. XRT Observations and Analysis

Analysis of the initial XRT data was reported by D'Ai et al. (GCN Circ. 28660). We have analysed 7.2 ks of XRT data for GRB 201015A, from 3.2 ks to 57.3 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode.

The light curve (Figure 2) can be modelled with a power-law decay with a decay index of α=1.49 (+0.24, -0.21).

A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.2 ± 0.4. The best-fitting absorption column is 2.3 (+4.6, -2.3) x 10²¹ cm^-2, at a redshift of 0.426, in addition to the Galactic value of 3.6 x 10²¹ cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.0 x 10^-11 (7.7 x 10^-11) erg cm^-2 count^-1.

4. UVOT Observations and Analysis

Analysis of the UVOT data was reported by Marshall and D'Elia (GCN Circ. 28662). 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 0.34 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

23^h37^m16.43^s +53°24'57.6" 1.7" XRT-final UKSSDC

23^h37^m16.46^s +53°24'57.7" 1.7" XRT-enhanced Evans et al. GCN Circ. 28647

23^h37^m14.4^s +53°26'45.0" 2.9' BAT-refined Markwardt et al. GCN Circ. 28658

Table 1. Positions from the Swift instruments.

Band Authors GCN Circ. Subject Observatory Notes

Optical Lipunov et al. 28633 Swift GRB201015.95: Global MASTER-Net
OT detection MASTER detection

Optical Lipunov et al. 28634 Swift GRB 201015A: Global MASTER-Net
observations report MASTER

Optical Malesani et al. 28637 NOT optical afterglow confirmation NOT detection

Optical Ackley et al. 28639 GOTO confirmation of afterglow detection Gravitational-wave Optical Transient Observer detection

Optical Hu et al. 28645 BOOTES-1 early optical afterglow
detection BOOTES-1 detection

Optical de Ugarte Postigo et al. 28649 Redshift from GTC/OSIRIS GTC redshift

Optical Zhu et al. 28653 Nanshan/NEXT early optical observations Xinjiang Astro. Obs. detection

Optical Belkin et al. 28656 CrAO/ZTSH optical observations CrAO detection

Optical Jelinek et al. 28664 FRAM-ORM afterglow detection FRAM detection

Optical Belkin et al. 28673 Assy and Mondy optical observations Mondy detection

Optical Grossan et al. 28674 NUTTelA-TAO / BSTI Early Measurements
(Preliminary) NUTTelA

Optical Rastinejad et al. 28676 MMT afterglow imaging MMT detection

Optical Zhu et al. 28677 Xinglong-2.16m optical observations Xinglong

Optical Kumar et al. 28680 HCT optical photometric follow-up Himalayan Chandra Telescope

Optical Kumar et al. 28681 GROWTH-India Telescope (GIT) upper limit GROWTH-India upper limits

Optical Moskvitin and Aitov 28721 SAO RAS optical observations SAO RAS detection

Optical Pozanenko et al. 29033 optical observations and supernova
identification CrAO light curve

Optical Rossi et al. 29306 evidence of supernova in LBT spectra LBT

Radio Fong et al. 28688 6 GHz VLA radio afterglow candidate
detection VLA detection

Radio Giarratana et al. 28939 radio afterglow with e-MERLIN e-MERLIN detection

Radio Rhodes et al. 28945 L-band observations with e-MERLIN e-MERLIN

Radio Marcote et al. 29028 5-GHz radio afterglow detection with
the EVN detection

X-ray Gompertz et al. 28822 Late X-ray Detections with Chandra Chandra detection

Gamma-ray Blanch et al. 28659 MAGIC observations of GRB 201015A:
hint of very high energy gamma-ray
signal MAGIC

Gamma-ray Fletcher and Veres 28663 Fermi GBM Sub-Threshold Detection Fermi GBM E_peak=14±6 keV

Other Izzo et al. 28661 redshift confirmation redshift

Other Minaev and Pozanenko 28668 classification as long GRB

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 3217 3367 147 20.69 ± 0.28

white 4402 4602 197 20.33 ± 0.16

v 3375 4949 331 >19.3

b 4197 4397 197 20.47 ± 0.33

u 3991 4191 197 >19.7

w1 3786 3986 197 >19.3

m2 3579 3779 197 >18.8

w2 4608 4808 197 >19.4

RA (J2000)	Dec (J2000)	Error	Note	Reference
23^h37^m16.43^s	+53°24'57.6"	1.7"	XRT-final	UKSSDC
23^h37^m16.46^s	+53°24'57.7"	1.7"	XRT-enhanced	Evans et al. GCN Circ. 28647
23^h37^m14.4^s	+53°26'45.0"	2.9'	BAT-refined	Markwardt et al. GCN Circ. 28658

Band	Authors	GCN Circ.	Subject	Observatory	Notes
Optical	Lipunov et al.	28633	Swift GRB201015.95: Global MASTER-Net OT detection	MASTER	detection
Optical	Lipunov et al.	28634	Swift GRB 201015A: Global MASTER-Net observations report	MASTER
Optical	Malesani et al.	28637	NOT optical afterglow confirmation	NOT	detection
Optical	Ackley et al.	28639	GOTO confirmation of afterglow detection	Gravitational-wave Optical Transient Observer	detection
Optical	Hu et al.	28645	BOOTES-1 early optical afterglow detection	BOOTES-1	detection
Optical	de Ugarte Postigo et al.	28649	Redshift from GTC/OSIRIS	GTC	redshift
Optical	Zhu et al.	28653	Nanshan/NEXT early optical observations	Xinjiang Astro. Obs.	detection
Optical	Belkin et al.	28656	CrAO/ZTSH optical observations	CrAO	detection
Optical	Jelinek et al.	28664	FRAM-ORM afterglow detection	FRAM	detection
Optical	Belkin et al.	28673	Assy and Mondy optical observations	Mondy	detection
Optical	Grossan et al.	28674	NUTTelA-TAO / BSTI Early Measurements (Preliminary)	NUTTelA
Optical	Rastinejad et al.	28676	MMT afterglow imaging	MMT	detection
Optical	Zhu et al.	28677	Xinglong-2.16m optical observations	Xinglong
Optical	Kumar et al.	28680	HCT optical photometric follow-up	Himalayan Chandra Telescope
Optical	Kumar et al.	28681	GROWTH-India Telescope (GIT) upper limit	GROWTH-India	upper limits
Optical	Moskvitin and Aitov	28721	SAO RAS optical observations	SAO RAS	detection
Optical	Pozanenko et al.	29033	optical observations and supernova identification	CrAO	light curve
Optical	Rossi et al.	29306	evidence of supernova in LBT spectra	LBT
Radio	Fong et al.	28688	6 GHz VLA radio afterglow candidate detection	VLA	detection
Radio	Giarratana et al.	28939	radio afterglow with e-MERLIN	e-MERLIN	detection
Radio	Rhodes et al.	28945	L-band observations with e-MERLIN	e-MERLIN
Radio	Marcote et al.	29028	5-GHz radio afterglow detection with the EVN		detection
X-ray	Gompertz et al.	28822	Late X-ray Detections with Chandra	Chandra	detection
Gamma-ray	Blanch et al.	28659	MAGIC observations of GRB 201015A: hint of very high energy gamma-ray signal	MAGIC
Gamma-ray	Fletcher and Veres	28663	Fermi GBM Sub-Threshold Detection	Fermi GBM	E_peak=14±6 keV
Other	Izzo et al.	28661	redshift confirmation		redshift
Other	Minaev and Pozanenko	28668	classification as long GRB

Filter	T_start(s)	T_stop(s)	Exp(s)	Mag
white	3217	3367	147	20.69 ± 0.28
white	4402	4602	197	20.33 ± 0.16
v	3375	4949	331	>19.3
b	4197	4397	197	20.47 ± 0.33
u	3991	4191	197	>19.7
w1	3786	3986	197	>19.3
m2	3579	3779	197	>18.8
w2	4608	4808	197	>19.4

Table 3. UVOT observations reported by Marshall and D'Elia (GCN Circ. 28662). 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.

January 17, 2021