Gamma-ray Burst 190731A

(All information courtesy of the instrument teams.)

Previous IAU Circulars

none

Results of Observations

GCN Circular #25240
The Fermi GBM team reports the detection of a likely LONG GRB
At 22:38:20 UT on 31 Jul 2019, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 190731A (trigger 586305505.368608 / 190731943).
The on-ground calculated location, using the Fermi GBM trigger data, is RA = 342.8, Dec = -73.9 (J2000 degrees, equivalent to J2000 22h 51m, -73d 54'), with a statistical uncertainty of 1.0 degrees.
The angle from the Fermi LAT boresight is 43.0 degrees.
The skymap can be found here: http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2019/bn190731943/quicklook/glg_skymap_all_bn190731943.png
The HEALPix FITS file, including the estimated localization systematic, can be found here: http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2019/bn190731943/quicklook/glg_healpix_all_bn190731943.fit
The GBM light curve can be found here: http://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2019/bn190731943/quicklook/glg_lc_medres34_bn190731943.gif
GCN Circular #25244
M. Ohno (Hiroshima Univ.), F. Longo (University and INFN, Trieste), M. Arimoto (Kanazawa Univ.), M. Axelsson (KTH and Stockholm Univ.), and F. Dirirsa (Univ. of Johannesburg) report on behalf of the Fermi-LAT team:
On July, 31, 2019 Fermi-LAT detected high-energy emission from GRB 190731A, which was also detected by Fermi-GBM (Fermi GBM Team, GCN 25240).
The best LAT on-ground location is found to be
RA, Dec = 339.94, -76.62 (J2000)
with an error radius of 0.28 deg (90 % containment, statistical error only). This was 40 deg from the LAT boresight at the time of the GBM trigger:
T0 = 22:38:20 UT.
The data from the Fermi-LAT show a significant increase in the event rate after the GBM trigger that is spatially correlated with the GBM emission with high significance. The photon flux above 100 MeV in the time interval 0-800 s after the GBM trigger is (1.91 +/- 0.65)E-5 ph/cm2/s. The highest-energy photon in this interval is a 3.8 GeV event observed at T0 + 234 s. The estimated photon index above 100 MeV is -2.17 +/- 0.26.
The Fermi-LAT point of contact for this burst is Masanori Ohno (ohno@astro.hiroshima-u.ac.jp).
A Swift ToO has been approved for this burst.
The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.
GCN Circular #25245
P. A. Evans (U. Leicester) reports on behalf of the Swift team:
Swift has initiated a ToO observation of the Fermi/LAT GRB 190731A. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00020914
Any uncatalogued X-ray sources detected in this analysis will be reported on this website and via GCN COUNTERPART notices. These are not necessarily related to the Fermi/LAT event. Any X-ray source considered to be a probable afterglow candidate will be reported via a GCN Circular after manual consideration.
Details of the XRT automated analysis methods are detailed in Evans et al. (2007, A&A, 469, 379; 2009, MNRAS, 397, 1177 and 2014, ApJS, 210, 8).
This circular is an official product of the Swift-XRT team.
GCN Circular #25246
Y. Asaoka (Waseda U), A. Yoshida, T. Sakamoto, V. Pal'shin, S. Sugita (AGU), Y. Kawakubo (LSU), K. Yamaoka (Nagoya U), S. Nakahira (RIKEN), S. Ozawa, S. Torii (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), and the CALET collaboration:
The long bright GRB 190731A (Fermi GBM Final Real-time Localization: Fermi GBM Team, GCN Circ. 25240; Fermi-LAT detection: Ohno et al., GCN Circ. 25244) triggered the CALET Gamma-ray Burst Monitor (CGBM) at 22:38:18.315 UTC on 31 July 2019. The burst signal was seen by all CGBM detectors.
The burst light curve shows a single multi-peaked emission episode which starts at T+3.1 sec, peaks at T+4.4 sec and ends at T+26.0 sec. The T90 and T50 durations measured by the SGM data are 14.6 +- 1.8 sec and 5.0 +- 0.5 sec (40-1000 keV), respectively.
The ground processed light curve is available at
http://cgbm.calet.jp/cgbm_trigger/ground/1248647800/
The CALET data used in this analysis are provided by the Waseda CALET Operation Center located at the Waseda University.
GCN Circular #25248
O.J. Roberts (USRA) and C. Meegan (UAH) report on behalf of the Fermi GBM Team:
"At 22:38:20.37 UT on 31 July 2019, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 190731A (trigger 586305505 / 190731943), which was also detected by the LAT (Ohno et al., GCN 25244). The GBM on-ground location is consistent with the LAT position.
The initial angle from the Fermi LAT boresight to the best location is 40 degrees.
The GBM light curve consists of several bright peaks with a duration (T90) of 15.9 +/- 0.4 s (50-300 keV). The time-averaged spectrum from T0+1.6 s to T0+17.9 s is best fit by a Band function with Epeak = 456 +/- 9, alpha index = -0.74 +/- 0.01 and beta index = -2.40 +/- 0.05.
The event fluence (10-1000 keV) in this time interval is (8.57 +/- 0.05)E-05 erg/cm^2. The 1s peak photon flux measured starting from T0+1.9 s in the 10-1000 keV band is 55.5 +/- 0.4 ph/s/cm^2.
The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html
For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"
GCN Circular #25250
K. Hurley, on behalf of the IPN,
I. G. Mitrofanov, D. Golovin, M. L. Litvak, and A. B. Sanin, on behalf of the HEND-Odyssey GRB team,
A. Kozlova, S. Golenetskii, R. Aptekar, D. Frederiks, D. Svinkin, and T. Cline on behalf of the Konus-Wind team,
A. Goldstein, M. S. Briggs, and C. Wilson-Hodge on behalf of the Fermi GBM team,
A. von Kienlin, X. Zhang, A. Rau, V. Savchenko, E. Bozzo, and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team,
S. Barthelmy, J. Cummings, H. Krimm, and D. Palmer, on behalf of the Swift-BAT team,
and
W. Boynton, C. Fellows, K. Harshman, H. Enos, and R. Starr, on behalf of the GRS-Odyssey GRB team, report:
The long-duration, bright GRB 190731A (Fermi LAT detection: Ohno et al., GCN 25244; CALET GBM detection: Asaoka et al., GCN 25246; Fermi GBM detection: Roberts & Meegan, GCN 25248) has been detected by FERMI (GBM trigger 586305505), INTEGRAL (SPI-ACS), Mars-Odyssey (HEND), Konus-Wind, CALET (GBM), and Swift (BAT), so far, at about 81500 s UT (22:38:20). The burst was outside the coded field of view of the BAT.
We have triangulated it to a GBM-HEND annulus centered at RA(2000)=321.552 deg (21h 26m 13s) Dec(2000)=-16.302 deg (-16d 18' 08"), whose radius is 61.012 +/- 0.062 deg (3 sigma).
The LAT position reported by Ohno et al. (GCN Circ. 25244) is consistent with the annulus. The annulus combined with the LAT (90 % containment, statistical-only) error circle gives the following error box:
```
  --------------------------------------------------------------
   RA(2000), deg                 Dec(2000), deg
  ------------------------------------------------------------
  Center:
   339.864 (22h 39m 27s) -76.572 (-76d 34' 19")
  Corners:
   338.734 (22h 34m 56s) -76.599 (-76d 35' 57")
   338.813 (22h 35m 15s) -76.724 (-76d 43' 27")
   341.083 (22h 44m 20s) -76.530 (-76d 31' 50")
   340.796 (22h 43m 11s) -76.424 (-76d 25' 25")
  -------------------------------------------------------------
```
The error box area is 244 sq. arcmin (a factor of 4 smaller than that of the LAT error circle), and its maximum dimension is 33.6 arcmin (the minimum one is 7.4 arcmin). The Sun distance was ~121 deg.
Both Swift XRT sourses found so far (www.swift.ac.uk/ToO_GRBs/00020914/) are consistent with the box.
This box may be improved.
A triangulation map is posted at http://www.ioffe.ru/LEA/GRBs/GRB190731_T81500/IPN/
The Konus-Wind time history and spectrum will be given in a forthcoming GCN Circular.
GCN Circular #25251
J.P. Osborne (U. Leicester), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-IASFPA), M. Perri (ASDC), J. D. Gropp (PSU), A. Tohuvavohu (PSU), J.A. Kennea (PSU), K.L. Page (U. Leicester) and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team:
Swift-XRT has performed follow-up observations of the Fermi/LAT-detected burst GRB 190731A (Ohno et al. GCN Circ. 25244), collecting 5.0 ks of Photon Counting (PC) mode data between T0+33.4 ks and T0+62.9 ks.
Eleven uncatalogued X-ray sources are detected, of which one ("Source 1") is fading with 3-sigma significance, and is therefore likely the GRB afterglow. Using 1953 s of PC mode data and 4 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 339.72015, -76.57744 which is equivalent to:
```
RA (J2000): 22h 38m 52.84s
Dec(J2000): -76d 34' 38.8"
```
with an uncertainty of 2.2 arcsec (radius, 90% confidence). This position is 4.0 arcmin from the Fermi/LAT position.
The light curve can be modelled with a power-law decay with a decay index of alpha=1.3 (+0.6, -0.7).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.5 (+/-0.5). The best-fitting absorption column is 5.9 (+2.8, -2.2) x 10^21 cm^-2, in excess of the Galactic value of 9.8 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.3 x 10^-11 (7.8 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
```
Total column:	     5.9 (+2.8, -2.2) x 10^21 cm^-2
Galactic foreground: 9.8 x 10^20 cm^-2
Excess significance: 3.6 sigma
Photon index:	     2.5 (+/-0.5)
```
If the light curve continues to decay with a power-law decay index of 1.3, the count rate at T+24 hours will be 0.015 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.9 x 10^-13 (1.2 x 10^-12) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis of the likely afterglow are at https://www.swift.ac.uk/ToO_GRBs/00020914/Source1.php. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/ToO_GRBs/00020914.
This circular is an official product of the Swift-XRT team.

GCN Circular #25256
V. Lipunov, E. Gorbovskoy (MASTER,Lomonosov MSU), D.Svinkin (Konus-Wind,Ioffe institute) V. Kornilov, N.Tyurina, P.Balanutsa, A.Kuznetsov, F.Balakin, V. Vladimirov,D. Vlasenko, I.Gorbunov,D.Zimnukhov, V. Senik, A.Chasovnikov, A.Pozdnyakov, D.Kuvshinov(Lomonosov Moscow State University, SAI, Physics Department), R. Rebolo, M. Serra (The Instituto de Astrofisica de Canarias IAC), R. Podesta, C.Lopez, F. Podesta, C.Francile (Observatorio Astronomico Felix Aguilar OAFA), H. Levato (Instituto de Ciencias Astronomicas, de la Tierra y del Espacio ICATE), D. Buckley (South African Astronomical Observatory SAAO), O. Gress, N.M. Budnev, O.Ershova (Irkutsk State University, API), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), V. Yurkov, A. Gabovich, Yu. Sergienko (Blagoveschensk Educational State University)
MASTER Global Robotic Net ( http://observ.pereplet.ru, Lipunov et al., 2010,Advances in Astronomy, vol. 2010, 30L) observed GRB 190731A (Fermi team GCN 25240) in alert (Lipunov et al. GCN 25243) and inspect modes.
MASTER-VWF (very wide field) cameras (D=82 mm, F/1.2, FOV=2x384 sq. degree) located in MASTER-SAAO robotic telescope was pointed to the GRB 190731A by Fermi GBM (trigger 586305505) localization. The first images obtain 21 seconds after notice and 45 second after trigger time at 2019-07-31 22:39:05.
Due to the MASTER-VWFC field of view both Fermi/LAT(Ohno et al., GCN 25244) and Swift/XRT (Evans et al. 25245, Osborne et al., GCN 25251,and also detected by CALET Asaoka et al. GCN25246 and triangulated by IPN Hurley et al. GCN25250) position are covered by these images.
We do not see any optical transients at Swift XRT position with upper limit 12.5m (MASTER-VWFC).
MASTER-SAAO robotic telescope was pointed to the GRB 190731A LAT localization (Fermi LAT team GCN 25244) errorbox 65745 sec after trigger time at 2019-08-01 16:54:08 UT, with upper limit up to 21.4 mag (MASTER-II). Observations started at twilight. The observations began at zenit distance = 65 deg, the sun altitude is -11.3 deg. During this observations we also not find any optical transient connected with GRB.
Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1093251
We obtain a following upper limits.

Tmid-T0  |      Date Time      |          Site       |             Coord (J2000)          |Filt.| Expt. | Limit| Comment
_________|_____________________|_____________________|____________________________________|_____|_______|_______|________
    65835 | 2019-08-01 16:54:08 |         MASTER-SAAO | ( 22h 42m 57.83s , -76d 43m 34.01s) |   C |   180 | 18.3 |
    66194 | 2019-08-01 17:00:06 |         MASTER-SAAO | ( 22h 38m 17.07s , -76d 43m 24.10s) |   C |   180 | 19.4 |
    66344 | 2019-08-01 17:00:06 |         MASTER-SAAO | ( 22h 38m 17.12s , -76d 43m 24.11s) |   C |   480 | 19.1 |  Coadd
    68464 | 2019-08-01 17:38:56 |         MASTER-SAAO | ( 22h 17m 50.68s , -76d  4m 50.21s) |   C |    60 | 19.3 |
    68844 | 2019-08-01 17:45:16 |         MASTER-SAAO | ( 22h 17m 51.60s , -76d  4m 41.03s) |   C |    60 | 19.3 |
    69225 | 2019-08-01 17:51:37 |         MASTER-SAAO | ( 22h 51m 04.79s , -76d  5m 15.39s) |   C |    60 | 19.1 |
    69789 | 2019-08-01 18:01:01 |         MASTER-SAAO | ( 22h 51m 07.30s , -76d  5m 25.37s) |   C |    60 | 19.4 |
    73540 | 2019-08-01 19:03:32 |         MASTER-SAAO | ( 22h 44m 49.14s , -78d  4m 44.09s) |   C |    60 | 19.4 |
    73976 | 2019-08-01 19:10:48 |         MASTER-SAAO | ( 22h 44m 50.07s , -78d  4m 35.94s) |   C |    60 | 19.4 |
    83563 | 2019-08-01 21:49:36 |         MASTER-SAAO | ( 22h 39m 03.78s , -76d 38m 29.08s) |   C |   180 | 19.8 |
    83743 | 2019-08-01 21:49:36 |         MASTER-SAAO | ( 22h 39m 03.83s , -76d 38m 29.08s) |   C |   540 | 21.0 |  Coadd
    83775 | 2019-08-01 21:53:07 |         MASTER-SAAO | ( 22h 39m 07.18s , -76d 38m 13.34s) |   C |   180 | 20.3 |
    83986 | 2019-08-01 21:56:39 |         MASTER-SAAO | ( 22h 39m 07.84s , -76d 38m 16.00s) |   C |   180 | 20.3 |
    84616 | 2019-08-01 21:56:39 |         MASTER-SAAO | ( 22h 39m 07.85s , -76d 38m 16.00s) |   C |  1440 | 21.0 |  Coadd
    84197 | 2019-08-01 22:00:10 |         MASTER-SAAO | ( 22h 39m 09.53s , -76d 38m 36.09s) |   C |   180 | 20.3 |
    84377 | 2019-08-01 22:00:10 |         MASTER-SAAO | ( 22h 39m 09.55s , -76d 38m 36.11s) |   C |   540 | 21.4 |  Coadd
    84469 | 2019-08-01 22:04:42 |         MASTER-SAAO | ( 22h 39m 13.22s , -76d 38m 16.65s) |   C |   180 | 20.3 |
    84680 | 2019-08-01 22:08:13 |         MASTER-SAAO | ( 22h 39m 13.30s , -76d 38m 16.35s) |   C |   180 | 20.5 |
    84892 | 2019-08-01 22:11:45 |         MASTER-SAAO | ( 22h 39m 14.79s , -76d 38m 35.89s) |   C |   180 | 20.4 |
    85072 | 2019-08-01 22:11:45 |         MASTER-SAAO | ( 22h 39m 14.79s , -76d 38m 35.91s) |   C |   540 | 21.0 |  Coadd
    85106 | 2019-08-01 22:15:19 |         MASTER-SAAO | ( 22h 39m 17.57s , -76d 38m 35.58s) |   C |   180 | 20.5 |
    85317 | 2019-08-01 22:18:49 |         MASTER-SAAO | ( 22h 39m 18.81s , -76d 38m 15.77s) |   C |   180 | 20.4 |
    85528 | 2019-08-01 22:22:20 |         MASTER-SAAO | ( 22h 39m 18.99s , -76d 38m 15.51s) |   C |   180 | 20.4 |
Filter C is a clear (unfiltred) band.

This GRB was also detected by CALET (Asaoka et al. GCN25246), triangulated by IPN (Hurley et al. GCN25250)
The observation and reduction will continue.

GCN Circular #25257
S. R. Oates (U.Warwick) and S. Dichiara (UMCP/GSFC) report on behalf of the Swift/UVOT team:
The Swift/UVOT began settled observations of the field of GRB 190731A 33372 s after the LAT trigger (Ohno et al., GCN Circ. 25244). No optical afterglow consistent with the XRT position (Osborne et al., GCN Circ. 25251) is detected in the initial UVOT exposures. Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the initial exposures are:
```
Filter         T_start(s)   T_stop(s)      Exp(s)         Mag

v                39548        40152          590         >20.0
b                45350        45715          355         >20.7
w2               33372        33977          596         >20.3
```
The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.13 in the direction of the burst (Schlegel et al. 1998).
GCN Circular #25258
P. Ghumatkar, V. Sharma, D. Bhattacharya and A. Vibhute (IUCAA), V. Bhalerao (IIT-B), A. R. Rao (TIFR) and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:
Analysis of AstroSat CZTI data showed the detection of a long GRB 190731A, which was also detected by Fermi GBM (GCN #25240), Global MASTER-Net (Lipunov V. et al., GCN #25242), Fermi-LAT (Ohno M. et al., GCN #25244), Swift ToO (Evans P. A. et al., GCN #25245), CALET Gamma-Ray Burst Monitor detection (Asaoka Y. et al., GCN #25246), IPN Triangulation (Hurley K. et al., GCN #25250) and Swift-XRT (Osborne J.P. et al., GCN #25251).
The source was clearly detected in the 40-200 keV energy range. The light curve shows multiple pulses of emission with the strongest peak at 22:38:24.0 UT. The measured peak count rate associated with the burst is 2165 cts/s above the background in the combined data of four quadrants, with a total of 18049 cts. The local mean background count rate was 520 cts/s. Using cumulative rates, we measure a T90 of 20 s. In preliminary analysis, we find that 1455 Compton events are associated with this event.
It was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range.
CZTI GRB detections are reported regularly on the payload site at http://astrosat.iucaa.in/czti/?q=grb. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC and PRL. The Indian Space Research Organisation funded, managed and facilitated the project.
GCN Circular #25274
A. Tsvetkova, S. Golenetskii, R.Aptekar, D. Frederiks, M. Ulanov, D. Svinkin, A. Lysenko, A. Kozlova and T. Cline on behalf of the Konus-Wind team, report:
The long-duration, hard-spectrum, very bright GRB 190731A (Fermi-LAT detection: Ohno et al., GCN 25244; CALET Gamma-Ray Burst Monitor detection: Asaoka� et al., GCN 25246; Fermi GBM detection: Roberts & Meegan, GCN 25248; IPN Triangulation: Hurley et al., GCN 25250; AstroSat CZTI detection: Ghumatkar et al., GCN 25258) triggered Konus-Wind at T0=81504.082 s UT (22:38:24.082).
The burst light curve shows a multi-peaked structure which starts at ~T0-1.5 s and has a total duration of~22.0 s. The emission is seen up to ~5 MeV.
As observed by Konus-Wind, the burst had a fluence of 1.32(-0.08,+0.08)x10^-4 erg/cm2, and a 64-ms peak energy flux, measured from T0+0.944 s, of 3.89(-0.46,+0.46)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range).
The time-integrated spectrum of the burst (measured from T0 to T0+23.808 s) is best fit in the 20 keV - 5 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.69(-0.05,+0.06), the high energy photon index beta = -2.30(-0.13,+0.11), the peak energy Ep = 406(-30,+30) keV, chi2 = 121/98 dof.
The spectrum near the peak count rate (measured from T0+0.256 to T0+1.536 s) is best fit in the 20 keV - 20 MeV range by the GRB (Band) model with the following parameters: the low-energy photon index alpha = -0.63(-0.07,+0.08), the high energy photon index beta = -2.69(-0.50,+0.29), the peak energy Ep = 875(-118,+120) keV, chi2 = 107/69 dof.
The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB190731_T81504/
All the quoted errors are at the 90% confidence level. All the quoted values are preliminary.

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Jochen Greiner, last update: 07-Aug-2019 [Disclaimer]