//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28011 SUBJECT: GRB 200623A: Fermi GBM Final Real-time Localization DATE: 20/06/23 03:28:09 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM The Fermi GBM team reports the detection of a likely SHORT GRB At 03:18:00 UT on 23 Jun 2020, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 200623A (trigger 614575085.637496 / 200623138). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 224.3, Dec = 60.4 (J2000 degrees, equivalent to J2000 14h 57m, 60d 23'), with a statistical uncertainty of 11.2 degrees. The angle from the Fermi LAT boresight is 25.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2020/bn200623138/quicklook/glg_skymap_all_bn200623138.png The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2020/bn200623138/quicklook/glg_healpix_all_bn200623138.fit The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2020/bn200623138/quicklook/glg_lc_medres34_bn200623138.gif //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28012 SUBJECT: Fermi GRB 200623A: Global MASTER-Net observations report DATE: 20/06/23 05:30:13 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, E. Gorbovskoy, V.Kornilov, N.Tyurina, P.Balanutsa, A.Kuznetsov, F.Balakin, V.Vladimirov, D. Vlasenko, I.Gorbunov, D.Zimnukhov, V.Senik, T.Pogrosheva, D.Kuvshinov, D. Cheryasov (Lomonosov Moscow State University, SAI, Physics Department), 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), R. Rebolo, M. Serra (The Instituto de Astrofisica de Canarias), D. Buckley (South African Astronomical Observatory), O.A. Gres, 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-IAC robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Spain (IAC Teide Observatory) started inspect of the Fermi GRB 200623A ( Fermi GBM team, GCN 28011) errorbox 924 sec after notice time and 957 sec after trigger time at 2020-06-23 03:33:58 UT, with upper limit up to 18.8 mag. The observations began at zenith distance = 63 deg. The sun altitude is -27.3 deg. The galactic latitude b = 45 deg., longitude l = 98 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=1387999 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 988 | 2020-06-23 03:33:58 | MASTER-IAC | (15h 03m 20.96s , +60d 01m 51.3s) | C | 60 | 18.8 | 988 | 2020-06-23 03:33:58 | MASTER-IAC | (14h 46m 59.24s , +60d 06m 59.1s) | C | 60 | 18.3 | 1108 | 2020-06-23 03:35:59 | MASTER-IAC | (14h 53m 55.06s , +62d 00m 52.3s) | C | 60 | 18.5 | 1108 | 2020-06-23 03:35:59 | MASTER-IAC | (14h 36m 29.92s , +62d 06m 01.8s) | C | 60 | 18.2 | 1226 | 2020-06-23 03:37:56 | MASTER-IAC | (15h 12m 34.01s , +58d 01m 45.3s) | C | 60 | 18.6 | 1226 | 2020-06-23 03:37:56 | MASTER-IAC | (14h 57m 07.88s , +58d 06m 52.4s) | C | 60 | 18.3 | 1346 | 2020-06-23 03:39:56 | MASTER-IAC | (15h 03m 20.54s , +60d 00m 47.4s) | C | 60 | 18.7 | 1346 | 2020-06-23 03:39:56 | MASTER-IAC | (14h 46m 59.37s , +60d 05m 55.7s) | C | 60 | 18.5 | 1466 | 2020-06-23 03:41:56 | MASTER-IAC | (14h 53m 54.70s , +61d 59m 46.6s) | C | 60 | 18.5 | 1466 | 2020-06-23 03:41:56 | MASTER-IAC | (14h 36m 30.27s , +62d 04m 56.3s) | C | 60 | 18.2 | 1587 | 2020-06-23 03:43:57 | MASTER-IAC | (15h 12m 38.65s , +57d 59m 56.1s) | C | 60 | 18.6 | 1587 | 2020-06-23 03:43:58 | MASTER-IAC | (14h 57m 13.35s , +58d 05m 03.5s) | C | 60 | 18.4 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28013 SUBJECT: GRB 200623A: Swift/BAT-GUANO detection and arcminute localization of a short GRB DATE: 20/06/23 13:18:09 GMT FROM: Aaron Tohuvavohu at U Toronto James DeLaunay (PSU), Aaron Tohuvavohu (U Toronto), Jamie Kennea (PSU), and Peter Veres (UAH) report: Swift/BAT did not trigger on GRB 2006023A (T0: 2020-06-23 03:18:00 UTC, Fermi/GBM Team GCN 28011). The Fermi/GBM notice, distributed at T0+24 seconds triggered the Swift Mission Operations Center operated Gamma-ray Urgent Archiver for Novel Opportunities (GUANO; Tohuvavohu et al. 2020, arXiv: 2005.01751). Upon trigger by these notices, GUANO sent a command to the Swift Burst Alert Telescope (BAT) to save 200 seconds of BAT event-mode data from [-50,+150] seconds around the time of the burst. All the requested event mode data was delivered to the ground. In a ground analysis of the data, we detect the burst in the full detector-summed rates (no localization information) with an SNR of ~12. The detected duration is ~0.2 seconds. With a maximum likelihood analysis (DeLaunay et al. 2020, in prep.) on the event-mode data we detect a location for the burst with a square root of the test statistic, sqrt(TS), of 9.8. The sqrt(TS) behaves similarly to SNR. Using the normal BAT imaging technique, we find an SNR of 6.4 at the same location. The BAT ground-calculated position is RA, Dec = 242.0952, +53.4678 deg which is RA(J2000) = 16h 8m 22.8s Dec(J2000) = +53d 28’ 4” with an uncertainty of 4 arcmin, (radius, sys+stat, 90% containment). The partial coding was 67.19%. This position is consistent with the Fermi GBM localization (GCN 28011), falling on the 58% containment contour. XRT and UVOT follow-up has been triggered. Results of follow-up observations will be reported in future circulars. GUANO is a fully autonomous, extremely low latency, spacecraft commanding pipeline designed for targeted recovery of BAT event mode data around the times of compelling astrophysical events to enable more sensitive GRB searches. A live reporting of Swift/BAT event data recovered by GUANO can be found at: https://www.swift.psu.edu/guano/ [GCN OPS NOTE: Per author's request, the sexagesimal Dec was changed from +51d 28' 4" to +53 28' 4".] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28015 SUBJECT: GRB 200623A: Swift ToO observations DATE: 20/06/23 13:56:58 GMT FROM: Phil Evans at U of Leicester P. A. Evans (U. Leicester) reports on behalf of the Swift team: Swift has initiated a ToO observation of the Swift/BAT GRB 200623A. Automated analysis of the XRT data will be presented online at https://www.swift.ac.uk/ToO_GRBs/00021005 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 Swift/BAT 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. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28016 SUBJECT: GRB 200623A: Correction to GCN 28013 DATE: 20/06/23 14:23:56 GMT FROM: Aaron Tohuvavohu at U Toronto The sexagesimal coordinates reported for the Swift/BAT-GUANO localization of GRB 200623A have a typo. The decimal coordinates in the original circular are correct. The correct coordinates are RA, Dec: 242.0952, +53.4678: RA(J2000) = 16h 8m 22.8s Dec(J2000) = +53d 28' 4" I apologize for any inconvenience caused. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28019 SUBJECT: GRB 200623A: Fermi GBM observation DATE: 20/06/23 21:46:47 GMT FROM: Peter Veres at UAH P. Veres and C. Meegan (both UAH) report on behalf of the Fermi GBM Team: "At 03:18:00.64 UT on 23 June 2020, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 200623A (trigger 614575085 / 200623138) which was also detected by the Swift/BAT-GUANO (DeLaunay et al., GCN 28013). The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight at the GBM trigger time is 36 degrees. The GBM light curve consists of a single pulse with a duration (T90) of about 0.6 s (50-300 keV). The time-averaged spectrum from T0-64 ms to T0 is best fit by a simple power law function with index -1.09 +/- 0.09. The event fluence (10-1000 keV) in this time interval is (5.2 +/- 0.6)E-7 erg/cm^2. The 64-ms peak photon flux measured starting from T0-64 ms in the 10-1000 keV band is 4.7 +/- 1.0 ph/s/cm^2. A power law function with an exponential high-energy cutoff fits the spectrum equally well with Epeak= 353 +/- 131 keV, alpha = -0.07 +/- 0.53. 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/" //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28020 SUBJECT: GRB 200623A: AbAO afterglow candidate within XRT #2 DATE: 20/06/23 23:00:03 GMT FROM: Alexei Pozanenko at IKI, Moscow S. Belkin (IKI), A. Pozanenko (IKI), R. Ya. Inasaridze (AbAO), V.R. Ayvazian (AbAO), G. V. Kapanadze (AbAO), E. Mazaeva (IKI), A. Volnova (IKI), I. Molotov (KIAM) report on behalf of GRB IKI FuN: We observed the field of Swift/BAT-GUANO position (DeLaunay et al., GCNs 28013, 28016) of GRB 200623A (Fermi GBM team, GCN 28011; Veres et al., GCN 28019) with AS-32 (0.7m) telescope of Abastumani Observatory starting on 2020-06-23 (UT) 18:46:58. We detected only one object within the XRT #2 source localization (https://www.swift.ac.uk/ToO_GRBs/00021005/). The source is not presented in SDSS DR12. We suggest the object could be afterglow of GRB 200623A. However at this time we cannot confirm variability of the object. Preliminary photometry of the object is following. Date UT start t-T0 Filter Exp. OT Err. UL (mid, days) (s) 2020-06-23 18:46:58 0.66456 R 56*60 21.88 0.17 22.6 No new objects were found in the localization of the XRT # 3 source. The photometry is based on nearby USNO-B1.0 stars UUSNO-B1.0_id R2 1434-0283797 15.99 1434-0253851 17.48 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28021 SUBJECT: GRB 200623A: TNG optical observations DATE: 20/06/23 23:09:31 GMT FROM: Paolo D'Avanzo at INAF - OAB P. D'Avanzo (INAF-OAB), V. D'Elia (ASI-SSDC), G. Andreuzzi, D. Carosati (INAF-TNG) on behalf of the CIBO collaboration report: We observed the field of GRB 200623A (Fermi/GBM Team, GCN Circ. 28011; DeLaunay et al., GCN Circ. 28013; Veres and Meegan, GCN Circular. 28019) with the Italian 3.6m TNG telescope equipped with DOLORES in imaging mode. A series of images were obtained with the r-sdss filter on 2020-06-23 from 21:23:29 UT to 21:44:01 UT (i.e. about 18.3 hours after the burst) covering the entire Swift/BAT-GUANO error circle reported by DeLaunay et al. (GCN Circ. 28013,). Further observations are in progress. No obvious afterglow candidate is detected inside the BAT-GUANO error circle. Inside the 5" radius error circle of the Swift/XRT source #3 (see Evans, GCN Circ. 28015 and https://www.swift.ac.uk/ToO_GRBs/00021005) we detect a faint source at the following coordinates: RA(J2000), Dec (J2000) = 16:07:59.11, +53:28:39.0 (+/- 0.5"). From preliminary photometry, we estimate for this object a magnitude r ~ 24.2 (AB, calibrated against the SDSS catalogue). This source is apparently not visible in the SDSS and Pan-STARRS archival images of this field. Given the faintness of the source, no conclusion can be derived about its variability and about its association to GRB 200623A. We note that the 5" radius error circle of the Swift/XRT source #3 is consistent with the catalogued galaxy SDSS J160758.62+532842.2 whose photometric redshift is 0.33 +/- 0.05. The position of the the Swift/XRT source #2 is outside the field of view of our images, therefore we cannot provide information on the optical afterglow candidate reported by Belkin et al. (GCN Circ. 28020). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28022 SUBJECT: GRB 200623A: OAJ deep multi-color imaging, XRT #2 is pre-detected DATE: 20/06/24 01:07:31 GMT FROM: Alexander Kann at IAA-CSIC D. A. Kann (HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), M. Blazek, C. C. Thoene, J. F. Agui Fernandez (all HETH/IAA-CSIC), V. Tilve, A. Moreno Signes, and H. Vasquez Ramio (all CEFCA) report: We observed the error circle of the short GRB 200623A (Fermi GBM detection and analysis: Fermi GBM Team, GCN #28011, Veres & Meegan, GCN #28019; Swift BAT/GUANO localization: DeLaunay et al., GCN #28013) with the T80 0.8m telescope at the Observatorio de Javalambre (Teruel, Spain). Observations consisted of 3 x 500 s in g', 3 x 500 s in r', 8 x 180 s in i', and 8 x 180 s in z', at midtimes 0.816779, 0.798439, 0.779694, and 0.755722 days after the GRB, respectively. At the position of XRT source #1, the known quasar from the Veron-Cetty & Veron 2006 catalog is clearly detected. At the position of XRT source #2, we clearly detect the source proposed by Belkin et al. (GCN #28020) as a candidate afterglow. Measured against three nearby SDSS comparison stars, we find (AB mags): g' = 23.70 +/- 0.30 mag; r' = 22.55 +/- 0.15 mag; i' = 21.54 +/- 0.15 mag; z' = 20.74 +/- 0.10 mag, indicating this is a very red source. We assume that the observations of Belkin et al. were performed without a filter, this would explain the brighter magnitude they find (their use of comparison stars from the USNO catalog may also play a role). These very red colors are untypical for a GRB afterglow. Furthermore, comparison with images form PanSTARRS clearly reveals a pre-detection of the source at a similar magnitude and color, see: https://www.iaa.csic.es/~deugarte/GRBs/200623A/200623A_color2.jpg for a comparison. We therefore believe it is unlikely that this source is associated with GRB 200623A (additionally, the XRT detection is of low significance for now). At the position of XRT source #3, we detected multiple sources in the vicinity also seen in PanSTARRS imaging. The faint source detected by the TNG (D'Avanzo et al., GCN #28021), may be vaguely detected in our r' and z' images, but it is unclear how much this could be due to the PSF of a nearby bright star. We present a second comparison image here: https://www.iaa.csic.es/~deugarte/GRBs/200623A/200623A_color.jpg No other obviously bright afterglow candidate is detected in the BAT error circle, however, a second epoch of comparable depth would be needed for a more detailed analysis. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28023 SUBJECT: GRB 200623A: Swift-XRT observations DATE: 20/06/24 16:22:54 GMT FROM: Boris Sbarufatti at PSU A. Tohuvavohu (U. Toronto), B. Sbarufatti (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), D.N. Burrows (PSU) and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team: Swift-XRT has performed follow-up observations of the Swift/BAT-detected burst GRB 200623A (James DeLaunay et al. GCN Circ. 28013), collecting 5.0 ks of Photon Counting (PC) mode data between T0+37.8 ks and T0+50.1 ks. Three uncatalogued X-ray sources have been detected, however none of them is above the RASS limit or shows definitive signs of fading. Therefore, at the present time we cannot identify which, if any, is the afterglow. Details of these sources are given below: Source 1: RA (J2000.0): 242.2874 = 16:09:8.97 Dec (J2000.0): +53.5321 = +53:31:55.6 Error: 4.4 arcsec (radius, 90% conf. [Enhanced position]) Count-rate: (3.5 [+1.2, -1.0])e-3 ct s^-1 Distance: 406 arcsec from Swift/BAT position. Flux: (1.09 [+0.39, -0.32])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV) Source 2: RA (J2000.0): 242.1106 = 16:08:26.55 Dec (J2000.0): +53.3466 = +53:20:47.9 Error: 5.1 arcsec (radius, 90% conf.) Count-rate: (1.19 [+0.79, -0.56])e-3 ct s^-1 Distance: 462 arcsec from Swift/BAT position. Source 3: RA (J2000.0): 241.9966 = 16:07:59.18 Dec (J2000.0): +53.4786 = +53:28:42.8 Error: 5.0 arcsec (radius, 90% conf.) Count-rate: (3.10 [+1.11, -0.91])e-3 ct s^-1 Distance: 272 arcsec from Swift/BAT position. Flux: (1.96 [+0.70, -0.58])e-13 erg cm^-2 s^-1 (observed, 0.3-10 keV) Source 1 is consistent with a known quasar, [VV2006] J160908.9+533153. Source 2 is poorly detected and is likely to be a background fluctuation. Source 3 is not a known X-ray source, its position is consistent with a background galaxy, SDSS J160758.62+532842.2 (D'Avanzo et al., GCN #28021). Follow up observation of source 3 are planned to be carried out at the end of this week. The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/ToO_GRBs/00021005. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28025 SUBJECT: GRB 200623A: Swift/UVOT Upper Limits DATE: 20/06/24 19:15:37 GMT FROM: Alice Breeveld at MSSL-UCL A. A. Breeveld (UCL-MSSL) and B. Sbarufatti (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began target-of-opportunity observations of the field of GRB 200623A 37910 s after the Guano and GBM trigger (Fermi GBM team, GCN Circ. 28011; Debaunay et al., GCN Circ. 28013). No significant new sources were found at the positions of the XRT candidate sources 1 and 3 (Tohuvavohu et al., GCN Circ. 28023). XRT source 2 was outside the field of view for all exposures. Preliminary 3-sigma upper limit 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 white 37910 45836 4299 >22.4 The magnitude in the table is not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.012 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28026 SUBJECT: GRB 200623A: MMT observations at XRT Source #3 DATE: 20/06/24 21:47:34 GMT FROM: Jillian Rastinejad at Northwestern Univ. J. Rastinejad, Y. Dong, W. Fong, K. Paterson, and A. Rouco Escorial (Northwestern) report: "We observed the location of the short-duration GRB 200623A at the position of XRT source #3 (Tohuvavohu et al. GCN 28023) within the GRB localization (Fermi GBM Team GCN 28011, DeLaunay et al. GCN 28013) with the MMTCam mounted on the MMT 6.5-meter telescope on Mount Hopkins, Arizona. We acquired 18 x 120-sec observations in the r-band at a mid-time of 2020 June 24.18 UT (25.03 hrs post-burst). The observations have a mean airmass of 1.11, seeing of 1.36", and were taken in thin clouds. In the vicinity of the XRT Source #3 position, we detect several sources that are also apparent in SDSS and Pan-STARRs imaging. We find the brightest nearby galaxy, SDSS J160758.62+532842.2 (D’Avanzo et al. GCN 28021) to be consistent with the catalogued magnitude in SDSS (Alam et al. 2015). At the position of the XRT source, the 3-sigma limiting magnitude within the error circle is r > 23.1 AB magnitude, calibrated to SDSS and not corrected for Galactic Extinction. We note that our imaging was not deep enough to detect the faint source found by D’Avanzo et al. (GCN 28021). Further observations are planned. We thank the MMT staff for their assistance with planning and executing these observations." [GCN OPS NOTE(24jun20): Per author's request, "GRB 200624A: " was added to the SUBJECT field of the circular.] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28033 SUBJECT: GRB 200623A : SMA observations at Swift/XRT Source #3 DATE: 20/06/26 07:19:35 GMT FROM: Yuji Urata at Nat. Central U. Kuiyun Huang (CYCU), Yuji Urata (NCU), Glen Petitpas (CfA) report We used SMA to observe the location of the Swift/XRT source #3 (Evans, GCN Circ. 28015) as one of the afterglow candidates of GRB200623A (Fermi/GBM Team, GCN Circ. 28011; DeLaunay et al., GCN Circ. 28013, 28016). The 230 GHz observation was started at ~1 days after the burst. No clear submm source at the Swift/XRT sources #3 position was found brighter than ~1 mJy. We thank the staff of SMA. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28034 SUBJECT: GRB 200623A: LBT optical observations DATE: 20/06/26 09:30:40 GMT FROM: Andrea Rossi at INAF A. Rossi (INAF-OAS) and P. D'Avanzo (INAF-OA Brera) report on behalf of the CIBO collaboration: We observed the field of GRB200623A (DeLaunay et al., GCN 28013) simultaneously in the r' and z' bands with the LBC imager mounted on LBT (Mt Graham, AZ, USA). Observations started at 05:58 UT on 2020-06-25, 50.7 hr after the GRB trigger and finished at 06:24 UT and allowed us to obtain 20min of exposure in each band. Observations were performed under good seeing conditions (seeing ~0.9") and reached a depth of r~26 mag. The images covered all the three sources found by XRT (Sbarufatti et al., GCN 28023). No new point source is detected within their error circles. Image subtraction against TNG r-band images obtained on 2020-06-23 (D'Avanzo et al., GCN 28021) using HOTPANTS (v5.1.11) does not reveal any flux variation in the candidate found within the error circle of the XRT source #3. The near-by galaxy at z~0.33 noticed by D'Avanzo et al. (GCN 28021) is too close to saturation in LBC images, preventing us to make any statement about possible flux variations within the galaxy. We also note that a faint, extended source is present within the XRT error circle of source #3, visible in both the r' and z' images, and not mentioned in previous reports about this event. This is also a candidate host galaxy of XRT source #3 though with a higher chance association probability compared to the brighter galaxy. Further Swift/XRT observations will help establishing variability and possibly reducing the X-ray position uncertainty. We acknowledge the excellent support from the LBTO and LBT-INAF staff, particularly B. Rothberg, F. Cusano, S. Paiano and D. Paris, in obtaining these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28036 SUBJECT: GRB 200623A: Further MMTCam Observations of XRT Source #3 DATE: 20/06/27 23:23:16 GMT FROM: Wen-fai Fong at Northwestern U W. Fong (Northwestern) reports: "We re-visited the location of XRT source #3 of the short GRB 200623A (Fermi-GBM Collab. et al., GCN 28011; DeLaunay et al., GCN 28013; Tohuvavohu et al., GCN 28023) with the MMT/MMTCam at a mid-time of 2020 June 26.176 UT (3.04 days post-burst and 2.0 days after our initial observations: Rastinejad et al., GCN 28026). We acquired 21x120-sec of r-band imaging in 0.88" seeing, and the 3-sigma depth of our image is 24.4 AB mag. Upon inspection of the XRT source #3 position (90% confidence), we detect the faint optical source first reported in TNG observations (D'Avanzo et al.; GCN 28021) with r = 24.3 +/- 0.3 mag, at the same flux level as previous detections. In addition to a few catalogued sources, we report on an additional source toward the Eastern edge of the XRT position and in the wings of the bright star, with RA = 16:07:59.64, Dec = +53:28:43.6 (J2000) and r~22.2 AB mag. This source was marginally detected in our previous set of imaging although partially blended with the bright star, and it is not possible to discern at present whether this source is point-like or extended in nature. Finally, we do not detect the extended LBT source at the center of the XRT position (Rossi and D'Avanzo et al., GCN 28034), likely due to lack of sensitivity. We perform image subtraction relative to our previous epoch, and do not detect any significant residuals. Thus, we find no evidence for significant variability in or around the XRT source #3 position, enabling a limit of r > 23.0 AB mag at 25.03 hrs post-burst on optical afterglow emission associated with this XRT candidate (c.f., Rastinejad et al., GCN 28026). We thank Nelson Caldwell and Michael Calkins at the MMT for the rapid scheduling and execution of these observations." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 28047 SUBJECT: GRB 200623A: Swift XRT further observations DATE: 20/06/30 22:08:27 GMT FROM: Boris Sbarufatti at PSU B. Sbarufatti (PSU), P.A. Evans (U. Leicester) and K. K. Simpson (PSU) report on behalf of the Swift XRT team. Swift performed a second observation of the field of GRB 200623A, with a 4.5 ks exposure. The only uncatalogued source in the field, Source 3 (Tohuvavohu et al., GCN 28023), is still detected and shows no evidence of fading, so we conclude that it is not the GRB afterglow. This circular is an official product of the Swift XRT team.