//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 27591 SUBJECT: GRB 200416A: Swift detection of a burst with an optical afterglow DATE: 20/04/16 07:19:36 GMT FROM: David Palmer at LANL P. A. Evans (U Leicester), V. D'Elia (SSDC), J.D. Gropp (PSU), N. J. Klingler (PSU), S. Laha (GSFC/UMBC/CRESST), A. Y. Lien (GSFC/UMBC), K. L. Page (U Leicester), D. M. Palmer (LANL) and A. Tohuvavohu (U Toronto) report on behalf of the Neil Gehrels Swift Observatory Team: At 07:05:17 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 200416A (trigger=966554). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 335.691, -7.530 which is RA(J2000) = 22h 22m 46s Dec(J2000) = -07d 31' 47" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a multi-peaked structure with a duration of about 10 sec. The peak count rate was ~3000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 07:06:57.1 UT, 99.9 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source located at RA, Dec 335.69906, -7.51816 which is equivalent to: RA(J2000) = 22h 22m 47.77s Dec(J2000) = -07d 31' 05.4" with an uncertainty of 3.5 arcseconds (radius, 90% containment). This location is 51 arcseconds from the BAT onboard position, within the BAT error circle. This position may be improved as more data are received; the latest position is available at https://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density in excess of the Galactic value (6.54 x 10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.2 (+3.00/-2.56) x 10^21 cm^-2 (90% confidence). UVOT took a finding chart exposure of 150 seconds with the White filter starting 102 seconds after the BAT trigger. There is a candidate afterglow in the rapidly available 2.7'x2.7' sub-image at RA(J2000) = 22:22:47.83 = 335.69929 DEC(J2000) = -07:31:05.9 = -7.51831 with a 90%-confidence error radius of about 0.75 arc sec. This position is 1.1 arc sec. from the center of the XRT error circle. The estimated magnitude is 16.47 with a 1-sigma error of about 0.14. No correction has been made for the expected extinction corresponding to E(B-V) of 0.06. Burst Advocate for this burst is P. A. Evans (pae9 AT star.le.ac.uk). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 27592 SUBJECT: GRB 200416A: Fermi GBM observation DATE: 20/04/16 13:41:38 GMT FROM: Elisabetta Bissaldi at INFN,Bari E. Bissaldi (Politecnico and INFN Bari) reports on behalf of the Fermi GBM Team: "At 07:05:17.38 UT on 16 April 2020, the Fermi Gamma-Ray Burst Monitor (GBM) triggered and located GRB 200416A (trigger 608713522 /200416295), which was also detected by the Swift/BAT (Evans et al. 2020, GCN 27591). The trigger was initially misclassified as a particle event by the flight software. The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight at the GBM trigger time is 92 degrees. The GBM light curve shows a double-peaked emission episode with a duration (T90) of about 9 s (50-300 keV). The time-averaged spectrum from T0-2 s to T0+6 s is adequately fit by a power law function with an exponential high-energy cutoff. The power law index is -0.87 +/- 0.15 and the cutoff energy, parameterized as Epeak, is 74 +/- 6 keV. The event fluence (10-1000 keV) in this time interval is (1.43 +/- 0.08)E-06 erg/cm^2. The 1-sec peak photon flux measured starting from T0-0.064 s in the 10-1000 keV band is 6.5 +/- 0.3 ph/s/cm^2. A Band function fits the spectrum equally well with Epeak= 64 +/- 9 keV, alpha = -0.66 +/- 0.24 and beta = -2.5 +/- 0.3. 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: 27594 SUBJECT: GRB 200416A: Swift-XRT refined Analysis DATE: 20/04/16 15:03:26 GMT FROM: Phil Evans at U of Leicester P. A. Evans (U Leicester) reports on behalf of the Swift-XRT team: We have analysed 677 s of XRT data for GRB 200416A (Evans et al. GCN Circ. 27591), from 84 s to 773 s after the BAT trigger. The data comprise 43 s in Windowed Timing (WT) mode (the first 9 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The refined XRT position is RA, Dec = 335.6986, -7.5179 which is equivalent to: RA (J2000): 22 22 47.66 Dec(J2000): -07 31 04.3 with an uncertainty of 3.5 arcsec (radius, 90% confidence). The light curve can be modelled with an initial power-law decay with an index of alpha=2.9 (+/-0.5), followed by a break at T+167 s to an alpha of 0.25 (+0.18, -0.25). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.86 (+0.22, -0.20). The best-fitting absorption column is 9.6 (+6.3, -3.1) x 10^20 cm^-2, consistent with the Galactic value of 6.5 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 3.6 x 10^-11 (4.3 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 9.6 (+6.3, -3.1) x 10^20 cm^-2 Galactic foreground: 6.5 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.86 (+0.22, -0.20) The GRB entered Swift's Moon-proximity observing constraint shortly after the trigger, and will not be observable until early on Monday April 20th; observations are planned for that time. The light curve appears to be in the plateau phase common to X-ray afterglows and is expected to break to a steeper decay at some point within the next ~24 hours, so we do not attempt to predict the flux at T0+24 hours. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00966554. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 27601 SUBJECT: GRB 200416A: Swift-BAT refined analysis DATE: 20/04/17 18:07:53 GMT FROM: Sibasish Laha at GSFC A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (GSFC), J. R. Cummings (CPI), P. A. Evans (U Leicester) H. A. Krimm (NSF), S. Laha (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), T. N. Ukwatta (LANL) (i.e. the Swift-BAT team): Using the data set from T-61 to T+242 sec from the recent telemetry downlink, we report further analysis of BAT GRB 200416A (trigger #966554) (P. A. Evans et al., GCN Circ. 27591). The BAT ground-calculated position is RA, Dec = 335.691, -7.525 deg which is RA(J2000) = 22h 22m 45.8s Dec(J2000) = -07d 31' 29.5" with an uncertainty of 1.4 arcmin, (radius, sys+stat, 90% containment). The partial coding was 33%. The mask weighted light curve shows multi-peaked structure. The overall structure starts at ~T-2 s and lasts till ~T+6 s. T90 (15-350 keV) is 5.04 +- 0.73 sec (estimated error including systematics). The time-averaged spectrum from T-1.31 to T+4.69 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.76 +- 0.15. The fluence in the 15-150 keV band is 8.7 +- 0.8 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T-0.05 sec in the 15-150 keV band is 3.8 +- 0.5 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/966554/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 27602 SUBJECT: GRB 200416A: Swift/UVOT Detection DATE: 20/04/18 06:40:43 GMT FROM: Kira Simpson at PSU GRB 200416A: Swift/UVOT Detection K. K. Simpson (PSU) and P. A. Evans (U. Leicester) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 200416A 102 s after the BAT trigger (Evans et al., GCN Circ. 27591). A source consistent with the XRT position (Evans GCN Circ. 27594) is detected in the initial UVOT exposures. The preliminary UVOT position is: RA (J2000) = 22:22:47.84 = 335.69934 (deg.) Dec (J2000) = -07:31:06.0 = -7.51833 (deg.) with an estimated uncertainty of 0.43 arc sec. (radius, 90% confidence). Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white 102 252 147 16.57 +/- 0.03 v 644 664 19 17.05 +/- 0.32 b 570 590 20 17.48 +/- 0.20 u 314 564 246 16.44 +/- 0.04 w1 694 714 20 16.59 +/- 0.23 m2 668 688 19 >16.3 w2 620 640 19 >17.5 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.06 in the direction of the burst (Schlegel et al. 1998).