//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 33260 SUBJECT: GRB 230204A: Swift detection of a possible burst (or possible transient Swift J1552.8-5055) DATE: 23/02/04 03:45:02 GMT FROM: David Palmer at LANL A. D'Ai (INAF-IASFPA), E. Ambrosi (INAF-IASFPA), V. D'Elia (SSDC & INAF-OAR), J. A. Kennea (PSU), A. Y. Lien (U Tampa), A. Melandri (INAF-OAB), D. M. Palmer (LANL), B. Sbarufatti (INAF-OAB), M. H. Siegel (PSU), A. Tohuvavohu (U Toronto) and M. A. Williams (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 02:56:57 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 230204A (trigger=1152509). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 238.164d, -50.858d which is RA(J2000) = 15h 52m 39s Dec(J2000) = -50d 51' 27" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). Due to a telemetry gap, the BAT lightcurve before T+8s is not immediately available, and no obvious variation is visible in the remainder of the lightcurve, as is typical for an image trigger. The XRT began observing the field at 02:59:24.1 UT, 146.8 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 238.1950, -50.9167 which is equivalent to: RA(J2000) = 15h 52m 46.80s Dec(J2000) = -50d 55' 00.1" with an uncertainty of 5.0 arcseconds (radius, 90% containment). The initial flux in the 2.5 s image was 2.77e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 156 seconds after the BAT trigger. No credible afterglow candidate has been found in the initial data products. The 2.7'x2.7' sub-image covers none of the XRT error circle. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The list of sources is typically complete to about 18 mag. No correction has been made for the large, but uncertain, extinction expected. We note that this source is near the Galactic plane (lat=2.38 deg) and was detected as a 64 s image trigger, which raises the possibility that this is a Galactic transient. We would name this source Swift J1552.8-5055 if it is not a GRB. Further analysis of the nature of this source will require the full downlinked dataset. Burst Advocate for this burst is A. D'Ai (antonino.dai AT inaf.it). 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: 33261 SUBJECT: GRB 230204A: Enhanced Swift-XRT position DATE: 23/02/04 07:39:42 GMT FROM: Phil Evans at U of Leicester P.A. Evans, M.R. Goad, J.P. Osborne and A.P. Beardmore (U. Leicester) report on behalf of the Swift-XRT team. Using 1193 s of XRT Photon Counting mode data and 1 UVOT images for GRB 230204A, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 238.19965, -50.91653 which is equivalent to: RA (J2000): 15h 52m 47.91s Dec (J2000): -50d 54' 59.5" with an uncertainty of 2.2 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 33263 SUBJECT: GRB 230204A/Swift J1552.8-5055: LCOGT Optical Counterpart Candidate DATE: 23/02/04 14:02:18 GMT FROM: Robert Strausbaugh at University of Minnesota R. Strausbaugh (University of Minnesota), A. Cucchiara (NASA) report on behalf of a larger collaboration: We observed the GRB 230204A/Swift J1552.8-5055 (D'Ai et al., GCN 33260) field with the LCOGT 1-meter Sinistro instrument at the Cerro Tololo Interamerican Observatory, Chile site, on February 4, from 07:24 to 7:57 UT (corresponding to 4.47 to 5.02 hours after GRB trigger time) with the Bessel R and I filters. We performed a series of 3x300s exposures in both bands. We detect a source consistent with the XRT enhanced error position (Evens et al., GCN 33261) that is not present in USNO, SkyMapper, or 2MASS catalogs. The coordinates for this candidate are: 238.19844d, -50.917039d. As the field is near the galactic plane, the field is quite crowded. It is possible that this source is present in the catalogs mentioned, but was not able to be resolved due to different plate scales. Future observations are planned to determine if the detected source is fading and other follow-up efforts are encouraged. The following magnitudes are calculated using the USNO-B1.0 catalog as reference: R = 17.75 +/- 0.02 I = 17.16 +/- 0.01 Due to the crowded field, these magnitudes may be contaminated by a nearby bright star. These magnitudes are not corrected for galactic extinction. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 33264 SUBJECT: GRB 230204A: Swift-XRT refined Analysis DATE: 23/02/04 18:03:23 GMT FROM: Phil Evans at U of Leicester J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), A. Melandri (INAF-OAB), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), D.N. Burrows (PSU) and A. D'Ai report on behalf of the Swift-XRT team: We have analysed 6.4 ks of XRT data for GRB 230204A (D'Ai et al. GCN Circ. 33260), from 136 s to 46.9 ks after the BAT trigger. The data comprise 250 s in Windowed Timing (WT) mode (the first 8 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Evans et al. (GCN Circ. 33261). The light curve can be modelled with a power-law decay with a decay index of alpha=2.37 (+0.16, -0.14). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.64 (+/-0.10). The best-fitting absorption column is 2.61 (+0.21, -0.20) x 10^22 cm^-2, in excess of the Galactic value of 1.0 x 10^22 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.5 (+/-0.4) and a best-fitting absorption column of 2.1 (+0.7, -0.6) x 10^22 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 7.6 x 10^-11 (1.2 x 10^-10) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 2.1 (+0.7, -0.6) x 10^22 cm^-2 Galactic foreground: 1.0 x 10^22 cm^-2 Excess significance: 2.8 sigma Photon index: 1.5 (+/-0.4) If the light curve continues to decay with a power-law decay index of 2.37, the count rate at T+24 hours will be 1.2 x 10^-5 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 9.2 x 10^-16 (1.4 x 10^-15) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01152509. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 33266 SUBJECT: GRB 230204A: Swift/UVOT Upper Limits DATE: 23/02/04 23:36:26 GMT FROM: Sam LaPorte at PSU S. J. LaPorte (PSU) and A. D'Ai (INAF-IASFPA) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 230204A 156 s after the BAT trigger (D'Ai et al., GCN Circ. 33260). No optical afterglow consistent with the XRT position (Evans et al. GCN Circ. 33261) is detected in the initial UVOT exposures. A known source with no significant signs of fading is detected 2.88 arcsec from the XRT position at: RA (J2000): 15h 52m 47.83s Dec (J2000): -50d 54' 56.74" Preliminary 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the first finding chart (FC) exposure and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 156 306 147 >17.5 u_FC 314 564 246 >19.1 white 156 1372 373 >17.8 v 645 1596 117 >15.9 b 570 1521 97 >17.9 u 314 5553 382 >19.1 w1 695 5489 274 >19.1 m2 670 1446 97 >18.8 w2 621 1571 117 >18.5 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 2.516 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 33279 SUBJECT: GRB 230204A: Swift-BAT refined analysis DATE: 23/02/06 03:46:38 GMT FROM: Amy Lien at GSFC T. Parsotan (GSFC/UMBC), S. D. Barthelmy (GSFC), A. D'Ai (INAF-IASFPA), H. A. Krimm (NSF), S. Laha (GSFC/UMBC), A. Y. Lien (U Tampa), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU) (i.e. the Swift-BAT team): Using the data set from T-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 230204A (trigger #1152509) (D'Ai et al., GCN Circ. 33260). The BAT ground-calculated position is RA, Dec = 238.166, -50.848 deg which is RA(J2000) = 15h 52m 39.8s Dec(J2000) = -50d 50' 52.8" with an uncertainty of 2.4 arcmin, (radius, sys+stat, 90% containment). The partial coding was 48%. The mask-weighted light curve shows a multi-peaked structure that starts at ~T-10 and ends at ~T+200 s. The most prominent peak occurs at ~T+148 s. T90 (15-350 keV) is 182.05 +- 16.73 sec (estimated error including systematics). The time-averaged spectrum from T-6.81 to T+195.62 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.72 +- 0.13. The fluence in the 15-150 keV band is 3.7 +- 0.3 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+148.12 sec in the 15-150 keV band is 0.9 +- 0.2 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/1152509/BA/