//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17377 SUBJECT: GRB 150203A: Swift detection of a burst DATE: 15/02/03 04:23:40 GMT FROM: David Palmer at LANL T. N. Ukwatta (LANL), W. H. Baumgartner (GSFC/UMBC), M. M. Chester (PSU), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the Swift Team: At 04:09:07 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 150203A (trigger=629578). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 98.415, +6.968 which is RA(J2000) = 06h 33m 39s Dec(J2000) = +06d 58' 04" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a complex structure with a duration of about 30 sec. The peak count rate was ~1500 counts/sec (15-350 keV), at ~1 sec after the trigger. The XRT began observing the field at 04:10:21.5 UT, 74.0 seconds after the BAT trigger. Using promptly downlinked data we find a bright, fading, uncatalogued X-ray source with an enhanced position: RA, Dec 98.3997, 6.9533 which is equivalent to: RA(J2000) = 06h 33m 35.92s Dec(J2000) = +06d 57' 11.9" with an uncertainty of 2.3 arcseconds (radius, 90% containment). This location is 76 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 http://www.swift.ac.uk/sper. A power-law fit to a spectrum formed from promptly downlinked event data gives a column density consistent with the Galactic value of 6.52 x 10^21 cm^-2 (Willingale et al. 2013). The initial flux in the 2.5 s image was 1.31e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 82 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 100% of the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. 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. Burst Advocate for this burst is T. N. Ukwatta (tilan.ukwatta AT gmail.com). 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/too.html.) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17378 SUBJECT: GRB 150203A: Prompt enhanced Swift-XRT position DATE: 15/02/03 04:39:36 GMT FROM: Phil Evans at U of Leicester P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Using promptly downlinked XRT event data for GRB 150203A, we find an enhanced XRT position of the afterglow: RA, Dec: 98.3993, 6.9532 which is equivalent to: RA (J2000) = 06 33 35.84 Dec (J2000) = +06 57 11.5 with an uncertainty of 2.1 arcseconds (radius, 90% confidence). Analysis of the promptly available data is online at http://www.swift.ac.uk/sper/629578. Position enhancement is is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17379 SUBJECT: GRB 150203A: KAIT Optical Upper Limit DATE: 15/02/03 04:42:56 GMT FROM: Weikang Zheng at UC Berkeley WeiKang Zheng and Alexei V. Filippenko (UC Berkeley) report on behalf of the KAIT GRB team: The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, responded to Swift GRB 150203A (Ukwatta et al., GCN 17377) starting at 04:10:55 UT, 108 s after the burst, with thin cloud condition. Observations were performed with an automatic sequence in the clear (roughly R), V, and I filters, and the exposure time was 20 s per image. We do not detect any new source neither in our single images, nor in the co-add of the first 5 images, within the enhanced XRT error (Evans, GCN 17378). The typical limiting magnitude of our single clear image is about 17.8 calibrated to USNO B1.0. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17380 SUBJECT: GRB 150203A: P60 observations DATE: 15/02/03 04:55:19 GMT FROM: Daniel Perley at Caltech D. A. Perley (Caltech) reports on behalf of a larger collaboration: The Palomar 60-inch robotic telescope responded to the Swift alert for GRB 150203A (Ukwatta et al., GCN 17377) and began automatic follow-up at 04:11:42 UT, 155 s after the BAT trigger. The telescope acquired a series of cycling 60-second r, i, and z exposures under good seeing conditions. We detect no source in or near the XRT position (Evans et al., GCN 17378), in any individual exposure or in a stack of the first several minutes of imaging acquired in each filter. An approximate limiting magnitude of the r-band stack (7 minutes of imaging at a median time of 13.0 minutes post-trigger) is >21.5 mag, calibrated relative to USNO B1.0. Given the low galactic latitude, no further follow-up is planned. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17383 SUBJECT: GRB 150203A: RATIR Optical and NIR Observations DATE: 15/02/03 06:42:32 GMT FROM: Nat Butler at Az State U Nat Butler (ASU), Alan M. Watson (UNAM), Alexander Kutyrev (GSFC), William H. Lee (UNAM), Michael G. Richer (UNAM), Chris Klein (UCB), Ori Fox (UCB), J. Xavier Prochaska (UCSC), Josh Bloom (UCB), Antonino Cucchiara (ORAU/GSFC), Eleonora Troja (GSFC), Owen Littlejohns (ASU), Enrico Ramirez-Ruiz (UCSC), José A. de Diego (UNAM), Leonid Georgiev (UNAM), Jesús González (UNAM), Carlos Román-Zúñiga (UNAM), Neil Gehrels (GSFC), and Harvey Moseley (GSFC) report: We observed the field of GRB 150203A (Ukwatta, et al., GCN 17377) with the Reionization and Transients Infrared Camera (RATIR; www.ratir.org) on the 1.5m Harold Johnson Telescope at the Observatorio Astronómico Nacional on Sierra San Pedro Mártir from 2015/02 3.19 to 2015/02 3.26 UTC (0.50 to 2.14 hours after the BAT trigger), obtaining a total of 1.28 hours exposure in the r, i, and z bands. We find no uncatalogued sources within the Swift-XRT error circle (Evans, et al., GCN 17378). In comparison with USNO-B1 and 2MASS, we obtain the following upper limits (3-sigma): r > 23.1 i > 23.3 z > 20.1 These magnitudes are in the AB system and are not corrected for Galactic extinction in the direction of the GRB. We thank the staff of the Observatorio Astronómico Nacional in San Pedro Mártir. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17384 SUBJECT: GRB 150203A: Enhanced Swift-XRT position DATE: 15/02/03 08:25:13 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 1115 s of XRT Photon Counting mode data and 2 UVOT images for GRB 150203A, 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 = 98.39900, +6.95372 which is equivalent to: RA (J2000): 06h 33m 35.76s Dec (J2000): +06d 57' 13.4" with an uncertainty of 1.9 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: 17386 SUBJECT: GRB 150203A: GROND Upper limits DATE: 15/02/03 08:54:48 GMT FROM: Karla Varela at MPE C. Delvaux, K. Varela and J. Greiner (all MPE Garching) report on behalf of the GROND team: We observed the field of GRB 150203A (SWIFT-629578; Ukwatta et al., GCN #17377) simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2m MPG telescope at ESO La Silla Observatory (Chile). Observations started on February 3rd, 2015, at 04:20 UT, 11 minutes after the GRB trigger. They were performed at an average seeing of 1.2" and at an average airmass of 2.1. The distance from the moon was only 28 deg. We do not detect a source inside the 2.1 arcsec error circle reported by Ukwatta et al. (GCN #17377). Based on a total exposure of 0.83 hours in g'r'i'z' and 0.80 hours in JHK, at a midtime of 0.7 hour after the burst, we measure the following preliminary upper limits (AB magnitudes system): g' > 23.5 mag, r' > 23.9 mag, i' > 24.0 mag, z' > 24.1 mag, J > 21.5 mag, H > 20.9 mag, and K > 18.6 mag. Given magnitudes are calibrated against GROND zeropoints as well as 2MASS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V) = 0.88 mag in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17387 SUBJECT: GRB 150203A: TAROT La Silla observatory optical observations DATE: 15/02/03 10:41:40 GMT FROM: Alain Klotz at IRAP-CNRS-OMP Klotz A., Turpin D. (IRAP-CNRS-OMP), Boer M., Gendre B., Siellez K., Dereli H., Bardho O. (UNS-CNRS-OCA), Atteia J.L. (IRAP-CNRS-OMP) report: We imaged the field of GRB 150203A detected by SWIFT (trigger 629578) with the TAROT robotic telescope (D=25cm) located at the European Southern Observatory, La Silla observatory, Chile. The observations started 37.1s after the GRB trigger (13.6s after the notice). The elevation of the field decreased from 45 degrees above horizon and weather conditions were good but the field of view is located at low galactic latitude (extinction estimated > 14 magnitudes in the R band). The first image is trailed with a duration of 60.0s (see the description in Klotz et al., 2006, A&A 451, L39). We do not detect any OT with a limiting magnitude of: t0+37.1s to t0+97.1s : Rlim = 15.8 The second image is 90.0s exposure in tracking mode: t0+391s to t0+481s : Rlim = 16.4 We co-added a series of exposures: t0+391s to t0+1203s : Rlim = 17.0 Magnitudes were estimated with the nearby USNO-B1 stars and are not corrected for galactic dust extinction. N.B. Galactic coordinates are lon=204.7072 lat= -0.7535 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17389 SUBJECT: GRB 150203A: Fermi GBM observation DATE: 15/02/03 11:09:45 GMT FROM: Hoi-Fung Yu at MPE V. Pelassa (UAH) and H.-F. Yu (MPE) report on behalf of the Fermi GBM Team: "At 04:09:10.06 UT on 03 Feb 2015, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 150203A (trigger 444629353 / 150203173), which was also detected by Swift (Ukwatta et al. 2015, GCN 17377). The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight is 97 degrees. The GBM light curve shows a single pulse with a duration (T90) of about 26 s (50-300 keV). The time-averaged spectrum from T0-2.048 s to T0+ 27.648 s is well fit by a power law function with an exponential high-energy cutoff. The power law index is -0.82 +/- 0.32 and the cutoff energy, parameterized as Epeak, is 59 +/- 8 keV. The event fluence (10-1000 keV) in this time interval is (1.29 +/- 0.13)E-06 erg/cm^2. The 1.024-sec peak photon flux measured starting from T0+13.952 s in the 10-1000 keV band is 1.8 +/- 0.3 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17391 SUBJECT: GRB 150203A: REM optical and NIR observations DATE: 15/02/03 16:21:15 GMT FROM: Paolo D'Avanzo at INAF-OAB P. D'Avanzo, S. Covino (INAF-OAB), V. D'Elia (ASI/ASDC & INAF/OAR) report on behalf of the REM team: We observed the field of GRB 150203A (Ukwatta et al., GCN 17377) with the 60-cm robotic telescope REM located at the La Silla Observatory (Chile). The observations started at 04:10:09 UT, 62 seconds after the GRB, and were carried out simultaneously with in the g, r, i, z and H bands. No source is detected at the X-ray afterglow position reported by Evans et al. (GCN 17384). At a mean t-t0 of 181 s, we obtain the following 3sigma upper limits: g > 17.8 mag r > 17.7 mag i > 17.5 mag H > 17.5 mag All magnitudes are in the AB system and are not corrected for Galactic reddening. The photometry is calibrated against the APASS (optical) and 2MASS (NIR) catalogues. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17395 SUBJECT: GRB 150203A: MITSuME Okayama upper limits DATE: 15/02/04 01:43:25 GMT FROM: Daisuke Kuroda at OAO/NAOJ D. Kuroda, K. Yanagisawa, Y. Shimizu, H. Toda (OAO, NAOJ), S. Nagayama (NAOJ), M. Yoshida (Hiroshima), K. Ohta (Kyoto) and N. Kawai(Tokyo Tech) report on behalf of MITSuME and OISTER collaboration: We observed the field of GRB 150203A (Ukwatta et al., GCNC 17377) with the optical three color (g', Rc and Ic) CCD camera attached to the MITSuME 50cm telescope of Okayama Astrophysical Observatory. The observation started on 2015-02-03 10:36:11 UT (~6.5 h after the burst). We did not find any new point source within the enhanced XRT circle (Evans et al., GCNC 17384) in all the three bands. Three sigma upper limits of the OT are listed below. We used GSC2.3 catalog for flux calibration. #T0+[day] MID-UT T-EXP[sec] g' Rc Ic ----------------------------------------------------- 0.36578 12:55:51 6060.0 >19.8 >19.5 >18.7 ----------------------------------------------------- T0+ : Elapsed time after the burst [day] T-EXP: Total Exposure time [sec] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17397 SUBJECT: GRB 150203A: Swift-XRT refined Analysis DATE: 15/02/04 04:23:04 GMT FROM: Phil Evans at U of Leicester B.P. Gompertz (U. Leicester), M. de Pasquale (INAF-IASFPA), A. Maselli (INAF-IASFPA), A. Melandri (INAF-OAB), J.A. Kennea (PSU), V. Mangano (PSU), M.C. Stroh (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester) and T.N. Ukwatta report on behalf of the Swift-XRT team: We have analysed 5.7 ks of XRT data for GRB 150203A (Ukwatta et al. GCN Circ. 17377), from 64 s to 24.0 ks after the BAT trigger. The data comprise 76 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. 17378). The light curve can be modelled with an initial power-law decay with an index of alpha=2.84 (+0.15, -0.13), followed by a break at T+355 s to an alpha of 0.59 (+0.09, -0.08). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.87 (+0.29, -0.27). The best-fitting absorption column is 1.20 (+0.35, -0.30) x 10^22 cm^-2, in excess of the Galactic value of 6.5 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 2.1 (+0.4, -0.3) and a best-fitting absorption column of 1.5 (+0.5, -0.4) x 10^22 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 5.3 x 10^-11 (1.2 x 10^-10) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.5 (+0.5, -0.4) x 10^22 cm^-2 Galactic foreground: 6.5 x 10^21 cm^-2 Excess significance: 3.5 sigma Photon index: 2.1 (+0.4, -0.3) If the light curve continues to decay with a power-law decay index of 0.59, the count rate at T+24 hours will be 0.011 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.6 x 10^-13 (1.2 x 10^-12) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00629578. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17399 SUBJECT: GRB 150203A: ISON-NM early optical limit DATE: 15/02/04 11:46:45 GMT FROM: Alexei Pozanenko at IKI, Moscow L. Elenin (KIAM), A. Volnova (IKI), E. Mazaeva (IKI), I. Molotov (KIAM), A. Pozanenko (IKI) report on behalf of larger GRB follow-up collaboration: We observed the field of the Swift GRB 150203A (Ukwatta et al., GCN 17377) with 0.4-m telescope of ISON-NM observatory in robotic mode starting on Feb., 03 (UT) 04:10:19 i.e. 72 seconds after burst trigger. We obtained 60 unfiltered images of 30 s exposure. We do not detect any source within enhanced XRT error circle (Evans et al., GCN 17384): Date UT start t-T0 Exp. Filter UL (3sigma) (mid.,days) (s) 2014-02-03 04:10:19 0.00130 2*30 Clear 18.0 2014-02-03 04:10:19 0.01836 60*30 Clear 19.7 The photometry is based on nearby USNO-B1.0 stars USNO-B1.0 RA Dec R2 0968-0105340 06:33:22.23 +06:53:43.2 15.41 0969-0108800 06:33:26.73 +06:56:58.4 14.77 0969-0108730 06:33:22.76 +06:55:10.3 15.73 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17400 SUBJECT: GRB 150203A: Swift/UVOT Upper Limits DATE: 15/02/04 13:38:23 GMT FROM: Margaret Chester at PSU M. M. Chester (PSU) and T. N. Ukwatta (LANL) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 150203A 83 s after the BAT trigger (Ukwatta et al., GCN Circ. 17377). No optical afterglow consistent with the enhanced XRT position (Evans et al. GCN Circ. 17384) 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 first finding chart (FC) exposures and subsequent exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white_FC 83 232 147 >20.6 white 83 1197 353 >21.2 v 624 1246 78 >18.7 b 550 1172 58 >19.4 u_FC 295 545 246 >20.0 u 295 1148 285 >20.0 w1 674 1278 61 >18.8 m2 649 1271 78 >18.7 w2 600 1222 78 >19.0 The magnitudes in the table are not corrected for the large Galactic extinction in the direction of the burst (reddening of E(B-V) = 0.9; Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17402 SUBJECT: GRB 150203A: RAPTOR Limits Beginning at the Gamma-Ray Emitting Interval DATE: 15/02/04 15:53:14 GMT FROM: James Wren at LANL J. Wren, W.T. Vestrand, P. Wozniak, and H. Davis, of Los Alamos National Laboratory report: The RAPTOR network of robotic optical telescopes made observations of Swift trigger 629578 (Ukwatta, et al., GCN 17377). Our narrow-field instruments located in Los Alamos, NM, USA, arrived on target 4.6 s after receipt of the notice (T+30.9 s after the BAT trigger time). No optical counterpart is detected within the Swift XRT counterpart location. Typical 3-sigma limiting magnitudes for our initial 5 s exposures were R~16.6 and I~15.7 based on comparision to the USNO-B1 R-band catalog. The burst location was also within the field of view of our wide-field sky monitors during the gamma-ray emitting interval. No optical counterpart is detected in any of our wide-field monitor images. Typical 3-sigma unfiltered limiting magnitudes during this period were V~9.7 based on comparison to the Tycho-2 V-band catalog. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17410 SUBJECT: GRB 150203A: Swift-BAT refined analysis DATE: 15/02/05 15:36:38 GMT FROM: Tilan Ukwatta at MSU T. N. Ukwatta (LANL), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), M. Stamatikos (OSU), J. Tueller (GSFC), (i.e. the Swift-BAT team): Using the data set from T-120 to T+1190 sec from the recent telemetry downlink, we report further analysis of BAT GRB GRB 150203A (trigger #629578) (Ukwatta, et al., GCN Circ. 17377).The BAT ground-calculated position is RA, Dec = 98.394, 6.952 deg which is RA(J2000) = 06h 33m 34.5s Dec(J2000) = +06d 57' 07.1" with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 84%. BAT light curve shows a single multi-peaked episode starting around T-2 sec, and ending around T+32 sec. The two main peaks of the light curve can be seen at T+1 sec and T+18 sec. T90 (15-350 keV) is 25.8 +- 5.0 sec (estimated error including systematics). The time-averaged spectrum from T-0.8 to T+32.3 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.90 +- 0.12. The fluence in the 15-150 keV band is 9.1 +- 0.6 x 10^-07 erg/cm2. The 1-sec peak photon flux measured from T+16.79 sec in the 15-150 keV band is 0.9 +- 0.1 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/629578/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 17425 SUBJECT: GRB 150203A iTelescope observation DATE: 15/02/07 11:36:49 GMT FROM: Takanori Sakamoto at AGU D. Kawamura, T. Sakamoto, A. Yoshida (AGU) We observed the field of GRB 150203A detected by Swift (trigger #629578; Ukwatta et al., GCN Circ. 17377) with the iTelescope.Net (http://www.itelescope.net) T11 (0.50 m Plane Wave) telescope located at the New Mexico Skies Observatory (NM, USA). 20 images of 60 sec exposures were taken in the R filter starting from February 3 4:22:11 (UT) about 13.3 minutes after the trigger and stopped on February 3 4:47:29 (UT). We do not detect the optical afterglow both in the individual images and the stacked image at the enhanced X-ray afterglow position (Evans et al., GCN Circ. 17378). The estimated five sigma upper limit of the combined image (total exposure of 1200 sec) is ~18.9 using the USNO-B1 catalog.