This file contains both GRBs: 060428A and 060428B //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5014 SUBJECT: GRB 060428: Swift detection of a burst DATE: 06/04/28 03:45:11 GMT FROM: Scott Barthelmy at NASA/GSFC V. Mangano (INAF-IASFPA), S. D. Barthelmy (GSFC), D. N. Burrows (PSU), J. R. Cummings (NASA/ORAU), N. Gehrels (NASA/GSFC), S. T. Holland (GSFC/USRA), J. A. Kennea (PSU), C. B. Markwardt (GSFC/UMD), F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL) and D. E. Vanden Berk (PSU) report on behalf of the Swift Team: At 03:22:48 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 060428 (trigger=207364). Swift slewed immediately to the burst. The BAT on-board calculated location is RA,Dec 123.568, -37.165 {08h 14m 16s, -37d 09' 52"} (J2000) with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve shows a main peak starting at ~T-5 sec and ending at ~T+15 sec. There is a possible second peak going from T+20 to T+40 sec. The peak count rate was ~2500 counts/sec (15-350 keV), at ~4 sec after the trigger. The XRT began observing the field at 03:23:56 UT, 69 seconds after the BAT trigger. XRT found a fading, uncatalogued X-ray source located at RA(J2000) = 08h 14m 10.9s, Dec(J2000) = -37d 10' 09.1", with an estimated uncertainty of 4.7 arcseconds (90% confidence radius). This location is 65 arcseconds from the BAT on-board position, within the BAT error circle. The initial flux in the 2.5s image was 3.2e-09 erg/cm2/s (0.2-10 keV). UVOT took a finding chart exposure of 400 seconds with the V filter starting 71 seconds after the BAT trigger. No 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 3-sigma upper limit is about 19.1 mag. The 8'x8' region for the list of sources generated on-board covers 100% of the XRT error circle. The limiting magnitude is expected to be about 17.5. No correction has been made for the large, but uncertain extinction expected. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5017 SUBJECT: GRB 060428B: Swift detection of a burst DATE: 06/04/28 09:31:30 GMT FROM: Scott Barthelmy at NASA/GSFC S. Campana (INAF-OAB), S. D. Barthelmy (GSFC), D. N. Burrows (PSU), J. R. Cummings (NASA/ORAU), N. Gehrels (NASA/GSFC), C. B. Markwardt (GSFC/UMD), K. L. Page (U Leicester), D. M. Palmer (LANL), P. Romano (INAF-OAB) and D. E. Vanden Berk (PSU) report on behalf of the Swift Team: At 08:54:38 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 060428B (trigger=207399). Swift slewed immediately to the burst. The BAT on-board calculated location is RA,Dec 235.350,+62.010 {15h 41m 24s,+62d 00' 36"} (J2000) with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). This is an image trigger (128 sec), so the lightcurve does not show any significant activity (as is typical). The XRT began observing the field at 08:58:02 UT, 204 seconds after the BAT trigger. XRT found a bright, fading X-ray source located at RA(J2000) = 15h 41m 25.6s, Dec(J2000) = +62d 01' 25.6", with an estimated uncertainty of 5.0 arcseconds (90% confidence radius). This location is 51 arcseconds from the BAT on-board position, within the BAT error circle. The initial flux in the 2.5s image was 2.3e-09 erg/cm2/s (0.2-10 keV). UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm) filter starting 212 seconds after the BAT trigger, and of 400 sec. with the V filter starting at 965 seconds after the BAT trigger. No 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 3-sigma V band upper limit is about 19.1 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 expected extinction corresponding to E(B-V) of 0.01. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5018 SUBJECT: GRB060428A: Swift XRT Team refined analysis DATE: 06/04/28 10:45:33 GMT FROM: Vanessa Mangano at INAF-IASFPA V. Mangano (INAF-IASFPA), E. Troja (INAF-IASFPA), D. N. Burrows (PSU) report on behalf of the Swift XRT Team: We have analyzed the first orbit data of GRB060428A (Mangano et al 2006, GCN 5014). The XRT data set consists of 39 s exposure in Windowed Timing (WT) mode followed by 1670 s exposure in Photon Counting (PC) mode. The refined position of the source is RA (2000) = 08h 14m 10.98s Dec (2000) = -37d 10' 10.3" with an uncertainty of 3.6 arcsec (90% confinement). This position is only 1.5 arcsec from the onboard detected position (Mangano et al 2006, GCN 5014). The 0.2-10 keV X-ray light curve shows an initial very fast decay with slope -6.3 +/- 0.4, a break at 144 +/- 6 s from the trigger and a flattening with a decay slope of -0.11 +/- 0.03. A small flare with a gaussian profile is present at 676 +/- 56 s after the trigger. The WT and PC spectra were fitted separately with an absorbed power law model and showed photon indices of 3.2 +/- 0.4 and 1.9 +/- 0.2, respectively (90% confidence level). The WT spectrum, covering the time interval 77-116 s, mostly accounts for the pre-break phase of the light curve. Both spectra are highly absorbed, but do not show evidence of an absorption column in excess with respect to the Galactic value of 8.5 x 10^21 cm^-2. The 0.2-10 keV unabsorbed fluxes of the two spectra are 2.9 x 10^-9 and 7.6 x 10^-11 erg cm^-2 s^-1, respectively. If decaying at the present rate the source will be at the flux level of 2.7 x 10^-11 erg cm^-2 s^-1 (corresponding to a count rate level of 0.18 counts s^-1) after one day. This Circular is an official product of the Swift XRT Team. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5019 SUBJECT: GRB 060428b: Optical afterglow candidate DATE: 06/04/28 11:15:34 GMT FROM: Paul Price at IfA,UH P.A. Price (IfA, Hawaii), T. Minezaki (IoA, Tokyo), L.L. Cowie, Y. Kakazu (IfA, Hawaii) and Y. Yoshii (IoA, Tokyo) report: We have observed the XRT localisation of GRB 060428B (GCN #5017) with the robotic MAGNUM telescope. Observations were made under clouds in R and I bands starting at 2006 Apr 28.38 UTC, with interruptions due to weather. Observations consisted of 10 x 65 sec exposures in R-band. We identify a source in the combined image, which does not appear to be in the DSS 2 red plate. While a precise astrometric solution is not yet available, our estimate of the position is approximately 3 arcsec west of the USNO-B1 source 1520-0246226 (at 15:41:25.96 +62:01:30.160 J2000), or around 15:41:25.5 +62:01:30 J2000 The source is approximately R ~ 19.6 mag at the time of our observations (from comparison with the USNO-B1 catalogue), and also appears in subsequent I-band and R-band combined images. An image of the field is available at http://www.ifa.hawaii.edu/~price/grb060428b.jpg //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5021 SUBJECT: GRB 060428b : Kiso R-band limit DATE: 06/04/28 13:16:35 GMT FROM: Yuji Urata at Saitama U M.Abe (ISAS/JAXA), Y. Sarugaku, H.Mito (Tokyo Univ.), Y.L. Qiu, W.K. Zheng (NAOC), K.Y. Huang(NCU), Y. Urata (Saitama Univ.) on behalf of EAFON report: "We have observed the GRB 060428B field (GCN #5017) using Kiso 1.05m telescope. The R and B band observations were started from 2.3 hours after the burst (after end of twilight). The limiting magnitude derived from USNOB1.0 is R=20.7 (SN=3). The candidate (GCN #5019) do not appear brighter than the limiting magnitude. This result indicates that the candidate is afterglow of GRB 060428B. Further analysis is in progress." This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5022 SUBJECT: GRB 060428A: Refined analysis of the Swift-BAT burst DATE: 06/04/28 13:34:17 GMT FROM: Scott Barthelmy at NASA/GSFC C. Markwardt (GSFC/UMD), L. Barbier (GSFC), S. Barthelmy (GSFC), J. Cummings (GSFC/NRC), E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (BYU-Idaho), H. Krimm (GSFC/USRA), V. Mangano (INAF-IASFPA), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC), G. Sato (ISAS), J. Tueller (GSFC) on behalf of the Swift-BAT team: Using the data set from T-239 to T+963 sec from recent telemetry downlinks, we report further analysis of BAT GRB 060428A (trigger #207364) (Mangano, et al., GCN 5014). The BAT ground-calculated position is RA,Dec = 123.535,-37.169 deg {8h 14m 8.5s, -37d 10' 8.6"} (J2000) +- 1.0 arcmin, (radius, sys+stat, 90% containment). The partial coding was 65%. The mask-weighted lightcurve shows a bright peak (starting at T-8 sec until T+20 sec with the peak at T+5 sec) and a weaker peak (T+22 sec until T+42 sec). T90 (15-350 keV) is 39.4 +- 2 sec (estimated error including systematics). The time-averaged spectrum from T-6.8 to T+43.0 is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 2.04 +- 0.11. The fluence in the 15-150 keV band is 1.4 +- 0.1 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+4.41 sec in the 15-150 keV band is 2.4 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5023 SUBJECT: GRB060428B, optical observation DATE: 06/04/28 15:08:51 GMT FROM: Eri Sonoda at U of Miyazaki/Japan E.Sonoda,S.Maeno,M.Yamauchi (University of Miyazaki) We have observed the field covering the error circle of GRB060428B (GCN 5017) with the unfiltered CCD camera on the 30-cm telescope at University of Miyazaki. The observation was started 12:02:52 UT, ~3.14 hour after the Swift trigger time. We have compared our data of 30 sec exposures with the USNO-A2.0 catalog, there is no new source at the position reported by P.A.Price et al.(GCN 5019). The upper limits are as follows: -------------------------------------------------------------- Start(UT) End(UT) Num. of frames Limit (mag.) -------------------------------------------------------------- 12:02:52 12:11:28 8 ~12.8 12:11:52 12:41:28 24 ~16.9 12:42:56 12:47:02 4 ~17.9 --------------------------------------------------------------- //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5024 SUBJECT: GRB060428A: Swift/UVOT observations. DATE: 06/04/28 15:30:29 GMT FROM: Massimiliano de Pasquale at MSSL-UCL M. De Pasquale (UCL-MSSL), V. Mangano (IASF Palermo) report on behalf of the Swift/UVOT team: The Swift/UVOT began taking data on the field of GRB060428A at 03:23:48 UT on 2006-04-28, 60 s after the BAT trigger (Mangano et al., GCN 5014), with the settling exposure. In the refined XRT error circle (Magano et al., GCN 5018), we find a weak (4 sigma detection) optical source in the V band at about V=20, not present in USNO B1.0 catalogue. This source however appears to be constant throughout the observation, thus further observations will be needed to determine if it is the optical afterglow of this burst. No other afterglow candidate was detected at the refined XRT position in summed images from any of the filters down to the following three-sigma upper limits. Filter T_range(s) Exp(s) 3sig_UL V 60-7526 1657 20.2 B 548-7116 442 20.5 U 524-13380 436 20.5 UVW1 500-12666 1358 20.0 UVM2 476-11758 1425 19.9 UVW2 563-7322 472 19.5 These upper limits are uncorrected for the strong estimated Galactic reddening of E_{B-V} = 1.25 mag (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5027 SUBJECT: GRB 060428B: KAIT observations DATE: 06/04/28 17:18:35 GMT FROM: Weidong Li at UC Berkeley KAIT/LOSS W. Li, R. Chornock, N. Butler, J. Bloom, and A. V. Filippenko (University of California, Berkeley), on behalf of the KAIT GRB team, report: The robotic 0.76-m Katzman Automatic Imaging Telescope (KAIT) at Lick Observatory observed GRB 060428B, detected with Swift (Trigger 207399; Campana et al. GCN 5017). The automatic sequence started at 08:57:50, 192 s after the burst. In a 15 s unfiltered image, no afterglow candidate is detected to a limiting magnitude of 18.7 (from comparison with the USNO B1.0 catalog). Our real-time image processing software detected the optical afterglow candidate reported by Price et al. (GCN 5019) in a 60 s unfiltered image started at 642 s after the burst, with the following precise (+/- 0.3") position: RA = 15:41:25.63 Dec = +62:01:30.3 (J2000.) A table of photometry (3-sigma limits and detections) is reported below. The photometry of the afterglow candidate suggests a flat luminosity evolution from 10 to 35 minutes after the burst, but we caution that the photometry may suffer larger uncertainties than reported due to relatively poor detections and the contamination of a nearby source. ====================================================================== Start UT t(GRB) exposure(s) Filter 3sigma-limit detection 08:57:50 192s 15.0 clear 18.7 08:58:27 229s 15.0 V 16.9 08:58:57 259s 15.0 I 17.2 08:59:28 290s 20.0 clear 19.0 09:00:04 326s 45.0 V 17.7 09:01:04 386s 45.0 I 18.3 09:02:05 427s 45.0 clear 19.2 09:03:07 489s 60.0 V 17.9 09:04:23 565s 60.0 I 18.3 09:05:40 642s 60.0 clear 19.58 +/- 0.13 09:10:51 953s 120.0 clear 19.64 +/- 0.13 09:18:51 1433s 240.0 clear 19.40 +/- 0.11 09:30:55 2157s 360.0 clear 19.52 +/- 0.11 ======================================================================== //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5028 SUBJECT: GRB 060428B: Xinglong I-band limit DATE: 06/04/28 17:38:45 GMT FROM: W.K. Zheng at NAOC Y.Q. Lou, X.F. Wang (THCA), M.Zhai, Y.L. Qiu, J.Y. Wei, J.Y. Hu, J.S. Deng (NAOC) K.Y. Huang (NCU), Y. Urata (Saitama Univ.) on behalf of EAFON report: We have observed the field of GRB060428B (GCN 5017) with the Xinglong 0.8m telescope 3.54 hours after the burst, The candidate (GCN 5019) do not appear within our 7x600s combined I-band image. Upper limit is 19.1(SN=3) Mag . This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5029 SUBJECT: GRB 060428B: Refined analysis of the Swift-BAT burst DATE: 06/04/28 18:41:16 GMT FROM: Scott Barthelmy at NASA/GSFC T. Sakamoto (NASA/ORAU), L. Barbier (GSFC), S. Barthelmy (GSFC), S. Campana (INAF-OAB), J. Cummings (NASA/ORAU), E. Fenimore (LANL), N. Gehrels (GSFC), D. Hullinger (BYU-Idaho), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), G. Sato (ISAS), J. Tueller (GSFC), M. Koss (UMD), M. Stamatikos (NASA/ORAU) on behalf of the Swift-BAT team: Using the data set from T-239 to T+963 sec from recent telemetry downlinks, we report further analysis of BAT GRB 060428B (trigger #207399) (Campana, et al., GCN 5017). The BAT ground-calculated position is RA,Dec = 235.378,+62.027 deg {15h 41m 30.8s,+62d 1' 35.8"} (J2000) +- 1.7 arcmin, (radius, sys+stat, 90% containment). The partial coding was 74%. The mask-weighted lightcurve shows a broad peak starting at T-20 sec until ~T+44 sec. T90 (15-350 keV) is 58 +- 3 sec (estimated error including systematics). The time-averaged spectrum from T-23.8 to T+41.9 is best fit by a power law with an exponential cutoff. This fit gives a photon index 0.94 +- 1.30, and Epeak of 21.7 +- 14.0 keV (chi squared 68.81 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 7.2 +- 0.9 x 10^-7 erg/cm2 and the 1-sec peak flux measured from T+20.78 sec in the 15-150 keV band is 0.6 +- 0.1 ph/cm2/sec. A fit to a simple power law gives a photon index of 2.58 +- 0.19 (chi squared 75.57 for 57 d.o.f.). All the quoted errors are at the 90% confidence level. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5031 SUBJECT: GRB060428B: Swift XRT Team refined analysis DATE: 06/04/28 21:03:14 GMT FROM: Eleonora Troja at INAF-IASFPA E. Troja (INAF-IASFPA), V. Mangano (INAF-IASFPA), P. Romano (INAF-OAB), D. N. Burrows (PSU) report on behalf of the Swift XRT Team: We have analyzed the XRT data of the first four orbits of GRB060428B (Campana et al 2006, GCN 5017). The data set consists of 205 s exposure in Windowed Timing (WT) mode followed by 8.4 ks exposure in Photon Counting (PC) mode. The refined position of the source is RA (2000) = 15h 41m 25.57s Dec (2000) = +62d 01' 28.94" with an uncertainty of 3.8 arcsec (90% confinement). This position was evaluated from PC data of the orbits 2-4, that are not affected by pile-up. This position is 3.35 arcsec from the onboard detected position (Campana et al 2006, GCN 5017) and 1.4 arcsec from the optical afterglow candidate found by Price et al 2006 (GCN 5019). To evaluete this offset we used the KAIT coordinates from Li et al.(GCN 5027). The 0.2-10 keV X-ray light curve shows an initial very fast decay with slope -4.4 +/- 0.07, a break at 689 +/- 28 s from the trigger and then a decay slope of -0.89 +/- 0.06. The WT spectrum from the first orbit was fitted with an absorbed power law model and showed a photon index of 2.82 +/- 0.08 (90% confidence level). The WT spectrum covers the 212-418 s time interval. The spectrum shows evidence of an absorption column at the level of (6.7 +/- 0.7) x 10^20 cm^-2 in excess with respect to the Galactic value of 1.7 x 10^20 cm^-2. The 0.2-10 keV unabsorbed flux is 9.8 x 10^-10 ergs cm^-2 s^-1. The PC spectrum of the orbits 2-4 (time interval 4.4-18.5 ks) is well fit by an absorbed powerlaw model with photon index 2.08 +/- 0.16. The 0.2-10 keV unabsorbed flux is 1.6^-12 ergs cm^-2 s^-1. If decaying at the present rate the source will reach the flux level of 2.6^-13 erg cm^-2 s^-1 (corresponding to a count rate level of 5 x 10^-3 counts s^-1) after one day. This Circular is an official product of the Swift XRT Team. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5033 SUBJECT: GRB 060428A: PROMPT Observations DATE: 06/04/29 02:15:04 GMT FROM: Josh Haislip at U.North Carolina J. Haislip, M. Nysewander, A. Foster, A. LaCluyze, D. Reichart, J. A. Crain, K. Ivarsen, J. Kirschbrown, C. MacLeod, A. Trotter, and J. Carpenter report on behalf of the UNC team of the FUN GRB Collaboration: Skynet observed the localization of GRB 060428A (Mangano et al., GCN 5014) with three of the 16-inch PROMPT telescopes at CTIO beginning 58 sec after the burst (44 sec after notification) in Ug'r'i'z' (three simultaneously). No new source is found to z' > 17.1 mag (3 sigma; 10 sec exposure) at 63 sec after the burst and z' > 19.1 (3 sigma; 4 x 40 sec exposures) at 5.3 min after the burst. PROMPT is currently being built and commissioned. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5034 SUBJECT: GRB 060428B: MDM Observations DATE: 06/04/29 12:08:19 GMT FROM: Jules Halpern at Columbia U. J. P. Halpern (Columbia U.) and N. Mirabal (U. Michigan) report: "We observed the optical afterglow (Price et al. GCN 5019; Li et al. GCN 5027) of Swift GRB 060428B (Campana et al. GCN 5017) in the R band on the MDM 1.3m telescope during the period April 29.15-29.49 UT, or 18.6-26.8 hours after the burst. The fading noted by Abe et al. (GCN 5021) has continued. We estimate R~22.5 at 24 hours post-burst based on calibration with Landolt standard stars. We note that all of the objects within 25" of the transient appear to be galaxies, including one having R=19.4 that is only 3" to the east. A combined image of 1 hour total exposure at 24 hours post-burst is available at http://www.astro.columbia.edu/~jules/grb/060428b/mdm.jpg This message may be cited." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5035 SUBJECT: GRB060428B: possible detection of an optical counterpart by Swift/UVOT. DATE: 06/04/29 16:13:07 GMT FROM: Massimiliano de Pasquale at MSSL-UCL M. De Pasquale (UCL-MSSL), S. Campana (INAF-OAB) report on behalf of the Swift/UVOT team: The Swift/UVOT began taking data on the field of GRB060428B at 08:57:52 UT on 2006-04-28, 194 s after the BAT trigger (Campana et al., GCN 5017). At the position of the optical afterglow claimed by Price et al. (GCN 5019) and Li et al. (GCN 5027), inside the XRT error circle (Troja et al., GCN 5031), we find a source near the detection limits in the V band and in the White filter, not present in the USNO B1.0 catalogue. The source is present in the first ~1000 seconds of observations, with a significance of ~3 sigma. It is not detected later. Filter T_range(s) Exp(s) Mag V 194-1233 356 19.5 +0.5 -0.3 V 5630-16900 1081 >20.4 White 211-960 227 19.7 +/- 0.3 White 5247-18579 1135 >20.7 The upper limits quoted above are at the 3 sigma level. The source is not detected in any of the other filters. The fading behaviour may indicate that it is the GRB060428B optical afterglow, however we do caution that detections are marginal and the results suffer from a contamination by an extended source, the galaxy quoted by Helpern et al. in GCN 5034. An association with the GRB cannot be excluded. No other afterglow candidate was detected at the refined XRT position in summed images from any of the filters down to the following three-sigma upper limits: Filter T_range(s) Exp(s) 3sigma U.L. V 194-16900 1441 20.5 B 413-17812 1308 21.4 U 390-16900 1357 21.1 UW1 367-19996 1227 20.6 UM2 443-12022 1358 20.6 UW2 323-6894 383 20.2 White 212-18579 1363 20.8 These upper limits are uncorrected for the estimated Galactic reddening of E_{B-V} = 0.01 mag (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5036 SUBJECT: GRB060428B: optical observation DATE: 06/04/29 17:06:34 GMT FROM: Alexei Pozanenko at IKI, Moscow V.Rumyantsev (CrAO), V.Biryukov (SAI, MSU), and A.Pozanenko (IKI) on behalf of larger GRB follow up collaboration report: We observed the optical afterglow (Price et al. GCN5019; Li et al. GCN5027) of Swift GRB060428B (Campana et al. GCN 5017) in the R band with Shajn 2.6m telescope of CrAO between April 28 (UT) 18:43 -- 20:41, i.e. 9.8 -- 11.8 hrs after the burst onset. The afterglow is visible on a combined image of a total exposure 3240 sec in a tail of the nearby galaxy (Halpern et al. GCN5034) and precise photometry is underway. Based on USNO A2.0 we estimate limiting magnitude of the combined image as R=24.3. Combined image can be found in http://grb.rssi.ru/GRB060428/grb060428_ZTSH_R.gif The message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5037 SUBJECT: GRB060428B - SDSS Pre-Burst Observations DATE: 06/04/29 17:10:01 GMT FROM: Richard J. Cool at U.of AZ/Steward Obs Richard J. Cool (Arizona), Daniel J. Eisenstein (Arizona), David W. Hogg (NYU), Michael R. Blanton (NYU), David J. Schlegel (LBNL), J. Brinkmann (APO), Donald Q. Lamb (Chicago), Donald P. Schneider (PSU), and Daniel E. Vanden Berk (PSU) report: The Sloan Digital Sky Survey (SDSS) imaged the field of burst GRB060428B prior to the burst. As these data should be useful as a pre-burst comparison and for calibrating photometry, we are supplying the images and photometry measurements for this GRB field to the community. Data from the SDSS, including 5 FITS images, 3 JPGS, and 3 files of photometry and astrometry, are being placed at http://mizar.as.arizona.edu/~grb/public/GRB060428B We supply FITS images in each of the 5 SDSS bands of a 8'x8' region centered on the GRB position (ra=235.357 (15:41:25.7), dec=62.0238 (62:01:25.7); GCN 5017), as well as 3 gri color-composite JPGs (with different stretches). The units in the FITS images are nanomaggies per pixel. A pixel is 0.396 arcsec on a side. A nanomaggie is a flux-density unit equal to 10^-9 of a magnitude 0 source or, to the extent that SDSS is an AB system, 3.631e-6 Jy. The FITS images have WCS astrometric information. In the file GRB060428B_sdss.calstar.dat, we report photometry and astrometry of 303 bright stars (r<20.5) within 15' of the burst location. The magnitudes presented in this file are asinh magnitudes as are standard in the SDSS (Lupton 1999, AJ, 118, 1406). Beware that some of these stars are not well-detected in the u-band; use the errors and object flags to monitor data quality. In the files GRB060428B_sdss.objects_flux.dat and GRB060428B_sdss.objects_magnitudes.dat, we report photometry of 501 objects detected within 6' of the GRB position. We have removed saturated objects and objects with model magnitudes fainter than 23.0 in the r-band. The fluxes listed in GRB060428B_sdss.objects_flux.dat are in nanomaggies while the magnitudes listed in GRB060428B_sdss.objects_magnitudes.dat are asinh magnitudes. **Be aware that at least a portion of the photometry provided in this release has been flagged as non-photometric. As photometry for objects with this flag set may have non-optimal calibration, we do not recommend these objects be used for photometric calibration. Non-photometric imaging may still be valuable as a pre-burst comparison and for astrometric calibration. All quantities reported are standard SDSS photometry, meaning that they are very close to AB zeropoints and magnitudes are quoted in asinh magnitudes. Photometric zeropoints are known to about 2% rms. None of the photometry is corrected for dust extinction. The Schlegel, Finkbeiner, and Davis (1998) predictions for this region are A_U=0.073 mag, A_g=0.054 mag, A_r = 0.039 mag, A_i=0.030 mag, and A_z=0.021 mag. There are currently no objects within 6 arcminutes of the GRB position in the SDSS spectroscopic database. SDSS astrometry is generally better than 0.1 arcsecond per coordinate. Users requiring high precision astrometry should take note that the SDSS astrometric system can differ from other systems such as those used in other notices; we have not checked the offsets in this region. More detailed information pertaining to our SDSS GRB releases can be found in our initial data release paper (Cool et al. 2006, astro-ph/0601218). See the SDSS DR4 documentation for more details: http://www.sdss.org/dr4. These data have been reduced using a slightly different pipeline than that used for SDSS public data releases. We cannot guarantee that the values here will exactly match those in the data release in which these data are included. In particular, we expect the photometric calibrations to differ by of order 0.01 mag. This note may be cited, but please also cite the SDSS data release paper, Adelman-McCarthy et al. (2006, ApJS, in press, astro-ph/0507711), when using the data or referring to the technical documentation. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5075 SUBJECT: GRB 060428B: spectroscopy DATE: 06/05/05 17:00:58 GMT FROM: Daniele Malesani at SISSA-ISAS,Trieste,Italy D. Fugazza (INAF/OABr), D. Malesani (SISSA), G. Chincarini (Univ. Milano-Bicocca & INAF/OABr), S. Covino, P. Romano, G. Tagliaferri (INAF/OABr), M. Della Valle (INAF/OAA), N. Masetti (INAF/IASF Bo), G. Andreuzzi, N. Pinilla Alonso (INAF/TNG), report on behalf of a larger collaboration: We observed the field of GRB 060428B (Campana et al., GCN 5017; Troja et al., GCN 5031), possibly an X-ray flash (Sakamoto et al., GCN 5029). We undertook spectroscopy of the object 3" close to the optical afterglow (Price et al., GCN 5019; Li et al., GCN 5027; Halpern & Mirabal, GCN 5034), considering it as a potential host galaxy. Low-resolution spectroscopy (~15 A FWHM) was obtained with TNG+DOLoRes, starting on 2005 May 3.89273, for a total exposure time of 1 hr. Inspection of the spectrum reveals a smooth, very red continuum. No prominent features were detected either in emission or in absorption. We thus consider unlikely that this object is the host galaxy of GRB 060428B. A plot of the spectrum can be found at the following URL: http://www.sissa.it/~malesani/GRB/060428B/spectrum.gif This message can be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 5111 SUBJECT: GRB 060428a, SMARTS optical/IR afterglow detection DATE: 06/05/10 23:56:25 GMT FROM: Bethany Cobb at Yale U B. E. Cobb (Yale), part of the larger SMARTS consortium, reports: Using the ANDICAM instrument on the 1.3m telescope at CTIO, we obtained optical/IR imaging of the error region of GRB 060428a (GCN 5014, Mangano et al.) with a mid-exposure time of 2006-04-29 00:17 UT, which is ~20.9 hours post-burst and again at 2006-04-30 23:46 UT (~68.4 hours post-burst). For each observation total summed exposure times amounted to 36 minutes in I and 30 minutes in J. In our first epoch images, a source is visible in both I and J within the X-ray error region reported by Mangano et al. (GCN 5018). This source may correspond to the V-band source detected by De Pasquale & Mangano (GCN 5024) in the Swift UVOT imaging. The coordinates are: RA: 8:14:10.8 DEC: -37:10:11.4 The source is absent in our second epoch images. Its transient nature (see magnitudes below) suggests that the source is the afterglow of GRB 060428a. time post-burst I magnitude J magnitude ------------------------------------------------------ 20.9 hours 21.14 +/- 0.16 18.98 +/- 0.14 68.4 hours >22.2+/-0.2 >19.6+/-0.2 These preliminary magnitudes were calibrated using several USNO-B1.0 stars in the I-band and several 2MASS standards in J. The afterglow decay index is constrained by our observations to be alpha >~ -0.8 from ~1 to 3 days post-burst. Because no optical source was detected with magnitude <20 at only minutes post-burst (see GCN 5033, Haislip et al. [z'>19.1 at 5.3 minutes] and GCN 5024, De Pasquale & Mangano [V=20 at 1 minute]), our I-band detection at 20.9 hours suggests that the early time decay rate of the afterglow must have been significantly more shallow than -0.8. This may partially account for the lack of detected variability of the UVOT source at early times. Possibly, a light curve break occurred between our two sets of observations.