//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6958 SUBJECT: GRB 071021: Swift detection of a burst DATE: 07/10/21 09:56:46 GMT FROM: Scott Barthelmy at NASA/GSFC T. Sakamoto (NASA/UMBC), S. D. Barthelmy (GSFC), A. P. Beardmore (U Leicester), D. N. Burrows (PSU), N. Gehrels (NASA/GSFC), C. Guidorzi (Univ Bicocca&INAF-OAB), C. B. Markwardt (CRESST/GSFC/UMD), P. T. O'Brien (U Leicester), J. P. Osborne (U Leicester), K. L. Page (U Leicester), D. M. Palmer (LANL), P. Romano (Univ. Bicocca & INAF-OAB) and S. D. Vergani (DIAS-DCU) report on behalf of the Swift Team: At 09:41:33 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 071021 (trigger=294974). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 340.636, +23.707 which is RA(J2000) = 22h 42m 33s Dec(J2000) = +23d 42' 24" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). As with most 64 second image triggers, there is no obvious variation in the count rate light curve. The XRT began observing the field at 09:43:44 UT, 130 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 340.6445, +23.7185 which is RA(J2000) = 22h 42m 34.6s Dec(J2000) = 23d 43' 06.5" with an uncertainty of 6.0 arcseconds (radius, 90% containment). This location is 50 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 is still in engineering mode after the gyro restorations, so there will be no data products for this trigger. Burst Advocate for this burst is T. Sakamoto (takanori AT milkyway.gsfc.nasa.gov). 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: 6959 SUBJECT: GRB 071021: Faulkes Telescope South optical candidate DATE: 07/10/21 10:47:13 GMT FROM: Andrea Melandri at Liverpool John Moores U C. Guidorzi (U. Bicocca & INAF-OAB), A. Melandri, I.A. Steele, R.J. Smith, C.J. Mottram, M.F. Bode, D. Carter, S. Kobayashi, D.F. Bersier, C.G. Mundell (Liverpool JMU), A. Gomboc (U. Ljubljana), P. O'Brien, E. Rol, N. Bannister (U. Leicester) report: The 2-m Faulkes Telescope South robotically followed up GRB071021 (Sakamoto et al., GCN Circ. 6958) beginning 258 seconds after the GRB trigger time (UT 09:41:33). We detect a fading uncatalogued source at RA = 22:42:35.41 Dec = +23:43:08.9 with un uncertainty of 0.7 arcsec on both coordinates. This position is 11.4 arcsec from the centre of first XRT error circle (Sakamoto et al., GCN Circ. 6958). We measure a magnitude of R = 17.8 +/- 0.3 for a 3x10 seconds coadded frame, from 258 to 308 seconds after the trigger time. In subsequent images the source clearly faded. Magnitudes are calibrated with respect to R2 mag of several nearby USNO-B1 objects. Observations are still ongoing. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6962 SUBJECT: GRB 071021: Xinglong TNT optical Upper Limit DATE: 07/10/21 17:17:44 GMT FROM: L.P. Xin at NAOC L.P. Xin, M. Zhai, Y.L. Qiu, J.Y. Wei, J.Y. Hu, J.S. Deng, J. Wang and W.K. Zheng on behalf of EAFON report: We have imaged the field of GRB 071021 (T. Sakamoto, et al.; GCN 6958) with the TNT 0.8m telescope at Xinglong Observatory started from 09:55:06.5 UT, 813.8880 after the burst. A series of White and R band images were obtained, no new source was found in our combined image within the error region of the XRT (T. Sakamoto, et al.; GCN 6958) and the location reported by C. Guidorzi et al (GCN 6959) The 3-sigma limit derived from USNO-B1.0 R2 mag were: ------------------------------------ Band Mid time Exp time Limit Mag White 0.72 hours 40*20s 20.32 R 1.38 hours 12*300s 20.85 R 3.25 hours 16*600s 21.69 This message may be cited. [GCN OPS NOTE(21oct07): Per author's request, the names for the 3 references were changed T. Sakamoto, T. Sakamoto, and C. Guidorzi.] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6963 SUBJECT: GRB 071021: Swift-XRT Team refined analysis DATE: 07/10/21 17:18:52 GMT FROM: Kim Page at U.of Leicester K.L. Page (U Leicester), N. Gehrels (NASA/GSFC) and T. Sakamoto (NASA/UMBC) report on behalf of the Swift-XRT team: We have analysed three orbits of Swift-XRT data obtained for GRB 071021 (Sakamoto et al. GCN Circ. 6958), totalling 1.7 ks of Windowed Timing (WT) data and 5.3 ks of Photon Counting (PC) data. Using the PC data we derive a refined position of RA, Dec = 340.64311, +23.71808, which is equivalent to RA(J2000) = 22 42 34.35 Dec(J2000) = +23 43 05.1 with an estimated error radius of 3.9 arcsec (90 percent containment). This is 4.8 arcsec from the onboard XRT position given by Sakamoto et al. in GCN Circ. 6958). The position is also 15.1 arcsec from the Faulkes Telescope South optical candidate (Guidorzi et al., GCN Circ. 6959) and therefore not consistent with it. The X-ray light-curve is initially quite flat, remaining at around 40-50 count s^-1 until 230 seconds after the trigger. There follows a very steep decay, until about 700 seconds post-trigger, when a series of strong flares are seen; this behaviour continues into the second orbit, with the third orbit showing the afterglow emission has decayed further. There is spectral evolution during the initial light-curve, although the WT data before the steep decay (135-245 seconds) can be modelled as an absorbed power-law, with Gamma = 2.12 +/- 0.09 and a total absorbing column of NH = (1.8 +/- 0.2)e21 cm^-2, considerably in excess of the Galactic value of 4.8e20 cm^-2. The 0.3-10 keV observed (unabsorbed) flux during this time is 1.3e-10 (1.9e-10) erg cm^-2 s^-1. Because of the flaring activity, it is not feasible accurately to predict a count-rate at 24 hours. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6964 SUBJECT: GRB 071021: retraction of Faulkes Telescope South candidate DATE: 07/10/21 18:17:51 GMT FROM: Cristiano Guidorzi at INAF-OAB C. Guidorzi (U. Bicocca & INAF-OAB), A. Melandri, I.A. Steele, R.J. Smith, C.J. Mottram, M.F. Bode, D. Carter, S. Kobayashi, D.F. Bersier, C.G. Mundell (Liverpool JMU), A. Gomboc (U. Ljubljana), P. O'Brien, E. Rol, N. Bannister (U. Leicester) report: The fading optical candidate reported in our previous message (Guidorzi et al., GCN Circ. 6959) has been found to be spurious due to technical problems. We apologise for the inconvenience caused. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6966 SUBJECT: GRB 071021, Swift-BAT refined analysis DATE: 07/10/21 19:33:04 GMT FROM: Scott Barthelmy at NASA/GSFC L. Barbier (GSFC), S. D. Barthelmy (GSFC), J. Cummings (GSFC/UMBC), E. Fenimore (LANL), N. Gehrels (GSFC), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/UMBC), G. Sato (GSFC/ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. Ukwatta (GWU) (i.e. the Swift-BAT team): Using the data set from T-239 to T+472 sec from recent telemetry downlinks, we report further analysis of BAT GRB 071021 (trigger #294974) (Sakamoto, et al., GCN Circ. 6958). The BAT ground-calculated position is RA, Dec = 340.573, 23.764 deg, which is RA(J2000) = 22h 42m 17.6s Dec(J2000) = 23d 45' 49" with an uncertainty of 3.4 arcmin, (radius, sys+stat, 90% containment). The partial coding was 78%. The mask-weighted light curve shows a slow rise starting at ~T-30 sec and peaking around T+85 sec. The remaining portion of the lightcurve is consistant with either a low-level constant emission out to ~T+225 sec or with a decline to background around T+150 sec and then another weak peak from ~T+180 to ~T+220 sec. This latter interpretation is consistant with a small flare in the XRT afterglow lightcurve around T+220 sec. T90 (15-350 keV) is 225 +- 10 sec (estimated error including systematics). The time-averaged spectrum from T-31.4 to T+252.2 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.70 +- 0.21. The fluence in the 15-150 keV band is 1.3 +- 0.2 x 10^-6 erg/cm2. The 1-sec peak photon flux measured from T+87.32 sec in the 15-150 keV band is 0.7 +- 0.1 ph/cm2/sec. All the quoted errors are at the 90% confidence level. This burst has several characteristics which are typical of high redshift bursts. Its duration is long (T90 = 225 sec) with relatively few (two) significant peaks. The 1-s peak flux is < 1.0 ph/cm2/s and the power-law photon index (1.70) is < 2. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6967 SUBJECT: GRB 071021: possible high-z burst DATE: 07/10/21 22:08:21 GMT FROM: Takanori Sakamoto at NASA/GSFC T. Sakamoto (GSFC/UMBC), N. Gehrels (GSFC) and Kim Page (U. Leicester) We point out that GRB 071021 has several signatures of high redshift. As pointed out in GCN 6966, it has BAT high-redshift indicators (Sakamoto et al. 2007 in prep.) as follows: - long duration T90 = 225 sec - relatively few (two) significant peaks - peak flux (1 s) < 1.0 ph/cm2/s - power-law photon index (1.70) < 2 Since May 2007, only this burst and GRB 071018 (GCN 6933) have satisfied all four indicators. GRB 071021 also has an X-ray afterglow lightcurve with strong late-time flares (GCN 6963; see http://gcn.gsfc.nasa.gov/gcn/other/071021_xrtlc.gif) reminiscent of high-redshift burst GRB 050904. It also has optical observations without detection (GCN 6961, 6962). Deep IR observations are strongly encouraged. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6968 SUBJECT: GRB 071021: optical and NIR observations DATE: 07/10/22 00:31:34 GMT FROM: Alberto Castro-Tirado at Inst.de Astro. de Andalucia A. J. Castro-Tirado (IAA-CSIC Granada), A. de Ugarte Postigo (ESO Santiago), M. Jelínek, J. Gorosabel, A. Marín Fernández de Capel (IAA-CSIC), C. Abia (Universidad de Granada), D. Pérez-Ramírez (Univ. de Jaén & U. Leicester), D. Malesani (DARK/NBI), S. Guziy (Univ. of Nikolaev) and R. Oreiro (IAC), on behalf of a larger collaboration, report: "Following the detection of GRB 071021 by SWIFT (Barthelmy et al. GCNC 6958) we have obtained JHK-band observations (300s each) with the 3.5m Telescopio Nazionale Galileo at Observatorio del Roque de los Muchachos in La Palma and optical observations with the 2.5m Nordic Optical Telescope (1200s, R-band) and with the 1.5m telescope (3960s, I-band) at Observatorio de Sierra Nevada. The NIR frames were obtained starting on 21.872 Oct (i.e. 11.25 hr after the BAT trigger). Within the XRT error box (Page et al. GCNC 6963) there seems to be an indication of a faint source at RA(J2000) = 22:42:34.31 Dec(J2000)= +23:43:06.5 (+/- 1"). The object seems to be barely detected in the -H and -K bands, but not in J, indicating a highly obscured object or a very high-z (~10) event, supporting in the latter case the SWIFT high-z indications (Sakamoto et al. GCNC 6967). A finding chart is available at: http://www.iaa.es/~deugarte/GRBs/071021/GRB071021_JHK.jpg Further analysis is ongoing. Additional NIR observations are needed to confirm the reality of this source and whether this is the NIR afterglow to GRB 071021." [GCN OPS NOTE(22oct07): Per author's request, the coordinates were corrected from "RA(J2000) = 10:58:11.3 Dec(J2000)=+53:50:56" to "RA(J2000) = 22:42:34.31 Dec(J2000)=+23:43:06.5".] [GCN OPS NOTE(24oct07): Per author's request, "U Leceister" was changed to "U. Leicester".] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6971 SUBJECT: GRB 071021: correction to GCNC 6968 DATE: 07/10/22 01:09:18 GMT FROM: Alberto Castro-Tirado at Inst.de Astro. de Andalucia A. J. Castro-Tirado (IAA-CSIC Granada), A. de Ugarte Postigo (ESO Santiago), M. Jelínek, J. Gorosabel, A. Marín Fernández de Capel (IAA-CSIC), C. Abia (Universidad de Granada), D. Pérez-Ramírez (Univ. de Jaén & U Leceister), D. Malesani (DARK/NBI), S. Guziy (Univ. of Nikolaev) and R. Oreiro (IAC), on behalf of a larger collaboration, report: "We apologize for the incorrect coordinates reported on GCNC 6968, regarding GRB 071021. The right ones (J2000 ± 0.5") are: RA = 22:42:34.31 Dec= +23:43:06.5 This message can be quoted." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6972 SUBJECT: GRB 071021: Z-band detection DATE: 07/10/22 02:18:51 GMT FROM: Daniele Malesani at Niels Bohr Inst,Dark Cosmology Center D. Malesani (DARK), S. Piranomonte (INAF/OARm), G. Tagliaferri, G. Chincarini, S. Covino (INAF/OABr), F. Fiore, L. Stella (INAF/OAR), report on behalf of the MISTICI collaboration: We observed the field of GRB 071021 (Sakamoto et al., GCN 6958) with the 8.2m VLT+FORS2 equipped with the z_Gunn filter (effective wavelength: 9100 A; FWHM: 1300 A). In a coadded image totalling 15 min exposure, we see a weak source at the coordinates provided by Castro-Tirado et al. (GCNs 6968, 6971). Our detection would suggest a redshift less than roughly 6.5. A finding chart is poste at: http://www.astro.ku.dk/~malesani/GRB/071021/071021_finder.jpg We acknowledge excellent support from the ESO staff, particularly Hugues Sana. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6973 SUBJECT: GRB 071021: Magellan R-band observation DATE: 07/10/22 02:29:40 GMT FROM: Edo Berger at Princton U E. Berger (Princeton/OCIW) and R. Covarrubias (LCO) report: "We observed the XRT error circle of GRB 071021 (GCNs 6963,6966) in the R-band using the LDSS3 instrument on the Magellan/Clay telescope. In a coadded image of 540 sec we do not detect any objects within the XRT error circle to a 3-sigma limit of R>23.1 mag. Further observations in R and I band are in progress." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6974 SUBJECT: GRB 071021: Magellan i-band observation DATE: 07/10/22 03:51:39 GMT FROM: Edo Berger at Princton U E. Berger (Princeton/OCIW) and R. Covarrubias (LCO) report: "We observed the XRT error circle of GRB 071021 (GCNs 6963,6966) in the i-band using the LDSS3 instrument on the Magellan/Clay telescope. In a coadded image of 1120 sec we do not detect any object within the XRT error circle to a 3-sigma limit of i>23 mag. Since no z-band magnitude was reported in GCN 6972 we cannot determine whether our limits are significantly deeper. However, our non-detection in r- and i-band appears to indicate a redshift of z~6-6.5 (for i-band effective wavelength = 7600A and FWHM = 1300A). Further observations are in progress." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6975 SUBJECT: GRB071021: MITSuME Okayama Optical Upper Limits DATE: 07/10/22 06:03:35 GMT FROM: Michitoshi Yoshida at Okayama Astrophysical Obs M. Yoshida, K. Yanagisawa, Y. Shimizu, S. Nagayama, H. Toda (NAOJ), and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration: We observed the field of GRB071021 (Sakamoto et al., GCN6958) with the three-color 50cm MITSuME Telescope at Okayama Astrophysical Observatory. The observations started at 9:45:30 Oct. 21 UT (3m58s after the trigger). No new point source was found in the XRT error circle of this burst (Barbier et al., GCN6966). The 3-sigma upper limits derived with the USNO B1.0 catalog are followings. ------------------------------------------------------------- Mid time Exp time G Rc Ic ------------------------------------------------------------- 2007-10-21 9:57:03 20min (60s x 20) >19.4 >19.1 >18.7 2007-10-21 10:48:01 99min (60s x 99) >20.3 >19.6 >19.3 ------------------------------------------------------------- //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6976 SUBJECT: GRB 071021: Subaru NIR observation DATE: 07/10/22 08:55:44 GMT FROM: Nobuyuki Kawai at Tokyo Tech H. Terada, T.-S. Pyo, K. Aoki, T. Hattori (Subaru Telescope/NAOJ) and N. Kawai (Tokyo Tech) report on behalf of the Subaru GRB team: "We observed the XRT error circle of GRB 071021 (GCNs 6963,6966) in the K, H, and J-bands using the IRCS instrument on the Subaru Telescope. We detected the afterglow candidate (Castro-Tirado et al. GCNs 6968, 6971, Malesani et al. GCN 6972) in the K-band image at approximately K~21 mag (midtime 2007-10-22 05:38 UTC). Further observations are in progress." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6980 SUBJECT: GRB 071021: (Relatively shallow) IR non-detections; motivation for optical spectroscopy DATE: 07/10/23 06:05:13 GMT FROM: Josh Bloom at UC Berkeley J. S. Bloom (UC Berkeley), J. X. Prochaska (UCO/Lick), D. A. Perley (UC Berkeley), H.-W. Chen (U Chicago), D. L. Starr (UC Berkeley & LCOGT), M. Modjaz, D. Poznanski (UC Berkeley) report: "We observed the field of GRB 071021 (Sakamoto et al. GCN 6958) with PAIRITEL (*) starting at 2007-10-22 04:53 UT in high wind and poor seeing conditions at Mt Hopkins, Arizona. In the first 1340 second stack, the IR source noted by Castro-Tirado et al. (GCN 6968/6971) is not detected to J=18.35 mag, H=16.87 mag, Ks=16.43 (2.5 sigma upper limit). This is not particularly constraining in light of the deep Subaru imaging (Terada et al. GCN 6976) at a similar epoch. We note that despite the z-band detection (Malesani et al. GCN #6972) the very high-redshift hypothesis of Sakamoto et al. (GCN 6967) is not yet ruled out. In particular, in high z QSO spectra there can be some transmitted flux (in the z-band filter transmission) through the Lyman-alpha forest between ~8000 Ang and 8500 Ang (see, e.g., Fan et al. 2006 **) for z > 6.3 sources. So long as the redshifted Lyman limit at the redshift of the emitting source is blueward of ~8500 Ang, this light would not be entirely suppressed. This consideration yields an upper limit: (1 + z_GRB)*912 Ang < 8500 Ang z_GRB <~ 8.3 At such redshifts, say z_GRB = 8, all reported long-wavelength observations to-date would be naturally accommodated: - the deep non-detections at R and i-band (Berger & Covarrubias, GCNs 6973,6974), being blueward of 912*[1+z_GRB]) - the faint detection at z-band (GCN 6972) due transmitted flux between 912*[1+z_GRB] = 8200 and 8500 Ang is allowed (as above) - the afterglow detections at H and K (GCN 6968; Terada et al. GCN 6976) - the apparent faintness of J-band flux (GCN 6968) relative to H and K given the Gunn-Peterson trough would extend to (1 + z_GRB)*1216 Ang =~ 1.1 micron. All of this assumes that the z-band source is not a foreground galaxy (in which case a higher-z GRB suggested by Castro-Tirado et al. is allowed). If indeed the GRB originated from z > 7, we would expect to see what would resemble emission lines between lam_obs = 912*[1+z_GRB] and ~8500 Ang, motivating the utility of *optical* spectroscopy of this source. Even without spectroscopy, when final magnitudes are reported along with filter transmission curves, a full SED should be illuminating." This message may be cited. (*) http://pairitel.org (**) http://www.journals.uchicago.edu/AJ/journal/issues/ v132n1/205115/205115.web.pdf //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6982 SUBJECT: Possible radio detection of GRB 071021 with the VLA DATE: 07/10/23 13:36:22 GMT FROM: Poonam Chandra at U Virginia/NRAO P. Chandra (UVA/NRAO) and D. A. Frail (NRAO) report on behalf of the Caltech-NRAO-Carnegie GRB Collaboration: "We observed the field centered on the XRT position of the Swift burst GRB 071021 (GCN 6958) using the VLA at a frequency of 8.46 GHz. The observations were taken at a mean time of 06.11 UT on 23nd Oct 07. We detect possible radio afterglow of GRB 071021 in agreement with NIR position (GCN # 6971) and the Swift-XRT afterglow position (GCN # 6963). Our 3-sigma detection yields the flux value of 149+/-44 uJy at the following position: RA(J2000) 22 42 34.25 Dec(J2000) +23 43 06.36 The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6983 SUBJECT: GRB071021: Optical+NIR observations DATE: 07/10/23 19:55:21 GMT FROM: Paul Price at IfA,UH P.A. Price (IfA, Hawaii), T. Minezaki (IoA, Tokyo), L. Cowie (IfA, Hawaii), Y. Yoshii (IoA, Tokyo) and Y. Kakazu (IfA, Hawaii) report: We observed the candidate optical afterglow of GRB071021 (GCN##6968, 6971,6972) with the robotic MAGNUM telescope + MIPS dual-beam imager. Some observations were significantly affected by cloud, but images in I, H and K were obtained through thin clouds. We do not detect any source in our images at the candidate afterglow position, to the following 3 sigma limits, derived from the USNO-1B and 2MASS catalogues: Filter midtime(UTC) Exp. time upper limits I 2007-10-22 6.9h 67min >22.5mag H 2007-10-22 7.7h 30min >20.4mag K 2007-10-22 6.1h 33min >19.8mag Our K-band upper limit is consistent with the detection of the afterglow in K band reported by Kawai et al. (GCN 6976; K~21 mag at 2007-10-22 05:38 UTC). This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6985 SUBJECT: GRB 071021: R-band detection and analysis DATE: 07/10/24 20:23:32 GMT FROM: Silvia Piranomonte at OAR S. Piranomonte (INAF/OAR), P. D'Avanzo (INAF/OABr), D. Malesani (DARK), A. Fernandez-Soto ( U.Valencia), G. Tagliaferri (INAF/OABr), G. Chincarini (U.Bicocca), S. Covino (INAF/OABr), F. Fiore (INAF/OAR), D. Fugazza (INAF/OABr), L. Stella (INAF/OAR), report on behalf of the MISTICI collaboration: We observed the field of GRB 071021 (Sakamoto et al., GCN 6958) with the 8.2m VLT+FORS2 equipped with the R filter (effective wavelength: 6550 A; FWHM: 1650 A). An eight-minute exposure was obtained on Oct 22.06688 , and a second, thirty-minute exposure, on Oct 22.99604. A weak source is detected in both images at the position of the candidate afterglow provided by Castro-Tirado et al. (GCNs 6968, 6971). The object has not faded significantly between both epochs, although the very low S/N (~2) in the first image does not allow for a strong statement regarding its variability. Combining our own data and all the available optical-NIR data (GCNs 6962, 6973, 6974, 6975, 6976, 6980, 6983) we have measured a photometric redshift z~5, but with a 2-sigma confidence interval that includes all values in the z=[0 ... 5.5] range. An alternative explanation for all the available data is that of a strongly reddened afterglow (detected as a fading source in the H- and K-band images), having taken place in a galaxy at a significantly lower redshift (detected in our deeper, bluer, R- and z-band images). This model should be checked via spectroscopy of the putative host galaxy. Our R-band images and the results of the preliminary photometric redshift analysis are posted at: http://ayalga.uv.es/~fsoto/grb/grb071021/ We acknowledge excellent support from the ESO staff, in particular Emanuela Pompei and Hugues Sana. This message may be cited. ------------------------------------------------- This mail sent through IMP: http://horde.org/imp/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 6993 SUBJECT: GRB071021 : CFHT Ks-band observation DATE: 07/10/25 06:55:17 GMT FROM: Yuji Urata at Saitama U Y. Urata (Saitama Univ.), K.Y. Huang (ASIAA), W.H. Ip (NCU), and L. Albert (CFHT/UH) on behalf of EAFON team: "We have observed the field of GRB 071021 (Sakamoto et al., GCN 6958) in Ks-band using the WIRCam instrument on the CFHT telescope. We marginally detected the afterglow (Castro-Tirado et al. GCNs 6968, 6971, Malesani et al. GCN 6972, Terada et al GCN 6976, Piranomonte et al. GCN 6985). The brightness derived from 2MASS stars is about Ks~21 at the mid time of the stacked image (2007-10-23-05:42). This result suggests that the NIR afterglow show shallow decay between October 22 and 23. Further analysis and observations are in progress." This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 7007 SUBJECT: GRB071021: MARGE Optical Limits DATE: 07/10/26 15:23:36 GMT FROM: Heather Swan at U.of Michigan/ROTSE H. Swan (U Mich), I. Smith (Rice), C. Akerlof (U Mich), E. Rykoff (UCSB) and M. Skinner (Boeing) report on behalf of the MARGE collaboration: The AEOS Burst Camera (ABC) on the AEOS telescope, located at the Maui Space Surveillance System on Haleakala, observed the field of GRB071021 (Swift trigger 294974 (T. Sakamoto et al, GCN 6958)). The images are unfiltered 10s exposures that started ~10 minutes after the trigger and ended ~ 2 hour later. We calibrated our images to the USNO-B1 R2 catalog. We do not see the NIR counterpart observed by A. J. Castro-Tirado et al. (GCN 6968), down to the following limiting magnitudes. We have not corrected for the galactic extinction, which is E(B-V)= 0.074 mag, according to the NED Extinction calculator. start UT end UT t_exp(s) mlim t_start-tGRB(s) Coadd? -------------------------------------------------------------------- 09:51:24.7 09:57:32.2 367.5 22.6 591.7 Y 09:51:24.7 12:09:06.9 8262.3 23.7 591.7 Y The ABC is an unfiltered camera, with enhanced sensitivity in the red end of the spectrum. This sensitivity to the red end of the spectrum allows us to see high (z < 6) bursts. The relatively deep upper limits we have obtained may assist efforts to better determine the redshift for this unusual event.