//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9198 SUBJECT: GRB 090423: Swift detection of a burst DATE: 09/04/23 08:14:38 GMT FROM: Hans Krimm at NASA-GSFC H. A. Krimm (CRESST/GSFC/USRA), A. P. Beardmore (U Leicester), P. A. Evans (U Leicester), O. Godet (U Leicester), C. Gronwall (PSU), C. Guidorzi (U Ferrara), P. T. O'Brien (U Leicester), K. L. Page (U Leicester), D. M. Palmer (LANL), M. Perri (ASDC), B. Sbarufatti (INAF-IASFPA), P. Schady (MSSL-UCL), G. Stratta (ASDC), G. Tagliaferri (INAF-OAB) and T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team: At 07:55:19 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 090423 (trigger=350184). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 148.895, +18.160 which is RA(J2000) = 09h 55m 35s Dec(J2000) = +18d 09' 37" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a double-peaked structure with a duration of about 20 sec. The peak count rate was ~2000 counts/sec (15-350 keV), at ~5 sec after the trigger. The XRT began observing the field at 07:56:31.8 UT, 72.5 seconds after the BAT trigger. Using promptly downlinked data we find a fading, uncatalogued X-ray source with an enhanced position: RA, Dec 148.8879, 18.1497 which is equivalent to: RA(J2000) = 09h 55m 33.08s Dec(J2000) = +18d 08' 58.9" with an uncertainty of 2.3 arcseconds (radius, 90% containment). This location is 44 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 2.89e+20 cm^-2 (Kalberla et al. 2005). UVOT took a finding chart exposure of 150 seconds with the White filter starting 77 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 25% of the BAT 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 BAT 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 0.03. Burst Advocate for this burst is H. A. Krimm (krimm 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: 9200 SUBJECT: GRB 090423: Faulkes Telescope South observations DATE: 09/04/23 09:42:02 GMT FROM: Andrea Melandri at Liverpool John Moores U A. Melandri (Liverpool JMU), C. Guidorzi (U. Ferrara), C.G. Mundell, D. Bersier (Liverpool JMU), P. O'Brien, N. Tanvir (U. Leicester) on behalf of a large collaboration report: On 2009 April 23 at 07:57:07 UT we observed the Swift-BAT GRB 090423 (Krimm et al., GCN Circ. 9198) with the 2-m Faulkes Telescope South. Observations started 108 seconds after the BAT trigger time and were performed using the B, R and i' filters. We could not find any uncatalogued object inside the XRT error circle down to the following limiting magnitudes: For single frames: Mid Time Exposure Filter Limit (min) (s) (mag) ------------------------------------- 16.05 60 i' > 18.0 21.30 120 r' > 20.0 24.29 120 i' > 19.0 ------------------------------------- For coadded frames: Time Range Exposure Filter Limit (min) (s) (mag) ------------------------------------- 13.58-53.82 660 r' > 20.8 15.55-45.95 420 i' > 20.5 ------------------------------------- Calibration was performed using few SDSS nearby stars on both filters. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9201 SUBJECT: GRB 090423: P60 Observations DATE: 09/04/23 09:46:20 GMT FROM: S. Bradley Cenko at Caltech S. B. Cenko (UC Berkeley) reports on behalf of a larger collaboration: We have imaged the field of GRB090423 (GCN 9198, Krimm et al.) with the automated Palomar 60-inch telescope beginning at 2009 23 April 7:58 UT (~ 3 minutes after the burst) in the Sloan r', i', and z' filters. In coadded images we find no sources inside the XRT error circle to the following limiting magnitudes (calculated with respect to several SDSS stars in the field): Mean UT t_b (min) Filter Magnitude --------------------------------------------------------------------- 23 Apr 08:11 16 r' > 21.5 23 Apr 08:15 20 i' > 21.5 23 Apr 08:17 22 z' > 20.5 The lack of an optical afterglow, together with the fact that the X-ray column density is consistent with the Galactic value (Krimm et al., GCN 9198), make GRB090423 an interesting candidate high-redshift event. We encourage observations at longer wavelengths to search for a NIR counterpart. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9202 SUBJECT: GRB 090423: UKIRT K-band observations DATE: 09/04/23 10:51:23 GMT FROM: Nial Tanvir at IofA U.Cambridge N. Tanvir (U. Leicester), A. Levan (U. Warwick), T. Kerr (JACH), T. Wold (JACH) We observed the field of GRB 090423 with WFCAM on UKIRT, beginning at 08:16 (UT), approximately 20 minutes post-burst. We detect a faint source in the K-band image just outside the revised XRT error circle, at coordinate: 09 55 33.29 +18 08 57.8 (J2000, estimated uncertainty 0.3 arcsec) The source has a magnitude K~17.5, but does not appear in SDSS images, and therefore is very red. The image is also extended in the E-W direction, and so might be (or include) a dusty host galaxy. However, we caution that the images are slightly trailed and so further work is required to determine whether this source is a point source or not. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9204 SUBJECT: GRB 090423: Swift-BAT refined analysis DATE: 09/04/23 12:45:50 GMT FROM: Scott Barthelmy at NASA/GSFC D. M. Palmer (LANL), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC), J. R. Cummings (GSFC/UMBC), E. E. Fenimore (LANL), N. Gehrels (GSFC), H. A. Krimm (GSFC/USRA), C. B. Markwardt (GSFC/UMD), A. M. Parsons (GSFC), T. Sakamoto (GSFC/UMBC), G. Sato (ISAS), M. Stamatikos (GSFC/ORAU), J. Tueller (GSFC), T. N. Ukwatta (GWU) (i.e. the Swift-BAT team): Using the data set from T-60 to T+243 sec from the recent telemetry downlink, we report further analysis of BAT GRB 090423 (trigger #350184) (Krimm, et al., GCN Circ. 9198). The BAT ground-calculated position is RA, Dec = 148.891, 18.165 deg, which is RA(J2000) = 09h 55m 33.8s Dec(J2000) = +18d 09' 55.7" with an uncertainty of 1.1 arcmin, (radius, sys+stat, 90% containment). The partial coding was 92%. The mask-weighted light curve shows a couple overlapping peaks starting at ~T-2 sec, peaking at T+4 sec, and ending at ~T+15 sec. T90 (15-350 keV) is 10.3 +- 1.1 sec (estimated error including systematics). The time-averaged spectrum from T-0.7 to T+11.7 sec is best fit by a power law with an exponential cutoff. This fit gives a photon index 0.80 +- 0.50, and Epeak of 48.6 +- 6.2 keV (chi squared 41.4 for 56 d.o.f.). For this model the total fluence in the 15-150 keV band is 5.9 +- 0.4 x 10^-7 erg/cm2 and the 1-sec peak flux measured from T+3.50 sec in the 15-150 keV band is 1.7 +- 0.2 ph/cm2/sec. A fit to a simple power law gives a photon index of 1.90 +- 0.10 (chi squared 59.9 for 57 d.o.f.). 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/350184/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9205 SUBJECT: GRB 090423: Enhanced Swift-XRT position DATE: 09/04/23 12:52:20 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 3221 s of XRT Photon Counting mode data and 7 UVOT images for GRB 090423, 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 = 148.88830, +18.14937 which is equivalent to: RA (J2000): 09h 55m 33.19s Dec (J2000): +18d 08' 57.7" with an uncertainty of 1.7 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, arXiv:0812.3662). This circular was automatically generated, and is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9206 SUBJECT: GRB 090423: UKIRT data further analysis DATE: 09/04/23 13:05:45 GMT FROM: Nial Tanvir at IofA U.Cambridge A. Levan (U. Warwick), N. Tanvir (U. Leicester), K. Wiersema (U. Leicester) Further analysis of the data reported in GCN 9202 reveals that the source did not fade appreciably (i.e. by more than ~0.15 mag) between observations with mid-times 25 and 41 minutes post-burst. However, we do believe that the extension of the image is consistent with it being a point source. We note that the revised XRT error circle (GCN 9205) now contains this source, making it likely the counterpart or host of this GRB. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9207 SUBJECT: GRB090423, RIMOTS optical upper limits DATE: 09/04/23 14:00:54 GMT FROM: Kenta Kono at Miyazaki U K.Kono, K.Noda, E.Sonoda, N.Ohmori, H.hayasi, A.Daikyuji, Y.Nisioka, M.Yamauchi (University of Miyazaki) We have observed the field covering the error circle of GRB090423 (Swift trigger 350184, GCN 9198, H. A. Krimm et al.) with the unfiltered CCD camera on the 30-cm telescope at University of Miyazaki. The observation was started 10:49:54 UT, about 3.0 hr 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 reported position. (GCN 9198, H. A. Krimm et al. GCN 9202, N. Tanvir et al. GCN 9204, D. M. Palmer et al. GCN 9205, P. A. Evans et al. ) the upper limits are as follows: -------------------------------------------------------------- Start(UT) End(UT) Num. of frames Limit (mag.) -------------------------------------------------------------- 10:49:54 10:50:24 1 16.5 10:49:54 11:45:01 45 19.4 --------------------------------------------------------------- //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9209 SUBJECT: GRB 090423: NIR photometry and evidence for spectral break DATE: 09/04/23 15:02:30 GMT FROM: Derek Fox at PSU A. Cucchiara (PSU), D. B. Fox (PSU), and E. Berger (Harvard) report: "On April 23.33 UT we imaged the field of Swift GRB 090423 (Krimm et al., GCN 9198) with NIRI on the Gemini-North telescope. We obtained 9x60 sec exposures in Y,J,H. In the coadded J and H images we clearly identify the object noted by Tanvir et al. (GCN 9202) and it appears point-like (see also Levan et al., GCN 9206). The object is not detected in Y-band. We derive the following magnitudes, calibrated using three 2MASS stars in the field: J mag: 19.29 +- 0.07 H mag: 17.71 +- 0.14 The resulting J-H color of 1.1 AB mag is very red, corresponding to a steep spectral slope of beta=3.8. Taken in conjunction with a flat H-K color (see GCN 9202), our non-detection in Y-band, and a red I-J color of 1.7 AB mag in comparison to P60 limits (GCN 9201), we suggest that there is a likely break in the spectrum at about 1.2 microns, with extinction an unlikely explanation due to the sharpness of the feature and the shallow slope to redder wavelengths. If this is due to Ly-alpha absorption, then the resulting redshift for GRB 090423 is z~9. Further analysis is in progress and additional observations are planned." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9210 SUBJECT: GRB090423 - Swift/UVOT upper limits. DATE: 09/04/23 17:06:23 GMT FROM: Massimiliano de Pasquale at MSSL-UCL M. De Pasquale (MSSL/UCL) and H. Krimm (GSFC/GWU) report on behalf of the Swift UVOT team: The Swift/UVOT took the first settled exposure of GRB 090423 starting 77 s after the BAT trigger (Krimm, et al., 2009, GCN Circ. 9198) in the white filter. We do not find any new source, at the enhanced position of the XRT afterglow (Evans, et al. 2009, GCN Circ. 9205) nor at the position of the K band candidate found by UKIRT (Tanvir, et al. 2009, GCN Circ. 9206). No source is detected even when all the images of all filters are summed. The 3-sigma upper limits for detecting a source in the white and u band first exposures, and subsequent co-added images in all filters are: Filter T_start T_stop Exp(s) Mag ---------------------------------------------------------- white 77 227 147 >20.7 u 290 540 246 >20.0 v 619 6162 413 >19.6 b 545 5497 413 >20.2 u 290 5342 462 >20.4 uvw1 668 6503 344 >20.1 uvm2 644 6367 413 >20.1 uvw2 594 5958 412 >20.5 white 77 5752 560 >21.3 --------------------------------------------------------- The quoted upper limits have not been corrected for the expected modest Galactic extinction along the line of sight corresponding to a reddening of E_{B-V} = 0.03 mag (Schlegel, et al., 1998, ApJS, 500, 525). All photometry is on the UVOT photometry system described in Poole et al. (2008, MNRAS, 383, 627). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9212 SUBJECT: GRB 090423: Swift-XRT refined analysis DATE: 09/04/23 20:06:55 GMT FROM: Matteo Perri at ISAC/ASDC G. Stratta and M. Perri (ASDC) report on behalf of the Swift-XRT Team: We have analysed the first 8.4 ks of Swift-XRT data obtained from GRB 090423 (trigger 350184; Krimm et al., GCN Circ. 9198), starting from T+110 s and ending at T+18 ks. The best position of the X-ray afterglow is the UVOT-enhanced XRT position given in Evans et al. (GCN Circ. 9205). The 0.3-10 keV X-ray light curve during the first Swift orbit shows a flare peaking at T+170s. Starting from the second orbit (T+3.9 ks) the curve is well described by a power-law model with index alpha=-1.3+/-0.1. The X-ray spectrum during the power-law decay is well fit by an absorbed power-law model with a photon index of 2.0+/-0.1 and a total column density of (8.7+/-2.5)e20 cm**-2. The Galactic column density in the direction of the source is 2.9e20 cm**-2 (Kalberla et al. 2005). The count-rate to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.7(4.6)E-11 erg cm**-2 count**-1. Errors are given at the 1-sigma level. We note that the X-ray column density is consistent, within 3 sigma, with the Galactic value, consistent with the possibility that the burst is at high redshift, as reported by Cucchiara et al. (GCN Circ. 9209). Assuming the X-ray emission continues to decline at the same rate, we predict a 0.3-10 keV XRT count rate of 5e-3 count/s at T+24 hr, which corresponds to an observed 0.3-10 keV flux of ~2e-13 erg/cm**2/s. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00350184. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9213 SUBJECT: GRB 090423: Correction to NIR photometry DATE: 09/04/23 20:36:32 GMT FROM: Antonino Cucchiara at PSU A. Cucchiara, D. B. Fox (PSU), and E. Berger (Harvard) report: "Further analysis of our Gemini+NIRI H-band imaging (Cucchiara, Fox & Berger, GCN 9209) has led to a significant correction in the H-band magnitudes for the afterglow/host (Tanvir et al., GCN 9202) of GRB 090423 (Kimm et al., GCN 9198). Our revised magnitudes for this object are: J mag: 19.29 +- 0.07 H mag: 18.57 +- 0.07 The revision to the H-band magnitude, in addition to the absence of any detection in our Y-band images, suggests a break in the spectrum below or within the J-band and above the Y-band, yielding, e.g., 7<~z<~9 in a Lyman-alpha interpretation. Further analysis is in progress and additional observations are planned. We apologize for any inconvenience." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9214 SUBJECT: GRB 090423: NOT z-band limit DATE: 09/04/23 23:17:44 GMT FROM: Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst D. Malesani (DARK/NBI), H. Dahle, I. Skorbakk (ITA, Oslo), E. Wuyts (Univ. Chicago), P. Jakobsson (Univ. Iceland), J. P. U. Fynbo, J. Hjorth (DARK/NBI), report on behalf of a larger collaboration: We observed the field of GRB 090423 (Krimm et al., GCN 9198) with the Nordic Optical Telescope equipped with the MOSCA camera. Observations were carried out using the SDSS z' filter, starting on Apr 23.874 UT (13.0 hr after the GRB trigger) and with a total exposure time of 1 hr. At the position of the NIR candidate afterglow (Tanvir et al., GCN 9202; Levan et al., GCN 9206; Cucchiara et al., GCN 9209), we do not detect any source down to a limiting magnitude z(AB) > 23.7, calibrated using the SDSS catalog. We acknowledge excellent support from the NOT visiting observers. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9215 SUBJECT: GRB 090423: GROND detection and preliminary photo-z DATE: 09/04/24 03:05:49 GMT FROM: Jochen Greiner at MPI F. Olivares, T. Kruehler, J. Greiner, R. Filgas (all MPE Garching) report on behalf of the GROND team: We observed the field of GRB 090423 (Swift trigger 350184, H. Krimm et al., GCN #9198) simultaneously in g'r'i'z'JHK with GROND mounted at the 2.2m MPI/ESO telescope at La Silla Observatory (Chile). Observations started on 23 Apr. 2009 at 23:08 UT, 15.2 h after the burst. We detect the source within the XRT error circle (Evans et al. 2009, GCN #9205) reported by Tanvir et al. (GCN #9202), Levan et al. (GCN #9206) and Cucchiara et al. (GCN# 9209) in the NIR channels. Preliminary photometry yields the following magnitudes and upper limits in stacked images at a midtime of 16.7 h after the burst, obtained using SDSS/2MASS stars as reference: Filter Exp [s] AB Mag MagErr ---------------------------------- g' 16 x 369 > 25.0 r' 16 x 369 > 25.1 i' 16 x 369 > 24.2 z' 16 x 369 > 24.0 J 480 x 10 21.6 0.1 H 480 x 10 21.2 0.1 K 480 x 10 20.9 0.1 These magnitudes imply a significant fading to what was reported earlier (GCNs #9202, #9213) and confirm this source to be the afterglow of GRB 090423. Furthermore, we confirm the red z-J color, and thus the probable high redshift nature of this event. After correcting for the foreground galactic extinction of E(B-V)=0.029 (Schlegel et al. 1998) and assuming no intrinisic extinction, a fit with Hyper-z (Bolzonella et al. 2000) results in a spectral index of 1.0 (+0.4,-0.5), comparable to that observed in X-rays (Stratta & Perri, GCN #9212), and a preliminary photometric redshift of z = 8.0+0.5-1.2. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9216 SUBJECT: GRB 090423: TNG Amici spectrum DATE: 09/04/24 03:17:30 GMT FROM: Paolo D'Avanzo at INAF-OAB C. C. Thoene (INAF-OAB), P. D'Avanzo (INAF-OAB/U. Bicocca), A. Fernandez-Soto (IFCA-Santander), S. Campana, D. Fugazza (INAF-OAB), L.A. Antonelli (INAF-OAR), G. Chincarini (Univ. Bicocca), S. Covino (INAF-OAB), V. D'Elia (INAF-OAR), A. De Ugarte-Postigo (ESO), D. Malesani (Dark/NBI), E. Palazzi (IASF-Bo), R. Salvaterra (INAF-OAB), A. Fiorenzano (TNG) report, on behalf of a larger collaboration: We observed the afterglow of GRB 090423 (Krimm et al. GCN 9198; Tanvir et al. GCN 9202; Levan et al., GCN 9206; Cucchiara et al., GCN 9209) with the Italian TNG 3.6m telescope located in the Canary Islands (Spain). The observations were performed using the Amici grism. We took a 2 hrs spectrum starting around Apr 23 at 22:16 UT (about 14.35 hours after the burst) and covering the range 600-2700 nm with a resolution of R ~ 50. A preliminary analysis of the combined spectrum shows a very weak signal at the position of the NIR afterglow. No signal is observed below observed lambda ~ 10500 Angstrom. Assuming that the lack of signal at bluer wavelengths is due to Ly-alpha absorption in the IGM this gives a redshift of z ~ 7.6 (in agreement with the estimate of Olivares et al., GCN 9215). We point out that our wavelength calibration is based on an archival wavelength table. We are very grateful for the excellent support of the TNG staff. [GCN OPS NOTE(24apr09): Per author's request, the author list was revised.] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9217 SUBJECT: GRB 090423: Deep z-band upper limit and confirmation of photo-z DATE: 09/04/24 03:51:52 GMT FROM: Daniel Perley at U.C. Berkeley D. A. Perley, S. B. Cenko, and J. S. Bloom (UC Berkeley) report on behalf of GRAASP: We initiated a series of 15 x 200 second exposures of the field of GRB 090423 (Krimm et al, GCN 9198) in z-band using GMOS on Gemini-South starting at 23:38 UT on 2009-04-23, 15.71 hours after the trigger. No source is visible in the XRT error circle (Evans et al., GCN 9205) or the NIR position (Tanvir et al., GCN 9202) in the co-added image. We estimate a limiting magnitude (3-sigma) of: z > 26.0 mag (t_mid = 16.25 hr) This observation is nearly co-eval with the GROND photometry (Olivares et al., GCN 9215) which detects the counterpart with a magnitude of J_AB = 21.6, implying a color of J-z > 4.4 (AB). This, along with the non-detection of a lower-redshift host galaxy candidate, the TNG spectrum (Thoene at al., GCN 9216), and the nearly flat JHK SED, confirms the very high redshift (z > 7) of this event. We thank Eleazar Carrasco and the Gemini observing staff for acquiring these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9218 SUBJECT: GRB 090423: Near infrared observation at Okayama Observatory DATE: 09/04/24 04:03:34 GMT FROM: Michitoshi Yoshida at Okayama Astrophysical Obs M. Yoshida, K. Yanagisawa, D. Kuroda, Y. Shimizu, S. Nagayama, H. Toda (OAO, NAOJ) and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration: We observed the field of GRB 090423 (Krimm et al. GCN 9198) with a near-infrared camera ISLE attached to the 188cm telescope of Okayama Astrophysical Observatory. We also obtained optical data using the optical three color CCD camera attached to the MITSuME 50cm telescope. We started the observation at 2009-04-23 10:32:27 UT, 2hr 37m after the burst. We detected a very faint source close to the position of the afterglow candidate reported by Tanvir et al. (GCN 9202) in our J band image. The coordinate of the source is J2000.0 9h 55m 33.3s +18d 08m 57.1s . J band magnitude of the source is 20.1 mag, which is much fainter than the previous report (Cucchiara et al. GCN 9213). We could not find any new source in the optical bands and the other near-infrared bands (H and Ks). The results of our photometry are listed below. We used three 2MASS stars near the burst for near- infrared flux calibration and GSC2.3 catalog for optical flux calibration. Near-infrared observation Band Mid-UT Td(day) EXP-T mag ------------------------------------------------------ J 10:53:33 0.12377 720s 20.1 $B!^(B 0.3 H 11:04:30 0.13138 960s > 19.3 Ks 10:56:31 0.12584 480s > 18.7 ------------------------------------------------------ Optical observation Mid-UT Td(day) EXP-T g' Rc Ic ------------------------------------------------------------ 11:43:56 0.15876 5940s >20.4 >20.2 >19.5 ------------------------------------------------------------ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9219 SUBJECT: GRB 090423: VLT/ISAAC spectroscopy DATE: 09/04/24 07:20:35 GMT FROM: Nial Tanvir at IofA U.Cambridge N. Tanvir (U. Leicester), A. Levan (U. Warwick), K. Wiersema (U. Leicester), J. Fynbo, J. Hjorth (DARK/NBI), P. Jakobsson (Reykjavik) report on behalf of a larger collaboration: We observed the afterglow of GRB 090423 with ISAAC on the VLT, beginning about 01:30 (UT), approximately 17.5 hours post-burst. Our provisional analysis shows a clear continuum at red wavelengths, but no flux below about 11200A, consistent with a break due to Lyman-alpha at a redshift z~8.2. However, we caution that we have not yet carefully calibrated the instrumental response, and further work is required to confirm this result. We thank the VLT observers for their excellent support in obtaining these data, particularly Valentin Ivanov and Giovanni Carraro. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9220 SUBJECT: GRB 090423 limiting magnitudes DATE: 09/04/24 11:36:15 GMT FROM: Arne A. Henden at AAVSO A. Henden (AAVSO), J. Gross (SRO), B. Denny (DC-3), D. Terrell (SwRI), and W. Cooney (SRO) report: We observed the field of GRB 090423 (Krimm et al., GCN 9198) using the 35cm telescope of Sonoita Research Observatory with an automated VOevent trigger for an R-band image sequence. Images began at 07:58:09UT on 2009-04-23, 170 seconds after the burst, under good conditions. The afterglow candidate reported by Tanvir et al. (GCN 9202), Levan et al. (GCN 9206), Cucchiara et al. (GCN 9209), and shown by Olivares et al. (GCN 9215) to have both faded and to have a photo-z of 8.0, is not detected in our images. We place 3-sigma constraints of 200 seconds midpoint (1min image) Rc < 18 350 seconds midpoint (6min stack) Rc < 20 using USNO-A red magnitudes. The 19 total images, covering the period 07:58:09 through 08:47:34, can be obtained from ftp://ftp.aavso.org/public/sro/grb090423/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9221 SUBJECT: GRB090423: Y-band field calibration DATE: 09/04/24 12:43:12 GMT FROM: Myungshin Im at Seoul Nat U M. Im, Y. Jeon, C. Choi, W. Park, I. Lee Seoul National Univ), Y.-B. Jeon (KASI) and Y. Urata (NCU) on behalf of EAFON team. We took a series of Y-band photometry calibration data for the field of GRB090423 using the 1.0m telescope at Mt. Lemmon (Arizona, US) operated by the Korea Astronomy Space Science Institute. For the Y-band photometry standards, we used P239-C and GD140 from UKIRT faint standards, and HIP 50459, a A0V star from Hipparcos catalog. The zero points obtained for these standards are applied to our observation of the GRB090423 field, yielding Y-band photometry (Vega) for objects in the GRB field down to Y(MKO) ~ 17.5 magnitude at 10-sigma. The expected zero point accuracy is ~0.1mag. To derive AB mag, add 0.63 mag to the values listed in the catalog. The calibration data and finding charts are available at http://astro.snu.ac.kr/~mim/grb/readme http://astro.snu.ac.kr/~mim/grb/grb090423_ycal.dat http://astro.snu.ac.kr/~mim/grb/yobj.reg http://astro.snu.ac.kr/~mim/grb/chart.gif We thank the LOAO operator, J. Yoon for his assistance for this observation. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9222 SUBJECT: GRB 090423: Refined TNG analysis DATE: 09/04/24 14:16:29 GMT FROM: Cristiano Guidorzi at Ferrara U,Italy A. Fernandez-Soto (IFCA-Santander), F. Mannucci (INAF-OAA), D. Fugazza (INAF-OAB), L.A. Antonelli (INAF-OAR), S. Campana (INAF-OAB), G. Chincarini (Univ. Bicocca), S. Covino (INAF-OAB), P. D'Avanzo (INAF-OAB/U. Bicocca), V. D'Elia (INAF-OAR), M. Della Valle (INAF-OACa/ESO), A. Fiorenzano (TNG), C. Guidorzi (Univ. Ferrara), E. Maiorano (IASF-Bo), J. Mao (INAF-OAB), R. Margutti (INAF-OAB/Univ. Bicocca), S. Marinoni (TNG), E. Palazzi (IASF-Bo), C. C. Thoene (INAF-OAB) report, on behalf of a larger collaboration (CIBO): We have performed an in-depth analysis of the TNG spectrum of GRB090423 taken on Apr 23 at 22:16 UT with the NICS/Amici combination (Thoene et al, GCN 9216). We have corrected the wavelength calibration, now based both on the observation of sky features and a fit to the instrument sensitivity. We detect in the spectrum flux at wavelengths lambda>1.1 microns, and a flux compatible with zero below that limit. Interpreting this wavelength as the onset of Lyman alpha absorption in the IGM, this leads us to deduce a value of z~8.1. We have also analysed all the available photometry (GCNs 9200, 9201, 9202, 9206, 9209, 9210, 9213, 9214, 9215, 9217, 9218 and 9220) and find that the data are well fit by an afterglow without intrinsic dust obscuration, a photometric redshift 7.6 L. Amati (INAF/IASF Bologna, Italy), F. Frontera (Univ. Ferrara and INAF/IASF Bologna, Italy), C. Guidorzi (Univ. Ferrara, Italy), E. Palazzi (INAF/IASF Bologna, Italy) report: On the basis of the spectral parameters and fluence measured by Swift/BAT (Palmer et al., GCN 9204) and the redshift of ~7.5 - 8.5 suggested by photometry and spectroscopy of the optical counterpart (Cucchiara et al., GCN 9213; Olivares et al., GCN 9215; Thoene et al., GCN 9216; Perley et al., GCN 9217; Tanvir et al., GCN 9219; Fernandez-Soto et al., GRB 9222) we find that GRB 090423 is fully consistent with the Ep,i - Eiso correlation (Ep,i ~ 440 keV and Eiso ~10^53 erg for z = 8, assuming a flat LambdaCDM cosmology with H0=70 km/s/Mpc and Omega_M = 0.27). In addition, the track of this GRB in the Ep,i - Eiso plane (http://www.iasfbo.inaf.it/~amati/grb090423.ps) implies a lower limit to the redshift of 1.4 (68% c.l.) and 0.9 (90% c.l.) in order to be consistent with the correlation. This further suggests that the event is not a local very reddened GRB. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9229 SUBJECT: GRB 090423: Fermi GBM observation DATE: 09/04/24 17:04:54 GMT FROM: Andreas von Kienlin at MPE A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team: "At 07:55:25.39 UT on 23 April 2009, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 090423 (trigger 262166127 / 090423330) which was also detected by the Swift (H. A. Krimm et al. 2008, GCN 9198) The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight is 75.6 degrees. The GBM light curve shows a single structured peak with a duration (T90) of about 12 s (8-1000 keV). There is an indication for extended emission until 30 s after the burst onset. The time-averaged spectrum from T0-7.040 s to T0+5.248 s is well fit by a power law function with an exponential high energy cutoff. The power law index is -0.77 +/- 0.35 and the cutoff energy, parameterized as Epeak, is 82 +/- 15 keV (chi squared 275 for 238 d.o.f.). At a redshift of about 8 (F. Olivares et al. 2008, GCN 9215; C. Thoene et al. 2008, GCN 9216; N. Tanvir et al. 2008, GCN 9219), the Epeak in the GRB rest frame, Epeak_rest, is 738 +/- 135 keV. The event fluence (8-1000 keV) in this time interval is (1.1 +/- 0.3)E-06 erg/cm^2. Using standard cosmology (Omega_matter = 0.27, Omega_lambda = 0.73, H0=71) the isotropic equivalent energy in the 8-1000 keV band is E_iso = (8.9 +/- 2.4)E+53 ergs. The 1-sec peak photon flux measured starting from T0-1.920 s in the 8-1000 keV band is 3.3 +/- 0.5 ph/s/cm^2. The spectrum can also be fit by using a Band function with Epeak = 54 +/- 22 keV and beta = -2.1 +/- 0.3. However alpha is poorly constrained. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9235 SUBJECT: GRB 090423: energetic, luminosity and jet break DATE: 09/04/24 21:57:44 GMT FROM: Giancarlo Ghirlanda at INAF/Brera L. Nava (INAF-OAB/Univ.Insubria); D. Burlon (MPE-Garching); G. Ghirlanda (INAF-OAB); G. Ghisellini (INAF-OAB); M. Nardini (SISSA) With the spectral parameters and fluence of GRB090423 as measured by Fermi (von Kienlin et al., GCN 9229) and given its redshift z=8.1 (Fernandez-Soto et al., GCN 9222), we estimate the isotropic equivalent energy Eiso = 1.03E53 and the isotropic equivalent peak luminosity Liso = 1.88E53 (the value of Eiso is consistent with that obtained with the Swift spectral results given in Palmer et al. GCN 9204). Given the rest frame peak energy Ep= 746 keV, we show ( http://www.brera.inaf.it/utenti/ghirla/GRB/090423.html ) that GRB090423 is consistent both with the Ep-Liso correlation (Yonetoku et al. 2004) and with the Ep-Eiso correlation (Amati et al. 2002, Ghirlanda et al. 2008, Nava et al. 2008; see also GCN 9227). Noteworthly, GRB090423 is remarkably similar to GRB 080913 and GRB 071020 with respect to the Amati and Yonetoku correlations. It is worth mentioning that these three GRBs are long bursts according to their observed T90 (12 s, 8 s and 4 s respectively) although, given their redshifts, T90 ~ 1 sec in the rest frame. Finally, considering the collimation corrected Ep-Egamma correlation (e.g. Ghirlanda et al. 2007), we estimate that a jet break should occur in the afterglow light curve between ~22 and 54 days (1 sigma consistency) or between ~10 and 130 days (3 sigma consistency) assuming a homogeneous circum-burst environment with standard parameters (see Nava et al. 2006, Ghirlanda et al. 2007). However, this break may not be observed in the X-ray which, given the typical steep-flat-steep decay already observed for this burst ( http://www.swift.ac.uk/xrt_curves/00350184/ ), could likely be due to another emission component (e.g. Ghisellini et al. 2009). This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9241 SUBJECT: GRB 090423: Swift/BAT spectral lag results DATE: 09/04/25 01:47:05 GMT FROM: Hans Krimm at NASA-GSFC H. A. Krimm (CRESST/GSFC/USRA), J. P. Norris (U. Denver), T. N. Ukwatta (GSFC/GWU), S. D. Barthelmy (GSFC), P. A. Evans (U. Leicester), N. Gehrels (GSFC), M. Stamatikos (GSFC/ORAU) Using the Swift/BAT data we have completed spectral lag analysis for the high redshift burst, GRB 090423 (Krimm et al., GCN 9198). Using 16-ms binning on the event data, for the "whole" burst (15 seconds), we obtain: chans 3->1: 0.046 +0.085 -0.058 seconds chans 3->2: 0.044 +0.070 -0.052 seconds For the peak 3 seconds of the burst we obtain: chans 3->1: 0.021 +0.054 -0.032 seconds chans 3->2: 0.006 +0.046 -0.071 seconds where the channels are 15-25 keV, 25-50 keV, and 50-100 keV. The lag in each case is consistent with zero, but the 1-sigma error bars are roughly as large as the median lag values for long bursts. Thus this burst is too dim for us to utilize lags as a discriminant for long vs. short. Given the relatively short duration of this burst, it is informative to look at other possible indicators of whether the burst is in fact a short burst seen at a large distance. The calculations below use z=8, which is roughly the average of the photometric and spectroscopic redshifts determined for this burst (Cucchiara et al., GCN 9213; Olivares et al., GCN 9215; Thoene et al., GCN 9216; Perley et al., GCN 9217; Tanvir et al., GCN 9219; Fernandez-Soto et al., GRB 9222). When converted to the rest frame, the T90 values (10.3 ± 1.1 sec, Swift/BAT 15-350 keV, Palmer et al., GCN 9204) and (12 sec, Fermi/GBM 8-1000 keV, Kienlin, GCN Circ. 9229) transform to 1.1 ± 0.1 sec and 1.3 sec, respectively. However, one must be careful in comparing these numbers to the BATSE short-hard burst divide (Kouveliotou et al., ApJ 413, L101, 1993). The BATSE duration distribution is in the observer frame. With a typical redshift of z = 1-2 for BATSE bursts, the dividing line between long and short in the rest frame is 0.7 to 1.0 seconds. Thus this burst is on the boundary and toward the long side. While the duration and lag are consistent with short bursts (with large errors), there are other observations which are more consistent with GRB 090423 being a long burst in the source frame. The spectral fits to the BAT data (Palmer et al., GCN 9204) are inconclusive as to whether this is a long or short burst. Both the photon index, alpha = 0.8 +/- 0.5, and Epeak = 440 keV in the source frame, from a cut-off power-law model fit, are consistent with the results for other short bursts detected by Swift/BAT. However, these numbers also fall within the distributions for long bursts (Krimm et al., in preparation). The main argument against this being a short burst is the isotopic energy. The analysis performed by Amati et al. (GCN 9227) gives the burst Eiso=1053 erg and shows that the burst is consistent with the Epeak-Eiso relation for long bursts. All previously known short bursts are outliers to this relation. The calculated value of Eiso is a factor of > 50 greater than that for most other short bursts. Furthermore it is questionable whether there would be sufficient time for a binary neutron star system to form and inspiral to a merger given the very early time interval since the Big Bang implied by z=8 (lookback time of ~13 Gyr, corresponding to an age of the universe of 0.6 Gyr). In conclusion, we can not say if GRB 090423 is short or long. Its duration in the source frame is at the boundary between the two classes, the lag analysis is inconclusive, the BAT spectral shape is inconclusive, the Amati relationship favors long burst and the merger time at such high redshift could be problematic for a short burst interpretation. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9242 SUBJECT: GRB 090423: Y-band field calibration update/correction DATE: 09/04/25 02:31:03 GMT FROM: Myungshin Im at Seoul Nat U M. Im, Y. Jeon, C. Choi, W. Park, I. Lee Seoul National Univ), Y.-B. Jeon (KASI) and Y. Urata (NCU) on behalf of EAFON team. The Y-band calibration data reported earlier by Im et al. (GCN 9221) have been updated with a revised zero point, and the catalog now includes more objects. The updated field calibration data are available at the same location as before: http://astro.snu.ac.kr/~mim/grb/readme http://astro.snu.ac.kr/~mim/grb/grb090423_ycal.dat http://astro.snu.ac.kr/~mim/grb/yobj.reg http://astro.snu.ac.kr/~mim/grb/chart.gif We thank the LOAO operator, J. Yoon for his assistance for this observation. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9244 SUBJECT: GRB090423: Y-band limit DATE: 09/04/25 04:12:16 GMT FROM: Myungshin Im at Seoul Nat U M. Im, C. Choi, Y. Jeon, W. Park, I. Lee (Seoul National Univ), Y.-B. Jeon (KASI) and Y. Urata (NCU) on behalf of EAFON team. We took a series of Y-band images of GRB090423 using the 1.0m telescope at Mt. Lemmon (Arizona, US) operated by the Korea Astronomy Space Science Institute. We do not detect the afterglow in a stacked image with the total exposure time of 78 min, placing an upper limit of Y < 19.8 (Vega) at 3-sigma at the mid point of UT April 24, 06:16. The photometry calibration was done using the calibration data reported in Im et al. (GCN 9242, 9221). We thank the LOAO operator, J. Yoon for his assistance for this observation. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9249 SUBJECT: VLA radio observation of high-z GRB 090423 DATE: 09/04/25 10:41:23 GMT FROM: Poonam Chandra at U Virginia/NRAO "Poonam Chandra (RMC), Dale A. Frail (NRAO) and S. R. Kulkarni (Caltech) report on behalf of a larger collaboration: "We used the Very Large Array to observe the field of view toward the high redshift GRB 090423 (GCN 9198) at a frequency of 8.46 GHz on 2009 Apr. 25.00 UT. We do not detect any radio emission either within the Swift-XRT error circle (GCN 9205) or at the UKIRT K-band position (GCN 9202). The 3-sigma upper limit on the radio flux density of GRB afterglow is 135 uJy (map rms 45 uJy). 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: 9251 SUBJECT: GRB 090423: Fermi GBM observation (correction of isotropic equivalent energy) DATE: 09/04/25 20:05:22 GMT FROM: Andreas von Kienlin at MPE A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team: "The isotropic equivalent energy of GRB 090423 given in GCN Circular 9229 has been erroneously computed. At a redshift of about 8 the correct value for the isotropic equivalent energy is E_iso = (1.0 +/- 0.3)E+53 ergs. This value was determined from the observed event fluence of (1.1 +/- 0.3)E-06 erg/cm^2 in the 8 to 1000 keV energy range (observer's frame!). We apologize for this mistake." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9261 SUBJECT: GRB 090423: GROND second epoch imaging and refined SED DATE: 09/04/26 18:38:40 GMT FROM: Thomas Kruehler at MPE/MPI T. Kruehler, J. Greiner and F. Olivares (all MPE Garching) report on behalf of the GROND team: We obtained a second epoch of imaging of the field of GRB 090423 (Swift trigger 350184, H. Krimm et al., GCN #9198), which started on 25 Apr. 2009 at 00:44 UT, 40.8 h after the trigger. In the second epoch, the NIR afterglow (Tanvir et al. GCN #9202) is undetected in stacked images with a total integration time of 4800~s in each of J, H and K down to limiting AB magnitudes of J_AB > 22.7, H_AB > 22.3 and K_AB > 21.6. Together with the magnitudes reported in Olivares et al. (GCN #9215) this implies a fading with a power law index faster than 1.2. This lower limit on the temporal decay index is consistent with that found for the X-ray afterglow at a similar time interval (G. Stratta & M. Perri, GCN #9212). In addition we report on a refined analysis of the GROND photo-z from Olivares et al. (GCN #9215). Using an improved photometric calibration and including the deep z' band upper limit from Perley et al. (GCN #9217) which is contemporaneous to our GROND imaging, we find a refined photometric redshift of 8.0+0.4-0.8 (90% confidence level). The error range is unlikely to improve due to the gap between the z' and J bands (for the negative error), and the width of the J filter band (for the positive error). This range covers the previous claims from photometric (GCNs #9213, #9215, #9217) and spectroscopic observations (GCNs #9219, #9222). The SED is well described with a power law of index ~1. No signatures of intrinsic dust are evident with an upper limit of A_V < 0.5, assuming a SMC dust reddening template. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9273 SUBJECT: GRB 090423: millimeter detection DATE: 09/04/28 00:29:21 GMT FROM: Alberto Castro-Tirado at Inst.de Astro. de Andalucia A. J. Castro-Tirado (IAA-CSIC Granada), M. Bremer and J.-M. Winters (IRAM Grenoble), J. Gorosabel, S. Guziy, M. Jelínek (IAA-CSIC), P. Kubánek (GACE, Univ. de Valencia), A. de Ugarte Postigo (ESO Santiago) and D. Pérez-Ramírez (Univ. de Jaén), report: "Following the detection by Swift of GRB 090423 (Krimn et al. GCNC 9198), millimeter observations were conducted on Apr 23 & 24 at the Plateau de Bure Interferometer. Consistent with the nIR afterglow (Tanvir et al. GCNC 9202) we clearly detect a source at 3-mm with a flux density of ~0.2 mJy (preliminary) on the combined dataset. Pending of confirming its variability we propose this as the likely millimeter afterglow to GRB 090423. Considering the reported redshift values around z ~ 8, this is the most distant radio source detected to date. Further observations are scheduled. We acknowledge the Bure staff for its excellent support." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9274 SUBJECT: GRB 090423: CARMA mm observations DATE: 09/04/28 01:57:49 GMT FROM: Poonam Chandra at U Virginia/NRAO D. C.-J. Bock (CARMA), P. Chandra (RMC), D. A. Frail (NRAO), and S. R. Kulkarni (Caltech) report on behalf of a larger collaboration: "We observed the field of view of GRB 090423 (GCN 9198) with the Combined Array for Research in Millimeter-Wave Astronomy (CARMA) at a frequency of 92.5 GHz at the mean observation time of 2009 April 25, 0440 UT. We do not detect mm emission either within the Swift-XRT error circle (GCN 9205) or at the UKIRT K-band position (GCN 9202). The 3-sigma upper limit on the flux density of GRB afterglow is 0.7 mJy. We acknowledge excellent support from the staff and observers at CARMA." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9322 SUBJECT: GRB 090423: 250 GHz upper limit for a z=8.2 GRB with MAMBO-2 at the IRAM 30m DATE: 09/05/04 18:21:20 GMT FROM: Dominik A. Riechers at Caltech D. A. Riechers (Caltech), F. Walter (MPIA Heidelberg), F. Bertoldi (AIfA Bonn), C. L. Carilli (NRAO), P. Cox (IRAM), C. Kramer (IRAM), D. Riquelme (IRAM) report: "We used the Max-Planck-Millimeter Bolometer (MAMBO-2) array at the IRAM 30-m telescope to observe the field of view toward the host galaxy of GRB 090423 (GCN 9198) at redshift z=8.2 (GCN 9219), RA 09:55:33.19, Dec +18:08:57.7 (J2000) at 250 GHz. Observations were carried out for 4.5 hr on 2009 April 25, centered at UT 18.5. We obtained a non-detection of S_nu(250 GHz,1.20 mm) = 0.23 +/- 0.32 mJy (1 sigma error), i.e. a 3 sigma upper flux density limit of 0.96 mJy on the GRB afterglow and the dust continuum in the host galaxy at 1.2 mm (rest-frame 130 um). Together with the 3 mm observations carried out at the Plateau de Bure Interferometer (GCN 9273), this indicates a flat spectral slope at millimeter wavelengths. The 117-element MAMBO-2 bolometer detectors cover 210-290 GHz (half power). The bolometers have a FWHM beam size of 10.7 arcsec, at a pixel spacing of 20 arcsec. Observations were carried out in ON-OFF observing mode under good weather conditions, with low sky noise and opactities of tau=0.1-0.26 (derived from skydips). Calibrations were performed on CW-LEO. We acknowledge the excellent support of the staff at IRAM. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain). This message may be cited." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9323 SUBJECT: GRB 090423: optical limit DATE: 09/05/05 00:21:38 GMT FROM: Alexei Pozanenko at IKI, Moscow V. Rumyantsev, E. Pavlenko, O. Antoniuk (CrAO), A. Pozanenko (IKI) report on behalf of larger GRB follow-up collaboration: We observed the error box of Swift GRB 090423 (Krimm et al. GCN 9198) on Apr. 23 between (UT) 090423 23:34:46 -- 090424 01:13:20 in R -filter with Shajn telescope of CrAO. The observation was planning and performed before the redshift z ~ 8 of GRB 090423 was confirmed (Cucchiara et al. GCN 9213; Olivares et al. GCN 9215; Thoene et al. GCN 9216; Tanvir et al. GCN 9219). Indeed we do not detect optical afterglow at the place of IR afterglow detection (Tanvir et al. GCN 9202; Levan et al. GCN 9206; Cucchiara et al. GCN 9209). Limiting magnitude of the combined image is following : T0+ Filter, Exposure, mag., err. (d) (s) 0.6877 R 93x60 >24.0 (3 sigma) The combined R-image can be found at http://grb.rssi.ru/GRB090423/GRB090423_ZTSh_a.gif //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9416 SUBJECT: GRB 090423: Fermi GBM T90 follow-up analysis results DATE: 09/05/21 14:26:47 GMT FROM: Andreas von Kienlin at MPE A. von Kienlin (MPE), C. Kouveliotou (NASA/MSFC) and V. Connaughton (UAH) report on behalf of the Fermi GBM Team: "We performed a detailed follow-up analysis of the T90 of the high redshift GRB 090423 (H. Krimm et al., GCN Circ. # 9198) to determine the nature of the extended pulse centered at T+30s as reported earlier (A. von Kienlin, GCN # 9229). Due to the low significance of the detection, we were not able to accurately locate this later pulse (the emission was only significantly seen with one of the two triggered detectors). We conclude, therefore, that this pulse is most probably due to background fluctuations. The final GBM T90 derived between 10-300 keV is 11.5 +/- 2.0 sec. This duration agrees within the error with the value of 10.3 +/- 1.1 sec reported by the Swift team (H. Krimm et al., GCN Report 211.2)" //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9503 SUBJECT: GRB 090423: WSRT Radio Observations DATE: 09/06/11 23:45:46 GMT FROM: Alexander van der Horst at NASA/MSFC A.J. van der Horst (NASA/MSFC/ORAU) reports on behalf of a large collaboration: "We observed the position of the high redshift GRB 090423 afterglow at 4.9 GHz with the Westerbork Synthesis Radio Telescope at May 22 11.47 UT to 23.46 UT, i.e. 29.15 - 29.65 days after the burst (GCN 9198). We do not detect a radio source at the position of the infrared counterpart (GCN 9202). The three-sigma rms noise in the map around that position is 75 microJy per beam. The formal flux measurement for a point source at the position of the optical counterpart is 44 +/- 25 microJy. We would like to thank the WSRT staff for scheduling and obtaining these observations." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 9582 SUBJECT: GRB 090423: Spitzer observations of the z~8.3 burst DATE: 09/06/26 21:12:05 GMT FROM: Edo Berger at Harvard R. Chary, J. Surace, S. Carey (SSC/Caltech), E. Berger (Harvard), and G. Fazio (SAO/Harvard) report on behalf of a larger collaboration: "As part of the IRAC Warm Instrument Characterization Campaign (IWIC), we observed the field of the z=8.3 GRB090423 (GCN 9198) for 72 hours using Spitzer/IRAC at 3.6 microns. The observations took place between 2009 June 5.01 and 10.81 UT, corresponding to about 46 days after the burst in the observer frame, or about 5 days in the rest-frame. We detect a weak source at the location of the near-IR afterglow (Tanvir et al. 2009 arXiv:0906.1577), confirmed through an astrometric tie to the Gemini-North near-IR images. Aperture-corrected photometry of the source results in a 3.6 micron flux density of 46+/-17 nJy (or 27.2+/-0.3 AB mag). The spectral energy distribution and power-law decay of the afterglow presented in Tanvir et al. 2009 predicts a 3.6 micron flux density of ~27.3 AB mag at the time of our observations. The detected source is thus consistent with being the afterglow. An image of the region can be found at: http://www.its.caltech.edu/~rchary/grb090423/ Light colors designate bright flux, dark colors are faint. The pixel scale in the IRAC image (left) is 0.4"/pixel. The right-hand image is the Gemini J-band image from Cucchiara et al. (GCN 9209). The red circles are 1" radius and show the position of the afterglow. Further analysis is ongoing, and a second epoch of observations is planned for February 2010 to assess the contribution of an underlying host galaxy to the measured flux."