//////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1147 SUBJECT: BEPPOSAX GRB011121 DATE: 01/11/21 22:15:21 GMT FROM: SAX Science Operations at IAS/CNR Frascati On Nov. 21, 18:47:21 UT a very bright GRB (011121) has been simultaneously detected in the BeppoSAX GRBM and WFC Preliminary coordinates from WFC are: R.A.(2000)= 173.326 DEC.(2000)= -76.033 The error radius at this stage of analysis is 5'. Luigi Piro BeppoSAX Mission Scientist //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1148 SUBJECT: IPN triangulation of GRB011121 DATE: 01/11/21 23:47:30 GMT FROM: Kevin Hurley at UCBerkeley/SSL K. Hurley and T. Cline, on behalf of the Ulysses GRB team, and C. Guidorzi, E. Montanari, F. Frontera, and M. Feroci, on behalf of the BeppoSAX GRBM team, report: Ulysses and the BeppoSAX GRBM observed GRB011121 (GCN 1147). As observed by Ulysses, this event had a 25-100 keV fluence of 2 x 10^-5 erg/cm^2, and a peak flux over 0.25 s of 2 x 10^-6 erg/cm^2 s. We have triangulated it to a preliminary annulus centered at RA(2000), Decl(2000)=65.922 o, -54.971 o, whose radius is 41.220 +/- 0.067 o (3 sigma). This annulus intersects the BeppoSAX error circle at just two points: RA(2000) Decl(2000) 11 h 34 m 21.3 s -76 o 05 ' 14 " 11 h 32 m 52.8 s -75 o 57 ' 13 " This limits the location to the north-eastern segment of the circle. This result may be refined. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1149 SUBJECT: GRB011121: BeppoSAX-WFC refined positions DATE: 01/11/22 01:29:58 GMT FROM: SAX Science Operations at IAS/CNR Frascati GRB011121: refined positions Refined coordinates from WFC are: R.A.(2000)= 173.6059 DEC.(2000)= -76.027 The error radius is 2' BeppoSAX could not perform a TOO due to constraints on visibility Luigi Piro BeppoSAX Mission Scientist //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1150 SUBJECT: GRB011121: possible optical counterpart DATE: 01/11/22 06:47:19 GMT FROM: Krzysztof Z. Stanek at CfA Lukasz Wyrzykowski (Warsaw University Observatory), K. Z. Stanek (Harvard-Smithsonian CfA) and P. M. Garnavich (Notre Dame) report: R-band observations of the optical afterglow of the GRB011121 carried out with the OGLE 1.3m telescope (+8kx8k OGLE-III mosaic) at the Las Campanas Observatory, starting at UT 011122 05:08 (10.3 hours after the burst), reveal a new, bright source in the refined BeppoSAX-WFC error box (GCN 1149). Its position, based on the GSC, is: 11:34:30.38, -76:01:41.3 (J2000). Comparing to star "A" (R=17.4) from the USNO catalog (located at 11:34:18.9, -76:01:38.1, J2000), we estimate the R-band magnitude of the possible GRB011121 afterglow to be R=18.3\pm 0.1 (subject to possible systematic error due to the calibration of the catalog). Additional data will be obtained. The E(B-V) Galactic reddening from Schlegel et al. is E(B-V)=0.5, or A_R=1.33. This message can be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1151 SUBJECT: GRB011121: fading behavior DATE: 01/11/22 08:04:55 GMT FROM: Krzysztof Z. Stanek at CfA K. Z. Stanek (Harvard-Smithsonian CfA), P. M. Garnavich (Notre Dame) and Lukasz Wyrzykowski (Warsaw University Observatory) report: Further R-band observations of the possible optical afterglow of the GRB011121 carried out with the OGLE 1.3m telescope (+8kx8k OGLE-III mosaic) 12.5 hours after the burst, indicate a fading behavior of the new source at 11:34:30.38, -76:01:41.3 (J2000) reported by Wyrzykowski et al. (GCN 1150): HJD-2450000 UT R_c exp 2235.71890 011122 05:19 18.31+-0.03 200 sec 2235.80322 011122 07:20 18.64+-0.03 200 sec Errors in the magnitudes are statistical only. The R-band magnitudes are relative to star "A" (11:34:18.9, -76:01:38.1, J2000), assuming its magnitude R=17.4 (see GCN 1150). Inspection of the Digitized Sky Survey shows a faint object 0.5" to the northeast of the OT. The source, possibly the host galaxy has a magnitude of approximately R=20.4 based on the assumed brightness of star A. We have also obtained BVI observations of the afterglow, reductions of which are under way. This message can be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1152 SUBJECT: GRB011121: possible redshift, continued decay DATE: 01/11/22 12:10:45 GMT FROM: Krzysztof Z. Stanek at CfA L. Infante (Pontificia Univ. Catolica de Chile), P. M. Garnavich (Notre Dame), K. Z. Stanek (Harvard-Smithsonian CfA) and Lukasz Wyrzykowski (Warsaw University Observatory) report: Spectra of the possible OT (Wyrzykowski et al.: GCN 1150) obtained with the Magellan Walter Baade 6.5m telescope and the LDSS-2 spectrograph on Nov. 22.3 (UT) show a smooth continuum with a peak flux near 650 nm. Narrow emission lines, likely from the host galaxy, are seen at 507.58 nm and 681.0 nm, which may correspond to [O II] 372.7 and [O III] 500.7 nm at a redshift of 0.36. The depressed blue end of the spectrum is most likely due to strong Galactic dust extinction. Also, additional R-band observation of the GRB011121 field carried out with the OGLE 1.3m telescope 13.75 hours after the burst indicates continuing fading behavior of the afterglow, as seen already by Stanek et al. (GCN 1151): HJD-2450000 UT R_c exp 2235.85176 011122 08:30 18.80+-0.03 600 sec This behavior is consistent with a power-law decay with an index of -1.65. The R-band magnitudes are relative to star "A" of Wyrzykowski et al. (see finding chart at http://cfa-www.harvard.edu/cfa/oir/Research/GRB/). The faint object 0.5" to the northeast of the OT reported by Stanek et al. is easily visible in 600 sec R-band exposure. Relatively low redshift and fast decay of its afterglow make GRB011121 an attractive search target for a possible supernova associated with this burst. This message can be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1153 SUBJECT: GRB 011121: Detection of Bright IR Counterpart DATE: 01/11/22 12:38:21 GMT FROM: Paul Price at RSAA, ANU at CIT P.A. Price, P. McCarthy, D.W. Fox, K. Koviak and J.S. Bloom report on behalf of the REACT GRB collaboration: On 2001 November 22.36 UT, K. Koviak observed the field of GRB 011121 (GCN #1149) with the du Pont 2.5m telescope at Las Companas Observatory. In a single 90 sec sky-subtracted observation in J-band, a source at the position of Stanek's transient (GCN ##1150,1151) is strongly detected at the 10-sigma level. We estimate the magnitude as J ~ 16 mag. Reductions of the nearly 2 hours of J and Ks band imaging are in progess, but clearly the source is bright in the NIR. Given the large Galactic extinction towards this source, we strongly encourage NIR observations of this afterglow. Further observations are in progress. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1154 SUBJECT: GRB011121: continued decay DATE: 01/11/23 07:33:52 GMT FROM: Krzysztof Z. Stanek at CfA L. Wyrzykowski (Warsaw University Observatory) and K. Z. Stanek (Harvard-Smithsonian CfA) report: Additional R-band observations of the GRB011121 OT carried out with the OGLE 1.3m telescope indicate continuing fading behavior of the afterglow (GCNs 1151, 1152): HJD-2450000 UT R_c exp 2236.71036 011123 05:06 20.35+-0.07 3x600 sec This measurement might be somewhat contaminated by the possible host galaxy. Combined with the last night data, this is consistent with a power-law decay with an index of -1.55, similar to -1.65 obtained from first night data alone (GCN 1152). The R-band magnitudes are relative to star "A" of Wyrzykowski et al. (see finding chart at http://cfa-www.harvard.edu/cfa/oir/Research/GRB/). This message can be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1155 SUBJECT: GRB 011121 J-Band Astrometry DATE: 01/11/23 23:35:28 GMT FROM: Shri Kulkarni at Caltech P.A. Price, D.W. Fox, J. S. Bloom & S.R. Kulkarni, California Institute of Technology, Pasadena report on behalf of a larger collaboration: "We have registered the J-band images of the field of GRB 011121 (GCN 1147, GCN 1148) obtained at Las Campanas Observatory by K. Koviak (see GCN 1153) against nearly one hundred stars whose stellar positions are listed in the USNO-A2.0 catalog. Individual RMS errors for this registration, are 0.24" and 0.20" respectively in RA and Dec. From this analysis we derive the following position for the NIR transient reported in GCN 1149: (J2000) RA 11:34:29.669, Dec -76:01:41.56. The nominal uncertainty in each coordinate is about 0.30 arcsec; this includes the 0.17 arcsec uncertainty between USNO-A2.0 and the ICRF (the latter defines the radio frame). It is clear that the transient reported in GCN 1153 is the NIR counterpart of the optical transient first reported by Wyrzykowski et al. (GCN 1150). We therefore conclude that the coordinates reported in GCN 1150 (and based on the GSC) are in error by 2.6 arsec (east-west axis). While this difference is more than three times the nominal error for positions derived from the GSC (Deutsch 1999) we believe that our astrometry based on USNO-A2.0 is secure." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1156 SUBJECT: GRB 011121: Radio Observations DATE: 01/11/24 00:09:06 GMT FROM: Shri Kulkarni at Caltech R. Subrahmanyan, Australia Telescope National Facility, S. R. Kulkarni & E. Berger, California Institute of Technology, and D. A. Frail, National Radio Astronomy Observatory report on behalf of a larger collaboration: "We imaged the error circle of GRB 011121 (GCN 1147, 1148) with the Australia Telescope Compact Array (ATCA), Narrabri, Australia. The observations were conducted in the 3-cm band. The observations started at UT 1600, November 22 2001 and lasted 12 hours. The rms of the combined 8640 & 8768 MHz image is 35 microJy and the beam is 1.37x1.21 arcsec (PA=-27 deg). Only one source is detected in the general vicinity of the optical transient (OT) reported by Wyrzkyowski et al. (GCN 1150). This source, hereafter ATCA 113429.6-760141, is is located at 11h 34m 29.63s -76d 01m 41.5s (J2000, uncertainty of about 0.2 arcsec). It has a peak flux of 0.2 mJy and is embedded in some radio nebulosity; the integrated flux is 0.25 mJy. The discrepancy between the position of ATCA 113429.6-760141 and the position of the optical transient (GCN 1150) motivated us to reinvestigate the optical/IR astrometry. As reported in GCN 1155, the coordinates of the OT as given in GCN 1150 are likely to be in error and that the true position of the OT/NIRT is, within errors, the same as that of ATCA 113429.6-760141. We conclude that ATCA 113429.6-760141 is the radio afterglow of GRB 011121. Separately, we note that the radio frame does not suffer from zonal errors. In contrast, GSC suffers from such errors (and USNO less so). Thus the position of ATCA 113429.6-760141 is quite secure and with additional observations the source will be located to an accuracy better than the usual radio-optical frame tie. The 2-arcsec nebulosity is likely the radio host galaxy of GRB 011121. If so, assuming that the nebulosity is 0.05 mJy (a lower limit; we could be missing some extended flux) and a typical spectral index of -0.5 (between 1.4 and 8.5 GHz) we obtain Star Formation Rate (SFR, M>5 solar masses; Salpeter IMF) of 13 solar masses per year or SFR(M > 0.1 Msun) of 70 solar masses per year. We encourage deep optical/IR imaging to fully reveal the extent of the presumed host galaxy." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1157 SUBJECT: GRB011121 DATE: 01/11/24 04:49:38 GMT FROM: Knut Olsen at CTIO K. Olsen, M. Brown, R. Schommer (NOAO), and C. Stubbs (U. Washington) report: On November 22 UT, we observed the OT associated with GRB011121 (Wyrzykowski, Stanek, and Garnavich: GCN 1150) with the CTIO 0.9-m telescope and UBVRI filters. The bright OT is clearly detected in each band. We performed aperture photometry on the transient through 2" apertures. We calibrated the photometry with observations, taken at nearby time and airmass, of stars E5-c and E5-59Y from Graham 1982, PASP, 94, 244. These stars have similar colors to the OT (E5-59Y: U-B = -0.02; E5-c: B-V = 0.89, V-R = 0.49, V-I = 0.96). We find: U = 20.7 +/- 0.2 at 08:19 UT B = 20.86 +/- 0.05 at 06:59 UT V = 20.00 +/- 0.05 at 07:10 UT R = 19.25 +/- 0.05 at 06:35 UT I = 18.66 +/- 0.05 at 06:48 UT where the errors reflect both random error and the estimated uncertainty in the absolute calibration. These magnitudes have been lowered by 0.051, 0.019, 0.03, 0.015, and 0.013 magnitudes in UBVRI, respectively, to account for the small difference in airmass at which the OT and the standards were observed. We assume "typical" CTIO extinction coefficients of 0.45 (U), 0.28 (B), 0.15 (V), 0.08 (R), and 0.11 (I) magnitudes per airmass. We have not attempted to adjust the magnitudes for difference in color between the OT and the standards; we estimate that such effects will be smaller then 0.01 magnitudes in BVRI, but perhaps as large as 0.05 magnitudes in U. Comparing the magnitude of the OT in R to that of star "A" (R=17.4; Wyrzykowski et al., GCN 1150) we find the R magnitude of the OT to be 18.46 +/- 0.02 (internal error only). There is thus a zero point difference of 0.79 magnitudes between our photometry and that of Wyrzykowski et al. Assuming E(B-V) = 0.5 (Schlegel et al. 1998) and adopting the extinction curve of Cardelli, Clayton, & Mathis (1989), we find extinctions of A_U = 2.43, A_B = 2.07, A_V = 1.55, A_R = 1.16, and A_I = 0.74. The intrinsic colors of the OT are thus (U-B)=-0.52, (B-V)=0.34, (V-R)=0.36, and (V-I)=0.53. Astrometry of the object, tied to the USNO-A2 catalog, shows the OT to be at 11 34 29.61 -76 01 41.5 (2000.0). This position agrees with that of Price et al. (GCN 1155), and is 2."4 further west than that of Wyrzykowski et al. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1158 SUBJECT: GRB011121: UBRI Observations DATE: 01/11/24 18:12:47 GMT FROM: Michael Brown at NOAO M. Brown, R. Schommer, K. Olsen, B. Jannuzi, A. Dey (NOAO), A. Fruchter, J. Rhoads (STSci) and the NOAO Deep Wide Field Survey Team. The GRB011121 optical transient (Wyrzykowski et al. GCN 1150) was imaged with the CTIO Blanco 4m with Chip2 of Mosaic-II in UBRI between 7:32 and 8:21 23 Nov 2001 UT. Two objects within 2" of each other were detected near the position reported in GCN 1150. The brighter object (located at 11:34:29.66 -76:01:41.49 J2000) is the optical transient while the fainter object (located at 11:34:30.15 -76:01:42.26 J2000) could be the host or a companion galaxy. Aperture photometry of the optical transient, candidate host/companion and Star A from GCN 1150 is provided below. The photometry is in the Johnson-Kron-Cousins system and has been calibrated with Landolt (1992) standards from regions SA113 and SA95. The photometry has been corrected for atmospheric extinction (to airmass 0) but has not been corrected for galactic extinction where the Schlegel et al. (1998) dust maps predict dust reddening of E(B-V)=0.496 magnitudes. The 1" aperture photometry misses approximately 0.6 magnitudes of the total flux while 3" aperture photometry of the candidate host/companion galaxy suffers from contamination from the optical transient. Star A is ~0.8 magnitudes fainter in R-band than originally reported in the USNO catalogue (and GCN 1150) and estimates of the fading of the optical transient should be corrected accordingly. Object Band Seeing UT 1" radius 2" radius 3" radius (arcsec) (23 Nov) ap. mag. ap. mag ap mag. OT U 1.95 7:59 23.6 +/- 0.2 22.4 +/- 0.1 22.1 +/- 0.1 OT B 1.45 7:45 23.3 +/- 0.1 22.6 +/- 0.1 22.4 +/- 0.1 OT R 1.45 7:32 21.8 +/- 0.1 21.1 +/- 0.1 20.8 +/- 0.1 OT I 1.50 8:16 21.2 +/- 0.1 20.3 +/- 0.1 20.0 +/- 0.1 Host? U 1.95 7:59 24.6 +/- 0.4 23.4 +/- 0.3 22.6 +/- 0.2 Host? B 1.45 7:45 24.4 +/- 0.1 23.1 +/- 0.1 22.5 +/- 0.1 Host? R 1.45 7:32 22.2 +/- 0.1 21.2 +/- 0.1 20.9 +/- 0.1 Host? I 1.50 8:16 21.3 +/- 0.1 20.3 +/- 0.1 20.0 +/- 0.1 Star A U 1.95 7:59 21.7 +/- 0.1 20.9 +/- 0.1 20.7 +/- 0.1 Star A B 1.45 7:45 20.5 +/- 0.1 20.0 +/- 0.1 20.0 +/- 0.1 Star A R 1.45 7:32 18.7 +/- 0.1 18.3 +/- 0.1 18.2 +/- 0.1 Star A I 1.50 8:16 17.6 +/- 0.1 17.6 +/- 0.1 17.5 +/- 0.1 The reduced images are available from the 1st author upon request (mbrown@noao.edu). This message can be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1159 SUBJECT: Correction: GCN1157 (GRB 011121) DATE: 01/11/24 21:23:49 GMT FROM: Knut Olsen at CTIO The values of the R and I-band extinctions reported in GCN 1157 incorrectly used the ratios of total to selective absorption appropriate for Johnson, rather than Cousins, filters. The correct extinction values are A_R=1.328 and A_I=0.964, rather than A_R = 1.16 and A_I = 0.74. The intrinsic colors are then (V-R) = 0.53 and (V-I) = 0.75. Many thanks to Kris Stanek for pointing out the mistake. Knut Olsen //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1160 SUBJECT: GRB011121: fainter still DATE: 01/11/25 00:14:55 GMT FROM: Krzysztof Z. Stanek at CfA K. Z. Stanek (Harvard-Smithsonian CfA) and L. Wyrzykowski (Warsaw University Observatory) report: Additional R-band observations of the GRB011121 OT carried out with the OGLE 1.3m telescope indicate continuing fading behavior of the afterglow (GCNs 1151, 1152, 1154): HJD-2450000 UT R_c exp 2237.8276 011124 07:47 21.97+-0.07 6x900 sec The R-band magnitudes are relative to star "A" of Wyrzykowski et al. (GCN 1150), which we now take to be R=18.2 after correction by 0.8 mag determined by Olsen et al. (GCN 1157) and Brown et al. (GCN 1158). This measurement might be fairly significantly contaminated by the possible host galaxy. It was derived with DaoPhot/Allstar PSF-fitting software (Stetson 1992), which near the OT finds another source located about 0.8"S and 1.8"E (see deep finding chart and PSF-fitting residua at http://cfa-www.harvard.edu/cfa/oir/Research/GRB/) with magnitude R=21.91+-0.07. We also correct our previous measurements by 0.8 mag: HJD-2450000 UT R_c exp 2235.71890 011122 05:19 19.11+-0.03 200 sec 2235.80322 011122 07:20 19.44+-0.03 200 sec 2235.85176 011122 08:30 19.60+-0.03 600 sec 2236.71036 011123 05:06 21.15+-0.07 3x600 sec Further, deep observations of the OT are strongly encouraged. We designate fainter comparison star "C" (see the WWW finding chart), which by comparison to "A" we measure to be R=20.09+-0.02 (statistical error only, no color term correction included). This message can be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1161 SUBJECT: GRB 011121: HST Scheduled DATE: 01/11/27 04:31:24 GMT FROM: Shri Kulkarni at Caltech S. R. Kulkarni, T. J. Galama and J. S. Bloom, California Institute of Technology reports on behalf of a large collaboration, "As a part of our AO-10 large program on GRBs we have triggered HST observations of GRB 011121. We will observe the optical afterglow of this GRB (GCN 1150) with WFPC2 on five different occasions (with the first visit being December 4, 2001). The sequence of observations is designed to either detect or place significant upper limits on possible underlying supernova component. We encourage overlapping ground-based observations over the next three weeks, particularly in the VRIZ bands." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1163 SUBJECT: GRB 011121: NIR observations, host galaxy? DATE: 01/11/29 01:12:02 GMT FROM: Paul Price at RSAA, ANU at CIT S. Ryder (AAO), K. Gunn and N. Seymour (University of Southampton) with P.A. Price, B.P. Schmidt and T.S. Axelrod (RSAA, ANU) report: We have observed the field of the afterglow of GRB 011121 (GCN #1150) with the newly-commissioned Infra-Red Imager and Spectrograph (IRIS2) on the Anglo-Australian Telescope at 2001 Nov 28.7 UT. Preliminary reduction of 40 individual 60 sec images in Ks with 1.8 arcsec seeing reveal a faint source at the position of the afterglow (GCN #1155), on the outskirts of a galaxy centered approximately 1.5" E and 0.7" S (ie 9 kpc at z=0.36). At the resolution and depth of our observations, we cannot distinguish between this source being distinct from the galaxy or corresponding to an extension of the galaxy. We estimate our limiting magnitude as K = 19.1 mag. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1164 SUBJECT: GRB 011121: J-band observations DATE: 01/11/29 23:13:15 GMT FROM: Saurabh Jha at Harvard-Smithsonian CfA M. M. Phillips (Carnegie), K. Krisciunas (CTIO), P. M. Garnavich, S. Holland (Notre Dame), S. Jha, K. Z. Stanek (Harvard-Smithsonian CfA) and P. McCarthy (Carnegie) report: We have observed the field of GRB 011121 with the 6.5m Magellan I Baade telescope (+ IR imager) on UT 2001 Nov 29.3 for a total of 4320s in the Js passband with 0.5" seeing in the combined image. A finder chart of the combined image is available at: http://cfa-www.harvard.edu/cfa/oir/Research/GRB/. The data have been calibrated via three IR standard stars also observed over the course of the night, from the list of Persson et al. (1998, AJ, 116, 2475). The Js passband is slightly narrower than the standard J, but we make no color correction and adopt Js = J because we lack sufficient data (both for the standard stars and the objects in the GRB field). The effects of the slight filter mismatch are expected to be small (see, for example, Krisciunas et al. 2001, AJ, 122, 1616). For the bright stars marked in the finder, we measure J = 17.82 +/- 0.03 (star D) and J = 18.59 +/- 0.03 (star E). A source at the position of the GRB afterglow is marginally detected, but because of its faintness, it is difficult to separate a possible point source from the underlying fuzz. Differential PSF-fitting photometry relative to the bright stars in the field yields J = 21.9 +/- 0.1 for the source at the position of the GRB afterglow. Because of the marginal detection, this should be viewed as an upper limit. Two other sources are detected near the GRB position. One bright source is located 0.8"S and 2.0"E of the GRB with J = 19.98 +/- 0.04. This object may be the core of the GRB host galaxy, but it is not clearly resolved -- it might be a foreground star. The other source (the "blob") located 1.6"S and 2.6" E of the GRB is clearly detected at J = 21.57 +/- 0.07, and is possibly extended. Adopting J ~ 16 mag for the GRB afterglow on Nov 22.36 (GCN 1153), the reported optical decay slope (GCN 1160) would predict J ~ 21 for the afterglow at the time of these observations. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1166 SUBJECT: GRB 011121 DATE: 01/11/30 16:55:44 GMT FROM: Jochen Greiner at Astrophys.Inst. Potsdam,Germany J. Greiner (AIP Potsdam, Germany), S. Klose, A. Zeh (both TLS Tautenburg, Germany), G. Lamer, R.D. Scholz, N. Lodieu (all AIP Potsdam, Germany), E.v.d. Heuvel, P. Vreeswijk, L. Kaper (all Univ. Amsterdam, The Netherlands), A.J. Castro-Tirado (IAA Granada, Spain), A. Fruchter (STScI, USA), J. Hjorth (Copenhagen, Denmark), and E. Pian (Oss. Astr. Trieste, Italy), V. Doublier, O. Hainaut, S. Hubrig, R. Johnson, A. Kaufer, M. Kuerster, E. Pompej, (all ESO, Chile), report for the large European GRB-Afterglow collaboration: Observations of the afterglow of GRB 011121 (GCN #1147 - #1161) have been performed at ESO (Chile) starting 8.4 hrs after the GRB, and continuing over 4 days. In particular, K band imaging has been obtained with SOFI at NTT (La Silla) and with ISAAC at Antu (Paranal) at 0.4-0.9 arcsec seeing conditions. The best-seeing images (taken Nov. 24, starting at 06:24 UT) resolve the afterglow and the surrounding emission to hitherto unprecedented resolution. We do not see any diffuse emission. Instead, besides the afterglow and the other "faint source" at 2 arcsec distance reported earlier in GCN #1160 and #1163 (which we denote as object "2"), we find two more sources (see the Figures at http://www.aip.de/grb011121): one in between these two objects, about 0.9 arcsec East of the afterglow (and denoted as "1" in the following), and one about 1 arcsec south-east of the "faint source" (denoted "3"). The location and relative brightness of these objects 1 and 3 make us believe that they are the cause for the earlier reports on "diffuse emission" (see Figure 3). Thus, it is conceivable that object "2" is not related to the GRB or its host. The source of the radio nebulosity (GCN #1156) remains to be resolved. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1167 SUBJECT: GRB 011121: Errata URL DATE: 01/11/30 19:58:34 GMT FROM: Jochen Greiner at Astrophys.Inst. Potsdam,Germany Errata GCN #1166: Sorry, the correct URL should read: http://www.aip.de/~jcg/grb011121.html Jochen Greiner //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1172 SUBJECT: Detection of the X-ray afterglow of GRB011121 by BeppoSAX DATE: 01/12/03 12:39:11 GMT FROM: SAX Science Operations at IAS/CNR Frascati Detection of the X-ray afterglow of GRB011121 by BeppoSAX L. Piro, P. Soffitta (IAS/CNR-Rome), L.A. Antonelli (OAR-Roma), J. in 't Zand, J. Heise (SRON, Utrecht), L. Nicastro (IFCAI/CNR, Palermo), L. Amati (ITeSRE/CNR, Bologna), F. Frontera, C. Guidorzi, E. Montanari (Ferrara Univ.), L. Reboa (BeppoSAX SDC, Telespazio, ROma), M. Corsi, S. Granata (BeppoSAX SOC, Roma), G. Gennaro (BeppoSAX OCC, Roma), S. Rebecchi (ASI SDC, Roma), L. Salotti (ASI, Roma) We have successfully performed a follow-up observation of GRB011121 with BeppoSAX starting on Nov.22, 16.01 UT. This is the first TOO (Target of Opportunity) observation of a GRB after the new gyroless mode was installed in October and being tested. We have detected the fading X-ray afterglow of GRB011121 with NFI (1SAX J113426-7601.4) at a position RA(2000)= 11h34m25.8s, Decl(2000)=-76 01' 22", with an error radius of 50". This position is 25" away from the optical transient (GCN#1150), well within the error, verifying the good quality of the aspect reconstruction in this new pointing mode. A detailed data analysis is in progress.glow of GRB011121 with NFI (1SAX J113426-7601.4) at a position RA(2000)= 11h34m25.8s, Decl(2000)=-76 01' 22", with an error radius of 50". This position is 25" away from the optical transient (GCN#1150), well within the error, verifying the good quality of the aspect reconstruction in this new pointing mode. A detailed data analysis is in progress. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1260 SUBJECT: HST Imaging of the afterglow and host of GRB 011121 DATE: 02/03/06 03:05:01 GMT FROM: Josh Bloom at CIT HST Imaging of the afterglow and host of GRB 011121 J. S. Bloom, on behalf of the Caltech-NRAO-CARA GRB Collaboration, reports: "The afterglow of GRB 011121 (GCN #1150) has been detected in a series of HST observations (see GCN #1161) which began on 4 Dec 2001 and will continue until April 2002. The afterglow appears to have faded in a manner consistent with the extrapolation of early-time optical observations. Preliminarily, we find no evidence of an intermediate-time light curve bump (from an underlying supernova, etc.). Source 1 (Greiner et al., GCN #1166 == 'Blob' of Phillips et al., #1164) is a red point source and source 2 appears to be a foreground star with colors similar to other stars in the field. Source 3 is clearly extended in the HST images and is likely the host galaxy of GRB 011121 (as suggested by Phillips et al., GCN #1164). The low redshift and large angular extent of the host make it one of the better GRB host candidates for determining detailed morphology (see also, e.g., the analysis of GRB 980703 by Holland et al. A&A, 371, 52, 2001). A PSF-subtraction of the nearby point sources (including the afterglow) in the latest F814W image reveals the host to be a fairly smooth galaxy with a half-light radius of ~0.88 arcsec (4.8 kpc in projection at a redshift of z=0.36, GCN #1152). Using the IRAF task GIMFIT2D to find the structural parameters of the host galaxy, we find the light is well fit by an exponential disk-bulge model. The bulge (Sersic index = 4; i.e., a de Vaucouleurs profile) accounts for 13 +/- 3% (1 sigma) of the light and the exponential disk (~10 deg inclined from face-on) accounts for the remainder. This provides some of the first morphological evidence for a significant mass from an old stellar population in a GRB host (see also Chary, Becklin & Armus ApJ, 556, 229, 2002 for a compilation of photometric evidence to this effect)." A series of images of the OT+host system (5 WFPC filters) may be found at: http://www.astro.caltech.edu/~jsb/grb011121-hst-ep1.gif This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1273 SUBJECT: GRB011121, possible supernova association DATE: 02/03/15 17:16:11 GMT FROM: Peter Garnavich at U of Notre Dame P. M. Garnavich, S. T. Holland (Notre Dame), S. Jha, R. P. Kirshner, D. Bersier, and K. Z. Stanek (CfA) We have reanalyzed R-band images of GRB 011121 obtained with the Walter Baade 6.5m Magellan telescope on 2001 Dec. 4.32 in light of the recently released HST images taken near the same time (Bloom, GCN 1260). The brightness of the afterglow in the Magellan data deviated from the steep powerlaw decline seen in the first three days after the burst and we attributed this to contamination from the host galaxy (e.g. Phillips et al. GCN 1164). However the Magellan magnitude of R=23.0+\-0.1, obtained by point-spread-function fitting is consistent with the WFPC2 magnitude of f702w=23.16+\-0.08 which has minimal host contamination. Both observations are nearly 2 magnitudes brighter than the early-time extrapolation. The full light curve is well fit by an initial powerlaw with index of 1.71+\-0.05 plus the light curve of SN 1998bw stretched and faded to a redshift of z=0.36 (Infante et al. GCN 1152). The Dec. 4 data is 10 days after explosion in the rest frame, while SN 1998bw peaked 17 days after GRB 980425, so later epochs may show a small rise in the f702w magnitude before final fading. The light curve can be viewed at http://www.nd.edu/~pgarnavi/grb011121/grb011121_sn.ps Assuming a flat cosmology with Omega_m=0.3 and a Hubble parameter of 65 km/s/Mpc, we derive an absolute magnitude for the possible supernova on Dec. 4 of Mv=-19.3+\-0.2 (corrected for a large Galactic extinction but not for host extinction), consistent with SN 1998bw near maximum. These observations could be strong evidence for a SN-GRB connection. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1274 SUBJECT: GRB 011121: HST Observations reveal an intermediate-time multicolor DATE: 02/03/18 05:24:55 GMT FROM: Josh Bloom at CIT GRB 011121: HST Observations reveal an intermediate-time multicolor bump J. S. Bloom, P. A. Price, S. R. Kulkarni, D. E. Reichart (Caltech), D. A. Frail (NRAO), E. Berger on behalf of the Caltech-NRAO-CARA GRB Collaboration, report: As a part of our AO-10 HST GRB program, we observed the afterglow (Wyrzykowski et al.; GCN #1150) of GRB 011121 (Piro et al.; GCN #1147). We obtained WFPC2 observations through multiple filters, designed to detect or constrain underlying supernovae following low-redshift GRBs. The observations presented here were obtained on 2001 Dec 4-5 and 2001 Dec 14-16. Recently, Garnavich et al. (GCN #1273) noted that the optical afterglow of GRB 011121 on day 13 showed an excess in the F702W filter over an extrapolation of fluxes measured at earlier epochs in the R-band filter. They suggested this excess is indicative of a contribution from an underlying supernova (SN) as has been discussed for some GRBs (e.g. GRB 980326, GRB 970228). Here we report further analysis of the HST data. In the following, we give the PSF-fit photometry for the first two epochs of our program in an 0.5 arcsec radius using the current WFPC zero-points from Dolphin (see http://www.noao.edu/staff/dolphin/wfpc2_calib/ ). The magnitudes have been corrected for the (sometimes considerable) charge-transfer inefficiency using the Dolphin methodology but not corrected for Galactic extinction; the uncertainties do not reflect the errors in the absolute zero-points. These brightnesses also include an uncertain contribution from the host galaxy at the position of the transient. As per the discussion in Holtzmann et al. 1995, the "infinite aperture" magnitudes will be ~0.1 mag brighter, Epoch delta T Filter ST Magnitude (days) --------------------------------------------- 1 13.09 F450W 24.64 +/- 0.07 1 13.16 F555W 23.88 +/- 0.05 1 13.23 F702W 23.16 +/- 0.05 1 14.02 F814W 22.79 +/- 0.03 1 14.15 F850LP 22.51 +/- 0.06 2 23.03 F555W 24.43 +/- 0.04 2 23.09 F702W 23.33 +/- 0.03 2 24.83 F814W 22.98 +/- 0.03 2 24.96 F850LP 22.59 +/- 0.09 --------------------------------------------- We confirm that the excess seen on day 13 in F702W is also present in other filters (F450W, F555W, F814W, and F850LP). Second, the excess is seen even at epoch 2 (day 23-25). Thanks to our extensive multi-band data, this is the first unambiguous detection of an intermediate-time bump (>~ 10 days) in a GRB afterglow simultaneously in more than 3 filters. As is common in the SN interpretation, we took the multi-band light curves of SN 1998bw and transformed the same to the redshift of GRB 011121 (z = 0.36, GCN #1152). In the SN 1998bw interpretation, one would expect the brightness to have increased by 0.03 mag in the F555W filter, 0.23 mag in the F702W filter, 0.30 mag in the F814W filter, and 0.19 mag in the F850LP filter between these two epochs. Instead, we find the brightness to decrease by 0.55 +/- 0.06 mag in the 555W filter, 0.17 +/- 0.06 mag in the 702W filter, 0.19 +/- 0.04 mag in the 814W filter, and 0.08 +/- 0.11 mag in the 850LP filter. Thus this curious bump is inconsistent with an underlying SN similar to SN 1998bw. We caution that all these excesses are measured with respect to extrapolations of early time ground based data and such extrapolations have not included possible jet breaks." This message can be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1276 SUBJECT: GRB 011121: Third HST Epoch DATE: 02/03/19 07:14:41 GMT FROM: Shri Kulkarni at Caltech S. R. Kulkarni, J. S. Bloom, P. A. Price, D. E. Reichart, Caltech and B. Schmidt, Mount Stromlo Observatory report on behalf of a larger collaboration: Here we report on the third HST epoch (19 Dec 2001 UT) of WFPC2 images of GRB 011121 (see GCN 1274). The third epoch was requested for observations 1 week after the second epoch but HST scheduling restrictions resulted in the data being taken earlier. We have performed PSF-fitting photometry on the transient and using the prescription of Dolphin and Holtzman (D-H) we measure the following magnitudes: Epoch delta T Filter D-H Magnitude (days) --------------------------------------------- 3 27.24 F555W 25.08 +/- 0.07 3 27.30 F702W 23.65 +/- 0.04 3 28.10 F814W 23.16 +/- 0.06 3 28.16 F850LP 22.72 +/- 0.06 --------------------------------------------- Note: (1) These magnitudes are measured magnitues and have not been corrected for extinction. (2) The magnitude system here is the same as that in GCN 1274. We have converted these magnitudes to fluxes and the light curve can be found at http://www.astro.caltech.edu/~der/1121lc_0.75mag.eps. We assumed that the excess over the power law decay of the afterglow is due to an underlying SN. To this end, we assumed assumed an SN 1998bw template (corrected for extinction of A_V=0.19), redshifted to that of the host galaxy of GRB 011121 (z=0.36, GCN 1152) and subject to the estimated Galactic extinction of A_V=1.64 towards GRB 011121 (see GCN 1158). A simple fit ("chi-by-eye") requires the 1998bw contribution to be dimmed by 0.75 mag. Even so, the fit is only approximate with clear deviations in some bands (e.g. F555W). A full-fledged proper fitting of the data must address two points. First (a minor concern) is the heavy extinction towards this direction. Second (a major issue) is that there is great evidence that cosmologically located GRBs are not spherical but jetted sources with opening angles of only a few degrees (e.g. Frail et al. 2001, ApJ 562, 55). In contrast, the asymmetry in SN 1998bw is sufficiently mild that this issue has been debated for some time in the literature. The fact that we see GRB 011121 means that we are seeing the explosion along the symmetry axis (or close to it). [The opening angle for GRB 011121, as with other GRBs, can be estimated from broad-band data. Indeed, if the true gamma-ray energy release from GRB 011121 is similar to those estimated from other cosmologically located GRBs then we estimate an opening angle of over 8 degrees]. Continuing, if cosmologically GRBs have an underlying SN then these SN are likely to be severely asymmetric. These strong asymmetries, more than any any other quantity (e.g., the amount of synthesized Nickel), will strongly affect the light curve (see Hoflich et al. 1999, ApJ 524, L107). Rapid rise in the SN light is easily explained by rapid expansion along the polar axis and the decline can be expected to be rapid as well. Thus we should be prepared to see a large diversity in the light curves of the underlying SN in cosmologically located GRBs. Within these expectations, it appears that the case for an underlying SN in GRB 011121 is well established. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1288 SUBJECT: GRB 011121: Fourth Epoch of HST Imaging DATE: 02/03/22 00:37:58 GMT FROM: Josh Bloom at CIT GRB 011121: Fourth Epoch of HST Imaging J. S. Bloom, S. R. Kulkarni, D. E. Reichart, P. A. Price, on behalf of the Caltech-NRAO-CARA GRB Collaboration and co-investigators on the large HST Cycle 10 GRB program (#9180), report: Following the discussion from Kulkarni et al. (GCN #1276) the fourth epoch of HST imaging (4 Feb 2002 UT) of the afterglow of GRB 011121 has revealed continued fading of the intermediate-time red bump (Garnavich et al. GCN #1273; Bloom et al. GCN #1274; GCN #1276). Following are the magnitudes and fluxes of the transient bump plus host contribution: Filter delta T lambda_eff f_nu(lambda_eff) Vega mags (days) (Ang) (microJy) (mag) --------------------------------------------------------------------- F555W 77.33 5604.61 0.123 +/- 0.014 V = 26.173 +/- 0.118 F702W 76.58 7042.09 0.224 +/- 0.019 R = 25.264 +/- 0.092 F814W 77.25 8149.18 0.294 +/- 0.020 I = 24.762 +/- 0.073 --------------------------------------------------------------------- These fluxes and magnitudes have not been corrected for Galactic or host extinction. The host galaxy contributes significantly to the flux at these late times. We estimate this contribution from the host to be f_nu(F555W) = (0.087 +/- 0.027) microJy, f_(F702W) = (0.127 +/- 0.026) microJy and f_nu(F814W) = (0.209 +/- 0.059) microJy. More information about the reductions may be found in: http://www.astro.caltech.edu/~jsb/Papers/grb011121-paper1.ps This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1463 SUBJECT: HST Imaging of the Host of GRB 011121 DATE: 02/08/02 19:02:08 GMT FROM: Josh Bloom at CIT HST Imaging of the Host of GRB 011121 J. S. Bloom (Caltech, Harvard/CfA) and P. A. Price (RSSA, ANU) report: "Deep late-time images of the field of GRB 011121 were acquired with the Hubble Space Telescope in from 21 April to 2 May 2002 UT as part of the large GRB program #9180 (Kulkarni, PI). Five filters were used---F450W, F555W, F702W, F814W, F850LP---with a total integration time of 4500 sec per filter. The transient afterglow plus intermediate-time bump, suggested elsewhere as an accompanying supernova (SN) to the GRB (Bloom et al. 2002, Garnavich et al. 2002), faded beyond detection in each filter. There is no apparent persistent emission at the burst location aside from diffuse light from the host galaxy. In Bloom et al. (table 1) we noted the estimated the contribution of this diffuse light to the total measured flux of the OT/SN; using the host images as a template for subtraction from earlier epochs, we confirm those estimations were correct to within the stated errors; here we provide a direct measurement of the diffuse host flux contributing to the 0.5" radius aperture PSF photometry: f_nu(host)[F450W, F555W, F702W, F814W, F850LP] = (0.038 +- 0.048), (0.067 +- 0.034), (0.154 +- 0.035), (0.195 +- 0.067), (0.305 +- 0.184) microJy. These fluxes have not been corrected for Galactic extinction. Two rather blue compact knots of emission are detected West of the galaxy core, near to the OT/SN. Knot #1 is positioned at 0.52"E, 0.01"N and knot #2 is 0.08"E, 0.28"N relative to the OT/SN location. [For reference, the OT/SN was 1.99" W, 0.85" N of the star labeled as "B" in figure 1 of Bloom et al.]. At the redshift of the host (z=0.362; Garnavich et al.) even the closest of these knot lies 1.5 kpc in projection from the burst site. A close-in color image of the host may be found at: http://cfa160.harvard.edu/~jsbloom/grb011121 Though we cannot rule out these knots as background galaxies, given the detection of Hydrogen Balmer-line and [OII] emission in the spectrum of the larger "host" galaxy, these knots are likely strong pockets of star formation in the host itself." This message may be cited. Paper References: ----------------- 1. Bloom et al., 2002, ApJ Letters, v572, 45-49 2. Garnavich et al., 2002, submitted to ApJ, (astro-ph/0204234)