//////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1383 SUBJECT: XRF 020427 DATE: 02/04/27 11:16:39 GMT FROM: Jean int Zand at SRON Jean in 't Zand, Fabrizio Reali, Stefano Granata, Paul Lowes and Luigi Piro report on behalf of the BeppoSAX team: BeppoSAX Wide Field Camera unit 2 detected a fast X-ray transient on April 27 at 3:48:40 UT. Quick-look analysis shows that it lasted 1.1 min, with a rise time of 0.1 min. The 10-28 to 2-10 keV hardness ratio is similar to the X-ray rich GRBs like 981226 and type-I X-ray bursters. The Gamma-Ray Burst Monitor covered this event, but no obvious signal was detected. We strongly suspect that this is an X-ray rich GRB or X-ray flash rather than an X-ray burst because 1) the time profile is unusual for an X-ray burst; 2) there is no evidence for softening in the decay; 3) the galactic latitude of -44.2 deg is unusual for an X-ray burst. We strongly encourage follow-up observations. The refined WFC position is: R.A. = 22h09m33.6s (332.3900 deg) Dec. = -65d19m36.6s (-65.3268 deg) (Eq. 2000.0) with an error radius of 3 arcmin (99% confidence). //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1384 SUBJECT: GRB020427 BeppoSAX NFI Observation DATE: 02/04/29 10:38:42 GMT FROM: Giangiacomo Gandolfi at IAS/CNR Frascati GRB020427 BeppoSAX NFI observation A short BeppoSAX TOO observation of GB020427 has been carried on about 13 hours after the GRB. A preliminary analysis of MECS (1.6-10 keV) image shows two unknown and faint sources in the WFC error circle, contaminating each other. A more refined analysis is required to desentangle the couple and to confirm the possible fading of one of the objects. A second (and final) BeppoSAX observation is planned this evening. No NFI position is available at the moment due to the bad contamination of the objects. Further follow-up observations are encouraged. Giangiacomo Gandolfi on behalf of BeppoSAX Mission Mission Scientist //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1386 SUBJECT: GRB(XRF) 020427: X-ray afterglow with BeppoSAX DATE: 02/05/09 14:42:36 GMT FROM: Lorenzo Amati at TESRE/CNR L. Amati, Istituto di Astrofisica Spaziale e Fisica Cosmica, CNR, Bologna; M. Capalbi, BeppoSAX Science Data Center, Rome; F. Frontera University of Ferrara and Istituto di Astrofisica Spaziale e Fisica Cosmica, CNR, Bologna; G. Gandolfi and L. Piro, Istituto di Astrofisica Spaziale e Fisica Cosmica, CNR, Rome; J. J. M. in 't Zand, Astronomical Institute, Uthrecht University; S. Granata and F. Reali, BeppoSAX Science Operation Center, Rome, report: "The 3' error box of GRB(XRF) 020427 provided by the BeppoSAX Wide Field Cameras (GCN 1383) was observed with the BeppoSAX MECS instrument (1.5-10 keV energy band) from Apr. 27.6220 (11.2 hr after the onset of the WFC event) to Apr. 27.7944 UT and from Apr. 29.4439 to Apr. 29.6833 UT, for a total exposure time of 14878 s. A previously unknown source lying inside the error box is detected at a 4.6 and 3.2 sigma level in the first and second observation, respectively, The source, designated 1SAXJ2209.3-6519, is located at R.A. = 22h09m23s.2, Decl. = -65o19'34.1" (equinox 2000.0; error radius 1'), which is 1'.1 from the WFC-determined centroid. The average count rate during the first observation is 0.0059 +/- 0.0013 count/s in the two MECS units, corresponding to a 2-10-keV flux of (4.18 +/- 0.9) x 10**-13 erg cm**-2 s**-1, assuming a Crab-like spectrum. The average flux decreased by a factor of about 2 during the second observation. Due to its position and fading behavior, 1SAX J2209.3-6519 is likely the X-ray afterglow of GRB(XRF) 020427. " This message can be cited //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1387 SUBJECT: XRF020427: Chandra Observations and Candidate X-ray Counterparts DATE: 02/05/10 02:58:17 GMT FROM: Derek Fox at CIT D. W. Fox (Caltech) reports on behalf of the Caltech-NRAO-CARA GRB Collaboration: "We have observed the error region of the X-ray flash XRF020427 (GCN 1383, 1384, 1386) with the Chandra X-ray Observatory for 13.8 ksec beginning May 6.2456 UT. Reduction of the data using standard Ciao procedures yields the following source catalog (listed in decreasing order of significance) for the most recent BeppoSAX/MECS localization region (GCN 1386): ID IAU Name Sig Cts HR ======================================================= 1 CXOU J220928.2-651932 26.8 57.6(78) 0.34(11) 2 CXOU J220925.9-651855 11.9 15.8(41) 0.13(9) 3 CXOU J220925.0-651919 7.3 20.0(46) 0.07(7) ======================================================= where "Sig" is the wavdetect-quoted significance of the source in the 0.3 to 7.0 keV band, "Cts" is the counts in this band over the 13.8 ks exposure, "HR" is the hardness ratio of 2.1-7.0 keV counts to 0.3-2.1 keV counts, and uncertainties in the trailing digits are indicated in parentheses. J2000 coordinates of the sources are implicit in their IAU names. Source CXOU J220925.0-651919 (ID 3) is coincident with a weak source (not a USNO star) from the Digitized Sky Survey (DSS/SES). Identification of the brightest source, CXOU J220928.2-651932 (ID 1), with the afterglow of XRF020427 would imply an average power-law decay index of approximately 1.8 from the epoch of the second BeppoSAX MECS observation (Apr 29.4439 UT) when referenced to the time of the burst (Apr 27.1588 UT). We therefore consider this source to be the most likely candidate counterpart." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1390 SUBJECT: GRB/XRF 020427, Radio Observations DATE: 02/05/15 23:54:26 GMT FROM: Edo Berger at Caltech M. H. Wieringa (ATNF), E. Berger, D. W. Fox (Caltech), and D. A. Frail (NRAO) report on behalf of a larger collaboration: "We observed the BeppoSAX MECS error circle of GRB/XRF 020427 (GCN 1386) at 8.7 GHz with the Australia Telescope Compact Array (ATCA) for 6.2 hours centered on May 11.8 UT. We detect one radio source within the MECS error circle with a flux density of 190+/-35 microJy at (+/-0.1 arcsec): RA=22:09:17.73, DEC=-65:19:35.8 (J2000) We find no counterparts to the three Chandra sources reported by D. Fox (GCN 1387), down to a 2-sigma limit of 70 microJy." This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1392 SUBJECT: XRF020427: Chandra Identification of a Likely X-ray Counterpart DATE: 02/05/20 19:12:51 GMT FROM: Derek Fox at CIT D. W. Fox (Caltech) reports on behalf of the Caltech-NRAO GRB Collaboration: "We have observed the error region of the X-ray flash XRF020427 (GCN 1383, 1384, 1386) with the Chandra X-ray Observatory for 12.5 ksec beginning May 14.1939 UT. Reduction of the data using standard Ciao procedures, and comparison with the source catalog from our first observation of May 6.2456 UT (GCN 1387), yields the following results for the BeppoSAX NFI error circle (Amati et al., GCN 1386): ID IAU Name CR_1 CR_2 Delta ======================================================= 1 CXOU J220928.2-651932 4.2(6) 1.8(4) -3.3 sigma 2 CXOU J220925.9-651855 1.2(3) 2.3(4) +2.1 3 CXOU J220925.0-651919 1.1(3) 0.8(3) -0.7 ======================================================= where "CR_1" and "CR_2" are the source count rates per ksec in the 0.3 to 7.0 keV band for the first and second Chandra observations, respectively, and "Delta" is the signed significance of the change in count rate from the first to the second observation, expressed in standard deviations. Uncertainties in the trailing digits are indicated in parentheses. The brightest source in the first epoch, CXOU J220928.2-651932 (ID 1), shows a pronounced fading between the two epochs, equivalent to a power-law decay with index 1.3 referenced to the epoch of the burst (Apr 27.1588). We conclude that this source is the likely X-ray afterglow of XRF020427. In addition, identification of three USNO stars on the Chandra images has allowed us to improve the aspect; the improved position of the likely afterglow (ID 1) is RA 22:09:28.265(46), Dec -65:19:31.78(32) (J2000) where the uncertainties are indicated in parentheses and correspond to an average radial uncertainty of 0.3 arcsec (one-sigma)." //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1394 SUBJECT: XRF 020427: Sudden Ionospheric Disturbance (SID) DATE: 02/05/24 19:16:01 GMT FROM: Peter Woods at UAH/MSFC G.J. Fishman, P.M.. Woods, C. Hossfield and L. Anderson report that the X-ray rich event of April 27, 2002 was detected as a Sudden Ionospheric Disturbance (SID) by Len Anderson in South Perth Australia, indicating that XRF 020427 (GCN 1383), produced a prodigious amount of ionizing x-ray flux. The disturbance is clearly seen, lasting about one minute, in a low-resolution all-day strip chart recording from a Very Low Frequency (VLF) radio receiver near Perth. Although a quantitative measure of the flux of this event could not be determined by this method, the SID magnitude (and thus the ionizing flux) is comparable to that observed from the Aug. 27, 1998 super-flare from SGR 1900+14 (Inan, et al., Geophys. Res. Lett., v.26, p.3357, 1999). A large flux of x-rays below ~15 keV was deduced from that flare (op. cit.). One intense gamma-ray burst, GRB830801, was also observed to produce a SID but at a much weaker level (Fishman and Inan, Nature v.331, p.418, 1988). The strong ionizing present in this burst confirms that this is a long, x-ray rich event of unknown origin, as suggested by in't Zand et al. (GCN 1383). Note: SIDs have been used to study solar flares since the 1950s. In this case, the SID was observed as a major change in the propagation of a continuous VLF radio transmission at 19.8 kHz from Northwest Cape, Australia. The VLF radio receiver trace can be seen at: http://gammaray.nsstc.nasa.gov/~woods/xrf020427.html This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1439 SUBJECT: GRB/XRF 020427, detection of an underlying system with the VLT DATE: 02/06/25 05:45:40 GMT FROM: Alberto Castro-Tirado at Inst.de Astro. de Andalucia GRB/XRF 020427, detection of an underlying system with the VLT ------------------------------------------------ A. J. Castro-Tirado and J. Gorosabel (Instituto de Astrofísica de Andalucía, IAA-CSIC, Granada) C. Sánchez-Fernández (ESA-VILSPA, Madrid) N. Lund and S. Brandt (DSRI, Copenhagen) J. M. Castro Cerón (ROA, San Fernando) communicate: "We have observed the field of the GRB/XRF 020427 (GCN Circulars 1383, 1384, 1386, 1390, 1394) on 11.388-11.397 June 2002 with the 8.2-m VLT telescope at Paranal ESO's observatory (equipped with FORS2). Imagery was obtained in the B- and R-bands (300-s exposure time each) under rather poor seeing conditions (1".2). The position of the likely X-ray afterglow detected by BSAX and followed-up by Chandra (GCN Circulars 1387, 1392) is coincident with the north part of a extended (about 4" x 2"), blue object with R = 23.3 +/- 0.2 and B = 23.8 +/- 0.4 which is consistent with the galaxy system reported independently by Fruchter et al. (GCN Circ. 1440). An identification chart is posted at www.iaa.es/~ajct/XRFs/xrf02042 //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 1440 SUBJECT: The Probable Host Galaxy of GRB/XRF 020427 DATE: 02/06/25 06:01:45 GMT FROM: Andrew S. Fruchter at STScI A. Fruchter, J. Rhoads, I. Burud, A. Levan (STScI), S. Patel, C. Kouveliotou (MSFC), Javier Gorosabel (IAA-CSIC, Granada), J. Hjorth (Copenhagen U.) report for the larger GOSH (Grb Optical Studies with HST) Collaboration: The field of XRF/GRB 020427 (Zand et al., GCN 1383) was observed with HST on 10 June 2002 using the STIS CCD camera in open mode (50ccd). The HST image was aligned to the USNO coordinate system using a wide-field image obtained by the Danish 1.5m telescope at La Silla on 11 May 2002. The position obtained by Fox et al. (GCN 1387, 1392) was then located on the HST image. We believe the combined error in the position of the X-ray transient and the transfer to the HST image is less than 0."45, one-sigma. The XRF appears to lie on a galaxy with V magnitude of ~24.7. This galaxy, which is extended in the NE-SW direction with a total length of ~1."5, has two neighbors within a few arseconds of similar magnitude and morphology, as well as a number of fainter neighbors. The position obtained by Fox et al. places the GRB preferentially towards an end of the galaxy. If we use only the header of the Chandra image to do the alignment, we find a location near a bright knot on the apparent host, about one-sigma from the Fox position. Images taken at a later date could allow a search for an optical counterpart. Observations of this field have also been undertaken independently at the VLT (see the accompanying GCN 1439, Castro-Tirado et al.). The VLT observations show the complex of the three similar galaxies to be blue, which is consistent with observations of GRB hosts in general (Fruchter et al., Ap J. 519L, 13, 1999). Images of the field are available at http://www.stsci.edu/~fruchter/GRB/020427 //////////////////////////////////////////////////////////////////////// TITLE: GCN GRB OBSERVATION REPORT NUMBER: 2380 SUBJECT: XRF 020427: Gemini-South Spectroscopic Observations of the Host DATE: 03/09/09 18:59:50 GMT FROM: Josh Bloom at Harvard/CFA XRF 020427: Gemini-South Spectroscopic Observations of the Host Galaxy P. G. van Dokkum (Yale) and J. S. Bloom (CfA) report: On 1 Sept 2003 UT, we observed the host galaxy of XRF 020427 with the newly commissioned GMOS Spectrograph on the Gemini South 8 m at CTIO in Chile. Using the detection of the host continuum down to at least 3800 Angstrom in three blue grating exposures, we place a firm upper limit to the redshift of the host at z < 2.3. In the presence of strong fringing, a preliminary reduction reveals a (formally significant) faint emission line at 8485 Angstrom in two dithered 1200 sec exposures. This line is also formally detected, blueshifted by about 1800 km/s, in the nearby galaxy to the South (see Bloom et al. ApJ, in press; astro-ph/0303514), giving added confidence to the detection and the physical association of these two galaxies. Without corroboration from other absorption or emission lines, however, we have been unable to associate this tentative line with a redshift for the host. A more detailed analysis is in progress." We thank the Director for Discretionary Time and the observing staff of Gemini for assistance.