Circular No. 6656
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION

GRB 970508

L. Piro, E. Costa, M. Feroci, and P. Soffitta, Istituto di Astrofisica Spaziale, CNR, Frascati; L. A. Antonelli, F. Fiore, and P. Giommi, BeppoSAX, Rome; A. Owens and A. Parmar, Space Science Department, ESTEC; S. Molendi, Istituto di Fisica Cosmica e Tecnologie Relative, CNR, Milano; G. Cusumano, Istituto di Fisica Cosmica e Applicazioni Informatica, CNR, Palermo; J. in 't Zand and J. Heise, Space Research Organization of the Netherlands, Utrecht; F. Frontera and G. Zavattini, Universita di Ferrara; L. Nicastro and E. Palazzi, Istituto Tecnologie e Studio Radiazioni Extraterrestri, CNR, Bologna; M. Smith, G. Gandolfi, V. Torroni, G. Spoliti, A. Coletta, M. Capalbi, S. Rebecchi, D. Ricci, L. Bruca, and G. Crisigiovanni, BeppoSAX, Rome; L. Salotti, G. Gennaro, and C. DeLibero, Nuova Telespazio, Rome; and R. C. Butler, Agenzia Spaziale Italiana, Rome, report:

"The BeppoSAX GRBM/WFC error box of GRB 970508 was observed with the BeppoSAX Narrow Field Instruments (NFI) on May 9.1375 UT for about 36 000 s (about 5.7 hr after the gamma-ray burst). A previously unknown x-ray source, 1SAX J0653.8+7916, has been detected by the MECS (units 2 and 3) and LECS at R.A. = 6h53m46s.7, Decl. = +79o16'02" (equinox 2000.0; estimated error radius 50"). This position lies in the BeppoSAX WFC error box (IAUC 6649, 6654). The previously known source, 1RXS J065213.8+790855, lying outside the WFC error box, is also detected at R.A. = 6h52m14s.8, Decl. = +79o09'16", consistent within the errors with the ROSAT measurement. The countrates of 1SAX J0653.8+7916 were 0.0070 +/- 0.0007 and 0.0043 +/- 0.0006 count/s in the MECs (2-10 keV) and LECS (0.5-5 keV), respectively, corresponding to fluxes of (6.3 +/- 0.6) and (7.0 +/- 0.8) x 10E-13 erg cmE-2 sE-1. The optical transient reported on IAUC 6654 coincides, within the errors, with 1SAX J0653.8+7916. A further observation with the BeppoSAX NFI is foreseen on May 11 to study the temporal evolution."

E. Costa, M. Feroci, L. Piro, P. Soffitta, L. Amati, and M. N. Cinti, Istituto Astrofisica Spaziale, CNR, Frascati; F. Frontera and G. Zavattini, Universita di Ferrara; L. Nicastro and E. Palazzi, Istituto Tecnologie e Studio Radiazioni Extraterrestri, CNR, Bologna; A. Tesseri, G. Gandolfi, M. Smith, D. Ricci, and A. Coletta, BeppoSAX, Rome; J. Heise and J. in 't Zand, Space Research Organization of the Netherlands, Utrecht; and M. Tavani, Columbia Astrophysics Laboratory and Istituto di Fisica Cosmica e Tecnologie Relative, CNR, Milano, report:

"The BeppoSAX Gamma Ray Burst Monitor (GRBM) was triggered on May 8.904 UT. A quick-look analysis of the GRBM light curve shows a rather weak gamma-ray burst (GRB) lasting about 15 s. The intensity at its maximum is about 450 counts/s. The GRB was also detected by the Wide Field Camera unit 2 with a maximum countrate of about 130 counts/s. Taking into account the off-axis position, the peak flux corresponds to about 1 Crab. From the WFC image, we have derived a preliminary position of R.A. = 6h54m21s, Decl. = +79o15'.8 (equinox 2000.0), with a 5' error radius. One catalogued source lies within the GRB WFC error box: 1RXS J065213.8+790855 is about 8' from the GRB error-box center. Observations in all bands are solicited."

M. Feroci, E. Costa, and L. Piro, Istituto Astrofisica Spaziale, CNR, Frascati; F. Frontera and G. Zavattini, Universita di Ferrara; L. Nicastro and E. Palazzi, Istituto Tecnologie e Studio Radiazioni Extraterrestri, CNR, Bologna; G. Celidonio, G. Gandolfi, and A. Coletta, BeppoSAX, Rome; and J. Heise, and J. in 't Zand, Space Research Organization of the Netherlands, Utrecht, report:

The BeppoSAX Gamma Ray Burst Monitor (GRBM) was triggered on Apr. 2.930 UT. A quick-look analysis of the GRBM light curve shows a rather weak, highly structured gamma-ray burst (GRB) lasting > 100 s. The intensity at its maximum is about 300 counts/s. The gamma-ray burst was detected by the Wide Field Camera (WFC) number 1 with a similar time profile and a maximum countrate of about 70 counts/s. Taking into account the off-axis position, the peak flux corresponds to about 0.46 Crab. From the WFC image, we have derived a preliminary position of R.A. = 14h50m24s, Decl. = -69o18'.0 (equinox 2000.0), with a 12' error radius. A refined position will result from the off-line analysis. A BeppoSAX TOO pointing of the Narrow Field Instruments was performed starting on Apr. 3.270, just 8 hr after the GRB trigger time. Observations in all bands are solicited." J. Heise and J. in 't Zand, Space Research Organization of the Netherlands; E. Costa, Istituto di Astrofisica Spaziale, CNR, Frascati; and F. Frontera, Istituto Tecnologie e Studio Radiazioni Extraterrestri, CNR, Bologna, report on behalf of the BeppoSAX-WFC team: "GRB 970402 was localized in the field of Wide Field Camera 1 using the known positions of five other x-ray sources in the same field (e.g., Cir X-1, 4U 1254-63, and Cen X-3) as verification. The position of GRB 970402 is R.A. = 14h50m16s, Decl. = -69o19'.9 (equinox 2000.0), with an error-circle radius of 3'."

E. Costa, M. Feroci, L. Piro, and M. N. Cinti, Istituto di Astrofisica Spaziale (IAS), CNR, Frascati; F. Frontera and G. Zavattini, Universita di Ferrara; L. Nicastro, E. Palazzi, D. Dal Fiume, and M. Orlandini, Istituto Tecnologie e Studio Radiazioni Extraterrestri (ITESRE), CNR, Bologna; J. in 't Zand, J. Heise, and R. Jager, Space Research Organization of the Netherlands (SRON), Utrecht; A. Parmar and A. Owens, Space Science Department, ESTEC; S. Molendi, Istituto di Fisica Cosmica e Tecnologie Relative, CNR, Milano; G. Cusumano, M. C. Maccarone, and S. Giarrusso, Istituto di Fisica Cosmica e Applicazioni Informatica, CNR, Palermo; L. A. Antonelli, F. Fiore, P. Giommi, J. M. Muller, L. Salotti, G. Gennaro, M. Stornelli, G. Crisigiovanni, R. Ricci, and A. Coletta, BeppoSAX, Rome; and R. C. Butler, Agenzia Spaziale Italiana, Rome, report:

"The BeppoSAX GRBM/WFC error box of GRB 970228 (IAUC 6572) was observed with the BeppoSAX Narrow Field Instruments on Feb. 28.458 UT for 15~000 s (8 hr after the gamma-ray burst). A previously unknown intense x-ray source, SAX J0501.7+1146, has been detected by the MECS and LECS at the same position (R.A. = 5h01m44s, Decl. = +11o46'.7, equinox 2000.0; estimated error radius 50"). This position lies at the edge of the reported BeppoSAX WFC error box (IAUC 6572). The source flux is (2.8 +/- 0.4) x 10E-12 erg cmE-2 sE-1 in the MECS (2-10 keV) and (4.0 +/- 0.6) x 10E-12 erg cmE-2 sE-1 in the LECS (0.5-10 keV). The field was observed again on Mar. 3.734, and a source was detected at a position consistent with the previous one, but at a flux level lower by a factor of 20. Given this very peculiar time variability, we conclude that the new BeppoSAX x-ray source is related to GRB 970228."

D. A. Frail, National Radio Astronomy Observatory; S. R. Kulkarni, California Institute of Technology; E. Costa, M. Feroci, and L. Piro, IAS, Frascati; L. Nicastro, D. Dal Fiume, and E. Palazzi, ITESRE, Bologna; F. Frontera, Universita di Ferrara; and R. Jager and J. Heise, SRON, report:

"Observations at 20 cm with the Very Large Array on Mar. 1.03 and 2.16 UT, and at 6 cm on Mar. 4.04, centered on the gamma-ray burst position given on IAUC 6572, have detected a single, unresolved radio source in the error circle of the x-ray transient seen by Costa et al. (above). The radio source is at R.A. = 5h01m41s.68 +/- 0s.01, Decl. = +11o47'05".1 +/- 0".2 (equinox J2000.0). Flux densities measured on these three days are 0.80, 0.76, and 0.62 mJy, respectively, with errors of order 0.15 mJy."

E. Costa and M. Feroci, Istituto Astrofisica Spaziale, CNR, Frascati; F. Frontera and G. Zavattini, Universita di Ferrara; L. Nicastro and E. Palazzi, Istituto Tecnologie e Studio Radiazioni Extraterrestri, CNR, Bologna; G. Spoliti, L. Di Ciolo, A. Coletta, G. D'Andreta, and J. M. Muller, BeppoSAX, Rome; and R. Jager, J. Heise, and J. in 't Zand, Space Research Organization of the Netherlands, Utrecht, communicate:

"The BeppoSAX Gamma Ray Burst Monitor (GRBM) was triggered on Feb. 28.123620 UT. A quick-look analysis of the GRBM light curve shows a moderately intense, multi-peaked gamma-ray burst lasting about 80 s, with one major structured peak followed by three minor peaks. The first peak intensity at maximum is about 3700 counts/s, while the trailing peaks show a decreasing intensity from 600 to 150 counts/s. The gamma-ray burst was detected by the Wide Field Camera (WFC) number 1 with a similar time profile and a peak countrate of about 400 counts/s. Taking into account the off-axis position, the peak flux corresponds to about 0.23 Crab. From the WFC image, we have derived a preliminary position of R.A. = 5h01m57s, Decl. = +11 46'.4 (equinox 2000.0), with a 3' error radius. A BeppoSAX TOO pointing of the Narrow Field Instruments was performed starting on Feb. 28.458, just 8 hr after the GRB trigger time. The relevant data analysis is in progress. Observations in all bands are solicited."

R. C. Butler, Agenzia Spaziale Italiana, Rome; L. Piro, E. Costa, and M. Feroci (cf. IAUC 6533); F. Frontera and D. Dal Fiume, TESRE, CNR, Bologna; J. Heise and R. Jager; B. Sacco, IFCAI, CNR, Palermo; L. Chiappetti, IFCTR, CNR, Milan; A. Parmar, Space Science Department, ESTEC; L. A. Antonelli and D. Ricci, BeppoSAX, Rome; J. M. Muller, BeppoSAX, Rome, and SRON, Utrecht; and A. Coletta, C. De Libero, and L. Salotti, BeppoSAX, Rome, write:

"BeppoSAX pointed its Narrow Field Instruments on the estimated position of GRB 970111 (IAUC 6533) during Jan. 12.09-13.38 UT. A quick analysis of the data shows two sources within the BeppoSAX WFC error box: (a) R.A. = 15h28m46s.3, Decl. = +19o44'50" (equinox 2000.0), with a MECS 2-10-keV flux of 0.0025 counts/s (corresponding to 3.8 x 10E-13 erg cmE-2 sE-1) and a LECS flux 0.1-10-keV of 0.0037 counts/s (about 4.4 x 10E-13 erg cmE-2 sE-1); (b) R.A. = 15h28m48s.3, Decl. = +19o38'34", with a MECS flux (2-10 keV) of 0.0013 counts/s (about 1.9 x 10E-13 erg cmE-2 sE-1). The spectrum of source 'a' is considerably softer than that of source 'b'. As some systematic effects can still be present, an error radius of 1' must still be assumed. Though the detection is highly significant, the countrates can have an uncertainty of 30 percent, due to systematic effects and to the application of a spectrum-independent correction for rough flux estimation."

                                                  Circular No. 6538
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION


NEW X-RAY BURSTER

L. Piro, Istituto Astrofisica Spaziale (IAS), CNR, Frascati; J. Heise and R. Jager, Space Research Organization of the Netherlands (SRON), Utrecht; M. Feroci, IAS; G. D'Andreta, G. Spoliti, and A. Coletta, BeppoSAX, Rome; H. Muller, BeppoSAX, Rome, and SRON; and D. Ricci, BeppoSAX, Rome, write:

"On Jan. 13.295011 UT, the BeppoSAX Wide Field Camera No. 1 (WFC1) detected an x-ray burst in the range 2-20 keV, seen in the ratemeter as a single peak and showing a fast rise (on the order of 10 s) with an exponential decay lasting about 150 s. This event is likely to be an x-ray burster and not a gamma-ray burst, as it was not seen by the BeppoSAX Gamma Ray Burst Monitor. The derived position (R.A. = 12h49m50s, Decl. = -59o10'.8, equinox 2000.0; estimated 10' error radius) does not correspond to any catalogued source. The peak flux corresponds to about 1.9 Crab. The WFC1 observed the same field for about 40 000 s before and 2500 s after the event, with no positive detection, leading to an upper limit to the steady flux from the burst source of about 10 mCrab."

                                                  Circular No. 6533
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION


GRB 970111

E. Costa, M. Feroci, and L. Piro, Istituto Astrofisica Spaziale, C.N.R., Frascati; F. Frontera and G. Zavattini, Universita di Ferrara; L. Nicastro and E. Palazzi, Istituto Tecnologie e Studio Radiazioni Extraterrestri, C.N.R., Bologna; G. Gandolfi, M. Smith, A. Coletta, G. D'Andreta, and G. Spoliti, BeppoSAX Science Operation Center, Roma; and R. Jager and J. Heise, Space Research Organization of the Netherlands, Utrecht, communicate:

The BeppoSAX Gamma Ray Burst Monitor (GRBM) was triggered on Jan. 11.405556 UT. Quick-look analysis carried out at the BeppoSAX Science Operation Center shows the following. From the GRBM lightcurve, we see an intense gamma-ray burst lasting about 50 s, with two major peaks of similar intensity spaced 9 s apart, and a third peak after 17 s. The fluxes of the three peaks are about 4500, 5500, and 700 counts/s. The burst is in the field of Wide Field Camera (WFC) number 2 with a peak countrate of about 300 counts/s. Taking into account the off-axis position, the peak flux corresponds to about 4 Crab. From the WFC image, we have derived a first estimation of the position at R.A. = 15h28m24s, Decl. = +19o40'.0 (equinox 2000.0); we conservatively estimate a 10' error radius. The procedure for a TOO pointing of BeppoSAX Narrow Field Instruments has been started. Observations in all bands are solicited.

                                                  Circular No. 6480
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
 
 
GRB 960720

L. Piro, E. Costa, M. Feroci, and M. Cinti, Istituto Astrofisica Spaziale, CNR, Frascati; F. Frontera, D. Dal Fiume, L. Nicastro, M. Orlandini, and G. Pizzichini, Istituto Tecnologie e Studio delle Radiazioni Extraterrestri, CNR, Bologna; J. Heise and R. Jager, Space Research Organization of the Netherlands, Utrecht; F. Fiore, P. Giommi, A. Matteuzzi, and H. Muller, Beppo-SAX Scientific Data Center, Rome; A. Parmar, Space Science Department, ESTEC; B. Sacco, Istituto Fisica Cosmica ed Applicazioni Informatica, Palermo; S. Molendi, Istituto di Fisica Cosmica e Tecnologie Relative, Milano; and R. C. Butler, Agenzia Spaziale Italiana, Rome, report:

BeppoSAX observed the error box of GRB 960720 (IAUC 6467) during Sept. 3.715-4.708 UT for a total of 46 000 s with the MECS telescope and 26 000 s with the LECS telescope, and discovered a source in both telescopes within the WFC error box at R.A. = 17h29m26s.0, Decl. = +49o04'35" (equinox 2000.0), about 2'.9 off the center of the Beppo-SAX WFC error box and about 1'.6 off the ROSAT source (IAUC 6469). We estimate about 1' for the systematic error in position reconstruction. BeppoSAX and ROSAT positions are consistent within systematic and statistical errors. The LECS (0.1-2 keV) and MECS (1.5-10 keV) countrates are 0.0010 +/- 0.0002 and 0.0021 +/- 0.0004 count/s, respectively. Taking into account point-spread-function corrections and the instrumental response, we derive (based on preliminary calibrations) the following fluxes: F(0.1-2 keV) = (1.5 +/- 0.6) 10E-13 erg cmE-2 sE-1 and F(2-10 keV) = (2.5 +/- 0.5) 10E-13 erg cmE-2 sE-1. The LECS flux is approximately a factor of three greater than the ROSAT flux, assuming a power-law spectrum with an energy index of 1.3-1.5. The LECS/MECS countrate ratio is consistent with no significant absorption in addition to the galactic one (2.6 x 10E20 cmE-2). No other source brighter than about 1 x 10E-13 erg cmE-2 sE-1 is found within the 10' WFC error box. At least two other sources of flux between 1 and 3 x 10E-13 erg cmE-2 sE-1 lie at about 15'-20' from the center of the WFC error box. Assuming a value of (log N - log S) of active galactic nuclei from GINGA background fluctuations and recent ASCA data, we estimate the probability of detecting a source with a flux of 2E-13 erg cmE-2 sE-1 within a 5' radius as about 10 percent."

                                                  Circular No. 6467
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION


GAMMA-RAY BURST

L. Piro, E. Costa, M. Feroci, M. Cinti, Istituto Astrofisica Spaziale, CNR, Frascati; F. Frontera, D. Dal Fiume, M. Orlandini, G. Pizzichini, Istituto Tecnologie e Studio delle Radiazioni Extraterrestri, CNR, Bologna; J. Heise, R. Jager, Space Research Organization of the Netherlands (SRON), Utrecht; H. Muller, Beppo-SAX Scientific Data Center, Rome

On July 20, 1996 11:36:53 UT a gamma-ray burst was simultaneously detected in the gamma-ray burst monitor (GRBM, 60-600 keV) and one of the Wide Field Cameras (WFC) X-ray detectors (2-30 keV) aboard Beppo-SAX. The burst had a peak flux of about 1200 cts/s (2 ph cmE-2 sE-1) in the GRBM, and 90 cts/s (about 10E-8 erg cmE-2 sE-1) in the WFC, with a fluence ratio F(2-30 keV)/F(60-600keV) of about 0.02. The WFC provided an image of the field with a resolution of 5 arcmin (FWHM). We conservatively estimate a maximum error box radius of 10 arcmin, corresponding to the maximum systematic deviation currently found in position reconstruction. The burst position is ALPHA(2000)=17h29m36s, DELTA(2000)=+49 02' 12". It will be possible to refine the position to a 2.5 arcmin error box radius after the systematic residuals are calibrated. This position lies within 0.25 degrees from the center of the 2 degree error box of a simultaneous BATSE event (trigger #5545, BATSE team, private communication) A search from all catalogues available from several on-line services in the Beppo-SAX error box gave no results. The Palomar Digitized Plates show several sources in the error box, but no one of these is characterized by peculiar colors.

L. Piro, Istituto Astrofisica Spaziale, CNR, Frascati, R.C. Butler, Agenzia Spaziale Italiana, G. Boella, Istituto Fisica Cosmica e Tecnologie Relative, CNR, Milano, L. Scarsi, Istituto Fisica Cosmica e Applicazioni Informatica, CNR, Palermo, J.A.M. Bleeker, Space Research Organization of the Netherlands, Utrecht, A. Parmar, Space Science Department ESA, Noordwijk, L. Chiappetti, IFCTR, B. Sacco, S. Giarrusso, A. Santangelo, IFCAI, F. Frontera, D. Dal Fiume, Istituto Tecnologie Studio Radiazioni Extraterrestri, CNR, Bologna, E. Costa, IAS, R. Jager, J. Heise, SRON, P. Giommi, SAX Scientific Data Center, Roma, on behalf of the SAX Team

BeppoSAX successfully performed its first scientific observation by pointing Cyg X-1 from June 22 to June 25. All the instruments performed nominally and showed that the source remains in its high state with a soft spectrum in the 0.1-10 keV energy band with an intensity of about 1 Crab. Below 10 keV the spectral shape is similar to that observed by ASCA (IAUC 6415). A hard component with a flux of about 0.3 Crab is visible in the energy range 10-300 keV. The source intensity is variable with a peak amplitude of about 40% at low and high energies. Typical intensities observed by the different instruments are: LECS (0.1-10 keV)= 350 cts/s with a flux of 1.3e-8erg/cm2/s in the 0.1-2 KeV range; MECS (1-10 keV)= 430 cts/s with a flux of 1.1e-8 erg/cm2/s in the 2-10 keV range; HPGSPC (4-120 keV)= 140 cts/s with a flux of 1.1e-8 erg/cm2/s in the 4-34 keV range; PDS(15-300 keV)= 65 cts/s with a flux of 0.9e-8 erg/cm2/s in the 15-300 kev range; WFC(2-30 keV)= 170 cts/s with a flux of 1.6e-8 erg/cm2/s in the 2-30 keV range.

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