archive: SETI New Insights from Observations of Mysterious Gamma-Ray Burst

SETI New Insights from Observations of Mysterious Gamma-Ray Burst

Larry Klaes ( lklaes@bbn.com )
Wed, 19 May 1999 10:33:36 -0400

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>Date: Tue, 18 May 1999 19:56:09 +0200 (MET DST)
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>From: ESO Education and Public Relations Dept.
>
>Date: Tuesday, May 18, 1999
>
>Subject: ESO PR 08/99 and Photos 22a-g/99 (Observations of GRB 990510)
>
>----------------------------------------------------------------------------
>
>Text with all links is available on the ESO Website at URL:
>
>http://www.eso.org/outreach/press-rel/pr-1999/pr-08-99.html
>
>----------------------------------------------------------------------------
>
>Dear subscribers,
>
>the press release attached below includes important new results about
>the recent Gamma-Ray Burst GRB 990510 that were obtained with various
>ESO telescopes, notably the VLT. It reports the ongoing work of
>several groups of astronomers. For the latest news about the progress,
>please consult the links included in the text or visit the VLT
>Information page at: http://www.eso.org/outreach/info-events/ut1fl/.
>
>Kind regards,
>
>ESO EPR Dept.
>
>----------------------------------------------------------------------------
> Information from the European Southern Observatory
>
> ESO Press Release 08/99
>
> 18 May 1999 [ESO Logo]
>
> For immediate release
> ------------------------------------------------------------------------
>
>Southern Fireworks above ESO Telescopes
>
>New Insights from Observations of Mysterious Gamma-Ray Burst
>
>International teams of astronomers are now busy working on new and exciting
>data obtained during the last week with telescopes at the European Southern
>Observatory (ESO).
>
>Their object of study is the remnant of a mysterious cosmic explosion far
>out in space, first detected as a gigantic outburst of gamma rays on May 10.
>Gamma-Ray Bursters (GRBs) are brief flashes of very energetic radiation -
>they represent by far the most powerful type of explosion known in the
>Universe and their afterglow in optical light can be 10 million times
>brighter than the brightest supernovae [1]. The May 10 event ranks among the
>brightest one hundred of the over 2500 GRB's detected in the last decade.
>
>The new observations include detailed images and spectra from the VLT 8.2-m
>ANTU (UT1) telescope at Paranal, obtained at short notice during a special
>Target of Opportunity programme. This happened just over one month after
>that powerful telescope entered into regular service and demonstrates its
>great potential for exciting science. In particular, in an observational
>first, the VLT measured linear polarization of the light from the optical
>counterpart, indicating for the first time that synchrotron radiation is
>involved. It also determined a staggering distance of more than 7,000
>million light-years to this GRB.
>
>The astronomers are optimistic that the extensive observations will help
>them to better understand the true nature of such a dramatic event and thus
>to bring them nearer to the solution of one of the greatest riddles of
>modern astrophysics.
>
>A prime example of international collaboration
>
>The present story is about important new results at the front-line of
>current research. At the same time, it is also a fine illustration of a
>successful collaboration among several international teams of astronomers
>and the very effective way modern science functions.
>
>It began on May 10, at 08:49 hrs Universal Time (UT), when the Burst And
>Transient Source Experiment (BATSE) onboard NASA's Compton Gamma-Ray
>Observatory (CGRO) high in orbit around the Earth, suddenly registered an
>intense burst of gamma-ray radiation from a direction less than 100 from the
>celestial south pole. Independently, the Gamma-Ray Burst Monitor (GRBM) on
>board the Italian-Dutch BeppoSAX satellite also detected the event (see GCN
>GRB Observation Report 304 [2]). Following the BATSE alert, the BeppoSAX
>Wide-Field Cameras (WFC) quickly localized the sky position of the burst
>within a circle of 3 arcmin radius in the southern constellation Chamaeleon.
>It was also detected by other satellites, including the ESA/NASA Ulysses
>spacecraft, since some years in a wide orbit around the Sun.
>
>The event was designated GRB 990510 and the measured position was
>immediately distributed by BeppoSAX Mission Scientist Luigi Piro to a
>network of astronomers. It was also published on Circular No. 7160 of the
>International Astronomical Union (IAU).
>
>>From Amsterdam (The Netherlands), Paul Vreeswijk, Titus Galama, and Evert
>Rol of the Amsterdam/Huntsville GRB follow-up team (led by Jan van Paradijs)
>immediately contacted astronomers at the 1-meter telescope of the South
>African Astronomical Observatory (SAAO) (Sutherland, South Africa) of the
>PLANET network microlensing team, an international network led by Penny
>Sackett in Groningen (The Netherlands). There, John Menzies of SAAO and
>Karen Pollard (University of Canterbury, New Zealand) were about to begin
>the last of their 14 nights of observations, part of a continuous world-wide
>monitoring program looking for evidence of planets around other stars. Other
>PLANET sites in Australia and Tasmania where it was still nighttime were
>unfortunately clouded out (some observations were in fact made that night at
>the Mount Stromlo observatory in Australia, but they were only announced one
>day later).
>
>As soon as possible - immediately after sundown and less than 9 hours after
>the initial burst was recorded - the PLANET observers turned their telescope
>and quickly obtained a series of CCD images in visual light of the sky
>region where the gamma-ray burst was detected, then shipped them off
>electronically to their Dutch colleagues [3]. Comparing the new photos with
>earlier ones in the digital sky archive, Vreeswijk, Galama and Rol almost
>immediately discovered a new, relatively bright visual source in the region
>of the gamma-ray burst, which they proposed as the optical counterpart of
>the burst, cf. their dedicated webpage at
>http://www.astro.uva.nl/~titus/grb990510/ .
>
>The team then placed a message on the international Gamma-Ray Burster
>web-noteboard (GCN Circular 310), thereby alerting their colleagues all over
>the world. One hour later, the narrow-field instruments on BeppoSax
>identified a new X-Ray source at the same location (GCN Circular 311), thus
>confirming the optical identification.
>
>All in all, a remarkable synergy of human and satellite resources!
>
>Observations of GRB 990510 at ESO
>
>Vreeswijk, Galama and Rol, in collaboration with Nicola Masetti, Eliana
>Palazzi and Elena Pian of the BeppoSAX GRB optical follow-up team (led by
>Filippo Frontera) and the Huntsville optical follow-up team (led by Chryssa
>Kouveliotou), also contacted the European Southern Observatory (ESO).
>Astronomers at the this Organization's observatories in Chile were quick to
>exploit this opportunity and crucial data were soon obtained with several of
>the main telescopes at La Silla and Paranal, less than 14 hours after the
>first detection of this event by the satellite.
>
> [ESO PR Photo 22a/99] ESO PR Photo [ESO PR Photo 22b/99] ESO PR Photo
> 22a/99 22b/99
>
> [Preview - JPEG: 211 x 400 pix - [Preview - JPEG: 400 x 437 pix -
> 72k] 297k]
>
> [Normal - JPEG: 422 x 800 pix - [Normal - JPEG: 800 x 873 pix -
> 212k] 1.1M]
>
> [High-Res - JPEG: 1582 x 3000 pix - [High-Res - JPEG: 2300 x 2509 pix -
> 2.6M] 5.9M]
>
>
>
> Caption to PR Photo 22a/99: This wide-field photo was obtained with the
> Wide-Field Imager (WFI) at the MPG/ESO 2.2-m telescope at La Silla on May
> 11, 1999, at 08:42 UT, under inferior observing conditions (seeing = 1.9
> arcsec). The exposure time was 450 sec in a B(lue) filter. The optical
> image of the afterglow of GRB 990510 is indicated with an arrow in the
> upper part of the field that measures about 8 x 16 arcmin2. The original
> scale is 0.24 pix/arcsec and there are 2k x 4k pixels in the original
> frame. North is up and East is left.
>
> Caption to PR Photo 22b/99: This is a (false-)colour composite of the area
> around the optical image of the afterglow of GRB 990510, based on three
> near-infrared exposures with the SOFI multi-mode instrument at the 3.6-m
> ESO New Technology Telescope (NTT) at La Silla, obtained on May 10, 1999,
> between 23:15 and 23:45 UT. The exposure times were 10 min each in the J-
> (1.2 5m; here rendered in blue), H- (1.6 5m; green) and K-bands (2.2 5m;
> red); the image quality is excellent (0.6 arcsec). The field measures
> about 5 x 5 arcmin2; the original pixel size is 0.29 arcsec. North is up
> and East is left.
>
> [ESO PR Photo 22c/99] ESO PR Photo [ESO PR Photo 22d/99] ESO PR Photo
> 22c/99 22d/99
>
> [Preview - JPEG: 400 x 235 pix - [Preview - JPEG: 400 x 441 pix -
> 81k] 154k]
>
> [Normal - JPEG: 800 x 469 pix - [Normal - JPEG: 800 x 887 pix -
> 244k] 561k]
>
> [High-Res - JPEG: 2732 x 1603 pix - [High-Res - JPEG: 2300 x 2537 pix -
> 2.6M] 2.3M]
>
>
>
> Caption to PR Photo 22c/99: To the left is a reproduction of a short (30
> sec) centering exposure in the V-band (green-yellow light), obtained with
> VLT ANTU and the multi-mode FORS1 instrument on May 11, 1999, at 03:48 UT
> under mediocre observing conditions (image quality 1.0 arcsec).The optical
> image of the afterglow of GRB 990510 is easily seen in the box, by
> comparison with an exposure of the same sky field before the explosion,
> made with the ESO Schmidt Telescope in 1986 (right).The exposure time was
> 120 min on IIIa-F emulsion behind a R(ed) filter. The field shown measures
> about 6.2 x 6.2 arcmin2. North is up and East is left.
>
> Caption to PR Photo 22d/99: Enlargment from the 30 sec V-exposure by the
> VLT, shown in Photo 22c/99. The field is about 1.9 x 1.9 arcmin2. North is
> up and East is left.
>
>The data from Chile were sent to Europe where, by quick comparison of images
>from the Wide-Field Imager (WFI) at the MPG/ESO 2.2-m telescope at La Silla
>with those from SAAO, the Dutch and Italian astronomers found that the
>brightness of the suspected optical counterpart was fading rapidly; this was
>a clear sign that the identification was correct (GCN Circular 313).
>
>With the precise sky position of GRB 990510 now available, the ESO observers
>at the VLT were informed and, setting other programmes aside under the
>Target of Opportunity scheme, were then able to obtain polarimetric data as
>well as a very detailed spectrum of the optical counterpart.
>
>Comprehensive early observations of this object were also made at La Silla
>with the ESO 3.6-m telescope (CCD images in the UBVRI-bands from the
>ultraviolet to the near-infrared part of the spectrum) and the ESO 3.6-m New
>Technology Telescope (with the SOFI multimode instrument in the infrared
>JHK-bands). A series of optical images in the BVRI-bands was secured with
>the Danish 1.5-m telescope, documenting the rapid fading of the object.
>Observations at longer wavelengths were made with the 15-m Swedish-ESO
>Submillimetre Telescope (SEST).
>
>All of the involved astronomers concur that a fantastic amount of
>observations has been obtained. They are still busy analyzing the data, and
>are confident that much will be learned from this particular burst.
>
>The VLT scores a first: Measurement of GRB polarization
>
> [ESO PR Photo 22e/99] ESO PR Photo Caption to PR Photo 22e/99:
> 22e/99 Preliminary polarization measurement
> of the optical image of the
> [Preview - JPEG: 400 x 434 pix - afterglow of GRB 990510, as observed
> 92k] with the VLT 8.2-m ANTU telescope
> and the multi-mode FORS1 instrument.
> [Normal - JPEG: 800 x 867 pix - The abscissa represents the
> 228k] measurement angle; the ordinate the
> corresponding intensity. The
> sinusoidal curve shows the best fit
> to the data points (with error
> bars); the resulting degree of
> polarization is 1.7 1 0.2 percent.
>
>A group of Italian astronomers led by Stefano Covino of the Observatory of
>Brera in Milan, have observed for the first time polarization (some degree
>of alignment of the electric fields of emitted photons) from the optical
>afterglow of a gamma-ray burst, see their dedicated webpage at
>http://www.merate.mi.astro.it/~lazzati/GRB990510/ . This yielded a
>polarization at a level of 1.7 10.2 percent for the optical afterglow of GRB
>990510, some 18 hours after the gamma-ray burst event; the magnitude was R =
>19.1 at the time of this VLT observation. Independently, the Dutch
>astronomers Vreeswijk, Galama and Rol measured polarization of the order of
>2 percent with another data set from the VLT ANTU and FORS1 obtained during
>the same night.
>
>This important result was made possible by the very large light-gathering
>power of the 8.2-m VLT-ANTU mirror and the FORS1 imaging polarimeter.
>
>Albeit small, the detected degree of polarization is highly significant; it
>is also one of the most precise measurements of polarization ever made in an
>object as faint as this one. Most importantly, it provides the strongest
>evidence to date that the afterglow radiation of gamma-ray bursts is, at
>least in part, produced by the synchrotron process, i.e. by relativistic
>electrons spiralling in a magnetized region. This type of process is able to
>imprint some linear polarization on the produced radiation, if the magnetic
>field is not completely chaotic.
>
>The spectrum
>
> [ESO PR Photo 22f/99] ESO PR Photo Caption to PR Photo 22f/99: A
> 22f/99 spectrum of the afterglow of GRB
> 990510, obtained with VLT ANTU and
> [Preview - JPEG: 400 x 485 pix - the multi-mode FORS1 instrument
> 112k] during the night of May 10-11, 1999.
> Some of the redshifted absorption
> [Normal - JPEG: 800 x 969 pix - lines are identified and the
> 288k] stronger bands from the terrestrial
> atmosphere are also indicated.
>
>A VLT spectrum with the multi-mode FORS1 instrument was obtained a little
>later and showed a number of absorption lines, e.g. from ionized Aluminium,
>Chromium and neutral Magnesium. They do not arise in the optical counterpart
>itself - the gas there is so hot and turbulent that any spectral lines will
>be extremely broad and hence extremely difficult to identify - but from
>interstellar gas in a galaxy 'hosting' the GRB source, or from intergalactic
>clouds along the line of sight. It is possible to measure the distance to
>this intervening material from the redshift of the lines; astronomers
>Vreeswijk, Galama and Rol found z = 1.619 1 0.002 [4]. This allows to
>establish a lower limit for the distance of the explosion and also its total
>power.
>
>The numbers turn out to be truly enormous. The burst occurred at an epoch
>corresponding to about one half of the present age of the Universe (at a
>distance of about 7,000 million light-years [5]), and the total energy of
>the explosion in gamma-rays must be higher than 1.4 1053 erg, assuming a
>spherical emission. This energy corresponds to the entire optical energy
>emitted by the Milky Way in more than 30 years; yet the gamma-ray burst took
>less than 100 seconds.
>
>Since the optical afterglows of gamma-ray bursts are faint, and their flux
>decays quite rapidly in time, the combination of large telescopes and fast
>response through suitable observing programs are crucial and, as
>demonstrated here, ESO's VLT is ideally suited to this goal!
>
>The lightcurve
>
>Combining results from a multitude of telescopes has provided most useful
>information. Interestingly, a "break" was observed in the light curve (the
>way the light of the optical counterpart fades) of the afterglow. Some 1.5 -
>2 days after the explosion, the brightness began to decrease more rapidly;
>this is well documented with the CCD images from the Danish 1.5-m telescope
>at La Silla and the corresponding diagrams are available on a dedicated
>webpage at http://www.astro.ku.dk/~jens/grb990510/ at the Copenhagen
>University Observatory. Complete, regularly updated lightcurves with all
>published measurements, also from other observatories, may be found at
>another webpage in Milan at http://www.merate.mi.astro.it/~gabriele/990510/
> .
>
>This may happen if the explosion emits radiation in a beam which is pointed
>towards the Earth. Such beams are predicted by some models for the
>production of gamma-ray bursts. They are also favoured by many astronomers,
>because they can overcome the fundamental problem that gamma-ray bursts
>simply produce too much energy. If the energy is not emitted equally in all
>directions ("isotropically"), but rather in a preferred one along a beam,
>less energy is needed to produce the observed phenomenon.
>
>Such a break has been observed before, but this time it occurred at a very
>favourable moment, when the source was still relatively bright so that
>high-quality spectroscopic and multi-colour information could be obtained
>with the ESO telescopes. Together, these observations may provide an answer
>to the question whether beams exist in gamma-ray bursts and thus further
>help us to understand the as yet unknown cause of these mysterious
>explosions.
>
>Latest News
>
> [ESO PR Photo 22g/99] ESO PR Photo Caption to PR Photo 22g/99: V(isual)
> 22g/99 image of the sky field around GRB
> 990510 (here denoted "OT"), as
> [Normal - JPEG: 453 x 585 pix - obtained with the VLT ANTU telescope
> 304k] and FORS1 on May 18 UT during a 20
> min exposure in 0.9 arcsec seeing
> conditions. North is up and east is
> left.
>
>Further photometric and spectroscopic observations with the ESO VLT,
>performed by Klaus Beuermann, Frederic Hessman and Klaus Reinsch of the
>Gvettingen group of the FORS instrument team (Germany), have revealed the
>character of some of the objects that are seen close to the image of the
>afterglow of GRB 990510 (also referred to as the "Optical Transient" - OT).
>
>Two objects to the North are cool foreground stars of spectral types dM0 and
>about dM3, respectively; they are located in our Milky Way Galaxy. The
>object just to the South of the OT is probably also a star.
>
>A V(isual)-band image (PR Photo 22g/99) taken during the night between May
>17 and 18 with the VLT/ANTU telescope and FORS1 now shows the OT at
>magnitude V = 24.5, with still no evidence for the host galaxy that is
>expected to appear when the afterglow has faded sufficiently.
>
>Outlook
>
>The great distances (high redshifts) of Gamma-Ray Bursts, plus the fact that
>a 9th magnitude optical flash was seen when another GRB exploded on January
>23 this year, has attracted the attention of astronomers outside the GRB
>field. In fact, GRBs may soon become a very powerful tool to probe the early
>universe by guiding us to regions of very early star formation and the
>(proto)-galaxies and (proto)-clusters of which they are part. They will also
>allow the study of the chemical composition of absorbing clouds at very
>large distances.
>
>At the end of this year, the NASA satellite HETE-II will be launched, which
>is expected to provide about 50 GRB alerts per year and, most importantly,
>accurate localisations in the sky that will allow very fast follow-up
>observations, while the optical counterparts are still quite bright. It will
>then be possible to obtain more spectra, also of extremely distant bursts,
>and many new distance determinations can be made, revealing the distribution
>of intrinsic brightness of GRB's (the "luminosity function"). Other types of
>observations (e.g. polarimetry, as above) will also profit, leading to a
>progressive refinement of the available data.
>
>Thus there is good hope that astronomers will soon come closer to
>identifying the progenitors of these enormous explosions and to understand
>what is really going on. In this process, the huge light-collecting power of
>the VLT and the many other facilities at the ESO observatories will
>undoubtedly play an important role.
>
>Notes
>
>[1] Gamma-Ray Bursts are brief flashes of high-energy radiation. Satellites
>in orbit around the Earth and spacecraft in interplanetary orbits have
>detected several thousand such events since they were first discovered in
>the late 1960s.
>
>Earlier investigations established that they were so evenly distributed in
>the sky that they must be very distant (and hence very powerful) outbursts
>of some kind. Only in 1997 it became possible to observe the fading
>"afterglow" of one of these explosions in visible light, thanks to accurate
>positions available from the BeppoSAX satellite. Soon thereafter, another
>optical afterglow was detected; it was located in a faint galaxy whose
>distance could be measured. In 1998, a gamma-ray burst was detected in a
>galaxy over 8,300 million light-years away.
>
>Even the most exotic ideas proposed for these explosions, e.g. supergiant
>stars collapsing to black holes, black holes merging with neutron stars or
>other black holes, and other weird and wonderful notions have trouble
>accounting for explosions with the power of 10,000 million million suns.
>
>[2] The various reports issued by astronomers working on this and other
>gamma-ray burst events are available as GCN Circulars on the GRB Coordinates
>Network web-noteboard.
>
>[3] See also the Press Release, issued by SAAO on this occasion.
>
>[4] In astronomy, the redshift (z) denotes the fraction by which the lines
>in the spectrum of an object are shifted towards longer wavelengths. The
>observed redshift of a distant galaxy or intergalactic cloud gives a direct
>estimate of the universal expansion (i.e. the "recession velocity"). The
>detailed relation between redshift and distance depends on such quantities
>as the Hubble Constant, the average density of the universe, and the
>'Cosmological' Constant. For a standard cosmological model, redshift z = 1.6
>corresponds to a distance of about 7,000 million light-years.
>
>[5] Assuming a Hubble Constant H0 = 70 km/s/Mpc, mean density Omega0 = 0.3
>and a Cosmological Constant Lambda = 0.
>
> ------------------------------------------------------------------------
>
>How to obtain ESO Press Information
>
>ESO Press Information is made available on the World-Wide Web (URL:
>http://www.eso.org/outreach/press-rel/). ESO Press Photos may be reproduced,
>if credit is given to the European Southern Observatory.
>
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>
>