Repo Rts from Observ Ers

Total Page:16

File Type:pdf, Size:1020Kb

Repo Rts from Observ Ers R E P O RTS FROM OBSERV E R S Gamma-Ray Bursts1 – Pushing Limits with the VLT H. Pedersen1a, J.-L. Atteia2, M. Boer 2, K. Beuermann3, A.J. Castro-Tirado 4, A. Fruchter 5, J. Greiner 6, R. Hessman2, J. Hjorth1b, L. Kaper 7, C. Kouveliotou 7,8, N. Masetti 9, E. Palazzi 9, E. Pian9, K. Reinsch 2, E. Rol 7, E. van den Heuvel7, P. Vreeswijk7, R. Wijers 10 1aCopenhagen University Observatory, [email protected]; 1bCopenhagen University Observatory; 2CESR, Toulouse; 3Universitäts-Sternwarte, Göttingen; 4LAEFF-INTA, Madrid, and IAA-CSIC, Granada, Spain; 5Space Telescope Science Institute, Baltimore, USA; 6Astrophysikalisches Institut Potsdam; 7Astronomical Institute “Anton Pannekoek”, Amsterdam; 8NASA/USRA, Huntsville, Alabama, USA; 9Ist. TeSRE, CNR, Bologna; 10Dept. of Physics and Astronomy, SUNY Stony Brook, USA 1. Introduction they could not be associated with any SAX, the simultaneous detection of known object population, be it solar- gamma-ray bursts by the GRBM and “New kids on the block” – perhaps system objects, stars from the Milky one of the WFCs proved to be crucial in this is the best way to describe cosmic Way, distant galaxies, or even quasars. identification of their counterparts at gamma-ray bursts among the multitude Their g-ray spectra do not show any ob- lower energies thanks to the rapid (4–5 of object types that can be studied by vious emission or absorption lines that hours) and accurate (~ 3¢) localisation optical telescopes. When they pop up, could help identify the physical proc- afforded by the WFCs. they give a lot of trouble, and for a while esses responsible for the phenomenon. The good scheduling flexibility of take the attention from all the work in Many gamma-ray bursts are surpris- BeppoSAX allows a prompt repointing progress. In this report we will describe ingly bright (in g-rays, 0.1–100 MeV) – of the NFIs at the gamma-ray burst er- how ESO observers are making most for a short moment they easily out- ror circle and efficient search of the out of these exciting opportunities, and shine the sum of all other celestial high- X-ray counterpart. In case of NFI de- how the VLT promises to integrate energy sources. Conversely, near the tection of a gamma-ray burst afterglow space and ground-based observations instrumental detection limit there are candidate in X-rays, the error circle is in a way never achieved before. But fewer events than expected from a ho- reduced to ~ 50² in radius. Meanwhile, first a few words on the historical back- mogeneous distribution through an the rapid dissemination of the error cir- ground. Euclidean space. This lack of faint cle centroid co-ordinates makes fast bursts could be explained by either a follow-up at ground-based telescopes 2. The Basics large Galactic halo population, or a cos- possible. mological origin for gamma-ray bursts. The first error circle thus established Cosmic gamma-ray bursts (GRB) During the early years, it was repeat- was for GRB 960720, but came 45 days are studied from spacecraft, since g-ra- ed over and over that optical observa- after trigger and did not result in the diation does not penetrate the Earth’s tions were needed to finally clinch the finding of a counterpart (in ’t Zand et al., atmosphere. The first detection was distance question. Only thereby could 1997). The next, GRB 970111, was an- made in 1967, but the phenomenon be- one know the total (absolute) amount of nounced promptly, and search in the came publicly known only in 1973, energy emitted, and then start dis- initially large WFC error circle turned up when 16 events were published, in the cussing in earnest, what is the funda- a number of sources, none of which lay Astrophysical Journal. This first paper mental physical process in gamma-ray in the refined error circle established a led to a flurry of theoretical works; for bursts. few days later2. Then, ‘third time lucky’, several years, the rate with which mod- came the burst of 28 February 1997, els were proposed kept pace with the 3. The BeppoSAX Legacy which revolutionised the field. It was de- detection of new events. Likewise, on tected in the WFC and located to a 3¢ the experimental side, numerous initia- In the beginning of 1997, this wish error circle. Prompt reorientation of the tives were taken. To date, more than 60 was fulfilled. The previous year, an satellite and activation of the NFIs 10 spacecraft have carried successful Italian-Dutch consortium had launched hours after the burst led to the localisa- gamma-ray burst detectors. The most the Satellite per Astronomia X, SAX, tion of a bright, previously unknown e fficient was BATSE on board the nicknamed BeppoSAX after the Italian X-ray source (Costa et al., 1997). Compton Gamma-Ray Observatory. Cosmic-ray and X-ray astronomy pio- A second NFI observation 3 days lat- This instrument has detected about one neer Giuseppe Occhialini. er showed that the source had faded by event every day, on average, since its The satellite was primarily intended a factor of 20. Subsequent observa- launch in April 1991. to study the 0.1–300 keV spectrum of tions with the ASCA and ROSAT satel- The hallmark of gamma-ray bursts is galactic and extragalactic sources with lites confirmed that the source faded a diversity: durations can be anything be- four Narrow-Field Instruments (NFIs). with a power-law, I µ (t – t GRB) where tween a few milliseconds and several The scientific payload onboard Beppo- time is counted in days, and a ~ –1.3. minutes. Gamma-ray burst ‘light- SAX also includes a Gamma-Ray Burst This type of decay had indeed been curves’ take numerous shapes, from Monitor (GRBM, 40–700 keV, all-sky predicted by Mészáros and Rees smooth, single peaks to very jagged, coverage), which is the non-imaging (1997). In their “fireball” model, a mix- multi-peaked graphs. They come from anticoincidence system of the high-en- ture of matter and photons expands at ever new directions, and until recently ergy NFI (the PDS), and two coded- mask Wi d e-Field Cameras (WFCs, 2–26 keV, 40° ´ 40° field), pointing at 2In hindsight, the NFI follow-up observation of this 1 This year’s Annual Review of Astronomy and right angles with respect to the NFIs. event shows a faint source. This source is consis- Astrophysics will include a review paper on tent with being an afterglow, given what we have Gamma-Ray Bursts, authored by Jan van Paradijs, Although gamma-ray burst investiga- learnt of afterglows from later events, but was not Chryssa Kouveliotou, and Ralph Wijers. tion was a secondary task of Beppo- recognised as such at the time. 32 tance, a supernova would have peaked Key to this process is the distribution at magnitude R ~ 25.2; i.e. about 50 via internet of positions derived from times fainter than observed for the OT. SAX, RXTE and from the Interplanetary Network, IPN, (consisting of Ulysses 5. A Treasure Hunt of Sorts and NEAR, in addition to near-Earth de- tectors like BATSE, SAX, and Wind). It had thus become obvious, that This service is operated by Goddard ground-based observers can harvest Space Flight Center (NASA) and has beautiful and important results, by more than 400 clients.3 maintaining close links to the space By the time this article goes to press, community. some 18 low-energy (optical, infrared, In this way, observations can start radio) counterparts have been identi- within hours from a gamma-ray burst, fied, worldwide.4 In a similar but larger perhaps even faster, hence raising the number of cases, no optical counterpart expectation that a counterpart will be encountered brighter than the 21st magnitude found for GRB 970228. 3http://gcn.gsfc.nasa.gov Such targets of opportunity are now 4For details, see Jochen Greiner’s site http://www.aip.de/~jcg/grb.html The present colla- Figure 1: The first optically identified gam - pursued with high priority at many ob- boration plans to establish a web site with informa- ma-ray burst, GRB 970228. This image, ob - servatories, including La Silla, Paranal tion on its activities and results; the URLwill be pro- tained at the NTT on March 13, 1997, gave and the Hubble Space Telescope. vided later. the earliest indication that the source was lo - cated in a remote galaxy (van Paradijs et al., 1997). “A” marks the combined light of the Figure 2a: The after - optical transient and candidate host galaxy, glow of GRB 970228. later verified by Hubble Space Telescope ob - The decay of the af - servations. terglow emission, over a wide range of energies is shown from -r a y s to the high speed and makes the interstellar near infrared (K- medium radiate synchrotron emission band). Time is mea - when it impacts on it; thus it is exactly sured in seconds, like a supernova remnant, except rela- following the mo - tivistic speeds are involved. ment of the gam - ma-ray burst, 1997 February 28.1236 4. The First Optical Transient UT. The lines indi - cate the power-law The initial 3¢ localisation from prediction for a spe - BeppoSAX’s WFC allowed independ- cific blast wave mod - ent ground-based optical observations el (from Wi j e r s , to start 20.8 hours after the gamma-ray Rees, and Mészá - burst. The late Jan van Paradijs, and ros, 1997, with re - his two students, Titus Galama and cent data added). Paul Groot, took this opportunity to make the observation, which forever changed gamma-ray burst astronomy.
Recommended publications
  • The Optical Afterglow of GRB 000911: Evidence for an Associated Supernova??
    A&A 378, 996–1002 (2001) Astronomy DOI: 10.1051/0004-6361:20011282 & c ESO 2001 Astrophysics The optical afterglow of GRB 000911: Evidence for an associated supernova?? D. Lazzati1,S.Covino2, G. Ghisellini2,D.Fugazza2,S.Campana2,P.Saracco2,P.A.Price3,4,E.Berger3, S. Kulkarni3, E. Ramirez–Ruiz1,A.Cimatti5, M. Della Valle5, S. di Serego Alighieri5,A.Celotti6, F. Haardt7,G.L.Israel8, and L. Stella8 1 Institute of Astronomy, University of Cambridge, Madingley Road, CB3 0HA Cambridge, UK 2 Osservatorio Astronomico di Brera, Via Bianchi 46, 23807 Merate (Lc), Italy 3 Palomar Observatory, 105-24, California Institute of Technology, Pasadena, CA 91125, USA 4 Research School of Astronomy & Astrophysics, Mount Stromlo Observatory, Cotter Road, Weston, ACT 2611, Australia 5 Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy 6 SISSA/ISAS, via Beirut 4, 34014 Trieste, Italy 7 Universit`a dell’Insubria, Via Lucini 3, 22100 Como, Italy 8 Osservatorio Astronomico di Roma, Via Frascati 33, 00040 Monteporzio Catone, Italy Received 12 July 2001 / Accepted 12 September 2001 Abstract. We present photometric and spectroscopic observations of the late afterglow of GRB 000911, starting ∼1 day after the burst event and lasting ∼8 weeks. We detect a moderately significant re–brightening in the R, I and J lightcurves, associated with a sizable reddening of the spectrum. This can be explained through the presence of an underlying supernova, outshining the afterglow ∼30 days after the burst event. Alternative explanations are discussed. Key words. gamma rays: bursts – supernovae: general 1. Introduction (Djorgovskij et al. 1999), a moderate amount of multiband data but lacked spectroscopic coverge.
    [Show full text]
  • On the Association of Gamma-Ray Bursts with Supernovae Dieter H
    Clemson University TigerPrints Publications Physics and Astronomy Summer 7-24-1998 On the Association of Gamma-Ray Bursts with Supernovae Dieter H. Hartmann Department of Physics and Astronomy, Clemson University, [email protected] R. M. Kippen Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville & NASA/Marshall Space Flight Center & NASA/Marshall Space Flight Center M. S. Briggs Physics Department, University of Alabama in Huntsville & NASA/Marshall Space Flight Center J. M. Kommers Department of Physics and Center for Space Research, Massachusetts nI stitute of Technology C. Kouveliotou Universities Space Research Association & NASA/Marshall Space Flight Center See next page for additional authors Follow this and additional works at: https://tigerprints.clemson.edu/physastro_pubs Recommended Citation Please use publisher's recommended citation. This Article is brought to you for free and open access by the Physics and Astronomy at TigerPrints. It has been accepted for inclusion in Publications by an authorized administrator of TigerPrints. For more information, please contact [email protected]. Authors Dieter H. Hartmann, R. M. Kippen, M. S. Briggs, J. M. Kommers, C. Kouveliotou, K. Hurley, C. R. Robinson, J. van Paradijs, T. J. Galama, and P. M. Vresswijk This article is available at TigerPrints: https://tigerprints.clemson.edu/physastro_pubs/83 Re-Submitted to ApJL 24-Jul-98 On the Association of Gamma-Ray Bursts with Supernovae R. M. Kippen,1,2,3 M. S. Briggs,4,2 J. M. Kommers,5 C. Kouveliotou,6,2 K. Hurley,7 C. R. Robinson,6,2 J. van Paradijs,5,8 D. H. Hartmann,9 T.
    [Show full text]
  • Physical Parameters of GRB 970508 and GRB 971214 from Their
    SUBMITTED 22-APR-99 TO ASTROPHYSICAL JOURNAL, IN ORIGNAL FORM 26-MAY-98 Preprint typeset using LATEX style emulateapj PHYSICAL PARAMETERS OF GRB 970508 AND GRB 971214 FROM THEIR AFTERGLOW SYNCHROTRON EMISSION R.A.M.J. WIJERS1 AND T.J. GALAMA2 SUBMITTED 22-APR-99 to Astrophysical Journal, in orignal form 26-MAY-98 ABSTRACT We have calculated synchrotron spectra of relativistic blast waves, and find predicted characteristic frequencies that are more than an order of magnitude different from previous calculations. For the case of an adiabatically expanding blast wave, which is applicable to observed gamma-ray burst (GRB) afterglows at late times, we give expressions to infer the physical properties of the afterglow from the measured spectral features. We show that enough data exist for GRB970508to compute unambiguously the ambient density, n =0.03cm−3, and the blast wave energy per unit solid angle, =3 1052 erg/4π sr. We also compute the energy density in electrons and magnetic field. We find that they areE 12%× and 9%, respectively, of the nucleon energy density and thus confirm for the first time that both are close to but below equipartition. For GRB971214,we discuss the break found in its spectrum by Ramaprakash et al. (1998). It can be interpreted either as the peak frequency or as the cooling frequency; both interpretations have some problems, but on balance the break is more likely to be the cooling frequency. Even when we assume this, our ignorance of the self- absorption frequency and presence or absence of beaming make it impossible to constrain the physical parameters of GRB971214 very well.
    [Show full text]
  • Evidence for Supernova Light in All Gamma-Ray Burst Afterglow A
    Clemson University TigerPrints Publications Physics and Astronomy Winter 12-13-2004 Evidence for Supernova Light in all Gamma-Ray Burst Afterglow A. Zeh Thüringer Landessternwarte Tautenburg S. Klose Thüringer Landessternwarte Tautenburg Dieter H. Hartmann Department of Physics and Astronomy, Clemson University, [email protected] Follow this and additional works at: https://tigerprints.clemson.edu/physastro_pubs Recommended Citation Please use publisher's recommended citation. This Article is brought to you for free and open access by the Physics and Astronomy at TigerPrints. It has been accepted for inclusion in Publications by an authorized administrator of TigerPrints. For more information, please contact [email protected]. 22nd Texas Symposium on Relativistic Astrophysics at Stanford University, Dec. 13-17, 2004 Evidence for Supernova Light in All Gamma-Ray Burst Afterglows A. Zeh, S. Klose Thur¨ inger Landessternwarte Tautenburg, 07778 Tautenburg, Germany D. H. Hartmann Department of Physics and Astronomy, Clemson University, Clemson, SC 29634-0978 We present an update of our systematic analyses of all Gamma-Ray Burst (GRB) afterglow data, now published through the end of 2004, in an attempt to detect the predicted supernova light component. We fit the observed photometric light curves as the sum of an afterglow, an underlying host galaxy, and a supernova component. The latter is modeled using published UBV RI light curves of SN 1998bw as a template. The total sample of afterglows with established redshifts contains now 29 bursts (GRB 970228 - GRB 041006). For 13 of them a weak supernova excess (scaled to SN 1998bw) was found. In agreement with our earlier result [47] we find that also in the updated sample all bursts with redshift ∼< 0.7 show a supernova excess in their afterglow light curves.
    [Show full text]
  • 1 the X-Ray Telescope on Board Swift
    1 THE X-RAY TELESCOPE ON BOARD SWIFT: STATUS AND MAIN RESULTS G. Tagliaferri1, S. Campana1, G. Chincarini1,2, P. Giommi3, G. Cusumano4, D.N. Burrows5, J.E. Hill5,6, J.A. Kennea5, J.A. Nousek5, J.P. Osborne7, P.T. O’Brien7, A. Wells7, L. Angelini6, and on behalf of the XRT team1 1INAF-Osservatorio Astronomico di Brera, Via Bianchi 46, 23807 Merate, Italy 2Universita` degli Studi di Milano-Bicocca, P.za delle Scienze 3, 20126 Milano, Italy 3ASI Science Data Center, Via G. Galilei, 00044 Frascati, Italy 4INAF-IASF Palermo, Via U. La Malfa 153, 90146 Palermo, Italy 5Pennsylvania State University, 525 Davey Lab, University Park, PA 16802, USA 6NASA Goddard Space Flight Center, MD 20771, USA 7University of Leicester, Department of Physics and Astronomy, Leicester, LE 17 RH, UK ABSTRACT of the GRBs, if not all, had an associated X-ray after- glow only about 60% of them had also an optical after- glow, i.e. a good fraction of them were dark–GRBs. For The X-ray Telescope (XRT), on board the Swift satellite, a general review on these topics see Zhang & Meszaros provides: automated source detection and position with (2004) and Piran (2005). Therefore, it was clear that to few arcsecond accuracy within few seconds from target properly study the GRBs, and in particular the associ- acquisition; CCD spectroscopy and imaging capability ated afterglows, we needed a fast-reaction satellite capa- (0.2-10 keV), with the capability of detecting a milliCrab ble of detecting GRBs and of performing immediate mul- source in about 10 seconds; automatic adjusting of the tiwavelength follow-up observations, in particular in the CCD readout mode to optimize the science return as the X-ray and optical bands.
    [Show full text]
  • Lecture 19 Black Holes and Gamma-Ray Bursts
    Black holes in nature – end points of stellar evolution • In our galaxy alone, theory suggests 50 million black holes (2 SN per century for 1010 years ¼ of which make black holes • Most massive galaxies have massive black holes Lecture 19 at their centers (109 galaxies) • Dozens of black hole binary x-ray sources per Black Holes and galaxy – at least Gamma-Ray Bursts • One gravitational radiation detection so far http://apod.nasa.gov/apod/astropix.html They are out there… Some Properties of Black Holes Kinds of black holes: • Entirely defined by their mass, rotation rate, and charge. All memory of how the hole was made Mass Size is lost. Almost like an elementary particle. “Black holes Class have no hair” (Wheeler, Israel, Hawking, etc.) (solar masses) • Believed that all the mass is concentrated at the AGN Supermassive ~105 - 1010 0.001 - 10 AU center in a small quantum-mechanical singularity Intermediate ~1000 ~ R • The effective density of stellar mass black holes, as ? earth defined by their event horizons is very high, but there are supermassive black hole in active galactic nuclei Stellar ~10 ~30 km with average densities no greater than water. they are just XRBin very big (this ignores the central concentration in a singularity though.) The average density matters to tidal forces. ? Primordial Up to ~Moon Up to ~0.1 mm • The gravitational field of a black hole close to the event horizon is complicated, but by the time you are ⎛ 2GM ⎞ ⎛ M ⎞ RS = 2 = 2.96 km ⎜ ⎟ several Schwarzschild radii away, it is indistinguishable ⎜ c ⎟ M ⎝ ⎠ ⎝ ⎠ from that of an ordinary star.
    [Show full text]
  • Monte Carlo Simulations of GRB Afterglows
    ABSTRACT WARREN III, DONALD CAMERON. Monte Carlo Simulations of Efficient Shock Acceleration during the Afterglow Phase of Gamma-Ray Bursts. (Under the direction of Donald Ellison.) Gamma-ray bursts (GRBs) signal the violent death of massive stars, and are the brightest ex- plosions in the Universe since the Big Bang itself. Their afterglows are relics of the phenomenal amounts of energy released in the blast, and are visible from radio to X-ray wavelengths up to years after the event. The relativistic jet that is responsible for the GRB drives a strong shock into the circumburst medium that gives rise to the afterglow. The afterglows are thus intimately related to the GRB and its mechanism of origin, so studying the afterglow can offer a great deal of insight into the physics of these extraordinary objects. Afterglows are studied using their photon emission, which cannot be understood without a model for how they generate cosmic rays (CRs)—subatomic particles at energies much higher than the local plasma temperature. The current leading mechanism for converting the bulk energy of shock fronts into energetic particles is diffusive shock acceleration (DSA), in which charged particles gain energy by randomly scattering back and forth across the shock many times. DSA is well-understood in the non-relativistic case—where the shock speed is much lower than the speed of light—and thoroughly-studied (but with greater difficulty) in the relativistic case. At both limits of speed, DSA can be extremely efficient, placing significant amounts of energy into CRs. This must, in turn, affect the structure of the shock, as the presence of the CRs upstream of the shock acts to modify the incoming plasma flow.
    [Show full text]
  • Theory of Gamma-Ray Burst Emission in Light of BSAX Results
    1 Theory of Gamma-Ray Burst Emission in Light of BSAX Results⋆ M. Tavani a,b a IFCTR/CNR, via Bassini 15, I-20133 Milano (Italy). b Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027 (USA). We briefly discuss the theoretical implications of recent detections of gamma-ray bursts (GRBs) by BSAX. Relativistic shock wave theories of fireball expansion are challenged by the wealth of X-ray, optical and radio data obtained after the discovery of the first X-ray GRB afterglow. BSAX data contribute to address several issues concerning the initial and afterglow GRB emission. The observations also raise many questions that are still unsolved. The synchrotron shock model is in very good agreement with time-resolved broad-band spectra (2–500 keV) for the majority of GRBs detected by BSAX. 1. A Year of Surprise optical and radio data, and many problems re- main unsolved at the moment. We briefly discuss The discovery of X-ray afterglows by BSAX here some of the open issues. revolutionized the field of GRB research [8,14, BSAX showed for the first time that a sub- 35]. The discovery cought us by surprise. Cer- stantial fraction of GRB energy is dissipated in tainly, there was no theoretical prediction of hard the X-ray range at late times (hours, days, some- [14,51] high-energy emission lasting hours-days times weeks) after the main impulsive events. after the main events. ‘Pre-BSAX models’ of Are classical GRBs the tip of the iceberg of more GRB shock waves predicted a much faster decay complex radiation processes lasting much longer of the hard component produced by the initial than expected from the cooling timescales of ini- impulsive particle acceleration (e.g., [25]).
    [Show full text]
  • Rapid ROSAT Observations of Small Gamma-Ray Burst Error Boxes
    Rapid ROSAT Observations of small Gamma-Ray Burst Error Boxes Jochen Greiner Astrophysical Institute Potsdam, 14482 Potsdam, Germany Abstract. I summarize the use of the ROSAT satellite over the last months for the investigation of well localized GRB error boxes. In particular, I report about the attempts for and results of quick follow-up observations (including the GRBs localized with BeppoSAX and RXTE) with ROSAT with its capability to achieve 10′′ locations of X-ray afterglow sources. INTRODUCTION The discovery of X-ray afterglow emission with the narrow-field instruments of the BeppoSAX satellite (Costa et al. 1997) has given a dramatic boost to both, observations and theoretical investigations of gamma-ray bursts (GRBs) over the last few months. In particular, this finding has triggered a wealth of rapid follow-up observations in the X-ray, optical, infrared and radio bands. This has even lead to the development of a strategy of localizing the X-ray afterglow of strong GRBs with non-imaging X-ray instruments (scanning with the PCA onboard RXTE). Also, a procedure has been set up to recognize when individual dwells of the RXTE all-sky monitor cover BATSE burst locations and to derive arcmin size locations within a few hours (Smith et al. 1998). arXiv:astro-ph/9711207v1 18 Nov 1997 X-ray follow up observations are primarily performed with the ASCA and ROSAT satellites. While ASCA’s unique strengths are the very rapid response time (1–2 days) and the high spectral resolution of its X-ray CCD camera (Murakami et al. 1998), ROSAT can provide arcsec positioning and, due to its superb sensitivity, a rather long lever arm for studying the X-ray intensity decay up to 14 days after a GRB.
    [Show full text]
  • Reverse Shock Emission in Gamma-Ray Bursts Revisited
    Reverse Shock Emission in Gamma-ray Bursts Revisited He Gao,∗ Peter M´esz´aros Department of Astronomy and Astrophysics, Department of Physics Center for Particle and Gravitational Astrophysics, Institute for Gravitation and the Cosmos 525 Davey Lab, Pennsylvania State University, University Park, PA 16802, USA June 27, 2018 Abstract A generic synchrotron external shock model is the widely preferred paradigm used to interpret the broad-band afterglow data of gamma- ray bursts (GRBs), including predicted observable signatures from a reverse shock which have been confirmed by observations. Investiga- tions of the nature of the reverse shock emission can provide valuable insights into the intrinsic properties of the GRB ejecta. Here we briefly review the standard and the extended models of the reverse shock emis- sion, discussing the connection between the theory and observations, including the implications of the latest observational advances. 1 Introduction Gamma-ray bursts (GRBs), which are the most extreme explosive events in the universe, generally present two phenomenological emission phases: arXiv:1507.01984v1 [astro-ph.HE] 7 Jul 2015 an initial prompt γ-ray emission and a longer-lived broadband afterglow emission. Regardless of the nature of the progenitor and the central engine, the radiation of the GRBs is believed to be caused by the dissipation of the kinetic energy of a relativistic jet which is beamed towards Earth (for reviews, see Ref [1, 2, 3, 4, 5]). Although the detailed physics of the prompt γ-ray emission is still uncertain, mainly owing to the poorly understanding composition of the GRB jet (e.g., the degree of magnetization) [6], a generic ∗[email protected] 1 synchrotron external shock model is the most widely accepted paradigm for interpreting the broad-band afterglow data [7, 8, 9, 10, 11, 12].
    [Show full text]
  • Arxiv:Astro-Ph/0102371V1 21 Feb 2001 Rswt Esrdrdhfs Rubytems Motn U Important Most the Arguably Redshifts
    Accepted to The Astronomical Journal The Prompt Energy Release of Gamma-Ray Bursts using a cosmological k-correction Joshua S. Bloom Palomar Observatory 105–24, California Institute of Technology, Pasadena, CA 91125, USA Dale A. Frail National Radio Astronomy Observatory, Socorro, NM 87801, USA Re’em Sari Theoretical Astrophysics 130-33, California Institute of Technology , Pasadena CA 91125, USA ABSTRACT The fluences of gamma-ray bursts (GRBs) are measured with a variety of instruments in different detector energy ranges. A detailed comparison of the implied energy releases of the GRB sample requires, then, an accurate accounting of this diversity in fluence measurements which properly corrects for the redshifting of GRB spectra. Here, we develop a methodology to “k-correct” the implied prompt energy release of a GRB to a fixed co-moving bandpass. This allows us to homogenize the prompt energy release of 17 cosmological GRBs (using published redshifts, fluences, and spectra) to two common co-moving bandpasses: 20–2000 keV and 0.1 keV–10 MeV (“bolometric”). While the overall distribution of GRB energy releases does not change significantly by using a k- correction, we show that uncorrected energy estimates systematically undercounts the arXiv:astro-ph/0102371v1 21 Feb 2001 bolometric energy by ∼5% to 600%, depending on the particular GRB. We find that the median bolometric isotropic-equivalent prompt energy release is 2.19 ×1053 erg with an r.m.s. scatter of 0.80 dex. The typical estimated uncertainty on a given k-corrected energy measurement is ∼20%. Subject headings: cosmology: miscellaneous — cosmology: observations — gamma rays: bursts 1.
    [Show full text]
  • Iron Line Signatures in X-Ray Afterglows of GRB by Bepposax
    ASTRONOMY & ASTROPHYSICS SEPTEMBER 1999, PAGE 431 SUPPLEMENT SERIES Astron. Astrophys. Suppl. Ser. 138, 431–432 (1999) Iron line signatures in X-ray afterglows of GRB by BeppoSAX L. Piro1,E.Costa1,M.Feroci1, G. Stratta1, F. Frontera2,3,L.Amati2,D.DalFiume2, L.A. Antonelli4,5,J.Heise6, J. in ’t Zand6,A.Owens7,A.N.Parmar7,G.Cusumano8,M.Vietri9, and G.C. Perola9 1 Istituto di Astrofisica Spaziale, C.N.R., Roma, Italy 2 Istituto T.E.S.R.E., C.N.R., Bologna, Italy 3 Dipartimento di Fisica, Universita’ di Ferrara, Italy 4 BeppoSAX Science Data Center, Rome, Italy 5 Osservatorio Astronomico di Roma, Italy 6 Space Research Organization in the Netherlands, Utrecht, The Netherlands 7 Space Science Department of ESA, ESTEC 8 Istituto Fisica Cosmica e Appl. Calc. Informatico, C.N.R., Palermo, Italy 9 Dipartimento di Fisica, Universita’ Roma Tre, Roma, Italy Received March 16; accepted June 25, 1999 Abstract. We report the possible detection (99.3% of sta- The measurement of X-ray Fe lines emitted directly by tistical significance) of redshifted Fe iron line emission in the GRB or its afterglow could provide a direct measure- the X-ray afterglow of Gamma-ray burst GRB 970508 ob- ment of the distance and probe into the nature of the cen- served by BeppoSAX. Its energy is consistent with the tral environment (Perna & Loeb 1998; M´esz´aros & Rees redshift of the putative host galaxy determined from op- 1998; Boettcher et al. 1999; Ghisellini et al. 1998). Neutron tical spectroscopy. In contrast to the fairly clean environ- star – neutron star merging should happen in a fairly clean ment expected in the merging of two neutron stars, the environment, with line intensities much below the sensitiv- observed line properties would imply that the site of the ity of current experiments.
    [Show full text]