Launch Of Swift Research Articles

Long-term evolutions of the cyclotron line energies in Her X-1, Vela X-1, and Cen X-3 as observed with Swift/BAT

We study the long-term evolution of the centroid energy of cyclotron lines – often referered to as cyclotron resonance scattering features (CRSFs) – in Her X-1, Vela X-1, and Cen X-3, using survey observations of the Burst Alert Telescope onboard Swift. We find a significant decrease of the fundamental CRSF energy in Her X-1 and the first harmonic line energy in Vela X-1 since the launch of Swift in 2004 and until 2010 and 2012, respectively. In both sources, the decreases stopped at some time, with a quite stable centroid energy thereafter. Unlike in Her X-1 and Vela X-1, the CRSF energy in Cen X-3 does not show a long-term decrease. It is observed not to change for at least the past 14 yr. The long-term variation of the line energy is a direct way to investigate the magnetic field structure in the polar regions of pulsars. Our results may stimulate the development of theoretical models, especially regarding how the accreted mass accumulates in the accretion mound or how the magnetic field distorts around the polar cap.

VERY HIGH ENERGY OBSERVATIONS OF GAMMA-RAY BURSTS WITH STACEE

Gamma-ray bursts (GRBs) are the most powerful explosions known in the universe. Sensitive measurements of the high-energy spectra of GRBs can place important constraints on the burst environments and radiation processes. Until recently, there were no observations during the first few minutes of GRB afterglows in the energy range between 30 GeV and ~1 TeV. With the launch of the Swift GRB Explorer in late 2004, GRB alerts and localizations within seconds of the bursts became available. The Solar Tower Atmospheric Cherenkov Effect Experiment (STACEE) was a ground-based, gamma-ray telescope with an energy threshold of ~150 GeV for sources at zenith. At the time of Swift's launch, STACEE was in a rare position to provide >150 GeV follow-up observations of GRBs as fast as three minutes after the burst alert. In addition, STACEE performed follow-up observations of several GRBs that were localized by the HETE-2 and INTEGRAL satellites. Between 2002 June and 2007 July, STACEE made follow-up observations of 23 GRBs. Upper limits are placed on the high-energy gamma-ray fluxes from 21 of these bursts.

A Path to the Stars: The Evolution of the Species

During the last years, a number of telescopes have been dedicated to the followup of the GRBs. But after the Swift launch, the average observed intensity of the GRBs showed to be lower than thought before. Our experience with the robotic 60 cm REM telescope confirmed this evidence, with a large number of lost GRBs. Then, we proposed to study the feasibility of a 4 m fast pointing class telescope, equipped with a multichannel imagers, from Visible to Near Infrared. In this paper, we present the main result of the feasibility study we performed so far.

X-ray and UV observations of nova V598 Puppis between 147 and 255 days after outburst

Aims: The launch of Swift has allowed many more novae to be observed regularly over the X-ray band. Such X-ray observations of novae can reveal ejecta shocks and the nuclear burning white dwarf, allowing estimates to be made of the ejecta velocity. Methods: We analyse XMM-Newton and Swift X-ray and UV observations of the nova V598 Pup, which was initially discovered in the XMM-Newton slew survey. These data were obtained between 147 and 255 days after the nova outburst, and are compared with the earlier, brighter slew detection. Results: The X-ray spectrum consists of a super-soft source, with the soft emission becoming hotter and much fainter between days ~147 and ~172 after the outburst, and a more slowly declining optically thin component, formed by shocks with kT ~ 200-800 eV (corresponding to velocities of 400-800 km s^-1). The main super-soft phase had a duration of less than 130 days. The Reflection Grating Spectrometer data show evidence of emission lines consistent with optically thin emission of kT ~100 eV and place a limit on the density of the surrounding medium of log(n_e/cm^-3) < 10.4 at the 90 % level. The UV emission is variable over short timescales and fades by at least one magnitude (at lambda ~ 2246-2600 angstrom) between days 169 and 255.

Detectability of gamma-ray emission from classical novae with Swift/BAT

Context. Classical novae are expected to emit gamma rays during their explosions. The most important contribution to the early gamma-ray emission comes from the annihilation with electrons of the positrons generated by the decay of 13 Na nd 18 F. The photons are expected to be down-scattered to a few tens of keV, and the emission is predicted to occur some days before the visual discovery and to last∼2 days. Despite a number of attempts, no positive detections of such emission have been made, due to lack of sensitivity and of sky coverage. Aims. Because of its huge field of view, good sensitivity, and well-adapted (14−200 keV) energy band, Swift/BAT offers a new opportunity for such searches. BAT data can be retrospectively used to search for prompt gamma-ray emission from the direction of novae after their optical discovery. Methods. We have estimated the expected success rate for the detection with BAT of gamma rays from classical novae using a Monte Carlo approach. Searches were performed for emission from novae occurring since the launch of Swift. Results. Using the actual observing programme during the first 2.3 years of BAT operations as an example, and sensitivity achieved, we estimate the expected rate of detection of classical novae with BAT as ∼0.2−0. 5y r −1 , implying that several should be seen within a 10 yr mission. The search for emission in the directions of the 24 classical novae discovered since the Swift launch yielded no positive results, but none of these was known to be close enough for this to be a surprise. Detections of a recurrent nova (RS Oph) and a nearby dwarf nova (V455 And) demonstrate the efficacy of the technique. Conclusions. The absence of detections is consistent with the expectations from the Monte Carlo simulations, but the long-term prospects are encouraging given an anticipated Swift operating lifetime of ∼10 years.

Gamma-ray bursts in the Swift era

Gamma-ray burst (GRB) research has undergone a revolution in the last two years. The launch of Swift, with its rapid slewing capability, has greatly increased the number and quality of GRB localizations and x-ray and optical afterglow lightcurves. Over 160 GRBs have been detected, and nearly all have been followed up with the on-board narrow field telescopes. Advances in our understanding of short GRBs have been spectacular. The detection of x-ray afterglows has led to accurate localizations from ground based observatories, which have given host identifications and redshifts. Theoretical models for short GRB progenitors have, for the first time, been placed on a sound foundation. The hosts for the short GRBs differ in a fundamental way from the long GRB hosts: short GRBs tend to occur in non-star forming galaxies or regions, whereas long GRBs are strongly concentrated within star forming regions. Observations are consistent with a binary neutron star merger model, but other models involving old stellar populations are also viable. Swift has greatly increased the redshift range of GRB detection. The highest redshift GRBs, at z∼5–6, are approaching the era of reionization. Ground-based deep optical spectroscopy of high redshift bursts is giving metallicity measurements and other information on the source environment to much greater distance than other techniques. The localization of GRB 060218 to a nearby galaxy, and association with SN 2006aj, added a valuable member to the class of GRBs with a detected supernova. The prospects for future progress are excellent given the >10 year orbital lifetime of the Swift satellite.

The Swift γ-ray burst mission

Swift is a first-of-its-kind multiwavelength transient observatory for GRB astronomy. It has the optimum capabilities for the next breakthroughs in determining the origin of GRBs and their afterglows, as well as using bursts to probe the early Universe. Swift will also perform the first sensitive hard X-ray survey of the sky. The mission is being developed by an international collaboration and consists of three instruments, the Burst Alert Telescope (BAT), the X-Ray Telescope (XRT), and the Ultraviolet and Optical Telescope (UVOT). The BAT, a wide-field γ-ray detector, will detect >100 GRBs per year with a sensitivity five times that of BATSE. The sensitive narrow-field XRT and UVOT will be autonomously slewed to the burst location in 20–75 s to determine 0.3–5.0 ′′ positions and perform optical, UV, and X-ray spectrophotometry. Strong education/public outreach and follow-up programs will help to engage the public and astronomical community. The Swift launch is planned for 2004.

The Swift GRB MIDEX mission

Swift is a first-of-its-kind multiwavelength transient observatory for γ-ray burst astronomy. It has the optimum capabilities for the next breakthroughs in determining the origin of γ-ray bursts and their afterglows, as well as for using bursts to probe the early Universe. Swift will also monitor the soft gamma repeaters and perform the first sensitive hard X-ray survey of the sky. The mission is being developed by an international collaboration and consists of three instruments, the Burst Alert Telescope (BAT), the X-ray Telescope (XRT), and the Ultraviolet and Optical Telescope (UVOT). The BAT, a wide-field γ-ray detector, will detect >100 γ-ray bursts per year with a sensitivity 5× that of BATSE. The sensitive narrow-field XRT and UVOT will be autonomously slewed to the burst location within 20–70 s to determine 0.3–5.0″ positions and perform optical, UV, and X-ray spectrophotometry. Strong education/public outreach and follow-up programs will help to engage the public and the astronomical community. Swift launch is planned for late 2004.

Stability, Asymmetry, and Discontinuity: The Launch of European Monetary Union

ALTHOUGH STILL LESS than one year old as this volume goes to press, European Economic and Monetary Union (EMU) is already under trial, charged with at least three offenses. The first is false advertising: Europeans, it is claimed, did not get the strong, stable currency they were promised, for within seven months of its birth the euro had lost 13.5 percent of its value against the dollar. The second is obfuscation: markets are finding the signals from the new monetary institutions confusing and inconsistent, and a scarcity of relevant information--from delays in releasing reliable euro area--wide statistics to lack of access to the deliberations of the Governing Council--makes it difficult to forecast economic developments and to understand the policy conduct of the new European Central Bank (ECB). The third is lack of impartiality: the ECB's new policies are claimed to be exacerbating asymmetries between fast-growing and slow-growing countries and validating the presumption that the costs and benefits of monetary cohabitation are unfairly distributed among small and large member states. This paper espouses a rather different thesis. In terms of its impact on financial market integration and the ability of its institutions to cope with cyclical contingencies, EMU is performing well above expectations. And it is doing so even though persistent asymmetries across countries represent a threat to the ability of the new policy framework to guarantee economic stability and promote further integration in Europe. It is clearly premature to attempt even a first assessment of the new European monetary architecture--it will take quite a few years before the track record of the ECB becomes sufficiently long and rich for such an evaluation. This paper is instead devoted to the more modest task of casting light on early developments in the euro area and their potential implications for the future of EMU, surveying the main points in the current debate, noting contrasting positions, and evaluating those positions in light of the available evidence. Our synthetic but comprehensive overview of the first few months in the life of the euro is thus aimed at disentangling those facts, empirical evidence, and institutional details that we consider useful toward a balanced interpretation of the current monetary and financial evolution in Europe. The paper is organized as follows. We begin by placing our analysis of the swift launch of the euro in the context of the macroeconomic convergence and integration that took place in Europe following the 1992-93 crisis of the European Monetary System (EMS). We then discuss the monetary strategies of the European System of Central Banks (ESCB), reviewing the official positions taken and the main criticisms leveled in the recent debate. Next we focus on the instruments of monetary policy in the euro area and on liquidity management and money market integration. We then present an update of developments in the bond and equity markets and a preliminary assessment of public debt management strategies by the eleven independent sovereign states coexisting in the euro area. We go on to deal with some open issues in the euro area banking sector, comment on the behavior of the euro in the currency markets, and analyze asymmetries across European regions and their implications for centralized monetary policy. Finally, we review the process of fiscal consolidation and the debate on the code of budgetary discipline in Europe.(1) The Launch of the Euro in Historical Perspective From a technical standpoint, the euro was born on December 31, 1998. That was the date when the fixed conversion rates among euro area currencies were determined, and thus when the national currencies were demoted to nondecimal denominations of the new currency.(2) It was also the start of the changeover weekend, during which clearing and settlement systems were retooled and trading positions and accounts redenominated from the old currencies into euros. …