5 pages including figures, in conference proceedings A Population Explosion: The Nature and Evolution of X-ray Binaries in Diverse Environments, eds. Bandyopadhyay, Wachter, Gelino, & Gelino
Simultaneous multiwavelength studies of X-ray binaries have been remarkably successful and resulted in improved physical constraints, a new understanding of the dependence of mass accretion rate on X-ray state, as well as insights on the time-dependent relationship between disk structure and mass-transfer rate. I will give some examples of the tremendous gains we have obtained in our understanding of XRBs by using multiwavelength observations. I will end with an appeal that while Spitzer cryogens are still available a special effort be put forth to obtaining coordinated observations including the mid-infrared: Whereas the optical and near-IR originate as superpositions of the secondary star and of accretion processes, the mid-IR crucially detects jet synchrotron emission from NSs that is virtually immeasurable at other wavelengths. A further benefit of Spitzer observations is that mid-infrared wavelengths can easily penetrate regions that are heavily obscured. Many X-ray binaries lie in the Galactic plane and as such are often heavily obscured in the optical by interstellar extinction. The infrared component of the SED, vital to the study of jets and dust, can be provided {\it only} by Spitzer; in the X-rays we currently have an unprecedented six satellites available and in the optical and radio dozens of ground-based facilities to complement the Spitzer observations.
As the highest-energy photons, gamma rays have an inherent interest to astrophysicists and particle physicists studying high-energy, nonthermal processes. Gamma-ray telescopes complement those at other wavelengths, especially radio, optical, and X-ray, providing the broad, mutiwavelength coverage that has become such a powerful aspect of modern astrophysics. Multiwavelength techniques of various types have been developed to help identify and explore unidentified gamma-ray sources. This overview summarizes the ideas behind several of these methods.
Multiwavelength observations may help us understand the physical nature of the ultraluminous X-ray sources (ULXs) found in external galaxies. Enabled by the arcsecond X-ray source positions now available from Chandra, there has been significant recent progress in the identification of optical and radio counterparts to ULXs. Recent results are reviewed on the identification of optical stellar counterparts to ULXs, the relation between ULXs and regions of active star formation, the study of optical nebular counterparts to ULXs, and the estimation of the luminosity of ULXs via their influence on …
Gamma-ray astrophysics depends in many ways on multiwavelength studies. The Gamma-ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT) Collaboration has started multiwavelength planning well before the scheduled 2007 launch of the observatory. Some of the high-priority multiwavelength needs include: (1) availability of contemporaneous radio and X-ray timing of pulsars; (2) expansion of blazar catalogs, including redshift measurements; (3) improved observations of molecular clouds, especially at high galactic latitudes; (4) simultaneous broad-band blazar monitoring; (5) characteriz…
High-energy gamma rays are a valuable tool for studying particle acceleration and radiation in the magnetospheres of energetic pulsars. The seven or more pulsars seen by instruments on the Compton Gamma Ray Observatory (CGRO) show that: the light curves usually have double-peak structures (suggesting a broad cone of emission); gamma rays are frequently the dominant component of the radiated power; and all the spectra show evidence of a high-energy turnover. For all the known gamma-ray pulsars, multiwavelength observations and theoretical models based on such observations offer the prospect of …
An overview is given of multiwavelength observations of young supernova remnants, with a focus on the observational signatures of efficient cosmic ray acceleration. Some of the effects that may be attributed to efficient cosmic ray acceleration are the radial magnetic fields in young supernova remnants, magnetic field amplification as determined with X-ray imaging spectroscopy, evidence for large post-shock compression factors, and low plasma temperatures, as measured with high resolution optical/UV/X-ray spectroscopy. Special emphasis is given to spectroscopy of post-shock plasma's, which off…
Our recent progress on time-dependent modeling of the multiwavelength spectra and variability of blazars with leptonic and hadronic jet models is reviewed. Special emphasis is placed on X-ray spectral variability of low-frequency peaked (LBLs) and intermediate BL Lac objects (IBLs). As an example, recent observational and modeling results of an extensive multiwavelength campaign of BL Lacertae in 2000 are presented. It is demonstrated how combined spectral and variability modeling of LBLs and IBLs can significantly constrain emission models and potential variability scenarios. In the case of B…
The optical-UV and X-ray instruments on-board XMM-Ndewton provide an excellent opportunity to perform simultaneous observations of violently variable objects over a broad wavelength range. The UV and X-ray bright BL Lac object PKS 2155-304 has been repeatedly observed with XMM-Ndewton about twice per year. In this paper, we present a detailed analysis of the simultaneous multiwavelength variability of the source from optical to X-rays, based on the currently available XMM-Ndewton observations. These observations probed the intra-day multiwavelength variability at optical-UV and X-ray wavelengt…
We present X-ray and optical observations of CXOMP J213945.0-234655, a high redshift (z=4.93) quasar discovered through the Chandra Multiwavelength Project (ChaMP). This object is the most distant X-ray selected quasar published, with an X-ray luminosity of L(X)=5.9x10^44 erg/s (measured in the 0.3-2.5 keV band and corrected for Galactic absorption). CXOMP J213945.0-234655 is a g' dropout object (>26.2), with r'=22.87 and i'=21.36. The rest-frame X-ray to optical flux ratio is similar to quasars at lower redshifts and slightly X-ray bright relative to z>4 optically-selected quasars observed wi…
The vast majority of the high-energy gamma-ray sources discovered by EGRET are still unidentified. Percentages range from 50% at high galactic latitudes, where blazars are responsible for almost all identified sources, to more than 90% near the galactic plane, where isolated neutron stars appear to be the only certified class of sources of high energy gamma-rays. In spite of all the efforts devoted to the identification problem, the only success story, so far, appears to be the chase for Geminga, where X-rays led the way to eventual optical identification. Similar searches are now starting to …
PG 1553+11 was the target of a coordinated three week multiwavelength campaign during 2003 April and May. A significant X-ray flare was observed during the second half of this campaign. Although no optical flare was recorded during the X-ray campaign, optical observations obtained immediately prior to the campaign displayed a higher flux than that recorded during the campaign. An optical flare was observed a few days after the end of the X-ray campaign and may be related to the X-ray flare. Radio observations were made at three frequencies, with no significant changes in flux detected near the…
We report multiwavelength observations of the two soft X-ray transients (SXTs) XTE J1859+226 and XTE J1118+480, which we observed with HST, RXTE and UKIRT. The two sources exhibited very different behaviour. XTE J1859+226 showed a thermal-viscous disc instability outburst modified by irradiation. XTE J1118+480, which we also observed with EUVE since it is located at a very high galactic latitude and suffers from very low extinction, is much more unusual. It exhibits i) a low X-ray to optical flux ratio and ii) a strong non-thermal contribution throughout the spectrum, which is likely to be due…
We report on the first results of a multi-wavelength approach to test the hypothesis that the X-ray emission from intermediate-mass stars is generated by late-type magnetically active companions. Our high spatial resolution observations of A/B-type stars in the IR using adaptive optics uncover hypothetical companion stars at arcsecond separations from the primary. The same targets are then followed-up in X-rays with Chandra to pinpoint the X-ray source. Finally, those A/B-type stars that are still detected with Chandra are studied with IR spectroscopy, where we search for temperature sensitive…
A few nearby interacting galaxies are known that host elevated number of ultraluminous X-ray sources. Here we report the results of a multiwavelength study of the X-ray source population in the field of the interacting pair of galaxies NGC5774/NGC5775. A total of 49 discrete sources are detected, including 12 ultraluminous X-ray source candidates. X-ray source positions are mapped onto optical and radio images to search for potential counterparts. Twelve sources in the field have optical counterparts. Optical colors are used to differentiate these sources, which are mostly located outside the …
We report optical and infrared observations of the massive X-ray binary system 4U1145-619 (V801 Cen) which show that the circumstellar disc of the Be star component is in decline. Infrared J,H,K,L magnitudes of V801Cen have been monitored from 1993 March to 1996 April. H alpha spectra have been obtained throughout the same period. We find that both the infrared excess and the Balmer emission have been in decline throughout the period of observations. A 13 year optical and X-ray history of the source has been collated, revealing a possible correlation between the optical and X-ray activity. In …
We present the results of a multiwavelength monitoring campaign targeting the gamma-ray source 2CG 135+1 in an attempt to confirm the association of this object with the radio/Be/X-ray binary system LSI +61o 303. The campaign included simultaneous radio, optical, infrared, and hard x-ray/gamma-ray observations carried out with a variety of instruments, covering (not continously) almost three binary cycles of LSI +61o 303 during the period April-July 1994. Three separate OSSE observations of the gamma-ray source were carried out, covering different phases of the radio lightcurve. Hard X-ray/gam…
We present multiwavelength observations of the newly discovered X-ray transient XTE J1118+480 obtained in the rising phase of the 2000 April outburst. This source is located at unusually high Galactic latitude and in a very low absorption line of sight. This made the first EUVE spectroscopy of an X-ray transient outburst possible. Together with our HST, RXTE, and UKIRT data this gives unprecedented spectral coverage. We find the source in the low hard state. The flat IR-UV spectrum appears to be a combination of optically thick disk emission and flat spectrum emission, possibly synchrotron, wh…
We present X-ray, radio, and infrared observations of the 68 ms pulsar PSR J1420-6048 and its surrounding nebula, a possible counterpart of the gamma-ray source GeV J1417-6100/3EG J1420-6038. Pulsed X-ray emission at the radio period is marginally detected by ASCA from a source embedded in the hard spectrum X-ray nebula AX J1420.1-6049. At radio wavelengths, the pulsar is found to be strongly linearly and circularly polarized, and the polarization sweep is measured. A comparison of high resolution ATCA radio imaging of the Kookaburra's upper wing (G313.6+0.3), which contains the pulsar and the…
Recent X-ray surveys have clearly demonstrated that a population of optically dull, X-ray bright galaxies is emerging at 2-10 keV fluxes of the order of 10^{-14} erg cm^{-2} s^{-1}. Although they might constitute an important fraction of the sources responsible for the hard X-ray background, their nature is still unknown. With the aim to better understand the physical mechanisms responsible for the observed properties, we have started an extensive program of multiwavelength follow-up observations of hard X-ray, optically quiet galaxies discovered with XMM-Newton. Here we report the results of …
Most counterparts of the identified low-latitude gamma-ray sources are Isolated Neutron Stars (INSs). They are characterized by an extremely high value of the X/optical flux ratio, therefore a systematic X-ray/optical coverage of the fields of unidentified low-latitude gamma-ray sources is the best way to unveil possible INS counterparts. Since the low-latitude sources are heavily affected by the interstellar absorption in both the X-ray and optical bands, we decided to apply the above strategy to two middle-latitude EGRET sources, which could belong to a local galactic population: 3EG J0616-3…
We report here on multiwavelength observations of the two new soft X-ray transients (SXTs) XTE J1859+226 and XTE J1118+480, which we observed with HST/RXTE/UKIRT. For XTE J1118+480 we also used EUVE since it is located at a very high galactic latitude and suffers from very low extinction. The two sources exhibited very different behaviour. XTE J1859+226 seems quite normal and therefore a good object for testing the accretion mechanisms in place during the outbursts, XTE J1118+480 is much more unusual because it exhibits i) a low X-ray to optical ratio and ii) a strong non-thermal contribution …
We present an X-ray and optical analysis of a 2-8 keV flux limited (fx > 10e-14 erg s^-1 cm^-2) sample of 126 AGN detected in 16 Chandra fields. This work represents a small though significant subset of the Chandra Multiwavelength Project (ChaMP). We have chosen this limiting flux to have a reasonable degree of completeness (50%) in our optical spectroscopic identifications. The optical counterparts of these AGN are characterized as either broad emission line AGN (BLAGN; 67%), narrow emission line galaxies (NELG; 22%) or absorption line galaxies (ALG; 11%) without any evidence of an AGN signat…
In April-May 2003, the blazar 1ES 1959+650 showed an increased level of X-ray activity. This prompted a multiwavelength observation campaign with the Whipple 10 m gamma-ray telescope, the Rossi X-ray Timing Explorer, the Bordeaux Optical Observatory, and the University of Michigan Radio Astrophysical Observatory. We present the multiwavelength data taken from May 2, 2003 to June 7, 2003 and compare the source characteristics with those measured during observations taken during the years 2000 and 2002. The X-ray observations gave a data set with high signal-to-noise light curves and energy spec…
In May 1994 the BL Lac object PKS 2155-304 was observed continuously for ~10 d with IUE and EUVE and for 2 d with ASCA, as well as with ROSAT and with ground- based radio, IR, and optical telescopes. The light curves show a well-defined X-ray flare (x2 increase in 1/2 d, with similar decay) followed by a broader, lower amplitude EUV flare ~1 day later, and a broad, low-amplitude UV flare ~2 d later (amplitude ~35%, duration >2 d). In the preceding week there was at least one X-ray flare of comparable amplitude or perhaps ongoing stochastic X-ray variations. An extremely rapid change in UV flux…
H.E.S.S. observations of the old-age (>10^4yr; ~0.5deg diameter) composite supernova remnant (SNR) W 28 reveal very high energy (VHE) gamma-ray emission situated at its northeastern and southern boundaries. The northeastern VHE source (HESS J1801-233) is in an area where W 28 is interacting with a dense molecular cloud, containing OH masers, local radio and X-ray peaks. The southern VHE sources (HESS J1800-240 with components labelled A, B and C) are found in a region occupied by several HII regions, including the ultracompact HII region W 28A2. Our analysis of NANTEN CO data reveals a dense m…
Using a simple unification model for AGN, with a fixed ratio of obscured to unobscured AGN of 3:1, we explain the X-ray, optical and infrared properties of the X-ray sources in the GOODS fields. That is, the GOODS data are consistent with the existence of a large population of obscured AGN out to high redshifts. About half of these are so obscured that they are missed even by hard X-ray observations, and are detected only in deep infrared observations. The previously reported decreasing trend of obscured to total AGN ratio with increasing X-ray luminosity can be explained entirely as a selecti…
Galaxy groups have been under-studied relative to their richer counterparts -- clusters. The Group Evolution Multiwavelength Study (GEMS) aims to redress some the balance. Here we describe the GEMS sample selection and resulting sample of 60 nearby (distance < 130 Mpc) galaxy groups and our multiwavelength dataset of X-ray, optical and HI imaging. ROSAT X-ray images of each group are presented. GEMS also utilizes near-infrared imaging from the 2MASS survey and optical spectra from the 6dFGS. These observational data are complemented by mock group catalogues generated from the latest LCDM simul…
The multiwavelength spectra of blazars appear to be dominated by nonthermal emission from a relativistic jet oriented close to the line of sight. The recent detection of many blazars at gamma-ray energies strongly supports this scenario. High quality multiwavelength monitoring data for the brightest one or two blazars suggest the optical through X-ray continuum is synchrotron emission from an inhomogeneous jet. The gamma-rays are likely due to Compton scattering of lower energy photons, either from within the jet or from the surrounding gas. The physical properties of the jet and the way in wh…
We report the results of simultaneous multiwavelength observations of the X-ray transient source SWIFT J1753.5-0127 performed with INTEGRAL, RXTE, NTT, REM and VLA on 2005 August 10-12. The source, which underwent an X-ray outburst since 2005 May 30, was observed during the INTEGRAL Target of Opportunity program dedicated to new X-ray novae located in the Galactic Halo. Broad-band spectra and fast timing variability properties of SWIFT J1753.5-0127 are analyzed together with the optical, near infra-red and radio data. We show that the source was significantly detected up to 600 keV with Compto…
We present an analysis of contemporaneous photospheric, chromospheric and coronal structures on the highly active K-dwarf star BO Mic (Speedy Mic). We localize a moderate flare in the stellar atmosphere and study its energetics, size and thermal behaviour. The analysis is based on strictly simultaneous X-ray, UV- and optical observations carried out by XMM-Newton and the VLT. We use Doppler imaging and related methods for the localization of features. Based on X-ray spectroscopy we study the the coronal plasma in and outside the flare. The flare emits in X-rays and UV, but is not detected in w…
The contribution of an astrophysics group based in Milan to the science with the IUE satellite during its almost 20 years lifetime has focussed on high energy sources, of both galactic (LMXRB, HMXRB, and black hole candidates) and extragalactic (AGN) nature. The results of this long term research and in particular of the latest multiwavelength campaigns conducted simultaneously with IUE are reviewed here.
Simultaneous multiwavelength observations were conducted for the BL Lac object 1ES1959+650 in a steady state in May 2006 with the MAGIC telescope and the X-ray satellites Suzaku and Swift. Swift can also provide multi-filter photometry in the UV-optical band. The source was clearly detected in all observed energy bands, from the optical to TeV. With respect to previous observations the source was in a low state in the very high energy (VHE) band (~10% Crab flux above 300 GeV) but in a relatively high state in the X-ray band. The light curves showed rather stable activities, with no significant…
We report on a multiwavelength campaign on the TeV gamma-ray blazar Markarian (Mrk) 421 performed during December 2002 and January 2003. These target of opportunity observations were initiated by the detection of X-ray and TeV gamma-ray flares with the All Sky Monitor (ASM) on board the Rossi X-ray Timing Explorer (RXTE) and the 10 m Whipple gamma-ray telescope.The campaign included observational coverage in the radio (University of Michigan Radio Astronomy Observatory), optical (Boltwood, La Palma KVA 0.6m, WIYN 0.9m), X-ray (RXTE pointed telescopes), and TeV gamma-ray (Whipple and HEGRA) ban…
This paper combines data from the three preceding papers in order to analyze the multi-waveband variability and spectral energy distribution of the Seyfert~1 galaxy NGC~4151 during the December 1993 monitoring campaign. The source, which was near its peak historical brightness, showed strong, correlated variability at X-ray, ultraviolet, and optical wavelengths. The strongest variations were seen in medium energy ($\sim$1.5~keV) X-rays, with a normalized variability amplitude (NVA) of 24\%. Weaker (NVA = 6\%) variations (uncorrelated with those at lower energies) were seen at soft $γ$-ray ener…
Observations at high energies yield important information on the structure and nature of AGN; when coupled with deep optical and near-infrared (photometric and spectroscopic) follow-up, they provide constraints on the mass of the growing black holes and, therefore, are essential to better understand the nature of the various components of the X-ray background light and can be used as test for the accretion paradigm. Conversely, optical and near-infrared surveys of galaxies are crucial to discriminate between different cosmological scenarios (e.g. hierarchical or monolithic growth of the struct…
We present new X-ray, radio, and optical data for the unusual galaxy/cluster system J2310-437. Our results confirm the presence of an active nucleus, and suggest an interpretation as an anomalous BL Lac object of bulk relativistic Doppler factor < 2, with an optically deficient radio-to-X-ray spectrum. The radio, optical, and soft X-ray flux densities could lie along a single power-law function, lacking the curvature typical of BL Lac objects. Compared with other known sources that may have comparable multifrequency spectra, J2310-437 is the most extreme. Its low isotropic optical/UV radiation…
Results from recent multiwavelength observations of blazars are reviewed, with particular emphasis on those involving the Rossi X-ray Timing Explorer (RXTE). I discuss blazars' spectral energy distributions, their correlated variability at various energies, and the insights they offer on the physical processes in the jet. New results on Mrk 501, PKS 2155--304, and PKS 2005--489 are highlighted.
As part of our multiwavelength campaign of GX 339-4 observations in 1996 we present our radio, X-ray, and gamma-ray observations made in July, when the source was in a hard state (= soft X-ray low state). The radio observations were made at the time when there was a possible radio jet. We show that the radio spectrum was flat and significantly variable, and that the radio spectral shape and amplitude at this time were not anomalous for this source. Daily light curves from our pointed observation July 9-23 using OSSE, from BATSE, and from the ASM on RXTE also show that there was no significant …
The 1998 September outburst of the black-hole X-ray binary XTE J1550-564 was monitored at X-ray, optical and radio wavelengths. We divide the outburst sequence into five phases and discuss their multiwavelength properties. The outburst starts with a hard X-ray spike, while the soft X-ray flux rises with a longer timescale. We suggest that the onset of the outburst is determined by an increased mass transfer rate from the companion star, but the outburst morphology is determined by the distribution of specific angular momentum in the accreting matter. The companion in XTE J1550-564 is likely to…
Some clusters of galaxies have been identified as powerful sources of non-thermal radiation, from the radio to X-ray wavelengths. The classical models proposed for the explanation of this radiation usually require large energy densities in cosmic rays in the intracluster medium and magnetic fields much lower that those measured using the Faraday rotation. We study here the role that mergers of clusters of galaxies may play in the generation of the non-thermal radiation, and we seek for additional observable consequences of the model. We find that if hard X-rays and radio radiation are respecti…
ECLAIRs is the next space borne instrument that will be fully dedicated to multi-wavelength studies of Gamma-Ray Bursts (GRBs). It consists of a coded mask telescope with a wide (~2 sr) field of view, made of 6400 CdTe pixels (~1000 cm^2), which will work in the 4-300 keV energy band. It is expected to localise ~80 GRBs/yr, thanks to the on-board real time event processing. The GRBs (and other transients) coordinates will be distributed within a few seconds from the onset of the burst with a typical uncertainty of ~5-10 arcmin. The detection system will also include a soft X-ray camera (1-10 k…
The remnant G347.3-0.5 exhibits strong shell emission in the radio and X-ray bands, and has a purported detection in the TeV gamma-ray band by the CANGAROO-II telescope. The CANGAROO results were touted as evidence for the production of cosmic ray ions, a claim that has proven controversial due to constraining fluxes associated with a proximate unidentified EGRET source 3EG J1714-3857. HESS has now seen this source in the TeV band. The complex environment of the remnant renders modeling of its broadband spectrum sensitive to assumptions concerning the nature and parameters of the circumremnant…
We present extensive optical, radio and infrared follow-up observations of a sample of 35 hard X-ray (2-10 keV) selected sources discovered serendipitously in the PV XMM-Newton observation of the radio-loud quasar PKS 0312-77 field, for which also an archival Chandra observation is available. The observations have been carried out as part of the HELLAS2XMM survey, a program aimed to understand the nature of the sources responsible for the bulk of the hard X-ray Background (XRB). The identification of the optical counterparts greatly benefits from the positional accuracy obtained from Chandra a…
We discuss morphological properties of the large-scale jets in powerful radio sources, which are now observed at radio, optical and X-ray frequencies, in order to determine the origin of their X-ray radiation and the nature of the particle acceleration responsible for their multiwavelength emission. We show that modeling knots of the these objects as stationary regions of energy dissipation within the uniform and continuous jet flow leads to several problems. Such problems are especially pronounced if the observed X-ray emission is due to inverse-Compton scattering of the CMB radiation. We exp…
We present the Chandra Multiwavelength Project (ChaMP) X-ray point source catalog with ~6,800 X-ray sources detected in 149 Chandra observations covering \~10 deg^2. The full ChaMP catalog sample is seven times larger than the initial published ChaMP catalog. The exposure time of the fields in our sample ranges from 0.9 to 124 ksec, corresponding to a deepest X-ray flux limit of f_{0.5-8.0} = 9 x 10^{-16} erg/cm2/sec. The ChaMP X-ray data have been uniformly reduced and analyzed with ChaMP-specific pipelines, and then carefully validated by visual inspection. The ChaMP catalog includes X-ray p…
We summarize the multiwavelength properties of X-ray sources detected in the 80 ks XMM-Newton observation of the Groth-Westphal Strip. We find 23 XMM-Newton sources within the WFPC2 fields. Ten spectroscopic redshifts are available from the DEEP and CFRS projects and 4 of these show broad Mg II emission (type 1 AGNs). Two of those without any broad lines, nevertheless, have [NeV] emission which is an unambiguous signature of AGN activity, one of which is a narrow-line Seyfert 1 and the other a type 2 AGN. We have made near-infrared (NIR) spectroscopic observations using the Subaru OHS/CISCO sp…
The current status of leptonic jet models for blazars is reviewed. Differences between the quasar and BL-Lac subclasses of blazars may be understood in terms of the dominance of different radiation mechanisms in the gamma-ray regime. Spectral variability patterns of different blazar subclasses appear to be significantly different and require different intrinsic mechanisms causing gamma-ray flares. As examples, recent results of long-term multiwavelength monitoring of PKS 0528+134, 3C 279, and Mrk 501 are interpreted in the framework of leptonic jet models. Short-term variability patterns give …
Of the blazars detected by EGRET in GeV gamma rays, 3C 279 is not only the best-observed by EGRET, but also one of the best-monitored at lower frequencies. We have assembled eleven spectra, from GHz radio through GeV gamma rays, from the time intervals of EGRET observations. Although some of the data have appeared in previous publications, most are new, including data taken during the high states in early 1999 and early 2000. All of the spectra show substantial gamma-ray contribution to the total luminosity of the object; in a high state, the gamma-ray luminosity dominates over that at all oth…
We analyze an X-ray flux-limited, complete sample of 93 AGN at z< 0.1, selected from the ROSAT Bright Survey. Two thirds of the sample are Seyfert 1 galaxies (Sy1) and one third are Narrow-Line Seyfert 1 galaxies (NLSy1). We have obtained optical images of all objects. By modeling the host galaxy and the AGN central component we decompose the optical emission into nuclear, bulge and disk components, respectively. We find that the nuclear optical luminosity, thought to be associated with the accretion disk surrounding the active black hole, correlates with the X-ray luminosity, the radio lumino…
We report on Spitzer and Gemini observations of the jet of Centaurus A in the infrared, which we combine with radio, ultraviolet and X-ray data. Spitzer detects jet emission from about 2 arcmin from the nucleus, becoming particularly bright after the jet flare point at ~3.4 arcmin. Where X-ray and infrared emission are seen together the broad-band data strongly support a synchrotron origin for the X-rays. The jet flare point is marked by a broad, diffuse region of X-rays which may be associated with a shock: we discuss possible physical mechanisms for this. The infrared jet persists after the …
We present our analysis of the multiwavelength photometric & spectroscopic observations of GRB 060210 and discuss the results in the overall context of current GRB models. All available optical data underwent a simultaneous temporal fit, while X-ray and gamma-ray observations were analysed temporally & spectrally. The results were compared to each other and to possible GRB models. The X-ray afterglow is best described by a smoothly broken power-law with a break at 7.4 hours. The late optical afterglow has a well constrained single power-law index which has a value between the two X-ray indices…
We present two BeppoSAX observations of BL Lac (2200+420) as part of a multiwavelength campaign performed in 2000. The source was in different states of activity: in June, the X-ray spectrum was faint and hard (alpha sim 0.8), with positive residuals towards low energies. In October we detected the highest [2-10] keV flux ever measured for the source. During this observation, the spectrum was soft (alpha sim 1.56) up to 10 keV, while above this energy a hard component was dominating. The BeppoSAX data are confirmed by simultaneous RXTE short observations. During the first observation the soft …
A series of {\sl ROSAT\/}, {\sl ASCA\/} and Compton Gamma-Ray Observatory ({\sl CGRO\/}) observations of the Seyfert galaxy NGC 4151 were carried out during the period 1993 November 30 to December 13 as part of an intensive campaign to study the multiwavelength spectral characteristics of its short time-scale variability. In the softest X-ray bands monitored by {\sl ROSAT} (0.1--0.4 keV, 0.5--1.0 keV) the source flux remained constant throughout the observing period. However, in an adjacent band (1.0--2.0 keV) significant variability was evident, the most obvious feature being a marked increas…
Markarian 421 was observed for about four days with BeppoSAX and the Whipple Observatory gamma-ray telescope in April 1998. A pronounced, well-defined, flare with hour-scale variability was observed simultaneously in X-rays and very high energy gamma-rays. These data provide the first evidence that the X-ray and TeV intensities are well correlated on time-scales of hours. While the rise of the flare occurred on a similar time-scale in the two wavebands, the decay of the flare was much more rapid in gamma rays, providing the first clear indication that the X-ray and gamma-ray emission may not b…
We present the results from a multiwavelength campaign on the TeV blazar 1ES 1959+650, performed in May, 2006. Data from the optical, UV, soft- and hard-X-ray and very high energy (VHE) gamma-ray (E > 100 GeV) bands were obtained with the SUZAKU and SWIFT satellites, with the MAGIC telescope and other ground based facilities. The source spectral energy distribution (SED), derived from SUZAKU and MAGIC observations at the end of May 2006, shows the usual double hump shape, with the synchrotron peak at a higher flux level than the Compton peak. With respect to historical values, during our campa…
Coronae express different facets of their energy release processes in different wavelength regions. While soft X-ray and EUV emission dominates the radiative losses of the thermal plasma, hard X-ray emission (>10 keV) can be produced from non-thermal high-energy particles accelerated as a consequence of flare processes, and radio emission is often emitted from mildly relativistic electrons trapped in magnetic fields. Combined measurements of all emissions are important to understand the ultimate mechanisms responsible for coronal energy release and heating. This presentation will summarize a n…
We present optical observations of the low-luminosity Seyfert 1 nucleus of NGC 4395, as part of a multiwavelength reverberation-mapping program. Observations were carried out over two nights in 2004 April at Lick, Wise, and Kitt Peak Observatories. We obtained V-band and B-band photometry, and spectra over the range 3500-6800 Angstroms. Simultaneous Hubble Space Telescope UV and Chandra X-ray observations are presented in companion papers. Even though NGC 4395 was in an extremely low state of activity, we detect significant continuum variability of 2-10%, increasing toward shorter wavelengths.…
We present B and R-band luminosity functions (LF) for a sample of 25 nearby groups of galaxies. We find that the LFs of the groups with low X-ray luminosity (L_X < 10^{41.7} erg/s) are significantly different from those of the X-ray brighter groups, showing a prominent dip around M_b = -18. While both categories show lack of late-type galaxies in their central regions, X-ray dim groups also show a more marked concentration of optical luminosity towards the centre. A toy simulation shows that in the low velocity dispersion environment, as in the X-ray dim group, dynamical friction would facilit…
Context. GRB050721 was detected by Swift and promptly followed-up, in the X-ray by Swift itself and, in the optical band, by the VLT operated, for the first time, in rapid response mode. A multiwavelength monitoring campaign was performed in order to study its afterglow behavior. Aims. We present the analysis of the early and late afterglow emission in both the X-ray and optical bands, as observed by Swift, a robotic telescope, and the VLT. We compare early observations with late afterglow observations obtained with Swift and the VLT in different bands in order to constrain the density of the …
We have investigated multiband optical photometric variability and stability of the H$α$ line profile of the transient X-ray binary IGR J01583+6713. We set an upper limit of 0.05 mag on photometric variations in the {\it V} band over a time scale of 3 months. The H$α$ line is found to consist of non-Gaussian profile and quite stable for a duration of 2 months. We have identified the spectral type of the companion star to be B2 IVe while distance to the source is estimated to be $\sim$ 4.0 kpc. Along with the optical observations, we have also carried out analysis of X-ray data from three short…