1. |
- Abramowski, A., et al.
(författare)
-
The 2010 very high energy gamma-RAY flare and 10 years of multi-wavelength observations of M 87
- 2012
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 746:2, s. 151-
-
Tidskriftsartikel (refereegranskat)abstract
- The giant radio galaxy M 87 with its proximity (16 Mpc), famous jet, and very massive black hole ((3-6) x 10(9) M-circle dot) provides a unique opportunity to investigate the origin of very high energy (VHE; E > 100 GeV) gamma-ray emission generated in relativistic outflows and the surroundings of supermassive black holes. M 87 has been established as a VHE gamma-ray emitter since 2006. The VHE gamma-ray emission displays strong variability on timescales as short as a day. In this paper, results from a joint VHE monitoring campaign on M 87 by the MAGIC and VERITAS instruments in 2010 are reported. During the campaign, a flare at VHE was detected triggering further observations at VHE (H.E.S.S.), X-rays (Chandra), and radio (43 GHz Very Long Baseline Array, VLBA). The excellent sampling of the VHE gamma-ray light curve enables one to derive a precise temporal characterization of the flare: the single, isolated flare is well described by a two-sided exponential function with significantly different flux rise and decay times of tau(rise)(d) = (1.69 +/- 0.30) days and tau(decay)(d) = (0.611 +/- 0.080) days, respectively. While the overall variability pattern of the 2010 flare appears somewhat different from that of previous VHE flares in 2005 and 2008, they share very similar timescales (similar to day), peak fluxes (Phi(>0.35 TeV) similar or equal to (1-3) x 10(-11) photons cm(-2) s(-1)), and VHE spectra. VLBA radio observations of 43 GHz of the inner jet regions indicate no enhanced flux in 2010 in contrast to observations in 2008, where an increase of the radio flux of the innermost core regions coincided with a VHE flare. On the other hand, Chandra X-ray observations taken similar to 3 days after the peak of the VHE gamma-ray emission reveal an enhanced flux from the core (flux increased by factor similar to 2; variability timescale <2 days). The long-term (2001-2010) multi-wavelength (MWL) light curve of M 87, spanning from radio to VHE and including data from Hubble Space Telescope, Liverpool Telescope, Very Large Array, and European VLBI Network, is used to further investigate the origin of the VHE gamma-ray emission. No unique, common MWL signature of the three VHE flares has been identified. In the outer kiloparsec jet region, in particular in HST-1, no enhanced MWL activity was detected in 2008 and 2010, disfavoring it as the origin of the VHE flares during these years. Shortly after two of the three flares (2008 and 2010), the X-ray core was observed to be at a higher flux level than its characteristic range (determined from more than 60 monitoring observations: 2002-2009). In 2005, the strong flux dominance of HST-1 could have suppressed the detection of such a feature. Published models for VHE gamma-ray emission from M 87 are reviewed in the light of the new data.
|
|
2. |
- Abdo, A. A., et al.
(författare)
-
The spectral energy distribution of fermi bright blazars
- 2010
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 716:1, s. 30-70
-
Tidskriftsartikel (refereegranskat)abstract
- We have conducted a detailed investigation of the broadband spectral properties of the gamma-ray selected blazars of the Fermi LAT Bright AGN Sample (LBAS). By combining our accurately estimated Fermi gamma-ray spectra with Swift, radio, infra-red, optical, and other hard X-ray/gamma-ray data, collected within 3 months of the LBAS data taking period, we were able to assemble high-quality and quasi-simultaneous spectral energy distributions (SED) for 48 LBAS blazars. The SED of these gamma-ray sources is similar to that of blazars discovered at other wavelengths, clearly showing, in the usual log nu-log nu F-nu representation, the typical broadband spectral signatures normally attributed to a combination of low-energy synchrotron radiation followed by inverse Compton emission of one or more components. We have used these SED to characterize the peak intensity of both the low-and the high-energy components. The results have been used to derive empirical relationships that estimate the position of the two peaks from the broadband colors (i.e., the radio to optical, alpha(ro), and optical to X-ray, alpha(ox), spectral slopes) and from the gamma-ray spectral index. Our data show that the synchrotron peak frequency (nu(S)(peak)) is positioned between 10(12.5) and 10(14.5) Hz in broad-lined flat spectrum radio quasars (FSRQs) and between 10(13) and 10(17) Hz in featureless BL Lacertae objects. We find that the gamma-ray spectral slope is strongly correlated with the synchrotron peak energy and with the X-ray spectral index, as expected at first order in synchrotron-inverse Compton scenarios. However, simple homogeneous, one-zone, synchrotron self-Compton (SSC) models cannot explain most of our SED, especially in the case of FSRQs and low energy peaked (LBL) BL Lacs. More complex models involving external Compton radiation or multiple SSC components are required to reproduce the overall SED and the observed spectral variability. While more than 50% of known radio bright high energy peaked (HBL) BL Lacs are detected in the LBAS sample, only less than 13% of known bright FSRQs and LBL BL Lacs are included. This suggests that the latter sources, as a class, may be much fainter gamma-ray emitters than LBAS blazars, and could in fact radiate close to the expectations of simple SSC models. We categorized all our sources according to a new physical classification scheme based on the generally accepted paradigm for Active Galactic Nuclei and on the results of this SED study. Since the LAT detector is more sensitive to flat spectrum gamma-ray sources, the correlation between nu(S)(peak) and gamma-ray spectral index strongly favors the detection of high energy peaked blazars, thus explaining the Fermi overabundance of this type of sources compared to radio and EGRET samples. This selection effect is similar to that experienced in the soft X-ray band where HBL BL Lacs are the dominant type of blazars.
|
|
3. |
- Abdo, A. A., et al.
(författare)
-
FERMI Large Area Telescope and multi-wavelength observations of the flaring activity of PKS 1510-089 between 2008 september and 2009 june
- 2010
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 721:2, s. 1425-1447
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the multi-wavelength observations of PKS 1510-089 (a flat spectrum radio quasar (FSRQ) at z = 0.361) during its high activity period between 2008 September and 2009 June. During this 11 month period, the source was characterized by a complex variability at optical, UV, and gamma-ray bands, on timescales down to 6-12 hr. The brightest gamma-ray isotropic luminosity, recorded on 2009 March 26, was similar or equal to 2 x 1048 erg s-1. The spectrum in the Fermi Large Area Telescope energy range shows a mild curvature described well by a log-parabolic law, and can be understood as due to the Klein-Nishina effect. The. -ray flux has a complex correlation with the other wavelengths. There is no correlation at all with the X-ray band, a weak correlation with the UV, and a significant correlation with the optical flux. The. -ray flux seems to lead the optical one by about 13 days. From the UV photometry, we estimated a black hole mass of similar or equal to 5.4 x 10(8)M(circle dot) and an accretion rate of similar or equal to 0.5M(circle dot) yr(-1). Although the power in the thermal and non-thermal outputs is smaller compared to the very luminous and distant FSRQs, PKS 1510-089 exhibits a quite large Compton dominance and a prominent big blue bump (BBB) as observed in the most powerful gamma-ray quasars. The BBB was still prominent during the historical maximum optical state in 2009 May, but the optical/ UV spectral index was softer than in the quiescent state. This seems to indicate that the BBB was not completely dominated by the synchrotron emission during the highest optical state. We model the broadband spectrum assuming a leptonic scenario in which the inverse Compton emission is dominated by the scattering of soft photons produced externally to the jet. The resulting model-dependent jet energetic content is compatible with a scenario in which the jet is powered by the accretion disk, with a total efficiency within the Kerr black hole limit.
|
|
4. |
- Ackermann, M., et al.
(författare)
-
MULTI-WAVELENGTH OBSERVATIONS OF BLAZAR AO 0235+164 IN THE 2008-2009 FLARING STATE
- 2012
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 751:2
-
Tidskriftsartikel (refereegranskat)abstract
- The blazarAO 0235+164 (z=0.94) has been one of the most active objects observed by Fermi Large Area Telescope (LAT) since its launch in Summer 2008. In addition to the continuous coverage by Fermi, contemporaneous observations were carried out from the radio to gamma-ray bands between 2008 September and 2009 February. In this paper, we summarize the rich multi-wavelength data collected during the campaign (including F-GAMMA, GASP-WEBT, Kanata, OVRO, RXTE, SMARTS, Swift, and other instruments), examine the cross-correlation between the light curves measured in the different energy bands, and interpret the resulting spectral energy distributions in the context of well-known blazar emission models. We find that the gamma-ray activity is well correlated with a series of near-IR/optical flares, accompanied by an increase in the optical polarization degree. On the other hand, the X-ray light curve shows a distinct 20 day high state of unusually soft spectrum, which does not match the extrapolation of the optical/UV synchrotron spectrum. We tentatively interpret this feature as the bulk Compton emission by cold electrons contained in the jet, which requires an accretion disk corona with an effective covering factor of 19% at a distance of 100 R-g. We model the broadband spectra with a leptonic model with external radiation dominated by the infrared emission from the dusty torus.
|
|
5. |
- Abdo, A. A., et al.
(författare)
-
THE FIRST FERMI MULTIFREQUENCY CAMPAIGN ON BL LACERTAE : CHARACTERIZING THE LOW-ACTIVITY STATE OF THE EPONYMOUS BLAZAR
- 2011
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 730:2, s. 101-
-
Tidskriftsartikel (refereegranskat)abstract
- We report on observations of BL Lacertae during the first 18 months of Fermi LAT science operations and present results from a 48 day multifrequency coordinated campaign from 2008 August 19 to 2008 October 7. The radio to gamma-ray behavior of BL Lac is unveiled during a low-activity state thanks to the coordinated observations of radio-band (Metsahovi and VLBA), near-IR/optical (Tuorla, Steward, OAGH, and MDM), and X-ray (RXTE and Swift) observatories. No variability was resolved in gamma rays during the campaign, and the brightness level was 15 times lower than the level of the 1997 EGRET outburst. Moderate and uncorrelated variability has been detected in UV and X-rays. The X-ray spectrum is found to be concave, indicating the transition region between the low- and high-energy components of the spectral energy distribution (SED). VLBA observation detected a synchrotron spectrum self-absorption turnover in the innermost part of the radio jet appearing to be elongated and inhomogeneous, and constrained the average magnetic field there to be less than 3 G. Over the following months, BL Lac appeared variable in gamma rays, showing flares (in 2009 April and 2010 January). There is no evidence for the correlation of gamma rays with the optical flux monitored from the ground in 18 months. The SED may be described by a single-zone or a two-zone synchrotron self-Compton (SSC) model, but a hybrid SSC plus external radiation Compton model seems to be preferred based on the observed variability and the fact that it provides a fit closest to equipartition.
|
|
6. |
- Aleksic, J., et al.
(författare)
-
Discovery of VHE gamma-rays from the blazar 1ES 1215+303 with the MAGIC telescopes and simultaneous multi-wavelength observations
- 2012
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 544, s. A142-
-
Tidskriftsartikel (refereegranskat)abstract
- Context. We present the discovery of very high energy (VHE, E > 100 GeV) gamma-ray emission from the BL Lac object 1ES 1215+303 by the MAGIC telescopes and simultaneous multi-wavelength data in a broad energy range from radio to gamma-rays. Aims. We study the VHE gamma-ray emission from 1ES 1215+303 and its relation to the emissions in other wavelengths. Methods. Triggered by an optical outburst, MAGIC observed the source in 2011 January-February for 20.3 h. The target was monitored in the optical R-band by the KVA telescope that also performed optical polarization measurements. We triggered target of opportunity observations with the Swift satellite and obtained simultaneous and quasi-simultaneous data from the Fermi Large Area Telescope and from the Metsahovi radio telescope. We also present the analysis of older MAGIC data taken in 2010. Results. The MAGIC observations of 1ES 1215+303 carried out in 2011 January-February resulted in the first detection of the source at VHE with a statistical significance of 9.4 sigma. Simultaneously, the source was observed in a high optical and X-ray state. In 2010 the source was observed in a lower state in optical, X-ray, and VHE, while the GeV gamma-ray flux and the radio flux were comparable in 2010 and 2011. The spectral energy distribution obtained with the 2011 data can be modeled with a simple one zone SSC model, but it requires extreme values for the Doppler factor or the electron energy distribution.
|
|
7. |
- Ackermann, M., et al.
(författare)
-
MULTIWAVELENGTH EVIDENCE FOR QUASI-PERIODIC MODULATION IN THE GAMMA-RAY BLAZAR PG 1553+113
- 2015
-
Ingår i: Astrophysical Journal Letters. - : Institute of Physics (IOP). - 2041-8205 .- 2041-8213. ; 813:2
-
Tidskriftsartikel (refereegranskat)abstract
- We report for the first time a gamma-ray and multiwavelength nearly periodic oscillation in an active galactic nucleus. Using the Fermi Large Area Telescope we have discovered an apparent quasi-periodicity in the gamma-ray flux (E > 100 MeV) from the GeV/TeV BL Lac object PG 1553+113. The marginal significance of the 2.18 +/- 0.08 year period gamma-ray cycle is strengthened by correlated oscillations observed in radio and optical fluxes, through data collected in the Owens Valley Radio Observatory, Tuorla, Katzman Automatic Imaging Telescope, and Catalina Sky Survey monitoring programs and Swift-UVOT. The optical cycle appearing in similar to 10 years of data has a similar period, while the 15 GHz oscillation is less regular than seen in the other bands. Further long-term multiwavelength monitoring of this blazar may discriminate among the possible explanations for this quasi-periodicity.
|
|
8. |
- Aleksic, J., et al.
(författare)
-
PG 1553+113 : FIVE YEARS OF OBSERVATIONS WITH MAGIC
- 2012
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 748:1, s. 46-
-
Tidskriftsartikel (refereegranskat)abstract
- We present the results of five years (2005-2009) of MAGIC observations of the BL Lac object PG 1553+113 at very high energies (VHEs; E > 100 GeV). Power-law fits of the individual years are compatible with a steady mean photon index Gamma = 4.27 +/- 0.14. In the last three years of data, the flux level above 150 GeV shows a clear variability (probability of constant flux < 0.001%). The flux variations are modest, lying in the range from 4% to 11% of the Crab Nebula flux. Simultaneous optical data also show only modest variability that seems to be correlated with VHE gamma-ray variability. We also performed a temporal analysis of (all available) simultaneous Fermi/Large Area Telescope data of PG 1553+113 above 1 GeV, which reveals hints of variability in the 2008-2009 sample. Finally, we present a combination of the mean spectrum measured at VHEs with archival data available for other wavelengths. The mean spectral energy distribution can be modeled with a one-zone synchrotron self-Compton model, which gives the main physical parameters governing the VHE emission in the blazar jet.
|
|
9. |
- Aleksic, J., et al.
(författare)
-
DETECTION OF VERY HIGH ENERGY gamma-RAY EMISSION FROM THE PERSEUS CLUSTER HEAD-TAIL GALAXY IC 310 BY THE MAGIC TELESCOPES
- 2010
-
Ingår i: The Astrophysical Journal Letters. - 2041-8205. ; 723:2, s. l207-L212
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the detection with the MAGIC telescopes of very high energy (VHE) gamma-rays from IC 310, a head-tail radio galaxy in the Perseus galaxy cluster, observed during the interval 2008 November to 2010 February. The Fermi satellite has also detected this galaxy. The source is detected by MAGIC at a high statistical significance of 7.6 sigma in 20.6 hr of stereo data. The observed spectral energy distribution is flat with a differential spectral index of -2.00 +/- 0.14. The mean flux above 300 GeV, between 2009 October and 2010 February, (3.1 +/- 0.5) x 10(-12) cm(-2) s(-1), corresponds to (2.5 +/- 0.4)% of Crab Nebula units. Only an upper limit, of 1.9% of Crab Nebula units above 300 GeV, was obtained with the 2008 data. This, together with strong hints (>3 sigma) of flares in the middle of 2009 October and November, implies that the emission is variable. The MAGIC results favor a scenario with the VHE emission originating from the inner jet close to the central engine. More complicated models than a simple one-zone synchrotron self-Compton (SSC) scenario, e. g., multi-zone SSC, external Compton, or hadronic, may be required to explain the very flat spectrum and its extension over more than three orders of magnitude in energy.
|
|
10. |
- Raiteri, C. M., et al.
(författare)
-
WEBT and XMM-Newton observations of 3C 454.3 during the post-outburst phase - Detection of the little and big blue bumps
- 2007
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 473:3, s. 819-827
-
Tidskriftsartikel (refereegranskat)abstract
- Context. The quasar-type blazar 3C 454.3 was observed to undergo an unprecedented optical outburst in spring 2005, affecting the source brightness from the near-IR to the X-ray frequencies. This was first followed by a millimetric and then by a radio outburst, which peaked in February 2006. Aims. In this paper we report on follow-up observations to study the multiwavelength emission in the post-outburst phase. Methods. Radio, near-infrared, and optical monitoring was performed by the Whole Earth Blazar Telescope (WEBT) collaboration in the 2006-2007 observing season. XMM-Newton observations on July 2-3 and December 18-19, 2006 added information on the X-ray and UV states of the source. Results. The source was in a faint state. The radio flux at the higher frequencies showed a fast decreasing trend, which represents the tail of the big radio outburst. It was followed by a quiescent state, common at all radio frequencies. In contrast, moderate activity characterized the near-IR and optical light curves, with a progressive increase of the variability amplitude with increasing wavelength. We ascribe this redder-when-brighter behaviour to the presence of a ""little blue bump"" due to line emission from the broad line region, which is clearly visible in the source spectral energy distribution (SED) during faint states. Moreover, the data from the XMM- Newton Optical Monitor reveal a rise of the SED in the ultraviolet, suggesting the existence of a "" big blue bump"" due to thermal emission from the accretion disc. The X-ray spectra are well fitted with a power- law model with photoelectric absorption, possibly larger than the Galactic one. However, the comparison with previous X-ray observations would imply that the amount of absorbing matter is variable. Alternatively, the intrinsic X-ray spectrum presents a curvature, which may depend on the X-ray brightness. In this case, two scenarios are possible. i) There is no extra absorption, and the X-ray spectrum hardens at low energies, the hardening being more evident in bright states; ii) there is a constant amount of extra absorption, likely in the quasar environment, and the X-ray spectrum softens at low energies, at least in faint X-ray states. This softening might be the result of a flux contribution by the high-frequency tail of the big blue bump.
|
|
11. |
- Hayashida, M., et al.
(författare)
-
THE STRUCTURE AND EMISSION MODEL OF THE RELATIVISTIC JET IN THE QUASAR 3C 279 INFERRED FROM RADIO TO HIGH-ENERGY gamma-RAY OBSERVATIONS IN 2008-2010
- 2012
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 754:2, s. 114-
-
Tidskriftsartikel (refereegranskat)abstract
- We present time-resolved broadband observations of the quasar 3C 279 obtained from multi-wavelength campaigns conducted during the first two years of the Fermi Gamma-ray Space Telescope mission. While investigating the previously reported gamma-ray/optical flare accompanied by a change in optical polarization, we found that the optical emission appears to be delayed with respect to the gamma-ray emission by about 10 days. X-ray observations reveal a pair of isolated flares separated by similar to 90 days, with only weak gamma-ray/optical counterparts. The spectral structure measured by Spitzer reveals a synchrotron component peaking in the mid-infrared band with a sharp break at the far-infrared band during the gamma-ray flare, while the peak appears in the millimeter (mm)/submillimeter (sub-mm) band in the low state. Selected spectral energy distributions are fitted with leptonic models including Comptonization of external radiation produced in a dusty torus or the broad-line region. Adopting the interpretation of the polarization swing involving propagation of the emitting region along a curved trajectory, we can explain the evolution of the broadband spectra during the gamma-ray flaring event by a shift of its location from similar to 1 pc to similar to 4 pc from the central black hole. On the other hand, if the gamma-ray flare is generated instead at sub-pc distance from the central black hole, the far-infrared break can be explained by synchrotron self-absorption. We also model the low spectral state, dominated by the mm/sub-mm peaking synchrotron component, and suggest that the corresponding inverse-Compton component explains the steady X-ray emission.
|
|
12. |
- Abeysekara, A. U., et al.
(författare)
-
A Luminous and Isolated Gamma-Ray Flare from the Blazar B2 1215+30
- 2017
-
Ingår i: Astrophysical Journal. - : Institute of Physics Publishing (IOPP). - 0004-637X .- 1538-4357. ; 836:2
-
Tidskriftsartikel (refereegranskat)abstract
- B2 1215+30 is a BL-Lac-type blazar that was first detected at TeV energies by the MAGIC atmospheric Cherenkov telescopes and subsequently confirmed by the Very Energetic Radiation Imaging Telescope Array System (VERITAS) observatory with data collected between 2009 and 2012. In 2014 February 08, VERITAS detected a large-amplitude flare from B2. 1215+30 during routine monitoring observations of the blazar 1ES. 1218+304, located in the same field of view. The TeV flux reached 2.4 times the Crab Nebula flux with a variability timescale of <3.6 hr. Multiwavelength observations with Fermi-LAT, Swift, and the Tuorla Observatory revealed a correlated high GeV flux state and no significant optical counterpart to the flare, with a spectral energy distribution where the gamma-ray luminosity exceeds the synchrotron luminosity. When interpreted in the framework of a onezone leptonic model, the observed emission implies a high degree of beaming, with Doppler factor delta > 10, and an electron population with spectral index p < 2.3.
|
|
13. |
- Dey, Lankeswar, et al.
(författare)
-
Authenticating the Presence of a Relativistic Massive Black Hole Binary in OJ 287 Using Its General Relativity Centenary Flare : Improved Orbital Parameters
- 2018
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 866:1
-
Tidskriftsartikel (refereegranskat)abstract
- Results from regular monitoring of relativistic compact binaries like PSR 1913+16 are consistent with the dominant (quadrupole) order emission of gravitational waves (GWs). We show that observations associated with the binary black hole (BBH) central engine of blazar OJ 287 demand the inclusion of gravitational radiation reaction effects beyond the quadrupolar order. It turns out that even the effects of certain hereditary contributions to GW emission are required to predict impact flare timings of OJ 287. We develop an approach that incorporates this effect into the BBH model for OJ 287. This allows us to demonstrate an excellent agreement between the observed impact flare timings and those predicted from ten orbital cycles of the BBH central engine model. The deduced rate of orbital period decay is nine orders of magnitude higher than the observed rate in PSR 1913+16, demonstrating again the relativistic nature of OJ 287's central engine. Finally, we argue that precise timing of the predicted 2019 impact flare should allow a test of the celebrated black hole no-hair theorem at the 10% level.
|
|
14. |
- Villforth, C., et al.
(författare)
-
Variability and stability in blazar jets on time-scales of years : optical polarization monitoring of OJ 287 in 2005-2009
- 2010
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 402:3, s. 2087-2111
-
Tidskriftsartikel (refereegranskat)abstract
- OJ 287 is a BL Lac object at redshift z = 0.306 that has shown double-peaked bursts at regular intervals of similar to 12 yr during the last similar to 40 yr. We analyse optical photopolarimetric monitoring data from 2005 to 2009, during which the latest double-peaked outburst occurred. The aim of this study is twofold: firstly, we aim to analyse variability patterns and statistical properties of the optical polarization light curve. We find a strong preferred position angle in optical polarization. The preferred position angle can be explained by separating the jet emission into two components: an optical polarization core and chaotic jet emission. The optical polarization core is stable on time-scales of years and can be explained as emission from an underlying quiescent jet component. The chaotic jet emission sometimes exhibits a circular movement in the Stokes plane. We find six such events, all on the time-scales of 10-20 d. We interpret these events as a shock front moving forwards and backwards in the jet, swiping through a helical magnetic field. Secondly, we use our data to assess different binary black hole models proposed to explain the regularly appearing double-peaked bursts in OJ 287. We compose a list of requirements a model has to fulfil to explain the mysterious behaviour observed in OJ 287. The list includes not only characteristics of the light curve but also other properties of OJ 287, such as the black hole mass and restrictions on accretion flow properties. We rate all existing models using this list and conclude that none of the models is able to explain all observations. We discuss possible new explanations and propose a new approach to understanding OJ 287. We suggest that both the double-peaked bursts and the evolution of the optical polarization position angle could be explained as a sign of resonant accretion of magnetic field lines, a 'magnetic breathing' of the disc.
|
|
15. |
- Kosenkov, Ilia A., et al.
(författare)
-
High-precision optical polarimetry of the accreting black hole V404 Cyg during the 2015 June outburst
- 2017
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966. ; 468:4, s. 4362-4373
-
Tidskriftsartikel (refereegranskat)abstract
- Our simultaneous three-colour (BVR) polarimetric observations of the low-mass black hole X-ray binary V404 Cyg show a small but statistically significant change of polarization degree (Delta(p) similar to 1 per cent) between the outburst in 2015 June and the quiescence. The polarization of V404 Cyg in the quiescent state agrees within the errors with that of the visually close (1.4 arc-sec) companion (pR = 7.3 +/- 0.1 per cent), indicating that it is predominantly of interstellar origin. The polarization pattern of the surrounding field stars supports this conclusion. From the observed variable polarization during the outburst, we show that the polarization degree of the intrinsic component peaks in the V band, p(V) = 1.1 +/- 0.1 per cent, at the polarization position angle of theta(V) =-7 degrees+/- 2 degrees, which is consistent in all three passbands. We detect significant variations in the position angle of the intrinsic polarization in the R band from -30. to similar to 0 degrees during the outburst peak. The observed wavelength dependence of the intrinsic polarization does not support non-thermal synchrotron emission from a jet as a plausible mechanism, but it is in better agreement with the combined effect of electron (Thomson) scattering and absorption in a flattened plasma envelope or outflow surrounding the illuminating source. Alternatively, the polarization signal can be produced by scattering of the disc radiation in a mildly relativistic polar outflow. The position angle of the intrinsic polarization, nearly parallel to the jet direction (i. e. perpendicular to the accretion disc plane), is in agreement with these interpretations.
|
|
16. |
- Poutanen, Juri, et al.
(författare)
-
Black hole spin-orbit misalignment in the x-ray binary MAXI J1820+070
- 2022
-
Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 375:6583, s. 874-
-
Tidskriftsartikel (refereegranskat)abstract
- The observational signatures of black holes in x-ray binary systems depend on their masses, spins, accretion rate, and the misalignment angle between the black hole spin and the orbital angular momentum. We present optical polarimetric observations of the black hole x-ray binary MAXI J1820+070, from which we constrain the position angle of the binary orbital. Combining this with previous determinations of the relativistic jet orientation. which traces the black hole spin, and the inclination of the orbit, we determine a lower limit of 40 degrees on the spin-orbit misalignment angle. The misalignment must originate from either the binary evolution or black hole formation stages. If other x-ray binaries have similarly large misalignments, these would bias measurements of black hole masses and spins from x-ray observations.
|
|
17. |
- Veledina, Alexandra, et al.
(författare)
-
Evolving optical polarisation of the black hole X-ray binary MAXI J1820+070
- 2019
-
Ingår i: Astronomy and Astrophysics. - : EDP SCIENCES S A. - 0004-6361 .- 1432-0746. ; 623
-
Tidskriftsartikel (refereegranskat)abstract
- Aims. The optical emission of black hole transients increases by several magnitudes during the X-ray outbursts. Whether the extra light arises from the X-ray heated outer disc, from the inner hot accretion flow, or from the jet is currently debated. Optical polarisation measurements are able to distinguish the relative contributions of these components. Methods. We present the results of BVR polarisation measurements of the black hole X-ray binary MAXI J1820+070 during the period of March-April 2018. Results. We detect small, similar to 0.7%, but statistically significant polarisation, part of which is of interstellar origin. Depending on the interstellar polarisation estimate, the intrinsic polarisation degree of the source is between similar to 0.3% and 0.7%, and the polarisation position angle is between similar to 10 degrees-30 degrees. We show that the polarisation increases after MJD 58222 (2018 April 14). The change is of the order of 0.1% and is most pronounced in the R band. The change of the source Stokes parameters occurs simultaneously with the drop of the observed V-band flux and a slow softening of the X-ray spectrum. The Stokes vectors of intrinsic polarisation before and after the drop are parallel, at least in the V and R filters. Conclusions. We suggest that the increased polarisation is due to the decreasing contribution of the non-polarized component, which we associate with the the hot flow or jet emission. The low polarisation can result from the tangled geometry of the magnetic field or from the Faraday rotation in the dense, ionised, and magnetised medium close to the black hole. The polarized optical emission is likely produced by the irradiated disc or by scattering of its radiation in the optically thin outflow.
|
|
18. |
- Kosenkov, Ilia A., et al.
(författare)
-
Disc and wind in black hole X-ray binary MAXI J1820+070 observed through polarized light during its 2018 outburst
- 2020
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 496:1, s. L96-L100
-
Tidskriftsartikel (refereegranskat)abstract
- We describe the first complete polarimetric data set of the entire outburst of a low-mass black hole X-ray binary system and discuss the constraints for geometry and radiative mechanisms it imposes. During the decaying hard state, when the optical flux is dominated by the non-thermal component, the observed polarization is consistent with the interstellar values in all filters. During the soft state, the intrinsic polarization of the source is small, similar to 0.15 per cent in B and V filters, and is likely produced in the irradiated disc. A much higher polarization, reaching similar to 0.5 per cent in V and R filters, at a position angle of similar to 25 degrees observed in the rising hard state coincides in time with the detection of winds in the system. This angle coincides with the position angle of the jet. The detected optical polarization is best explained by scattering of the non-thermal (hot flow or jet base) radiation in an equatorial wind.
|
|
19. |
- Kravtsov, Vadim, et al.
(författare)
-
Optical polarization signatures of black hole X-ray binaries
- 2022
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 514:2, s. 2479-2487
-
Tidskriftsartikel (refereegranskat)abstract
- Polarimetry provides an avenue for probing the geometry and physical mechanisms producing optical radiation in many astrophysical objects, including stellar binary systems. We present the results of multiwavelength (BVR) polarimetric studies of a sample of historical black hole X-ray binaries, observed during their outbursts or in the quiescent (or near-quiescent) state. We surveyed both long- and short-period systems, located at different Galactic latitudes. We performed careful analysis of the interstellar polarization in the direction on the sources to reliably estimate the intrinsic source polarization. Intrinsic polarization was found to be small (<0.2 per cent) in sources observed in bright soft states (MAXI J0637−430 and 4U 1957+115). It was found to be significant in the rising hard state of MAXI J1820+070 at the level of ∼0.5 per cent and negligible in the decaying hard state and during its failed outbursts, while Swift J1357.2−0933 showed its absence in the rising hard state. Three (XTE J1118+480 , V4641 Sgr , V404 Cyg) sources observed during quiescence show no evidence of significant intrinsic polarization, while MAXI J1820+070 is the only black hole X-ray binary which showed substantial (>5 per cent) intrinsic quiescent-state polarization with a blue spectrum. The absence of intrinsic polarization at the optical wavelengths puts constraints on the potential contribution of non-stellar (jet, hot flow, accretion disc) components to the total spectra of black hole X-ray binaries.
|
|
20. |
- Kravtsov, Vadim, et al.
(författare)
-
Orbital variability of the optical linear polarization of the gamma-ray binary LS I+61 degrees 303 and new constraints on the orbital parameters
- 2020
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 643
-
Tidskriftsartikel (refereegranskat)abstract
- We studied the variability of the linear polarization and brightness of the gamma -ray binary LS I +61 degrees 303. High-precision BVR photopolarimetric observations were carried out with the Dipol-2 polarimeter on the 2.2 m remotely controlled UH88 telescope at Mauna Kea Observatory and the 60 cm Tohoku telescope at Haleakala bservatory (Hawaii) over 140 nights in 2016-2019. We also determined the degree and angle of the interstellar polarization toward LS I +61 degrees 303 using two out of four nearby field stars that have Gaia's parallaxes. After subtracting the interstellar polarization, we determined the position angle of the intrinsic polarization theta similar or equal to 11 degrees, which can either be associated with the projection of the Be star's decretion disk axis on the plane of sky, or can differ from it by 90 degrees. Using the Lomb-Scargle method, we performed timing analyses and period searches of our polarimetric and photometric data. We found statistically significant periodic variability of the normalized Stokes parameters q and u in all passbands. The most significant period of variability, P-Pol=13.244 +/- 0.012 d, is equal to one half of the orbital period P-orb=26.496 d. The fits of the polarization variability curves with Fourier series show a dominant contribution from the second harmonic which is typical for binary systems with circular orbits and nearly symmetric distribution of light scattering material with respect to the orbital plane. The continuous change of polarization with the orbital phase implies co-planarity of the orbit of the compact object and the Be star's decretion disk. Using a model of Thomson scattering by a cloud that orbits the Be star, we obtained constraints on the orbital parameters, including a small eccentricity e<0.2 and periastron phase of (p)approximate to 0.6, which coincides with the peaks in the radio, X-ray, and TeV emission. These constraints are independent of the assumption about the orientation of the decretion disk plane on the sky. We also extensively discuss the apparent inconsistency with the previous measurements of the orbital parameters from radial velocities. By folding the photometry data acquired during a three-year time span with the orbital period, we found a linear phase shift of the moments of the brightness maximum, confirming the possible existence of superorbital variability.
|
|
21. |
- Kravtsov, Vadim, et al.
(författare)
-
Peering into the tilted heart of Cyg X-1 with high-precision optical polarimetry
- 2023
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 678
-
Tidskriftsartikel (refereegranskat)abstract
- We present high-precision optical polarimetric observations of the black hole X-ray binary Cygnus X-1 that span several cycles of its 5.6-day orbital period. The week-long observations on two telescopes located in opposite hemispheres allowed us to track the evolution of the polarization within one orbital cycle with the highest temporal resolution to date. Using the field stars, we determined the interstellar polarization in the source direction and subsequently its intrinsic polarization Pint = 0.82%±0.15% with a polarization angle θint = 155 ±5. The optical polarization angle is aligned with that in the X-rays recently obtained with the Imaging X-ray Polarimetry Explorer. Furthermore, it is consistent within the uncertainties with the position angle of the radio ejections. We show that the intrinsic polarization degree is variable with the orbital period with an amplitude of ∼0.2% and discuss various sites of its production. Assuming that the polarization arises from a single Thomson scattering of the primary star radiation by the matter that follows the black hole in its orbital motion, we constrained the inclination of the binary orbit i > 120 and its eccentricity e < 0.08. The asymmetric shape of the orbital profiles of the Stokes parameters also implies the asymmetry of the scattering matter distribution in the orbital plane, which may arise from the tilted accretion disk. We compared our data to the polarimetric observations made in 1975"1987 and find good agrement within 1 between the intrinsic polarization angles. On the other hand, the polarization degree decreased by 0.4% over half a century, suggesting secular changes in the geometry of the accreting matter.
|
|