: : and and ? ? source source stars

509) 509) - - magnetars (IAA-CSIC Granada) Galactic Galactic neutron neutron new new between between in a in a link link (Nature, 405, pp. 506 (Nature, 405, pp. 506 isolated isolated on behalf of a large Collaboration VILLAFRANCA DEL CASTILLO , 30 OCT 2008 flaring flaring dim dim

Alberto J. CASTRO-TIRADO missing missing a a Rapid Rapid

CollaborationCollaboration A.J. Castro-Tirado (1), A. de Ugarte Postigo (2,1), J. Gorosabel (1), M. Jelínek (1), T. A. Fatkhullin (3), V. V. Sokolov (3), P. Ferrero (4), D. A. Kann (4), S. Klose (4), D. Sluse (5), M. Bremer (6), J. M. Winters (6), D. Nuernberger (2), D. Pérez-Ramírez (7), M. A. Guerrero (1), J. French (8) , G. Melady (8), L. Hanlon (8), B. McBreen (8), K. Leventis (9), S. Markoff (9), S. Leon (6), A. Kraus (10), F. J. Aceituno (1), R. Cunniffe (1), P. Kubánek (1) S. Vítek (1), S. Schulze (4), A. C. Wilson (11), R. Hudec (12), V. Simon (12), J. M. González-Pérez (13), T. Shahbaz (13), S. Guziy (14), S. B. Pandey (15), L. Pavlenko (16), E. Sonbas (17), S. Trushkin (3), N. Bursov (3), C. Sánchez.-Fernández (18) & L. Sabau-Graziati (19)

(1) IAA-CSIC, Camino Bajo de Huétor, 50, E-18008 Granada, Spain (2) ESO, Alonso de Córdova 3107, Vitacura, Santiago, Chile (3) SAO-RAS, Nizhnij Arkhyz, Karachai-Cirkassian Rep., 369167 Russia (4) Thüringer Landessternwarte Tautenburg, Sternwarte 5, D-07778 Tautenburg, Germany (5) Laboratoire d'Astrophysique, EPFL, Observatoire, 1290 Sauverny, Switzerland (6) IRAM, 300 rue de la Piscine, 38406 Saint Martin d'Héres, France (7) Facultad de Ciencias Experimentales, Universidad de Jaén, Campus Las Lagunillas, E-23071 Jaén, Spain (8) School of Physics, University College, Dublin, Ireland (9) Astronomical Institute ‘Anton Pannekoek’, Univ. of Amsterdam, The Netherlands (10) MPI fur Radioastronomie, Bonn, Germany (11) Department of Astronomy, University of Texas, Austin, TX 78712, USA (12) Astronomical Institute of the Czech Academy of Sciences, Ondrejov (13) IAC, Vía Láctea s/n, La Laguna, Tenerife, Spain (14) Nikolaev State University, Nikolskaya 24, 54030 Nikolaev, Ukraine (15) ARIES, NainiTal, India (16) Crimean Astrophysical Observatory, Nauchnyv, Ukraine (17) Univ. of Cukurova, Dep. of Physics, Adana, Turkey (18) ESAC Villafranca del Castillo (Madrid), Spain (19) INTA, Ctra. de Ajalvir km. 4, 28750 Torrejón de Ardoz (Madrid), Spain OutlineOutline

„ IntroductionIntroduction (neutron(neutron stars,stars, ,pulsars, magnetarsmagnetars,, ……)) „ GRBGRB 070610:070610: aa veryvery unusualunusual XX--ray/optray/opt counterpartcounterpart „ SWIFTSWIFT J1955+2604:J1955+2604: ExtragalacticExtragalactic oror GalacticGalactic ?? „ DistanceDistance scalescale „ ItsIts nature:nature: aa likelylikely magnetarmagnetar (but(but aa UCXRBUCXRB cannotcannot bebe completelycompletely excluded)excluded) „ Implications:Implications: aa missingmissing linklink inin thethe NSNS familyfamily ?? I.I. IntroductionIntroduction

NeutronNeutron stars,stars, pulsars,pulsars, magnetarsmagnetars,, …… NeutronNeutron starstar ““flavoursflavours””

„ AccretionAccretion--poweredpowered (mainly(mainly XX--rayray binaries)binaries) „ RotationRotation--poweredpowered (ordinary(ordinary pulsars)pulsars) „ UltraUltra--strongstrong magneticmagnetic fieldfield--poweredpowered ((magnetarsmagnetars)) „ RotationRotation andand magneticmagnetic fieldfield poweredpowered (one(one case!)case!) UltraUltra--strongstrong BB--powered:powered: MagnetarsMagnetars

„ First detection on 5 Mar 1979 by Mazets et al. (1979): a tremendous, short burst of soft gamma- rays arising from the SNR N49 in LMC. Dubbed “SGR 0525-65” (“Soft Gamma-ray Repeater”). „ The localization superimposed to the SNR N49 (Cline et al. 1979) made straightforward its relationship to a NS „ Another SGRs discovered in the next decades (half a dozen so far) „ An X-ray burst arising from SGR 1806-20 was detected in 1993, confirming the NS origin (Murakami et al. 1993) „ Detection of pulsations in SGR 1806-20 (Kouveliotou et al. 1998) proposed a rotating NS with B~5 x 1014 G „ The model (Duncan & Thompson 1992) „ Anomalous X-ray pulsars join magnetars in A magnetic twist gives rise to X-ray 2000’s. emissions (from R. Duncan) II.II. TheThe γγ--rayray burstburst 070610070610

AA veryvery unusualunusual XX--rayray andand opticaloptical counterpartcounterpart (SWIFT(SWIFT J1955+2605)J1955+2605) GRB 070610 2 2 et et ray ray - - 1.0) 1.0) X X - Pagani - Pagani erg/cm erg/cm 7 7 Pagani Pagani - - ( ( /BAT as a /BAT as a 0.25 0.25 10 10 detection of a GRB detection of a GRB · · ± ± Swift Swift ) = (63.5, ) = (63.5, indistinguishable 0.4) 0.4) 3100s later ( 3100s later ( ± ± l , b l , b ray repeater bursts) ray repeater bursts) ( ( - - (2.4 Swift (2.4 et al. GCN 6491)

Swift et al. GCN 6491) /XRT detected an /XRT detected /XRT detected an /XRT detected ~5s (longer and harder than ~5s (longer and harder than 90 90 Tueller Tueller Detected on 10 June 2007 20:52:26 UT by al. GCN 6489) at galactic ccordinates T soft gamma Photon index 1.76 Fluence ( Swift counterpart et al. GCN 6490) with a column density slightly lower than the Galactic. normal burst, Detected on 10 June 2007 20:52:26 UT by al. GCN 6489) at galactic ccordinates T soft gamma Photon index 1.76 Fluence ( Swift counterpart et al. GCN 6490) with a column density slightly lower than the Galactic. normal burst, from cosmic GRBs „ „ „ „ „ „ „ „ „ „ TheThe opticaloptical counterpartcounterpart

„ Stefanescu et al. (GCN 6492) reported the detection of a variable optical counterpart. „ de Ugarte Postigo et al. (GCN 6501) confirmed the detection with observations from the 1.5m OSN. „ D.A. Kann et al. (GCN 6505) suggested a Galactic origin, based on unusual flaring activity and location near the galactic plane: l=63.3º b=-1º „ Dubbed SWIFT J195509+261406. OurOur datasetdataset BetweenBetween 11 minuteminute andand 11 yearyear afterafter thethe burst:burst: „ RadioRadio observationsobservations fromfrom RATANRATAN--600600 andand 100m100m EffelsbergEffelsberg „ MillimetreMillimetre observationsobservations fromfrom PlateauPlateau dede BureBure && IRAMIRAM „ NIRNIR imagingimaging fromfrom 8.2m8.2m VLTVLT (including(including AO)AO) „ OpticalOptical datadata fromfrom 1.51.5--mm OSN,OSN, 0.30.3--mm BOOTESBOOTES--2,2, 0.40.4--mm WATCHER,WATCHER, 1.341.34--mm TLS,TLS, 6.06.0--mm BTABTA andand 8.28.2-- mm VLTVLT „ XX--rayray datadata fromfrom SwiftSwift/XRT/XRT && XMMXMM--NewtonNewton OpticalOptical andand XX--rayray lightlight curvescurves Early light curve / early flares (I)

„ We recorded ~ 40 flare episodes „ Up to I~14.8, timescales of ~20sec - 7 min „ Amplitudes up to 1 7 mag OpticalOptical lightlight curvecurve (I)(I) Early light curve / early flares (II)

An example of a dense series of VRI Dense series of VRI observations (duration observations (duration ~75 min) (June 10, ~65 min) (June 11, 2007). J1955 was clearly 2007). J1955 was near the detection limit, detected. The I and R data are not quite but peaks of several flares are resolved. simultaneous. Significant fluctuations of the Amplitude of the brightest R band flare is brightness are apparent (~1 mag, timescale > 1 mag(R). Baseline brightness is below ~15 min). Baseline brightness is well- the detection limit. defined both in R and I. OpticalOptical lightlight curvecurve (II)(II) Early light curve / early flares (III) Statistical distribution of R and I magnitudes in the June 11 series. The most abundant faintest and negative skewness imply that the I observed brightness fluctuations have the form of peaks (spikes) from a well-defined baseline R brightness. The mutual similarity of the statistical distributions of R and I magnitudes in this night series enables to determine the mean R-I from the mean mag in each filter. Comparison of the color index R-I from the June 11 series with the color of OAs of GRBs from Simon et al. (2004). Colors of the ensemble are de-reddened for the Galactic and are in the observer frame. The color of J1955 was

dereddened by AV = 4 mag, near the lower limit AV=3.6 mag of the suggested range. Further increase of AV leads to the decrease of the color index (arrow). (R-I)0 of J1955 is thus similar to that of the ensemble of OAs and is consistent with the synchrotron emission (e.g. Sari et al. 1998). Thus thermal emission is ruled out. OpticalOptical lightlight curvecurve (III)(III)

2 3 OpticalOptical lightlight curvecurve (IV)(IV) Late flaring

„ AfterAfter thethe thirdthird dayday activityactivity decreasesdecreases „ AA faintfaint sourcesource waswas stillstill detectabledetectable „ LastLast flareflare ((nIRnIR)) isis detecteddetected 1111 daysdays afterafter OpticalOptical lightlight curvecurve (V)(V)

Light curve- 3 (quiet level) 3 3 OpticalOptical lightlight curvecurve (VI)(VI) Baseline flux evolution

„ The emission between flares 24281211 JuneSeptemberOctoberJune 20072007 2007 2007 slowly decreased until it disappeared. „ No detectable quiescent counterpart once the flaring emission ceased „ Limits: H, I > 23 (VLT, SAO, this work) R > 26.5 (Keck, Kasliwal et al. paper, ApJ 2008) I > 24.5 (Keck, Kasliwal et al. paper, ApJ 2008) OpticalOptical spectroscopyspectroscopy…… andand MurphyMurphy’’ss lawlaw „ Attempted at the 6.0m BTA the 11th and the 12th (bad weather; green) „ Finally achieved on the 13th when the source was already I~23 (arrow) „ 6x600s BTA spectra showed not even a detection of continuum III.III. DistanceDistance scalescale

TheThe HH columncolumn inin thethe lineline ofof sightsight vsvs thethe absorptionabsorption columncolumn fromfrom thethe XX--rayray spectrumspectrum

TheThe redred giantsgiants clumpclump methodmethod DistanceDistance scalescale (I)(I)

G. Kanbach & A. Stefanescu DistanceDistance scalescale (II)(II)

„ X-ray (Swift/XRT data): PL +3 21 -2 NH = (7.2 -2) x 10 cm

→ AV=3.6 – 7.5 mag 21 -2 following E(B-V) = NH/5.9x10 cm

„ H I observations (21 cm line) (Effelsberg), 3 x 3 raster p.

21 -2 → NH I =(8.1±1.2) x 10 cm DistanceDistance scalescale (III)(III)

+3 21 -2 „ X-ray → NH=(7.2 -2) x 10 cm → AV=3.6 – 7.5 mag „ H I observations 21 -2 → NH I = (8.1±1.2) x 10 cm

„ H2 observations (PdB) CO(J=1-0) 21 -2 → NH2 =(3.0±0.4) x 10 cm → Cloud at a kinematic distance of 3.7

kpc producing 50% of the NH → d > 3.7 kpc (tangent point)

„ → NH = N H I + 2 N H2 = (14.1±2.0) x 1021cm-2 → GALACTIC origin ! DistanceDistance scalescale (III)(III)

„ “Red clump” method (López-Corredoira et al. 2005, Durant and van Kerwijk 2006)

„ → AV = 3.6 – 7.5 mag „ → D~ 4 kpc IV.IV. TheThe SWIFTSWIFT J1955+2605J1955+2605 naturenature

AA magnetarmagnetar (very(very likely)likely) OROR anan ultracompactultracompact lowlow--massmass XX--rayray binarybinary ?? WhatWhat isis thethe naturenature ofof thethe sourcesource ?? (I)(I) Observational Facts

„ GammaGamma--rayray burstburst--likelike ““eventevent”” triggeringtriggering thethe activityactivity „ XX--ray,ray, opticaloptical andand nIRnIR (but(but nono radio)radio) flaringflaring eventsevents „ XX--rayray andand opticaloptical baselinebaseline emissionemission detecteddetected asas wellwell betweenbetween thethe flaresflares butbut nono atat radioradio oror softsoft (15(15-- 4040 keVkeV)) gammagamma--rays.rays. „ DramaticDramatic opticaloptical flaringflaring activityactivity forfor ~~22 daysdays „ NoNo quiescentquiescent counterpartcounterpart onceonce thethe activityactivity ceasedceased (only(only deepdeep limitslimits inin radio,radio, NIRNIR && XX--rays)rays) „ GalacticGalactic originorigin WhatWhat isis thethe naturenature ofof thethe sourcesource ?? (II)(II)

„ Cosmological GRB? Light curve behaviour and location rule it out.

„ Microquasar/Fast X-ray ? (Uemura et al. 1999, Kasliwal et al. 2008) Unlike V4641 Sgr, where strong gamma- ray and radio emission was detected (reaching around 1 Crab in gamma-rays and few mJy in radio, compared to < 0.01 Crab and < 0.1 mJy respectively for the SWIFT source).

„ Bursting ? GRO J1744-28, where further gamma-ray activity was observed, is also quite different. No pulsations measured in the SWIFT source for the time being. WhatWhat isis thethe naturenature ofof thethe sourcesource ?? (III)(III) „ AnAn ultraultra--compactcompact lowlow--massmass XX--rayray binarybinary ?? Flares could be produced by blobs of homogeneous synchrotron-emitting plasma of size of 107 cm and magnetic field of strength 105 G.

The blobs can be found in a magnetized corona (Merloni et al. 2000) or a wind ((rather than in the outer regions of a collimated jet). This model cannot be ruled out WhatWhat isis thethe naturenature ofof thethe sourcesource ?? (IV)(IV) „ AA softsoft gammagamma--rayray repeater?repeater?

SGRs are magnetars (young NS with B = 1014-15 G) with a prolific bursting rate when they are “switched-on”.

Flares would be due to coherent plasma bunches (Thompson & Beloborodov 2005), leading easily to the observed optical of : 1035 (D/5 kpc)2 erg/s WhatWhat isis thethe naturenature ofof thethe sourcesource ?? (V)(V)

„ SGRSGR hypothesishypothesis supportedsupported by:by:

1.1. thethe lognormallognormal distributiondistribution burstburst fluxes.fluxes.

SWIFT source (Castro-Tirado et al. 2008) SGR 1900+14 (Woods et al. 1999) WhatWhat isis thethe naturenature ofof thethe sourcesource ?? (VI)(VI)

2.2. similaritiessimilarities withwith otherother transienttransient magnetarsmagnetars::

SGR 1900+14 (Woods et al. 1999) -harder, intermediate-duration bursts with comparable energy releases to GRB 070610 also observed in magnetars

-similar X-ray decaying light curves SGR 1627-41 (Kouveliotou et al. 2003) WhatWhat isis thethe naturenature ofof thethe sourcesource ?? (VII)(VII) (Stefanescu et al. 2008) 3.3. AA possiblepossible periodicityperiodicity inin thethe XX--rayray datadata::

-similar period as seen in other magnetars (few s) V.V. ImplicationsImplications

AA missingmissing linklink inin thethe NSNS familyfamily ?? ImplicationsImplications

„ AA newnew magnifestationmagnifestation ofof magnetarmagnetar activity,activity, becomingbecoming oneone ofof thethe fewfew hundredhundred GalacticGalactic onesones becomingbecoming activeactive inin fewfew xx 10104 yr.yr. „ TheThe quiescentquiescent XX--rayray luminosityluminosity :: LxLx << 99 xx 101031 (D/5(D/5 kpc)kpc)2 erg/serg/s isis intermediateintermediate betweenbetween transienttransient magnetarsmagnetars (including SGRs/AXPs): LxLx == (2(2--4)4) xx 101035 erg/serg/s andand dimdim isolatedisolated neutronneutron starsstars ((DINsDINs):): LxLx == (2(2--20)20) xx 101030 erg/serg/s „ TheThe missingmissing linklink betweenbetween magnetarsmagnetars andand DINsDINs ?? ConclusionsConclusions ConclusionsConclusions

„ WeWe observedobserved aa normalnormal GRBGRB andand foundfound aa peculiarpeculiar galacticgalactic sourcesource ((bb == --1.0)1.0) withwith intenseintense flaringflaring activity.activity. „ OpticalOptical flaresflares ofof overover 44 magnitudesmagnitudes andand durationsdurations ofof ~1~1 minmin (not(not observedobserved inin ““classicalclassical SGRsSGRs””,, notnot onlyonly aa ““highhigh GalacticGalactic extinctionextinction”” problem).problem). „ AnAn ultracompactultracompact LMXBLMXB ?? „ TheThe fifthfifth SGRSGR inin thethe GalaxyGalaxy ?? FirstFirst opticaloptical couterpartcouterpart detecteddetected forfor suchsuch object.object. „ TheThe missingmissing linklink betweenbetween magnetarsmagnetars andand DINsDINs ??