PoS(GRB 2012)100 http://pos.sissa.it/ ∗ [email protected] [email protected] Speaker. A significant fraction of the Long Gamma-rayphase Bursts which (GRBs) may in the be Swift due samplethe show to Swift a ongoing satellite plateau show energy similar injection. behavior.mediately to We The a find remnant BH of many (or NS-NS Short even mergersthere GRBs collapse may would at detected not be all) by collapse a forming im- instead plateau ais phase . in a This the stable model X-ray magnetar, predicts lightcurve or that to followed a all by steep of a decay the shallow Short if decay GRBdence the phase, lightcurves, BAT-XRT of if magnetar we energy it collapses injection find to by that a a agravitational magnetar. significant BH. wave observatories. This fraction By model may fitting can show this be evi- tested model using the next generations of ∗ Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. c

Gamma-Ray Bursts 2012 Conference -GRB2012, May 07-11, 2012 Munich, Germany P. T. O’Brien A. Rowlinson Astronomical Institute "Anton Pannekoek", University ofAmsterdam, Amsterdam, The Postbus 94249, Netherlands 1090 GE E-mail: Department of Physics & Astronomy, University7RH, of United Leicester, University Kingdom Road, Leicester, LE1 E-mail: Energy injection in short GRBs andmagnetars the role of PoS(GRB 2012)100 2 ].

≤ 18 , 2 M 90 T ∼ 25 ]. 26 P. T. O’Brien , 17 X-ray Telescope , ]. As the magnetar 28 5 , 7 Swift , enabled the detection of 29 Swift ]. This progenitor theory requires 20 , SGRBs have been fitted using a broken 50% of SGRBs have a shallow decay, or 8 , we compare the lightcurve break times , ∼ 1 15 Swift ]. If the magnetar is stable the plateau will be 2 30 ]. We find 9 ]. ]. The afterglow properites and identified host . In Figure 24 1 13 , 11 SGRBs detected by the Burst Alert Telescope (BAT) with ] has revolutionised the study of early X-ray emission in gamma-ray ]. Also the rapid slewing capabilities of Swift 10 31 , observations led to the discovery of features such as flares and plateaus in 23 , Swift 21 satellite [ ], it has been shown that many neutron star mergers may result in a delayed collapse 6 Swift The combined lightcurves BAT-XRT for all the Assuming constant radiative efficiency, the electromagnetic energy injection from the magne- Here we consider all The With the increasing number of SGRB X-ray afterglows, it has become apparent that SGRBs plateau, phase showing evidence of energy injection.in The their SGRBs afterglows which required are 2 plotted or more in breaks Figure 2. Evidence of energy injection in SGRB lightcurves (XRT). We identify those with ajection plateau from phase the in central theirdirectly engine. lightcurves to suggesting the ongoing For lightcurves. energy 28 This in- work SGRBsMNRAS). is with described sufficient in detail data, in we Rowlinson et fit al. the (2012, magnetar submitted to model power-law utilising the method described in [ tar produces a plateau in the X-ray lightcurve [ followed by a shallow decay phasedecay as phase it in spins the down, lightcurve however whensteep if the decay it phase magnetar is has collapses unstable been to there observed form in will a several be black LGRB a hole. and steep SGRB This lightcurves plateau [ and to a black hole or may not collapse at all [ the faint and rapidly decaying shortcandidate host GRB (SGRB) identifications X-ray [ afterglows whichof has SGRBs led are to consistent a with numbera of the neutron popular star progenitor and theory: black hole the merger forming of a two black neutron hole stars [ or An alternative model is thatcoalescing the to form merger a of highly two magnetised,tional rapidly neutron energy rotating to stars prevent does immediate (magnetar) gravitational which not collapse has form to enough a a rota- black hole black [ hole, instead s, until March 2012, which were promptly slewed to and observed by the also have features caused by energySGRB injection progenitor in their theories lightcurves. as However, accretion thisa is is small problematic expected amount for to of end material within ejected a into few eccentric seconds orbits and which there may is accrete only at late times [ Energy injection in short GRBs and the role of 1. Introduction bursts (GRBs). confirmation via the coincident detection of gravitational waves and a SGRB. spins down, its rotational energy isDuring transfered this to graviational spin waves down and process electromagneticsupport the radiation. its magnetar mass via may rapid reach rotation, adependent resulting in critical on collapse point, the to at equation a black which ofneutron hole. it state star This can of [ critical no a point is longer neutron highly star. Following the recent discovery of a many long GRB (LGRB) lightcurves,central showing engine evidence [ of prolonged energy injection from the PoS(GRB 2012)100 , , ]. 1 − 28 19 (3.2) (3.1) (3.3) ]. We erg s 19 49 P. T. O’Brien is the radius of 6 R , G 15 7). The data were fit with an . 0 3 3 2 ∼ , , ]. 1 2 − 9 − − em em is the moment of inertia in units of  T T 3 , 45 1 1 49 49 I , , − − em 0 0 , T 1 L L T 3 6 ] and has previously been applied by [ − is the plateau luminosity in 10 45 − − 6 I 30 R 49 , 10 05 0 2 . 45 erg s I L 2 + 49 1 3 s, =  3 3 2025 . − 49 , , 4 2 0 0 P L is the break from the steep decay phase to the plateau phase = 1 15 , ) = p 2 T is the initial period of the compact object in milliseconds. The B ( 3 49 − , , 0 em P L ] (when no was available, we used z cm and 6 2 is the magnetic field strength at the poles in units of 10 is the plateau duration in 10 3 15 , , p em B T , is the time-dependent luminosity in 10 Left: These GRBs have 2 or more breaks in their lightcurve: Black - 051221A, red - 060313, 2 marks the end of the plateau. The blue filled histograms correspond to the SGRB sample used in ) 2 T ]. This model is consistent to the late-time residual spin-down regime described in [ ( where The model fitted in this work is as described in [ g cm 49 26 , ]. In some cases, we allowed the power-law component to vary. These equations apply to the 45 , em 14 the neutron star in 10 equations of vacuum dipole spin-down given above neglectdue the to enhanced neutrino-driven angular mass momentum loss, losses which are important at early times after the magnetar forms [ fit the equations below directlyusing to a the k-correction observed [ data whichadditional has underlying been power-law extrapolated component to whose the decay[ restframe rate is governed by the curvature effect 10 electromagnetic dominated spin down regime,be as the extremely gravitational rapid wave and dominatedemission regime produce is would a 100% efficient negligble and electromagnetic isotropic. signal. We have assumed that the 17 to those for LGRBs showingorders that of the magnitude SGRB earlier breaks, than before those and for after LGRBs. plateau phases, are occuring 3. Fitting the magnetar model L Figure 1: green - 061201, dark- blue 100702A, - light 070724, green lightSGRB - blue lightcurves 101219A, with - cyan a 090426, - plateau 120305A. magenta phase. Right: - 090515, T Histograms yellow showing - the 100625A, break orange times for the this Paper and overplotted in red are the LGRB values determined by [ while T Energy injection in short GRBs and the role of magnetars PoS(GRB 2012)100 200 s. The ∼ P. T. O’Brien ] and the unshaded ]. Blue stars = good 16 ]. The initial rotation 27 26 G[ 15 10 ] and [ ≥ 17 ) neutron star [

(2.1 M

4 ]. 3 ] and the lower limit for the magnetic field is 29 10ms [ ≤ A graph showing the magnetic field and spin period of the magnetar fits produced. The solid Example fits for two of the SGRBs in this sample. GRB 051221A (left) is best fit by a stable Nevertheless, these expressions reasonably approximate theneutron spin-down stars of of very most highly magnetized relevancefor in relatively this powerful magnetar paper. winds, Isotropic sincemagnetar emission (unlike outflow following is the cannot also collapse be a ofmaterial reasonable confined a expected assumption massive efficiently following star) a by the NS the merger [ relatively small quantity of surrounding region shows the expected regionperiod needs for to an be unstablefit pulsar, as to defined the in magnetarmagnetar [ model which with collapses a to form stable a magnetar, BH, Green and Red circles triangles = = good poor fit fit to to the model. the model with an unstable Figure 3: (dashed) red line represent the spin break up period for a 1.4 M grey data points are excluded from the fit. Figure 2: magnetar and GRB 120305A (right) is best fit by a magnetar which collapses to a black hole at Energy injection in short GRBs and the role of magnetars PoS(GRB 2012)100 P. T. O’Brien ], the detection . All candidates 3 12 ] and, for the un- 4 A two-solar-mass (2011) 1537 75% had a good fit to the ∼ 419 (2010) 173001 , 27 , (2009) 1171 ]. Although the inspiral phase is 22 702 MNRAS Short gamma-ray bursts with extended , , for GRB 051221A, consistent with the CQGra , 333 (1998) L87 , 2 ApJ (2010) 1081 , A&A , 467 , 200 s. 5 ∼ Nature , ], the spin down of the magnetar [ 1 (2001) 2879 The Prompt Energy Release of Gamma-Ray Bursts using a 121 , Formation of very strongly magnetized neutron stars - Implications for (1992) L9 AJ , 392 , Gamma-ray Burst Afterglow Plateaus and Gravitational Waves: ApJ , Gamma-ray burst afterglows and evolution of postburst fireballs with energy TOPICAL REVIEW: Predictions for the rates of compact binary coalescences gamma-ray bursts injection from strongly magnetic millisecond Multi-messenger Signature of a Millisecond Magnetar? emission from magnetar birth: jet formation and collimation neutron star measured using Shapiro delay observable by ground-based gravitational-wave detectors Cosmological k-Correction The detection of multiple gravitational wave signals with associated features in the gamma-ray This model may be testable via the detection of gravitational waves from all three phases of The derived magnetic field strengths and spin periods are plotted in Figure 28 SGRBs had sufficient data for fitting to the magnetar model and [6] Demorest P. 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References distance limits are increased towill within provide 1300 a Mpc significant increase (5900 to Mpc the for expected the rates. inspiral phase only) and this this model: insprial to form a magnetar [ have spin periods in excessthe of predicted the maximum/minimum shortest values allowed for spinperiod. the periods. magnetic The fields Almost lines and all in an ofalthough the estimated some the figure maximum have represent spin magnetar relatively low candidates spin periods. lie within the expected magnetic5. field Gravitational strengths, wave signals going to have the brightestdetect associated all gravitational three wave phases signal, for Advanced sourcesthe LIGO within expected 100 may rates Mpc be are (445 able very Mpcmagnetic low to for for radiation. the the inspiral Using simultaneous phase the detection only) predicted of although sensitivity gravitational waves for and the electro- Einstein Telescope [ Energy injection in short GRBs and the role of magnetars 4. Results model. For the SGRBs whichExample had fits to a the poor magnetar fitformation model this of are may a shown simply stable in be magnetar, Figure and duethe GRB to magnetar 120305A insufficient collapsing which to data has form or a a flares. steep black decay hole phase at associated with stable magnetar candidates, the collapse to form a black hole [ PoS(GRB 2012)100 , , , , 28 , ApJ MNRAS 27 , , , (2007) (2005) P. T. 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