* Astronomy

Blobrana · L

RE: Swift J1822.3-1606

Blobrana · L

Title: A new low-B magnetar: Swift J1822.3-1606
Authors: A. Camero-Arranz, N. Rea, G. L. Israel, P. Esposito, J. A. Pons, R. P. Mignani, R. Turolla, S. Zane, M. Burgay, A. Possenti, S. Campana, T. Enoto, N. Gehrels, E. Gogus, D. Gotz, C. Kouveliotou, K. Makishima, S. Mereghetti, S. R. Oates

We report on the long term X-ray monitoring with Swift, RXTE, Suzaku, Chandra, and XMM-Newton of the outburst of the newly discovered magnetar Swift J1822.3-1606 (SGR 182-1606), from the first observations soon after the detection of the short X-ray bursts which led to its discovery (July 2011), through the first stages of its outburst decay (April 2012). Our X-ray timing analysis finds the source rotating with a period of P = 8.43772016(2) s and a period derivative Pdot = 8.3(2) x 10e-14 s s-1, which entails an inferred dipolar surface magnetic field of 2.7 x 10e13 G at the equator. This measurement makes Swift J1822.3-1606 the second lowest magnetic field magnetar (after SGR 0418+5729; Rea et al. 2010). Following the flux and spectral evolution from the beginning of the outburst, we find that the flux decreased by about an order of magnitude, with a subtle softening of the spectrum, both typical of the outburst decay of magnetars. By modelling the secular thermal evolution of Swift J1822.3+1606, we find that the observed timing properties of the source, as well as its quiescent X-ray luminosity, can be reproduced if it was born with a poloidal and crustal toroidal fields of Bp ~ 1.5 x 10e14 G and Btor ~ 7 x 10e14 G, respectively, and if its current age is ~550 kyr (more details in Rea et al. 2012).

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Blobrana · L

Title: The New Magnetar Swift J1822.3-1606
Authors: P. Scholz, C.-Y. Ng, M. A. Livingstone, V. M. Kaspi, A. Cumming, R. Archibald

On 2011 July 14, a transient X-ray source, Swift J1822.3-1606, was detected by Swift BAT via its burst activities. It was subsequently identified as a new magnetar upon the detection of a pulse period of 8.4 s. Using follow-up RXTE, Swift, and Chandra observations, we have determined a spin-down rate of \dot{P} ~3 x 10^{-13}, implying a dipole magnetic field of ~5 x 10^{13} G, second lowest among known magnetars, although our timing solution is contaminated by timing noise. The post-outburst flux evolution is well modelled by surface cooling resulting from heat injection in the outer crust, although we cannot rule out other models. We measure an absorption column density similar to that of the open cluster M17 at 10' away, arguing for a comparable distance of ~1.6 kpc for Swift J1822.3-1606. If confirmed, this could be the nearest known magnetar.

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Blobrana · L

A magnetic monster's dual personality

Is it a magnetar or is it a pulsar? A second member of a rare breed of dead, spinning star has been identified thanks to an armada of space-based X-ray telescopes, including ESA's XMM-Newton.
The recently discovered star appears to be a hybrid of these two stellar breeds: the spinning stellar skeleton appears as a pulsar while hiding an intense internal magnetic field much like a magnetar.
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Blobrana · L

Title: Swift J1822.3-1606: Post-outburst evolution of a nearby magnetar
Authors: P. Scholz, C.-Y. Ng, M. A. Livingstone, V. M. Kaspi, A. Cumming, R. Archibald

Swift J1822.3-1606 was discovered on 2011 July 14 by the Swift Burst Alert Telescope following the detection of several bursts. The source was found to have a period of 8.4377 s and was identified as a magnetar. Here we present a phase-connected timing analysis and the evolution of the flux and spectral properties using RXTE, Swift, and Chandra observations. We measure a spin frequency of 0.1185154316(5) s^{-1} and a frequency derivative of -3.5±0.2 x10^{-15} at MJD 55761.0, in a timing analysis that includes a significant non-zero second frequency derivative that we attribute to timing noise. This corresponds to an estimated spin-down inferred dipole magnetic field of B~5 x 10^{13} G, consistent with previous estimates though still possibly affected by unmodelled noise. We find that the post-outburst 1--10 keV flux evolution is well modelled with a double-exponential decay with decay timescales of 15.6±0.6 and 148±13 days. However we also fit the light curve with a crustal cooling model which suggests that the cooling results from heat injection into the outer crust and provides constraints on the impurity fraction in the crust. Based on proximity and similarity in absorption column density, we suggest that Swift J1822.3-1606 may have a distance comparable to that of the H{ii} region M17, 1.6±0.3 kpc, making it one of the closest magnetars yet known. We find that the hardness-flux correlation observed in magnetar outbursts also characterises the outburst of Swift J1822.3-1606. We compare the properties of Swift J1822.3-1606 with those of other magnetars and their outbursts.

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Blobrana · L

Title: A new low magnetic field magnetar: the 2011 outburst of Swift J1822.3-1606
Authors: N. Rea (CSIC-IEEC), G. L. Israel, P. Esposito (INAF), J. A. Pons (Alicante), A. Camero-Arranz (CSIC-IEEC), R. P. Mignani (MSSL), R. Turolla (Padova), S. Zane (MSSL), M. Burgay, A. Possenti, S. Campana (INAF), T. Enoto (Stanford), N. Gehrels (NASA), E. Gogus (Sabanci), D. Gotz (CEA), C. Kouveliotou (NASA), K. Makishima (Tokyo), S. Mereghetti (INAF), S. R. Oates (MSSL), D. M. Palmer (LANL), R. Perna (Boulder), L. Stella, A. Tiengo (INAF)

We report on the long term X-ray monitoring with Swift, RXTE, Suzaku and XMM-Newton of the outburst of the recently discovered magnetar Swift J1822.3-1606 (SGR 1822-1606), from the first observations soon after the detection of the short X-ray bursts which led to its discovery, through the first stages of its outburst decay (covering the time-span from July 2011, until end of February 2012). We also report on archival ROSAT observations which witnessed the source during its likely quiescent state, and on Swift J1822.3-1606's upper limits on radio-pulsed and optical emission during outburst, with the Green Bank Telescope (GBT) and the Gran Telescopio Canarias (GTC), respectively. Our X-ray timing analysis finds the source rotating with a period of P=8.43772013(2)s and a period derivative \dot{P}=9.1(4)x10^{-14} s/s, which entails an inferred dipolar surface magnetic field of B=2.8x10^{13} G at the equator. This measurement makes Swift J1822.3-1606 the second magnetar with a dipolar magnetic field lower than the electron critical field (after SGR 0418+5729; Rea et al. 2010). Following the flux and spectral evolution from the beginning of the outburst until now, we find that the flux decreased by about an order of magnitude, with a subtle softening of the spectrum, both typical of the outburst decay of magnetars. By modelling the secular thermal evolution of Swift J1822.3-1606, we find that the observed timing properties of the source, as well as its quiescent X-ray luminosity, can be reproduced if it was born with a poloidal and toroidal surface fields of B_{p} ~ 2x10^{14} G and B_{tor}~10^{16} G, respectively, and if its current age is ~0.5 Myr.

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