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Register a new userX-ray Timing Observations of PSR J1930+1852 in the Crab-like SNR G54.1+0.3
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We present new X-ray timing and spectral observations of PSR J1930+1852, the young energetic pulsar at the center of the non-thermal supernova remnant G54.1+0.3. Using data obtained with the Rossi X-ray Timing Explorer and Chandra X-ray observatories we have derived an updated timing ephemeris of the 136 ms pulsar spanning 6 years. During this interval, however, the period evolution shows significant variability from the best fit constant spin-down rate of $dot P = 7.5112(6) times 10^{-13}$ s s$^{-1}$, suggesting strong timing noise and/or glitch activity. The X-ray emission is highly pulsed ($71pm5%$ modulation) and is characterized by an asymmetric, broad profile ($sim 70%$ duty cycle) which is nearly twice the radio width. The spectrum of the pulsed emission is well fitted with an absorbed power law of photon index $Gamma = 1.2pm0.2$; this is marginally harder than that of the unpulsed component. The total 2-10 keV flux of the pulsar is $1.7 times 10^{-12}$ erg cm$^{-2}$ s$^{-1}$. These results confirm PSR J1930+1852 as a typical Crab-like pulsar.
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We report the discovery of very high energy gamma-ray emission from the direction of the SNR G54.1+0.3 using the VERITAS ground-based gamma-ray observatory. The TeV signal has an overall significance of 6.8$sigma$ and appears point-like given the 5$^{arcminute}$ resolution of the instrument. The integral flux above 1 TeV is 2.5% of the Crab Nebula flux and significant emission is measured between 250 GeV and 4 TeV, well described by a power-law energy spectrum dN/dE $sim$ E$^{-Gamma}$ with a photon index $Gamma= 2.39pm0.23_{stat}pm0.30_{sys}$. We find no evidence of time variability among observations spanning almost two years. Based on the location, the morphology, the measured spectrum, the lack of variability and a comparison with similar systems previously detected in the TeV band, the most likely counterpart of this new VHE gamma-ray source is the PWN in the SNR G54.1+0.3. The measured X-ray to VHE gamma-ray luminosity ratio is the lowest among all the nebulae supposedly driven by young rotation-powered pulsars, which could indicate a particle-dominated PWN.
In the summer of 2012, during a Pulsar Search Collaboratory workshop, two high-school students discovered J1930$-$1852, a pulsar in a double neutron star (DNS) system. Most DNS systems are characterized by short orbital periods, rapid spin periods and eccentric orbits. However, J1930$-$1852 has the longest spin period ($P_{rm spin}sim$185 ms) and orbital period ($P_{rm b}sim$45 days) yet measured among known, recycled pulsars in DNS systems, implying a shorter than average and/or inefficient recycling period before its companion went supernova. We measure the relativistic advance of periastron for J1930$-$1852, $dot{omega}=0.00078$(4) deg/yr, which implies a total mass (M$_{rm{tot}}=2.59$(4) M$_{odot}$) consistent with other DNS systems. The $2sigma$ constraints on M$_{rm{tot}}$ place limits on the pulsar and companion masses ($m_{rm p}<1.32$ M$_{odot}$ and $m_{rm c}>1.30$ M$_{odot}$ respectively). J1930$-$1852s spin and orbital parameters challenge current DNS population models and make J1930$-$1852 an important system for further investigation.
Recent XMM-Newton observations reveal an extended (150) low-surface brightness X-ray halo in the supernova remnant G21.5-0.9. The near circular symmetry, the lack of any limb brightening and the non-thermal spectral form, all favour an interpretation of this outer halo as an extension of the central synchrotron nebula rather than as a shell formed by the supernova blast wave and ejecta. The X-ray spectrum of the nebula exhibits a marked spectral softening with radius, with the power-law spectral index varying from Gamma = 1.63 +/- 0.04 in the core to Gamma = 2.45 +/- 0.06 at the edge of the halo. Similar spectral trends are seen in other Crab-like remnants and reflect the impact of the synchrotron radiation losses on very high energy electrons as they diffuse out from the inner nebula. A preliminary timing analysis provides no evidence for any pulsed X-ray emission from the core of G21.5-0.9.
While theoretical dust condensation models predict that most refractory elements produced in core-collapse supernovae (SNe) efficiently condense into dust, a large quantity of dust has so far only been observed in SN 1987A. We present the analysis of Spitzer Space Telescope, Herschel Space Observatory, Stratospheric Observatory for Infrared Astronomy (SOFIA), and AKARI observations of the infrared (IR) shell surrounding the pulsar wind nebula in the supernova remnant G54.1+0.3. We attribute a distinctive spectral feature at 21 $mu$m to a magnesium silicate grain species that has been invoked in modeling the ejecta-condensed dust in Cas A, which exhibits the same spectral signature. If this species is responsible for producing the observed spectral feature and accounts for a significant fraction of the observed IR continuum, we find that it would be the dominant constituent of the dust in G54.1+0.3, with possible secondary contributions from other compositions, such as carbon, silicate, or alumina grains. The smallest mass of SN-formed dust required by our models is 1.1 $pm$ 0.8 $rm M_{odot}$. We discuss how these results may be affected by varying dust grain properties and self-consistent grain heating models. The spatial distribution of the dust mass and temperature in G54.1+0.3 confirms the scenario in which the SN-formed dust has not yet been processed by the SN reverse shock and is being heated by stars belonging to a cluster in which the SN progenitor exploded. The dust mass and composition suggest a progenitor mass of 16$-$27 $rm M_{odot}$ and imply a high dust condensation efficiency, similar to that found for Cas A and SN 1987A. The study provides another example of significant dust formation in a Type IIP SN and sheds light on the properties of pristine SN-condensed dust.
We report the discovery of a star-forming loop around the young, Crab-like supernova remnant (SNR) G54.1+0.3 using the AKARI infrared satellite. The loop consists of at least eleven young stellar objects (YSOs) embedded in a ring-like diffuse emission of radius ~1. The YSOs are bright in the mid-infrared and are also visible in the Spitzer Space Telescope Galactic plane survey images. Their Spitzer colors are similar to those of class II YSOs in [3.6]-[5.8] but significantly redder in [8]-[24], i.e., 0<[3.6]-[5.8]<1.2 and 5<[8]-[24]<9. Most of them have near-infrared counterparts in the 2MASS JHKs images, and some of them have an optical counterpart too. Their JHKs colors and magnitudes indicate that the YSOs are massive (<= 10 Msun) pre-main-sequence stars at the same distance to the SNR, i.e., 8 kpc, which supports the association of the star-forming loop with the SNR. The dereddened spectral energy distributions are similar to eraly Herbig Be stars, which are early B-type pre-main-sequence stars with inner disks that have been destroyed. The confinement to a loop structure indicates that the YSOs are young, i.e., <= 2 Myr. We propose that their formation is triggered by the progenitor star of G54.1+0.3, which has a mass of <= 15 Msun. The triggering must have occurred near the end of the progenitors life, possibly after it had evolved off the main sequence.
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