Hubble Space Telescope (HST) preexplosion image acquired in 1999 (Program 6359; PI: Stiavelli). The location of the progenitor of SN 2009ip is marked by an arrow. SN 2009ip exploded in the outskirts of its host galaxy NGC 7259 at an angular distance of ∼43. 4 from the host center, corresponding to ∼5 kpc. (A color version of this figure is available in the online journal.) 

Contexts in source publication

Context 1

... recent obser- vations have questioned this picture, revealing the limitations of our current understanding of the last stages of massive star evolution and in particular the uncertainties in the commonly as- sumed mass-loss prescriptions (Humphreys & Davidson 1994;Smith & Owocki 2006). Here, we present observations from an extensive, broadband monitoring campaign of SN 2009ip ( Figure 1) during its double explosion in 2012 that revealed extreme mass-loss properties, raising questions about our understanding of the late stages of massive star evolution. ...

Context 2

... spectra are consistent with a thermal bremsstrahlung model with kT = 60 keV and intrinsic neutral hydrogen absorption NH int = 0.10 +0.06 −0.05 × 10 22 cm −2 . The spectra are displayed in Figure 10 and show some evidence for an excess of emission around ∼7-8 keV (rest-frame), which might be linked to the presence of Ni or Fe emission lines (see, e.g., SN2006jd and SN2010jl; Chandra et al. 2012aChandra et al. , 2012b). ...

Context 3

... t > t pk − 7 days the UV + BVRI SED is well fitted by a blackbody spectrum with a progressively larger radius ("hot" blackbody component in Figure 11). The temperature evolution tracks the bolometric luminosity, with the photosphere becoming appreciably hotter in correspondence with light-curve bumps. ...

Context 4

... rapid decrease in radius is observed around t pk + 70 days. After this time the R HOT mimics the temporal evolution of the bolometric light-curve (see Figure 11). In SNe dominated by interaction with preeexisting material, the photospheric radius typically increases steadily with time, reaches a peak and then smoothly transitions to a decrease (see, e.g., SN 1998S, Fassia et al. 2000SN 2005gj, Prieto et al. 2007). ...

Context 5

... around t pk + 59 days the UV emission fades more slowly and we observe a change in the evolution of the UV and optical colors: from red to blue ( Figure 11, lower panel; Figure 12, upper panel). This can also be seen from Figure 2, where the NIR emission displays a more rapid decay than the UV. ...

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... around t pk + 59 days the UV emission fades more slowly and we observe a change in the evolution of the UV and optical colors: from red to blue ( Figure 11, lower panel; Figure 12, upper panel). This can also be seen from Figure 2, where the NIR emission displays a more rapid decay than the UV. ...

Context 7

... furthermore find clear evidence for excess of NIR emis- sion with respect to a simple blackbody fit (see Figure 13) as we first reported in Gall et al. (2012), based on the analysis of the VLT/X-shooter spectra (Figures 19 and 20). The NIR spectra of Figure 7 rule out line emission as a source of the excess. ...

Context 8

... furthermore find clear evidence for excess of NIR emis- sion with respect to a simple blackbody fit (see Figure 13) as we first reported in Gall et al. (2012), based on the analysis of the VLT/X-shooter spectra (Figures 19 and 20). The NIR spectra of Figure 7 rule out line emission as a source of the excess. ...

Context 9

... we use the SED best-fitting models above to compute the bolometric luminosity of SN 2009ip. Displayed in Figure 11 is the contribution of the "hot" blackbody. The "cold" blackbody contribution is marginal, being always (2-4)% the luminosity of the "hot" component. ...

Context 10

... plot does not include the late-time X-ray limit obtained on 2013 April 4.5 (t pk + 183 days). (Figure 14), it yet still retained evidence for absorption with core velocity v ≈ −5000 km s −1 . By 2012 Figure 9. Left panel: Swift-XRT image of the field of SN 2009ip collecting data before and after the optical peak (−32 days < t − t pk < −2 days and +29 days < t −t pk < +83 days), for a total exposure time of 110 ks. ...

Context 11

... color version of this figure is available in the online journal.) September 30 (t pk − 3 days, Figures 19 and 20) the spectrum no longer shows evidence for the high-velocity components in absorption and is instead dominated by He i and H i lines with narrow profiles, likely indicating that the photosphere is imbedded within a low-speed outflow. In the following months, SN 2009ip progressively evolves from a typical SN IIn (or LBV-like) spectrum with clear signs of interaction with the medium to a spectrum dominated by broad absorption features, which is more typical of SNe IIP ( Figure 21). ...

Context 12

... 30 (t pk − 3 days, Figures 19 and 20) the spectrum no longer shows evidence for the high-velocity components in absorption and is instead dominated by He i and H i lines with narrow profiles, likely indicating that the photosphere is imbedded within a low-speed outflow. In the following months, SN 2009ip progressively evolves from a typical SN IIn (or LBV-like) spectrum with clear signs of interaction with the medium to a spectrum dominated by broad absorption features, which is more typical of SNe IIP ( Figure 21). ...

Context 13

... two X-shooter spectra (Figures 19 and 20) sample two key points in this metamorphosis, providing a broadband view of these spectral changes at high resolution. The major spectral changes during the 2012b explosion can be summarized as follows. ...

Context 14

... During the first week after peak, H Balmer lines showed a narrow core with extended Thomson-scattered wings ( Figure 14 8. More importantly, SN 2009ip progressively develops broad absorption dips that have never been observed in LBV-like eruptions, while this is typical of a variety of SN explosions ( Figure 17). ...

Context 15

... the first week after peak, H Balmer lines showed a narrow core with extended Thomson-scattered wings ( Figure 14 8. More importantly, SN 2009ip progressively develops broad absorption dips that have never been observed in LBV-like eruptions, while this is typical of a variety of SN explosions ( Figure 17). Broad absorption dips disappear ∼200 days after peak (Figure 30). ...

Context 16

... Hα line profile experienced a dramatic change in mor- phology. Figure 14 By t pk − 7 days the broad components dominating the line profile 10 days before ( Mauerhan et al. 2013) have weakened to the level that most of the emission originates from a much narrower component with FWHM ≈ 1000 km s −1 . Absorption from high-velocity material (v ≈ −5000 km s −1 , measured at the minimum of the absorption feature) is still detected when the 2012b explosion luminosity is still rising. ...

Context 17

... high-resolution spectra collected on t pk − 5 and t pk − 4 days allow us to resolve different blue absorption components with central velocities km s −1 ) and broad (FWHM ≈ 2000-3000 km s −1 ) compo- nents, with the broad component becoming more prominent with time. At t pk + 11 days (time of the third bump of the bolo- metric light-curve, Figure 11), high-velocity absorption features reappear, with absorption minima at v ≈ −12,000 km s −1 and v ≈ −8000 km s −1 (σ ∼ 1000 km s −1 ). The low-velocity P Cygni absorption is also detected at v ≈ −1200 km s −1 . ...

Context 18

... comparing the H Paschen and Brackett emission lines using our two highest resolution spectra collected around the peak (narrow-line emission dominated spectrum at t pk − 3 days) and 28 days after peak (when broad components start to emerge, see Figures 19 and 20), we find that for both epochs the line profiles are dominated by the narrow component (FWHM ≈ 170 km s −1 ) with limited evolution between the two. ...

Context 19

... conclude by noting that, observationally, t pk +17 days (i.e., 2012 October 20) marks an important transition in the evolution of SN 2009ip: around this time the broad Hα component evolves from FWHM ∼ 3000 km s −1 to FWHM ∼ 10,000 km s −1 ( Figure 16); the photospheric radius R HOT flattens to R HOT ∼ 1.6×10 15 cm while the temperature transitions to a milder decay in time (Section 3, Figure 11). Starting from t pk − 3 days He i features become weaker until He i λ7065 is not detected at t pk + 28 days ( Figure 19). ...

Context 20

... conclude by noting that, observationally, t pk +17 days (i.e., 2012 October 20) marks an important transition in the evolution of SN 2009ip: around this time the broad Hα component evolves from FWHM ∼ 3000 km s −1 to FWHM ∼ 10,000 km s −1 ( Figure 16); the photospheric radius R HOT flattens to R HOT ∼ 1.6×10 15 cm while the temperature transitions to a milder decay in time (Section 3, Figure 11). Starting from t pk − 3 days He i features become weaker until He i λ7065 is not detected at t pk + 28 days ( Figure 19). ...

Context 21

... conclude by noting that, observationally, t pk +17 days (i.e., 2012 October 20) marks an important transition in the evolution of SN 2009ip: around this time the broad Hα component evolves from FWHM ∼ 3000 km s −1 to FWHM ∼ 10,000 km s −1 ( Figure 16); the photospheric radius R HOT flattens to R HOT ∼ 1.6×10 15 cm while the temperature transitions to a milder decay in time (Section 3, Figure 11). Starting from t pk − 3 days He i features become weaker until He i λ7065 is not detected at t pk + 28 days ( Figure 19). ...

Context 22

... from ∼30 days after peak, NIR emission from the Ca ii triplet λλ8498, 8542, 8662 progressively emerges ( Figure 18; see also Fraser et al. 2013, their Figure 4). The appearance of this feature is typically observed during the evolution of Type II SN explosions (see, e.g., Pastorello et al. 2006). ...

Context 23

... previous outburst of SN 2009ip showed this feature (2012a outburst included; see Pastorello et al. 2013); no broad Ca ii triplet feature has ever been observed in an LBV-like eruption, either. Figure 18 also shows the emergence of broad absorption dips around 8400 Å and 8600 Å, which likely results from the combination of O i and Ca ii. ...

Context 24

... broad absorption features appear in our spectra starting nine days after peak (see yellow bands in Figures 7, 17, 19, and 20). Absorption features of similar strength and velocity have never been associated with an LBV-like eruption to date and are more typical of SNe ( Figure 21). These absorption features are unique to the 2012b As the photosphere recedes into the ejecta it illuminates material moving toward the observer with different velocities. ...

Context 25

... has a key role in determining the mass-loss history of the progenitor, with low metallicity generally leading to a suppression of mass loss, therefore allowing lower-mass stars to end their lives with massive cores. SN 2009ip is positioned in the outskirts of NGC 7259 ( Figure 1). The remote location of SN 2009ip has been discussed by Fraser et al. (2013). ...

Context 26

... extensive photometric coverage allows us to accurately constrain the bolometric luminosity and total energy radiated by SN 2009ip. SN 2009ip reaches a peak luminosity of L pk = (1.7 ± 0.1) × 10 43 erg s −1 ( Figure 11). The total energy radiated during the 2012a outburst (from 2012 August 1 to September 23) is (1.5 ± 0.4) × 10 48 erg while for the 2012b explosion we measure E rad2 = (3.2 ...

Context 27

... rapid rise and decay times of the major 2012b explosion (Figure 25) suggest that the shock wave is interacting with a compact shell(s) of material (see, e.g., Chevalier & Irwin 2011, their Figure 1). The relatively fast fading of CSM-like features and subsequent emergence of Type IIP features shown in Figure 21 supports a similar conclusion. ...

Context 28

... rapid rise and decay times of the major 2012b explosion (Figure 25) suggest that the shock wave is interacting with a compact shell(s) of material (see, e.g., Chevalier & Irwin 2011, their Figure 1). The relatively fast fading of CSM-like features and subsequent emergence of Type IIP features shown in Figure 21 supports a similar conclusion. We consider a model where the ejecta from the 2012b explosion initially interact with an optically thick shell of material, generating the UV-bright, major peak in the light-curve. ...

Context 29

... Equations (A2) and (A3), the progenitor mass-loss rate is ˙ M ≈ 0.07(v w /200 km s −1 ) M yr −1 . We choose to renormalize the mass-loss rate to 200 km s −1 , which is the FWHM of the narrow emission component in the Hα line (e.g., Figure 16). We note that the inferred temporary mass-loss rate is appreciably below the expectations from a terminal explosion, but considerably higher than LBVs at maximum (which typically have ˙ M ≈ 10 −4 -10 −5 M yr −1 ; Humphreys & Davidson 1994). ...

Context 30

... use v ≈ 5000 km s −1 . Using the bolometric luminosity of Figure 11, we find that the total mass swept up by the shock from t w = 32 days until the end of our monitoring (112 days since explosion) is M thin w ≈ (0.05/η) M . The total mass in the environment swept up by the 2012b explosion shock is therefore M tot = M w + M thin w ≈ (0.2-0.3) M for η = 50%-30%. ...

Context 31

... 12a w = w(R)dR. The evolution of the blackbody radius of Figure 11 suggests v ≈ 2500 km s −1 39 The mass swept up by the shock by the time of break-out is ≈0.05 M . 40 Using the line of reasoning of Section 7.1, the relation between M ej and E just found implies M Ni < 0.02 M for E = 10 51 erg and M Ni < 0.07 M for E = 10 50 erg, consistent with the limits presented in Section 7.1. ...

Context 32

... spectra show evidence for narrow-line emission (Section 4) typically observed in SNe IIn (and LBVs), which is usually interpreted as signature of the ejecta interaction with material deposited by the progenitor wind before explosion. For SN 2009ip we observe during the 2012b event a velocity gra- dient in the narrow emission from Hα (Figure 16, panel (c)), with increasing velocity with time. This increase is consistent with being linear with time. ...

Context 33

... values correspond to the velocity of material seen in absorption (i.e., placed outside the photosphere). The radius of the hot blackbody R HOT of Figure 11 tracks the position of the photosphere with time. Assuming free expansion of the ejecta and the explosion onset time (t pk − 20 days) derived in the previous sections, we can predict at which time t v ejecta moving at a certain velocity v will overtake the photosphere at R HOT . ...

Context 34

... the 2012b explosion we detect high-velocity material in absorption starting from ∼1 week after peak. Around peak the spectrum of SN 2009ip is optically thick and shows no evidence for material with v ∼ −12,000 km s −1 (Figures 19 and 20). However, in no way could a perfectly spherical photosphere with apparent v ≈ 4000-5000 km s −1 mask the fast-moving ejecta at any time during the evolution, and in particular until the first week after peak, as we observed. ...

Context 35

... can also have a role in the spatial distribu- tion of the interacting material, as supported by the observed co-existence of broad and (unresolved) intermediate compo- nents in the spectrum (Figure 14). In this respect, Chugai & Danziger (1994) proposed the possibility of an enhanced mass loss on the equatorial plane of SNe IIn to explain the interme- diate velocity component in SN 1988Z, other explanations be- ing a clumpy CSM or, again, an asymmetric flow. ...

Context 36

... time-resolved broadband SED analysis of Section 3 identifies the presence of a NIR excess of emission ( Figure 13) with respect to a blackbody spectrum. Contemporaneous NIR spectroscopy (Section 2.3) shows that the NIR excess cannot be ascribed to line emission (Figure 7), therefore pointing to a physical process producing NIR continuum emission with luminosity L ∼ 4 × 10 41 erg s −1 . ...

Context 37

... we use a simplified approach. From the SED analysis of Section 3 we find that the equivalent NIR blackbody radius is R COLD ∼ 4 × 10 15 cm with very limited evolution with time ( Figure 11). The cold blackbody temperature is also stable, with T COLD ∼ 3000 K. Considering that our simplified approach overestimates the true dust temperature of hundreds of degrees (up to 20% according to Nozawa et al. 2008) the real dust temperature should be closer to ∼2500 K. ...

Context 38

... SED fitting indicates the presence of a NIR excess with similar radius during the 2012a eruption as well (Figure 11), suggesting that the origin of the preexisting material is rather linked to the eruption episodes of the progenitor of SN 2009ip in the years before. The same conclusion was independently reached by Smith et al. (2013). ...

Context 39

... & Barlow 1975). The mild spectral index of the NIR excess (see Figure 13) implies a mild density gradient at large radii, with β < 2 (i.e., significantly flatter than the standard wind profile expected in the case of constant mass-loss rate). This finding suggests a significant increase in the mass-loss rate of the progenitor star during the years preceding the 2012 double outburst. ...

Context 40

... finding suggests that the true evolutionary state of the progenitor of SN 2009ip might be different from a classical LBV. With luminosity be- tween ∼10 6 and ∼10 7 L , the progenitor of SN 2009ip falls into the region where radiation pressure starts to have a ma- jor role in supporting the star against gravity (e.g., Owocki & Shaviv 2012, their Figure 12.1): we speculate that the dom- inance of radiation pressure over gas pressure in the enve- lope might have an important role in determining the repeated outbursts of SN 2009ip. ...

Context 41

... mechanism behind the precursor plus major outburst is not unique to SN 2009ip (see, e.g., SN 2010mc); it is likely driven by few physical parameters and likely represents an important evolutionary channel for massive stars. Future observations will reveal if SN 2009ip was able to survive. ...

Context 42

... r is in cgs units; and ˙ M is the progenitor mass-loss rate. We consider here their model (a) (see their Figure 1), where the break-out happens inside the dense wind shell of radius R w so that R bo < R w . For SN 2009ip it turns out that R bo R w , which leads to comparable estimates of the explosion and the environment parameters even if one were to use their model (b). ...

Context 43

... reduces to the Fourier power spectrum in the uniform sampling limit. As shown in Figure 31, most power is concentrated between ∼30 and ∼50 days, with a peak around 40 days. To evaluate the impact of the aliasing and to quantify how significant the power is with respect to the white noise case (i.e., no preferred timescale), we carried out the following Monte Carlo simulation. ...

Context 44

... randomized the magnitudes among the same observation times and generated 10 4 synthetic profiles with the same variance as the real one. For each period we derived the corresponding confidence levels of 1σ , 90%, 99%, and 99.9%, as shown in Figure 31. Comparing the real LS periodogram with the MC generated confidence levels, we conclude that power in excess of white noise around 40 days is significant at 99.9% confidence, and we identify this timescale as the dominant one in the overall variance. ...

Context 45

... these parame- ters, the corresponding unabsorbed (absorbed) flux is (1.9 ± 0.2) × 10 −14 erg s −1 cm −2 ((1.7 ± 0.2) × 10 −14 erg s −1 cm −2 ) in the 0.3-10 keV band. The spectrum is displayed in Figure 10. A Swift-XRT spectrum extracted around the peak (−2 days < t−t pk < +13 days, total exposure of 86 ks) can be fit by a thermal bremsstrahlung model, assuming kT = 60 keV and NH int < 3.1×10 21 cm −2 at the 3σ c.l. ...