Results from a Systematic Survey of X-Ray Emission from Hydrogen-poor Superluminous SNe

We present the results from a sensitive X-ray survey of 26 nearby hydrogen-poor superluminous supernovae (SLSNe-I) with Swift, Chandra and XMM. Our campaign constrains the SLSN evolution rom a few days until 2000 days after explosion, reaching a luminosity limit of Lx 1040 ergs-1 and reveals the presence of significant X-ray emission at the location of PTF12dam. No SLSN-I is detected above Lx 1041 ergs-1, suggesting that the luminous X-ray emission Lx 1045 ergs-1 associated with SCP60F6 is not common among SLSNe-I. We constrain the presence of off-axis GRB jets, ionization breakouts from magnetar central engines and the density in the sub-pc environments of SLSNe-I through IC emission. Our deepest limits rule out the weakest uncollimated GRB outflows, suggesting that if the similarity of SLSNe-I with GRB/SNe extends to their fastest ejecta, then SLSNe-I are either powered by energetic jets pointed far away from our line of sight ( > 30), or harbor failed jets that do not successfully break through the stellar envelope. Furthermore, if a magnetar central engine is responsible for the exceptional uminosity of SLSNe-I, our X-ray analysis favors large magnetic fields B > 21014 G and ejecta masses Me j > 3M in agreement optical/UV studies. Finally, we constrain the pre-explosion mass-loss rate of stellar progenitors of SLSNe-I. For PTF12dam we infer M_ < 210-5Myr-1, suggesting that the SN shock interaction with the CSM is unlikely to supply the main source of energy powering the optical transient and that some SLSN-I progenitors end their life as compact stars surrounded by a low-density medium similar to long GRBs and Type Ib/c SNe.