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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
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To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

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subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"

23410 results found.

  1. GRB 250831A: Swift-XRT counterpart detection
  2. GRB 250831A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  3. GRB 250831A: SVOM/VT upper limit with VHF data
  4. GRB 250831A: SVOM detection of a soft burst
  5. GRB 250830B: Swift-XRT observations
  6. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  7. LIGO/Virgo/KAGRA S250830bp: Coverage and upper limits from MAXI/GSC observations
  8. LIGO/Virgo/KAGRA S250830bp GLADEnet Completeness: Potential Host Galaxies in the 90% Credible Volume
  9. LIGO/Virgo/KAGRA S250830bp: Updated Sky localization, EM Bright Classification, and Source Classification
  10. LIGO/Virgo/KAGRA S250830bp: Identification of a GW compact binary merger candidate
  11. EP-WXT trigger 01709200994: Liverpool Telescope upper limits
  12. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  13. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  14. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  15. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  16. EP250828a: Optical counterpart detection with Kinder observations
  17. EP250828a: Liverpool Telescope upper limits
  18. EP-WXT trigger 01709200800 : KAIT optical observations
  19. EP250828a: KAIT optical upper limit
  20. EP250827a: Swift/UVOT Detection
  21. EP250828a: NOT optical counterpart confirmation
  22. EP250828a: SVOM/VT optical candidate
  23. EP250828a: Seimei/TriCCS optical counterpart detection
  24. GRB 250828B: Swift detection of a burst
  25. EP250828a: Optical upper limit with Kinder observations
  26. LIGO/Virgo/KAGRA S250818k: uGMRT 1.3 GHz observations of AT2025ulz
  27. EP250828a: Einstein Probe detection of an X-ray transient
  28. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  29. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  30. EP250827a: confirmation of optical rebrightening with LCO
  31. GRB 250826A: SVOM/GRM observation
  32. EP250827A: An optical rebrightening was detected by LCO.
  33. EP250827a: Swift-XRT counterpart detection
  34. EP250827a: TRT optical observations
  35. EP250827a: Einstein Probe detection of an X-ray transient
  36. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  37. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  38. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  39. Fermi GRB 250824B: Global MASTER-Net observations report
  40. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  41. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  42. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  43. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  44. GRB 250823A: Swift-XRT refined Analysis
  45. EP250821a: MeerKAT radio counterpart
  46. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  47. GRB 250823A: COLIBRÍ optical observations
  48. GRB 250823A: SVOM/VT optical observation
  49. GRB 250823A: Swift/UVOT Detection
  50. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  51. GRB 250823A: Enhanced Swift-XRT position
  52. GRB 250823A: LCOGT Optical Detection
  53. GRB 250823A: Swift detection of a burst
  54. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  55. LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
  56. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  57. LIGO/Virgo/Kagra S250818k: STEP/T80N upper limits on 2025ulz
  58. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  59. IPN triangulation of GRB 250821B (long/bright)
  60. GRB 250821A: Kilonova-Catcher optical upper limits
  61. EP250821a: Swift/XRT counterpart fading
  62. GRB 250812A: SVOM/ECLAIRs refined analysis
  63. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  64. EP250821a: Swift/UVOT further observations.
  65. GRB 250821A: VLT/FORS2 Optical Observation
  66. GRB 250821B: SVOM/GRM observation
  67. EP250821a: SVOM/VT optical observation
  68. GRB 250821A: NOT z-band upper limit
  69. GRB 250821A: KAIT optical upper limit
  70. GRB 250821A: Swift-XRT refined Analysis
  71. LIGO/Virgo/KAGRA S250818k : Tautenburg observations, upper limits
  72. GRB 250821A: Enhanced Swift-XRT position
  73. GRB 250821A: Swift/UVOT Upper Limits
  74. EP250821a: Swift XRT and UVOT counterpart detection
  75. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  76. EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations
  77. GRB 250821A: LCOGT Optical Upper Limits
  78. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  79. LIGO/Virgo/KAGRA S250818k: 10 GHz VLA observations of AT2025ulz
  80. GRB 250821A: Swift detection of a burst
  81. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  82. LIGO/Virgo/KAGRA S250818k: EP/FXT observation of AT 2025ulz
  83. EP250821a: Einstein Probe detection of an X-ray transient
  84. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  85. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  86. LIGO/Virgo/KAGRA S250818k: Pan-STARRS grizy-band imaging and photometry of AT2025ulz
  87. LIGO/Virgo/KAGRA S250818k: Swift observations of AT 2025ulz
  88. LIGO/Virgo/KAGRA S250818k: ATLAS pre-discovery limits for AT2025ulz
  89. GRB 250814A: Swift/UVOT Upper Limits
  90. GRB 250813B: Swift/UVOT Upper Limit
  91. IPN triangulation of GRB 250816A (short)
  92. IPN triangulation of GRB 250814C (short)
  93. IPN triangulation of GRB 250804B (short)
  94. GRB 250818B: Kilonova-Catcher optical afterglow detection
  95. LIGO/Virgo/KAGRA S250818k: AstroSat CZTI non-detection and upper limits
  96. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  97. LIGO/Virgo/KAGRA S250818k: Updated Sky localization and EM Bright Classification
  98. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  99. GRB 250818A: AstroSat CZTI detection
  100. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz

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