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GCN Circulars

GCN Circulars are rapid bulletins submitted by and distributed to the community. 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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43888 results found.

  1. LIGO/Virgo/KAGRA S250818k: J-GEM follow-up observation for AT2025ulz
  2. LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
  3. LIGO/Virgo/KAGRA S250818k: JinShan optical observations of AT2025ulz
  4. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  5. LIGO/Virgo/Kagra S250818k: STEP/T80N upper limits on 2025ulz
  6. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  7. GRB 250806A: Gemini observations of host galaxy candidate
  8. IPN triangulation of GRB 250821B (long/bright)
  9. GRB 250821A: Kilonova-Catcher optical upper limits
  10. EP250821a: Swift/XRT counterpart fading
  11. GRB 250812A: SVOM/ECLAIRs refined analysis
  12. GRB 250821A: Swift-BAT refined analysis
  13. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  14. LIGO/Virgo/KAGRA S250818k: NOT optical observations of AT2025ulz
  15. EP250821a: VLT X-shooter spectroscopic redshift z = 0.577
  16. LIGO/Virgo/KAGRA S250818k: GRAWITA TNG NIR observations of AT2025ulz
  17. GRB 250821A: GECAM-B detection
  18. GRB 250821B: SVOM/GRM observation
  19. EP250821a: SVOM/VT optical observation
  20. Fermi GRB 250821B: Global MASTER-Net observations report
  21. GRB 250821A: NOT z-band upper limit
  22. GRB 250821C: Fermi GBM Final Real-time Localization
  23. GRB 250821A: KAIT optical upper limit
  24. LIGO/Virgo/KAGRA S250818k: Continued fading and reddening of AT2025ulz from Keck/LRIS imaging observations
  25. GRB 250821A: Swift-XRT refined Analysis
  26. Swift GRB 250821A: Global MASTER-Net observations report
  27. GRB 250821B: Fermi GBM Detection
  28. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of AT 2025ulz
  29. GRB 250821B: BALROG localization (Fermi Trigger / GRB 250821672)
  30. LIGO/Virgo/KAGRA S250818k : Tautenburg observations, upper limits
  31. GRB 250821B: Fermi GBM Final Localization of a Bright Burst
  32. GRB 250821A: Enhanced Swift-XRT position
  33. EP250821a: Rapidly fading optical source detected in Las Cumbres followup
  34. EP250821a: Swift XRT and UVOT counterpart detection
  35. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  36. EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations
  37. GRB 250821A: LCOGT Optical Upper Limits
  38. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  39. LIGO/Virgo/KAGRA S250818k: 10 GHz VLA observations of AT2025ulz
  40. GRB 250821A: Prompt enhanced Swift-XRT position
  41. GRB 250821A: Swift detection of a burst
  42. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  43. LIGO/Virgo/KAGRA S250818k: EP/FXT observation of AT 2025ulz
  44. EP250821a: Einstein Probe detection of an X-ray transient
  45. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  46. GRB 250819A: Insight-HXMT detection
  47. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  48. GRB 250818B: 10 GHz VLA detection
  49. LIGO/Virgo/KAGRA S250818k: Pan-STARRS grizy-band imaging and photometry of AT2025ulz
  50. LIGO/Virgo/KAGRA S250818k: Swift observations of AT 2025ulz
  51. LIGO/Virgo/KAGRA S250818k: Multi-band Gemini GMOS Detections
  52. LIGO/Virgo/KAGRA S250818k: ATLAS pre-discovery limits for AT2025ulz
  53. IPN triangulation of GRB 250816A (short)
  54. IPN triangulation of GRB 250814C (short)
  55. IPN triangulation of GRB 250804B (short)
  56. GRB 250818B: FTW optical and NIR observations show reddening of the counterpart
  57. GRB 250818B: Kilonova-Catcher optical afterglow detection
  58. LIGO/Virgo/KAGRA S250818k: AstroSat CZTI non-detection and upper limits
  59. GRB 250818B: Liverpool Telescope optical detections
  60. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  61. LIGO/Virgo/KAGRA S250818k: Updated Sky localization and EM Bright Classification
  62. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  63. GRB 250818A: AstroSat CZTI detection
  64. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz
  65. LIGO/Virgo/KAGRA S250818k: Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  66. Fermi Gamma-ray Burst Monitor trigger 777342746/250820022 is not a GRB
  67. LIGO/Virgo/KAGRA S250818k: FTW Fast reddening of AT 2025ulz
  68. GRB 250820A: Fermi GBM Final Real-time Localization
  69. GRB 250818B: optical afterglow detection with Lesedi (GOTO25fzq)
  70. GRB 250818B: TRT Optical Observation
  71. Fermi GRB 250816A: Global MASTER-Net observations report
  72. GRB 250818B: SAO RAS optical observations
  73. Swift GRB 250818A: Global MASTER-Net observations report
  74. GRB 250818B: NOT optical observations
  75. GRB 250818A: Swift-XRT refined Analysis
  76. GRB 250818B: EP-FXT counterpart detection
  77. GRB 250818A: Swift-BAT refined analysis
  78. Fermi Gamma-ray Burst Monitor trigger 777251788/250818970 is not a GRB
  79. LIGO/Virgo/KAGRA S250818k: FTW optical and NIR observations of AT 2025ulz
  80. GRB 250818C: Fermi GBM Final Real-time Localization
  81. GRB 250818B: Keck redshift of the optical afterglow
  82. Fermi trigger No 776849714: Global MASTER-Net observations report
  83. GRB 250818B: KAIT optical observations
  84. LIGO/Virgo/KAGRA S250818t: Updated Sky localization
  85. LIGO/Virgo/KAGRA S250818k: Candidates from the Zwicky Transient Facility
  86. GRB 250818A: Enhanced Swift-XRT position
  87. GRB 250813B: SVOM/ECLAIRs refined analysis
  88. GRB 250818A: Fermi GBM Observation
  89. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  90. GRB 250818B: SVOM/VT optical observation
  91. GRB 250814A: Further GRAWITA TNG NIR observations
  92. GRB 250818B: Swift-XRT afterglow detection
  93. GRB 250818B: GOTO optical counterpart candidate
  94. GRB 250818B: SVOM detection of a short burst
  95. LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate
  96. GRB 250818A: Swift detection of a burst
  97. GRB 250818A: Fermi GBM Final Real-time Localization
  98. sb25081602: Swift-XRT observations
  99. GRB 250816A: SVOM/GRM observation of a short burst
  100. SVOM/sb25081602: detection of a likely X-ray transient

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