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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').
  1. GRB 250328A: VLT/HAWK-I near-infrared afterglow candidate
  2. GRB 250329A: VLT/X-shooter redshift z = 2.921
  3. GRB 250329A: SVOM/VT optical counterpart confirmation
  4. GRB 250329A: SVOM detection of a burst
  5. GRB 250329A: SVOM/COLIBRÍ (F-GFT) Detection of a Bright Optical Counterpart Candidate
  6. GRB 250327B: J-band observations with WINTER
  7. GRB 250327B: MASTER detection of OT rebrightening
  8. GRB 250327B: LCO optical counterpart detection
  9. GRB 250328A: GWAC-F50A optical upper limit
  10. GRB 250328A: SVOM detection of a burst
  11. FRB 20250316A: FTW optical observations
  12. LIGO/Virgo/KAGRA S250328ae: NED Galaxies in the 4-Update Localization Volume
  13. EP250302a: SPI-ACS/INTEGRAL Upper Limit
  14. GRB 250327B: CrAO and SAO RAS Optical Observations
  15. GRB 250327B: OHP/T193 spectroscopic observations and redshift confirmation
  16. GRB 250327B: further optical observations by LCOGT
  17. EP250315a: Pan-STARRS r and i-band imaging and photometry
  18. GRB 250327b: Liverpool Telescope optical observations
  19. GRB 250322A: GRANDMA/TNOT optical upper limits
  20. LIGO/Virgo/KAGRA S250328ae: Updated Sky localization
  21. GRB 250327A: SVOM/VT upper limits on the XRT position
  22. LIGO/Virgo/KAGRA S250328ae: Identification of a GW compact binary merger candidate
  23. GRB 250327B: SVOM/COLIBRÍ (F-GFT) follow-up observations
  24. GRB 250327B: Las Cumbres optical counterpart detection
  25. GRB 250327B: Swift-XRT detection of the X-ray afterglow
  26. GRB 250327B: 1.6m Mephisto optical observations
  27. GRB 250327B: NOT spectroscopic redshift z = 3.035
  28. GRB 250327A: Swift-XRT refined Analysis
  29. GRB 250327B: GOTO optical counterpart detection
  30. GRB 250327B: SVOM/VT optically bright counterpart
  31. GRB 250327B: SAO RAS optical candidate
  32. GRB 250327B: SVOM detection of a burst
  33. FRB 20250316A: Gemini Imaging and Spectroscopy of the Sub-arcsecond Localization Region of FRB 20250316A
  34. FRB 20250316A: The sub-arcsecond localization of FRB 20250316A using CHIME/FRB Outriggers coincides with reported X-ray counterparts
  35. GRB 250327A: J-band observations with WINTER
  36. GRB 250327A: SVOM/VT optical candidate
  37. FRB 20250316A: Pan-STARRS r and i-band imaging and photometry
  38. GRB 250327A: Fermi GBM observation
  39. Fermi GRB 250327A: Global MASTER-Net observations report
  40. Swift GRB 250327A: Global MASTER-Net observations report
  41. GRB 250327A: DDOTI Optical Observations
  42. GRB 250327A: COLIBRÍ optical upper limit
  43. GRB 250327A: Swift detection of a burst
  44. GRB 250327A: Fermi GBM Final Real-time Localization
  45. Fermi trigger No 764700395: Global MASTER-Net observations report
  46. LIGO/Virgo/KAGRA S250326y: Updated Sky localization
  47. Konus-Wind detection of GRB 250322A (short)
  48. IPN triangulation of GRB 250322B
  49. LIGO/Virgo/KAGRA S250326y: Identification of a GW compact binary merger candidate
  50. EP250321a: Mondy AZT-33IK Continued Optical Observations
  51. Swift follow-up observations of FRB250316A and EP J120944.2+585060
  52. GRB 250322A: third epoch of NOT optical observations
  53. GRB 250322A: Swift-BAT refined analysis
  54. The EP-WXT trigger 01709133021 (designated as EP250324a) is not a real source
  55. GRB 250321B: ISON-Kitab RC-36 Optical Upper Limit
  56. FRB 250316A: NOT optical upper limit for the X ray source EP J120944.2+585060
  57. GRB 250322A: further NOT optical observations
  58. EP-WXT trigger 01709133021: Optical upper limit through Kinder observations
  59. GRB 250322A: Swift/UVOT Upper Limits
  60. EP250324A: COLIBRÍ/DDRAGO Optical Observations
  61. GRB 250322A: VLT/X-shooter redshift confirmation of the putative host galaxy
  62. FRB 250316A: COLIBRÍ/DDRAGO Optical follow up of the X ray source EP J120944.2+585060
  63. GRB 250322B: NuSTAR detection of the prompt emission and regular dips during the burst
  64. GRB 250321B: Swift-XRT observations
  65. GRB 250322A: Swift-XRT refined Analysis
  66. EP250321a: TNOT Observation of Optical Counterpart
  67. FRB 250316A: DDOTI Continued Optical Observations (Third Epoch)
  68. GRB 250322A: Gemini-North redshift of candidate host galaxy
  69. EP250304a: VLT/MUSE spectroscopic observation of its associated supernova SN 2025fhm
  70. SVOM/sb25032302: SVOM detection of a long X-ray transient
  71. GRB 250322A: AstroSat CZTI detection of a short burst
  72. GRB 250322B: AstroSat CZTI detection of a bright long burst
  73. GRB250322A: STEP/T80S optical limits
  74. GRB 250322A: Gemini-South optical observations
  75. GRB 250322A: VLT optical observations
  76. GRB 250322A: VLT near-infrared observations
  77. FRB 250316A: DDOTI Continued Optical Observations
  78. GRB 250322A: NOT optical upper limits
  79. GRB 250322A: Enhanced Swift-XRT position
  80. GRB 250321B: SVOM/COLIBRÍ (F-GFT) follow-up observations
  81. FRB 20250316A: Kinder optical upper limits of the Einstein Probe candidate X-ray source EP J120944.2+585060
  82. GRB 250322A: MASTER optical observation
  83. EP250321a: Liverpool Telescope optical follow-up
  84. EP250321a: Mondy AZT-33IK Optical Observations
  85. GRB 250322A: Swift detection of a short burst
  86. FRB 20250316A: detection of a candidate associated X-ray source EP J120944.2+585060 by Einstein Probe
  87. EP250321a: refined analysis of the EP-WXT and EP-FXT observations
  88. EP250321a: KAIT optical observations
  89. EP250321A: COLIBRÍ Continuing Optical Observations
  90. GRB 250225B: GECAM-A detection
  91. GRB 250312A: GECAM-A detection
  92. GRB 250321B: Swift ToO observations
  93. EP250321a: WFST optical observations
  94. GRB 250320B: NuSTAR detection of the prompt emission from two broad bursts and preliminary analysis
  95. GRB 250321C: Fermi GBM Final Real-time Localization
  96. GRB 250320A: NuSTAR Detection of the Prompt Emission and Preliminary Results
  97. GRB 250320B: Fermi GBM Observation
  98. EP250321a: Xinglong 216 decaying optical observations
  99. GRB 250321A: Swift-BAT refined analysis
  100. GRB 250321A: Swift-XRT refined Analysis

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